Even if you have to stop working out at the gym completely, muscle atrophy isn't immediate. Even if you have to stop working out at the gym completely, muscle atrophy isn't immediate. The insitute says that most men will lose … If you have to cut back on exercise for whatever reason, and you don’t want to lose any hard-earned muscle, you may be able to get away with doing only two strength workouts per week, according to Olson. This type of fitness fades pretty quickly, unfortunately. According to Harvard Health Publishing, after age 30 you begin to lose as much as three to five per cent of muscle mass per decade. How quickly you’ll lose muscle once you stop training depends on different factors, but in general, you’ll notice losses in 3–4 weeks. Some … As well as asking how long does it take to lose muscle, we should also consider how long this type of fitness hangs around. Does it matter in the long-term? Hence, the detrained athletes didn’t lose any muscle mass during a three week break from training (LaForgia et al., 1999). And the more muscle you have, the more you stand to lose. However, let’s assume that 2-3 weeks detraining in beginners leads to muscle loss. A 2015 study found that active young adults lost one-third of their leg strength after just two weeks of inactivity. Some aspects of fitness last a month before beginning to decline. For cardio, it takes less time to break down your fitness; as stated above, it could take years to lose all your muscle. But, their muscle glycogen stores did shrink.