Physical activity
Training for muscle growth. Update on scientific evidence 2023.
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MPH, MSc
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This "science" is often interpreted as the application of average results to every living individual (nomothetic fallacy). However, clinical decision-making actually involves something very different: gathering general principles and adapting them to the individual. In the topic at hand, the ideal training for a person depends on general physiological factors (resistance training is needed, protein is needed for muscle hypertrophy, etc.), individual physiological aspects (individuals start from different physical conditions and respond differently to different stimuli), and psychological and environmental aspects (individual preferences, available resources, etc.). People therefore respond differently to different training volumes, have different metabolic and behavioral responses, recovery and rest needs, etc.
Volume: Total training volume refers to the number of sets and repetitions per muscle group. It has long been known that a single set increases muscle hypertrophy, however, there is evidence that higher training volume is beneficial for muscle hypertrophy (Schoenfeld et al 2017). Some recent studies show that a higher volume (32 vs. 16 sets) favors people with training experience (Brigatto et al 2022). In general, the evidence suggests that there is a linear progression up to a point that depends on the individual's experience. A systematic umbrella review finds that, in general, more than 10 sets per week should be performed to optimize hypertrophy (Bernárdez-Vázquez et al 2022). It is reasonable to conclude that the lower limit optimizes muscle growth in less experienced individuals, and the upper limit is necessary as the individual becomes more adapted to training.
Intensity: Intensity in strength training refers to the weight lifted in relation to the person's strength. The percentage of a maximum repetition or % 1RM, which is 100% of the weight that the person can lift for 1 repetition, is often used as a measure. The necessary and sufficient stimulus to create muscle hypertrophy needs to reach a certain level of resistance. We can approximately perform 8-10 repetitions with 70-80% of our 1RM. Generally, 65% 1RM is used, although it has always been known that loads should be increased and fewer repetitions performed to develop muscle strength, generally below 6 repetitions, while ranges between 6-12 repetitions are used for hypertrophy. Systematic reviews show that strength gains require working with a higher weight load with fewer repetitions, while hypertrophy does not require such high weight loads (Carvalho et al, 2022). Therefore, it seems that muscle hypertrophy is facilitated by a higher volume of work with a lower load than the opposite. The intensity of the lift must be differentiated from the intensity of a training session, which involves mechanical work with load, repetition speed, and rest between sets, producing a metabolic effect as a result. Therefore, as the person progresses, variations in intensity can be considered by modifying different parameters.
Time under tension: The mechanical tension to which the muscle is subjected during resistance exercise is related to hypertrophy through growth signals mediated by the activation of mechanosensors and metabolic products that differ depending on the time of muscle tension. Schoenfeld has researched the literature on this variable and found no differences when training with repetition durations ranging from 0.5 to 8 seconds (Schoenfeld et al 2015). However, as training progresses, varying the time under tension of the concentric and eccentric phases may improve performance and perhaps hypertrophy.
Frequency: One resistance training session is sufficient to stimulate protein synthesis and produce muscle hypertrophy. Training of muscle groups once a week has been compared with training two or three times a week, maintaining the volume (i.e., the same total training, but distributed over several sessions). Some studies have suggested greater muscle gain when workouts are divided into several days, however systematic reviews show that the main factor is volume, and not so much the distribution of training days (Grgic et al 2018). This would imply that total volume is the main factor in optimizing both muscle growth and recovery.
Range of motion: It has long been known that the mechanical tension produced by stretching can be an important stimulus for hypertrophy, and that the lack of mechanical tension from immobilization promotes atrophy. In general, weight training is performed with a controlled range of motion throughout the entire range that allows for safe muscle movement. In general, there is evidence that working with a wide ROM improves strength, although the evidence for hypertrophy is not consistent (Pallarés et al 2021). However, recent research suggests that working in restricted ranges may be superior to working through full ranges of motion, provided that the muscles are placed in the maximum position of tension by stretching (Pedrosa et al 2022, Maeo et al 2021, Maeo et al 2022).
Muscle failure: Muscle failure is generally reached when the person is unable to perform another repetition due to local muscle fatigue. For many years, it has been theorized that achieving maximum muscle development involved performing a number of repetitions to muscle failure. However, a recent systematic review found no superiority in training to failure (Grgic et al 2022).
Repetitions in reserve (RIR): Since the old school days of bodybuilding, it has been thought that for muscle growth, total repetitions do not imply effective repetitions, and that the only effective repetitions for hypertrophy are the last ones. Arnold himself talked about this almost half a century ago in Pumping Iron. High loads are required to maximize the recruitment of high-threshold motor units, although repetitions close to failure are also required to recruit fibers that are not recruited with the first repetitions. This would imply that loads should be set that allow for reserve repetitions that bring you close to failure, and also that it is possible to hypertrophy with lower loads but with a higher volume and repetitions close to failure. There are different routes that signal hypertrophy, and it is ideal to combine them as you progress in your training. A higher number of repetitions implies greater metabolic stress in certain aspects (growth signals stimulated by lactate accumulation, etc.), and possibly greater recruitment of slow fibers. This is an important concept that would mediate the concept of volume that we have already seen. However, the evidence from RIR has not been consistent.
Phases: there is evidence that both concentric (shortening) and eccentric (lengthening) contractions produce anabolism. Systematic reviews of studies argue that training should probably be optimized by addressing both actions (Schoenfeld et al 2017), and can be adapted to VBT or contraction velocity-based training (Held et al 2022), as well as different times under tension.
Rest between sets: Short-duration anaerobic work is highly dependent on phosphagen metabolism, with phosphocreatine resynthesis being a key aspect. Long rest intervals of several minutes are generally prescribed to maintain high strength and intensity, which should translate into improvements in muscle strength outcomes. Shorter rest times are generally prescribed for muscle hypertrophy. Grgic has conducted a systematic review, with a cutoff point separating times of less than one minute and greater than one minute. Given that different physiological effects are achieved that likely impact hypertrophy in different ways, changing rest types is probably optimal for optimizing long-term muscle growth (Grgic et al 2017).
Variation: It is intuitive that variation is important given that the neuromuscular system adapts to repeated movement, and that this aspect is more important for trained individuals. There is some evidence that exercise variation promotes greater gains (Kassiano et al, 2022). However, it is important that variations are well targeted and do not constitute random training. On the other hand, there is also some evidence that periodization of training improves strength, although there is no evidence that it equally favors hypertrophy (Moesgaard et al 2022). However, periodization should be more advantageous the more trained the person is.
Schedules: It has been documented that muscle strength is greater in the afternoon than in the morning. However, in studies comparing morning and afternoon training, strength progression is similar at both times, so people progress regardless of their training schedule. There are not enough studies to demonstrate the potential advantage of morning training over other times of day (Grgic et al 2019). Therefore, the training schedule should be individualized according to the person's availability and preferences.
Order of exercises: The order of training is another key factor, and there is evidence that exercises performed first allow for greater strength and intensity, and some studies have found that they result in greater strength gains (Nunes et al 2021).
Individualization: Individualization may be more important than "evidence-based" training, given that the average results of studies do not show significant positive effects of interventions, but rather provide information on minimal aspects that must be understood when planning a training program. Adapting training to the individual depends on their goals, circumstances, proper assessment on our part, training preferences, fitness level, progression and adaptation to training, motivation, etc.
Progression: it is important to progress in order to continue improving. Inevitably, the quantitative aspect of muscle and strength development declines after a certain point, so we must move from the quantitative and basic to adding qualitative elements, and improve from there, adding functionality and attacking different angles with more specialized exercises and technical aspects. Progress can be made in terms of strength or volume, but also by improving or varying motor control of the movement, changing exercises, working different angles, changing thresholds in relation to muscle failure, performing some pre-exhaustion techniques, changing the concentric and eccentric tension time, working on concentric speed, etc.
Specific techniques: As training progresses, the use of specific techniques can improve progression. For example, blood flow restriction training can lead to improvements in strength, hypertrophy, and various markers of athletic performance (Wortman et al 2020). The reduced use of loads makes it particularly interesting for people with injuries and older adults.
Combination of workouts: the scientific literature has documented an interference effect of aerobic exercise on strength and power, although studies have not always been consistent (Lundberg et al 2022). Muscle mass retention and athletic performance may be optimized if the same muscle groups are not overworked when performing a combination of anaerobic and aerobic exercise, so this should be taken into account to optimize results.
Gender: it may come as a surprise that gains in strength and hypertrophy can be equal to or greater in women than in men (Roberts et al 2020). Men lift more weight and have greater muscle mass in absolute terms, which is different from the gains obtained from training in terms of muscle mass and baseline strength.
Psychology: People tend to overestimate what can be achieved in the short term and underestimate what can be achieved in the long term. However, it is common for people to project their high initial motivation onto distant months, overestimating their long-term motivation and underestimating the need for self-control. We must also remember that overweight people in particular tend to underestimate the calorie content of what they eat and overestimate the energy expenditure of the physical activities they do.
The limitations of the studies are extensive, as they are often small and differ in terms of volume, duration, and the subjects selected (gender, age, training time, dietary differences, medications, etc.). In terms of results, body composition and the many ways in which hypertrophy can be measured using measures of lean body mass, regional lean mass, muscle thickness, cross-sectional muscle histologies, or muscle circumference are particularly problematic. Finally, it is possible that each muscle group actually responds differently. Many studies are conducted with different muscle groups, and what is optimal for one muscle group or type of exercise may not be optimal for others.
Cite as: Bordallo. A. Training for muscle growth. Update on scientific evidence 2023. - ICNS. Available at https://www.icns.es/en/news/science-of-training-for-muscle-growth
Copyright© ICNS Institute
Volume: Total training volume refers to the number of sets and repetitions per muscle group. It has long been known that a single set increases muscle hypertrophy, however, there is evidence that higher training volume is beneficial for muscle hypertrophy (Schoenfeld et al 2017). Some recent studies show that a higher volume (32 vs. 16 sets) favors people with training experience (Brigatto et al 2022). In general, the evidence suggests that there is a linear progression up to a point that depends on the individual's experience. A systematic umbrella review finds that, in general, more than 10 sets per week should be performed to optimize hypertrophy (Bernárdez-Vázquez et al 2022). It is reasonable to conclude that the lower limit optimizes muscle growth in less experienced individuals, and the upper limit is necessary as the individual becomes more adapted to training.
Intensity: Intensity in strength training refers to the weight lifted in relation to the person's strength. The percentage of a maximum repetition or % 1RM, which is 100% of the weight that the person can lift for 1 repetition, is often used as a measure. The necessary and sufficient stimulus to create muscle hypertrophy needs to reach a certain level of resistance. We can approximately perform 8-10 repetitions with 70-80% of our 1RM. Generally, 65% 1RM is used, although it has always been known that loads should be increased and fewer repetitions performed to develop muscle strength, generally below 6 repetitions, while ranges between 6-12 repetitions are used for hypertrophy. Systematic reviews show that strength gains require working with a higher weight load with fewer repetitions, while hypertrophy does not require such high weight loads (Carvalho et al, 2022). Therefore, it seems that muscle hypertrophy is facilitated by a higher volume of work with a lower load than the opposite. The intensity of the lift must be differentiated from the intensity of a training session, which involves mechanical work with load, repetition speed, and rest between sets, producing a metabolic effect as a result. Therefore, as the person progresses, variations in intensity can be considered by modifying different parameters.
Time under tension: The mechanical tension to which the muscle is subjected during resistance exercise is related to hypertrophy through growth signals mediated by the activation of mechanosensors and metabolic products that differ depending on the time of muscle tension. Schoenfeld has researched the literature on this variable and found no differences when training with repetition durations ranging from 0.5 to 8 seconds (Schoenfeld et al 2015). However, as training progresses, varying the time under tension of the concentric and eccentric phases may improve performance and perhaps hypertrophy.
Frequency: One resistance training session is sufficient to stimulate protein synthesis and produce muscle hypertrophy. Training of muscle groups once a week has been compared with training two or three times a week, maintaining the volume (i.e., the same total training, but distributed over several sessions). Some studies have suggested greater muscle gain when workouts are divided into several days, however systematic reviews show that the main factor is volume, and not so much the distribution of training days (Grgic et al 2018). This would imply that total volume is the main factor in optimizing both muscle growth and recovery.
Range of motion: It has long been known that the mechanical tension produced by stretching can be an important stimulus for hypertrophy, and that the lack of mechanical tension from immobilization promotes atrophy. In general, weight training is performed with a controlled range of motion throughout the entire range that allows for safe muscle movement. In general, there is evidence that working with a wide ROM improves strength, although the evidence for hypertrophy is not consistent (Pallarés et al 2021). However, recent research suggests that working in restricted ranges may be superior to working through full ranges of motion, provided that the muscles are placed in the maximum position of tension by stretching (Pedrosa et al 2022, Maeo et al 2021, Maeo et al 2022).
Muscle failure: Muscle failure is generally reached when the person is unable to perform another repetition due to local muscle fatigue. For many years, it has been theorized that achieving maximum muscle development involved performing a number of repetitions to muscle failure. However, a recent systematic review found no superiority in training to failure (Grgic et al 2022).
Repetitions in reserve (RIR): Since the old school days of bodybuilding, it has been thought that for muscle growth, total repetitions do not imply effective repetitions, and that the only effective repetitions for hypertrophy are the last ones. Arnold himself talked about this almost half a century ago in Pumping Iron. High loads are required to maximize the recruitment of high-threshold motor units, although repetitions close to failure are also required to recruit fibers that are not recruited with the first repetitions. This would imply that loads should be set that allow for reserve repetitions that bring you close to failure, and also that it is possible to hypertrophy with lower loads but with a higher volume and repetitions close to failure. There are different routes that signal hypertrophy, and it is ideal to combine them as you progress in your training. A higher number of repetitions implies greater metabolic stress in certain aspects (growth signals stimulated by lactate accumulation, etc.), and possibly greater recruitment of slow fibers. This is an important concept that would mediate the concept of volume that we have already seen. However, the evidence from RIR has not been consistent.
Phases: there is evidence that both concentric (shortening) and eccentric (lengthening) contractions produce anabolism. Systematic reviews of studies argue that training should probably be optimized by addressing both actions (Schoenfeld et al 2017), and can be adapted to VBT or contraction velocity-based training (Held et al 2022), as well as different times under tension.
Rest between sets: Short-duration anaerobic work is highly dependent on phosphagen metabolism, with phosphocreatine resynthesis being a key aspect. Long rest intervals of several minutes are generally prescribed to maintain high strength and intensity, which should translate into improvements in muscle strength outcomes. Shorter rest times are generally prescribed for muscle hypertrophy. Grgic has conducted a systematic review, with a cutoff point separating times of less than one minute and greater than one minute. Given that different physiological effects are achieved that likely impact hypertrophy in different ways, changing rest types is probably optimal for optimizing long-term muscle growth (Grgic et al 2017).
Variation: It is intuitive that variation is important given that the neuromuscular system adapts to repeated movement, and that this aspect is more important for trained individuals. There is some evidence that exercise variation promotes greater gains (Kassiano et al, 2022). However, it is important that variations are well targeted and do not constitute random training. On the other hand, there is also some evidence that periodization of training improves strength, although there is no evidence that it equally favors hypertrophy (Moesgaard et al 2022). However, periodization should be more advantageous the more trained the person is.
Schedules: It has been documented that muscle strength is greater in the afternoon than in the morning. However, in studies comparing morning and afternoon training, strength progression is similar at both times, so people progress regardless of their training schedule. There are not enough studies to demonstrate the potential advantage of morning training over other times of day (Grgic et al 2019). Therefore, the training schedule should be individualized according to the person's availability and preferences.
Order of exercises: The order of training is another key factor, and there is evidence that exercises performed first allow for greater strength and intensity, and some studies have found that they result in greater strength gains (Nunes et al 2021).
Individualization: Individualization may be more important than "evidence-based" training, given that the average results of studies do not show significant positive effects of interventions, but rather provide information on minimal aspects that must be understood when planning a training program. Adapting training to the individual depends on their goals, circumstances, proper assessment on our part, training preferences, fitness level, progression and adaptation to training, motivation, etc.
Progression: it is important to progress in order to continue improving. Inevitably, the quantitative aspect of muscle and strength development declines after a certain point, so we must move from the quantitative and basic to adding qualitative elements, and improve from there, adding functionality and attacking different angles with more specialized exercises and technical aspects. Progress can be made in terms of strength or volume, but also by improving or varying motor control of the movement, changing exercises, working different angles, changing thresholds in relation to muscle failure, performing some pre-exhaustion techniques, changing the concentric and eccentric tension time, working on concentric speed, etc.
Specific techniques: As training progresses, the use of specific techniques can improve progression. For example, blood flow restriction training can lead to improvements in strength, hypertrophy, and various markers of athletic performance (Wortman et al 2020). The reduced use of loads makes it particularly interesting for people with injuries and older adults.
Combination of workouts: the scientific literature has documented an interference effect of aerobic exercise on strength and power, although studies have not always been consistent (Lundberg et al 2022). Muscle mass retention and athletic performance may be optimized if the same muscle groups are not overworked when performing a combination of anaerobic and aerobic exercise, so this should be taken into account to optimize results.
Gender: it may come as a surprise that gains in strength and hypertrophy can be equal to or greater in women than in men (Roberts et al 2020). Men lift more weight and have greater muscle mass in absolute terms, which is different from the gains obtained from training in terms of muscle mass and baseline strength.
Psychology: People tend to overestimate what can be achieved in the short term and underestimate what can be achieved in the long term. However, it is common for people to project their high initial motivation onto distant months, overestimating their long-term motivation and underestimating the need for self-control. We must also remember that overweight people in particular tend to underestimate the calorie content of what they eat and overestimate the energy expenditure of the physical activities they do.
The limitations of the studies are extensive, as they are often small and differ in terms of volume, duration, and the subjects selected (gender, age, training time, dietary differences, medications, etc.). In terms of results, body composition and the many ways in which hypertrophy can be measured using measures of lean body mass, regional lean mass, muscle thickness, cross-sectional muscle histologies, or muscle circumference are particularly problematic. Finally, it is possible that each muscle group actually responds differently. Many studies are conducted with different muscle groups, and what is optimal for one muscle group or type of exercise may not be optimal for others.
Cite as: Bordallo. A. Training for muscle growth. Update on scientific evidence 2023. - ICNS. Available at https://www.icns.es/en/news/science-of-training-for-muscle-growth
Copyright© ICNS Institute
#physicalexercise
References:
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Brigatto FA, Lima LEM, Germano MD, Aoki MS, Braz TV, Lopes CR. High Resistance-Training Volume Enhances Muscle Thickness in Resistance-Trained Men. J Strength Cond Res. 2022 Jan 1
Carvalho L, Junior RM, Barreira J, Schoenfeld BJ, Orazem J, Barroso R. Muscle hypertrophy and strength gains after resistance training with different volume-matched loads: a systematic review and meta-analysis. Appl Physiol Nutr Metab. 2022 Apr
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Maeo S, Huang M, Wu Y, Sakurai H, Kusagawa Y, Sugiyama T, Kanehisa H, Isaka T. Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths. Med Sci Sports Exerc. 2021 Apr 1
Maeo S, Wu Y, Huang M, Sakurai H, Kusagawa Y, Sugiyama T, Kanehisa H, Isaka T. Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position. Eur J Sport Sci. 2022 Aug 11:1-11. doi: 10.1080/17461391.2022.2100279
Moesgaard L, Beck MM, Christiansen L, Aagaard P, Lundbye-Jensen J. Effects of Periodization on Strength and Muscle Hypertrophy in Volume-Equated Resistance Training Programs: A Systematic Review and Meta-analysis. Sports Med. 2022 Jul
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Pallarés JG, Hernández-Belmonte A, Martínez-Cava A, Vetrovsky T, Steffl M, Courel-Ibáñez J. Effects of range of motion on resistance training adaptations: A systematic review and meta-analysis. Scand J Med Sci Sports. 2021 Oct
Pedrosa GF, Lima FV, Schoenfeld BJ, Lacerda LT, Simões MG, Pereira MR, Diniz RCR, Chagas MH. Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. Eur J Sport Sci. 2022 Aug
Roberts BM, Nuckols G, Krieger JW. Sex Differences in Resistance Training: A Systematic Review and Meta-Analysis. J Strength Cond Res. 2020 May
Schoenfeld BJ, Ogborn D, Krieger JW. Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. J Sports Sci. 2017 Jun
Schoenfeld BJ, Ogborn DI, Krieger JW. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Med. 2015 Apr
Schoenfeld BJ, Ogborn DI, Vigotsky AD, Franchi MV, Krieger JW. Hypertrophic Effects of Concentric vs. Eccentric Muscle Actions: A Systematic Review and Meta-analysis. J Strength Cond Res. 2017 Sep
Wortman RJ, Brown SM, Savage-Elliott I, Finley ZJ, Mulcahey MK. Blood Flow Restriction Training for Athletes: A Systematic Review. Am J Sports Med. 2021 Jun
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