An equivalent circuit model for onset and offset exercise response

Abstract

BackgroundThe switching exercise (e.g., Interval Training) has been a commonly used exercise protocol nowadays for the enhancement of exerciser’s cardiovascular fitness. The current difficulty for simulating human onset and offset exercise responses regarding the switching exercise is to ensure the continuity of the outputs during onset-offset switching, as well as to accommodate the exercise intensities at both onset and offset of exercise.MethodsTwenty-one untrained healthy subjects performed treadmill trials following both single switching exercise (e.g., single-cycle square wave protocol) and repetitive switching exercise (e.g., interval training protocol). During exercise, heart rate (HR) and oxygen uptake (VO 2) were monitored and recorded by a portable gas analyzer (K4b 2, Cosmed). An equivalent single-supply switching resistance-capacitor (RC) circuit model was proposed to accommodate the observed variations of the onset and offset dynamics. The single-cycle square wave protocol was utilized to investigate the respective dynamics at onset and offset of exercise with the aerobic zone of approximate 70% - 77% of HR max, and verify the adaption feature for the accommodation of different exercise strengths. The design of the interval training protocol was to verify the transient properties during onset-offset switching. A verification method including Root-mean-square-error (RMSE) and correlation coefficient, was introduced for comparisons between the measured data and model outputs.ResultsThe experimental results from single-cycle square wave exercises clearly confirm that the onset and offset characteristics for both HR and VO 2 are distinctly different. Based on the experimental data for both single and repetitive square wave exercise protocols, the proposed model was then presented to simulate the onset and offset exercise responses, which were well correlated indicating good agreement with observations.ConclusionsCompared with existing works, this model can accommodate the different exercise strengths at both onset and offset of exercise, while also depicting human onset and offset exercise responses, and guarantee the continuity of outputs during onset-offset switching. A unique adaption feature by allowing the time constant(Continued on next page) (Continued from previous page)and steady state gain to re-shift back to their original states, more closely mimics the different exercise strengths during normal daily exercise activities.

Feedback control of oxygen uptake during robotics-assisted end-effector-based stair climbing

“…The identification ofVO 2 and HR dynamics using a single test for each subject provided a good basis for direct comparison of the respective time constants. Previous studies suggest that τ for HR is generally higher than for VO 2 (Bearden & Moffatt, 2001;Zhang et al, 2014). The statistical analysis of the five data sets obtained here confirm this hypothesis for the end-effector robot form of exercise, with a p-value for the observed difference of 0.048.…”

“…The purposely low-pass characteristics of the control approach developed in Riedo and Hunt (2016) therefore promised to be suitable for this new application also. A further contribution of the present work is a comparison of HR andVO 2 dynamics, because HR can conveniently be measured simultaneously withVO 2 : based on previous studies using other exercise modalities (Bearden & Moffatt, 2001;Zhang et al, 2014), it was hypothesized that the time constant of the heart rate response would be higher than that for oxygen uptake.…”

Effects of endurance, circuit, and relaxing training on cardiovascular risk factors in hypertensive elderly patients

“…However, limited data are available on the effectiveness of this exercise approach on the reduction of CVDs risk factors in old hypertensives (Guimaraes et al 2010;Lamina 2010). Besides the potential appeal of CT for the old population, it is important to note that the physiological mechanisms activated by CT are different to those involved in ET in terms of central hemodynamics stimulation (Zhang et al 2014). The limited heart rate (HR) and cardiac output responses are indeed counterbalanced by high stimulation of the peripheral circulation as during small muscle mass exercise (Esposito et al 2010(Esposito et al , 2011.…”

Heart Rate Kinetics and Sympatho-Vagal Balance Accompanying a Maximal Sprint Test

“…Acknowledging the correlation between the kinetics of oxygen uptake and HR, the statement mentioned above might explain the HR persistence after intense exercise. Considering that (i) the cardiac output is the product of stroke volume and HR, and that (ii) in exercises exceeding ∼60% of individual's maximum HR the stroke volume stops raising, it follows that HR remains the only responsible for covering the need of a high perfusion after strenuous exercise (Zhang et al, 2014). In this perspective, our sprint exercise apparently crossed the anaerobic threshold; thus, no wonder that we could observe the clipping in HR recovery.…”

“…Although t delay has been frequently reported in the literature, it has been often dismissed from analysis due to the difficulty in inquiring the specific chemical dynamics involved during this period (Zhang et al, 2014). Besides that, the persistence of an high HR immediately after the end of an intense exercise might also depend on the high respiratory frequency (Pierpont et al, 2000;Borresen and Lambert, 2008).…”