If it is the surest way to gain strength and muscle mass, resistance training is nevertheless an activity governed by many variables with which you must know how to juggle to obtain the desired results: intensity, volume, frequency, choice of exercises, rest intervals, type of resistance, etc. In previous articles, we have already discussed the impact of volume and frequency on potential muscle gains. One of the variables that is often overlooked is tempo, which is the speed at which repetitions are performed. The tempo is usually written this way : 1-0-2-0. Four numbers representing the time spent in seconds in each of the 4 phases of a single repetition : Concentric phase - Isometric phase - Eccentric phase - Isometric phase. Adopting a slow tempo would be associated with an improvement in the muscle response thanks to the increased time under tension and stronger metabolic stress...
Some meta-analyzes on the subject have shown that, whatever the tempo (slow or fast), the muscle adaptations (muscle hypertrophy and strength) were similar. However, the studies composing them were often carried out with beginners, and only the overall tempo was taken into account. If the eccentric phase seems to affect hypertrophy the most, the lack of rigor of certain protocols (lack of volume and / or intensity equalization) unfortunately do not allow clear conclusions to be drawn on the importance of the tempo of the eccentric phase. So, what would be the impact of a slow or fast eccentric tempo on muscle hypertrophy and strength ?
To answer this question, researchers decided to compare the impact of a different eccentric tempo on muscle hypertrophy and strength during an isolation exercise (single joint) performed unilaterally, and in a counterbalanced manner. For this, they recruited 13 well-trained participants (1RM Squat = 2.06 ± 0.4 x bw) to whom they asked to perform unilateral leg extensions. With one leg, they performed the exercise with a 1-0-1-0 tempo (Fast eccentric) and with the other leg, they performed with a 1-0-3-0 tempo (Slow eccentric). For both conditions, total work (sets x reps x load) and intensity (8-10 RM) were equalized. The program consisted of 2 weekly training sessions, for 8 weeks. Three sets were performed during the first 4 weeks, a fourth series was added during the last 4 weeks.
To study the impact of tempo on strength, the researchers evaluated the 1RM in leg extension before and after the 8 weeks of training. To assess the impact on hypertrophy, the researchers measured, via ultrasound, the thickness of the quadriceps in two places : proximal (40% of the length of the femur) and distal (60% of the length of the femur). In addition to this, the researchers systematically proposed a questionnaire to assess the rate of perceived exertion (RPE) for each set, of each leg.
The main results of this study showed that whatever the chosen tempo, both legs gained strength during this exercise in the same way : + 9.1kg (17%) for the "Fast eccentric" leg and + 10.4kg (22.1%) for the "Slow eccentric" leg. Regarding the hypertrophy of the quadriceps, the gain was similar for both legs at the proximal level (0.24 cm for the fast eccentric and 0.20 cm for the slow eccentric), while at the distal level, the "fast eccentric" allowed a higher gain (0.23 vs. 0.13 cm). Finally, concerning the RPE, it was significantly higher for the sets performed with a slow eccentric tempo (the sets were much harder).
Even if the protocol chosen in this study is more suitable for hypertrophy than for muscle strength, its results confirm what other studies have already shown before : the tempo would have little influence on strength gains, and volume would be a much more influential variable. Be careful, however, most protocols do not equalize the volume of training during experiments, which makes comparison of studies very difficult.
Regarding muscle hypertrophy, other studies have already observed heterogeneous gains in terms of localization. A power-oriented program with faster repetitions has already demonstrated more marked distal hypertrophy compared to a strength-oriented program with slower repetitions. This could be caused by stresses applied to the muscle heterogeneously during faster contractions.
From a practical point of view, the two tempos allowed similar gains in muscle strength and hypertrophy. According to these results, the greater difficulty imposed by the slower eccentric tempo (and therefore the greater perceived fatigue) would not be necessary. The only difference observed in this study concerns the statistically greater distal quadriceps hypertrophy observed with the rapid eccentric tempo. However, the difference observed on average was 15 mm between the two conditions, which is in fact a tiny difference from a practical point of view. Still, this gain, even tiny, could benefit very advanced practitioners (bodybuilders), not to mention the interest of training with the most explosive eccentric phase possible for some high-level athletes.
Obviously, more studies will be needed to understand the effects of varying tempo on strength and hypertrophy, with polyarticular exercises like the squat or bench press and other isolation exercises (on the upper limb AND lower limb).
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