Do slower reps build more muscle?

Enes, Swinton, Schoenfeld and colleagues searched for interventions that compared different eccentric or concentric tempos while holding every other training variable constant, in healthy adults, with lean or muscle mass measured before and after.

Fourteen studies were included: in 4 the concentric phase was manipulated, in 9 the eccentric phase, and 1 crossover study manipulated both. They pooled within-group changes and, as the main analysis, pairwise differences between dichotomised "slower" repetitions (1.7-4.5 s, about 3.5 s on average) and "faster" repetitions (0.3-2 s, about 1 s).

Both tempos grew muscle: pooled within-group effects were 0.43 (95% credible interval 0.29 to 0.58) for faster and 0.34 (0.22 to 0.47) for slower. The pairwise difference trivially favoured faster repetitions (0.09, −0.04 to 0.22); the probability that the difference was at least small was 0.450, at least medium 0.001, and at least large below 0.001.

Subgroups by muscle action, body region and training to failure gave trivial to small effects with varying certainty. The authors conclude that tempo has minimal overall effect on hypertrophy, with possible differences under specific conditions.

How this bears on the Russian static-dynamic method (Seluyanov): indirect. The method's claims (practice descriptions, not this paper) are that slow, continuous-tension sets of roughly 30-60 s at a light load, taken to a burning sensation with short rests, grow type I fibres and their mitochondria and so improve endurance.

This review tested only lean or muscle mass, with tempo the single variable. The slowest tempos in it (up to 4.5 s per repetition, usually one phase slowed) are faster than the closest tested form of the method, low-intensity slow movement with tonic force generation (LST, about 3 s down and 3 s up with no relaxation).

It therefore says slowing a repetition does not add size; it does not test continuous tension, the method's tempo range, fibre type, mitochondria or endurance.