Quote Originally Posted by Tuckervill View Post
I'm concerned that it's not safe, either--after a minute of squat thrusts I'm at my max? A sprint of maybe a 10th of a mile? Can this be healthy?
If you doctor has given you the green light, i.e. you don't have risk factors, your resting HR is under 100, you don't have a family history of heart condition or anything would be indicative of a heart condition, I don't think there would be a problem hitting your max quickly. Of course you would have previously warmed up.

I think a good fitness yardstick is not so much how fast your HR goes up but how fast it goes back down when you enter a recovery phase. As you train, your heart will become faster at adapting to what you're asking it to do: you need it to push a lot of blood and oxygen down to your muscles, it beats fast; you stop running and need less blood, it slows down.

Remember that fitness builds up during recovery...

This being said, I'm no physiologist or cardiologist so this is all based on my experience and readings...