Hi welcome to HCM I have gone thru your query regarding cramps in the rear thigh during stretches in the rear thigh during stretches . I can unerstand your concern Dear ,cramps can occur due to many reasons ,one of them is supposed to be , lack of water content in our body . It is suggested to include lot of water in your daily regime besides all essentisl nutrients and supplements full of antioxidants for stronger immunity with all the workouts you are following . It is welcoming fact that you been doing 3 pilates/yoga combination classes for 5 weeks now and you feel much more supple and fitter . Now , as you have realised the importance of yoga combination classes you should keet it up for life so that your immune system stays stronger to help you stay diseases free life ahead . Avoid processed foods carbs , sugar , fried ,fast foods , Tea , coffee ,alcohol and smoking , stress and Constipation all will produce biochemical and metabolic conditions in your body that will decrease your immunity, so avoiding is definitely the first step in the right direction to detoxing the body, boosting the immune system . All are the pillers of our strong immune system responsible for healthy disease free life Take Hoeopathic Cuprum Met 30 / 2-3 doses / 1/2 hourly . for relief from cramps . Always remember, if pain is severe or incapacitating, please see your doctor / professional Hope this helps solves your query .Take care .All the best .Get well soon Don t hesitate to come back in case of any further query .