We asked an exercise scientist how many days a week you need to work out to actually make a difference

How much should you exercise? Many of us have certain ideas in our heads about what works best to keep us "in shape" and what does not.

Five days a week, four days a week? Is two enough?

Luckily, science has come to the rescue with a surprising conclusion, and a somewhat tough one to swallow if you have trouble motivating yourself to work out.

We spoke recently to Shawn Arent, an exercise scientist at Rutgers University and asked him about this. He said that there is a huge difference between working out two and three days a week. While any amount of exercise is an improvement over none at all, if you're already in decent shape, exercising for just two days a week won't get you much additional benefit.

Here's what he told us when we asked him how often you should exercise:

"A minimum of three days per week, for a structured exercise program. Technically, you should do something every day, and by something I mean physical activity - just move. Because we're finding more and more that the act of sitting counteracts any of the activity you do.

"So let's say you go work out for an hour a day and then you sit for the rest of the day - the health consequences are awful from the sitting standpoint. There's a recent study that just came out on that. So, you need to be active at other points in the day as well besides just the exercise.

"But there's an interesting split between exercising two days per week and three days per week, and it has to do with the frequency you stimulate the system. So with three days per week - you get significant gains early on, and you're going to want to progress beyond that three, ideally. Two days per week, you don't get much change - you just don't do it frequently enough to have some of the other positive health outcomes that come along with it.

"In terms of resistance training - [you should do it] 2-5 days per week, it depends on the level you're at, in terms of how advanced you are and how you train your body. Early on we can get pretty good gains in kids and older adults with two days per week, but we still want to progress them pretty quickly to three or four days per week.