Why when I start cardio

[Mr I]

Can't I sleep for shit

[Bouncer]

kicks up CNS and metabolism would be my guess.

[TrapsBrah]

I had a similar issue when I could do cardio later at night before going to sleep. Try switching it to early in the morning or just drink some alcohol it's a cns depressant.

[Trestan Jacob]

Doing it right before bed may make it harder to sleep. Cardio is a better bet in the morning I'd think.