The ASSIST Trial: Acute Effects of Manipulating Strength Exercise Volume on Insulin Sensitivity in Adults Living With Obesity: A Randomized Controlled, Crossover, Clinical Trial

ABSTRACT Aims To investigate the influence of exercise volume on the transient increase in insulin sensitivity and β‐cell function that occurs in the hours following an acute bout of strength exercise. Materials and methods Fifteen (14 females) adults living with obesity (47.4 ± 9.7 years, 44.3 ± 4.1% body fat) performed three randomized sessions separated by at least four washout days: (1) high volume (21 sets); (2) low volume (7 sets), and (3) control. An oral glucose tolerance test (OGTT) was performed the following morning, and indexes of insulin sensitivity and β‐cell function were calculated using glucose, insulin, and C‐peptide assessed during the OGTT. Every participant completed each arm of the experiment and was included in the data analysis ( n = 15). Researchers who conducted data and statistical analysis were blinded to individuals and sessions. Results One‐way repeated measure analysis of variance followed by Tukey as post hoc showed that indexes of insulin sensitivity improved after the high‐volume session ( p < 0.05) but not after the low‐volume session ( p > 0.05) (effect size [EF] for high and low volume, respectively): insulin area under the curve (AUC) [−0.53 and −0.05], C‐peptide AUC [0.58 and 0.18], Cederholm index [0.59 and 0.11], skeletal muscle index [0.89 and 0.60], Gutt index [0.78 and 0.20], Stumvoll index [0.81 and 0.18], and the simple index [0.52 and 0.16]). β‐cell function showed a strong tendency to improve ( p < 0.06) after the high‐volume session (EF for high and low volume, respectively): C‐peptidogenic index [0.58 and −0.20], C‐peptide oral disposition index [0.72, −0.33]. No adverse effects were observed during data collection. Conclusions These results suggest that adults living with obesity who are seeking to improve insulin sensitivity should perform high‐volume strength exercises.