Case Studies in Physiology: Exercise-induced diaphragm fatigue in a paralympic champion rower with spinal cord injury

Abstract

Introduction. The aim of this case report was to determine whether maximal upper-body exercise 24 was sufficient to induce diaphragm fatigue in a Paralympic champion adaptive rower with low-lesion 25 spinal cord injury (SCI). Case Presentation. An elite arms-only oarsman (age 28 y, stature 1.89 m, 26 mass 90.4 kg) with motor-complete SCI (T12) performed a 1000 m time-trial on an adapted rowing 27 ergometer. Exercise measurements comprised pulmonary ventilation and gas exchange, diaphragm 28 EMG-derived indices of neural respiratory drive and intrathoracic pressure-derived indices of 29 respiratory mechanics. Diaphragm fatigue was assessed by measuring pre- to post-exercise changes 30 in the twitch transdiaphragmatic pressure (Pdi,tw) response to anterolateral magnetic stimulation of the phrenic nerves. The time-trial (248 ± 25 W, 3.9 min) elicited a peak O2 uptake of 3.46 L·min−1 31 and a peak pulmonary ventilation of 150 L·min−1 32 (57% MVV). Breath-to-stroke ratio was 1:1 during the 33 initial 400 m and 2:1 thereafter. The ratio of inspiratory transdiaphragmatic pressure to diaphragm 34 EMG (neuromuscular efficiency) fell from rest to 600 m (16.0 vs. 3.0). Potentiated Pdi,tw was 35 substantially reduced (−33%) at 15-20 min post-exercise, with only partial recovery (−12%) at 30-35 36 min. Conclusions. This is the first report of exercise-induced diaphragm fatigue in SCI. The 37 decrease in diaphragm neuromuscular efficiency during exercise suggests that the fatigue was partly 38 due to factors independent of ventilation (e.g., posture and locomotion).