Influence of Aerobars Positions in Ultra Cycling on Musculoskeletal Loadings

Sammanfattning

Ultra-endurance cycling exposes athletes to prolonged static postures, leading to a high prevalence of overuse injuries, particularly in the lower back and knees. While aerobars are widely used to reduce aerodynamic drag, their internal musculoskeletal loads remain poorly understood. This study aims to quantify the biomechanical impact of aerobar use compared to standard road positions and evaluate the specific influence of stack and inclination settings on lumbar and lower limb joint reaction forces. Ten experienced cyclists performed trials on an instrumented ergometer at 70% of their Functional Threshold Power (FTP) across six conditions: hoods, drops, and four aerobar configurations varying in stack (high/low) and inclination (0°/15°). A custom automated musculoskeletal modeling workflow using OpenSim was developed to compute compressive and shear forces for lumbar and lower limb joints. Results revealed that the flat aerobar position (0°) significantly reduced L4-L5 compressive forces (17.5 ± 10.9 N/kg) compared to the standard hoods position (20.9 ± 4.8 N/kg), likely due to effective skeletal support. However, tilting the aerobars to 15° significantly increased spinal loading. A mechanical trade-off was identified: aerobar use shifted the load distally, more than doubling hip compression forces (~46 N/kg) and significantly increasing knee forces compared to road positions. These findings suggest that while flat aerobars reduce spinal joint loading, they impose severe stress on the lower limbs, highlighting the need for injury-specific bike fitting strategies in ultra-endurance.