Regular exercise increases insulin sensitivity.
Endurance athletes who treat their diabetes with insulin may sometimes reduce the amount of insulin they inject while training.
Because insulin is absorbed more rapidly from sites involved in physical activity, before exercising it is best to inject into a site not especially taxed in your activity (the stomach, for example).
It is important to discuss your medication with your diabetes care team, who will advise you on the most appropriate treatment and any changes that need making to your normal regime.