The effect of muscle fatigue on lower extremity kinematics in physically active females

Abstract

<b>Objective:</b> To investigate the effect of fatigue on dynamic knee valgus and hip joint movement during a single leg squat in physically active females. <b>Design and Setting:</b> All data were collected in lowers Athletic Training Research Laboratory, Texas State University-San Marcos. <b>Subjects:</b> Thirty healthy, physically active females (age = 21 + 2.13t years, mass = 61.02 + 7.33 kg, height = 167.34 + 6.08 cm, Q angle = 17.75 + 2.21 degrees) with no reports of injuries, impairments or surgeries to the low back or lower extremities within the past two years. <b>Measurements:</b> All subjects stood on a box (height specified and adjusted according to leg length) and then completed two single leg squats to approximately 70 degrees of knee flexion prior to isokinetic strength testing and after the fatigue protocol. Frontal plane knee motion and sagittal plane hip motion was evaluated and recorded using two 2-D SportsCam High Speed Cameras. Isokinetic (60 deg/sec) concentric knee (flexion/extension) strength was measured and evaluated, followed by an immediate isokinetic (60 deg/sec) concentric knee (flexion/extension) fatigue protocol. Subjects were evaluated as fatigued once they fell below 50% of the previously recorded knee (flexion/extension) peak torque. <b>Results:</b> Two paired t-tests for pre and post dynamic knee valgus and hip flexion angles were calculated. A significant difference was found with hip flexion. The mean score on the posttest (136.48 + 10.98) showed an increase in hip flexion angle when compared to the pretest (140.43 ± 10.03); t (29) = 4.05, p < .01, accounting for 95% of the variance in the difference between the scores. Paired t-tests for the pre and post mean dynamic valgum revealed no significant difference during the single leg squat as hypothesized. Effect size for the difference between pre and post fatigue dynamic valgum ranged from -1.29 to 3.20 and hip flexion from -3.22 to 4.31 respectively. <b>Conclusion:</b> Frontal plane dynamic knee movement showed no significant difference between pre and post fatigue assessments. However, the sagittal plane mean hip flexion angle did report a significant difference between the pre and post fatigue measurements. These results demonstrate the need for further investigation of the role that the knee musculature plays in hip flexion angles during dynamic movement, pre and post fatigue.