Variability in the running surface can cause an athlete to alter their gait. Most literature report running on grass, a treadmill or athletics running tracks using inertial sensors. This study compares the signals obtained by 9 degrees of freedom (DOF) inertial-magnetic sensors incorporating an accelerometer (±16 g), gyroscope (±2000°/s) and magnetometer (±8 gauss). The sensors were placed on the participant`s shank, knee, lower spine and upper spine, and the participants were asked to run on three different surfaces (running track, hard sand and soft sand). The calculated player loads for a 400 m run on each surface type was very similar. The mean and standard deviation values were 577 ± 130, 581 ± 128, 568 ± 124 for soft sand, hard sand and the running track, respectively. This did not correlate with the participant`s self-assessment RPE (Rate of perceived exertion), which demonstrated running on soft sand to be significantly more challenging, yielding a mean and standard deviation of 5.3 ± 2.5 (Hard to Very Hard). Soft sand running had a decreased swing time duration but increased variability (0.44 ± 0.02 s—Swing Time, 6.5 ± 1.1%—CV), hard sand running had the longest swing and intermediate variability duration (0.46 ± 0.02 s—Swing Time, 3.30 ± 2.58 %—CV) and running track running had the medium swing time but lowest variability (0.45 ± 0.02 s, 2.7 ± 0.9%—CV). Gait dominance was not consistent across the surfaces for each participant and remained below a ratio of 0.4. These results provide an insight into how athletes modify their gait mechanics to accommodate different running surfaces.
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