The effect of downhill running on impact shock and asymmetry

Abstract

Biomechanical studies are important for the prevention and treatment of injuries. Of special interest is running locomotion and its effect on impact shock. Impact shock magnitudes are often 2-3 times greater at the tibia during running compared to walking and have been reported to increase with decreasing grade conditions. The primary goal of this study was to determine the effect of downhill running on impact shock and asymmetry over varying grades. The secondary and tertiary goals of this study were to determine if there was significant symmetry difference between lower-limb preference groups and between training groups, respectively. Seventeen subjects (10 female, 7 male) were sampled from two populations with different types of downhill training (trained versus untrained) experience. The procedures included two visits, the first of treadmill familiarization and preference testing and the second for impact shock data collections. The data collection visit included a self-directed warm-up on the treadmill followed by a 16-minute running session that included four different running grade conditions (0%, -3%, -6% and -9%).

Four samples of 5 consecutive tibial impact shock magnitudes (TIS) of each limb were collected at each running grade condition using piezoelectric accelerometers. Symmetry indices (SI) were calculated using TIS for left and right limbs from a previously established equation. The results indicate that measured SI was not significantly influenced by decreasing running grade conditions for all subjects. Also, there were no significant differences between preference groups across running grade conditions. A trend suggested differences between training groups across grade conditions, and analysis of covariance for stride length and step frequency indicated a significant difference between downhill trained and untrained subjects (p < - 0.038). Post-hoc analysis indicated a significant difference in left and right step length for downhill trained runners across grade conditions (p<0.05). It is possible that a learned unilateral forward stepping technique is present for those who frequently incorporate steep downhill running in their training. Further research is needed to determine ways of reducing SI for preventative measures, as well as determining possible longitudinal affects of asymmetry.