BIOMECHANICAL EFFECTS OF ANKLE STABILIZER AND GENDER ON THE ANKLE JOINT DURING HALF-SQUAT PARACHUTE LANDING

© WenxinNiu, YangWang, YuboFan
© Государственный музей истории космонавтики им. К.Э. Циолковского, г. Калуга
Секция "К.Э. Циолковский и проблемы космической медицины и биологии"
2010 г.

INTRODUCTION

Parachute landing is a hazardous activity to the ankle joint and females are more likely to be injured. Biomechanical Effects of ankle external stabilizers on the ankle was unclear during half-squat parachute landing (HSPL), and a search of the literature did not reveal known gender differences in biomechanics during parachute landing.

METHODS

Eight male and eight female healthy adults were recruited. Each barefooted individual jumped from platforms with three different heights (low: 0.32 m; medium: 0.52 m; and high: 0.72 m) and landed on a force plate in a standard HSPL technique. To evaluate the biomechanical effects of the external stabilizers, another experiment included three conditions (no stabilizer, elastic tape and semi-rigid brace) when each individual dropped from the high height.

The ground reaction force (GRF) was collected in the right foot and normalized to body weight (BW). Position data of the right shank and foot were collected by a 3-D motion capture system. With the software Visual3D, angular displacement and velocity peaks of ankle dorsiflexion, inversion and abduction were calculated. Surface electromyogram (EMG) signals were measured in the tibialis anterior (TA) and lateral gastrocnemius (LG). The average EMG amplitudes were calculated over a period of 100 ms before and after touch-down. Multivariate analysis of variance (ANOVA) was used to analyze the effects of the dropping height, gender, and stabilizer factors. Statistically significant difference was defined with p<0.05.

RESULTS

The anterior-posterior (A-P) GRF (men 1.01 BW; women 0.79 BW), rate of loading (ROL), (men 260 BW/s; women 127 BW/s), and absolute EMG amplitude of TA (pre-landing: men 219 µv; women 129µv; post-landing: men 573 µv; women 288µv) in the men’s group were significantly higher than in the women’s group, whereas peak angular velocity of dorsiflexion in the women’s group (1627 °/s) was significantly higher than in the men’s (1188 °/s).

DISCUSSION

Men were impacted more severely during landing, with significantly greater A-P GRF and ROL. This finding did not agree with the epidemiological reality that women are more likely to sustain ankle injuries during HSPL. There are two biomechanical explanations for this fact. First, women tend to produce greater peak dorsiflexion angular velocity, because they are prone to transform the kinetic energy to ankle motion, whereas their male colleagues are more likely to transform it to friction between the plantar surface and the ground. Second, compared with men, women have lower EMG activity in their ankle flexors but similar EMG activity in their ankle extensors. This variance may lead to different co-contraction of the flexors and extensors, which make women more susceptible to ankle injuries.

Both ankle stabilizers significantly decrease the A-P GRF, but increase M-L GRF. Because these two components are both in the horizontal plane, this disproportionate change may result in the direction change of the horizontal. Quantitatively, the horizontal GRF increased after utilization of the ankle stabilizers. This performance may be related to the effects of stabilizers on joint kinematics. Restricted with stabilizers, the kinetic energy absorbed originally by the joint motion has to be released by greater impart forces.

Stabilizers significantly decreased peak ankle angular displacements. No significant effect was found on the peak angular velocity of any stabilizer during half-squat landing. It indicated that peak angular velocity commonly occurred before the angular peak, and the restriction of joint rang of motion had small effect on the angular velocity. Ankle stabilizers, especially the semi-rigid brace are capable of arousing more active EMG of men’s ankle flexor during half-squat landing, but women does not share this predominance. Both stabilizers are unable to change the differences in the co-contraction of the flexors and extensors between both genders. Therefore, it is suggested that male parachuters should be equipped with more rigid external stabilizers to arouse their muscle, while women should wear more soft stabilizers to maintain some range of motion of the joint.

 
 

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