Figure 3.

Assessment of neuromuscular fatigue by peripheral nerve and transcranial magnetic stimulations in chronic cardiorespiratory disorders using various exercise modalities. (A) Deficits in voluntary activation of the unfatigued (i.e., with no prior fatiguing exercise) knee extensors by transcranial magnetic stimulation has been demonstrated in patients with chronic obstructive pulmonary disease (COPD) showing peripheral muscle weakness in comparison to their counterparts with no muscle weakness. *p < 0.05: patients with vs. with no peripheral muscle weakness. Reproduced and modified, with the permission of the publisher from: Alexandre et al. (2020). (B) Lower maximal voluntary strength and voluntary activation by transcranial magnetic stimulation of the knee extensors but similar resting twitch have been shown in patients with severe obstructive sleep apnea syndrome throughout single-joint exercise (repeated knee extensions to task failure, starting at 35% of maximal voluntary strength) in comparison to healthy controls. Greater magnitude (long-interval intra-cortical inhibition) and duration (cortical silent period) of intra-cortical inhibition have also been reported using transcranial magnetic stimulation in these patients compared to their healthy counterparts. *Indicates a significant difference for a given parameter throughout exercise between patients with obstructive sleep apnea using healthy controls as a reference (p < 0.05). Data obtained before and after treatment by continuous positive airway pressure were pooled since the intervention did not improve cortical impairments in patients. 50% and 100% refer to data obtained at 50% and 100% of the duration of the shortest test i.e., before or after treatment by continuous positive airway pressure. Reproduced and modified, with the permission of the publisher from: Marillier et al. (2018a). (C) Voluntary activation measured using the twitch interpolation technique in response to magnetic stimulation of the femoral nerve in controls and in patients with fibrotic interstitial lung disease before and after a constant-load (60% peak work rate) exercise test to symptom limitation under medical air. Voluntary activation did not significantly differ between controls and patients, being unaltered by exercise in both groups, despite severe exertional hypoxemia in patients. Voluntary activation was assessed ~3 min after whole-body exercise in these subjects. Time delay between exercise cessation and fatigue assessment is a limitation to capture central fatigue after whole-body exercise. Similar observations have been made in patients with heart failure (Hopkinson et al., 2013). Reproduced and modified, with the permission of the publisher from: Marillier et al. (2021a).