The purpose of this study was to determine whether a high intensity (HI) versus a moderate (MI) or low-intensity (LI) training program would be more effective in improving the isokinetic knee extension muscular performance in healthy inactive men and women. Sixty-four participants, men and women, were randomly assigned to one of four groups: control group (C), LI (50% of 1RM), the MI group (70% of 1RM) and the HI (90% of 1RM). Participants exercised on three resistance exercise machines: leg extension, leg curls and leg press. The isokinetic testing method (concentric mode) applied prior to and at the end of the training period (16 weeks, three 3 times per week) to assess the knee muscular performance. MANOVA repeated measures revealed that the HI group demonstrated the most strength gains following a speed specificity pattern (most considerable improvement occurred at or near slow speeds from 7.3% to 11.2% for male and from 2.3% to 15.2% for female). In addition, males demonstrated a greater improvement of knee extension power output than females. In conclusion, HI strength training is proposed for elderly men and women as the most effective protocol. Furthermore only at low-velocity testing, women of the HI showed a greater change than men (p < 0.05). Regarding strength increase in relation to various testing velocities, a greater increase was found in HI at low velocities, with the other training groups exhibiting almost similar strength increase at all tested speeds.