A popular theory among fitness professionals is that taking short rest periods between sets maximizes muscular growth. The theory is primarily based on the hormone hypothesis, whereby limiting inter-set rest promotes greater elevations in post-exercise growth hormone, IFG-1 and testosteron...
February 14, 2016
Proper manipulation of program variables is essential for maximizing the hypertrophic response to resistance training. Variations in volume, loading and rest intervals all have been shown to impact muscular adaptations.
One variable that hasn’t received as much attention is lifting tempo – i.e. how fast you perform a repetition. When you’re using very heavy loads this is moot; although you’ll necessarily need to try to move the weight quickly, the actual concentric speed will be fairly slow. To illustrate this point, a study by Mookerjee and Ratamess found that the first concentric repetition of a 5RM bench press took 1.2 seconds to complete while the fourth and fifth repetitions took 2.5 and 3.3 seconds, respectively. These findings occurred despite subjects being instructed to perform the reps explosively.
When the loads are lightened, however, you have a lot more control over lifting cadence. A wide range of volitional tempos are possible depending on the magnitude of load. Recommendations on the topic are highly disparate depending on who you listen to. Some fitness pros advocate explosive lifts while others recommend slowing tempo down to where a single repetition takes 45 seconds to complete as seen in this video
In an effort to synthesize the evidence and gain clarity on the issue, I collaborated on a meta-analysis with uber-pros James Krieger and Dan Ogborn. The study titled, Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis was recently published in the journal, Sports Medicine. In case you’re not aware, a meta-analysis pools data from all studies on a given topic and then statistically quantifies the results to provide a gauge of how meaningful the differences are between conditions.
Here’s the scoop.
What We Did
An extensive search of the literature was carried out for randomized controlled trials that directly compared the effects of different training tempos on muscle hypertrophy in healthy individuals. Studies had to last a minimum of 6 weeks and both groups had to perform reps to the point of momentary concentric muscle failure. A total of 8 studies comprising 204 total subjects ultimately met inclusion criteria – a surprisingly low number for such an important topic.
What We Found
There was no difference in hypertrophy between lifting durations of 2 to 6 seconds when using dynamic constant external resistance (typical free weights and machines). A single study using isokinetic dynamometry showed that durations of a half-second up to 8 seconds produced similar hypertrophy, although the generalizability of this study to traditional training methods is somewhat questionable.
There does seem to be a threshold as to how slow you can go, as evidence suggests that “superslow” lifting (i.e. durations above 10 seconds) is suboptimal for hypertrophy. The research on this topic is limited thereby making it difficult to draw firm conclusions, but a recent study found that a traditional speed group increased muscle cross sectional area by 39% compared to only 11% in a group performing reps at a tempo of 10 seconds up, 4 seconds down. These results held true despite an almost five-fold greater time-under-tension for the superslow group. A follow-up study by the same lab showed satellite cell content and myonuclear domain – important components in the ability to increase muscle mass over time – were substantially greater with traditional compared to superslow training. These findings are consistent with research showing that muscle activation is reduced up to 36% when training at very slow speeds (5 seconds concentric and eccentric). And since maximal hypertrophy is predicated on recruiting the full spectrum of muscle fibers and keeping them stimulated for a sufficient period of time, it is logical to speculate that training in a superslow fashion is inferior if your goal is to optimize muscular gains.
What are the Practical Implications
Current research indicates that a wide range of lifting durations can be used to maximize hypertrophy. Given the limited number of studies and their diverse methodology, however, the topic is far from settled. Based on the evidence it would seem prudent to take no more than about 3 seconds on the concentric portion of the movement. Beyond this cadence, you’d need to reduce the load to a point where it could negatively impact the ability to fully stimulate the highest threshold motor units. Eccentric actions should be performed so that the load is controlled against the forces of gravity; simply letting the weight drop fails to provide sufficient muscular tension for the majority of the action (and it also increases the risk of joint-related injury). As with concentric actions, there does not seem to be any advantage to slowing the movement down to more than about 3 seconds and it is possible that doing so might actually be detrimental to growth. I’d add that the reps should be carried out with sufficient control so that a mind-muscle connection can be established with the target musculature – the current body of evidence suggests that such a strategy is beneficial for maximizing muscle activation, which may in turn lead to greater gains.
I’ll note that the above recommendations are rather liberal, giving the benefit of doubt to somewhat slower tempos. My general feeling is that the concentric portion of a rep should be around 1-2 seconds – the most important thing here is to control of the weight by using an internal focus to visualize the target muscle as you lift. Although results of our meta-analysis showed no “statistically significant” differences in tempos up to 3 secs concentric, data from Tanimoto et al show a substantially greater effect size (a measure of the “meaningfulness” of results) for muscle growth favoring traditional (1 sec on concentric and eccentric – effect size 1.08) vs slower (3 secs concentric and eccentric – effect size 0.74) lifting cadences. It therefore would seem a slightly faster tempo is warranted, at least on multi-joint exercises
Could combining different repetition durations potentially enhance the hypertrophic response to training? It’s impossible to say as no study to date has investigated this possibility. As such, the best advice therefore is to experiment for yourself and see if this may spur additional growth. Remember: the best research often comes from what is learned in the trenches!
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