Exercise makes us happier, fitter, stronger and more energetic. But while many people still don’t reach the minimum recommended target of 150 minutes of moderate physical activity each week, it turns out that others are overdoing it by exercising so hard they risk illness, injury, disrupted sleep, low mood and diminished libido. “If you exercise too hard for too long, you could end up hitting a downward spiral,” says Dr Lee Bell, a senior lecturer in sport and exercise science at Sheffield Hallam University, who has researched the effects of working out to extremes. “More exercise isn’t always better for you.”
In recent years, the trend for entering ultramarathons and triathlons, lifting heavy weights at the gym and signing up for high-intensity classes such as Hyrox and CrossFit well into our forties and beyond has resulted in people pushing so hard that they end up ill or injured. There is evidence that gymgoers are also overlooking the importance of rest days. This week a survey by the David Lloyd Clubs gym chain revealed that a quarter of adults refuse to spend time on recovery post-workout as it feels “unproductive”, with more than a third thinking a rest day is a sign of being less fit than other gymgoers and will hinder their progress. The results of such thinking, Bell says, are side-effects that can set you back for weeks, even months. “If your body isn’t recovering well and you are fatigued before your next workout, it can take its toll,” he says.
Garry Trainer, the celebrity osteopath who advises elite footballers, says many of his clients are midlifers who end up overdoing exercise. “I’ve seen a lot more people presenting with overuse injuries, especially middle-aged people who try to keep doing what they did ten years ago, or even more,” says Trainer, who has a clinic at Home, a wellness centre in Primrose Hill, London. “The result can be acute injuries such as muscle strains and tears, or overuse issues such as tendon problems.”
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Bell uses the analogy that we each have a bucket of stress and if that bucket is already half full with the stresses of daily life, it won’t take much for it to overfill when workout stress is added to the mix. When exercise tips the balance so that your capacity to recover is hampered, you eventually reach a point of diminishing returns. “Exercise starts to feel harder and your performance declines,” he says. “Despite your efforts, you are not seeing the fitness gains.”
But how do we know if we are overdoing it at the gym? Here is a guide to exercising within safe limits:
How much exercise is too much?
There’s no formula to tell you when you are exercising too much. Some well-conditioned people can train hard five days a week, whereas for others two days is too much. “It is very different for everyone and is not universally quantifiable,” Bell says. “What’s more important is how your body and mind respond to the exercise you’re doing.”
The clearest warning sign that you are overdoing it is when workouts start to feel harder and performance begins to suffer. “If you are pushing hard with exercise, but can still lift the same weights, or run as fast on a consistent basis, then you are within sensible limits,” Bell says. “But if your performance at the gym plummets, your regular route takes longer to complete and there is a theme of feeling sore, tired and demotivated, you probably need to step back.”
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Don’t increase intensity or duration by more than 10 per cent a week
Taking a cautious, progressive approach to exercise is extremely unlikely to cause harm. “If you add a bit more weight to a bar or a machine each week, or a few extra repetitions or kilometres, it is less risky and there will be fewer side-effects,” Bell says. “You are also more likely to notice any adverse changes earlier.”
A widely accepted rule of thumb is to increase intensity or duration by no more than 10 per cent each week. Although some researchers recently warned that even a single run too far or too hard can put you at risk of overuse injuries. For a paper in the British Journal of Sports Medicine, Rasmus Oestergaard Nielsen, an associate professor in the department of public health at Aarhus University, Denmark, tracked 5,205 midlife recreational runners over 18 months and found that most injuries occurred when a runner ramped up the distance in a single run compared with their longest run in the previous 30 days. “Play it safe and build up slowly is the best message,” Bell says.
You must allow time to recover after HIIT or weightlifting
Our body cycles between periods of stress and repair when we work out consistently. Intense exercise stresses muscle enough to cause damage and micro-tears to fibres, increasing energy-producing mitochondria in our cells so that we become fitter and stronger. “These adaptations don’t occur during a workout, but when you are recovering,” Trainer says. “Only with adequate recovery will fitness improve.”
And many people underestimate the time required to recuperate after an intense training session. One in five respondents to the David Lloyd survey believed that it takes their body less than 12 hours to recover from an hour of high-intensity exercise, yet the reality is that your muscles probably need one to two days to repair fully after a hard workout.
“Diving straight back into another hard workout when you are not fully recovered can leave you vulnerable to injury,” Trainer says. “Your body needs time to heal and back-to-back intense sessions are not the way to do that.”
Older muscles may recover quicker post-workout
Our bodies tend to take longer to recover the older we get. “Our repair systems slow down,” Trainer says. “You may find that you need an extra day or two to get back to normal after a long, hard run or cycle.”
But that is not always the case. Dr Lawrence Hayes, a lecturer in physiology at Lancaster University, recently published findings in the Journal of Ageing and Physical Activity that found post-workout muscle soreness was consistently lower in the over-35s compared with those in the 18-25 age bracket. Contrary to expectation, older muscles also displayed fewer biochemical signs of damage than more youthful counterparts after the same resistance-exercise session.
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“If you do take an extra day off, make sure you stay active, with walking, light swimming or stretching and balancing exercises, to accelerate the recuperation process,” Trainer says. A 2022 study in the Strength and Conditioning Journal showed that this is more beneficial than complete rest for reducing muscle soreness after intense exercise.
Muscles should not feel excessively sore several days later
Some muscle fatigue is inevitable the day after a hard workout, but prolonged extreme discomfort is a different matter. If even walking downstairs is a struggle four to five days afterwards, then you have probably overdone it. Severe delayed onset muscle soreness (DOMS) lasting up to a week can be counterproductive, as it probably means you will have to skip workouts over the following days to recover. Lifting weights that are too heavy, running up hills or attempting a boot-camp class beyond your fitness level are all classic routes to extreme DOMS.
“It’s a myth that extreme muscle soreness means you will get fitter more quickly,” says Dr Rob Erskine, associate professor in neuromuscular physiology at Liverpool John Moores University. “That level of muscle discomfort is unnecessary.” The key, Erskine says, is to build up gradually. “As you get used to the higher load, you won’t experience the same inflammatory response to muscles,” he says.
Keep tabs on your resting heart rate
Checking your pulse first thing before you get out of bed and before your first cup of tea or coffee will give you a measure of your resting heart rate (RHR). You can monitor your RHR manually by placing your first two fingers onto the opposite wrist and counting the number of beats in a 15-second period, then multiplying that by four to obtain your beats per minute (BPM), or you can wear a fitness tracker. What you need to keep an eye on are trends over time.
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An RHR that is elevated by 5–10 bpm over a few weeks could be a sign that you are overdoing it, according to a review of evidence on overtraining published in Sports Medicine and Health Science this year. For most adults under 40, an RHR of 60-75 bpm is normal. Midlifers aged 40–60 typically have an RHR of 65-80 bpm and older adults (60+) an RHR of 70-85 bpm, although there are always outliers, and if you have done a lot of endurance training in the past, your RHR might be lower than average for your age.
Too much exercise can cause low mood and brain fog
Tipping the balance with too much exercise won’t just make you physically tired, it may also leave you mentally exhausted. A study of triathletes in Current Biology found that while endurance exercise is generally good for health, overdoing it can cause brain fog. Heavy training loads were shown to reduce activity in the lateral prefrontal cortex, a part of the brain that controls decision-making, thinking and reasoning.
It can also make you moody and irritable, according to scientists from the Laboratory of Sport Psychology at the Sport Research Institute at the Universitat Autonoma de Barcelona. They tracked a group of cyclists and observed that the more intense their training, the lower their mood the next day. “Feeling drained for a day or two after a tough workout is just a sign of normal fatigue and nothing to worry about,” Bell says. “But if that tiredness is ongoing, you need to reassess your workout regimen.”
Check for changes in your sleep pattern
You might think that the harder or longer you exercise, the better you will sleep. But this is not always the case. In fact, studies have shown that too much exercise may raise levels of the stress hormone cortisol, potentially disrupting your body clock and interrupting regular sleep patterns.
Australian sports scientists reporting in Frontiers in Physiology showed that sleep quantity and quality decline after sharp increases in exercise training loads and found that “poor sleep is a common complaint among overreached or overtrained” individuals. A team from the National Institute of Sport, Expertise and Performance, in France, showed that overtrained triathletes not only slept less well than those with a manageable training load but fidgeted more for a less restful night’s sleep.
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Has your libido taken a nosedive?
Too tired for sex? Fatigue from overtraining or under-recovering can have the knock-on effect of leaving you lethargic and uninterested in sex. Male ultramarathon and triathlon competitors are particularly prone to a drop in libido, with one study from the University of North Carolina showing endurance training on a regular basis “to be significantly associated with decreased libido scores in men”.
Intense training can leave you vulnerable to colds
Regular exercise is known to support a healthy immune system. During moderate aerobic exercise, such as running, swimming and cycling, the number of some immune cells (including the levels of “natural killer cells” that fight off infections in the bloodstream) spikes, helping to protect against infection.
It was once thought that the immune system is suppressed in the hours immediately after intense endurance exercise, although researchers at the University of Bath dismissed that as a myth several years ago. However, training intensively or for long durations, on top of other stresses, can make you vulnerable over time.
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“Overdoing it can leave you prone to upper respiratory tract infections, such as coughs and colds,” Bell says. “The nature of endurance exercise produces more changes to inflammatory markers, fluctuations in stress and other hormones, and changes in white blood cell markers linked to infection than strength training. So if you are training for a triathlon or a marathon and repeatedly getting ill, it is time to maybe dial things back a bit.”
Don’t feel guilty about taking a few days off
If you are feeling jaded or under the weather, take a few days off. “Don’t think you have to keep pushing on, as the reality is that you will probably do more damage and find you need to take a few weeks off down the line,” Bell says. “The evidence suggests you won’t lose much fitness at all if you take a step back for five to seven days, and you will probably come back feeling more mentally and physically refreshed.”
Doing a form of physical activity that you don’t consider to be a workout — such as gentle yoga, going for a walk or an outdoor dip — can make all the difference to your frame of mind and help you to recuperate fully.