Thanks. Great reply! Weight is not really a problem for me yet (according to this BMI index I'm underweight, fwiw), but this year I lost muscle and gained weig

Thanks. Great reply! Weight is not really a problem for me yet (according to this BMI index I'm underweight, fwiw), but this year I lost muscle and gained weight (in fat). I'd like to reverse that. My problem is with exercise: when I feel like exercising I do it like I used to be able to. But then the next few days I can't exercise because my muscles are sore and weak. And generally I have a hard time getting into the habit. I used to cycle ~120 km per week to school but now I live closer to school...so I used to burn one day's food by cycling and I'm not eating less now. I don't care about looks and muscles, but I'd like to get in shape to be able to run & cycle better again and feel fitter. What type of exercise do you recommend? How do you motivate yourself to exercise?