We know that exercise is good for us. Is it ever possible to do too much? What is the evidence?
How much aerobic exercise is good for us?
The evidence that exercise is good for our health is clear and compelling. That’s why the World Health Organisation (WHO),the NHS and the Harvard magazine, for example, all recommend at least 150 minutes of aerobic activity at moderate intensity per week (like brisk walking, dancing or mowing the lawn) – equivalent to 30 minutes a day, 5 days a week.
And the WHO suggests that more exercise (like 300 minutes of moderate intensity exercise per week) provides ‘additional health benefits.’
What about strength exercise?
The WHO and NHS also recommend muscle strengthening exercises for at least 2 days a week (like digging in the garden, carrying heavy shopping, push ups, sit ups or lifting weights).
What difference does exercise make?
Most types of exercise reduce or delay the risk of a range of illnesses – and increase our chances of living a long and healthy life. For example the American Heart Association identifies that increasing daily activity and exercise reduces the risk of heart disease by reducing the potential for hardening of the arteries and reducing other risk factors such as obesity, high cholesterol, and high blood pressure.
Is it ever possible to do too much exercise?
Overtraining syndrome (OTS) has been known to sports scientists for a number of years. However OTS is much less prevalent, as a 2003 article explained, 'It occurs where an athlete is training vigorously, yet performance deteriorates. One sign of OTS is suppressed immune function, with an increased incidence of upper respiratory tract infection (URTI). An increased incidence of URTIs is also associated with high volume/intensity training, as well as with excessive exercise (EE), such as a marathon, manifesting between 3-72 hours post-race.'
OTS usually results in short term, relatively minor health issues. However, a number of recent reports published in peer reviewed journals suggest long-term excessive and strenuous exercise may cause more harm than good to your health – although this is usually at levels of exercise well above what most people do.
For example, it has been suggested that too much exercise may be bad for our gut health. A 2017 review of published evidence referred to 'exercise-induced gastrointestinal syndrome' which it indicated has the ability to create acute disturbance in the health of the gastrointestinal tract - including possibly 'leaky gut.'
A 2014 Danish study tracked the health of 1098 healthy joggers and 3,950 healthy non-joggers over a 12-year period. Light and moderate joggers (a speed of around 5mph and no more than three times a week or for 2.5 hours in total) had lower mortality than otherwise healthy non-joggers. However, strenuous joggers (who ran at speeds higher than 7 miles per hour or more than four hours a week) tended to die at a higher rate than light and moderate joggers and at a similar rate to healthy non joggers. The link remained when factors such as age, sex, the history of heart disease or diabetes, smoking and the levels of alcohol consumed were taken into consideration. This study concluded that the effects of exercise are horse-shoe shaped i.e. beyond a certain point, physical activity not only stops enhancing health but may start hurting it.
In another study, published in the US in 2015, over a million women aged 50-64, recruited in breast screening clinics in the UK, completed a questionnaire on their daily and weekly physical activities e.g. housework, gardening, walking, cycling and any work or exercise causing “sweating or a fast heartbeat.” How often they were physically active, for how long and in what ways was recorded and the participants were followed up for 9 years. What the researchers found was that women who engaged in physical activity had a lower risk of heart attack and stroke than women who didn’t. However, doing even more exercise didn’t seem to provide any further protection – and there was some evidence of increased risk for the most active.
A Swedish study, published in 2013, considered 52,755 male participants who took part in a 90km cross-country skiing event every year over a period of nine years. It found 919 (i.e a little under 2%) experienced arrhythmia (irregular heartbeat). A fast finishing time and a high number of completed races were associated with higher risk of arrhythmias.
A possible reason for research findings like this is that, in a small number of people, intensive exercise (like running a marathon) may trigger an undiagnosed heart condition and strenuous exercise over a long period of time may lead to abnormal heart enlargement and weakened heart muscle or to scarring of the heart muscle. However, many of the studies that show this are small and show a link but no proven cause-effect relationship between excessive training and cardiac abnormalities.
Dr Dermot Phelan, Director of the Sports Cardiology Center at Cleveland Clinic, did not participate in the Swedish study and analysis, but reviewed it and believes care should be taken in interpreting these results:
“Exercise and even strenuous exercise is clearly associated with enormous heart health benefits in the vast majority of people when compared to people who do not exercise but, in a very small minority who have underlying problems, exercise can trigger arrhythmia,” he says. “While there is emerging evidence that prolonged strenuous exercise can increase risk of atrial fibrillation, the long-term risk of this is small compared to inactivity.”
A review of the published evidence, published in 2018, concluded: Collectively, these data suggest: (1) there is limited evidence that supports the “Extreme exercise hypothesis,” the most compelling relating to the increased risk of atrial fibrillation at high volumes of exercise; (2) cardiac anomalies may be present in a small proportion of the most active veteran athletes; and (3) the combination of high-intensity physical activity in the presence of known or occult CVD, seems to be the major cause of exercise-related fatalities.
Overall what the studies into exercise and health suggest is that:
- Exercise has enormous health benefits for the majority of people when compared to those who do not exercise.
- However, in a small group who may have an underlying heart condition or who engage in particularly strenuous long term exercise, excessive exercise could possibly trigger heart problems.
- Exercise should also be avoided if you have a virus, as this increases health risks.
If you have symptoms that suggest a possible heart problem, a history of a heart condition or risk of heart disease, check with your doctor before starting more strenuous exercise. Otherwise moderate exercise and physical activity is strongly recommended.
Can we become addicted to exercise?
One special case is people addicted to exercise. As the article explained, ‘an individual who is addicted to exercise will continue exercising regardless of physical injury, personal inconvenience or disruption to other areas of life including marital strain, interference with work and lack of time for other activities.’ An example of exercise addiction was reported by the BBC in 2019. However, the number of people addicted in this way is likely to be small. As with all addictions, professional help should be sought.
These usually involve either sudden or gradual damage to: muscles, bones (e.g. stress fractures), ligaments, tendons, joints and cartilage. Knee injuries are one of the most common sport injuries amongst runners.
Most football injuries affect the lower extremities, which are defined as the groin and pelvis, hip and thigh, knee, calf, foot and ankle, with Hamstring Strain, Sprained Ankle, Knee Cartilage Tear, Hernia and Anterior Cruciate Ligament as the top five most severe injuries reported worldwide.
However, Patient info advises that the risk can be greatly reduced by common sense measures – like warming up before exercise, increasing exercise levels gradually, and not over training, with some risks due to poor technique or equipment or underlying, undiagnosed heart problems.
Which types of exercise are more or less strenuous?
Exercises with moderate intensity include: Walking fast, riding a bike, jogging, doubles tennis, hiking etc. House work such as vacuuming, mowing the lawn, washing the car etc. also burns calories and helps with fitness.
Intensive exercises include: Running, swimming, football, rugby, aerobics, singles tennis and martial arts.
More extreme exercises include: marathons, ultramarathons, ironman distance triathlons, and very long distance bicycle races.
Conclusions
- Exercise is beneficial for most of us irrespective of our age, provided we do it at moderate levels and keep within duration guidelines i.e. no more than an hour a day.
- Longer exercise from time to time, like preparing for an occasional 5K or 10K fun run or going on a walking holiday is also likely to be beneficial.
- However, significant over exercising such as repeated endurance running can be counterproductive and, in a small number of cases, could lead to heart damage.
- New runners, with no previous running experience, do have a risk of sustaining musculoskeletal injuries in training for such events, so should build up gradually.
- People who engage in above average amounts of exercise may later encounter some exercise related problems but overall tend to enjoy above average health.
Reviewed and updated by Kayhan Nouri-Aria, July 2019, Next review date July 2023.