The debate about how much is the right amount of exercise can seem never-ending. The minimum recommendation in the UK is 30 minutes of “moderate” exercise five times per week, not that most adults are meeting it. Some health specialists think alternative regimes will do us more good, such as shorter bouts of very intense exercise three to four times a week; or limiting periods of inactivity to a maximum of 60 minutes at any one time.
The trouble with this debate is that it risks assuming that exercise is always good for you. In reality, this is not always the case. Most of us know about the need to warm up properly and avoid exercising when we are under the weather, but some risks may not yet have reached the public consciousness. What follows is a few words of caution for anyone working themselves into a sweat. You never know, they may just save your life.
1. Easy does it
People who are unaccustomed to exercise and throw themselves in at the deep end can develop an unpleasant condition called delayed onset muscle soreness. It involves aching and tender muscles and a reduced range of motion of the joint at the affected area. It can last for several days and peaks about 48 hours after exercise.
The condition is caused by the body reacting to the trauma of sudden exercise: white blood cells infiltrate the muscles and digest damaged tissue, causing acute inflammation. How to avoid this experience? Anyone starting an exercise programme should build it up gradually.
2. Don’t overstimulate
In extreme cases of delayed onset muscle soreness, the enzymes released by the muscles from the digestion of damaged tissue can induce a condition called rhabdomyolysis in which enzymes from damaged muscle cells are released into the blood. In severe cases this can lead to kidney failure but fortunately this appears to be relatively rare.
Using electrical stimulation devices as a substitute or supplement to exercise can also reportedly induce rhabdomyolysis. These devices work by attaching electrodes to different muscle groups and have become increasingly popular in recent years. Now, however, clinicians are issuing warnings about the dangers of using them excessively.
3. Hey, Ironman …
If you are thinking about seriously pushing yourself, a brief lesson on the function of the heart is in order. The heart works in two phases, a contraction phase and a relaxation phase. In the contraction phase, blood is ejected from the right and left ventricles into the arteries through contraction of the heart muscle. In the relaxation phase, blood fills the ventricles to prepare for the next contraction.
The average human heart contracts about 70 times per minute, 24 hours per day and accumulates about 3 billion contractions over a 75-year period. It is considered that the heart can cope with even strenuous exercise, rising to about 200 beats per minute to pump enough blood and oxygen around the body.
Yet studies investigating the effects of prolonged intensive exercise such as an Ironman triathlon have shown a temporary decline in the heart’s relaxation function after the athlete has stopped exercising. This effect has been termed “cardiac stunning”.
Perhaps more worrying, some participants in these gruelling events have displayed biomarkers of cardiac damage usually only found after a heart attack – albeit the levels tend to be only just over the threshold to indicate damage and the effects appear to be short term. Yet subsequent studies also suggest it could be detrimental to cardiac function in the longer term.
Having said all that, it is worth stressing that not all exercise is detrimental to the heart. Exercise maintains heart function and in the case of heart-attack patients following a rehab programme, can substantially improve it.
4. Immunity care
A bout of moderate exercise is considered to boost our immune function by prompting an increase in the number of white blood cells in our blood. In contrast, completing three or four hours of strenuous exercise – par for the course for professional athletes – has been linked to a decline in immune function over the next 24 hours.
After that it would return to normal, however for people like athletes doing this on a daily basis, longer-term studies have demonstrated that repeated strenuous exercise over several weeks can suppress immune function by lowering the number of white blood cells and making them function less effectively. It would then take considerably longer for the immune system to correct itself.
What to do about this? You can alleviate some of the effects with a good diet (or exacerbate them by eating poorly). Better still, you can also keep the bugs at bay with good personal hygiene. It is no coincidence that this message is drilled into athletes competing in the Olympics nowadays.
None of this is intended to suggest that moderate exercise is not good for us. Doctors and sports scientists would agree that it maintains and promotes good heart, muscle, immune and also metabolic function. We might still be debating the best regime, but it’s still rightly a major goal for health professionals to educate the public about the beneficial effects of exercise.
That said, there are limits. People need to be more aware of the risks of doing too much too soon – and of taking things to extremes. Exercise is good for you, but take the wrong approach and you might wish you had stayed on the couch.