Author(s): FOHRMANN, D., WINTER, I., SIMON, A., DALOS, D., GRONWALD, T., HOENIG, T., ROLVIEN, T., HOLLANDER, K. , Institution: MSH MEDICAL SCHOOL HAMBURG, Country: GERMANY, Abstract-ID: 1539

INTRODUCTION:
Lower-Body Positive Pressure Treadmills (LBPPT) enable fine-grained control over the external load during running. These devices provide body weight support (BWS) through an overpressure in a chamber surrounding the athletes and running surfaces. Previous research on the effects of BWS on running biomechanics revealed changes in spatiotemporal (1) and kinematic variables (2). However, most studies neither provided sex-specific analyses nor included nonlinear running stability, a measure for locomotor control capabilities. Biomechanics and running injury epidemiology differ between sexes (3, 4). Hence, this work aimed to investigate how BWS affects running biomechanics in male and female athletes.
METHODS:
Twenty-six competitive distance runners (15 female, age: 33.6±9.8 years, BMI: 21.6±2.4 kg⸱m-2) completed one running session on an LBPPT (AlterG 500 Pro). Following a familiarisation period, the experimental protocol consisted of nine running bouts at randomly ordered unloading stages of 0 – 80% BWS in steps of 10%. Each bout lasted three minutes at 12 km/h with no rest in between. We measured plantar pressure with two pressure-sensing insoles (200Hz, loadsol, novel) as well as acceleration and angular velocity at the right foot and right tibia using inertial measurement units (500Hz, ICM-20601, TDK InvenSens). We calculated stance time, swing time, normalized ground contact time, and maximum plantar force during stance from the insole data. From the inertial sensor data, we calculated peak tibial acceleration and running stability as the largest short-term finite-time divergence exponent λs (5). Linear mixed-effects models were used to investigate the effects of BWS, sex, and their interaction on all biomechanical variables.
RESULTS:
All variables were significantly affected by increasing BWS with the largest effects for reduced maximum plantar force (β=-0.81 [-0.86 to -0.76], p<0.001), increased swing time (β=0.74 [0.67 to 0.82], p<0.001), and decreased normalized ground contact time (β=-0.61 [-0.66 to -0.56], p<0.001). Running stability decreased at the tibia (β=0.10 [0.02 to 0.17], p=0.009) but increased at the foot (β=-0.12 [-0.22 to -0.02], p=0.017). There were no significant BWS*sex interaction effects among the variables under investigation.
CONCLUSION:
Our results confirm previous studies showing reduced external load metrics and changes in spatiotemporal running patterns with increasing BWS. Running stability was also affected by BWS but the small effect sizes question its practical relevance. We showed that despite overall differences between male and female runners’ technique, both sexes respond similarly to BWS. These are important findings especially for practitioners when planning return-to-sport programs with an LBPPT available.

REFERENCES:
1. Neal et al., J Orthop Sports Phys Ther. 2016
2. Hodges-Long et al., Phys Ther Sport. 2020
3. Hollander et al., Sports Med. 2021
4. Xie et al., Front Physiol. 2022
5. Hoenig et al., Eur J Sport Sci. 2019