Resistance training tempo has minimal effect on muscle growth

When both slower tempos (1.7–4.5 seconds, averaging ~3.5 seconds per repetition) and faster tempos (0.3–2 seconds, averaging ~1 second) were analyzed for within-group muscle gains, the effect sizes were nearly identical: 0.43 for faster tempos versus 0.34 for slower tempos, both with overlapping 95% credible intervals. When comparing the two tempos head-to-head in the same studies, faster tempos showed only a trivial advantage over slower tempos (pooled difference = 0.09), with only a 45% probability that the true between-group difference was at least a small effect. Subgroup analyses by muscle action type (eccentric or concentric), body region (upper or lower body), and whether training was taken to failure produced consistently trivial to small effects across conditions. The authors emphasize that while resistance training tempo appears to have minimal overall influence on hypertrophy outcomes, the certainty of some subgroup estimates varied, leaving open the possibility of tempo effects under specific conditions not yet fully characterized.

The within-group effect sizes (0.43 vs 0.34) both represent meaningful muscle gains, indicating that both approaches work—the question is whether the tempo itself drives the difference, and the evidence says it does not substantially. The probability calculation is striking: there is a 55% credible interval around zero, meaning the data cannot rule out that faster tempos are negligibly better than slower ones. Subgroup heterogeneity is worth noting; some conditions (for example, training to failure versus not training to failure) did show slightly larger tempo-related differences, but these remained small. The effect sizes in both groups align with typical resistance training gains seen in well-controlled trials (0.3–0.4 standard deviations), suggesting that any stimulus—fast or slow—within a reasonable rep range (1–4 seconds per rep) recruits muscle effectively. One limitation is that the included studies were relatively small and heterogeneous in participant age, training status, and exercise selection, which may have obscured tempo effects in specific populations. The lack of a clear tempo advantage does not mean tempo is irrelevant to fatigue, joint stress, or exercise feel—it simply means hypertrophy outcome is robust across a wide tempo range.