The gluteus maximus is more active on the trail leg, while the gluteus medius is more active on the lead leg. 5 Hip abductors that exhibit high activity during pitching include the gluteus maximus and medius. 10–12 The lead leg (contralateral to the throwing arm) functions to decelerate the knee, provide a stable base, and absorb the force transferred from the deceleration and follow through phases. On the trail leg (ipsilateral to the throwing arm) the abductors function to stabilize the pelvis and provide balance during the wind-up and early cocking phases. The hip abductor muscle group also has a direct influence on both lower extremities during throwing. 9 Moreover, greater trunk lean occurred in participants with hip weakness despite increased activation of the trunk musculature. During a dynamic single-leg landing task, individuals with hip abductor and extensor weakness had increased trunk lean towards the stance limb. They also have an indirect effect on motion at the trunk via the attachment of the gluteus maximus to the pelvis and lumbar spine, via the thoracolumbar fascia. The hip abductor muscle group has a direct effect on motion at the hip via their proximal and distal attachment sites. 2–4 Disruptions in the kinetic chain can increase forces at the shoulder and elbow, and these increased forces have been associated with arm injuries in baseball players. 1,2 Any alterations in proximal segmental sequencing or force transfer can alter the kinetics and kinematics at the distal joints, leading to increased joint and soft tissue stress. The proximal segments of the hip and trunk are estimated to contribute 50% of the kinetic energy and force during dynamic overhead arm activities. When throwing a baseball, force is initiated by the legs, transferred to the trunk and then to the upper extremity for ball release. The lower extremities and trunk are critical components for power generation during throwing or hitting sports. These deficits could translate to altered pitching performance and injury. Specifically in pitchers, hip abduction weakness was related to increased movement of the lower extremity and lumbopelvic regions during the dynamic SLSD task. Hip abduction strength contributes to dynamic control of the trunk and legs. Also for pitchers on the trail leg, increased hip abduction torque weakly correlated with decreased pelvic drop (r= -0.28, p=0.021). For pitchers, on the lead leg increased hip abduction torque weakly correlated with a decrease in knee valgus (r= 0.24, p=0.049). There were no significant correlations for position players. Pearson correlations examined the relationships between hip abduction torque and SLSD motions. A value of 180° indicated no knee valgus. Trunk lean, trunk flexion, pelvic drop, knee valgus, and hip flexion were measured using Dartfish at heel touchdown. Video cameras captured the SLSD, with participants standing on one leg while lowering their contralateral heel to touchdown on the floor from a 0.203m (8in.) step. Bilateral hip abduction isometric strength was measured using a handheld dynamometer (HHD), and then multiplied by distance from the greater trochanter to the HHD and expressed as hip abduction torque. One hundred-eighteen Minor League baseball players (age=21.6 ± 2.0 years n=68 pitchers, n=50 position players) participated.
To determine the relationship between hip abduction isometric strength and movement during the SLSD of trunk lean, pelvic drop, knee valgus, and hip flexion. Hip abduction weakness may impact movement quality during the SLSD, however the relationships between movement and strength are unclear. The single-leg step down task (SLSD) is a clinical tool to assess movement and control of the lower extremity and trunk.
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