Networks of respiratory‐muscular coupling in exercise and fatigue in young adults

Figures

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  FIGURE 1. Instantaneous breathing rate time series. (a) To estimate the BR, the TFS of the filtered respiration signal is computed, and then the frequency with the maximum power at each time step is extracted (blue and red colors refer to low and high spectral power, respectively). Finally, frequency is multiplied by 60, and a move‐mean average filter is passed to smooth the estimated BR. (b) Comparison of BR time series estimation using PD and TFR with 5‐ and 20‐s windows for clear and noisy respiration waveforms. When the waveform was clean, all the approaches showed similar BR estimation. However, when the waveform is was noisy, PD detected false respiration cycles, estimating large BR with high variability, while TFR could gather the actual respiration cycle frequency. The larger the TFR analysis window, the smoother BR is estimated.

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  FIGURE 2. Dynamics of breathing rate and spectral power of EMG frequency bands from one representative participant. (a) Breathing rate (BR) time series and EMG signals recorded from each muscle. Both BR and EMG amplitude gradually increase with accumulation of fatigue during the cycling test performed until exhaustion. (b) Normalized time series of BR (Orange lines; right vertical axis) and spectral power EMG frequency bands (F1, F5, and F10; blue lines; left vertical axis) in the Beginning (left panels) and End (right panels) segments of Exercise 1 for the Respiration‐LegL sub‐network. At the Beginning of Exercise 1, the EMG spectral power time series were weakly coupled with BR. In contrast, at the End of Exercise 1, coupling strength increased markedly across all frequency bands, as reflected by higher correlation coefficients C between BR and the EMG frequency bands. By the end of exercise, BR shows a gradual rise and becomes less variable due to parasympathetic withdraw, while EMG frequency‐band time series progressively increase, indicating greater motor‐unit recruitment and overall neuromuscular activation with fatigue accumulation.

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  FIGURE 3. Dynamic network of respiratory‐muscular coupling, and its reorganization with fatigue accumulation. (a) Dynamic network of respiratory‐muscular interactions between respiration and major muscles involved in the cycling test of Exercise 1. Group‐averaged map where network links represent the links strength (correlation coefficients C(BR, F i )) between breathing rate (BR) and myoelectrical rhythms (frequency bands F i ) from Leg and Back muscles. Each respiratory‐muscle sub‐network contains 10 links quantifying the degree of coupling between BR and 10 muscle frequency bands F i . Line width and color indicate link strength (thicker/darker lines correspond to stronger coupling, Methods). Network maps derived from data corresponding to the Beginning (first third) and End (last third) segments of Exercise 1 show reorganization of the respiratory‐muscular network with accumulation of fatigue. Each muscle is represented as a semicircle with color nodes for different frequency bands F i . Coupling between BR and EMG frequency bands from LegL/LegR and BackL/BackR muscles from a dynamic multiplex network with pronounced heterogeneity, characterized by distinct topology and a hierarchical…

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  FIGURE 4. Dynamic network of respiratory‐muscular coupling, and network reorganization with residual fatigue across exercise bouts. (a) Dynamic networks of respiratory‐muscular coupling between breathing rate (BR) and EMG frequency bands from Leg/Back muscles involved in the cycling test for consecutive Exercise 1 and Exercise 2 bouts. Shown are group‐averaged network maps, where network links represent the coupling (correlation coefficients C(BR, F i )) between BR and myoelectrical rhythms (frequency bands F i ) from Leg and Back muscles. Sub‐networks in the respiratory‐muscular network contain 10 links that quantify the degree of coupling between BR and 10 bands F i within a given muscle. Each muscle is represented as semicircle with color nodes for different bands F i . Line width and color indicate network link strength (thicker/darker lines correspond to stronger coupling, Methods). Network maps derived from data during Exercise 1 and Exercise 2 show reorganization of topology and link strength with residual fatigue. (b) Links strength profiles of respiratory‐muscular sub‐networks for consecutive exercise bouts. Each of the 10 bars in the profile represents a link in the corresponding…