Conducting Maximal and Submaximal Endurance Exercise Testing to Measure Physiological and Biological Responses to Acute Exercise in Humans

Summary

To assess the influence of exercise intensity on physiologic and biologic responses, two different exercise testing protocols were utilized. Methods outlining exercise testing on a cycle ergometer as an incremental maximal oxygen consumption test and endurance, steady state submaximal endurance test are described.

Abstract

Regular physical activity has a positive effect on human health, but the mechanisms controlling these effects remain unclear. The physiologic and biologic responses to acute exercise are predominantly influenced by the duration and intensity of the exercise regimen. As exercise is increasingly thought of as a therapeutic treatment and/or diagnostic tool, it is important that standardizable methodologies be utilized to understand the variability and to increase the reproducibility of exercise outputs and measurements of responses to such regimens. To that end, we describe two different cycling exercise regimens that yield different physiologic outputs. In a maximal exercise test, exercise intensity is continually increased with a greater workload resulting in an increasing cardiopulmonary and metabolic response (heart rate, stroke volume, ventilation, oxygen consumption and carbon dioxide production). In contrast, during endurance exercise tests, the demand is increased from that at rest, but is raised to a fixed submaximal exercise intensity resulting in a cardiopulmonary and metabolic response that typically plateaus. Along with the protocols, we provide suggestions on measuring physiologic outputs that include, but are not limited to, heart rate, slow and forced vital capacity, gas exchange metrics, and blood pressure to enable the comparison of exercise outputs between studies. Biospecimens can then be sampled to assess cellular, protein, and/or gene expression responses. Overall, this approach can be easily adapted into both short- and long-term effects of two distinct exercise regimens.

Introduction

Physical activity is defined as any bodily movement produced by skeletal muscles that require energy expenditure¹. Exercise is a physical activity that involves repetitive bodily movement done to improve or maintain one or more components of physical health². At one time, physical activity was not recommended for those who were seriously ill. For individuals with cancer, heart failure, or even for those who were pregnant, bed rest was preferred over physical activity. Clinical practice has since drastically changed, as the benefits of exercise on overall health are becoming undeniable³. Regular exercise has been shown to help reduce cardiovascular disease risk, all-cause mortality, cancer risk and hypertension, improve blood sugar control, facilitate weight loss or maintenance, and prevent bone and muscle loss^4,5,6,7,8.

The extensive benefits of exercise have now led many to utilize exercise as a type of "medicine" and an alternative or adjunct treatment option for a variety of conditions³. Shulman et al. demonstrated that a combination of treadmill and resistance exercise could result in improvements in gait speed, aerobic capacity and muscular strength which could improve motor control and overall quality of life in patients with Parkinson's disease⁹. In heart failure patients, exercise intolerance and inadequate pharmaceutical interventions contribute to a poor quality of life¹⁰. Initial results from heart failure patients undergoing exercise training in the HF-ACTION trial demonstrated improvement in quality of life and reductions in hospitalizations and mortality¹¹. Additionally, the application of exercise to alter the cardiotoxic effects of anthracycline-containing chemotherapy (e.g., doxorubicin) has demonstrated that regardless of when it is initiated with respect to the patients chemotherapy administration (before, during or after), exercise can provide beneficial effects such as reducing the decline in aerobic capacity, attenuating the left ventricular dysfunction and reducing oxidative damage¹².

The benefits of exercise in health and wellness are not just in its application as a medicine/treatment, but also as a diagnostic tool. Exercise testing is, for example, used to diagnose exercise intolerance, ischemia in the heart, or to understand the cause of shortness of breath¹³. Perhaps more importantly, exercise testing may be utilized to identify subclinical dysfunction. The human body is in most situations "overbuilt," such that dysfunction or pathophysiology can often remain hidden and unapparent to an individual for months or years. This observation may explain why conditions such as pulmonary arterial hypertension or pancreatic cancer can silently increase in severity such that by the time symptoms are noticed, these conditions tend to be very advanced and extremely difficult to treat². In some of these situations, exercise testing can provide a stress stimulus to the body which increases demand above that of daily living and at times can identify dysfunction (cardiac, respiratory, metabolic) that was not seen at rest, helping to diagnose a disease and begin treatment earlier.

In order to fully maximize the therapeutic and diagnostic potential of exercise, standardized methods to quantify the responses to physical activity are needed to accurately assess the contributions of exercise to overall immune health. Variations in workload, inclination, duration, type of exercise, and the timing of sample collection can all influence measurements of physiological responses. Here, we outline methods for maximal and submaximal endurance exercises to gather physiological data while collecting samples for biological responses. This methodology was used to understand how acute exercise affected the distribution and frequency of leukocyte populations in peripheral blood¹⁴ by measuring immune cell populations at various time points before and after exercise by flow cytometry with 10-color flow protocols that permit the quantification of all major leukocyte subsets simultaneously¹⁵. The following protocol can be used as a standardized method for two distinct exercise regimens for measuring physiological and biological responses to exercise.

Protocol

The protocol was approved by the Mayo Institutional Review Board and conformed to the Declaration of Helsinki. All participants provided written informed consent before participating in the testing described. 1. Calibration and Setup of Metabolic Cart Flow and volume (pneumotach) calibration NOTE: Specific materials and equipment are listed in the Materials Table. Open the pulmonary function and gas exchange software to calibrate for the test.</l…

Representative Results

The application of maximal or submaximal endurance exercise testing provides a stimulus or stressor in which the body responds to meet the increased physiological demands. Various modes of exercise can be used to compare the physiological and biological responses to a particular exercise by itself or when a drug/intervention is used, or to evaluate the differences in responses between different exercise loads. Maximal and endurance exercise loads differ in the duration (short/long respect…

Discussion

There is great potential for exercise to be incorporated as an adjunct/alternative therapeutic tool. Indeed, an emerging body of evidence strongly suggests that physical activity promotes good health. The use of exercise as a medicine or diagnostic tool would require an understanding of the right amount or "dose" of exercise to achieve the desired effect. The optimal dose of exercise should be estimated, as too much exercise may be detrimental to improving health. As such, an exercise regimen may need to be tailo…

Materials

Metabolic cart/portable system	MCG Diagnostics	Mobile Ultima CPX System	The flow calibration syringe, and calibration gases should come with system. There are numerous possible options/alternatives.
Pulmonary function software (Breeze Suite)	MCG Diagnostics		Software used will depend on the metabolic system
Upright cycle ergometer	Lode ergoline	960900	Numerous possible options/alternatives
12-Lead ECG	GE Healthcare	CASE Exercise Testing System	Used for 12 lead ECG capture, control bike. Having a full 12-lead is ideal for maximal exercise test so can monitor for arhythmias, but alternative for just HR would be a wireless chest strap heart rate monitor
Pulse oximeter	Masimo	MAS-9500	Usually multiple probe options: finger, forehead, ear lobe.  Usually avoid finger as tight handlebar grip can cause measurement inaccuracies
Pneumotach (preVent Flow Sensor)	MCG Diagnostics	758100-003	Alternative systems can use a turbine
Nose piece (disposable)	MCG Diagnostics	536007-001	Numerous possible options/alternatives
Mouthpeice with saliva trap	MCG Diagnostics	758301-001	Suggest filling the saliva trap with paper towel/gauze and tape cap to limit dripping
Headband	Cardinal Health	292866	Used to secure the forehead pulse oximeter and the lines for the cart
Stethescope	3M Littman	3157SM	Numerous possible options/alternatives
Blood pressure cuff	HCS	HCS9005-7	Cuff size will depend on the population planning to test
ECG Electrodes	Cardinal Health	M2570	only needed with lead based ECG/HR monitoring
K2EDTA tube 5mL	Becton Dickinson	368661
*The table provides a list of the supplies and equipment utilized in this protocol and comments related to the equipment. Brand name/company is provided, but the use of other brands will not affect the results, key is to keep it consistent throughout testing in a particular study.