Author(s): VAN EVERY, D., LAMONT, G., BHINDER, A., CHOW, J., D’SOUZA, A., GREYVENSTEIN, D., LEES, M., MIZZI, V., NAPHIN, C., PROWTING, J., REBALKA, I., ROXBURGH, L., YANG, Y., PHILLIPS, S., Institution: MCMASTER UNIVERSITY, Country: CANADA, Abstract-ID: 1582

INTRODUCTION:
Skeletal muscle is central to metabolic health and physical function. Resistance training (RT) increases hypertrophy and strength, yet only ~1 in 5 females participate, often due to barriers such as fear of heavy lifting, excessive muscularity, or injury. Females also show greater fatigue resistance and may be well suited to lower-load RT. In males, hypertrophy is largely load-independent when sets are taken to volitional failure, but comparable evidence in females is limited because they remain underrepresented in RT research.

We compared the effects of higher versus lower load RET on skeletal muscle hypertrophy and strength. It was hypothesized that there would be equivalent adaptation between conditions.
METHODS:
Thirty-six healthy young females (aged 24 ± 6 years; yrs; 14 untrained; 22 trained) completed a supervised full-body RET program (2x/week) for 10 weeks. Participants were randomized to either higher-load training (HL;~70-85% one repetition maximum [1RM], 8-12 repetitions) or lower-load training (LL: ~30-50% 1RM, 20-25 repetitions). All sets were performed to volitional failure. Outcome measures included vastus lateralis cross-sectional area (VLCSA) via ultrasound; whole body lean body mass (LBM) assessed by dual-energy X-ray absorptiometry (DXA); maximal dynamic strength (leg press and incline chest press 1RM); and isometric strength (MVC) was assessed via knee extension using dynamometry. Linear mixed-effects models were employed, and equivalence was evaluated using two one-sided tests with Hedges’ g and predefined trivial bounds (±0.20).
RESULTS:
Training age did not significantly influence adaptations (all interactions p = 0.31). VLCSA increased significantly in both groups (p < 0.001) (HL: +3.72 cm²; LL: +3.16 cm²), with no significant between-group difference (p = 0.33; g = 0.11, 90% CI −0.08 to 0.30). Whole-body LBM also increased (p = 0.039) (HL: +997 g; LL: +683 g), with trivial between-group differences (p = 0.61; g = 0.05, 90% CI −0.05 to 0.15). Equivalence was not statistically demonstrated under conservative bounds.
Leg press strength increased substantially in both groups (HL: +120 kg; LL: +106 kg; p < 0.001), with a small, non-significant between-group difference (p = 0.34; g = 0.24, 90% CI −0.12 to 0.60). MVC increased numerically more in HL (+24.3 vs +13.1 Nm), but the overall time effect was not statistically significant (p = 0.061), and the between-group difference was small-to-moderate with wide uncertainty (g = 0.37, 90% CI −0.06 to 0.79). In contrast, incline chest press 1RM showed a clearer advantage for HL (p = 0.003; g = 0.26, 90% CI 0.09 to 0.44).

CONCLUSION:
In healthy young females, LL RT performed to failure elicits robust hypertrophy comparable in magnitude to HL training. Strength gains were substantial across both conditions, with HL primarily conferring advantages for BP strength. We show that muscle hypertrophy can be achieved across wide loading ranges in females, while reinforcing load specificity for certain strength outcomes