Tensing your muscles has been shown to release endorphins and make you feel better. But it does not tone them, although many people believe that it does. We have long known about the power of exercise to relieve stress, improve moods, increase energy levels and even fight chronic diseases like high blood pressure. The problem is that most people don’t do enough physical activity on a regular basis to get all these benefits.
And tensing muscles doesn’t count as such an activity because tense muscles are not under any load and thus don’t burn any calories or build up strength in the way that running, weight-lifting or other forms of exercise do.