Friday, May 06, 2011

The Avoirdupois Problem, part III

I'm starting to think about my preparations for a fast fall marathon (sub-4hrs), half marathon,  and 10k.

Initial realization:  I need to lose some weight and the earlier I start the better. If I want to be fast, I need to be light.

Way back  I spoke about my original return to slimness after becoming an porky blob with terrible lipid numbers. I didn't have to count calories or anything, I just reduced my food intake while I gradually upped my miles. I have managed now to stay in the 169-173 lb range for the last couple of years without effort.


After the recent trip and generally low mileage weeks I've floated up to 175.  And..while back I bought a fancy new scale with a body fat readout and it's been saying that I have 24% body fat. This number was kind of shocking and I've been ignoring it. But it's probably not that far off.

I don't look like I have 24% body fat to most people: I'm 6'1" tall and have the kind of body that accumulates fat all over rather than just on my stomach. Kinda like an all-over wet suit.

However, if true, it's actually good news in a perverse kind of way because it means I have a lot to lose safely, and therefore a lot of speed to gain.

I recently read Matt Fitzgerald's book "Racing Weight" and he suggests that for somebody of my age a target percentage of 8-17% is reasonable. 

(As you get older you accumulate fat on your internal organs and it is not possible to lose this fat in an easy way. Try to get too low on your fat percentage and you will slow down because you lose muscle mass rather than just fat.)

If that 24% number is true, that means that at 174 lbs I have 43 lbs of fat. 174 - 43 = 131 lbs of lean body mass.

At 17% body fat,  I would need to get down to 157 lbs  (131lbs lean and 26 lbs fat)...i.e. lose 17 lbs. At 15% body fat,  I would need to get down to 154 lbs  (131lbs lean and 23 lbs fat)...i.e. lose 20 lbs. This is basically what I weighed in college. Zowie.

Hitting these weights is not going to be easy. I found before that below 170 lbs I need to really work hard to get the weight lower. Matt's book has a lot of good ideas about how to push down to these kinds of percentages.

How much speed can I gain from getting down to 154? One site says a rule-of-thumb is "2 seconds per mile per pound"..for a 20 lb loss that would be 40 seconds per mile or about 17 minutes in a marathon...not bad! But a fixed delay per pound seems overly simplistic: if you weigh more an added pound is less noticeable and therefore should have less percentage effect.

A science derived calculator is  here .  It allows you to play around with both age grading and weight grading...I get a result of about 11 minutes for dropping 20lbs (again, for the marathon distance). (To use for weight grading only: enter your stats and note your age/weight graded time, now change your weight to your target and speed up your entered race time until the age/weight graded time is the same as noted before.)

On hilly trail courses I suspect the benefits from being lighter are much much greater than either of these estimates (probably 1% improvement in pace for every 1% weight lost). In addition, Matt F quotes studies that report having fat on your legs (like me) is more of a handicap than fat on your belly (because your legs are moving back and forth I assume). So I think 11 minutes for a marathon is a lower bound.

There are training advantages to being lighter besides the immediate racing speed. For the same amount of time, you are logging more miles, which builds even more fitness. Or you can keep the paces as before and reduce the stress on your body and really build up the miles (if you have the time).


So far, I'm suspecting  this 24% number (actually 23.8 this morning ;) may be a bit high, so I'm going to get a better reading in a water tank with these guys in a couple of weeks to calibrate the scale. So if the tank says 21% I know that the scale reads 3% too high.

I'm also getting  BMR (base metabolic rate) testing just for fun. As I get closer and closer to the target weight it will get more and more difficult to lose weight....counting calories should help make sure I am down enough to do the job, but not losing too much and mess up my training or losing muscle. Getting BMR from a measurement, rather than an estimator tool will make this a lot more accurate.

Both of these tests together only cost $90, so it's not that big a deal. Besides, science is fun! 8)


Only about 15 miles for the week so far, I've been recovering from the jet lag which takes a while. Last night I slept 10 hours straight and feel a lot better today. 

The plan for the weekend  is a 7-10 miles on Saturday and 15-22 on Sunday, with pace and distance totally guided by how I feel. This will be my first long run since the S2S on April 10th....I really like my long weekend runs and have been missing them (due to 50k recovery and then travel)!

Sunday will be two weeks out from Copenhagen, marathon #7 in the year-of-8!  Since my mileages are low I don't really worry about tapering that much...we have this down to a science now ;) 

The only interesting wrinkle (besides the usual weather variable) will be the effect of jet lag. I'm flying in a few days before, but not enough to adapt fully. 

PS: Still no medal or coaster in the mail from S2S. Bah.


  1. You are a man who likes to crunch some numbers! All interesting stuff, though. I have no doubt you'll get where you want to be. It's worth it, no?

  2. Good stuff, Paul! Entered my 1/2 marathon data and my Weight Age Graded Time is 1:34:17... awesome.

    Good luck to your weight reduction goal and to your upcoming race.

  3. No medal? Oh geez. I got mine a few weeks ago, but no coaster, I dare not dream that big. I think I might get the same tests you are getting; they sure look fun. And I too, could buckle down and lose 10 pounds.

  4. Excellent post, Paul...a real interest of mine. I'll bet that your "hunch" about your BFP by the "scale" (I'll assume the manufacturer's name starts with a "T") is correct, i.e., your true BFP is a bit lower. You'll notice a big positive difference if you get down to 160-162; probably much less so below that, and you might feel hungry and tired to the point where it interferes with running performance and life in general.

    We had a great run and hike in BB last weekend. Small group which made it really nice. Did Pinnacles and the coast and now back in Tall Tree enjoying the cooler weather today. Hope your runs go well. Where do you usually do your running? Have fun, Ann


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