5: Defining Physical Activityand Exercise

Defining Physical Activityand Exercise


According to the 2020 WHO guidelines, physical activity (PA) is defined as “any bodily movement produced by skeletal muscles that requires energy expenditure” (Bull, 2020). Other alternatives of this definition were proposed in the literature and used; however, all are derived from the same initial definition by Caspersen et al. (Caspersen, 1985).

In terms of mode, there are four PA domains: (i) occupational (i.e., work), (ii) domestic (i.e., household chores), (iii) transportation/utilitarian, and (iv) leisure time (Strath, Smith, & Swartz, 2013). Examples of these physical‐activity domains are shown in Table 5.1. The assessment of PA should include all four domains as they impact health and should be considered separately. This is evident as an increase in one PA domain (e.g., occupation activity) may lead to decreased activity in another domain (e.g., leisure time) that causes an overall increase in sedentary time. Sedentary time is positively correlated with poor health and premature death as it will be discussed in Chapter 6.

PA is further classified as structured or incidental. Structured PA or exercise is a planned, structured program designed to beneficially promote health and physical fitness. Incidental PA is not planned and usually is the result of daily activities at work, at home, or during transport (Strath et al., 2013).

PA and exercise can be quantified based on (Hills, 2014): (i) mode or type of activity, i.e., specific activity performed; (ii) frequency of performing the activity, i.e., number of sessions per day or per week; (iii) duration of performing activity, i.e., time (minutes or hours) of the activity bout during a specified time frame; and (iv) intensity of performing the activity, i.e., rate of energy expenditure (Table 5.2) (Strath et al., 2013).


The result of participating in PA or exercise is the expenditure of energy, which is commonly quantified in terms of intensity. There are several methods to quantify PA intensity (Liguori, 2020) : energy expenditure as a result of PA, metabolic equivalents (METs), oxygen consumption (VO2), heart rate (HR), heart rate reserve (HRR), and specifying a percentage of oxygen uptake reserve (VO2R). Each of these methods has strengths and limitations (Hills, 2014; Liguori, 2020).


PA is commonly quantified by determining the energy expended for physical activity. Assessing energy expenditure and estimated PA in free‐living individuals is very important in the global context of non‐communicable diseases (NCDs), such as malnutrition, obesity, and diabetes.

Table 5.1 Physical‐activity domains.

Source: (Strath et al., 2013).

Occupational Work‐related: involving manual labor tasks, walking, carrying or lifting objects
Domestic Housework: yard work, child care, chores, self‐care, shopping, incidental
Transportation/ utilitarian Purpose of going somewhere: walking, bicycling, climbing/descending stairs to public transportation, standing while riding transportation
Leisure time Discretionary or recreational activities: sports, hobbies, exercise, volunteer work

Table 5.2 Physical‐activity dimensions: mode, frequency, duration, and intensity.

Source: (Strath et al., 2013).

Dimension Definition and context
Mode Specific activity performed (e.g., walking, gardening, cycling). Mode can also be defined in the context of physiological and biomechanical demands/types (e.g., aerobic versus anaerobic activity, resistance or strength training, balance, and stability training).
Frequency Number of sessions per day or per week. In the context of health‐promoting PA, frequency is often qualified as number of sessions (bouts) ≥10 min in duration/length.
Duration Time (minutes or hours) of the activity bout during a specified time frame (e.g., day, week, year, past month).
Intensity Rate of energy expenditure. Intensity is an indicator of the metabolic demand of an activity. It can be objectively quantified with physiological measures (e.g., oxygen consumption, heart rate, respiratory exchange ratio), subjectively assessed by perceptual characteristics (e.g., rating of perceived exertion, walk‐and‐talk test), or quantified by body movement (e.g., stepping rate, 3‐dimensional body accelerations).
Schematic illustration of components of total daily energy expenditure and measurement approaches.

FIGURE 5.1 Components of total daily energy expenditure and measurement approaches.

Source: (Hills, 2014 / Frontiers Media S.A. / CC BY‐3.0).

The gold‐standard method by which total energy expenditure (TEE) is assessed in a free‐living context is the doubly labeled water technique. However, this method requires sophisticated laboratory‐based equipment for sample analysis, which are high cost and time‐prohibitive, thus restricting its use to large‐scale studies only. The most common approach to assess TEE is by measuring oxygen consumption and/or the production of carbon dioxide via indirect calorimetry or by using prediction equations. Direct calorimetry, in which heat production is measured in a metabolic chamber, is not widely used (Hills, 2014).

TEE represents the total energy that a person expends in a day for processes essential for life (e.g., to digest, absorb, and convert food as well as exercise). It is comprised of three components including: resting energy expenditure, physical‐activity energy expenditure, and the thermic effect of food (Figure 5.1).

Resting energy expenditure (REE) or the resting metabolic rate (RMR) represents the energy expended at rest by an individual in fasting conditions and a thermo‐neutral environment. It accounts for approximately 60% of the TEE. It is the largest proportion of TEE. RMR is typically slightly higher than the basal metabolic rate (BMR), which is measured under stricter conditions.

The thermic effect of food (TEF), also called the specific dynamic action (SDA) or dietary‐induced thermogenesis, is the energy expended processing and storing food as well as assimilating nutrients. The TEF accounts for approximately 10% of the TEE (Calcagno, 2019).

The activity energy expenditure (AEE) represents all energy expended above the resting level and includes the exercise energy expenditure (ExEE) as well as non‐exercise activity thermogenesis (NEAT) (Hills, 2014). ExEE is required for intentional (e.g., sports‐related) PA and accounts for between 0% and 10% of the total daily energy expenditure, although in extremely active individuals, it may constitute up to 60% to 70% of TEE. NEAT (e.g., daily living activities, fidgeting, maintenance of posture) accounts for the roughly 20% of remaining TEE (Calcagno, 2019).

If we know the REE and assume that the TEF constitutes 10%, which is relatively stable, we can then calculate the AEE:

StartLayout 1st Row upper A upper E upper E k c a l normal slash normal d a y equals 0.9 times upper T upper E upper E k c a l normal slash normal d a y minus upper R upper E upper E k c a l normal slash normal d a y 2nd Row left-parenthesis upper H i l l s comma 2014 right-parenthesis EndLayout

PA can be expressed either in kilocalories (kcal) or in metabolic equivalents of task (METs). One kcal is equivalent to the energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius. When 1 L of oxygen is used, approximately 5 kcal of energy are released. Therefore, if a 70 kg individual walks for 60 min at an intensity that requires a 1 L/min rate of oxygen consumption, they would consume 60 L of oxygen. In this case, the TEE (including the REE) for those 60 min would be ~300 kcal (i.e., 60 L x 5 kcal/L). The total daily energy for PA is the sum of all the physical activities performed on a given day.


The physical‐activity level (PAL) is a way to describe a person’s daily physical activity as a number, and it can be estimated using the average 24‐hour TEE and BMR.

upper P upper A upper L equals upper T upper E upper E division-sign upper B upper M upper R

For example, a male with a PAL of 1.68 and a mean BMR of 6.0 MJ/day (1434 kcal/day) has a mean energy requirement of 1.68 × 6.0 = 10.08 MJ/day (2409 kcal/day).

The mean PAL per day is derived from multiplying the energy cost of each activity (expressed as multiples of BMR, or physical‐activity ratio (PAR) with the time spent in each activity (Table 5.3) [Joint Food and Agriculture Organization (FAO) of the United Nations, World Health Organization (WHO) & United Nations University (UNU) (1985)].

There are different levels of activity associated with an individual’s lifestyle. The categories are shown in Table 5.4. PAL values that can be sustained for a long period of time by free‐living adult populations range from about 1.40 to 2.40. Although there is no physiological basis for establishing the duration of that period, it may be defined as one month or longer [Joint Food and Agriculture Organization (FAO) of the United Nations, World Health Organization (WHO) & United Nations University (UNU) (1985)].

Table 5.3 Factorial calculations of total energy expenditure for a population group.

Source: Joint Food and Agriculture Organization (FAO) of the United Nations, World Health Organization (WHO) & United Nations University (UNU) (1985).

Main daily activities Time allocation Energy cost1 Time × energy cost Mean PAL2
Hours PAR Multiple of 24‐hour BMR
Sedentary or light activity lifestyle
Sleeping 8 1 8.0
Personal care (dressing, showering) 1 2.3 2.3
Eating 1 1.5 1.5
Cooking 1 2.1 2.1
Sitting (office work, selling produce, tending shop) 8 1.5 12.0
General household work 1 2.8 2.8
Driving car to/from work 1 2.0 2.0
Walking at varying paces without a load 1 3.2 3.2
Light leisure activities (watching TV, chatting) 2 1.4 2.8
Total 24
36.7 36.7/24 = 1.53
Active or moderately active lifestyle
Sleeping 8 1 8.0
Personal care (dressing, showering) 1 2.3 2.3
Eating 1 1.5 1.5
Standing, carrying light loads 8 2.2 17.6
(waiting on tables, arranging merchandise)3
Commuting to/from work on the bus 1 1.2 1.2
Walking at varying paces without a load 1 3.2 3.2
Low‐intensity aerobic exercise 1 4.2 4.2
Light leisure activities (watching TV, chatting) 3 1.4 4.2
Total 24
42.2 42.2/24 = 1.76
Vigorous or vigorously active lifestyle
Sleeping 8 1 8.0
Personal care (dressing, bathing) 1 2.3 2.3
Vigorous or vigorously active lifestyle

Eating 1 1.4 1.4
Cooking 1 2.1 2.1
Non‐mechanized agricultural work (planting, weeding, gathering) 6 4.1 24.6
Collecting water/wood 1 4.4 4.4
Non‐mechanized domestic chores (sweeping, washing clothes and dishes by hand) 1 2.3 2.3
Walking at varying paces without a load 1 3.2 3.2
Miscellaneous light leisure activities 4 1.4 5.6
Total 24
53.9 53.9/24 = 2.25

1 Energy costB16s of activities, expressed as multiples of basal metabolic rate, or physical‐activity ratio (PAR).

2 PAL = physical‐activity level, or energy requirement expressed as a multiple of 24‐hour BMR.

3 Composite of the energy cost of standing, walking slowly, and serving meals or carrying a light load.

Table 5.4 Classification of lifestyles in relation to the intensity of habitual physical activity, or PAL

Source: Joint Food and Agriculture Organization (FAO) of the United Nations, World Health Organization (WHO) & United Nations University (UNU) (1985).

Category PAL value
Sedentary or light activity lifestyle 1.40–1.69
Active or moderately active lifestyle 1.70–1.99
Vigorous or vigorously active lifestyle 2.00–2.401

1 Physical activity level (PAL) values >2.40 are difficult to maintain over a long period of time.


Another way for an individual to measure PA intensity is the Borg rating of perceived exertion scale (Borg, 1982).

The scale is based on an individual’s experiences during PA, namely HR, breathing rate, sweating, and muscle fatigue. It includes a rating from 6, meaning “no exertion at all” to 20, a “maximal exertion” of effort (Table 5.5). It is important to know that this is a subjective measure. However, it may provide a good estimate of someone’s HR during PA (Borg, 1982).

Table 5.5 The Borg scale of perceived exertion.

Source: (Borg, 1982).

How you might describe your exertion Borg rating of your exertion Examples (for most adults <65 years old)
None 6 Reading a book, watching television
Very, very light 7 to 8 Tying shoes
Very light 9 to 10 Chores like folding clothes that seem to take little effort
Fairly light 11 to 12 Walking through the grocery store or other activities that require some effort but not enough to speed up your breathing
Somewhathard 13 to 14 Brisk walking or other activities that require moderate effort and speed your HR and breathing but don’t make you out of breath
Hard 15 to 16 Bicycling, swimming, or other activities that take vigorous effort and get the heart pounding and make breathing very fast
Very hard 17 to 18 The highest level of activity you can sustain
Very, veryhard 19 to 20 A finishing kick in a race or other burst of activity that you can’t maintain for long

HR: heart rate.


One metabolic equivalent (1 MET) represents the amount of oxygen used during resting conditions or sitting quietly, and it is assumed to be 3.5 mL of oxygen per kg of body weight per minute (3.5 mL O2/kg/min). Thus, tasks that require twice that amount (7 ml O2/kg/min) require 2 METs and those triple the amount of oxygen require 3 METs, and so on.

Table 5.6 Metabolic equivalents (METs) values of common physical activities classified as light, moderate, or vigorous intensity.

Source: (Liguori, 2020).

Very Light/Light (<3.0 METs) Moderate (3.0–5.9 METs) Vigorous (≥6.0 METs)
Walking slowly around home, store, or office = 2.0a
Walking 3.0 mi · h−1 = 3.0a
Walking at very brist pace 4.0 mi · h−1 = 5.0a
Walking, jogging, and running
Walking at very, very brisk pace 4.5 mi · h−1 = 6.3a
Walking/hiking at moderate pace and grade with no or light pack (<10 lb) = 7.0
Hiking at steep grades and pack 10–42 lb = 7.5–9.0
Jogging at 5 mi · h–1 = 8.0a
Jogging at 6 mi · h–1 = 10.0a
Running at 7 mi · h–1 = 11.5a
Household and occupation
Standing performing light work, such as making bed, washing dishes, ironing, preparing food, or store clerk = 2.0–2.5
Household and occupation
Cleaning, heavy — washing windows, car, clean garage = 3.0
Sweeping floors or carpet, vacuuming, mopping — 3.0–3.5
Carpentry — general = 3.6
Carrying and stacking wood = 5.5
Mowing lawn — walk power mower = 5.5
Household and occupation
Shoveling sand, coal, etc. = 7.0
Carrying heavy loads, such as bricks = 7.5
Heavy farming, such as bailing hay — 8.0
Shoveling, digging ditches = 8.5
Leisure time and sports
Arts and crafts, playing
cards = 1.5
Billiards = 2.5
Boating — power = 2.5 Croquet = 2.5
Darts — 2.5
Fishing — sitting — 2.5
Playing most musical
instruments = 2.0–2.5
Leisure time and sports
Badminton — recreational = 4.5
Basketball — shooting around = 4.5
Dancing — ballroom slow = 3.0; ballroom fast = 4.5
Fishing from riverbank and walking = 4.0
Golf — walking, pulling clubs = 4.3
Sailing boat, wind
surfing = 3.0
Table tennis = 4.0
Tennis doubles = 5.0
Volleyball — noncompetitive = 3.0–4.0
Leisure time and sports
Bicycling on flat — light (10 − 12 mi· h–1) = 6.0 Basketball game = 8.0
Bicycling on flat — moderate effort (12 − 14 mi · h–1) = 8.0; fast (14 − 16 mi · h–1) = 10.0
Skiing cross‐country — slow (2.5 mi · h–1) = 7.0;
fast (5.0 − 7.9 mi · h–1) = 9.0 Soccer — casual = 7.0;
competitive = 10.0
Swimming leisurely = 6.0b; swimming — moderate/ hard = 8.0 − 11.0b
Tennis singles — 8.0
Volleyball — competitive at gym or beach = 8.0

a On flat, hard surface.

b MET values can vary substantially between individuals.

A sample of select activities in METs for each of the intensity rates is presented in Table 5.6 (Liguori, 2020).

METs are an easy, useful, and standardized way to describe the absolute intensity of several physical activities (Liguori, 2020). Absolute intensity is the amount of energy needed for an activity without considering the cardio‐respiratory fitness or aerobic capacity of an individual. Absolute intensity is expressed in METs. Conversely, relative intensity is the level of effort based on the individual’s level of cardio‐respiratory fitness (Piercy et al., 2018), and it is expressed as either the maximal oxygen uptake (VO2max, the maximum amount of oxygen used in 1 minute), or maximal heart rate (HRmax).

Any kind of PA can be performed at a variety of intensities. According to the current Physical Activity Guidelines for Americans, published in 2018 (Piercy et al., 2018), the absolute rates of energy expenditure during PA are considered as light, moderate, or vigorous (high) intensity.

According to the most recent WHO definition of PA, an energy expenditure of 1 MET refers to the REE. Therefore, sedentary behaviors are defined as any waking behaviors characterized by an energy expenditure ≤ 1.5 METs in a sitting, reclining, or lying position (Tremblay et al., 2017a). Indicators of sedentary behaviors are usually screen time and sitting time.

Light intensity activities are defined as activities performed at or under 3 METs, which require the least amount of effort compared to moderate and vigorous activities. Some examples include walking slowly (i.e., shopping, walking around the office), doing household shores (e.g., preparing food, and washing dishes) or activities of daily living (e.g., sitting at your computer, making the bed, eating).

Moderate‐intensity activities are activities that require 3.0 to 5.9 METs. Examples include walking briskly, playing doubles tennis, raking the yard, slow dancing, or washing windows.

Vigorous‐intensity activities are defined as activities that require 6.0 or more METs. Vigorous activities are performed using the highest amount of oxygen consumption to complete the activity. Examples include running, jogging, playing soccer, swimming, shoveling snow, and carrying heavy loads.

An easy and practical way to determine whether an activity is of moderate or vigorous intensity is the talk test. While performing a moderate‐intensity activity, an individual can talk, but not sing. However, during a vigorous‐intensity activity, they cannot say more than a few words without taking a breath.

Aerobic capacity decreases with age after peaking in young adulthood. Therefore, relative intensity is a better guide for older adults than absolute intensity.


Maximal oxygen uptake (VO2max) is one of the most widely used measurements in exercise science. The VO2max measurement applies from elite athletes to individuals with several pathologic conditions. It is considered the gold standard for assessing a person’s cardio‐respiratory fitness. People who present with a low VO2max have an increased risk of premature death and developing several NCDs, whereas individuals with a high VO2max have a lower likelihood of developing NCDs, all‐cause mortality, and coronary artery disease (Buttar, Saboo, & Kacker, 2019).

The VO2max is the maximum amount of oxygen (or true maximum aerobic capacity) that the body can use during work, and the value does not change despite an increase in workload over time. This can be established using direct or indirect methods. VO2max is expressed as liters per minute (L/min), an absolute value, or in milliliters of oxygen per kilogram (kg) of body weight per minute (ml/kg/min) as the relative VO2max.

In the direct method, VO2max is estimated in laboratories by trained personnel using elaborate, expensive equipment. Individuals are submitted to an ergometric test with progressive loads to analyze their pulmonary ventilation by measuring inspired oxygen (O2) and expired carbon dioxide (CO2) through breath analysis.

Photos depict VO2max test with direct measurement in badminton.

FIGURE 5.2 VO2max test with direct measurement in badminton.

Source: (Rusdiana, 2020).

The individual breathes room air via a mouthpiece (with the nose occluded) that is connected by plastic tubes to an automated, computerized system called a metabolic cart. The mouthpiece is designed to allow the expired air (or a sample of it) to enter the metabolic cart where it is analyzed for its O2 and CO2 content. After resting samples are taken, the individual is subjected to a standardized exercise protocol on a treadmill or stationary bike (Figure 5.2) (Rusdiana, 2020). The exercise begins at a very low workload and increases every 2 to 3 minutes, depending on the exercise protocol. The workload is determined by a standardized and progressive increase in the speed and/or elevation of a treadmill or the increased resistance of a bike. HR and oxygen uptake are continuously monitored and recorded. Blood pressure is measured and recorded every 2 to 3 minutes.

Exercise protocols are designed to fatigue most people within 10 to 12 minutes. When the individual reaches fatigue, the test is terminated. This is the maximal aerobic capacity of the individual. The oxygen used by the body at the point of fatigue is the individual’s VO2max, which is expressed in L/min or ml/kg/min.

The advantage of measuring VO2max is its high accuracy, since it allows the assessment of an individual’s exercise intensity based on a measured—not estimated—aerobic capacity. Its high cost and time requirements make it prohibitive for the population at large, so this method is mostly used in patients with specific needs and for research purposes.

Since the VO2max is not practical for measuring the exercise intensity during training, indirect methods are used instead. These methods include field tests, estimating a person’s aerobic capacity based on their HR (which corresponds to the percentage of oxygen consumption), their distance covered, and/or their time completing a trial.


The easiest and most straightforward method to establish exercise intensity is to measure the percentage of the maximum heart rate (HRmax). This method is based on the concept that the HR increases linearly with an increase in workload and oxygen consumption (Figure 5.3).

Theoretically, when the VO2max is achieved, HRmax is also achieved. Thus, a percentage of the individual’s HRmax can be used to establish their desired exercise intensity (Table 5.7).

The HRmax of an individual can be easily estimated, with an acceptable degree of accuracy, by subtracting the individual’s age from 220.

upper H upper R m a x equals 220 minus a g e

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May 13, 2023 | Posted by in CARDIOLOGY | Comments Off on 5: Defining Physical Activityand Exercise

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