It remains controversial whether maximal effort attained by high external resistance is required to optimize muscle adaptation to strengthening exercise. Here, we compared different training protocols reaching maximal effort with either high resistance (HImax, 80% of one repetition maximum (1RM)) or low resistance (LOmax, ≤40% 1RM). Thirty-six young volunteers were randomly assigned to 9 weeks leg extension training at either HImax (one set of 10-12 repetitions at 80% 1RM), LO (one set of 10-12 repetitions at 40% 1RM, no maximal effort), or LOmax (one set of 10-12 repetitions at 40% 1RM, preceded (no rest) by 60 repetitions at 20-25% 1RM). Knee extension 1RM was measured pre and post intervention, and before the 7, 13, and 19 training session. Pre and post intervention, knee extensor static (PTstat) and dynamic (PTdyn) peak torque, maximal work (MW), and speed of movement at 20% (S20), 40% (S40) and 60% (S60) of PTstat were recorded with a Biodex dynamometer. All groups showed a significant increase in 1RM, with a greater improvement in HImax from the 13 session on (p<0.05). HImax was the only group that significantly increased PTstat (+6.5%, p=0.01). LOmax showed a significantly greater increase in S20 (+6.5%), PTdyn (+8.2%) and MW (+13.8%) than both HImax and LO (p=0.044 for S20, p=0.030 for PTdyn, p=0.025 for MW), and was the only group that increased in S40 (+8.8%, p=0.032). In conclusion, significant differences between HImax and LOmax on force-velocity characteristics of the knee extensors were found, although maximal effort was achieved in both training regimens. Thus, LOmax may not be considered as a replacement for HImax, but rather as an alternative with different training-specific adaptations.