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The purpose of this study was to derive normative values for range of motion and single-leg hop tests on athletes with no history of knee injury. Subjects measured for range of motion included 578 healthy males (mean age, 14.5 years) and 311 healthy females (mean age, 14.0 years). Subjects performing single-leg hop included 1,635 healthy males (mean age, 14.5 years) and 873 healthy females (mean age, 14.2 years). Measurements were taken during preseason athletic physicals. Mean range of motion was 5-0-140 for males and 6-0-143 for females. Mean single-leg hop for both legs was 155 cm for males and 121 cm for females. The paper discusses the importance of measuring terminal hyperextension as well as the importance of normal side-to-side variations in ROM and the single-leg hop test. The results of the single-leg hop test should not be used exclusively but rather in conjunction with other information gathered during the clinical visit.

The purpose of this study was to investigate muscle activation patterns during a landing task in boys and girls through the use of muscle synergies. Electromyographical data from six lower extremity muscles were collected from 11 boys and 16 girls while they performed single-leg drop-landings. Electromyographical data from six leg muscles were rectified, smoothed, and normalized to maximum dynamic muscle activity during landing. Data from 100 ms before to 100 ms after touchdown were submitted to factor analyses to extract muscle synergies along with the associated activation and weighing coefficients. Boys and girls both used three muscle synergies. The activation coefficients of these synergies captured muscle activity during the prelanding, touchdown, and postlanding phases of the single-leg drop-landing. Analysis of the weighing coefficients indicated that within the extracted muscle synergies the girls emphasized activation of the medial hamstring muscle during the prelanding and touchdown synergy whereas boys emphasized activation of the vastus medialis during the postlanding synergy. Although boys and girls use similar muscle synergies during single-leg drop-landings, they differed in which muscles were emphasized within these synergies. The observed differences in aspects related to the muscle synergies during landing may have implications with respect to knee injury risk.

A greater knee valgus angle is a risk factor for lower extremity injuries. Visually observed medial knee displacement is used as a proxy for knee valgus motion during movement assessments in an attempt to identify individuals at heightened risk for injury. The validity of medial knee displacement as an indicator of valgus motion has yet to be determined during a single-leg squat. This study compared three-dimensional knee and hip angles between participants who displayed medial knee displacement (MKD group) during a single-leg squat and those who did not (control group). Participants completed five single-leg squats. An electromagnetic motion tracking system was used to quantify peak knee and hip joint angles during the descent phase of each squat. MANOVA identified a difference between the MKD and control group kinematics. ANOVA post hoc testing revealed greater knee valgus angle in the MKD (12.86 ± 5.76) compared with the control (6.08 ± 5.23) group. There were no other differences between groups. Medial knee displacement is indicative of knee valgus motion; however, it is not indicative of greater knee or hip rotation, or hip adduction. These data indicate that clinicians can accurately identify individuals with greater knee valgus angle through visually observed medial knee displacement.

The purpose of this study was to investigate the influence of gender and somatotypes on single-leg upright standing postural stability in children. A total of 709 healthy children from different schools were recruited to measure the anthropometric somatotypes and the mean radius of center of pressure (COP) on a force platform with their eyes open and eyes closed. The results were that (a) girls revealed significantly smaller mean radius of COP distribution than boys, both in the eyes open and eyes closed conditions, and (b) the mesomorphic, muscular children had significantly smaller mean radius of COP distribution than the endomorphic, fatty children and the ectomorphic, linear children during the eyes closed condition. The explanation for gender differences might be due to the larger body weight in boys. The explanation for somatotype differences might be due to the significantly lower body height and higher portion of muscular profile in the mesomorphic children.

Few studies have explored osteogenic potential of prepubertal populations. We conducted a 28-week school-based exercise trial of single-leg drop-landing exercise with 42 prepubertal girls (6 to 10 yrs) randomly assigned to control (C), low-drop (LD) or high-drop (HD) exercise groups. The latter two groups performed single-leg drop-landings (3 sessions/wk⁻¹ and 50 landings/session⁻¹) from 14cm(LD) and 28cm(HD) using the nondominant leg. Osteogenic responses were assessed using Dual Energy X-ray Absorptiometry (DXA). Single-leg peak ground-reaction impact forces (PGRIF) in a subsample ranged from 2.5 to 4.4 × body-weight (BW). No differences (p > .05) were observed among groups at baseline for age, stature, lean tissue mass (LTM), leisure time physical activity, or average daily calcium intake. After adjusting for covariates of body mass, fat mass and LTM, no differences were found in bone mineral measures or site-specific bone mineral density (BMD) at the hip and lower leg among exercise or control groups. Combining data from both exercise groups failed to produce differences in bone properties when compared with the control group. No changes were apparent for between-leg differences from baseline to posttraining. In contrast to some reports, our findings suggest that strictly controlled unimodal, unidirectional single-leg drop-landing exercises involving low-moderate peak ground-reaction impact forces are not osteogenic in the developing prepubertal female skeleton.

This study assessed the agreement between K_vert calculated from 4 different methods of estimating vertical displacement of the center of mass (COM) during single-leg hopping. Healthy participants (N = 38) completed a 10-s single-leg hopping effort on a force plate, with 3D motion of the lower limb, pelvis, and trunk captured. Derived variables were calculated for a total of 753 hop cycles using 4 methods, including: double integration of the vertical ground reaction force, law of falling bodies, a marker cluster on the sacrum, and a segmental analysis method. Bland-Altman plots demonstrated that K_vert calculated using segmental analysis and double integration methods have a relatively small bias (0.93 kN⋅m^–1) and 95% limits of agreement (–1.89 to 3.75 kN⋅m^–1). In contrast, a greater bias was revealed between sacral marker cluster and segmental analysis (–2.32 kN⋅m^–1), sacral marker cluster and double integration (–3.25 kN⋅m^–1), and the law of falling bodies compared with all methods (17.26–20.52 kN⋅m^–1). These findings suggest the segmental analysis and double integration methods can be used interchangeably for the calculation of K_vert during single-leg hopping. The authors propose the segmental analysis method to be considered the gold standard for the calculation of K_vert during single-leg, on-the-spot hopping.