The aim of this investigation was to determine the effect of percutaneous neuromuscular stimulatory (PNS) pulse duration on whole muscle contractile properties of the human biceps brachii muscle as measured by a laser-based mechanomyographic (MMG) technique. This study quantified the effect of PNS pulse duration on muscle contractile properties to facilitate the development of standardized techniques to utilize MMG as an in-clinic assessment tool. Ten male volunteers, aged 19 to 33 years, participated in the study. Percutaneous neuromuscular stimulation (maximum of 180V and 85mA) was delivered by a transcutaneous electrical neuromuscular stimulation (TENS) device, through bipolar surface electrodes, to the short head of the right bicep brachii. The duration of the PNS pulse was randomly varied so that 10 trials were recorded at each of 10 PNS pulse durations, ranging from 50 μs, at 50-μs increments. In total, 100 trials for each subject were available for analysis. A laser MMG sensor detected the lateral displacement of the muscle belly during the development of isometric tension after each PNS pulse had been delivered. The parabolic MMG waveforms were analysed and statistically compared to determine whether PNS pulse duration influenced the recorded contractile properties of the biceps brachii. The results showed that the duration of the PNS pulse significantly (P<0.05) influenced the measured contractile properties of the biceps brachii as determined by the MMG technique. At PNS pulse durations below 300 μs, the contractile properties of the biceps brachii were more variable and more consistent with a slower contracting, or inadequately stimulated, muscle. At PNS pulse durations above 300 μs, the contractile properties of the muscle were considered stable and were similar to those previously reported for biceps brachii using a tensiometric technique. In conclusion, PNS pulse durations above 300 μs provide both a maximal lateral displacement of the muscle's belly and stable measures of its contractile properties.