Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading

Introduction: Differences between male and female muscle-tendon units have been previously observed. It is unknown if a sex-related difference exists in the plantarflexor response to repeated stretch-shortening cycles, as occurs during activities of daily living such as walking and running. Methods: An adapted force sledge was used with three dimensional motion analysis to investigate the response of the plantarflexors of 34 age and training-matched males and females during stretchshortening cycle impacts. Results: Contact times and flight times were found to be similar between groups. Statistically significant differences in absolute peak force and rates of force development were observed during loading. With normalisation to plantarflexor muscle volume, small and moderate effect sizes were observed for all force and rate of force development variables but only peak force remained statistically significant. Differences in absolute stiffness, peak negative and positive power and work were statistically significant with moderate effect size, but with normalisation only differences in peak negative power and work remained statistically significant with a moderate effect size. Conclusion: These results show females have lower force, rate of force production and force absorption capabilities, which are of relevance in injury prevention and rehabilitation, and informing personalised engineering design. Level of evidence: III b (individual case-control study).