Those of you who exercise several times a week without fail - congratulations, you are better humans than most of us. But we've got some bad news: if you ever want to take a break from exercising, say you've got a holiday planned or you've had an injury, you're going to start to lose those fitness gains surprisingly fast. According to the Tech Insider video above, within the first week that you stop working out, noticeable changes will start to occur as you inch ever closer to the point of being out of shape.

As exercise physiologist Shawn Arent from Rutgers University in the US explains, the decline during the first week will have a significant effect on your training, it's not exponential to the point that you end up right back where you started - yet. Give it one to three months, and depending on how fit you were at your peak, you could end up right back where you started.

And we're not just talking regular gym enthusiasts - professional athletes can fall into the same trap too. "The fitter you are, the harder you fall," Harry Pino, a senior exercise physiologist at the New York University Langone Medical Centre told io9.

Signe Dean investigated some of the effects for us last month:

"When we stop engaging our bodies in physical activities, it causes all these measures of fitness to decline - a process known as deconditioning or detraining. And the fitter you are, the faster you tend to lose the benefits of exercise, even if your baseline fitness remains better than average. The first to go is VO2 max (maximal oxygen uptake), and before you know it, muscle strength, stamina, and coordination follow. You can also expect a rise in blood sugar levels, and even blood pressure."

And that's the stuff you can't see. You can expect weight gain and shrinking muscles too.

The good news? Just as your fitness and muscle tone are quick to go when you stop working out, they're also quick to return when you start back up again. And Arent actually recommends taking a week off now and then because this can actually be really beneficial, especially if you've been training really hard - you'll very quickly get back whatever you lost while lounging around on the beach anyway.

Just don't let that week off turn into weeks off.  

And while we're on the subject of growing and shrinking muscles, we should also warn you that if you're currently working towards building Superman-level muscles, be warned - the maximum size of your muscles is determined entirely by your genetics. The boys at AsapSCIENCE explain why: