Ankle Muscles Reaction Time During Sudden Inversion In Individuals With Or Without Functional Ankle Instability

Abstract

Muscle reaction time (RT) represent the time lag from event to muscle activation. Person with functional ankle instability (FAI) often experiences “giving way” during activities. Whether this is because of muscle activation delay is still unclear. PURPOSE: To compare RT of ankle muscles using a sudden ankle inversion (30 degrees) apparatus in individuals with or without FAI. METHODS: A total of eight subjects volunteered to participate for this study including two subjects with FAI (FAI group, 25.5 ± 2.1 yrs, 171.5 ± 0.7 cm, 76.5 ± 17.7 kg,CAIT score: 18.5 ± 3.5) and six control subjects without FAI (control group, 23.7 ± 0.5 yrs, 175.3 ± 4.7 cm, 78.7 ± 11.6 kg, CAIT score:28.3 ± 1.4).Using Cumberland ankle instability tool questionnaire (CAIT) to identify whether subjects were with FAI. Scores of ≤ 23 indicate FAI. Subjects were asked to stand on the two platforms for each legs of sudden ankle inversion apparatus. The platforms were initial locked by electromagnetic force. After unlocking, one of them inclined downward to 30 degrees ankle inversion. During the test, RT of tibialis anterior (TA), peroneus longus (PL) and peroneus brevis (PB) were assessed through surface electromyography (EMG). The RT of the muscles was determined as the time between the unlocking of the platform and the increase to 5 SDs higher than the mean resting activity during stance. EMG data were collected at 1000Hz and band-pass filtered at 10 and 450 Hz and low-pass filtered at 10 Hz. Data were analyzed using independent t- test. RESULTS: The RT of TA, PL and PB in FAI group were 46.3 ± 1.4 ms, 45 ± 4.2 ms and 42.7 ± 5.7 ms. PB activated first and TA activated last in FAI group. The RT of TA, PL and PB in control group were 43.3 ± 6.4 ms, 50.4 ± 9 ms and 44.4 ± 14.7 ms. TA activated first and PL activated last in FAI group. There were no significant difference in RT for TA (p=0.277), PL (p=0.229) and PB (p=0.439) between groups. CONCLUSION: The RT of TA, PL and PB induced by sudden ankle inversion (30 degrees) in individuals with and without FAI were not different. But the sequences of activation were different. The activations of PL and PB in individuals with FAI were not delayed compared with individuals without FAI. The activation of TA might be also an important factor for ankle stability. Further studies are needed to clarify the function of TA during sudden inversion in subjects with FAI.