Ground reaction force differences in the countermovement jump in girls with different levels of performance

Peak Loads Associated With High-Impact Physical Activities in Children

Physical activities involving impact loading are important for improving bone strength and mineral density in children. There is little research quantifying impact loads associated with various high-impact activities.

PURPOSE

Examine the magnitude of peak ground reaction forces (pGRF) across different jumping activities in children.

METHODS

Eight children between 8 and 12 years (9.63 [1.49] y; 1.42 [0.08] m; 33.69 [4.81] kg), performed 5 trials of a broad jump, countermovement jump, jumping jack, leap jump, and drop jump on a force plate. The pGRF were determined during the landing phase of each activity and expressed in units of body weight (BW). A repeated-measures analysis of variance was employed to assess differences in pGRF across activities.

RESULTS

Drop jump exhibited the greatest pGRF (3.09 [0.46] BW) in comparison with the vertical jumping jack (2.56 [0.21] BW; P < .001) and countermovement jump (2.45 [0.22] BW; P = .001), as well as the horizontal broad jump (2.25 [0.2] BW; P = .003), and leap jump (2.01 [0.1] BW; P = .002).

CONCLUSION

Peak loads between 2 and 3.1 BW were exhibited across each jump activity, which is moderate compared with magnitudes in most jump interventions seeking to improve bone health. All conditions except drop jump exhibited loading <3 BW, suggesting these activities may not produce sufficient loads to improve bone outcomes.

Analyses of Countermovement Jump Performance in Time and Frequency Domains

This study aimed to analyze counter-movement jump (CMJ) performance in time and frequency domains. Fortyfour Division I American football players participated in the study. Kinetic variables were collected from both dominant and non-dominant legs using two force plates. Normalized peak power, normalized net impulse, and normalized peak force significantly correlated with jump height (r = .960, r = .998, r = .725, respectively with p < .05). The mean frequency component was significantly correlated with CMJ performance (r = .355 with p < .05). The reliability of the frequency variables was higher than the time domain variables. Frequency domain variables showed weaker correlations with jump height compared with time domain variables. Frequency domain analysis provides frequency components, which represent the rate of energy transmission from the eccentric phase to the end of the push-off phase. Frequency component information may provide additional information for the analyses of CMJ performance for athletes.

Development of vertical and forward jumping skills in typically developing children in the context of referent control of motor actions

The empirically based referent control theory of motor actions provides a new framework for understanding locomotor maturation. Mature movement patterns of referent control are characterized by periods of minimization of activity across multiple muscles (global electromyographic [EMG] minima) resulting from transient matching between actual and referent body configurations. We identified whether locomotor maturation in young children was associated with (a) development of referent control and (b) children's frequency of participation in everyday activities evaluated by parents. Kinematics and EMG activity were recorded from typically developing children (n = 15, 3-5 years) and young adults (n = 10, 18-25 years) while walking, vertical or forward jumping. Presence and location of global EMG minima in movement cycles, slopes of ankle vertical/sagittal displacements, and shoulder displacement ratios were evaluated. Children had fewer global EMG minima compared to adults during specific phases of vertical and forward jumps. Ankle displacement profiles for walking and jumping forward were related to each other in adults, whereas those for walking and vertical jumping were related in children. Higher frequency of participation was significantly correlated with more mature jumping patterns in children. A decrease in the number of global EMG minima and changes in ankle movement patterns could be indicators of locomotor immaturity in typically developing children.

Reliability of Sargent Jump Test in 4- to 5-Year-Old Children

We assessed the test-retest reliability of the Sargent jump (VJ) for vertical jumping performed by 4 and 5 years old pre-schoolers. The VJ was administered three times (familiarization, test, and retest) to 163 children (mean age: 4.48 ± 0.5 years; 55.8% girls). The results were compared with those obtained in the standing long jump (SLJ) and in the 25 -m dash test to identify how its performance correlated with other measures of leg power. Systematic change in the mean and retest correlations with these other measures were used to help analyze VJ test-retest reliability. Additionally, Pearson correlation coefficients were used to examine the degree of association between the test and retest trials of the VJ. The VJ showed a higher correlation and agreement in the 4-year-old, compared with the 5-year old, group (r_c = 0.956 vs. 0.796; α = 0.95 vs. 0.84; ICC: 0.828; 95% CI: 0.730-0.891 vs 0.739; 95% CI: 0.589-0.834). Effect sizes were small ( d ≤ 0.285) for all the VJ tests performed. Fair to poor significant relationships were established between the VJ (test), VJ (retest), and the SLJ. No significant association was observed between the VJ and the 25 -m dash tests. Our findings suggest that the Sargent jump test is reliable when executed by 4- and 5-year-olds. The lack of a strong association with other measures of leg power should be taken into account at the time of selecting the most appropriate test to assess this strength dimension.

Joint dynamics and intra-subject variability during countermovement jumps in children and adults

The present study investigated lower limb joint work, lower limb joint energy transport and intra-subject variation of the joint dynamics during countermovement jumps in children and adults. Twelve healthy men and eleven healthy boys performed ten maximal countermovement jumps. Three dimensional kinematics and kinetics were recorded in synchrony. Hip, knee and ankle joint eccentric and concentric work, joint energy transfer, intra-subject variation of joint moment, joint power and joint moment components were calculated. The children had lower eccentric and concentric hip work and lower eccentric knee work but no group difference was observed in the concentric knee joint work and ankle joint work. Eccentric hip and knee joint energy transfer and concentric hip joint energy transfer were higher in adults. The children had higher intra-subject variation in the eccentric and concentric hip joint work, hip joint moment and hip and knee joint power. Higher intra-subject variation was observed in horizontal joint reaction force components for the children and higher intra-subject variation in the segment angular inertia components was observed for the adults. The joint dynamics of children during countermovement jumps were less efficient in producing proximal joint work, transferring energy through joint centres and characterized by a higher intra-subject variation.

Assessing vertical jump developmental levels in childhood using a low-cost motion capture approach

Understanding the developmental levels of fundamental movement skills has a critical role in the improvement of motor competence in childhood. In this respect, the use of Microsoft Kinect to assess vertical jumping skill and to predict developmental levels in 9- to 12-yr.-old children was evaluated. 41 boys and girls repeated the countermovement jump test three times. Vertical jumping skill levels were categorized using observational records, while kinematic and temporal parameters were estimated using a biomechanical model based on data acquired by the Kinect. Multivariate analysis of variance (MANOVA) and discriminant analysis verified that the height of the jump and the flight height predict the primary differences in jumping skill developmental levels, and the Kinect-based assessment discriminates these levels.