Effect of Small and Large Energy Surpluses on Strength, Muscle, and Skinfold Thickness in Resistance-Trained Individuals: A Parallel Groups Design.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 37914977 · doi:10.1186/s40798-023-00651-y
What was done
Twenty-one resistance-trained lifters performing resistance training 3 days per week for 8 weeks were randomized into three dietary groups: maintenance energy (MAIN), moderate surplus (~5% [MOD]), and high surplus (~15% [HIGH]). Due to COVID-19 disruptions, 17 participants completed the intervention. Outcomes assessed were skinfold thickness (ST), squat and bench press 1-repetition maximum (1-RM), and muscle thickness (MT) of the biceps brachii, triceps brachii, and quadriceps. Analyses included Bayesian ANCOVA for group differences and Bayesian linear regressions assessing body mass (BM) changes against adaptations.
What was found
ANCOVAs showed no evidence of group differences for MT or squat 1-RM. However, the HIGH group increased bench 1-RM more than MOD (BF10 = 9.9) and MAIN (BF10 = 14.5). The HIGH group also increased ST more than MAIN (BF10 = 4.2), with weak evidence for MOD increasing ST over MAIN (BF10 = 2.4). Regression showed strong evidence that BM change predicted ST change (BF10 = 14.3, R² = 0.49) and weak evidence predicting biceps brachii MT change (BF10 = 1.4, R² = 0.24).
Why it matters
This study suggests that larger energy surpluses during resistance training primarily accelerate body fat accumulation rather than substantially boosting muscle hypertrophy or lower-body strength gains in trained lifters.
Limits
The sample size was very small (n = 17 completers across three arms), reducing statistical power. The intervention lasted only 8 weeks, training volume was moderate, and skinfold thickness is an indirect surrogate for body fat compared to direct imaging modalities.