Postural strategy and back muscle oxygenation during inspiratory muscle loading

Purpose: Most healthy individuals show a multi-segmental control strategy during challenging standing conditions, whereas others show a rigid ankle-steered strategy which is assumed as suboptimal. Respiratory demanding tasks exert a perturbing effect on balance, although the underlying mechanisms remain poorly understood. The purpose of this study was to investigate whether inspiratory resistive loading (IRL) affects postural strategy, back muscle oxygenation and blood volume during postural control. Methods: We assessed the acute effects of increased respiratory effort by measuring center of pressure displacement in 12 healthy individuals during upright standing on an unstable support surface, whilst breathing against an IRL. Simultaneous ankle and back muscle vibration was used to evaluate the proprioceptive strategy (multi-segmental versus ankle-steered) during postural control. Back muscles oxygenation and blood volume were assessed using near-infrared spectroscopy (NIRS) (tissue oxygenation index (TOI), deoxyhaemoglobin (HHb), oxyhaemoglobin (O2Hb) and combined haemoglobin (cHb)). Results: An increased proprioceptive gain at the ankles and decreased gain at the back was observed after ~7 minutes of IRL. Retrospectively, the group was subdivided based on participants’ dominant proprioceptive use during baseline postural control. During IRL the ankle-steered group showed an increased reliance on ankle proprioception, compared to a multi-segmental group (-5.9±3.1cm and 1.0±1.9cm, respectively, p 0.05). Conclusion: Individuals who adopted an ankle-steered strategy during IRL showed a progressive decline in back muscle oxygenation and blood volume. In contrast, IRL did not affect back muscle oxygenation and blood volume in individuals who showed a multi-segmental strategy in upright standing.status: publishe