I agree I also would not recommend that you carry out heavy exercises, because you are not eating all day this may make you ill. However some people are strong and can workout on an empty stomach. For this it is recommended that you workout just an hour before you can eat. I'm not sure that you can get away with calling yoga strenuousness. In fact its one of the toughest workouts I know of. Don't be fooled by all the kneeling, stretching and chanting. Yoga is no joke.For a low impact workout I would recommend walking.