Changes in electromyographic activity, mechanical power, and relaxation rates following inspiratory ribcage muscle fatigue

Abstract

Muscle fatigue is a complex phenomenon enclosing various mechanisms. Despite technological advances, these mechanisms are still not fully understood in vivo. Here, simultaneous measurements of pressure, volume, and ribcage inspiratory muscle activity were performed non-invasively during fatigue (inspiratory threshold valve set at 70% of maximal inspiratory pressure) and recovery to verify if inspiratory ribcage muscle fatigue (1) leads to slowing of contraction and relaxation properties of ribcage muscles and (2) alters median frequency and high-to-low frequency ratio (H/L). During the fatigue protocol, sternocleidomastoid showed the fastest decrease in median frequency and slowest decrease in H/L. Fatigue was also characterized by a reduction in the relative power of the high-frequency and increase of the low-frequency. During recovery, changes in mechanical power were due to changes in shortening velocity with long-lasting reduction in pressure generation, and slowing of relaxation [i.e., tau (τ), half-relaxation time (½RT), and maximum relaxation rate (MRR)] was observed with no significant changes in contractile properties. Recovery of median frequency was faster than H/L, and relaxation rates correlated with shortening velocity and mechanical power of inspiratory ribcage muscles; however, with different time courses. Time constant of the inspiratory ribcage muscles during fatigue and recovery is not uniform (i.e., different inspiratory muscles may have different underlying mechanisms of fatigue), and MRR, ½RT, and τ are not only useful predictors of inspiratory ribcage muscle recovery but may also share common underlying mechanisms with shortening velocity.

Methods and Applications in Respiratory Physiology: Respiratory Mechanics, Drive and Muscle Function in Neuromuscular and Chest Wall Disorders

“…Sarmento and colleagues ( Sarmento et al, 2021 ) found that 1) inspiratory rib cage muscles (sternocleidomastoids, scalenes and parasternals) differed in their responses to fatigue and recovery, as reflected by changes in spectral surface EMG variables, 2) loss of mechanical power in rib cage muscles resulted from reduced shortening velocity, and 3) relaxation properties recovered better from fatigue than do contractile characteristics. Recovery of fatigue varied, with median frequency returning to pre-fatigue values faster than the high/low (H/L) frequency spectrum suggesting that mechanisms of fatigue differed depending on the specific inspiratory muscle.…”

“…Relating the electrical activity of the diaphragm to its force generation during quiet breathing or maximal respiratory efforts is used to assess diaphragmatic weakness and its propensity to fatigue under conditions of increased load ( Bellemare and Grassino, 1982 ; Bellemare and Roussos, 1995 ; Sarmento et al, 2021 ). Assessing the ratio of diaphragm compound muscle action potential (CMAP) amplitude to transdiaphragmatic twitch pressure is also used to distinguish between defects in neuromuscular transmission defects (when both quantities decrease) and defects in muscle contractility (when twitch pressure is decreased in presence of a normal CMAP) ( Aldrich et al, 1986 ).…”

“…More recently, measurement of sniff nasal inspiratory pressures (SNIP) have been found to be better tolerated and reproducible ( Ti and Fit Ting, 1999 ; Sarmento et al, 2021 ). Nasal pressure is measured in an occluded nostril as the patient sniffs through the opposite nasal passage and is closely associated with and easier to perform than Pimax ( Laroche et al, 1988 ; Ti and Fit Ting, 1999 ) and FVC ( Nicot et al, 2006 ) measurements.…”

“…Nasal pressure is measured in an occluded nostril as the patient sniffs through the opposite nasal passage and is closely associated with and easier to perform than Pimax ( Laroche et al, 1988 ; Ti and Fit Ting, 1999 ) and FVC ( Nicot et al, 2006 ) measurements. In a study of 61 patients with NMD and COPD, recording of esophageal pressure during a maximal sniff was found to be useful in assessing inspiratory muscle strength and easier to perform than the MIP ( Sarmento et al, 2021 ). Many patients had normal sniff Pes despite low MIPs, suggesting that performing MIP was challenging because of dyspnea and weakness of facial muscles with difficulty in maintaining static pressures.…”

Non-invasive assessment of fatigue and recovery of inspiratory rib cage muscles during endurance test in healthy individuals

“…Fatigue is also influenced by the recruitment pattern, which depends on the activity performed. Recently, Sarmento et al [ 8 ] analyzed fatigue development (70% of maximal inspiratory pressure) and recovery of sternocleidomastoid, scalene, and parasternal muscles of healthy individuals during one type of RET and observed changes in mechanical power and shortening velocity. However, literature lacks data regarding fatigue behavior between different RET modalities.…”