Thanks! I obviously would love to immediately jump into the ~5:30 mile I could run in high school, but coming from 450 that may not be possible and I definitely don't want an injury to set me back. I hadn't even planned on running until I weighed under 250, but I've been feeling good and thought I'd slowly start introducing it to build up my strength. The game plan is a 12-week schedule from that goes from walking to running incrementally. Last week I was walking 4 minutes and running 1 (a ~13 minute mile pace) for 30 minutes and today I increased that to alternating 2 minutes running, 3 minutes walking (an ~11-minute mile pace).
Last week I was starting to feel my knees - not really pain, but I took it as a warning not to push too hard too quickly. Today when I started running for 2 minute stretches my knees felt fine but towards the end I was starting to feel my shins tighten. Like you, I can easily handle the cardio but my musculoskeletal fitness is still lagging...