Search Results

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r ² = 0.13), knee flexion (r ² = 0.18), and knee extension (r ² = 0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r = –0.37), knee flexion (r = –0.43), and knee extension (r = –0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.

Expectations may be for both legs to function identically during single- and double-leg vertical jumps. However, several reasons might prevent this from occurring. The goals of this investigation were twofold: assess the presence of side-to-side jump height differences during single-leg jumps in a homogenous group of healthy subjects and determine if those with a jump height asymmetry possessed consistent biomechanical differences during single- and double-leg jumps. Thirteen men and 12 women with competitive volleyball experience volunteered for the study. Significance was assessed at p < 0.05. The men jumped significantly higher than the women in all conditions and possessed differences in several anthropometric, kinematic, and kinetic parameters. Based on a three-jump average, all subjects had one leg that they could jump higher with (the dominant leg, DL). The men generated significantly greater maximum ground reaction forces and ankle joint powers on their DL whereas the women had no differences during the single-leg jumps. The only side-to-side differences that existed during the double-leg jumps were in the average ground reaction forces during propulsion. These findings suggest that equality of single-leg jump performance is the exception rather than the norm, with identification of consistent biomechanical attributes difficult within a group. Furthermore, any differences are not likely to cross over to other tasks, with men and women utilizing slightly different jump techniques.

Context: Single leg balance testing is a commonly used tool in sports medicine; however, there has been no consensus on trial duration needed to obtain reliable measures. Objective: This investigation sought to determine the minimum trial duration required to obtain the highest intrasession single and average trial reliability for single leg balance testing on stable and unstable surfaces using dominant and nondominant limbs. Design: Intrasession reliability. Setting: Biomechanics laboratory. Participants: 70 healthy (35 men, 35 women), physically active young adults aged 22.8 ± 2.8 y divided into 3 subgroups (n = 10, 30, 30) across a 3-phase study. Methods: 3 phases of single leg balance testing were performed. For phase 1, the duration of time each participant could maintain posture on each limb/surface were computed. Phase 2 considered performance for 6 cumulative time intervals (5s, 10s, 15s, 20s, 25s, 30s). Phase 3 served to solidify results of phase 2 by computing reliability of 15s trials. Main outcome measures: Overall stability index of the center of pressure and platform tilt. Results: Intraclass correlation coefficients for phase 2 ranged from .74 (5s interval for nondominant limb on unstable surface) to .94 (20s interval for nondominant limb on stable surface). Phase 3 intraclass correlation coefficients ranged from .66 to .78 for single trial and .85 to .92 for 3 trial average with coefficients of variation ranging from 23.9% to 40.4% for single trial and 13.8% to 23.0% for 3 trial average. Conclusions: These results ultimately suggest 15s as the optimal trial duration to provide reliable measures while reducing compensatory event occurrence.

Kinematic differences have been linked to the gender discrepancies seen in knee injuries. A medially posted orthotic decreases frontal and transverse plane motions in the lower extremity during ambulation, squatting and landing. This study investigated the effect of a medial post on amount and timing of lower extremity motions during a single-leg squat in male and female athletes. We hypothesized there would be differences in these kinematic variables dependent upon sex and post conditions. Twenty male and female athletes performed single-leg squats with and without a five degree full-length medial post. Maximum joint angles were analyzed using a two-way, repeated-measures analysis of variance to determine if the differences created by post condition were statistically significant, whether there were gender differences, or interactions. Differences in maximum motion values and the time at which they occurred were found between men and women at the hip, knee and ankle. The post decreased all frontal plane measures in both sexes and resulted in earlier attainment of maximum ankle eversion and delayed maximum knee valgus. A medially posted orthotic may be beneficial not only in limiting motion, but in affecting the time in which stressful motions occur.