Resistance training volume is an important acute variable when analyzing the current body of literature in relationship to strength and hypertrophy, however specific recommendations in relationship to weekly set total and weekly frequency are ambiguous.
Resistance training volume recommendations should be highly individualized and evidence based according to training status and individual goals (Arazi & Asadi, 2011). In order to determine effects of volume on strength and hypertrophy, research must assess multiple aspects including skeletal muscle molecular adaptations, cross-sectional area, satellite cell proliferation, measured strength tests, production of metabolic stress, and mechanical tension associated with varying amounts of volume and frequency. Difficulties can be seen isolating these variables in the current body of literature due to the wide variety of research design. By analyzing the effects of acute resistance training variables, volume and frequency can be isolated and measured to determine recommendations for all populations.
In the past several years, the internet has made workout programs readily available to anyone with a phone or computer. There is certainly not a one size fits all approach and different techniques are not inherently bad, however there is a lack of evidence based training recommendations in circulation. Many of the workout programs circulating are simply based on anecdote and seem to have little evidence to support the volume and frequency of their recommendations. Training volume has gained support for being one of the most important factors for skeletal muscle hypertrophy and strength (Heaselgrave, Blacker, Smeuninx, McKendry, & Breen, 2019). The purpose of this investigation is to synthesize an evidence based approach to make general recommendations of volume in terms of sets per week and number of days per week for optimal strength and hypertrophy utilizing a resistance training program.
Resistance Training Volume With Frequency Equated
Volume and frequency are two separate variables however they are intertwined in programming as well as the literature. Sooneste, Tanimoto, Kakigi, Saga, and Katamoto (2013) effectively isolated volume as a variable in their study examining its effects on hypertrophy. When determining effects of volume on skeletal muscle strength and hypertrophy, there are many acute variables to hold constant in order to isolate volume. A variable that is not often taken into account is individual differences in genetics when determining significance. Sooneste et al. (2013) controlled this by evaluating 1 set vs 3 set per session training on separate arms of each subject. While significant effects where not seen due to sample sizes and length of study, the results suggest that the higher volume group training 3 sets twice per week lead to greater increase in cross sectional area and strength. Tibana et al. (2017) had similar findings that training with higher volume lead to less undesirable effects on the skeletal muscle proteins. Tibana et al. (2017) found that 8 sets of resistance training three days per week lead to significant effects which concurs with Hanssen et al. (2013). Hanssen et al. (2013) found that with 3 set exercises three sessions per week lead to greater amounts of satellite cells in lower body skeletal muscle, specifically the vastus lateralis. With frequency held constant at two or three days per week it can be stated that at 3 sets per muscle group is more effective than one set for strength and skeletal muscle growth.
Manipulations of Resistance Training Frequency With Volume Equated
Training frequency is often analyzed in individuals attempting to train fewer days per week and accomplish similar amounts of volume when compared to a five day bodybuilding style training program or those looking to maximize their recovery. Tavares et al. (2017) found no difference in muscle cross sectional area and strength when training training frequency was reduced. The maintenance of training adaptations is effective even with less frequency (Tavares et al., 2017). When training volume is equated, the same amount of stress is placed on the muscle groups being activated in a weekly time period leading to no significant change in adaptions (Arazi & Asadi, 2011). Tavares et al. (2017) then investigated the use of a de-load protocol in order to examine adaptations to less frequency and found that adaptations are kept from prior training protocol. Arazi & Asadi (2011) and Tavares et al. (2017) identify that a frequency of one to three days a week can lead to similar adaptations in skeletal muscle strength and hypertrophy. Serra et al. (2015) conducted an 8 month long study analyzing volume as a constant while resistance training either 2 days, 3 days or 4 days per week. Serra et al. (2015) concluded that anywhere from two to four training sessions per week are sufficient in order to produce strength gains. This conclusion concurs with Arazi & Asadi (2011) as well as Colquhoun et al. (2018), Lasevicius et al. (2019), and Yue, Karsten, Larumbe-Zabala, Seijo, & Naclerio (2018) who found that between 2 sessions and 4 sessions resistance training per week yielded similar adaptations in muscle strength and muscle hypertrophy.
Resistance Training Volume in Relationship to Exercise Intensity
Increasing resistance training volume is one way to insure more metabolic stress and mechanical tension on skeletal muscle to produce adaption from resistance training. Although the effects of higher volume have been will documented in the literature, increasing training volume has its limitations (Mangine et al. 2015). Mangine et al. (2015) found that a lower volume approach with greater intensity was significantly more effective at building strength and hypertrophy. Part of the aim of this study was to asses the effect of endocrine response on strength and hypertrophy which was shown to have no effect further isolating volume and intensity in the study. Volume and intensity were different between groups with the low volume group having greater intensity and also greater results in muscle strength and hypertrophy. Analyzing the findings of Hanssen et al. (2013), Tibana et al. (2017) and Soonest et al. (2013), a research design that equates volume and intensity functions as an independent variable would make a complete argument. Findings where intensity is not equated and volume is a variable leads the practitioner to evaluate more than just exercise volume when attempting to optimize results. With intensity equated, higher amounts of training volume can be more effective to improve muscle strength and hypertrophy (Sooneste et al., 2013).
Molecular Adaptations to Low Volume Resistance Training in Comparison to High Volume Resistance Training
Adaptations to high volume protocols have anecdotally been reported by bodybuilders however studies comparing adaptations from high intensity lower volume training have been limited in number (Mangine et al., 2015). Mangine et al. (2015) hypothesized that adaptations to a lower volume protocol are found in this study because of the higher intensity level. Mangine et al. (2015) speculated that training adaptations can be highly neurologically based on programs that demand a higher load, therefore it is pertinent to recommend a variety of repetitions and intensity levels as acute resistance training variables. Other factors to consider to influence bodybuilding style high volume training protocols is the variety of exercise selection to aid in accumulation of metabolic stress (Mangine et al., 2015). Endocrine responses to higher training volume may also lead to greater cellular adaption to resistance training in a protocol lasting longer than 10 weeks (Mangine et al., 2015). Higher volume training protocol also leads to greater number of satellite cell increase with an increase in MyoD and myogenin (Hanssen et al., 2013). The response from 3 sessions per week and multiple sets in satellite cell proliferation leads to greater cross sectional area as well as a greater ability to adapt to resistance training with an increased number of cell nuclei (Hanssen et al., 2013).
Effects of Resistance Training Volume on Strength
The relationship between volume and strength adaptations continues to be explored in the literature. Naclerio et al. (2013) evaluated different amounts of volume in order to increase strength and power in athletes which can also lead to practical recommendations for individuals in different populations. Three different protocols were used, all of them three days per week for six weeks the only difference being volume. One group performed 3 sets per muscle group per session, another group performed 6 sets per muscle group per session, and the high volume group performed 9 exercises per muscle group per session. Perhaps the most important control of this study is intensity remained the same through all groups as well the repetition ranges used. Naclerio et al. (2013) only examined changes in volume while other variables are held constant. While other factors do have implications to hypertrophy and strength, when making recommendations on volume specifically Naclerio et al. (2013) finds that the higher volume is a more effective training approach for improving maximal strength. The high volume training group in this case performed 27 sets per muscle group per week, which is on the high end of volume measured in the literature. Naclerio et al. (2013) showed significant and positive results on strength with athletes performing 27 sets per week. A potential limitation of Naclerio et al. (2013) was the length of time (6 weeks) in order to evaluate training adaptations. Looking at implications for long term progress, further research should be explored in order to conclude effects of long term high volume training, potential diminishing results, rate of injuries, and likelihood of overtraining.
Resistance Training Load is Inferior to Volume to Influence Skeletal Muscle Hypertrophy
Many individuals follow the belief that higher load resistance training will produce more skeletal muscle adaptions than lower load training (Mitchell et al., 2012) and heavy loads are often recommended to individuals looking to maximize muscle hypertrophy. Mitchell et al. (2012) set out to examine the empirical evidence and compare the results of high load resistance training (90% 1 repetition maximum) to a low load (30% 1 repetition maximum) on skeletal muscle hypertrophy. They proposed that if the fatigue level and intensity remained consistent between groups, the adaptations would be just as significant in the lower load group based on prolonged stimulation of myofibrillar protein synthesis (Mitchell et al., 2012). Mitchell et al. (2012) also speculates that with this hypothesis, skeletal muscle hypertrophy will be greater in higher volume training protocols. Mitchell et al. (2012) hypothesized that stimulating myofibrillar protein synthesis rates is a key to causing skeletal muscle training adaptions and this can be done effectively with increasing training volume as opposed to increasing training loads. Mitchell at al. (2012) also gives other potential direct influencers to skeletal muscle hypertrophy such as changes in microRNA expression, satellite cell number, and intramuscular anabolic signaling protein activation. These along with the stimulation of myofibrillar protein synthesis are training adaptations caused by stimulus such as volume and intensity that should be explored further in the literature. The most significant finding by Mitchell et al. (2012) is that the high load (80%-3) group and low load (30%-3) group had similar hypertrophy responses. This finding reinforces that low loads are sufficient to elicit muscle hypertrophy however the context is important because similar fatigue levels must be reached in order to achieve similar fiber recruitment (Mitchell et al, 2012). It is speculated that the increase signaling of p70S6K which upregulates initiation of mRNA translation and increases muscle protein synthesis rates is an important step caused by different training conditions. An important finding by Mitchell et al. (2012) is that they did not observe an increase in phosphorylation of p70S6K one hour post exercise in the low load (30%-3) group like they did in the high load (80%-3) group but they did observe an increase in phosphorylation of p70S6K four hours post exercise in the low load (30%-3) group. This leads researchers to believe there is a different time course in anabolic signaling with light loads versus heavy loads. This supports the hypothesis that higher training loads do not influence hypertrophy more than lighter training loads.
Volume and Sarcoplasmic Hypertrophy
While there are many studies such as Naclerio et al. (2013) that find greater skeletal muscle adaptions to a higher volume training protocol, the cellular adaptations are not well characterized (Haun, 2019). Haun et al. (2019) sought to explore the influence of a high volume resistance training protocol on actin, myosin, sarcoplasmic protein, mitochondrial and glycogen concentrations. Haun et al. (2019) followed a protocol that increased training volume from 10 sets at 10 repetitions per week on primary movements analyzed to 32 sets of 10 repetitions per week. Haun et al. (2019) analyzed the cellular adaptations to high volume resistance training protocol in order to determine what causes the increase in cross-sectional area of skeletal muscle. While there is a widespread belief that an increase of cross-sectional area is due to an increase in contractile proteins, Haun et al. (2019) found that the increase in cross-sectional area is due to the increase in sarcomeres in parallel, not the increase in contractile proteins. Haun et al. (2019) confirms evidence from other studies that myofibril protein density may decrease following long periods of higher volume resistance training, therefore high volume resistance training causes an increase in cross-sectional area due to sarcoplasmic expansion rather than an increase in actin and myosin density. Haun et al. (2019) showed a decrease in actin, myosin and mitochondrial density in high volume training groups. A significant upregulation of several enzymes involved in glycolysis and ATP generation were observed in higher volume training groups. It can be hypothesized that future research can examine the effects of other training methods in conjunction with higher volume training in attempt to cause an increase in skeletal muscle protein density causing an increase in skeletal muscle cross-sectional area using a different pathway. These findings that skeletal muscle adaptations are due to sarcoplasmic expansion and enzyme upregulation are significant for future research. Future research should be tailored to explore how to most efficiently stimulate sarcoplasmic expansion and enzyme upregulation in order to maximize training adaptations.
Minimum Amount of Volume to Maintain Skeletal Muscle Hypertrophy
While making recommendations for optimal progress in skeletal muscle strength and hypertrophy, it is relevant to examine where the line lies for maintaining resistance training adaptations. Bickel, Cross, and Bamman (2011) examine the effects of reduced volume of resistance training and detraining in 20-35 year olds and 60-75 year olds. The results of Bickel et al. (2011) lead to a recommendation of the minimum volume required to maintain adaptations to resistance training. Bickel et al. (2011) state the positive morphological adaptions of resistance training are not maintained if resistance training ceases. The findings of Bickel et al. (2011) are significant because it has previously been stated that older adults will not recover as fast to resistance training bouts, yet they require more stimulation and volume during times of less of resistance training than younger adults to maintain morphological adaptations (Bickel et al., 2011). The most significant finding of Bickel et al. (2011) was that a once per week exercise dose was sufficient to maintain positive neuromuscular adaptations. The largest difference was in the exercise dose required to maintain myofiber hypertrophy in young adults was one ninth the original volume. Bickel et al. (2011) showed a wide gap in potential volume prescription to maintain strength and hypertrophy. While determining that continued myofiber adaptions can occur with one third the original training volume of three days per week and three sets of 8-12 repetitions (Bickel et al, 2011). The optimal volume and frequency for skeletal muscle adaptations to resistance training could be different. Naclerio et al. (2013) found that a higher volume protocol lead to greater adaptations in skeletal muscle strength. When examining the optimal amount of resistance training volume for skeletal muscle adaptations, there may be a base for the volume required (Bickel, 2011) and an upper limit were results may begin to plateau (Heaselgrave, 2019).
Systemic Hormones Effects on Strength and Hypertrophy
Training programs and nutritional strategies have long been designed to augment fiber recruitment and systemic hormone response in order to maximize muscle hypertrophy (Morton et al., 2016). Morton et al. (2016) mentions some of the models used in previous research to determine systemic hormone response were done performing unilateral exercise, therefore do not have practical application to the effects of bilateral training. This is due to the effect of cross-education having and influence on the outcomes of the studies using unilateral training (Morton et al., 2016). Morton et al. (2016) set out to provide a reference for both training load and systemic hormone response in relations to skeletal muscle hypertrophy. Morton et al. (2016) conducted this study with 49 subjects, a test size large enough to allow for detection of significance at 15% cross-sectional area and 10% difference in lean body mass with a 90% power based on previous work in trained men. The strength of this study is in the length of the protocol (12 weeks) and the number of subjects (49). Morton et al. (2016) points out that low load resistance training often leads to greater training volume which leads to greater adaptation when intensity levels were equated. In a volume matched situation they found the higher load group to have greater adaption due to an increase in intensity levels. Morton et al. (2016) makes the point that many of the volume equated studies looking at training adaptions have subjects lift in a lower repetition/high load condition to failure to determine the volume that the higher repetition/lower load group will then use. This brings about inherent issues not allowing the high repetition group to go to failure and result in an inferior stimulus. Therefore it is concluded by Morton et al. (2016) that lower loads must be lifted to the same intensity and in many cases greater volume than higher load training groups. Morton et al. (2016) also points out the necessity of practicing the chosen strength outcome (lift heavy loads if the goal is to lift heavy loads) because the neural adaptions to lifting heavy will benefit lifting heavier loads. The theory of systemic hormone levels having anabolic effects has been hypothesized for a number of years (Morton et al, 2016). When looking at the impact of resistance training loads on hormone levels and the effect on anabolism, it can be concluded that systemic hormones have no significant effect on skeletal muscle adaptions to resistance training (Haun et al., 2019; Mitchell et al., 2012; Morton et al., 2016).
Conclusion and Recommendations
Increasing strength and hypertrophy in skeletal muscle is a complicated process involving many different factors. Training more frequently at the same training volume is a specific single measurable variable that has been well explored leading research to focus on different variables. The implications for future research on this subject involve intensity, recovery status, neurological drive, time under tension, training to failure, rep speed and also exercise selection. Lasevicius et al. (2019) points out that motor learning theory says the results would be different however in short term studies there may not be enough time to see significance in that theory. The other factor is if the total number of repetitions are held consistent even with an extra training session, the individual is getting just as much practice in the movement. Based on the findings of Arazi & Asadi (2011) Lasevicius et al. (2019), and Serra et al. (2015) it can be concluded that at this time volume has a more significant effect on strength and hypertrophy than frequency of training bouts.
The effects of training volume on skeletal muscle strength and hypertrophy are significant (Morton et al, 2016; Naclerio et al, 2013). Progressive overload in order to maximize the amount of volume has been shown to be an effective strategy to cause adaption in strength (Naclerio et al., 2013) and hypertrophy (Haun et al., 2019) of skeletal muscle. Training loads and systemic hormone response to resistance training are not drivers of adaptation to resistance training (Morton et al., 2016) where as the increase of volume has been shown to improve microRNA expression, satellite cell number, intramuscular anabolic signaling protein activation, and stimulation of myofibrillar protein synthesis (Mitchell at al, 2012). Further research is needed in order to tie these pieces together and to determine an upper limit for volume. Higher volume protocols have been shown to be more effective at causing adaptions in muscle strength and hypertrophy (Haun et al., 2019; Naclerio et al., 2013) but there is a gap where the upper limit exists and where that limit is for experienced individuals compared to untrained individuals.
An effective strategy for maximizing resistance training adaptions is to incorporate as much training volume as each individual can be adapted to within the limits of the recovery process (Sooneste et al., 2013). An evidence based strategy to incorporate more volume into a practical training protocol is to gradually increase training frequency to three sessions per week on primary compound movements with multiple sets (Hanssen et al., 2013; Mangine et al., 2015; Sooneste et al., 2013). Implementing accessory movements to supplement compound movements may increase metabolic stress and enhance strength and hypertrophic responses to resistance training (Mangine et al., 2015). In order to maximize resistance training adaptions to increase strength and hypertrophy a variety of repetition ranges may be utilized (Mangine et al., 2015).
An Evidence Based Recommendation on Training Frequency
1 to 4 sessions per week per muscle group depending on training status and individual preferences (Arazi & Asadi, 2011; Colquhoun et al., 2018; Lasevicius et al., 2019; Serra et al., 2015; Yue et al., 2018). It may practical to increase number of sessions per week with higher amounts of training volume to maximize adaptations (Heaselgrave et al., 2019).
An Evidence Based Recommendation on Total Weekly Set Volume
From 16 total working sets to 32 total working sets per week for optimal progress in both strength and hypertrophy (Haun et al., 2019; Mitchell et al., 2012; Morton et al., 2016; Naclerio et al., 2013. It may practical to increase number of sets per week over time depending on adaptation and training experience (Heaselgrave et al., 2019). Periodization as well as other training variables will also cause variability within this range (Sooneste et al., 2013)
An Evidence Based Recommendation on Minimum Amount of Volume and Frequency to Maintain Skeletal Muscle Adaptations to Resistance Training
1 session 3 sets per week or 1/9th of the original amount of training volume previously performed to maintain skeletal muscle adaptations in strength and hypertrophy (Bickel et al., 2011).
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