Children Who Are Overweight Display Altered Vertical Jump Kinematics and Kinetics From Children Who Are Not Overweight

Relationship between Asymmetry Indices, Anthropometric Parameters, and Physical Fitness in Obese and Non-Obese High School Students

Impaired balance is associated with an increased risk of lower extremity injuries. The purpose of this study was to investigate the relationship between age, anthropometric measurement, and asymmetry index (AI) in an adolescent high school population. Twenty-six male students (15 ± 1.0 years) were randomly selected. Body composition, measurements of vertical jump height using a countermovement jump test (CMJ), and dynamic single stance balance using the Y-balance test (YBT), were collected over 4 weeks. Hierarchical multiple linear regression analyses were used as dimension reduction techniques in four different blocks to determine valid predictors for AIs. In the first regression analysis, controlling for age, body mass, height, and body mass index (BMI), the regression coefficient (B = 0.383, 95% confidence interval [CI] [0.088, 0.679], p < 0.05) associated with body fat indicated that with each additional unit of body fat, the YBT AI increased by 0.383 units. In the second regression analysis, controlling for age, body mass, and BMI, the regression coefficients associated with height (B = -1.692, 95% CI [-3.115, -0.269], p < 0.05] and body fat percentage (B = 0.529, 95% CI [0.075, 0.983], p < 0.05) indicated that with each additional unit of height or body fat percentage, the CMJ AI decreased by 1.692 units and increased by 0.529 units. Grouping participants based on body fat percentage had a significant effect on the AIs (p < 0.05) of the CMJ and YBT. The AI of the CMJ was 15% higher, and that of the YBT was 7% higher in non-obese students than obese students. These findings contribute to the knowledge of the local community and the emerging body of literature on motor skills and competence related to weight in this population.

Obese Youth Demonstrate Altered Landing Knee Mechanics Unrelated to Lower-Extremity Peak Torque When Compared With Healthy Weight Youth

Obese (OB) youth demonstrate altered knee mechanics and worse lower-extremity performance compared with healthy weight (HW) youth. Our objectives were to compare sagittal plane knee landing mechanics between OB and HW youth and to examine the associations of knee and hip extension peak torque with landing mechanics in OB youth. Twenty-four OB and 24 age- and sex-matched HW youth participated. Peak torque was measured and normalized to leg lean mass. Peak knee flexion angle and peak internal knee extension moment were measured during a single-leg hop landing. Paired t tests, Pearson correlation coefficients, and Bonferroni corrections were used. OB youth demonstrated worse performance and lower knee extension (OB: 12.76 [1.38], HW: 14.03 [2.08], P = .03) and hip extension (OB: 8.59 [3.13], HW: 11.10 [2.89], P = .005) peak torque. Furthermore, OB youth demonstrated lower peak knee flexion angles (OB: 48.89 [45.41 to 52.37], HW: 56.07 [52.59 to 59.55], P = .02) and knee extension moments (OB: -1.73 [-1.89 to -1.57], HW: -2.21 [-2.37 to -2.05], P = .0001) during landing compared with HW youth. Peak torque measures were not correlated with peak knee flexion angle nor internal knee extension moment during landing in either group (P > .01). OB youth demonstrated altered landing mechanics compared with HW youth. However, no associations among peak torque measurements and knee landing mechanics were present.

The Kinematic and Kinetic Development of Sprinting and Countermovement Jump Performance in Boys

Background

The aim of the study was to examine the kinematics and kinetics of sprint running and countermovement jump performance between the ages of 8–9, and 11–12 years old boys in order to understand the developmental plateau in performance.

Methods

18 physically active boys (Age: 10.1 ± 1.6), in an under 9 years old (U9) and an under 12 years old (U12) group performed 15 m sprints and countermovement jumps. A 3D motion analysis system (200 Hz), synchronized with four force platforms (1,000 Hz), was used to collect kinematic and kinetic data during the first stance phase of the sprint run and the countermovement jump.

Results

The U12 group had a significantly greater height (U9: 1.364 ± 0.064 m; U12: 1.548 ± 0.046 mm), larger mass (U9: 30.9 ± 3.5 kg; U12: 43.9 ± 5.0 kg), superior sprint performance over 0–5 m (U9: 1.31 ± 0.007 s; U12: 1.23 ± 0.009 s) and 0–15 m (U9: 3.20 ± 0.17 s; U12: 3.01 ± 0.20 s), and increased jump height (U9: 0.17 ± 0.06 m; U12: 0.24 ± 0.10 m) than the under nine group. During the first stance phase of the sprint the U12 group had a significantly greater vertical (U9: 0.22 ± 0.02 BW/s; U12: 0.25 ± 0.03 BW.s) and horizontal impulse (U9: 0.07 ± 0.02 BW/s; U12: 0.09 ± 0.03 BW.s) than the U9 group. When performing a countermovement jump the U12 group had a significantly greater mean average eccentric force (U9: 407.3 ± 55.0 N; U12: 542.2 ± 65.1 N) and mean average concentric force (U9: 495.8 ± 41.3 N; U12: 684.0 ± 62.1 N). Joint kinematics for the countermovement jump were significantly different between age groups for the ankle range of motion (U9: 80.6 ± 17.4°; U12: 64.1 ± 9°) and knee minimum joint angle (U9: −5.7 ± 3.9°; U12: 0.0 ± 4.4°). Conclusion: The study demonstrates for the first time that the development of physically active boys between the ages of 8–9 to 11–12 years increased the ground reaction forces and impulses during sprint running and countermovement jumps, but that sprint running technique had not developed during this period. Furthermore, countermovement jump technique was still emerging at the age of 8–9 years old. Practitioners need to implement on-going fine-grained sprint running and CMJ technique sessions to ensure that the increased force producing capabilities that come with age are appropriately utilized.