The American College of Sports Medicine is widely quoted as recommending 150 minutes of moderate intensity exercise a week, split over 3-5 sessions per week. You might do shorter, more frequent sessions or perhaps longer, less frequent sessions. Typically we try and aim for at least three bouts of endurance exercise a week to meet those requirements.
How the American College of Sports Medicine classifies ‘moderate intensity exercise’ isn’t exactly how an amateur sportsman or regular gymgoer might classify it. For most people, moderate intensity means light jogging, gentle cycling and basically what many gym goers would consider to be very low intensity. If you incorporate interval training this might allow you to lessen the volume of exercise you have to do.
It’s also recommended that in addition to endurance exercise you incorporate two sessions of load-bearing exercise – essentially weight lifting. This is hugely important in terms of bone health and maintaining muscle volume. As we get older we tend to lose muscle. This can lead to falls, and if the bones are weak, to fractures. To maintain a decent quality of life, some form of resistance training is vital. In fact a lot of problems associated with old age are attributable to people not doing some form of resistance exercise.
Resistance exercises, whether using weights or bodyweight, will protect bone density into old age
The flipside to this question is 'can you exercise too much'?. That is largely dependent on the individual. For some people exercising 180 minutes a week will prove to be genuinely challenging. At the other end, when you look at extreme endurance athletes, they exercise 20 to 30 hours a week. That’s 1,800 minutes. And they can maintain that. So it’s very much down to the individual.
However, everyone can overdo it – and everyone has a threshold. Unfortunately, it’s not possible to pin down exactly how much exercise is too much because everyone is different. But if you go beyond your personal threshold you can, among other things, compromise your immune system, making you more vulnerable to bugs like the common cold. By over-exercising you can also over-use or overload joints, making it more likely you will injure yourself. Typically this will happen in resistance training where you load the bar too quickly, lose your form and hurt yourself.