Vestibular contributions to cycling balance across different speeds

Abstract

Balance control relies on the integration of visual, proprioceptive and vestibular information, with the relative contribution of these sensory signals depending on task demands. Although vestibular contributions to standing and walking have been extensively investigated, their role in cycling balance remains largely unknown. This study used electrical vestibular stimulation (EVS) to introduce a vestibular-driven error signal and investigate how vestibular perturbations influence balance-related kinematics and upper-body muscle activity during seated cycling and whether these responses are modulated by cycling speed. Sixteen healthy young adults performed non-pedalling treadmill cycling trials at 5, 10 and 18 km/h under both non-EVS and stochastic EVS conditions. Steer and roll kinematics and activity of six upper-body muscles involved in steering and postural stabilization were recorded. Time-domain measures quantified changes in response magnitude, while gain and coherence between EVS and steering rate, roll rate and muscle activity were calculated in the frequency domain to characterize vestibular coupling. EVS significantly increased root mean square (RMS) steering rate and RMS roll rate and increased mean activity in all investigated muscles except the erector spinae. RMS steering rate and EVS-steering gain decreased significantly with increasing cycling speed, whereas RMS roll rate and EVS-roll gain were not significantly affected by speed. Significant EVS coupling was observed with steering rate over approximately 0.5-8 Hz and roll rate over 0.5-4 Hz. Vestibular coupling with muscle activity was generally low and muscle-specific, with coherence observed over 0.5-3 Hz for flexor digitorum, 0.5-6 Hz for biceps brachii and erector spinae and 0.5-8 Hz for triceps brachii, deltoid anterior and deltoid posterior. Muscle response gain decreased significantly with increasing cycling speed for all investigated muscles, while coherence was largely maintained across speeds. Together, these findings demonstrate that vestibular perturbations systematically influence cycling balance through steer and roll kinematics and coordinated upper-body muscle responses. Greater steering and muscular response gains at lower cycling speeds, despite largely preserved coherence, suggest that vestibular input remains coupled to balance control across speeds while the magnitude of the resulting motor responses is modulated according to the dynamic stabilization demands of the bicycle-rider system.