Effect Of Change In Running Speeds On Shock Attenuation Among Children

Abstract

Shock attenuation (SA) is the process by which the impact shock caused by the collision between the foot and ground is reduced. In adult runners, SA increases with increases in speed; however, there are no SA data on children runners. It has been hypothesized that impact characteristics are a factor related to overuse running injuries. With children being involved with age-group sports that incorporate running, it is important to understand how children manage impact. PURPOSE: To examine SA characteristics for children running on a treadmill at different speeds. METHODS: Physically active children (n=4; 11±1.0yrs; 48±12.1kg, 149±4.2cm), free from any current or previous lower extremity injury, ran at 3 different speeds which included preferred (speed at which subjects can run for 15 min comfortably), 0.5 m/s faster and 0.5 m/s slower than preferred running speed. Accelerometers (1008Hz) were secured to the anterior-medial region of the distal aspect of right tibia and at the frontal region of the head. Ten right footfalls per subject-condition were evaluated. Peak impact accelerations for the leg (LgPk) and head (HdPk) were recorded over 30 seconds and SA was calculated in the time domain using the formula: SA= [1-(HdPk/ LgPk)]*100. Stride Frquency (SF) was calculated by identifying the time between two consecutive peaks from the leg acceleration profile. Stride length (SL) was calculated using the formula: Vel = SL/SF. A repeated measures ANOVA was used to compare each dependent variable (i.e., SA, SL) across speeds. RESULTS: SA was different (p<0.05) between the faster (69±4.4%) and the slower (61±7.5%) speeds. However, it was not different (p>0.05) between preferred (67±4.5slow (61±7.5%) or fast (69±4.4%) speeds. SL was significantly different (p<0.05) between all speeds fast (1.9±1.0m), preferred (1.7±.1m) and slow (1.4±. 12m). CONCLUSIONS: Based on these preliminary data, it appears that SA and SL increase with speed for children runners. However, the lack of change in S A between the slow and preferred speed was not expected.