We all know exercise is good for us, but do we know exactly why? The first things that often spring to mind are the correlation between regular exercise and keeping your heart healthy and excess weight off. But what causes these associations, are these even proven, and are there more reasons that should be motivating us to swap an evening on the sofa for an activity that increases our heart rate instead?

How much exercise do we need?

If you are trying to get fit exercise works, regular exercise improves your heart and muscles and increases your lifespan. Evidence for the benefits of exercise for the prevention of age-related disease, including cancer has been accumulating for quite some time[i]. Experts cannot agree on the amount of exercise we should do. Current UK public health guidelines call for adults to engage in at least five 30 minute sessions of moderate intensity activity per week to reduced risk of chronic diseases[ii]. Others disagree, claiming a few minutes of daily intense exercise, such as cycling or running, in the form of a short, sharp shock, is enough to fool your body into thinking it’s getting a good workout[iii]. So how much exercise should we all be doing? This depends entirely on your body composition, goals, and overall levels of health. That being said it has been found that around 270 hours (5.19 hours a week!) of annual exercise adds around three years to your lifespan and delays the onset of many diseases[iv].

Why do some people find exercising harder than others?

When it comes to being dedicated to exercising it’s not just willpower that plays a role. If you ever wondered why some people find exercising a chore, whilst for others being active comes naturally and is pleasurable, your genes can be held accountable. A study examining twin cohorts in Europe and Australia looked at exercise habits of 40,000 twin adults. Results showed that a liking for participating in exercise several times a week was around 70% heritable[v]. This shows exercise is easier for some than others. However, environmental factors do still play a part, and regarding exercise a social activity, one that is engaged in with a friend, increases the likelihood of regular participation.

Exercising more and not losing weight?

The modern obesity epidemic does not correlate with the increasing numbers of gym-goers, outdoor exercisers and participants in team sports. The New York Marathon started in 1970 with 100 participants, 10 years later in London. By 2015 nearly 1 million have crossed the finish line. So if we are exercising more then why are our waistlines gradually expanding?

The reason why so many of us don’t lose weight exercising is that our bodies compensate. Our bodies are programmed to stop us losing weight via fat, and we have to expend 5 times more energy to get rid of fat than muscle[vi]. Some fat may be converted to muscle, but this doesn’t convert on the scales so don’t be disheartened if you increase your exercise routine but find you weigh more.

Another factor which comes into play is our exercise and reward behavioral patterns. We have unreliable memories when it comes to recalling exercise and in general have a tendency to over-exaggerate our output expenditure and then over-eat. Marketing doesn’t help, with many brands promoting “muscle recovery” sweet shakes and snacks which can easily contain more energy than has been expended.

To overcome this try wearing a heart-rate monitor or fitness tracker, tailored to your body composition, this will enable you to accurately see your energy expenditure and avoid overdoing the “reward” foods after exercising. Interestingly these monitors show enormous variations between individuals. Those who naturally fidget and move about can expend up to 300kcals a day more so than a restful person.

Exercise and health

If exercise alone doesn’t result in significant weight loss, then it goes to show without dietary restriction exercise has little influence. This begs to question, is it worth exercising if it doesn’t help you reduce weight? And this answer is absolutely yes. The major risk for heart disease is associated with being unfit, smoking and not having a balanced diet. A study of 30,000 European adults doing no exercise carried twice the risk of early death as obesity. Plus doing just 20 minutes of brisk walking for a totally sedentary person (which is one in five Europeans) would reduce their risk of premature death by a quarter[vii]. Exercise is a good investment in time for most people.


  • Where possible break up sedentary time. Sitting, regardless of how much exercise you do, is an independent risk factor of heart disease and mortality. Sitting for prolonged periods can compromise metabolic health. Sedentary behaviors, typically seated desk work, TV viewing, and sitting in automobiles are being associated with an increase in premature mortality risk[viii]. Take the stairs, try to walk more and opt for height-adjustable desks.
  • Invest in an activity tracker to more accurately monitor your energy expenditure.
  • Find pleasure in your activity. Don’t force yourself to do something you hate, the likelihood of you keeping it up is low.

Article featured on the Plenish Cleanse blog.

[iii] Mosley, M., Fast Exercise (Atria Books, 2013)

[iv] Spector, T (2015) Diet Myth; The Real Science Behind What We Eat

[v] Stubbe, J.H., PLoS One (2006); 1: e22. Genetic influences on exercise participation in 37,051 twin pairs from seven countries.

[vi] Hall, K.D., Lancet (2011); 378: 826-37. Quantification of the effect of energy imbalance on body weight.