A number of acute and overuse knee pathologies share a mechanism involving a poor dynamic alignment of the limb creating increased stress in the tissues. Inappropriate execution of a correct strategy during landing has been suggested to involve insufficient activity of the hip abductor and external rotator muscles. Limited data describing the relationships between hip-abductor muscle fatigue and hip/knee joint mechanics exists.
To investigate the effect of fatigue of the hip abductor muscles on knee valgus angle.
30 asymptomatic subjects: 15 female (age 20.4 ± 1.4, range 18–26 years; height 1.66 m, range 1.60–1.76 m; weight 63.9 kg, range 58–68 kg) and 15 male subjects (age 22 ± 3.2, range 18–28 years; height 1.84 m, range 1.65–1.90 m; weight 82.1 kg, range 69–93 kg).
Main outcome Measures:
Knee valgus (frontal plane projection) angle was assessed during a step landing task before and following a fatiguing protocol of the hip abductor muscles involving repeated 10 s maximal isometric contractions of the hip abductor muscles, until strength was recorded as 50% of preintervention score.
Males showed no significant change in knee valgus angle at initial ground contact (p = .9 ES 0.1) or in maximum knee valgus (p = .64 ES 0.5) following the fatiguing. Females showed a significant increase in maximum knee valgus angle following the fatiguing (p = .0018 ES 1.0), though the knee valgus angle at initial contact was not changed (p = .12 ES 0.67). They also demonstrated a significant increase in the change in knee valgus angle between initial contact and maximum following the fatiguing (p = .0004 ES 0.88).
Females appear more susceptible to the effects of hip muscle fatigue, leading to a detrimental change in landing kinematics which may then predispose them to knee injury.
Lee Herrington is a Senior Lecturer in Sports Rehabilitation at the University of Salford in Salford, United Kingdom.