Why 15-20 lb fat? How do you know? I would recommend:
1) get weighed in a tank (submerged in water) to determine your body fat percentage. In Los Angeles can have this done at a freestanding facility or a "truck" with a tank in it that goes to various locations for about $45; check the internet in your area for "body fat analysis" - you can get a "recheck" in 2-3 months for a reduced cost, like $10 in LA; NOT standing on a scale or calipers. High level MALE endurance athletes are 4-7% body fat. This is difficult to achieve without very high intensity and high volume training, so maybe shooting for 10% may be reasonable (I was weighed in a tank in college at UCLA for a study and was 6'0", 156#, 5.8% body fat, age 20, running 80-90 miles/week, 3 hard interval workouts/week, not that now); also need to consider your age;
2) to lose a pound of pure fat need to be negative about 3500 calories, or negative deficit of about 500 calories/day will lead to one pound/week (7 days x 500 cal/day = 3500 cal);
3) if you do not perform some level of upper body resistance work your muscle mass will "melt away" except for the legs; adding some weight/body weight exercises with core exercises will prevent some of this and allow you to maintain critical strength. Just look at most high level cyclists or marathoners (2:15 or less); lots of leg muscle, minimal upper body muscle mass; my perception is that when you calorie restrict and exercise heavily you lose "non essential" (ie. not being used for your primary activity) muscle mass equal to or faster than your fat loss; so do some core/dips/pull ups/sit ups/push ups etc. No need to "work" legs as you are running;
4) being lighter, if all the loss is body fat, will certainly increase your ability to run faster and preserve your joints and Achilles tendon; pure physics as you are moving much less mass over time and distance; also, since your heart and lungs are unchanged, your maximum oxygen uptake will rise as a purely mathematical function ie. if your maximum oxygen uptake is 50 cc/kg/min at 220# it will be 58cc/kg/min; of course, this becomes useful only if you are training hard;
5) assess your biomechanics. The human body is built to run and landing on your forefoot or midfoot allows you to utilize your Achilles tendon properly; landing on your "heel" is much less efficient. Look at a high level marathon on TV at the front pack; concentrate on viewing their heels only; 95% of the runners, even going 26 miles, never touch their heels to the ground. If you are running race pace on hard sand, if you look back at imprints, there should be little or no heel strike. Converting from a "heel" strike to landing on the forefoot should be done gradually over 2- 3 months to avoid injury; can start by gradually increasing the amount of time you land on your forefoot (like 30 seconds each mile, increasing 30 seconds each week) until you convert to total forefoot/midfoot landing. Although there is some
dis agreement over the "ideal" footstrike, I look at high performance athletes and anthropology (NATURE |VOL 432 | 18 NOVEMBER 2004 |
www.nature.com/nature
- "Endurance Running and the Evolution of Homo".
Hope this helps.