Shank Muscular Pattern Altered During Pre-initial Contact In Men With Functional Ankle Instability

Purpose: To evaluate tibial muscular activities during 250/100 ms before/after initial foot contact (FC) during treadmill running in men with FAI. It was hypothesized that activities and co-contraction of tibial muscles in the FAI group were less than in the control group. Methods: 15 male college students with right side FAI / 15 age-matched healthy controls (age: 22.0±2.6 / 23.7±1.1 yrs, height: 179.0±4.6 / 176.7±3.5 cm, body mass: 72.7±7.7 / 70.0±5.0 kg, Cumberland Ankle Instability Tool:18.0±4.5 / 29.3±1.0) were recruited. Written informed consent was obtained before data collection. Electrodes were placed on the belly of the soleus (SOL), lateral gastrocnemius (GL), and tibialis anterior (TA) of the right leg in line with the muscle fibers. After warm-up, kinematic and electromyographic data at a preferred running speed on a treadmill was collected synchronously by 6-infrared high-speed cameras and surface EMG at 100 and 2000 Hz sampling frequencies, respectively. The lowest vertical position of the heel marker determined FC time. After the removed mean, filtered using a 4th Butterworth bandpass by 10-500 Hz, and full wave rectified, the surface EMG data during the 250/100 ms before/ after FC during 15 stride cycles in the third minute of 5-minute running was divided into 7 phases by every 50-ms. The average activity of the TA, GL, and SOL, as well as the co-contraction index of TA/GL and TA/SL pair of each phase were calculated. Two-way repeated ANOVA was used for the statistical test, and the Bonferroni post hoc test was used when needed. Results: In the FAI group, the average activity of TA was less (3.36±1.59 vs. 4.82±2.34), and SOL was greater (1.51±1.65 vs. 0.63±0.57) than the control group, as well as TA/SOL was lower (0.72±0.22 vs. 0.88±0.10) than control group during 250-150 ms before FC (p<.05). In the control group, TA/GL (0.62±0.31)) and TA/SOL (0.65±0.34) during 50-ms before FC were greater than that (0.50±0.32) and (0.55±0.30) during 50-ms after FC (p<.002). No differences were observed between neighbor phases in the FAI group (p>0.002). Conclusion: We have observed altered TA and SOL muscle activities during 250-150 ms pre-initial contact in men with FAI.