Teen with SMA type 3

In Sept 2015 my 15 year old started getting cramps and extreme fatigue. He was trying out for basketball in HS but couldn't keep up. Before that he's always been very athletic, playing all the sports his school offered, riding his mountain bike, snowboarding, etc. I took him to his doctor in Oct and he was finally diagnosed in April. At first they thought he had Limb Girdle Muscular Dystrophy and so he was not doing any exercise. Now we understand that moderate excerise is good for him and will help him maintain his strength. He's also on a healthy diet of good fats, proteins, low carbs and very low sugar.