Measuring biomechanical loads and asymmetries in junior elite long-distance runners through triaxial inertial sensors

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Summary Background Despite its various positive health effects, long-distance running implies substantial biomechanical loads on the musculoskeletal system, especially in a competitive context. The incidence of running-related overuse injuries is high, especially for the tibia being one of the predominant injury localisations. Tibial impact accelerations are an established valid proxy measure for impact forces and, as such, considered a more direct estimate of tibial bone load than ground reaction forces. Assessing individual tibial and upper-body impact accelerations may help balancing biomechanical loads during training for long-distance running and triathlon. Material and methods We employed inexpensive, wireless, lightweight, triaxial inertial measurement units (IMUs) as wearables for measuring tibial, sacral and scapular impact loads and asymmetries in 45 healthy junior-elite long-distance runners at submaximal running speeds. Moreover, we investigated the effects of ground surface vs. running speed on tibial load in 8 well-trained, healthy runners and triathletes. Results Mean peak tibial accelerations in junior elite long-distance runners ranged between 14 ± 3 and 16 ± 3 g (g ≈ 9.81 m s−1) for running speeds of 14–16 km h−1. Corresponding mean peak sacral and scapular accelerations amounted to 4 ± 1 g to 5 ± 1 g (32 ± 8% of tibial load) and 4 ± 1 g (27 ± 6%), respectively. Observed lateral asymmetries in tibial and scapular accelerations yielded mean absolute values of 9 ± 8% (95th percentile of 24%) and 9 ± 10% (32%). The effect of running speed on tibial accelerations was approximately twice as large as the effect of ground surface. Among asphalt, tartan, treadmill and turf, only turf induced a significantly lower tibial load in well-trained runners. Conclusions IMU sensors represent a promising tool for assessing biomechanical loads and asymmetries in running under field conditions. With the orientation values derived in this study, they may be used to reduce individual risks of overuse injuries and, in future, possibly to assess running efficiency. Level of evidence Ib.