Muscle mass accretion is accomplished by heavy-load resistance training. The effect of light-load resistance exercise is far more sparsely investigated with regards to the potential effect upon muscle size and contractile strength. We applied a resistance exercise protocol where the same individual trained one leg at 70% of 1 repetition maximum (1RM) (HL) while training the other leg at 15.5% 1RM (LL). Eleven sedentary men (age: 25±1 yrs) trained for 12 weeks, 3-times per week. Before and after the intervention muscle hypertrophy was determined by magnetic resonance imaging, muscle biopsies were obtained bilaterally from vastus lateralis for determination of myosin heavy chain (MHC) composition, and maximal muscle strength was assessed by 1RM testing and in an isokinetic dynamometer at 60°^.s^-1. Quadriceps muscle cross-sectional area increased (P<0.05) 8±1% and 3±1% in the HL and LL leg, respectively, with a greater gain in HL than LL (P<0.05). Likewise, 1RM strength increased (P<0.001) in both legs (HL: 36±5%, LL: 19±2%), albeit more so with HL (P<0.01). Isokinetic 60°^.s ^-1 muscle strength improved by 13±5% (P<0.05) in HL but remained unchanged in LL (4±5%, n.s.). Finally, MHC IIX protein expression was decreased with HL but not LL, despite identical total workload in HL and LL. Our main finding was that LL resistance training was sufficient to induce a small but significant muscle hypertrophy in healthy young men. However, LL resistance training was inferior compared to HL training in evoking adaptive changes in muscle size and contractile strength, and was insufficient to induce changes in MHC composition.