Evaluation of Fatigue of Respiratory and Lower Limb Muscles During Prolonged Aerobic Exercise

Abstract

The respiratory muscles may fatigue during prolonged exercises and thereby become a factor that limits extreme physical activity. The aim of the current study was to determine whether respiratory muscle fatigue imposes a limitation on extreme physical activity of well-trained young men. Electromyography (EMG) signals of respiratory (external intercostal and sternomastoid) and calf muscles (gastrocnemius) were measured (N = 8) during 1 hr of treadmill marching at a speed of 8 km/hr with and without a 15 kg backpack. The root mean square (RMS) and the mean power frequency of the EMG signals were evaluated for calculating fatigue indices. The EMG RMS revealed that the respiratory and calf muscles did not fatigue during the marching without a backpack load. The study did show, however, a significant rise in the EMG values when a backpack was carried with respect to the no-load condition (p < .05), which suggests that respiratory muscles should be trained in military recruits who are required to carry loaded backpacks while marching.

Load carriage, human performance, and employment standards

“…Since the dynamic respiratory volumes are effort dependent, whilst maximal airflows are effort related, but with a significant effort-independent (flow-resistive) component, then the conditions are right for the respiratory system to limit maximal exercise (Stickland et al 2008). In fact, electromyographic analysis of the sternocleidomastoid and external intercostals has revealed increased neuromuscular activity during loaded endurance exercise (Nadiv et al 2012), and this supports the notion of a load carriage-induced respiratory muscle fatigue. In turn, this may elicit an autonomically mediated reduction in oxygen delivery to the working muscles through intramuscular vasoconstriction as the work of breathing increases (Harms et al 1997;St Croix et al 2000).…”

Thoracic load carriage-induced respiratory muscle fatigue

“…The findings of this study are however in agreement with previous research which mimicked the restrictive characteristics of a backpack (but not the load mass) and observed reductions in twitch trans-diaphragmatic pressure during 10 min cycling exercise at 40% maximal workload (Tomczak, Guenette, Reid, McKenzie, & Sheel, 2011), which presumably would be exacerbated with the addition of chest wall loading (this study). In addition, a reduction in the mean power frequency of both the external intercostals and the sternocleidomastoid was demonstrated following 25kg load carriage which according to the authors is suggestive of impaired respiratory muscle function (Nadiv et al, 2012).…”

“…Interestingly, studies which have mimicked this inspiratory volume limitation (but not the mass of the load) through chest wall restriction using inelastic strapping demonstrate significant diaphragm fatigue (Tomczak et al, 2011). Recent indirect assessment of the accessory musculature which are tasked with increasing thoracic volume, demonstrated a reduction in the mean power frequency of the external intercostals and the sternocleidomastoid with 15kg load, which the authors suggest is illustrative of impaired respiratory muscle function (Nadiv et al, 2012). The effects of load carriage upon the pressure generating capacity of the respiratory muscles is however yet to be determined.…”

An Upper-Limb Power-Assist Exoskeleton Using Proportional Myoelectric Control

“…As the time-domain indicator of EMG, the root mean square (RMS) was calculated and used as the feature. The RMS was calculated as [32]: $\mathit{\text{RMS}}=\sqrt{\frac{1}{N}\sum _{i=1}^N{v}_i^2}$where v i is the voltage at the i -th sampling and N is the number of sampling points.…”