Active Insufficiency
Description
Previous studies have suggested that ankle position and hip position can influence hamstring strength, but none have considered the influence of both joint positions at the same time. The aim of the study was to investigate the effect of ankle and hip position on peak torque (PT), normalized PT (NPT), angle of PT (APT) and electromyographic (EMG) activity during isokinetic knee flexion. Thirteen physically active men performed three maximal isokinetic unilateral knee flexion repetitions at angular velocities of 60 and 180°/s on the isokinetic dynamometer. The individual EMG activity of the gastrocnemius (GL), biceps femoris (BFl) and semitendinosus (ST) muscles was detected using wireless SEMG system. Ankle and hip position had a significant impact on the PT and NPT (p < .05). Specifically, the highest PT and NPT were produced in the dorsal-flexion sitting position, then in the plantarflexion sitting position, followed by the dorsal-flexion in the supine position, while the lowest PT and NPT were produced in the supine position with plantarflexion for both angular velocities. Ankle and hip position and angular velocity have a significant impact on the APT: the PT occurred between 25 and 41° at 60°/s, and between 40 and 62° at 180°/s. Neither ankle nor hip position affected SEMG activity of BFl, ST and GL muscles for both angular velocities. Hip and ankle position influence the passive tension and active insufficiency, which ultimately affects hamstrings PT, but not muscle activity.
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To evaluate the research question, analysis of the dominant leg knee flexion on the isokinetic dynamometer was used to determine dynamic changes elicited by different ankle and hip joint positions at two different angular velocities. Also, the SEMG analysis was performed to determine the differences in the activation of certain muscles between the mentioned hip and ankle joints positions. A within-subject study design was used during a single testing session, with subjects flexing the knee under four joint positions: hip flexion with dorsiflexion (HFDF), hip flexion with plantarflexion (HFPF), hip extension with dorsiflexion (HEDF) and hip extension with plantarflexion (HEPF), and also under two angle velocities: 60 and 180°/s. The primary outcome variables of interest were peak torque (PT), normalized peak torque to body mass (NPT), angle of peak torque (APT) and maximal normalized surface EMG muscle activation.