Inspiratory muscle training improves exercise capacity with thoracic load carriage. Issue 3 (9th February 2018)

• Record Type: Journal Article
• Authors: Shei, Ren‐Jay; Chapman, Robert F.; Gruber, Allison H.; Mickleborough, Timothy D.
• Is Part Of: Physiological reports. Volume 6:Issue 3(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-02-09
• Subjects: Diaphragm fatigue -- flow limitation -- performance -- respiratory muscles -- ventilation; Physiology -- Periodicals; 571
• DOI: 10.14814/phy2.13558
• Languages: English
• ISSNs: 2051-817X

Abstract

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. Abstract : Thoracic load carriage exercise impairs exercise performance and induces diaphragmatic fatigue. Six weeks of inspiratory muscle training improved respiratory muscle strength and performance in a fixed‐workload run to exhaustion with load carriage, but did not alter diaphragmatic fatigue at the point of volitional exhaustion. Therefore, inspiratory muscle training can be a useful training tool to optimizes physical performance with load carriage.