How Fast Do You Get Out of Shape?

One study observed that conditioned athletes who had been training regularly for at least a year and then suddenly stopped lost half of the aerobic conditioning after 3 months.

In contrast, research shows that beginner exercisers who have worked out for about 2 months experience a complete loss of all aerobic conditioning after 2 months of not working out. 

I’m not sure this is the intent here, but I find this very positive and encouraging. It is not all for naught just because you missed a workout. If you’re a “beginner” level exerciser with any kind of regularity, once you start building up strength and aerobic ability, it doesn’t disappear overnight - it’ll take months to go back to zero. I find that very motivating in terms of progress… whether you can see it or not, you are scaling the mountain and it will take you just as long to get back down as it did to get up.

The section on muscle is less encouraging, but it seems more vague than the information on the aerobic study. Still - the more you build it up, the longer it will take to lose.  This stuff reminds me of binge/diet mentalities - if you miss a workout or two, it’s easy to be like “fuck it, I’m off the tracks” but really, your body is generally not going downhill any faster than it took you to get uphill, which is amazing.

Surprisingly, disuse atrophy and muscle fiber type conversion can occur in as little as 72 hours, and, similar to aerobic fitness, thedegree of atrophy depends on how often the muscle is used. Muscles, such as the hamstrings, which we tend to use quite often in every day activities such as standing, will tend to atrophy slower than muscles that we use less often, such as the quadriceps. And the fitter the muscle, the slower it will atrophy.