Effect of combined dynamic and static workload on heart rate recovery cost

Investigation of precision task demands on workers’ muscular activities, heart rate, and perceived exertion rating

BACKGROUND: Manual material handling (MMH) tasks significantly contribute to musculoskeletal disorders in manual workers. OBJECTIVES: In this study, we assessed the physical factors of precision lifting tasks that affect muscular activities (electromyography, EMGs), heart rate, and perceived exertion rating in ten healthy male workers aged 25–35 years, while considering the safety aspect of the common types of safety footwear. METHODS: The independent variables that were assessed are as follows: 1) lifting method (precise and inexact), 2) lifting frequency (one and four liftings/min), and 3) type of safety footwear worn by the worker (light, medium, or heavy). The response variables data, represented by EMG signals, for four muscular activities (biceps brachii, deltoid, trapezius, and erector spinae), heart rate, and perceived exertion were analyzed using a three-factor within-subjects design. RESULTS: The results showed that wearing heavy safety shoes increases the effort used with precise lifting methods in trapezius and erector spinae muscular activities. We also observed that the heart rate and perceived exertion increased rapidly at four lifts/min compared to one lift/min, regardless of the lifting method. CONCLUSIONS: The advantages of choosing appropriate safety footwear must be carefully assessed before replacing the conventional working safety shoes.

Heart rate recovery: a practical clinical indicator of abnormal cardiac autonomic function

The autonomic nervous system (ANS) and cardiovascular function are intricately and closely related. One of the most frequently used diagnostic and prognostic tools for evaluating cardiovascular function is the exercise stress test. Exercise is associated with increased sympathetic and decreased parasympathetic activity and the period of recovery after maximum exercise is characterized by a combination of sympathetic withdrawal and parasympathetic reactivation, which are the two main arms of the ANS. Heart rate recovery after graded exercise is one of the commonly used techniques that reflects autonomic activity and predicts cardiovascular events and mortality, not only in cardiovascular system disorders, but also in various systemic disorders. In this article, the definition, applications and protocols of heart rate recovery and its value in various diseases, in addition to exercise physiology, the ANS and their relationship, will be discussed.

Dynamic modelling of heart rate response under different exercise intensity

Heart rate is one of the major indications of human cardiovascular response to exercises. This study investigates human heart rate response dynamics to moderate exercise. A healthy male subject has been asked to walk on a motorised treadmill under a predefined exercise protocol. ECG, body movements, and oxygen saturation (SpO2) have been reliably monitored and recorded by using non-invasive portable sensors. To reduce heart rate variation caused by the influence of various internal or external factors, the designed step response protocol has been repeated three times. Experimental results show that both steady state gain and time constant of heart rate response are not invariant when walking speed is faster than 3 miles/hour, and time constant of offset exercise is noticeably longer than that of onset exercise.

Optimizing heart rate regulation for safe exercise

Safe exercise protocols are critical for effective rehabilitation programs. This paper aims to develop a novel control strategy for an automated treadmill system to reduce the danger of injury during cardiac rehabilitation. We have developed a control-oriented nonparametric Hammerstein model for the control of heart rate during exercises by using support vector regression and correlation analysis. Based on this nonparametric model, a model predictive controller has been built. In order to guarantee the safety of treadmill exercise during rehabilitation, this new automated treadmill system is capable of optimizing system performance over predefined ranges of speed and acceleration. The effectiveness of the proposed approach was demonstrated with six subjects by having their heart rate track successfully a predetermined heart rate.

Dynamic analysis for blood flow parameters of cardiovascular system on work load

In order to study the dynamic mechanism of blood flow parameters of cardiovascular system on work load, a dynamic mathematical model which can be used to describe quantitatively blood flow parameters of human body on different work load is put forward in this paper. With the help of this model, the correlation of blood flow parameters is studied using the analytic method of function of multiple variables. The experimental results are consistent with the analytic results of dynamic model.

A new method of using heart rate to represent energy expenditure: the Total Heart Beat Index

OBJECTIVES

To develop a new method of representing energy expenditure using heart rate and to determine its reproducibility compared with the criterion standard of oxygen cost.

DESIGN

Repeated-measures design.

SETTING

University gait analysis laboratory and gymnasium at 2 spinal injury units.

PARTICIPANTS

Twenty unimpaired adults and 17 subjects with spinal cord injury (SCI).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Heart rate and oxygen consumption were measured on 20 unimpaired adults walking under controlled steady-state and nonsteady-state conditions. New methods of estimating energy expenditure by using heart rate were compared with oxygen consumption, oxygen cost, and Physiological Cost Index (PCI). Nine subjects with SCI, walking with and without functional electric stimulation, were assessed to determine use of these new measures with this group. Sensitivity to change of the new measurement techniques was investigated in 10 subjects with SCI, comparing wheelchair pushing to walking.

RESULTS

The Total Heart Beat Index (THBI) was developed as a new index, calculated by dividing the total heartbeats during activity by distance traveled. High repeatability was found under steady-state and nonsteady-state conditions (intraclass correlation coefficients,.893-.995). Sensitivity to change in activity level was also shown.

CONCLUSIONS

The THBI is a simple parameter to calculate from continuous heart rate data and provides a reproducible alternative to gas analysis and the PCI.

Heart rate recovery post-exercise as an index of parasympathetic activity

The time constant (T) obtained by fitting post-exercise heart rate (HR) recovery to a first order exponential decay curve has been promoted as an index of parasympathetic activity. However, acceptance has been limited because reported data are inadequate to assess goodness of fit for the model, determine the best exercise protocol, or optimize the duration of post exercise monitoring. Consequently, we evaluated T for nine healthy volunteers (age 24-46) following treadmill exercise at maximal (max) and two stages sub-max exercise (Bruce protocol). T stabilized only after 3 min of post-exercise monitoring. With max exercise, T varied unacceptably with small changes in onset of monitoring, e.g. -16.7+/-16.6 (-13.2%) in the first 5 s, and residuals of the fitted curve were non-random. In contrast, sub-max exercise produced consistent T values, e.g. -1.9+/-3.2 (-4.2%) in the first 5 s, and residuals were more nearly random. In conclusion, first order decay is an inadequate model for HR recovery following max exercise, but may be reasonable for sub-max levels.

Chronodiagnostic acquisition of recovery speed of heart rate under bathing stress

Cycling on an ergometer is one effective means of measuring cardiovascular function while applying stress on the heart. Bathing in a hot water bath applies a low stress to the heart. The electrocardiograms of a healthy adult male (aged 35 at the start of study) were recorded while taking a hot water bath with no electrode attached to the body over a period of 2 years (376 days over a 762 day period). The recovery speed following the initial overshoot of the heart rate (HR) was observed. The bathtub was designed for the automatic acquisition of ECG data. Immediately after immersion in the tub, the HR reached a peak within 20 s and then exponentially decreased toward the lowest rate in the 120 s of bathing. The initial recovery speed of the HR from the stress of bathing had a specific rhythm in the subject. Spectrum analysis of the speed series indicated that slow recovery speed appeared in cyclic periods of approximately 1 year, 42 days and 17 days. The methodology may provide a chronodiagnostic index of an exercise test for cardiovascular function.