My 17-year-old type-1 daughter is a competitive swimmer, and I know that during her swim season she has to reduce her
insulin by a fair amount, and still she sometimes gets lows that can really take it out of her. She's also on the pen system, which has worked well for her. Is your son on Lantus (glargine) at night? When she switched to that, with Novolog at mealtimes, her numbers stablized and she has since then had fewer lows during workouts.