The influence of frequency, intensity, volume and mode on muscle hypertrophy
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Sports Med. 2007;37(3):225-64.
The influence of frequency, intensity, volume and mode of strength training on whole muscle cross-sectional area in humans.
I thought I'd summarize this comprehensive paper both for my own benefit and for those who want the highlights. I've restricted my summary to the parts of the paper that talk about your typical "dynamic external resistance" training. The gist of the paper is that while we do know what works for hypertrophy (pretty much everything, to an extent), we really don't know what's optimal, especially in trained individuals and in the long run. Dan also posted some excerpts on his forum:
http://hypertrophy-research.com/phpB...opic.php?t=213
Results
No relationship could be found between frequency of training and the increase per day in muscle cross sectional area. When the intensity was plotted against the rate of increase, a weak tendency was found for the rate to increase with increasing intensity. The highest rates of increase tended to occur around 75% of 1RM. When volume was plotted against the rate of increase, greater gains in muscle mass were seen initially with increasing volume while there were diminishing returns as the volume increased further. The highest rates of increase tended to occur with 30-60 repetitions per session.
Discussion
Frequency: For hypertrophy, studies suggest that training two or three times per week is superior to training one time per week, even when volume is equal. However, there doesn't appear to be a benefit of three sessions per week over two. "Although some interesting trends can be discerned from the data... there is clearly a need for further research on training frequency in both highly-trained and less-trained subjects."
Intensity: "The studies reviewed in this article show that there is a remarkably wide range of intensities that may produce hypertrophy. Still, there seems to be some relationship between the load (or torque) and the rate of increase in CSA." This is not linear, but seemed to peak around 75%. "Thus, the results of this review support the typical recommendations with intensity levels of 70–85% of maximum when training for muscle hypertrophy, but also show that marked hypertrophy is possible at both higher and lower loads."
Volume: "Overall, moderate volumes (≈30–60 repetitions per session for DER training) appear to yield the largest responses." An exception to this is with very high loads (90% 1RM or 120% to 230% 1RM with eccentrics) where high rates of growth have been shown with volumes as low as 12-14 repetitions per session. To date, relatively few studies have directly compared the effects of different volumes of work on the hypertrophic response as measured by scanning methodology." The paucity of data clearly warrants further research.
Mode of Training and Type of Muscle Action: You often hear statements like "eccentric training produces the greatest muscle hypertrophy". "This review demonstrates that given sufficient frequency, intensity and duration of work, all three types of muscle actions can induce significant hypertrophy at impressive rates and that at present, there is insufficient evidence for the superiority of any mode and/or type of muscle action over other modes and types of training in this regard." In fact, the data suggest that pure eccentric training is inferior to both concentric and eccentric+concentric training, though this is still a subject of debate rather than a scientific certainty.
Rest Periods and the Role of Fatigue: "Upon closer examination, it appears that when maximal or near-maximal efforts are used, it is advantageous to use long periods of rest. This is logical in light of the well known detrimental effects of fatigue on force production and electrical activity in the working muscle. If high levels of force and maximum recruitment of motor units are important factors in stimulating muscle hypertrophy, it makes sense to use generous rest periods between sets and repetitions of near-maximal to maximal efforts... On the other hand, when using submaximal resistance, the size principle dictates that motor unit recruitment and firing rates are probably far from maximal until the muscle is near fatigue or unless the repetitions are performed with the intention to execute the movement very quickly."
Interactions Between Frequency, Intensity, Volume and Mode: "Based on the available evidence, we suggest that the time-tension integral is a more important parameter than the mechanical work output (force × distance)... Overall, we feel that the trends observed in this review are consistent with the model for training-overtraining continuum proposed by Fry,[186] where the optimal training volume and also the volume threshold for overtraining decreases with increasing intensity... Regarding training for hypertrophy in already highly-trained individuals, there is at present insufficient data to suggest any trends in the dose-response curves for the training variables."
Eccentrics: "Taken together, the results of these studies support the common recommendation of using somewhat lower frequencies and volumes for high-force eccentric exercise than for conventional resistance training..."
Order of endurance/strength training: "It has been suggested that strength training should be performed first, in order not to compromise the quality of the strength-training session.[194] However, this order may not necessarily be the best choice for inducing increases in muscle mass. Deakin[195] investigated the impact of the order of exercise in combined strength and endurance training and reported that gene expression associated with muscle hypertrophy responded more strongly when cycling was performed before strength training, instead of vice versa. Interestingly, in the study of Sale et al.,[111] performing cycling first seemed to induce the greatest increase in muscle area. Still, because the lack of studies investigating the effects of the order of exercise in concurrent training on hypertrophy, no firm conclusions can be drawn on this issue."
Time Course of Muscle Hypertrophy: "Until recently, the prevailing opinion has been that neural adaptations play the dominant role during the first 6–7 weeks of training, during which hypertrophy is usually minor." However, several investigations [13,27,54,87,105,118,128] have demonstrated significant hypertrophy at the whole muscle level after short periods of training (3–5 weeks). "Thus, there now plenty of evidence that significant hypertrophy can take place early on given proper frequency, intensity and volume of training," even prior to changes in muscle CSA. "As argued by Phillips,[198] the idea that early gains in strength are due exclusively to neural adaptations seems doubtful... In some strength-training studies, the increase in muscle volume is delayed, while in others, the rate of growth is rapid. We speculate that less-damaging training modes may allow the hypertrophy response to start earlier. Regimens that include eccentric muscle actions, especially those involving maximal effort, appear to require a careful initiation and progression of training to avoid muscle damage and muscle protein breakdown [excessive apoptosis and proteolysis]."
The Stimulus for Muscle Hypertrophy in Strength Training: "Two studies by Martineau and Gardiner[216,217] have provided insight into how different levels of force and different durations of tension may affect hypertrophic signaling in skeletal muscle... they remarked that both peak tension and time-tension integral must be included in the modeling of the mechanical stimulus response of skeletal muscle... Based on the data reviewed in this paper, we speculate that hypertrophic signalling in human skeletal muscle is very sensitive to the magnitude of tension developed in the muscle. Hence, for very short durations of work, the increase in muscle size will be greater for maximal-eccentric exercise than for maximal-concentric exercise of similar durations... The response is presumably also dependent on the total duration of work and increases initially with greater durations. Thus, both short durations of maximal eccentric exercise and somewhat longer durations of concentric, isometric and conventional dynamic resistance exercise can result in impressive increases in muscle volume. However, especially with maximal eccentric exercise, damage also seems to come into play as the duration of work increases even further and the acute and/or cumulative damage may eventually overpower the hypertrophic process."
