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Muscular hypertrophy is the term given to the growth and increase of skeletal muscle via the enlargement of muscle fiber cross-sectional area. This manifests specifically as an increase in the girth (not length) of individual muscle fibers, ultimately leading to increases in overall muscle size. Biologically speaking, muscular hypertrophy is expressed as an overall positive accumulation of the contractile proteins actin and myosin (i.e., protein synthesis > protein degradation), as well as an increase in the number of myofibrils within a muscle fiber. The aim of this article is to break down everything you need to know about the role that velocity plays in the hypertrophy response to training.
The onset and magnitude of hypertrophic adaptation within skeletal muscle depends upon the training stimulus, and ultimately, the long-term manipulation of acute training variables. To appropriately stimulate muscle growth, periodisation of training is essential to optimise mechanical and metabolic stress as well as promote optimal recovery periods. Mechanical factors include the lifting of heavy external loads (>85% 1-RM), the accumulation of eccentric muscle control, and low-moderate training volumes, all of which are typically associated with traditional strength training. This leads to the optimal recruitment of higher threshold motor units essential to muscle growth. Metabolic factors include moderate-high training volumes, moderate external loads (>70% 1-RM), and short rest periods, generally more characteristic of traditional body-building training. This predominantly targets the glycolytic energy system, resulting in increased metabolic reactions and metabolite production directly associated with tissue growth.
Muscular hypertrophy is a constant battle between damage and repair. Exercise-induced muscle damage (EIMD) stimulates various proteins within the body known to have a marked impact on muscle growth. The mechanical deformation caused by EIMD results in protective structural changes in an effort to strengthen the damaged tissue as a means of protecting it from further damage. While the exact (hormonal, mechanical, metabolic, immune, etc.) processes are still somewhat theorised, it is known that the inflammation and protein turnover associated with EIMD may be important for long term hypertrophy.
The general consensus is that moderate-high training volumes (volume: repetitions x sets; volume load: load x repetitions x sets) provide the greatest stimulus for hypertrophic adaptation. As previously stated, greater training volume accelerates a series of metabolic reactions, ultimately leading to increased protein synthesis and structural changes within the skeletal muscle. This volume is most commonly prescribed as a moderate-high number of repetitions, over a moderate-high number of total sets (Table 1).
Within the literature, there is constant debate surrounding whether a dose-response is apparent between training volume and hypertrophic potential, that is, does completing a higher training volume always result in a greater adaptation? When evaluating the results of longitudinal research on the topic, many studies have failed to show statistically significant differences in hypertrophy between lower and higher training volume groups when considering total sets completed per week.
However, this data should not be taken at face value due to a series of confounding variables. Generally speaking, the bulk of data is obtained from less-than-optimal samples, including low sample sizes, and un- or lesser-trained participant groups. As research has demonstrated resistance-trained individuals respond differently to hypertrophy targeted training than novices, the practical transfer of such research to trained athletes is limited at best.
A recent meta-analysis by Schoenfeld and colleagues(2) (comprising of 34 treatment groups across 15 research studies) demonstrated a dose-response between total weekly sets and muscular hypertrophy. While the findings indicated that increased training volume produced greater gains in muscle hypertrophy, the analysis was only able to determine this for up to 10 weekly sets per muscle group (or two to three exercises per muscle group). Contemporary work by Schoenfeld (3) further confirmed this, however, demonstrating significant increases in muscle hypertrophy when a greater number of sets were completed (up to 15 working sets per week per muscle group). Overall, the data suggests a graded dose-response is apparent in resistance trained participants, with higher training volumes leading to a greater hypertrophic response, even over relatively short training periods (8 weeks). However further research is required before definitive conclusions can be drawn.
It is worth noting that in general, research studies focus on only one to two exercises per muscle group and manipulate repetitions and total sets to gain necessary volume. However, when exploring observational research, interviews with bodybuilders, or more exhaustive bodybuilding training guidelines, four or more exercises per muscle group are generally employed and recommended (4).
This undoubtedly has significant impact on the total volume load accrued over a given session for a particular muscle group and thus directly impacts the hypertrophic adaptation potential. This is one of many discrepancies between research and applied work that is apparent in applied subjects, and is worth acknowledging due to the likely impact on adaptation
With reference to the previously-aforementioned acute training variables, training intensity and volume are arguably the most important when it comes to determining the type and extent of neurological and morphological adaptation following progressive resistance training. As previously discussed, training volume is relatively straightforward - both in terms of calculation and implementation into a resistance training programme.
Conversely, the quantification of training intensity is not so easily achieved, and generally relies on either maximal assessment of an athlete’s strength (1-RM), or extrapolation of data following a sub-maximal test (such as a 10-RM). While these practices are still widely used, many researchers and practitioners acknowledge the limitations of the use of such methods as means to dictate training intensity.
Several researchers have proposed and demonstrated how movement velocity may offer a more sensitive approach to defining and manipulating training intensity (5). The velocity at which the concentric section of a lift is performed has been shown to be related to its relative load (i.e. %1-RM). This relationship has been shown to remain unchanged despite significant increases in absolute strength and has therefore been theorised as a potential auto-regulatory approach for prescribing training intensity. Additionally, as repetitions within a set continue, the attainable concentric velocity will decrease as mechanical and metabolic stress are accrued. As such, it has been proposed that monitoring this velocity drop-off may offer additional means to monitor athlete fatigue within a session, ensuring optimal volume is achieved while reducing the risk of overtraining.
An introduction to the Output Sports system which may be used as a tool to aid research in understanding how to optimise Hypertrophy through resistance training.
With specific reference to hypertrophy, the current research is somewhat limited. In this regard, the main focus of contemporary literature is not to compare “fast” to “deliberately slow” repetitions. This specific aspect of lifting is somewhat more definitive, with systematic reviews generally concluding that a wide range of repetition durations and concentric velocity strategies can be employed with the primary aim of muscular hypertrophy. The more pertinent topic is the impact velocity loss has on maximising muscular hypertrophy. Here, research has explored employing various velocity loss strategies (ranging from 15-50%) based on the first or fastest repetition within a set, monitoring variables such as total training volume, cross-sectional area and muscular strength. As a repetition within a set falls below this predetermined threshold (i.e. 40% velocity loss), the set is ended, and the rest period initiated.
The theory suggests that implementing a specific velocity loss strategy will allow sufficient volume to be accrued, while reducing unnecessary repetition completion, limiting fatigue within and between sessions. Authors have suggested that a 20% velocity stop is the equivalent to completing approximately half the repetitions within a set that could be completed (if going to failure), with 40-50% velocity loss at, or approaching volatile failure. The data generally supports the use of larger velocity loss protocols when compared to the same programme employing a smaller velocity loss (i.e. 40% > 20%), which may come as no surprise as these groups will commonly be completing significantly greater training volume.
The only paper to date which has compared more than two velocity stop protocols (15% vs. 25% vs. 50%) concluded that a higher velocity stop thresholds allowed a greater volume load to be accrued, which maximised the muscular hypertrophy adaptation witnessed (6). Again, however, is this any surprise? We already know that volume load is a key determinant in inducing favourable hypertrophic response, and thus having a group complete significantly higher volume is always going to promote a greater adaptation potential.
For this reason, maybe the question we should be asking (or answering) is not how can we use velocity to enable optimal volume to be achieved, but how can we use velocity to ensure the optimal load is lifted for said volume? Research on this topic is somewhat scarce currently, with only a handful of authors exploring load dictation via use of real-time velocity. However, the research currently available has demonstrated that this method has great potential when compared to more traditional loading approaches (5). Within this study, participant’s load was dictated via traditional 1-RM percentages or based on attainable mean concentric velocity. If athletes were able to achieve higher velocities than the target, intensity was increased, likewise if they were unable to achieve the target velocity, intensity was decreased.
The results demonstrated that the velocity-based group achieved significantly greater strength adaptations despite completing significantly less training volume. While this research didn’t explore hypertrophy adaptations (it is likely the velocity group would have made lesser gains here due to the lesser accrued volume), the method by which the load was dictated was demonstrated to be far more sensitive than traditional approaches, facilitating greater adaptation across a range of assessments. The method for dictating load in this, and contemporary literature by the same research team was developed by Moore and colleagues(7) and has been made into a freely available web-based application (https://matlab-webapps.port.ac.uk/webapps/home/).
While no research has currently explored such methods in relation to hypertrophy adaptation, the benefits shown from this optimal loading approach would surely transfer effectively into such training methods, enabling greater efficiency of training intensity to be dictated optimising volume load and thus muscular hypertrophy.
Due to the general scarcity of meaningful velocity-based hypertrophy research currently available, the recommendations for practitioners and individuals looking to utilise a velocity-based training approach are somewhat theoretical at this stage. What this does mean however, is that there is a good opportunity for future research within this area to provide meaningful data and application. Currently, the only hypertrophy research on this topic has focused on the implementation of velocity stops at varying percentages. While this research has demonstrated significant results, the message of training volume is relatively unchanged, with the guidelines still supporting higher volume loads when pursuing hypertrophy.
There appears to be a graded dose response in relation to the velocity stop employed, whereby a larger velocity drop-off will facilitate a greater hypertrophy response, however this isn’t overtly ground-breaking based on traditional hypertrophy research. Future studies should explore velocity stops in comparison to traditionally employed repetition and volume ranges, and even the potential of repetitions to failure. This would provide meaningful data on the efficacy of the velocity stop method in comparison to well established protocols.
Where the research has provided more meaningful and practically applicable findings is with regards to dictating training intensity. The limitation of this current body of research is that no direct measures of hypertrophy have been assessed, however the findings regarding optimal load dictation would likely transfer effectively. Collectively this research suggests that using mean concentric velocity as a means to dictate training load may offer a more sensitive approach when compared to traditional %1-RM.
Theoretically, the use of such methods could allow the optimisation of volume load based on the athlete’s performance of preceding sets, increasing the efficiency of such programming. Future research should look to explore this proposal, assessing if such loading methods could be utilised within a hypertrophy targeted programme, and the effect this would have on variables when compared to more traditionally employed loading methods.
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Dr. Harry Dorrell is a Lecturer in the School of Sport and Exercise Science at the University of Lincoln and currently works with a range of athletes and squads in the University. Dr. Dorrell’s research interests include the acute and longitudinal effects of strength and power training on performance, and specifically the method by which training load is dictated.
1. Haff, G. G., & Triplett, N. T. (Eds.). (2015). Essentials of strength training and conditioning 4th edition. Human kinetics.
2. Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. Journal of Sports Sciences, 35(11), 1073-1082.
3. Schoenfeld, B. J., Contreras, B., Krieger, J., Grgic, J., Delcastillo, K., Belliard, R., & Alto, A. (2019). Resistance training volume enhances muscle hypertrophy but not strength in trained men. Medicine and Science in Sports and Exercise, 51(1), 94.
4. Helms, E. R., Fitschen, P. J., Aragon, A. A., Cronin, J., & Schoenfeld, B. J. (2015). Recommendations for natural bodybuilding contest preparation: resistance and cardiovascular training. The Journal of Sports Medicine and Physical Fitness, 55(3), 164-178.
5. Dorrell, H. F., Smith, M. F., & Gee, T. I. (2020). Comparison of velocity-based and traditional percentage-based loading methods on maximal strength and power adaptations. The Journal of Strength & Conditioning Research, 34(1), 46-53.
6. Pareja‐Blanco, F., Alcazar, J., Cornejo‐Daza, P. J., Sánchez‐Valdepeñas, J., Rodriguez‐Lopez, C., Hidalgo‐de Mora, J., ... & Ortega‐Becerra, M. (2020). Effects of velocity loss in the bench press exercise on strength gains, neuromuscular adaptations, and muscle hypertrophy. Scandinavian Journal of Medicine & Science in Sports, 30(11), 2154-2166.
7. Moore, J., & Dorrell, H. (2020). Guidelines and resources for prescribing load using velocity based training. The International Universities Strength and Conditioning Association Journal, 1(1), 1-14.