Lately I've started to notice that my knees hurt for several days after any kind of “impact” activity such as running(even on sand) and sometimes even hiking. I think I might be developing “runner's knee” from years of running and constantly playing basketball. At this point, I'd rather just save my knees for squats, deadlifts, snowboarding, and surfing lol. On mornings that I feel like doing a little bit of HIIT, can you guys recommend anything that won't aggravate my knee condition? Are swimming and maybe just plain pushups/crunches/bodyweight squats good? And how exactly could I design them to fit into the 4:30 low-intensity and 30 second high-intensity intervals?(with sprinting it's simple 🙂