MOVEMENT VARIABILITY IN PRE-TEEN AND TEENAGE ATHLETES DURING SPORTS RELATED TASKS

BACKGROUND: Movement variability may affect injury assessment and may change as athletes mature. HYPOTHESIS/PURPOSE: We hypothesized that pre-teen athletes would exhibit greater variability than teenage athletes when performing drop jump, heel touch, and single leg hop motions. METHODS: 55 uninjured pediatric athletes were divided into pre-teen (age 7-12 years; n=29; 11 female) and teenage (age 13-15 years; n=26; 13 female) groups of similar size. All participants performed 2-3 repetitions per side of three sports related tasks: drop jump (41 cm), heel touch (single-leg squat from 15 cm or 23 cm step, depending on whether subject height <155 cm), and single leg hop for distance. 3D kinematics were recorded using motion capture during the loading phase of each task. To assess intra-individual variability, we examined the standard deviation (SD) and range (maximum-minimum) of key metrics among the multiple repetitions of each task performed by each participant. Variability was compared between age groups using 2-sided t-tests. RESULTS: In the drop jump and heel touch, the younger group was more variable than the older group (Figure 1.1 left). The median within-subject SD of repeat measurements varied from 1-6° in the sagittal plane, 1-3° in the frontal plane, and 1-4° in the transverse plane over both groups (Table 1.2), while the within-subject range of measurements varied from 2-11° in the sagittal, 2-5° in the frontal, and 2-7° in the transverse planes (Table 1.3). Representing a worst-case scenario, the 95th percentile for range of measurements was >15° for many sagittal plane variables and >10° for many frontal and transverse plane variables in the younger group. In the singl- leg hop, the older group was much more variable than the younger group in the sagittal plane, particularly at the trunk, pelvis, and ankle (Figure 1.1 right). The younger group was still more variable than the older group at the trunk and pelvis in the transverse plane. Median within-subject variability ranged from 2-9° for SD and 3-17° for range of repeat measurements. CONCLUSION: There was substantial within-subject variability in performing sports related tasks for pediatric athletes of all ages. Variability was generally lower for older athletes, but was particularly high in the older group for sagittal plane trunk and pelvis motion during single-leg hop landing, which may reflect the need to adjust for less constrained positioning of a larger proximal mass. The high variability in performing sports tasks suggests that multiple trials should be analyzed for a more complete and representative evaluation.