Comparison Of Asymmetry In Achilles Tendon Loading Variables Between Male And Female Recreational Runners

Achilles tendon (AT) injuries often occur unilaterally in running with males having a higher reported incidence compared to females. PURPOSE: To examine asymmetry between limbs based on gender in AT-related loading variables during running. METHODS: 16 female (21.9 ± 1.6 yrs; mass: 68.2 ± 9.4 kg; height: 171.6 ± 7.1 cm) and 16 male (23.1 ± 1.31 yrs, mass: 75.2 ± 14.9 kg; height: 174.9 ± 8.6 cm) recreational runners participated in a single session. After a standardized walking warmup, each runner ran for 3.5 minutes at 3.3 m/s. Data were recorded for the last 30 seconds of the run. Three-dimensional kinematics (180 Hz) from a 16-camera motion analysis system and kinetics (1800 Hz) from an instrumented treadmill were measured. These data were input into a 16-segment musculoskeletal model where inverse dynamics and static optimization were used to calculate muscle forces of the gastrocnemius and soleus from each limb. Subject-specific ultrasound measures were taken to determine AT cross sectional area (CSA). AT stress was calculated from AT force/AT CSA. Five steps at the end of the run were processed for each limb and percent asymmetry was calculated using the following equation: [|left leg -right leg| / (left leg + right leg) / 2] x 100%. Independent samples t-tests were run to examine gender differences in all asymmetry variables (α = 0.05). RESULTS: No differences were observed in asymmetry between gender in the following variables: stance time (p = 0.124, Cohen’s d = 0.42), peak vertical ground reaction force (p = 0.318, Cohen’s d = 0.17), peak soleus muscle force (p = .397, Cohen’s d = 0.09), peak AT force (p = 0.099, Cohen’s d = 0.47), and peak AT CSA (p = 0.107, Cohen’s d = 0.45). Asymmetry between gender was shown in AT stress (p = 0.005) with a large effect size (Cohen’s d = 0.96) and peak gastrocnemius muscle force (p = .043) with a medium effect size (Cohen’s d = 0.63). Females had an 8.83 KPa higher AT stress asymmetry and a 3.31BW larger peak gastrocnemius muscle force asymmetry compared to males. CONCLUSIONS: Differences were shown in AT stress and peak gastrocnemius muscle force asymmetry based on gender. Further research appears warranted to understand how asymmetry may be different based on gender in the AT stress of healthy and injured runners. Supported by: University of Wisconsin- La Crosse graduate studies and Gundersen Health System.