The current UK physical activity guidelines for adults aged 19-64 years
indicate that individuals should be active daily, performing moderate intensity
activity which adds up to at least 150 minutes a week. Alternatively, comparable
benefits can be achieved through 75 minutes of vigorous intensity activity over the
same period. Adults should also include activities to improve muscular strength on
at least 2 days of the week and should minimise the time spent sitting for long
periods (Physical Activity Task Force, 2011, O'Donovan et al., 2010). It is
recognised that for most individuals, exercising above these levels will bring further
health benefits and that these enhanced levels may be required for improvements in
fitness or for weight loss.
Until relatively recently, accurately programming individualised exercise
intensities for cardiovascular exercise was more difficult. Advances in exercise
science however have elicited a means to quantify the energy cost of physical
activities thus making it easier to measure and prescribe cardiovascular exercise. A
Metabolic Equivalent Task (MET) is a unit used to estimate the amount of oxygen
used by the body during physical activity, where 1 MET is the energy expended at
rest. Tables have been compiled for a very large variety of tasks with their MET
value, including exercising, work activity and home activities. The US Center for
Disease Control and the American College of Sports Medicine have collaborated on
these, and a comprehensive list has been published (Ainsworth et al., 2011). For
example, brisk walking at ~4 mph is 4 METs, jogging at 5 miles∙h-1 is 8
METs and running at 9 miles∙h-1 is 15 METs.
Exercise can therefore be standardised into 'MET minutes', so ten minutes exercise brisk walking is 40 MET minutes.
While current UK
physical activity guidance does not provide recommended levels of activity in
METs, American guidelines are similar to those from the UK and recommend 500-
1000 METs of activity a week. So to achieve this you could brisk walk (4 METs) for
between 125-250 minutes a week, jog at 5 miles∙h-1 (8 METs) for between 62-125
minutes a week or run at 9 miles∙h-1 (15 METs) for between 33 and 66 minutes or
through any combination of other activities based on their metabolic equivalents. For
weight loss purposes METs can also be used to determine weight loss goals where 1
MET is equivalent to 1 kcal·kg−1·h−1. So for an 80 kg individual exercising for 60
minutes, brisk walking (4 METs) would burn 320 kcal, jogging at 5 miles∙h-1 (8
METs) would burn 640 kcal and running at 9 miles∙h-1 (15 METs) would burn 1500
METs have also been related to levels of cardiorespiratory fitness in
mLO2∙kg−1∙min−1 where 1 MET is equivalent to 3.5 mLO2∙kg−1∙min−1.
Most individuals who have played sport to any significant competitive level will appreciate that the recommended guidelines for health are substantially less than the exercises levels needed to keep even moderately fit for sport. When measured against people living an active working life as a hunter-gatherer or early farmer they are also substantially less. It is important to appreciate that the studies were predominantly assessing cardiovascular effect, and were looking at minimal levels to improve cardiovascular function and reduce risk. It therefore comes as no suprise that a recent study looking at dose-response relationships between physical activity and the risks of breast cancer, colon cancer, diabetes, ischaemic heart disese and ischaemic stroke events show that increase above this minimum level are strongly associated with lower risks of all these conditions. Most health gains accrue at total activity levels of 3000-4000 MET minutes, with benefits increasing up to around 10000 MET minutes, with diminishing returns.
To achieve a level of 3000 MET minutes, someone will have to undertake a daily activity level of climbing stairs for 10 minutes, vacuuming for 15 minutes, gardening for 20 minutes, running for 20 minutes and walking or cycling for 25 minutes.
This does perhaps explain why so many people who believe they are exercising to a healthy level do not experience any change in their perceptions of their health or fitness, do not lose weight and do not find physical activity significantly easier. The current guidelines from USA and UK could be regarded as inadequate when measured against a target of a healthy population. It is particulalry important to put objective numbers to exercise levels if any meaningful outcome is to be achieved. We do have a reasonable understanding of numbers in relation to healthy eating, and recognise that five portions of fruit or vegetables a day will not be achieved by eating five grapes. Unfortunately the current exercise guidelines do appear to be the equivalent of suggesting five grapes are sufficient, whereas five apples should be the goal.