Cameron J. Mitchell

The effect of resistance training with higher- and lower-loads on muscle mass and strength has been extensively studied, while changes in muscle endurance have received less attention. This trial aimed to assess the effect of training load on absolute muscle endurance (AME) and relative muscle endurance (RME). Sixteen untrained women (22.7 ± 3.3 yr: mean ± SD) had one arm and leg randomly assigned to train with higher loads (HL; 80–90% 1RM), and the contralateral limbs trained with lower loads (LL; 30–50% 1RM) thrice weekly to volitional fatigue for 10 weeks. Heavy and light load AME and RME, strength, and muscle mass were assessed pre- and post-training. Strength increased more in the HL compared to LL leg ( P < 0.01), but similar increases in strength were observed between upper body conditions ( P = 0.46). Lower body heavy and light load AME improved in both conditions, but HL training induced a larger improvement in heavy load AME (HL: 9.3 ± 4.3 vs. LL: 7.5 ± 7.1 repetitions, time × limb P < 0.01) and LL training induced a larger improvement in light load AME (LL: 24.7 ± 22.2 vs. HL: 15.2 ± 16.7 repetitions, time × limb P = 0.04). In the upper body, HL and LL training induced similar increases in both heavy (time × limb P = 0.99), and light load (time × limb P = 0.16) AME. Dual-energy X-ray absorptiometry showed no change in leg fat-and-bone-free mass (FBFM) for either condition, and an increase in only LL arm FBFM. AME improved in a manner specific to the training loads used. ClinicalTrials.gov (NCT04547972).