Validity of measures of reactive balance training intensity

Intensity is a key component of exercise prescription. However, balance training intensity is not well defined. Consequently, balance training studies often do not report exercise intensity, which hinders implementing these interventions and developing exercise guidelines. This study aimed to validate measures of reactive balance training intensity. Healthy young (n=11) and older (n=9) adults experienced moving platform balance perturbations of varying magnitudes. Candidate intensity measures were: number of reactive steps; centre of mass displacement, velocity, and acceleration, and margin of stability 100 ms post-perturbation; peak electrodermal response; and OMNI Perceived Exertion Scale and Balance Intensity Scale scores. Correlations were examined between perturbation magnitude and candidate intensity measures. We also compared candidate intensity measures between backward- and forward-fall perturbations and between age groups using generalized linear mixed models. Peak centre of mass acceleration 100 ms after the perturbation was significant positively correlated with perturbation magnitude, with no significant age-group or direction effects, suggesting that this is a valid measure of absolute perturbation intensity. Number of reactive steps, peak electrodermal response, and OMNI Perceived Exertion Scale and Balance Intensity Scale scores were significantly positively correlated with perturbation magnitude, and were significantly higher for backward-fall compared with forward fall perturbations and for older adults compared to younger adults at the same magnitude, suggesting that these are valid measures of relative perturbation intensity. These measures could be used to prescribe and report intensity of reactive balance training in future studies.