Department of Exercise Science and Health Promotion

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.

This study examined the effect of repetitions per set as a function of changing load (percentage of one-repetition maximum) on the accuracy of intraset repetitions in reserve (RIR) predictions in the back squat and bench press. Twelve resistance trained men completed three multi-set back squat and bench press training sessions that differed in the number of target repetitions (session 1: 10 repetitions; session 2: 8 repetitions; session 3: 6 repetitions). The last set of each session was performed until muscular failure in which subjects verbally indicated when they perceived 4 RIR and 1 RIR. For each RIR prediction, RIRDIFF [perceived RIR - actual RIR] was calculated.
Differences in RIRDIFF were analyzed using both raw RIRDIFF (including positive and negative values) and absolute RIRDIFF (absolute values) via MANOVA and factorial ANOVA. The model controlled for the covariates session-type, percentage of 1RM, and total repetitions per set. Overall, RIR accuracy at the predicted 1 RIR was significantly greater (i.e., lower absolute RIRDIFF) than at the predicted 4 RIR in both the bench press (4 RIR: 1.00 ± 0.18 vs. 1 RIR: 0.69 ± 0.12; p = 0.028) and the squat (4 RIR: 1.43 ± 0.31 vs. 1 RIR: 0.79 ± 0.26; p = 0.007). No covariates significantly affected RIR accuracy (p = 0.085 – 0.518) at the predicted 1 RIR. However, at the predicted 4 RIR, the covariate repetitions per set affected raw RIRDIFF in both the squat (p = 0.007) and bench press (p < 0.001), indicating that subjects tended to overpredict RIR in lower repetition sets and underpredict RIR in higher repetition sets.

This study examined whether accuracy of intraset RIR predictions changes over time. Nine resistance trained men completed three bench press training sessions per week for six weeks, with the last set of each session performed until muscular failure. During the set to failure, subjects verbally indicated when they perceived 4 repetitions in reserve (RIR) and 1 RIR during the set. For each RIR prediction, the difference between perceived RIR and actual RIR was calculated as RIRDIFF. We analyzed differences in RIRDIFF using both the raw RIRDIFF (including positive and negative values) and the absolute values of all RIRDIFF using a factorial MANOVA. Covariates included proximity to failure of the RIR prediction, total repetitions performed per set, percentage of one-repetition maximum lifted, the week of training, and the session (1, 2, or 3 within each seek). For the raw RIRDIFF all covariates, except for percentage of 1RM (p > 0.05) were significantly related to the outcome measure at both the predicted 4 and 1 RIR (p < 0.001 to p = 0.04). Specifically, RIRDIFF was significantly higher in weeks 1-4 versus weeks 5-6 (p < 0.001 to p = 0.005). However, the only covariate which significantly impacted the absolute value RIRDIFF at both the predicted 4 (p = 0.033) and 1 RIR (p = 0.022) was total repetitions per set. These results indicate that trained men tend to shift from overpredicting to underpredicting RIR over time and that more repetitions in a set is related to more inaccurate RIR predictions. However, the actual accuracy (i.e., absolute value RIRDIFF) did not significantly change over six weeks of training.