Figure 4

Cycle-by-cycle and breath-by-breath temporal resolutions of the EMG and volume of oxygen uptake signals. (A) Visual representation of 30 seconds of data during a change in workload (power output; solid black line) and the total EMG intensity (EMG; red line) and volume of oxygen uptake ($\dot{V}$O₂; blue line) responses. The cycle-by-cycle figure shows the individual pedal cycles (vertical lines) and the cycle-by-cycle variation in the EMG that is matched well with variation in power output at this temporal resolution. Moving from cycle-by-cycle to the breath-by-breath temporal resolution (mean EMG and power output between breaths) the EMG and power output curves are smoothed since there were 3.19 ± 0.27 pedal cycles per breath across all workloads. Also shown is the time delay (dashed lines) of 28.33 ± 4.31 seconds between a change in the EMG signal and power output and the subsequent change in$\dot{V}$O₂. (B) A global perspective over 110 seconds moving from raw EMG sampled at 2000 Hz to cycle-by-cycle temporal resolution at approximately 1.58 Hz at 95 pedal revolutions per minute (rpm) to breath-by-breath temporal resolution at approximately 0.50 Hz at 30 breaths per minute (bpm). This clearly shows the cycle-by-cycle variation of the EMG and power output that is reduced moving to breath-by-breath resolution, while the primary features of the underlying kinetics are preserved. The processed EMG, power output and$\dot{V}$O₂ values have been normalized to the mean across the 110 seconds of data, while the raw EMG is normalized to the absolute maximum.