Yes it's pretty normal to experience hypos through heat and exercise, heat opens up the blood vessels which can speed up insulin absorption so it's best to either look at reducing your bolus injection (if on a bolus/basal regime) before exercise or on a hot day and regular testing as well as keeping a good stock of glucose nearby like fruit juice or glucose tablets.
As Juicyj said, it's a regular situation. Since I'm in a same boat with you, I'd recommend you to have a snack - apple slices for instance - before exercise. Consider training with a partner, if it's possible - it would be safer for you. And don't forget to measure your glucose level before and after exercising.