Personal trainer Matt Hart replies: It really depends on what kind of training you were predominantly doing. Muscular strength and power is lost relatively slowly, with little or no de-training occurring in the first four weeks of inactivity unless the limb is in a cast and completely isolated from movement.

Complete isolation of a limb will result in rapid muscle and strength loss, which is noticeable in a matter of days.

With regard to cardiovascular endurance, sometimes a short lay-off for a few days can do you the world of good and many people notice an improvement in performance after this. However, de-training to the aerobic system is commonplace after just two weeks of inactivity. In reality the fitter you are, the more you'll notice the de-training effect, be it strength, power or endurance because top-end fitness is quickly lost. Rest assured though that once you start training again, you'll quickly get it all back - a phenomenon known as 'muscle memory'.