The effect of diaphragm fatigue on the multidimensional components of dyspnoea and diaphragm electromyography during exercise in healthy males.

The purpose of this study was to examine the effect of diaphragm fatigue on the multidimensional components of dyspnoea and diaphragm electromyography (EMGdi ) during cycling. Sixteen healthy males (age = 27 ± 5 yr, V ̇ O 2 max  = 45.8 ± 9.8 ml kg-1  min-1 ) completed two high-intensity, time-to-exhaustion cycling tests in randomized order: (i) inspiratory pressure threshold loading (PTL) prior to exercise to induce diaphragm fatigue (pre-DF) and (ii) no PTL (control). Diaphragm fatigue after PTL was confirmed via cervical magnetic stimulation of the phrenic nerves. Dyspnoea intensity and unpleasantness were measured throughout exercise with the 0-10 category-ratio Borg scale and following exercise using the Multidimensional Dyspnoea Profile (MDP). EMGdi was continuously recorded via a multipair oesophageal electrode catheter. Time-to-exhaustion decreased with pre-DF vs. control (9.0 ± 5.5 vs. 10.7 ± 7.5 min, P = 0.023). Pre-DF increased dyspnoea intensity ratings by 0.6 ± 1.0 Borg 0-10 units at the highest equivalent submaximal exercise time (HESET) a participant could achieve in both conditions (P = 0.020). Dyspnoea unpleasantness ratings increased with pre-DF by 0.5 ± 1.0, 0.7 ± 1.2 and 0.9 ± 1.4 (all P < 0.05) Borg 0-10 units during the 2nd, 3rd and 4th minutes of exercise, respectively. There was a significant correlation between the change in breathing unpleasantness ratings at HESET and the change in time-to-exhaustion (r = 0.66, P = 0.006). The immediate perception domain, a combination of peak unpleasantness and specific dyspnoea descriptor intensity ratings, was the only component of the MDP that was significantly increased with pre-DF (4.3 ± 1.9 vs. 3.6 ± 1.8, P = 0.04). There were no significant differences in EMGdi . In conclusion, diaphragm fatigue has negative effects on multiple domains of dyspnoea, which may partially explain why exercise performance decreases with it.