Muscle gain is dependent upon the difference between muscle protein synthesis (MPS) and muscle protein breakdown (MPB), otherwise known as net protein balance (NPB). For muscle gain to occur, the rate of MPS must exceed the rate of MPB, resulting in positive NPB.

This framework makes the importance of diet especially clear: Mechanical loading of skeletal muscle — commonly achieved through resistance exercise — stimulates MPS, but it also increases MPB. The ingestion of amino acids — particularly essential amino acids — helps further stimulate MPS while also suppressing MPB, helping ensure a positive NPB overall.^[38]

Different methods of body composition assessment allow for the direct or calculated measurement of the mass of different types of body components, such as fat, bone, water, lean mass, etc. Whole-body assessments of body composition differ according to the number of components, or “compartments,” into which the total body mass is divided. There are three main models of body composition:^[3]

• A 4-compartment model divides the body’s mass into total body water, bone mineral content, fat mass, and fat-free mass.
• A 3-compartment model (e.g., DXA-DEXA|dual-energy X-ray absorptiometry) divides the body’s mass into bone mineral content, fat mass, and fat-free mass.
• A 2-compartment model (e.g., hydrodensitometry or underwater weighing, air displacement plethysmography, bioelectrical impedance analysis) divides the body’s mass into fat mass and fat-free mass.

The 4-compartment model is considered the gold standard, but it requires a variety of equipment and is costly and time-consuming, so it’s not commonly used.

Delayed Onset Muscle Soreness (DOMS) is considered an indirect marker of muscle damage, which is characterized by ultrastructural changes in skeletal muscle (e.g., Z-band streaming^[99]). Muscle damage is a common occurrence after unfamiliar and vigorous exercise, particularly exercise that involves high force eccentric muscle contractions.^[100]

It’s been suggested that muscle damage promotes enhanced tissue remodeling or muscle hypertrophy,^[101] and the notion that DOMS are one of the best indicators of effective training is rampant among individuals who regularly perform resistance exercise.

However, resistance exercise interventions that produce minimal muscle damage can promote muscle gain,^[102] and can even result in as much muscle gain as those that produce substantial muscle damage.^[103] Additionally, concentric-only and eccentric-only resistance exercises (“concentric” refers to the active lifting of the weight, as opposed to the lowering or “eccentric” portion) promote similar muscle gain, even though the latter exercises induce more muscle damage.^[104][105] Thirdly, although modes of exercise such as prolonged or downhill running can provoke significant DOMS,^[100] they do not promote significant muscle gain.

The most notable evidence demonstrating that muscle damage does not mediate muscle gain stems from a randomized controlled trial by Damas and colleagues published in 2016.^[106] Over a 10-week resistance exercise intervention, there was an inverse correlation between muscle damage/DOMS and muscle gain; muscle gain was not observed until the initial muscle damage from the training intervention had attenuated.

Taken together, the evidence suggests that muscle damage does not seem to be necessary for muscle growth, and that training programs which produce substantial muscle damage may not enhance muscle gain.^[107] Therefore, individuals interested in muscle gain should not aim to get as sore as possible after their workouts, although a small-to-moderate amount of DOMS may occur during the initial week of a new training program or after a particularly intensive workout. Moreover, the evidence above suggests that the school of thought that progressing through a training plateau requires a new, acutely damaging training stimulus to “shock” complacent muscles into further growth may be misguided. Muscle hypertrophy seems to occur only in significant amounts after muscle damage has attenuated,^[106] suggesting that avoiding DOMS through steadily ramping up intensity over time may be superior to an acute beat-down.

Constantly chasing the DOMS dragon (so to speak) may have additional negative effects on muscle gain. The pain associated with DOMS can reduce motivation and deter some individuals from sticking to their resistance exercise program. For those not deterred, DOMS and muscle damage can also negatively affect resistance exercise performance — and thus muscle gain — by impairing movement patterns, resulting in reduced range of motion and reduced activation of the targeted musculature along with diminished force capacity.^[108]

Training to muscular failure, otherwise known as momentary failure (i.e., the point at which another concentric repetition cannot be completed with proper form), is not necessary to increase muscle strength.^[109] In fact, ending each set a few reps shy of failure appears to be superior to training to failure for maximizing gains in 1RM strength.^[110][111]

In contrast, training closer to failure appears to be better for increasing muscle size in a dose-response manner,^[112] meaning that on a per set basis, a set performed to failure is the most conducive to muscle gain. However, a notable caveat to this relationship is the influence of load: training to failure is not as important when lifting heavy loads (≥80% of 1-repetition maximum), while in the case of lighter loads (from around 40% to 75% of 1-repetition maximum), training to failure is notably more effective than stopping a few reps shy of failure.

An increasingly common way to prescribe resistance exercise is to use a velocity loss threshold (VLT). The performance of resistance exercise according to a VLT means that once a certain percentage of velocity loss from the fastest repetition (typically the first) of a set is obtained, the set is terminated. For example, a VLT of 25% would mean that the individual stops performing repetitions once they complete a rep that has a velocity 25% slower than the fastest repetition. Consequently, a lower VLT typically means sets are completed further away from muscular failure than sets with a higher VLT. Evidence suggests that VLTs ≤ 25% are superior to greater VLTs for increasing strength.^[110][111] Why might that be the case? One hypothesis for the superior effects of lower VLTs is mitigating muscle damage.^[110]Training to muscular failure produces greater muscle damage and neuromuscular fatigue than ending sets a few reps shy of muscular failure.^{[113][114][115]} Muscle damage negatively affects the recruitment of high-threshold motor units and the ability of muscles to produce force,^[113] as well as motor skill learning.^[116] It also delays recovery from exercise, which can lead to a reduction in training frequency and less exposure to the exercise(s) on which the individual is interested in increasing strength. Therefore, training to muscular failure can compromise increases in muscle strength, particularly for complex movement patterns, by impairing training quality.^[110] By training with a lower VLT, an individual can lift heavy loads (≥ 80% of 1-repetition maximum—the most important factor for increasing strength) and practice the exercise of interest more often. Another hypothesis is that training with lower VLTs preserves maximum force-generating capacity through its effects on muscle fiber-type distribution.^[110] One 8-week study found that training with a 40% VLT produced a reduction in the proportion of type IIX muscle fibers (the fastest and most powerful muscle fiber type) compared to a 20% VLT.^[117] Because type II muscle fibers possess a higher force-generating capacity and generate force more rapidly than type I muscle fibers, training regimens that retain or increase the proportion of type II muscle fibers are theoretically superior for strength adaptations.

Training volume refers to the total amount of work carried out in a single training session, which can be summed over weeks or months of training. Evidence indicates that volume is a major driver of muscle gain,^[10] and thus, tracking training volume can be important to ensure the dose of training is sufficient to facilitate positive adaptations, without reaching a point of diminishing returns and overtraining.

There are many different ways to track volume. Volume load (i.e., sets multiplied by repetitions multiplied by weight load) is a popular and adequate method. However, it falls short in protocols that utilize sets of very high repetitions (e.g., 25–30 repetitions per set). In these protocols, volume load can be especially high, but muscle gain is no greater than that achieved with the same number of sets performed using a higher load and a lower number of repetitions.^[7] Another shortcoming of volume load becomes apparent when comparing different exercises. For example, using the same number of sets and repetitions, volume load will virtually always be higher for a leg press than a leg extension, but a leg press will not necessarily produce greater quadriceps hypertrophy.

A reliable method to quantify training volume implies similar muscle gain at matched training volumes, independent of other training variables. Evidence suggests that counting the total number of hard sets (i.e., sets performed within four repetitions of muscular failure) when the repetition range lies between about 6 and 30 repetitions fulfills this criterion.^[118] As discussed in the FAQ below, “Are heavy or light weights better for muscle gain?”, beyond 20 repetitions or so, a set should probably only be counted as a “hard set” if it is performed to muscular failure.

However, when trying to quantify training volume between a program that consists of low-repetition sets (i.e., <5 repetitions per set) and a program that consists of moderate-repetition sets (i.e., 8–12 repetitions per set), it seems best to use volume load.^[118] Some evidence indicates that, when equated for total number of sets, moderate loads (8–12 repetition maximum) are superior to very heavy loads (2–4 repetition maximum) for muscle gain.^[119] In contrast, when moderate loads and very heavy loads are equated for volume load, no differences in muscle gain have been observed between groups.^{[120][121][122]}

In exercise science research, muscle groups deemed prime movers during multi-joint and single-joint exercises are classified the same from a set standpoint.^[123] For example, one set of a lat pulldown is counted as one set when considering biceps brachii hypertrophy, and the same goes for one set of bench press when considering triceps brachii hypertrophy. Similarly, one set of a barbell back squat and one set of leg extensions are both counted as one set when examining quadriceps hypertrophy, although in the former, other muscles such as the gluteus maximus are heavily involved.

This information is critical for interpreting the results of meta-analyses on the relationship between volume and muscle hypertrophy, particularly for the limb muscles. One meta-analysis found that around 12–20 sets per muscle group per week is optimal for muscle growth; however, that should not be interpreted to mean 12–20 sets of single-joint biceps or triceps movements should be performed to maximize the growth of these muscle groups.^[10] Rather, based on the studies included in the meta-analysis and how these studies calculated training volume, this set range implies a myriad of possible combinations of single-joint and multi-joint exercises (e.g., five sets of biceps curls, five sets of lat pulldowns, and five sets of cable rows, totaling 15 sets for the biceps per week).

There are good reasons, both biomechanically and physiologically, to suggest that single-joint exercises may be more effective for hypertrophy of the limb muscles than multi-joint exercises,^[124][125] and as such, one set of an upper-body multi-joint exercise should count less toward the volume for the limb muscles than one set of a single-joint exercise. However, it’s difficult to pinpoint the precise amount of volume that should be assigned to multi-joint exercises due to differences in exercise selection (e.g., narrow vs. wide grip), training experience, and anatomical structure and mobility (which influences range of motion about a given joint and thus muscle activation).^[126]

As a general rule of thumb, one set of a multi-joint press (i.e., bench press or shoulder press) can be counted as half a set for the triceps,^{[125][127][128][129]} and the same can be said for a multi-joint pull (i.e., row or pulldown) and the biceps.^{[124][130][131]}

Whether an individual chooses to count one set of an upper-body multi-joint exercise as one set or half a set toward the limb muscles is less important than being consistent with the method used to quantify training volume, although the latter may be more accurate in terms of the stimulus the limb muscles are receiving.

For muscle gain, each muscle group should be trained at least once per week. The available evidence generally does not indicate a benefit to higher training frequencies,^[132] particularly when volume is equated between interventions. However, it seems likely that when weekly training volume exceeds 10 sets per week, a higher training frequency would be advantageous, as opposed to performing 10+ sets for a muscle group in a single session.^[14]

For strength, training frequency can be conceptualized as the number of times per week an exercise is performed, as strength is ultimately specific to the test being used to assess it. In accordance with the data on muscle gain, there does not appear to be an advantage to training frequencies of more than once per week in the context of volume-equated training programs.^[133][134]

It’s important to highlight that the above data represents the average response, which may not apply to the reader, as the response to a given training frequency can radically differ between individuals.

In one study that had participants perform high-frequency (5x per week) resistance exercise with one leg and low frequency (2x or 3x per week) resistance exercise with the other leg, it was found that some individuals gained more muscle and strength on the leg assigned to the high-frequency condition and some individuals gained more muscle and strength on the leg assigned to the low-frequency condition, while others experienced no difference between conditions.^[135]

Furthermore, only about 32% of individuals displayed an aligned response, i.e., the same resistance training frequency was better for both muscle gain and strength. Therefore, it’s prudent that the individuals experiment with different training frequencies to find what works best for them for increasing muscle size and strength.

A handful of studies have demonstrated that workouts consisting of 1 set per exercise performed 2–3 times per week can significantly increase muscle size and strength,^[136][137] albeit the increase is less than it would be if more work was performed, especially in the context of muscle gain. According to a 2017 meta-analysis, performing <5 sets per muscle group per week produced muscle gain, but the percentage increase (5.4%) was less than that of 5–9 sets (6.6%) and 10+ (9.8%) sets per week.^[138]

Even those with a bit of resistance training experience under their belt can make meaningful — but suboptimal — progress with a relatively low dose of exercise. According to a meta-analysis published in 2020,^[139] performing a single set of 6–12 repetitions to failure with a load of 70%–85% of 1-repetition maximum (1RM) two to three times per week for 8–12 weeks can increase squat and bench press 1RM by about 17.5 and 8.25 kilograms, respectively, in individuals with at least one year of training experience.

There is also evidence in powerlifters demonstrating that relatively small amounts of work can significantly increase strength. According to a study consisting of multiple experiments published in 2021,^[12] a program with the following characteristics can promote meaningful increases in 1RM strength on the powerlifts (i.e., the barbell back squat, bench press, and deadlift) over 6–12 weeks:

• Volume: 3–6 sets of 1–5 repetitions per week
• Load: ≥ 80% of 1RM
• Frequency: 1–3 sessions per week
• Proximity to failure: 1–4 repetitions shy of failure

Some people may be okay with doing the bare-bones amount of resistance exercise necessary to make some semblance of progress in muscle size and strength, but what about those with more serious goals? Are they doomed to suboptimal gains due to their lack of time? Not necessarily.

There are ways to structure a workout to reduce the amount of time spent in the gym without leaving gains on the table. One strategy is to perform supersets (i.e., sets of two exercises performed in succession, with limited to no rest between them) involving exercises for agonist and antagonist muscles. For example, one study had participants perform the bench press and bench pull (a row) exercises.^[140] For 8 weeks, one group took 4 minutes of rest between each set of both exercises, while the other group took 4 minutes of rest between supersets, which resulted in the workouts taking approximately half the time. In the end, increases in 1RM were similar between groups for both exercises.

Another strategy is to perform rest-pause sets, which involves performing a set to failure, taking a brief rest (typically 20 seconds), and repeating this cycle until a prespecified number of total repetitions is completed. In a 6-week study, the traditional group performed each exercise for 3 sets of 6 repetitions using 80% of 1RM and rested 2–3 minutes between sets, while the rest-pause group performed an initial set with 80% of 1RM until failure, rested for 20 seconds, and repeated this cycle until they completed a total of 18 repetitions.^[141] This resulted in the training sessions lasting around 57 and 35 minutes in the traditional and rest-pause groups, respectively.

In the end, increases in 1RM strength did not differ between groups, while the increase in thigh muscle thickness (but not arm or chest thickness) was greater in the rest-pause group. However, this difference was likely due to the fact that the rest-pause group exerted a greater degree of effort during their workouts, as a set of 6 repetitions with 80% of 1RM typically means ending the set a few repetitions shy of muscular failure, and as stated in “Do I need to train to muscular failure?”, there is an advantage to training to failure for muscle gain.

Skeletal muscle is remarkably plastic and can adapt to an array of circumstances in accordance with the demands imposed upon it. Consequently, consistent, progressive resistance exercise leads to increases in muscle size and strength. But life happens, and sometimes the performance of resistance exercise isn’t so consistent. In fact, it’s quite common for people to take off a few weeks from resistance exercise altogether, whether that be due to obligations outside of the gym, decreased motivation, illness or injury, etc. So, what exactly happens during these periods, and how long does it take for these changes to manifest?

While the principle of “use it or lose it” holds true, it ultimately comes down to the amount of time off from resistance exercise. In athletes (powerlifters and division I American football players), 14 days of detraining (i.e., no formal resistance exercise or structured physical activity) led to a nonsignificant reduction of about 2 kilograms in 1-repetition maximum (1RM) back squat and bench press strength.^[142] There was also a nonsignificant 5.2% reduction in vastus lateralis type I muscle fiber area and a significant 6.4% reduction in type II muscle fiber area.

In a separate study, in which men with some resistance training experience performed a 4 weeks of a resistance exercise intervention for 4 weeks and then detrained for 2 weeks, there were no changes in rectus femoris cross-sectional area or in total lean mass. Furthermore, the gains in 1RM leg press strength accrued during the training period were maintained.^[143]

In addition to these findings, which suggest that 1RM strength is relatively robust in men, 6 weeks of detraining in men with some resistance training experience did not significantly reduce 1RM bench press or squat strength.^[144]

There have also been a couple of studies in untrained men that examined long-term changes in muscle size and strength between a group that continuously performed resistance exercise and a group that cycled through periods of 6 weeks of training and 3 weeks of detraining.^[145][146] In these studies, increases in muscle size and strength were similar between groups.

Evidently, taking a week (or three) off from the gym doesn’t have much impact on muscle size and strength in men. However, more substantial decreases in muscle size and strength have been reported during detraining periods of 8–12 weeks.^[147] This leads to the question: how much work is required to mitigate these adverse effects?

In one study that had untrained men perform resistance exercise 3 times per week for 8 weeks and then reduce their training frequency to either once or twice per week and reduce the amount of volume performed by 50%–60%, quadriceps cross-sectional area and half squat 1RM were both maintained.^[143]

In a second study,^[148] younger and older adults (20–35 and 60–75 years old, respectively) underwent 16 weeks of progressive resistance exercise, training the quadriceps 3 days per week. The participants then reduced their training frequency to once per week and reduced their training volume to one-ninth of what was performed during the initial 16-week training program.

In younger adults, it was found that the increase in thigh lean mass from the initial 16 weeks of training was maintained throughout the maintenance protocol. In contrast, the initial increase in thigh lean mass was not maintained in older adults (60–75 years old). Notably, a less severe reduction in training volume, one-third of what was performed during the initial 16-week training program, was also insufficient to maintain thigh lean mass in these participants.

For strength, knee extension 1RM was significantly higher at the end of the maintenance protocol (week 48) compared to the end of the initial 16-week training period in younger adults, whereas in older adults, the initial increase in knee extension 1RM was maintained throughout the maintenance protocol.

As evidenced by the above, younger adults can get away with doing very little resistance exercise for an extended period without experiencing reductions in muscle size or strength, but older adults don’t seem to have the same luxury, at least when it comes to retaining muscle size.

In younger adults, the evidence suggests that 1–3 weeks of detraining after several weeks of regular, progressive resistance exercise does not pose a significant risk of muscle and strength loss. Furthermore, reducing training frequency to 1–2 times per week and performing approximately one-ninth of previous training volume may be sufficient to maintain muscle size and strength.

Evidence indicates that muscle growth occurs heterogeneously across the length of a muscle and between individual portions of a given muscle group.^[155] This suggests that a variety of exercises that work muscles in different planes and angles of pull may be needed to maximize muscle gain and promote complete muscular development.

In studies that have compared differences in muscle gain between groups performing either multiple exercises or a single exercise, performing multiple exercises has been found to promote more complete muscular development. For instance, performing a combination of Smith machine squats, leg presses, deadlifts, and lunges caused hypertrophy in all heads of the quadriceps, whereas performing only the Smith machine squat did not.^[156]

In a separate study, performing leg presses, half squats, and machine hack squats caused hypertrophy of the proximal, middle, and distal portions of the lateral thigh, whereas only performing leg presses failed to promote significant hypertrophy of the lateral thigh.^[157] Additionally, performing a combination of barbell curls, preacher curls, and dumbbell incline curls tended to cause more hypertrophy in the proximal and middle portions of the elbow flexors compared to performing only barbell curls.^[157]

Thirdly, performing lying barbell triceps extensions and bench press was found to produce greater hypertrophy in the triceps brachii than performing bench press alone, with lying barbell triceps extensions reported to cause preferential hypertrophy of the long head of the triceps, while the bench press caused preferential hypertrophy of the lateral head of the triceps.^[125]

In further support of the utility of varying exercise selection, leg extensions cause preferential growth of the rectus femoris,^[158] a head of the quadriceps that is not effectively hypertrophied by multi-joint lower body exercises like squats.^[159]

Squats also do not effectively hypertrophy the hamstrings,^[159] so hamstring-specific exercises are needed. Leg curls and Romanian deadlifts should be included in a resistance exercise program to maximize hypertrophy of the hamstrings.^[160]

Similarly, the upper (clavicular) portion of the pectoralis major is best stimulated with an incline (about 30 degrees) bench press, whereas the middle and lower portions of the pectoralis major are best stimulated with a horizontal or decline bench press.^[161] Thus, presses at different bench angles should be included to maximize development of the pectoralis major.

Exercises for a given muscle group can be varied within a session (e.g., performing squats and leg extensions in the same session), between sessions (e.g., performing squats on Monday and leg extensions on Thursday), or cycled throughout the weeks of a resistance training program (e.g., performing squats during weeks 1–3 and leg extensions weeks 3–6).

If you’ve spent any appreciable amount of time in the fitness space on social media, you may have come across the term “muscle confusion” — the idea that workouts should be constantly varied in order to provide a novel stimulus and enhance muscular adaptations. Does the science back this idea up?

In an 8-week study that had resistance-trained men perform workouts composed of unilateral leg presses and leg extensions,^[162] one leg was randomly assigned to perform the same workout each session, while the other leg cycled through 4 different workouts that varied in (i) the number of repetitions performed per set, (ii) the number of sets performed, (iii) the type of contraction (i.e., only eccentric contractions were performed), and (iv) the amount of rest taken between sets.

It was found that muscle gain did not differ between interventions. Furthermore, intraindividual analysis indicated that none of the participants experienced greater muscle growth from one intervention than the other.

This suggests that frequent variation does not enhance muscle gain. However, as noted in the response to the question of, “Are a variety of exercises necessary to maximize muscle gain?” there is indeed a benefit to including a variety of exercises within a training program. In the aforementioned study, the exercises performed remained constant, while other variables were manipulated. Does frequent variation in exercise selection affect muscle gain?

There is very little research examining this question. In the best study currently available, resistance-trained men were randomly assigned to one of two 8-week resistance exercise programs. The control program featured upper-body and lower-body workouts consisting of the same exercises each workout, and the interventional program featured upper-body and lower-body workouts consisting of exercises randomly selected from a database of 80 different exercises each workout.^[163]

In the end, there were no significant differences between groups for changes in muscle thickness of the individual quadriceps’ muscles. However, it’s worth highlighting that there was a large increase in intrinsic motivation in the group that varied their exercise selection, while there was a nonsignificant decrease in the group that kept exercise constant, which may be important for long-term adherence.

While the results suggest that frequent variation in exercise selection does not affect muscle gain, this was a single 8-week study. Over the longer term, however, there may be disadvantages to overdoing the variation. It’s possible that too-frequent variation in exercise selection could impair muscle gain by increasing the difficulty of achieving and quantifying progressive overload (i.e., the gradual increase in stress which, when imposed on the body, facilitates continued adaptations)^[164] — the primary stimulus for muscle gain. Also, rotating exercises too frequently may cause excessive fatigue because an unaccustomed stimulus promotes muscle damage.^[165] This could lead to a subsequent reduction in training volume and frequency, and thus an impairment in muscle gain.^[164]

With respect to strength, the story is a bit different. Given the important role of the specificity principle in strength gain,^[166][167] it follows that to maximally increase strength for a given exercise, that exercise should be emphasized in the training program and performed in a manner that facilitates improvements in the strength test of interest. For example, in a study that had one group train with a load corresponding to a 3–5 repetition maximum (RM) and another group train with a load corresponding to 20–28RM, the former experienced greater increases in 1RM strength, while the latter performed better on a test of repetitions to failure at 60% of 1RM.^[168]

Further evidence for this stems from the study mentioned above.^[163] It was found that absolute changes in 1-repetition maximum bench press strength favored the control group (4.7% vs. 0.77%), which regularly included the bench press in their upper body workouts, while the exercise variation group performed the bench press much less frequently (exactly how much was not specified) due to the nature of their program.

It’s been suggested that free weights are better for increasing muscle strength because they require greater degrees of balance and muscle coordination than machine-based exercises.^[169] These factors also lead to a greater recruitment of stabilizing muscles during free-weight exercises,^[14] which contributes to the speculation that free weights are also better for muscle gain. Others have postulated that free weights are superior for muscle gain because they produce higher levels of muscle activation^[170] and a greater release of anabolic hormones.^[171]

Contrary to the above hypotheses, the available evidence does not indicate that free weights are universally better for increasing strength; rather, free weights are better than machines for increasing free-weight strength, and machines are better than free weights for increasing machine-based strength.^[172] Ultimately, the efficacy of either tool is dependent upon how strength is tested.

With respect to muscle gain, specifically in terms of the direct muscle group being trained, limited evidence indicates that machines and free weights are equally effective.^[172] Furthermore, in a 10-week study that assigned untrained men to perform a resistance exercise program consisting of free weights only, machines only, or free weights only for 5 weeks and machines only for 5 weeks, there were no differences between groups for changes in upper arm, chest, or thigh circumference.^[173]

It stands to reason that stabilizing muscles would experience greater growth with free weights, although there is a scarcity of research directly examining these. Nevertheless, the best way to grow a specific muscle is to perform an exercise that directly, rather than indirectly, targets it. So, instead of prioritizing the performance of one exercise over another because it stimulates a greater number of muscles due to their role as synergists or stabilizers in the movement, it’s likely better to perform a variety of exercises, each of which directly targets different muscles, to maximize muscle gain. For further evidence in support of this hypothesis, see “Are a variety of exercises necessary to maximize muscle gain?”.

Evidence indicates that low (<60% of 1-repetition maximum) and high (≥60% of 1-repetition maximum) loads produce similar muscle gain.^[8] However, this notion starts to fall apart at the extremes.

Very light loads (15%–20% of 1-repetition maximum) seem to be inferior to higher loads for muscle gain,^[174][175] and in order for loads at the lower end of the “hypertrophy repetition continuum” (i.e., 30% of 1-repetition maximum) to be as effective as higher loads, each set must be performed to muscular failure (i.e., the point at which another concentric repetition cannot be performed with proper form).^{[176][177][178]}

This is much easier said than done, however. Training with low loads (30%–50% of 1-repetition maximum) to muscular failure tends to produce more discomfort, displeasure, and a higher rating of perceived exertion than training with higher loads.^[179][180] As such, not everyone possesses the capacity to reach the point of muscular failure with low loads, making them a suboptimal option for muscle gain for many people.

On the other hand, very high loads (i.e., a 2- to 4-repetition maximum) may be inferior to moderate-to-high loads for muscle gain. One study found greater increases in lateral thigh muscle thickness when resistance-trained men performed 3 sets of an 8- to 12-repetition maximum compared to 3 sets of a 2- to 4-repetition maximum.^[119] In another study that equated volume load (i.e., load multiplied by repetitions multiplied by sets) between conditions, 7 sets of a 2- to 4-repetition maximum were as effective as 3 sets of an 8- to 12-repetition maximum at increasing biceps muscle thickness. However, the very-high-load group reported high levels of fatigue, both physically and psychologically, and joint-related issues, which was not the case in the moderate-load group.^[120]

Therefore, in order for very high loads to produce similar muscle gain to moderate-to-high loads, more sets need to be performed, which takes more time to complete and risks inducing a greater strain on connective tissue. From a practical standpoint, training with moderate-to-high loads (i.e., a 5- to 10-repetition maximum) may be the best approach for muscle gain for most people.

Periodization refers to the manipulation of training variables over time or the long-term planning of training, with the goal of preventing overtraining while optimizing peak performance.^[181]

Linear periodization (LP) is characterized by increasing intensity and decreasing volume (i.e., lifting heavier loads for fewer reps) over time. Undulating periodization (UP) is characterized by more frequent variations in volume and intensity than LP. Weekly UP (WUP) involves fluctuations in volume and intensity from week to week, whereas daily UP (DUP) involves fluctuations in volume and intensity from workout to workout.

For example, consider a training program that involves performing resistance exercise twice per week for 8 weeks. Sample LP, WUP, DUP, and nonperiodized programs might look like this:

A 2022 meta-analysis reported that periodized programs were superior to nonperiodized programs for increasing 1RM strength, with a trivial-to-small effect size reported.^[182] Concerning the type of periodization, UP (which included studies that utilized either DUP or WUP) was superior to LP for increasing 1RM strength, with a trivial-to-small effect size reported. Additionally, UP was only superior to LP in studies featuring trained participants.

In contrast, periodized programs were not reported to be superior to nonperiodized programs for muscle gain.^[182] It may be the case that the methods used to assess changes in muscle size were not sensitive enough to detect small differences between groups, as a number of the included studies used indirect measures. However, there is good reason, physiologically, to doubt the superiority of periodized programs for muscle gain.

Because a variety of loads produce similar muscle gain,^[7] and high and low loads do not appear to reliably induce different degrees of type I and type II fiber hypertrophy,^[183] there doesn’t seem to be any strong physiological rationale to substantiate how varying training loads across a training program would produce superior muscle growth,^[183] at least under ideal conditions. It may be the case that varying training loads increases the individual’s motivation to exercise, fostering greater adherence to the program and increasing the amount of effort they exert during their workouts, which would theoretically enhance muscle gain over the long term.

Lifting tempo refers to the speed at which the individual intentionally lifts and lowers a weight, which is only under control to a certain extent, as the speed of the concentric portion (i.e., the active lifting of the weight, as opposed to the lowering or eccentric portion) will inevitably be slow when lifting a maximal load (e.g., a 1-repetition maximum) or squeezing out the last couple of repetitions during a high-repetition set to failure.

There is evidence to suggest that lifting with a very slow tempo on the concentric portion (10 seconds) can impair muscle gain.^[184] Another study found that lifting with a faster tempo on the concentric portion (1 second vs. 3 seconds) was better for muscle gain.^[185]

With respect to the eccentric portion of a repetition, there is evidence to suggest that slower (4 seconds vs. 1 second) is better.^[186]

The limited evidence available indicates that a slower tempo during the eccentric phase and a faster tempo during the concentric phase is probably beneficial for muscle hypertrophy,^[187] but there aren’t strict guidelines that should be adhered to, with the exception of avoiding repetition durations that are intentionally very slow (> 10 seconds per repetition).^[188]

For the purpose of muscle gain, the individual should strive for a relatively-explosive lifting motion, then lower under control. Further evidence for the lack of a need to focus on a specific lifting tempo stems from a 2020 study that found that lifting with a strict tempo of 2 seconds on the concentric portion and 2 seconds on the eccentric portion was no better than a self-selected lifting tempo for muscle gain.^[189]

The same recommendation more or less applies for increasing strength: the concentric portion of the repetition should be explosive,^[190] and there aren’t strict guidelines that should be adhered to for the eccentric portion, with the exception of avoiding very slow eccentric motions.

In two studies that examined the effects of different tempos on the eccentric during a 1-repetition maximum bench press test, slower tempos (4–10 seconds) decreased the amount of load lifted compared to faster tempos (either self-selected or 2 seconds).^[191][192] Considering the importance of lifting heavy loads for increasing strength (see “What type of exercise is best for muscle size and strength?”), it’s prudent that those with serious strength goals utilize relatively fast tempos on the eccentric phase to maximize the amount of load they are able to lift.

If the goal is to increase strength on a particular exercise, that exercise should unquestionably be performed first in the workout,^[193] as performing the exercise in an unfatigued state will allow the individual to lift heavier loads, which is of the utmost importance for maximizing gains in strength.

In terms of muscle gain, the overall body of evidence suggests muscle gain does not differ between programs that start workouts with a multi-joint exercise followed by a single-joint (SJ) exercise and programs that start workouts with a single-joint exercise followed by a multi-joint (MJ) exercise.^[193] However, the results of this meta-analysis are limited by the fact that most studies measured changes in muscle size only in the muscle that was the primary agonist in the single-joint exercise, but functioned as a synergist or supporting muscle in the multi-joint exercise. For example, a few studies measured changes in biceps brachii size between a group that performed workouts of a lat pulldown followed by a biceps curl and a group that performed workouts of a biceps curl followed by a lat pulldown.

The results indicated that changes in biceps brachii size are similar between groups, but what about changes in latissimus dorsi size? Does regularly performing a biceps curl before a lat pulldown compromise increases in latissimus dorsi size? This question has not been adequately examined, but limited evidence suggests that this may indeed be the case.

A 2020 study not included in the aforementioned meta-analysis compared changes in the cross-sectional area (CSA) of the pectoralis major in a group that performed workouts consisting of the barbell bench press followed by the lying barbell triceps press (MJ+SJ) and a group that performed workouts consisting of the lying barbell triceps press followed by the barbell bench press (SJ+MJ).^[125] Although there was technically no significant difference between groups, pectoralis major growth in SJ+MJ was approximately half that of MJ+SJ (5.6% vs. 10.6%).

This result may be due to the fact that the triceps brachii functions as a synergist in the bench press. Thus, performing the lying barbell triceps press first in the workout fatigued the triceps brachii and consequently impaired subsequent bench press performance, reducing the hypertrophic stimulus attained by the pectoralis major.

Further research is needed, but the same rule of thumb for strength likely applies to muscle gain: the exercise most important to the primary goal of the training program should be performed first in the workout. For example, if the individual’s primary goal is to increase the size of their chest, they should start their workout with an exercise where the chest muscles are the primary agonist, whether that be a multi-joint (e.g., barbell bench press) or a single-joint exercise (e.g., a machine chest fly).

Dual-energy X-ray absorptiometry (DXA-DEXA|DXA) is an increasingly common means to assess body composition, particularly among elite athletes competing at the international level,^[39] and it is considered the standard by many in the field of sports science.^[40] The ability of DXA to quickly provide detailed body composition estimates is a notable advantage over other body composition methods, but it is not without limitations.

A variety of factors can significantly affect the accuracy of DXA measurements. For example, recent food and fluid intake, supplemental creatine, physical activity, and cold water immersion can all affect DXA estimates of fat mass and fat-free mass (FFM).^{[41][42][43][44][45]}

To illustrate the magnitude of effect that the acute manipulation of some of these variables can have on body composition data, consider the reported changes in FFM over a 3-day period in a combat sport athlete making weight for competition.^[46] Body composition was assessed after a 12-hour overnight fast on each day.

On the day before their weigh-in (day 1), the individual ingested one meal containing 300 kcal alongside 500 mL of fluid, and they utilized a sauna to promote further body water loss. On day 2, they weighed in for their competition. On the day after their weigh-in (day 3), they consumed food and fluid ad libitum. These practices resulted in a reported FFM of 53.0 kilograms on day 1, 50.9 kilograms on day 2, and 56 kilograms on day 3. This corresponds to approximately a 4% change in FFM between days 1 and 2 and a 10% change between days 2 and 3. Given the fact that it’s physiologically impossible for skeletal muscle and organ mass to undergo significant changes over such a short timespan, these data highlight how influential changes in glycogen and body water can be on DXA measurements.

As such, a strict standardized protocol for the use of DXA is necessary to make the most of the data it provides.^[40] Scans should be performed:

• By the same skilled technician, on the same scanner, using the same software and reference database
• In minimal, lightweight clothing
• In a glycogen replete and hydrated state
• After abstaining from intense exercise and alcohol for at least 24 hours
• In an overnight-fasted and rested state, including abstaining from fluid intake upon waking
• After voiding the bladder

To track changes in body composition over time, scans should be taken at least 8 weeks apart.^[40] Moreover, similar nutrition and training practices should be followed in the 24 hours prior to each scan. For women, scans should occur in the same phase or on the same day of the menstrual cycle.

No, but it will likely help, especially in resistance-trained individuals. Although an energy surplus has been shown to provide an important anabolic effect independent of resistance exercise,^[47][48] and combining an energy surplus with resistance training seems to enhance muscle gain,^[49] an energy surplus is not required to gain muscle, as progressive resistance exercise is ultimately the primary stimulus for muscle gain.

Muscle gain has been shown to occur when resistance exercise is performed in conjunction with a hypocaloric diet.^[50][51][52] However, the participants in these studies were untrained and had overweight or obesity. Notwithstanding that caveat, it is notable that muscle gain still occurred in the face of severe energy restriction. One study had the participants consume a liquid formula diet providing about 800 kcal per day (80 grams of protein, 97 grams of carbohydrate, and 10 grams of fat) for 90 days,^[50] while a separate 4-week study featured a 40% reduction in energy intake from baseline.^[52]

The possibility of achieving significant muscle gain while consuming a hypocaloric diet seems to be diminished in lean, resistance-trained individuals,^[53][49] but gains are still possible. While not a widespread phenomenon, there have been a few studies in resistance-trained individuals that reported significant muscle gain in combination with a significant reduction in fat mass.^[54] Notably, a central theme among these studies was the consumption of a high-protein diet (2.2-3.4 grams of protein per kilogram of body weight per day).

One small study provides some insight into the difficulty of building muscle while consuming a hypocaloric diet as a resistance-trained individual. Elite athletes followed a 4-day-per-week resistance exercise program while consuming a diet (containing 1.6 grams of protein per kilogram of body weight per day) that achieved a weekly body weight loss of either 0.7% (SLOW) or 1.4% (FAST).^[55] The participants in each group lost a similar amount of total body weight (−5.5% vs. − 5.6%; FAST achieved this feat more quickly than SLOW, with a range from 4-12 weeks), but SLOW increased lean body mass (+2.1%), whereas there was no change in FAST.

Compared to the catabolic environment promoted by a hypocaloric diet, a eucaloric (weight-maintaining) diet is able to support processes involved in muscle protein synthesis and anabolic signaling and tends to increase fat-free mass when combined with resistance exercise, albeit to a relatively modest extent.^[49]

Individuals interested in maximizing muscle gain are advised to consume a hypercaloric diet. A eucaloric diet can also promote a sufficiently anabolic environment for muscle gain, but the magnitude of muscle gain seems to be relatively limited compared to that of a hypercaloric diet. Lastly, while muscle gain can occur with a hypocaloric diet, this effect is mostly limited to untrained individuals with overweight or obesity. As such, resistance-trained individuals who are relatively lean should minimize the amount of time they spend consuming a hypocaloric diet if they’re interested in maximizing muscle gain.

It’s theorized that because untrained individuals are further from their genetic limit for muscle mass, they may be able to gain muscle faster than trained individuals, and thus would benefit from a larger energy surplus.^[22] Supporting evidence for this statement comes from an 8-week randomized controlled trial in untrained men that performed resistance exercise and added a 2,000 kcal supplement to their diet.^[56] The participants gained a significant amount of fat-free mass (2.9–3.4 kilograms) without changes in fat mass.

In trained individuals, a substantial energy surplus seems to disproportionately increase fat mass, without further benefiting muscle gain. An 8–12 week weight-gain intervention in elite athletes found that a large energy surplus (600 kcal per day) produced a similar increase in lean body mass as an ad libitum diet that featured a modest energy surplus (by 1.7 kg vs. 1.2 kg),^[57] but fat mass significantly increased with the large energy surplus (by 1.1 kg, vs. 0.2 kg for the modest surplus).

A 4-week trial in competitive male bodybuilders reported similar findings. The group consuming “higher amounts of energy” (6,100 kcal per day) gained more muscle mass than the group consuming “moderate amounts of energy” (4,500 kcal per day): 1.0 kilograms vs. 0.4 kilograms. However, the group consuming “higher amounts of energy” also gained considerably more body fat: 1.2% (a relative increase from baseline of 7.4%) vs. 0.1% (a relative increase from baseline of 0.8%).

Based on the available evidence, it’s recommended that individuals interested in muscle gain consume a hypercaloric diet containing 10%–20% in excess of that s required to maintain body weight, and that advanced lifters aim for the lower end of this range.^[22] In practice, this corresponds to a targeted weight gain of about 0.25%–0.5% of body weight per week.

A hypocaloric diet impairs muscle protein synthesis^[58][59][60] and increases muscle protein breakdown.^[61] It can also unfavorably alter the anabolic hormone response to resistance exercise.^[62] Furthermore, prolonged consumption of a hypocaloric diet can disrupt endocrine system function, suppressing levels of reproductive and metabolic hormones and causing unfavorable changes in bone metabolism biomarkers.^[63] For these reasons, a hypocaloric diet would be expected to negatively affect muscle size and strength.

A 2021 meta-analysis that compared the effects of performing resistance training in an energy deficit or without an energy deficit reported that an energy deficit impaired lean mass gains;^[64] more specifically, it was estimated that an energy deficit of 500 kcal per day could prevent gains in lean mass. However, an energy deficit did not impair strength gains; interventions that prescribed resistance training with and without an energy deficit both resulted in a significant increase in muscle strength. The average energy deficit in these studies was 567 kcal per day.

A caveat to these findings is that the studies included in the above meta-analysis were between 3 and 28 weeks long, with an average intervention duration of 16 weeks. While the results suggest that increases in muscle strength can occur in an energy deficit in the short term, spending too much time in an energy deficit will undoubtedly compromise long-term strength gains. Because larger muscles have greater force-generating capacity,^[35] and an energy surplus enhances muscle gain,^[49] individuals interested in maximizing strength gains should spend a notable amount of time consuming a hypercaloric diet.

A ketogenic diet aims to induce physiological ketosis (i.e., an increase in levels of ketone bodies in the blood, typically to levels above 0.5 mmol/L) through severe restriction of carbohydrate intake, typically to less than 50 grams of carbohydrate per day or to less than 10% of total energy intake from carbohydrate. Ketogenic diets are an increasingly popular option among endurance athletes and people interested in fat loss,^[65] including bodybuilders and strength athletes.

Longitudinal studies of resistance-trained individuals consistently show that a ketogenic diet is inferior to a higher-carbohydrate diet for muscle gain.^{[66][67][68][69]} However, a limitation of these studies is that the group consuming a ketogenic diet lost a significant amount of body weight. A hypocaloric diet is known to facilitate a catabolic environment, including a breakdown of muscle proteins and an impairment in muscle protein synthesis and anabolic signaling pathways.^[70]

One 8-week randomized controlled trial in resistance-trained men that did a better job of equating energy intake between groups reported that a higher-carbohydrate diet increased lean body mass compared to a ketogenic diet.^[71]

Collectively, these studies suggest that the primary reason a ketogenic diet is inferior for muscle gain is its appetite-suppressing effect,^[72] negating the ability to achieve positive calorie balance. However, there are some other reasons to think that a ketogenic diet may be less anabolic than a higher-carbohydrate diet.

Because hypertrophy-oriented resistance exercise is primarily fueled by carbohydrate,^[73][74][75] a ketogenic diet could impair resistance exercise performance — the primary stimulus for muscle gain — by limiting the regeneration of adenosine triphosphate (ATP), expediting the onset of muscle fatigue, and impairing the muscles’ ability to contract with high force.^[76][77][78]

Additionally, ketogenic diets may induce a “fasting-like” state, causing a potential shift in the balance of anabolic and catabolic pathways in skeletal muscle;^[79] namely, increasing the activation of the AMPK pathway, which signals to activate protein breakdown and suppress mammalian target of rapamycin (mTOR) signaling, a central regulator of protein synthesis and muscle growth.

Although it is possible to gain muscle on a ketogenic diet given adequate energy and protein intake, taken together the evidence suggests that more muscle gain can be achieved on a higher-carbohydrate diet.^[80]

Plant-based proteins are thought to be inferior to animal-based proteins because (i) they generally contain lower amounts of essential amino acids overall; (ii) they often contain an inadequate amount of one or more specific EAAs (typically lysine, methionine, and/or leucine), and a sufficient amount of all EAA are needed to sustain muscle protein synthesis (MPS); and (iii) they are generally less digestible, meaning that a lower amount of EAA are available for muscle tissue after consuming plant-based proteins.^[81]

There are ways around these issues, however. For starters, while whole food sources of plant-based proteins are generally less digestible than whole food sources of animal-based protein sources, this does not appear to be the case for protein powders.^[82]

Second, it’s possible to compensate for lower amounts of EAA simply by consuming a larger amount of plant-based protein. Research indicates that when a dose of 30 grams of a plant-based protein powder is consumed — regardless of whether it’s derived from wheat, potato, corn, pea, or a combination of sources — a rise in MPS is achieved that is comparable to that of milk protein.^{[83][84][85][86]} Similar results were also reported in a study that compared chicken breast to a lysine-enriched meat alternative composed of wheat and chickpea protein.^[87]

Moreover, most of us don’t consume a single isolated protein source. From a whole diet perspective, protein intake is typically derived from a variety of foods.

Finally, it’s important to consider the elephant in the room here: acute increases in MPS aren’t necessarily predictive of longer term muscle gains,^[88] and the accumulation of muscle mass occurs over a weeks-to-months timescale, rather than minutes-to-hours. So, it’s prudent to question the model used to assess differences in the “muscle-building ability” of plant- and animal-based proteins. This brings us to the central question of importance: can vegan and omnivorous diets similarly support resistance exercise-induced adaptations?

The answer seems to be yes. In two separate studies in young adults that included a resistance exercise intervention and randomized the participants to consume a high-protein diet (≥1.6 grams per kilogram of body weight per day), either mostly from animal-based proteins or exclusively from plant-based proteins, both found comparable increases in muscle size and strength between groups after a few months.^[89][90]

In sum, the collective evidence suggests that as long as total daily protein intake is sufficiently high and a variety of plant-based proteins are consumed, vegan and omnivorous diets are equally effective for increasing muscle size and strength.

The available research indicates that a total daily protein intake of 1.6–2.2 grams per kilogram of body weight per day is best to maximize gains in muscle size and strength. But how should one go about consuming this much protein? It appears that multiple protein feedings per day may be best, based on a few lines of evidence.

Muscle protein synthesis (MPS) is a saturable process; that is, ingesting a certain amount of protein at a meal produces a maximal MPS response and ingesting more protein will not further increase MPS. Protein-feeding studies using various doses of whey protein indicate that about 0.24 grams of protein per kilogram of body weight, on average, maximizes the MPS response in young adults, while a dose of 0.40 grams of protein per kilogram of body weight, on average, maximizes the MPS response in older adults.^[91]

In addition, the rise in MPS following protein ingestion is transient, and MPS reverts to baseline levels after a few hours.^[92][93]

Corresponding with these data, it’s been shown that ingesting 20 grams of whey protein every 3 hours is more effective at stimulating MPS over a 12-hour period than ingesting 10 grams of protein every 1.5 hours or 40 grams of protein every 6 hours.^[94]

In similar studies that had two groups consume diets with equivalent amounts of protein but different distribution patterns, one found greater 24-hour MPS rates with a diet that provided 30–33 grams of protein at each main meal, compared to a diet that provided 11, 16, and 63 grams of protein at breakfast, lunch, and dinner, respectively;^[95] while the second found that a protein distribution of 0.33, 0.46, and 0.48 grams of protein per kilogram of body weight at breakfast, lunch, and dinner, respectively, was slightly better for increasing lean mass over 12 weeks than a distribution of 0.12, 0.45, and 0.83 grams per kilogram of body weight at breakfast, lunch, and dinner, respectively.^[96]

Because muscle gain is ultimately dependent on rates of MPS exceeding rates of muscle protein breakdown over time (see “How does muscle gain occur?” under “What is muscle size and strength?”), it follows that multiple maximal MPS responses per day would be beneficial for muscle gain. This relationship seems to reach a point of diminishing returns, however, as one study in rugby players found no difference between six and four protein feedings per day for increasing lean mass.^[97] However, weighing the collective evidence, it’s reasonable to assume that three to four protein feedings per day is superior to one.

Therefore, in the context of a total daily protein intake of 1.6–2.2 grams per kilogram of body weight per day, it’s recommended that individuals consume 0.40–0.55 grams of protein per kilogram of body weight across roughly four meals per day.^[98]

Stark differences in muscle and strength gain have been reported between individuals performing the same standardized resistance training program.^{[149][150][151][152]} For example, one study reported that changes in muscle size and strength varied from –11% to 30% and –8% to 60%,^[149] respectively, whereas another reported a variation of –2% to 59% and 0% to 250%,^[151] respectively.

While genetic and physiological differences between individuals,^[26] as well as lifestyle factors (i.e., nutrition, sleep, stress), help to explain a large proportion of the response to a given resistance exercise program, training history is another influential factor, and one that is rarely considered in resistance exercise studies. For example, it’s been shown that a resistance exercise program that increased volume by 20% over what participants previously performed was better for muscle gain than a nonindividualized program.^[153]

On the other hand, a program containing a decrease in volume has also been shown to promote substantial muscle gain in some participants,^[154] further demonstrating that the response to resistance exercise is highly individual.

Besides interindividual differences in the response to resistance exercise, evidence suggests that particular styles of resistance exercise can produce substantially different effects within an individual. In one study that had participants perform high-frequency (5x per week) resistance exercise with one leg and low-frequency (2x or 3x per week) resistance exercise with the other leg, it was found that some individuals gained more muscle and strength on the leg assigned to the high-frequency condition and some individuals gained more muscle and strength on the leg assigned to the low-frequency condition, while others experienced no difference between conditions.^[135]

To throw another monkey wrench in the works, only about 32% of individuals displayed an aligned response, i.e., one in which the same resistance training frequency was better for both muscle gain and strength. This suggests that, within an individual, not only are certain resistance exercise programs more effective than others, but also that the best program to increase strength is likely different from the best program for muscle gain, so it may be prudent for the individual to prioritize one goal over the other.

In a nutshell, the best resistance exercise program for one person is unlikely to be the best for another, so each person will have to experiment to find what works best for them. When a plateau in progress occurs, some individuals will benefit from increasing their training frequency and/or volume, while others will benefit from decreasing one or both of these variables.