THE EFFECT OF RESISTANCE TRAINING VOLUME ON INDIVIDUAL-LEVEL SKELETAL MUSCLE ADAPTATIONS

Purpose: This study examined inter-individual response variation in muscle size and strength following training with different resistance training (RT) volumes. We hypothesized that despite clear gross variability, we would not detect clear evidence of inter-individual response variation for the primary outcomes. Additionally, we hypothesized that higher weekly set volumes would benefit muscle hypertrophy but not strength outcomes at the group-level. Methods: Sixteen recreationally trained individuals had their lower limbs randomized into either a low (LV = 8 sets per week) or high volume (HV = 16 sets per week) training condition for an initial 11-week intervention (phase 1). After a washout period, a second identical 11-week intervention (phase 2) was conducted with limbs re-randomized to the training conditions. Primary outcomes measured were vastus lateralis (VL) cross-sectional area (CSA), muscle thickness (MT), leg press one-repetition maximum (1RM), and isometric force (MVIC) at baseline, midpoint, and post-intervention for each phase. Results: Higher RT volumes benefited muscle hypertrophy (CSA = 2.04 cm2 [95% HDI: 0.11, 3.81], MT = 0.55 mm [95% HDI: -0.06, 1.19]) to a larger degree than strength outcomes (1RM = 4.05 kg [95% HDI: -1.67, 10.14], MVIC = 0.66 kg [95% HDI: -3.83, 5.07]) at the group-level. Clear gross variability was observed for all primary outcomes, but we did not detect strong evidence in support of true inter-individual response variation (CSA = 0.17 cm2 [95% HDI: 0, 3.54], MT = 0 mm [95% HDI: 0, 1.1], 1RM = 0.59 kg [95% HDI: 0, 7.92], MVIC = 4.49 kg [95% HDI: 0, 9.43]).Conclusion: Higher volumes appear to benefit muscle hypertrophy but not strength at the group-level. Additionally, we failed to detect strong evidence of interindividual response variation to different RT weekly set volumes, despite clear gross
variability.