I am just starting the STS program. Is it all right to do Hiit workouts like Crossfire on the days I am not doing the STS workout? Or is that too much?
It is fine to do crossfire during cardio days. When it is done effectively it does demand a lot to the body and create a metabolic response. Which means you get an afterburn during 24 hours following cardio day. Twice per week is the maximum recommended.