The effects of high intensity interval training on muscle size and quality in overweight and obese adults

Objectives: Despite growing popularity of high intensity interval training (HIIT) for improving health and fitness, limited data exist identifying the effects of HIIT on muscle characteristics. The purpose of the current study was to investigate the effects of a 3-week HIIT intervention on muscle size and quality in overweight and obese men and women. Design: Randomized controlled trial. Methods: Forty-four overweight and obese men and women (mean +/- SD; age: 35.4 +/- 12.3 years; height: 174.9 +/- 9.7 cm; weight: 94.6 +/- 17.0 kg; %fat: 32.7 +/- 6.5%) completed the current study. During baseline and post testing, muscle cross sectional area (mCSA) and echo intensity (El) were determined from a panoramic scan of the vastus lateralis obtained by B-mode ultrasonography. Body composition variables were measured using dual energy X-ray absorptiometry. Participants were randomized into either a 1:1 work-to-rest ratio HIIT group (SIT; n = 16), a 2:1 work-to-rest ratio HIIT group (LIT; n =19), or control (CON; n = 9). HIIT participants performed five, 2-min bouts (LIT) or 10, 1-min bouts (SIT) at 85-100% VO2peak for 9 sessions over three weeks. Results: Analysis of covariance demonstrated a significant increase in mCSA for SIT (p = 0.038; change (Delta) = 3.17 +/- 3.36 cm(2)) compared to CON (Delta = -0.34 +/- 2.36 cm(2)). There was no significant difference in El across groups (p = 0.672). Conclusions: HIIT may be an effective exercise modality to influence muscle size in overweight and obese individuals. Future studies should investigate muscle characteristics and remodeling in an overweight population following interventions of longer duration and varying work-to-rest protocols. (C) 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.