IN VIVO ARCHITECTURE OF THE TIBIALIS ANTERIOR DURING GAIT

Abstract

The tibialis anterior (TA) controls dynamic movement of the ankle during functional activities such as walking in humans. Previously, the type of muscle contraction (concentric, eccentric, or isometric) occurring during each phase of the gait cycle has been defined through measurement of joint angle changes and electromyographic (EMG) activity alone. From these observations, it has been assumed that the TA contracts eccentrically during loading response (LR) and concentrically during initial swing (ISw). PURPOSE The purpose of this study was to use ultrasound imaging in addition to joint angle changes and EMG to determine the type of muscle contraction of the TA during gait. METHODS Eleven healthy subjects (22.6 ± 1.5yrs; 8 males, 3 females) performed treadmill walking at 3.0 miles per hour. Ultrasound imaging of the fascicle length, integrated EMG activity (normalized to maximum isometric voluntary contraction), as well as knee and ankle joint angles were measured. Foot switches were utilized to indicate the time at which heel strike and toe-off occurred during the gait cycle. Descriptive analyses were conducted to determine changes in fascicle length during the gait cycle. RESULTS Average fascicle length changes for LR, pre-swing (PSw), and ISw were 1.2% ± 8.6% (shortening), 1.9% ± 12.0% (lengthening) and 9.7% ± 6.4% (shortening), respectively. During each of these phases of the gait cycle, the TA integrated EMG activity was 35–41% of the maximum isometric voluntary contraction demonstrating that the TA was active during these phases of the gait cycle. CONCLUSION The TA fasicles are at constant length (isometric contraction) during LR and PSw while the ankle plantarflexes 6 ± 4 degrees and 7 ± 4 degrees, respectively, and shortens (concentric contraction) nearly 10% during ISw while the ankle dorsiflexes 17 ± 4 degrees. Understanding how the TA functions during specific phases of the gait cycle, such as LR and ISw, is valuable for evaluation and rehabilitation of patients with movement disorders.