Physical Activity Factor
Regular physical activity is an important characteristic of a healthy lifestyle that significantly helps to reduce the risks of non-communicable diseases and chronic health conditions, including obesity, diabetes, hypertension, osteoporosis, osteoarthritis, and many forms of cancer. There are also significant mental and emotional benefits associated with leading a physically active life, helping to reduce the risks of depression, anxiety, stress, and other mental health disorders.
Defining Physical Activity
Physical activity describes any bodily movement that increases body temperature and energy expenditure. It can comprise of unstructured tasks like gardening, cleaning and other domestic chores, or more structured activities like walking, cycling and swimming.
If structured physical activities are specifically performed for the purpose of improving health, including managing bodyweight (e.g. jogging, power walking), then they are generally classified as exercise. There will however be times when structured physical activities are not necessarily performed for their health benefits, as would be the case with walking or cycling to work.
If physical activities are performed competitively, then they would normally be classified as a sport (e.g. a race).
Prevalence of Physical Inactivity
There is widespread research to support the fact that too many people are physically inactive. According to data from the World Health Organisation (2020), 1 in 4 adults globally are classified as physically inactive. This means that they do not meet the recommended 150-300 minutes per week of moderate-intensity physical activity. Furthermore, the WHO also report that over 80% of the world’s adolescent population are insufficiently active.
In the UK however, data published by Public Health England (2018) in their physical activity profiles report reveals that only two-thirds of adults are getting enough daily physical activity. In this report, adults were classified as active, fairly active, or inactive, relative to how closely they were achieving the recommended volume of activity each week. Around a quarter of adults in this report were classified as physically inactive, demonstrating that they performed almost no meaningful physical activity throughout the week.
The factors affecting physical activity levels are varied and complex, with socioeconomic status (income, education, employment etc), ethnicity, cultural influences and geographical location all contributing. Physical Activity levels appear to be lower in those from more deprived areas and households and interestingly, it also seems to reduce gradually over time with increasing age. Those aged 75 and over were found to be the most inactive of all age groups.
Physical Activity Guidelines
The World Health Organisation (WHO) recommend that adults should perform at least 150-300 minutes per week of moderate-intensity aerobic physical activity, like walking, cycling or jogging. Alternatively, this can be substituted for 75-150 minutes of more vigorous-intensity aerobic activity which might include cardiovascular exercises like jogging, cycling, rowing or other forms of aerobic activity, and/or participating in sport. WHO also advise adults to engage in muscle-strengthening activities at a moderate intensity for all major muscle groups (e.g weight training, callisthenics), on at least 2 days of the week. They also state that people should actively try to limit the amount of time spent being sedentary (e.g. sitting) and should aim to do more than the above recommendations to counteract the effects of prolonged periods of inactivity on their health.
In the UK, the Chief Medical Officer publishes guidelines on the amount and type of physical activity different category groups of people (age, disability, pregnancy etc) should be performing in order to improve their health. For adults aged 19 and over, the guidelines almost mirror those published by WHO, with a minimum of 150 minutes of moderate-intensity activity, or 75 minutes of more vigorous physical activity being recommended. Adults can again perform a combination of these. The CMO also suggests that exercises to build strength should be performed on at least 2 days per week, which can include carrying heavy bags, manual labour around the house, gym work, yoga or Pilates. The CMO actively encourages adults to reduce the time they spend being sedentary, but also recommend that activities should be performed to improve balance, especially in older adults to reduce the risk of falls. This could include dancing, tai chi, bowls or programmes like yoga.
Measuring Physical Activity Levels
Physical activity can be measured in frequency, duration and intensity.
Frequency typically refers to the number of periods a person is physically active throughout the course of a week. For example, if somebody has a physically active job and they perform lots of bodily movement and physical work through the week (Monday-Friday), but are less active at weekend, then their frequency would be 5. Conversely, they could have a sedentary desk-based job, but be busy at home in the garden most weekends. This person would likely have a frequency of 2 unless they performed other activities outside of work to mitigate this.
Duration refers to the amount of time each period of physical activity lasts. Naturally, this will vary from one task or episode to the next, so it is often necessary to take an average. If for example occupational work forms the majority of a person’s physical activity, it will be necessary to evaluate a typical working day. It is also necessary to account for periods of inactivity, like breaks, administrative duties and meetings. In reality, a worker may only be physically active for part of the working day.
Intensity is broadly classified in the CMO and WHO guidelines as ‘moderate’ or ‘vigorous’ with examples of each being provided. It is important to be clear however what the difference between moderate and vigorous is, and the best way to illustrate this is with the Ratings of Perceived Exertion or RPE scale. RPE is a universal and subjective measure of exercise intensity that is based on the perception of exertion (e.g. how hard a person feels that they are working). The RPE scale ranges from 0-10, with 0 being no exertion, and 10 being maximum exertion. Moderate intensity activities range between 4-6 on the RPE scale, whereas vigorous physical activities would usually be between 7-8 on this scale.
An example RPE scale is provided below for illustration purposes:
Physical Activity Factor (PAF)
Physical Activity Factor, or PAF, is an objective measure of an individual’s physical activity profile based on the volume and intensity of physical activity that they perform. The formula for PAF is as follows:
V (F x D) x I = PAF
Volume is determined by multiplying the frequency by the duration (frequency x duration = volume), thereby providing a weekly sum of physical activity in minutes. Minutes is the preferred metric because it makes it easier to compare to the WHO and CMO guidelines, although it can be converted to hours and minutes relatively easily by dividing it by 60.
Intensity is determined using the rating of perceived exertion (0-10 scale) for the activity/activities that are performed. If multiple activities of different intensity are performed, then these should be recorded and the average intensity for all activities should be used in the PAF calculation.
PAF provides a valid measure of both the quantity and quality of physical activity completed, giving more insight into a person’s activity profile than frequency and duration alone. An individual may complete a sufficient volume of physical activity but if this activity is not intense enough, then their PAF score will be suppressed.
If, for example, an individual was physically active on 5 days per week for 60-minutes and their intensity was around 6 on the RPE scale, their PAF would be calculated as follows:
5 x 60 = 300 (volume) x 6 = 1800
Calculate your physical activity factor below:
Classifying Physical Activity Factor (PAF)
The table below provides a summary of PAF scores and their respective classifications. It should be noted that each classification threshold also has a minimum volume of physical activity also, to prevent the PAF from being artificially inflated from subjective intensity estimations, or those individuals that perform several short and intense bouts of physical exercise, but who are generally inactive at other times.
It is worth remembering that the WHO and CMO guidelines advise people to actively avoid prolonged periods of inactivity and seek to remain as active as possible throughout the day. The following PAF criteria help to support that objective because those that only achieve the minimum volume of activity can only achieve an average to good classification.
Cautionary note: It is of course possible to manipulate the PAF score by using extreme and unrealistic data values (e.g. a duration of 1000 minutes), although such actions would not be of value to anyone. For most individuals reporting genuine physical activity frequencies, durations and intensities, PAF can provide a logical and reliable way of reporting and tracking the quality and quantity of physical activity completed.
Physical Activity Fact Sheet. World Health Organisation (26th November 2020).
Physical Activity Profiles. Public Health England (November 2018).
UK Chief Medical Officer’s Physical Activity Guidelines. Department of Health and Social Care (7th September 2019).