Is it OK to work out during the Two-Week Test? (Also: why have I gained weight during the Two-Week Test)?

It’s perfectly fine to work out or train, but it’s important to do so only at a low intensity. At MAF, we define “low-intensity training” as all the training that occurs below the MAF HR (Maximum Aerobic Function Heart Rate). This is because during the Two-Week Test, you are eating very few carbs, which means that your muscles, in turn, don’t have as many stored carbs (a.k.a. sugar) as usual. Also, you start to burn a greater percentage of carbs the higher above the MAF HR you go. So, the combination of not having carbs and asking your body to exercise in an intensity that asks for them produces the perfect storm.

In order to increase the supply of sugar, your body produces cortisol, which is the major stress hormone. So, when you have very little sugar to begin with, and you train at a high intensity (that asks for a lot of sugar), your body has to release massive amounts of cortisol in order to provide the requisite sugar. This means that training above a low intensity when you also don’t have a lot of sugar stored in your muscles is NOT a good idea—medium- or high-intensity training is a lot more stressful than usual.

In fact, we can generalize this to all stresses: if you are stressed out at work, or have an argument, a greater percentage of your energy comes from sugar (although you may not be using that much more energy overall). But the same thing happens: when you are in a low-carb diet and stressed, the stress becomes compounded. If this happens over and over (or the stressor lasts for a few days) you might begin to see the some of the beginning effects of chronic cortisol levels in the body—chief among them being weight gain and inflammation.

So it’s as important to do low-intensity training, as it is to keep a “low-intensity lifestyle” during the Two-Week Test.