Monday, 06 March, 2006
Pushing the limits
One of the informal measures I use to determine my level of fitness is to see which is stronger: my legs or my heart. If my legs are pumping as hard as they can, screaming "Stop!" while my heart is chuckling, "Is that all you got, Bub?", then I know that my legs need a little work. Give me a month or two of training and my legs will be screaming down to engineering for more power and ol' Scotty will be crying, "I canna give it any more, Captain! She's about to blow already!" Spock, by the way, is deep in meditation hoping that the madness that has infected the human crew won't claim him. Chekov is staring blankly at the viewscreen, plotting a course for Boobella III where the women are busty, blonde, and very friendly.
It doesn't take too much training for my legs to outpace my heart. My maximum heart rate, according to the "220 minus age" rule of thumb, is 176 beats per minute. When I'm out of shape I have a tough time getting my legs to push my heart that hard. But when I've been training regularly I can push my heart rate to 190 and keep it there for five or ten minutes. My doctor about jumped out of his skin when I told him that, and ended up giving me a five minute lecture about how there's no significant cardiovascular fitness gain by pushing my body that hard and that by doing so I risk tearing plaque from my artery walls (assuming there is any) and causing an instant heart attack. I decided that I won't tell my doctor about those experiments any more.
He's right, though. From a cardiovascular fitness standpoint, you gain almost nothing by pushing your body beyond about 80% of your maximum heart rate. The ideal aerobic exercise range, and where your body burns fat most efficiently, is between 65% and 80%: in my case between 114 and 141 beats per minute. Pushing beyond that you enter anaerobic territory, where you're starving your body of oxygen and burning muscle glycogen rather than fat. It's great training for professional athletes who regularly push their bodies to the limit, but mere mortals should be very cautious about exercising that hard.