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Resistance Training Volume is the Key to Muscle Size
Zachary Mang, M.S., Juliet St. Germain, and Len Kravitz, Ph.D.

Resistance training volume (RTV) is the amount of total work performed during a session of lifting and is commonly expressed as the product of repetitions X number of sets X intensity load (Figueiredo et al, 2017). Any one of these variables can be adjusted to increase volume in a resistance training (RT) program. For example, one can increase RTV by performing extra sets of an exercise, adding more repetitions, or increasing the weight being lifted. Exercisers commonly cite “lack of time” as a large barrier to exercise, which explains why low-volume training has gained much popularity (Figueiredo et al., 2017). However, Figueirdo et al. submit that recent publications consistently report that high RTV produces superior muscular adaptations in muscle size (i.e., hypertrophy), which will be the focus of this research column.

Study #1: Schoenfeld, B.J., Contreras, B., Krieger, J. et al. (2019). Resistance training volume enhances muscle hypertrophy but not strength in trained men. Medicine and Science in Sports and Exercise. 51(1), 94-103.

Participants: Thirty-four healthy resistance-trained men (ave age =24yrs) were randomly assigned into three groups: low-volume (1-set per exercise), moderate-volume (3-sets per exercise), and high-volume (5-sets per exercise).
Intervention: The study lasted for 8-weeks and subjects lifted 3 days per week. Seven total-body exercises were used, 8-12 repetitions were performed per set, and 90-120 seconds of rest was provided between sets. Muscle thickness was used to measure hypertrophy, which was determined via ultrasound at 4 body sites (biceps, triceps, mid-thigh, and lateral-thigh).

Results: Low, moderate, and high-volume RT programs were all effective for muscle size adaptations. However, the high-volume training proved to be the strongest stimulus for hypertrophy development.. Additionally, significant preintervention to postintervention increases in strength and endurance in all groups was observed, with no statistically significant between-group differences.

Study #2: Amirthalingam, T., Mavros, Y., Wilson, G.C., et al. (2017) Effects of a modified German volume training program on muscular hypertrophy and strength. Journal of Strength and Conditioning Research. 31(11), 3109-3119.

Participants: In this study, 19 healthy men (ages 19-24 years) with at least 1-year of RT experience were randomly assigned to German volume training (GVT) (10 sets X 10 reps) or modified-GVT (5 sets X 10 reps).
Intervention: The study lasted 6-weeks and lifting occurred 3-days per week in a split-routine fashion. For example, session 1 targeted the upper back and chest (i.e., flat bench press, incline bench press, latissimus pull-down, and seated row), session 2 targeted the legs (i.e., leg extension, leg flexion, leg press, lunges, and heel raisers), and session 3 targeted the arms and shoulders (i.e., upright row, shoulder press, bicep curls, and triceps push-down). Dual energy x-ray absorptiometry (DXA) scans measured lean-mass and ultrasound was used for muscular hypertrophy adaptations at 4-sites: biceps, triceps, hamstrings, and quadriceps.

Results: The DXA scans revealed that both groups increased their total body lean mass similarly (+2.7% for the modified-GVT and +1.9% for GVT group), However, the modified-GVT group had superior increases in the lean mass of their trunk (+4.1% vs. +1%) and arms (+7.8% vs. +3.4%), respectively. The ultrasound scans revealed conflicting results, as the GVT group had superior increases in triceps thickness (+10.7% vs. +5.6%), but the modified-GVT group had superior increases in biceps thickness (+7.3% vs. +0.9%). Both, the GVT and modified-GVT proved to be beneficial for hypertrophy. However, excessive volume may impede muscular adaptations. Fitness pros should modify their client training programs accordingly. Amirthalingam and colleagues summarize that to maximize hypertrophic training effects, the researchers recommend a training volume of 4-6 sets per exercise that is performed. The researchers submit that it seems gains will plateau beyond this set range and may even regress due to overtraining.

Mechanisms of Multiple-Set Training
Why does multiple-set training evoke greater hypertrophy than single-set training? Muscle hypertrophy is a multifaceted process which has not been completely explained in research. However, mechanical load, that is the weight lifted, is arguably a key and perhaps the most important mechanism activating muscle hypertrophy (Wackerhage, 2019). A high RTV exercise stimulus produces sustained mechanical tension on the muscles, which potentially increases the post-exercise activity of intracellular molecules responsible for increasing muscle protein synthesis. Mitchell et al. (2012) discuss that a possible mechanism is with the protein p70S6K. Their research suggests that resistance training, particularly when sets are taken to fatigue, activates p70S6K, which then leads to metabolic changes that increase muscle protein synthesis. Additionally, higher volumes in RT likely trigger more metabolic stress of muscle. Metabolic stress changes that occur in muscle include a low concentration of phosphocreatine, a high lactate concentration, and a low ph in muscle (i.e., more acidic environment) (Wackerhage et al., 2019). These metabolic stress changes have been shown to promote muscle hypertrophy (Wackerhage et al., 2019). It is probable that these metabolic changes are greater during multiple-set resistance training programs as compared to single-set training programs.

Practical Recommendations and Conclusions
Hypertrophy occurs along a spectrum of volumes, so trainers are encouraged to undulate low, moderate, and high-volume programs to increase adherence and prevent overtraining with their clients. For instance, 1-2 set training can be used for a recovery block and 3-5 set training can be utilized for blocks of overload and/or overreaching. The research strongly suggests that RTV is the primary driver for hypertrophy, and higher-volume programs generally result in greater muscle growth. However, the relationship between RTV and hypertrophy may be described as an inverted U-shape, meaning that adaptations diminish when too few or too many sets are performed. Therefore, it follows that enthusiastic lifters may best optimize muscular hypertrophy adaptations by performing multiple sets not exceeding 5 sets per exercise (in a training session). Wackerhage et al. (2019) add that for optimal hypertrophy, clients should train at 40-80% of their 1-repetition maximum, using loads greater than 60% if strength is also a target goal. Wackerhage and colleagues also summarize research indicating to rest over 2 minutes between sets, and consume a diet that contains at least 1.6 grams of protein per kilogram of body weight. And remember, with every rep we all get stronger.

Side Bar #1: To maximize hypertrophy, how heavy should you lift?
For years, it was believed that heavy loads (>65% 1-RM) were required to induce muscle growth. However, more recent research shows that muscle growth occurs along a spectrum of intensities (Mitchell et al, 2012). Do heavy weights work? Yes. Do light weights work? Yes. The key is to perform sets to momentary muscular fatigue, when a client cannot complete the final repetition of a set (Mitchell et al, 2012).

Zachary Mang, M.S. is a youth baseball coach in Albuquerque, NM and a doctoral student in Exercise Science at the University of New Mexico. His research interests include metabolic adaptations to resistance training, oxidative adaptations in response to heat acclimation, and molecular responses to exercise as they pertain to health and fitness.

Juliet St. Germain, B.S. graduated Summa Cum Laude from the UNM Exercise Science program and will continue her education pursuing a doctorate in Physical Therapy at Northern Arizona University. Her research interests include exercise for clinical populations as well as physical therapy rehabilitation for cardiovascular and neurological populations.

Len Kravitz, PhD, CSCS, is the program coordinator of exercise science at the University of New Mexico, where he received the Outstanding Teacher of the Year and Presidential Award of Distinction. He just released his third book, <I>HIIT Your Limit: High-Intensity Interval Training<I> (Amazon)

Figueiredo, C. de salles, B.F., Trajano, G.S. (2017). Volume for muscle hypertrophy and health outcomes: The most effective variable in resistance training, Sports Medicine, 48:499-505.

Mitchell, C.J., Churchard-Venne, T.A., West, D.W.D. et al. (2012). Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Journal of Applied Physiology, 113(1): 71-77.
Accessed March 29, 2019

Wackerhage, H., Schoenfeld, B.J., Hamilton, D.L. et al. (2019). Stimuli and sensors that initiate skeletal muscle hypertrophy following resistance exercise, Journal of Applied Physiology, 126, 30-43.