Differences in Strike Index Between Land Treadmill and Aquatic Treadmill Running in Experienced Distance Runners

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Sydney Schaefer, Eadric Bressel


Strike index (SI) is a quantitative measure (%) of foot contact at the beginning of the stance phase of gait. A greater SI is indicative of a more forefoot (anterior) strike pattern. High incidence of running related injuries, and knowledge that a rearfoot strike pattern leads to greater injury rates than a forefoot strike pattern, highlight the need for more evidence-based injury prevention techniques. One potential injury prevention technique is running on an aquatic treadmill (ATM). Differences in SI must be known when comparing land treadmill (LTM) running and ATM running, due to the injury prevention potential of ATM running and the impact of SI on running related injuries. Physical properties of water (e.g. drag force), and kinematic observations suggest that SI is likely greater when running in water compared to on land. To test this, experienced distance runners (5 years of competitive running) completed two sessions of running; one on the LTM and one on the ATM. Each session consisted of approximately ten minutes of running; five minutes of familiarization at 5 mph and five minutes of testing at 6.5, 7, 7.5, 8, and 8.5 mph. SI was computed for the two conditions at the five testing speeds using 2-D video recordings and analysis (Logger Pro). Using a repeated measures ANOVA, preliminary data of four participants revealed an effect of environment on SI approaching significance (p = .061, F=5.3). A mean difference (%) in SI of (mean ± SD) 30.9 ± 34.05, 31.87 ± 35.67, 32.33 ± 32.09, 44.38 ± 29.32, and 43.31 ± 35.18 was seen for speeds of 6.5, 7, 7.5, 8, and 8.5 mph respectively. SI was greater across all speeds for the ATM condition suggesting that there may be positive implications to ATM training given the possible decreased injury risks associated with a high SI.

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