Shock Attenuation and Impact Characteristics for Children Running At Different Stride Lengths

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OCLC: 192073161

Abstract

The purpose of this study was to quantify shock attenuation (SA) and impact characteristics for children (boys and girls) running with different stride lengths (SL). Ten physically active children (10.7±1.1 yrs; 40Ü0.3 kg; 145.2±7.3 cm) ran at a constant speed of 3m/s ± 5% range to complete three stride length conditions: Preferred stride length (PSL), -15%PSL and +15%PSL. During PSL, participants were given no instructions regarding stride length. During -15%PSL and +15%PSL, participants were required to strike markers placed on the floor that resulted in stride length of -15% and +15% of PSL. Ground reaction forces were recorded (1008 Hz) using a force plate (Kistler Instrument) that was mounted flush with the floor in the middle of a 20m runway. Accelerometers (1008 Hz) were securely mounted on the distal aspect of the tibia and on frontal aspect of the forehead. Impact force and shock attenuation in time and frequency domain (calculated as the ratio of head and leg impact accelerations and ratio of power spectral density of head and leg acceleration respectively) were recorded for each running trial. One way repeated measure ANOVA (condition by subject) were performed on the subject means to compare each dependent variable (SA, impact peak (IP), active peak (AP), loading rate (LR)) between three stride length conditions (PSL, - 15%PSL, +15%PSL). Results indicated that SA (PSL: 84+4.2%, +15%PSL: 87+6.4%, - 15%PSL: 83+6.3%) in the time domain (p = 0.053) and in the frequency domain (PSL: - 38+9.3dB, +15%PSL: -39+9.9dB, -15%PSL:-40+10.8 dB) (p = 0.655) were not significantly different among conditions. The mean values for SA in the time domain across conditions indicated a trend that SA increased with increasing SL. IP (PSL: 16+3.1 N/Kg, +15%PSL: 16+2.9 N/Kg, -15%PSL: 15+2.0 N/Kg) (p = 0.16) and LR (PSL: 736+152.4 N/Kg, +15%PSL: 681+191.9 N/Kg, -15%PSL: 593+136.8 N/Kg) (p = 0.065) were not significantly different across the SL conditions. Planned comparison results for LR indicated that -15%PSL was different (p = 0.025) from +15%PSL. No differences were observed between PSL and +15%PSL (p = 0.413) and -15%PSL and PSL (p = 0.124). However, a trend for LR was observed, that it increased with increasing SL. AP (PSL: 24+2.8 N/Kg, +15%PSL: 23+3.7 N/Kg, -15%PSL: 23+2.6 N/Kg) was significantly different (p - 0.045) between conditions. Planned comparisons identified that PSL was significantly different (p = 0.024) from +15%PSL and from -15%PSL (p = 0.016). No difference was observed between -15%PSL and +15%PSL (p = 0.813). Mean values of the three conditions suggest that AP decreased with changes in SL. The SA, IP, AP and LR have been shown to increase with increasing SL in adults (Derrick et al. 1998). These findings suggest that children may manage impact and shock differently than adults. It is possible that our results may have been influenced by intra-subject variability, which was high among these child runners. Future investigations on child runner performance, focusing on variability as well as comparative adult patterns, are warranted.

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