Neuromuscular electrical stimulation (NMES) is a physical therapy intervention used to treat muscle weakness. NMES-elicited forces during therapy are correlated with strength gains. Patient discomfort limits NMES-elicited forces potentially compromising strength gains and the efficacy of this invention. The purpose of this study was to determine if NMES containing two different electrical stimulation pulse durations (200 or 500 μs) affected the knee extensor muscle torques subjects tolerated. Other NMES characteristics were identical in the two conditions: monophasic square-wave pulses; 75 pulses per second; and electrical stimulation train duration of one second. The primary dependent variable of interest was the percentage of maximum voluntary isometric contraction (MVIC) tolerated. The two pulse duration conditions were tested during a single session on the opposing lower extremities of 15 subjects. Subjects tolerated 49.3 ± 18.7% of MVIC torques in the 500-μs condition versus 44.5 ± 17.9% of MVIC torques in the 200-μs condition, which was a statistically significant difference (p = 0.02). Further research is needed to explore if the differences observed in this study would lead to clinically significant differences in strength gains and to see if the findings of this study can be generalized to other forms of NMES that contain other types of wave forms.