Abstract
Thoracic load carriage (LC) exercise impairs exercise performance compared to unloaded exercise, partially due to impaired respiratory mechanics. We investigated the effects of LC on exercise and diaphragmatic fatigue in a constant‐load exercise task; and whether inspiratory muscle training (IMT) improved exercise capacity and diaphragmatic fatigue with LC. Twelve recreationally active males completed three separate running trials to exhaustion (T lim) at a fixed speed eliciting 70% of their V˙O2max. The first two trials were completed either unloaded (UL) or while carrying a 10 kg backpack (LC). Subjects then completed 6 weeks of either true IMT or placebo‐IMT. Posttraining, subjects completed an additional LC trial identical to the pretraining LC trial. Exercise metabolic and ventilatory measures were recorded. Diaphragm fatigue was assessed as the difference between preexercise and postexercise twitch diaphragmatic pressure (P di, tw), assessed by bilateral stimulation of the phrenic nerve with esophageal balloon‐tipped catheters measuring intrathoracic pressures. T lim was significantly shorter (P < 0.001) with LC compared with UL by 42.9 (29.1)% (1626.5 (866.7) sec and 2311.6 (1246.5) sec, respectively). The change in P di, tw from pre‐ to postexercise was significantly greater (P = 0.001) in LC (−13.9 (5.3)%) compared with UL (3.8 (6.5)%). Six weeks of IMT significantly improved T lim compared to pretraining (P = 0.029, %Δ +29.3 (15.7)% IMT, −8.8 (27.2)% Placebo), but did not alter the magnitude of diaphragmatic fatigue following a run to exhaustion (P > 0.05). Minute ventilation and breathing mechanics were unchanged post‐IMT (P > 0.05). Six weeks of flow‐resistive IMT improved exercise capacity, but did not mitigate diaphragmatic fatigue following submaximal, constant‐load running to volitional exhaustion with LC.
Highlights
Thoracic load carriage (LC) impairs exercise performance compared with unloaded exercise by imposing extra stress on the cardiopulmonary and limb locomotor muscle systems (Muza et al 1989; Brown and McConnell 2012; Dominelli et al 2012)
We have demonstrated for the first time that (1) diaphragmatic fatigue occurs following constant-load running to volitional exhaustion with thoracic LC, as indicated by a significant postexercise reduction in Pdi, tw, and (2) six weeks of flow-resistive inspiratory muscle training (IMT) improved running time to exhaustion with thoracic LC
Our novel findings demonstrate that 6 weeks of flow-resistive IMT improves exercise capacity with thoracic LC
Summary
Carrying a load on the thoracic cavity (load carriage, LC) using apparatuses such as backpacks and load-bearing vests is often required to transport equipment and supplies in a variety of occupational and recreational settings (Muza et al 1989; Brown and McConnell 2012; Dominelli et al 2012). Thoracic LC impairs exercise performance compared with unloaded exercise by imposing extra stress on the cardiopulmonary and limb locomotor muscle systems (Muza et al 1989; Brown and McConnell 2012; Dominelli et al 2012). Thoracic LC reduces forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1.0), and increases the elastic power output of breathing (Muza et al 1989; Bygrave et al 2004; Legg and Cruz 2004; Dominelli et al 2012). IMT Improves Thoracic Load Carriage Exercise Capacity
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