The Exercise Respons in Physical Activity and Exercise

The Exercise Respons. Let’s begin with some definitions and concepts required for understanding all the units to come. Exercise is a single acute bout of bodily exertion or muscular activity that requires an expenditure of energy above resting level and that in most, but not all, cases results in involuntary movement. Exercise sessions are typically planned and structured to improve or maintain one or more components of physical fitness.

Exercise A single acute bout of bodily exertion or muscular activity that requires an expenditure of energy above resting level and that in most, but not all, cases results in voluntary movement.
Homeostasis The state of dynamic equilibrium (balance) of the internal environment of the body.
Exercise Response The pattern of homeostatic disruption or change in physiological variables during a single acute bout of physical exertion.

The Terms of Physical Activity and Exercise

The term physical activity, in contrast, generally connotes movement in which the goal (often to sustain daily living or recreation) is different from that of exercise, but which also requires the expenditure of energy and often provides health benefits. For example, walking to school or work is physical activity, while walking around a track at a predetermined heart rate is exercise. Exercise is sometimes considered a subset of physical activity with a more specific focus (Caspersen et al., 1985).

From a physiological standpoint, both involve the process of muscle action/energy expenditure and bring about changes (acute and chronic). Therefore, the terms exercise and physical activity are often used interchangeably in this article. Where the amount of exercise can actually be measured, the terms workload or work rate may be used as well.

Homeostasis

Homeostasis is the state of dynamic equilibrium (balance) of the body’s internal environment. Exercise disrupts homeostasis, causing changes that represent the body’s response to exercise. An exercise response is the pattern of change in physiological variables during a single acute bout of physical exertion.

A physiological variable is any measurable bodily function that changes or varies under different circumstances. For example, heart rate is a variable with which you are undoubtedly already familiar. You probably also know that heart rate increases during exercise.

However, to state simply that heart rate increases during exercise does not describe the full pattern of the response. For example, the heart rate response to a 400-m sprint is different from the heart rate response to a 50-mi bike ride.

To fully understand the response of heart rate or any other variable, we need more information about the exercise itself. Three factors are considered when determining the acute response to exercise:

1. The exercise modality
2. The exercise intensity
3. The exercise duration

Exercise Modality

Exercise modality (or mode) means the type of activity or the particular sport. For example, rowing has a very different effect on the cardiovascular-respiratory system than does football.

Modalities are often classified by the type of energy demand (aerobic or anaerobic), the major muscle action (continuous and rhythmical, dynamic resistance, or static), or a combination of the energy system and muscle action.

Walking, cycling and swimming are examples of continuous, rhythmical aerobic activities; jumping, sprinting, and weight lifting are anaerobic and or dynamic resistance activities. To determine the effects of exercise on a particular variable, you must first know what type of exercise is being performed.

Exercise Modality or Mode The type of activity or sport; usually classified by energy demand or type of muscle action.

Exercise Intensity

Exercise intensity is most easily described as maximal or submaximal. Maximal (max) exercise is straightforward; it simply refers to the highest intensity, greatest load, or longest duration an individual is capable of doing.

Motivation plays a large part in the achievement of maximal levels of exercise. Most maximal values are reached at the endpoint of an incremental exercise test to maximum; that is, the exercise task begins at a level the individual is comfortable with and gradually increases until he or she can do no more.

The values of the physiological variables measured at this time are labeled as “max”; for example, the maximum heart rate is symbolized as HRmax.

Submaximal exercise may be described in one of two ways. The first involves a set load, which is a load that is known or is assumed to be below an individual’s maximum. This load may be established by some physiological variable, such as working at a specific heart rate (perhaps 150 b˙min−1); at a specific work rate (e.g., 600 kgm˙min−1 on a cycle ergometer); or for a given distance (perhaps a 1-mi run). Such a load is called an absolute workload.

If an absolute workload is used, and the individuals being tested vary in fitness, then some individuals will be challenged more than others.

Generally, those who are more fit in terms of the component being tested will be less challenged and so will score better than those who are less fit and more challenged. For example, suppose the exercise task is to lift 80 lb in a bench press as many times as possible, as in the YMCA bench press endurance test.

As illustrated in Table 1.1, if the individuals tested were able to lift a maximum of 160, 100, and 80 lb once, respectively, it would be anticipated that the first individual could do more repetitions of the 80-lb lift than anyone else.

Similarly, the second individual would be expected to do more repetitions than the third, and the third individual would be expected to do only one repetition. In this case, the load is not submaximal for all the individuals, because Terry can lift the weight only one time (making it a maximal lift for Terry). 

Nonetheless, the use of an absolute load allows for the ranking of individuals based on the results of a single exercise test and is therefore often used in physical fitness screenings or tests.

The second way to describe submaximal exercise is as a percentage of an individual’s maximum. A load may be set at a percentage of the person’s maximal heart rate, maximal ability to use oxygen or maximal workload. This value is called a relative workload because it is prorated or relative to each individual.

All individuals are therefore expected to be equally challenged by the same percentage of their maximal task. This should allow the same amount of time or number of repetitions to be completed by most, if not all, individuals. For example, for the individuals described in Table 1.1, suppose that the task now is to lift 75% of each one’s maximal load as many times as possible. The individuals will be lifting 120, 75, and 60 lb, respectively.

If all three are equally motivated, they should all be able to perform the same total number of repetitions. Relative workloads are occasionally used in physical fitness testing. They are more frequently used to describe exercises that are light, moderate, or heavy in intensity or to prescribe exercise guidelines.

There is no universal agreement about what exactly constitutes light, moderate, or heavy intensity. In general, uses the following classifications:

1. Low or light: ≤54% of maximum
2. Moderate: 55–69% of maximum
3. Hard or heavy: 70–89% of the maximum
4. Very hard or very heavy: 90–99% of the maximum
5. Maximal: 100% of the maximum
6. Supramaximal: >100% of the maximum

Maximum is defined variously in terms of workload or work rate, heart rate, oxygen consumption, weight lifted for a specific number of repetitions, or force exerted in a voluntary contraction. Specific studies may use percentages and definitions of the maximum that vary slightly.

Exercise Duration

Exercise duration is simply a description of the length of time the muscular action continues. The duration may be as short as 1–3 seconds for explosive action, such as a jump, or as long as 12 hours for a full triathlon (3.2-km [2-mi] swim, 160-km [100-mi] bicycle ride, and 42.2-km [26.2-mi] run).

In general, the shorter the duration, the higher the intensity that can be used. Conversely, the longer the duration, the lower the intensity that can be sustained. Thus, the amount of homeostatic disruption depends on both the duration and intensity of the exercise. 

Exercise Categories

This part combines the descriptors of exercise modality, intensity, and duration into six primary categories of exercise. Where sufficient information is available, the exercise response patterns for each are described and discussed:

1. Short-term, light to moderate submaximal aerobic exercise.

Exercises of this type are rhythmical and continuous in nature and utilize aerobic energy. They are
performed at a constant workload for 10–15 minutes at approximately 30–69% of maximal work capacity.

2. Long-term, moderate to heavy submaximal aerobic exercise.

Exercises in this category also utilize rhythmical and continuous muscle action. Although predominantly aerobic, anaerobic energy utilization may be involved. The duration is generally between 30 minutes and 4 hours at constant workload intensities ranging from 55 to 89% of the maximum.

3. Incremental aerobic exercise to the maximum.

Incremental exercises start at light loads and continue by a predetermined sequence of progressively increasing workloads to an intensity that the exerciser cannot sustain or increase further. This point becomes the maximum (100%). The early stages are generally light and aerobic, but as the exercise bout continues, anaerobic energy involvement becomes significant. Each workload/work rate is called a stage, and each stage may last from 1 to 10 minutes, although 3 minutes is most common. Incremental exercise bouts typically last between 5 and 20 minutes for the total duration.

4. Static exercise.

Static exercises involve muscle contractions that produce an increase in muscle tension and energy expenditure but do not result in meaningful movement. Static contractions are measured as some percentage of the muscle’s maximal voluntary contraction (MVC), the maximal force that the muscle
can exert.

The intent is for the workload to remain constant, but fatigue sometimes makes that impossible. The duration is inversely related to the percentage of maximal voluntary contraction (%MVC) that is being held, but generally ranges from 2 to 10 minutes.

5. Dynamic resistance exercise.

These exercises utilize muscle contractions that exert sufficient force to overcome the presented resistance, so that movement occurs, as in weight lifting. Energy is supplied by both aerobic and anaerobic processes, but anaerobic is dominant.

The workload is constant and is based on some percentage of the maximal weight the individual can lift (1-RM) or a resistance that can be lifted for a specified number of times. The number of repetitions, not time, is the measure of duration.

6. Very-short-term, high-intensity anaerobic exercise.

Activities of this type last from a few seconds to approximately 3 minutes. They depend on high-power anaerobic energy and are often supramaximal.

Source: Exercise Physiology For Health, Fitness, and Performance. p 5-6. Sharon A. Plowman and Denise L. Smith.