She’s as skinny as a stick of macaroni

Elite endurance runners seem have one obvious physical characteristic in common.  They are lean mean running machines.   It makes sense – the lighter you are the less mass you must carry along for the 42.2 kilometre ride.  That translates to a lower energy expenditure in moving your body through space and potentially reduced impact on all your joints and ligaments.  According to an article posted in Runner’s World Magazine (which I have summarized here), the average runner will gain 3.3 pounds per decade (that’s about 3/4 inch in waist girth) even with mileage in the neighbourhood of 40 miles (60 klicks) per week.  As the years go by we start slowing because of our aging bodies and because of our expanding waistlines.  Fortunately, “fitness can trump fatness” and beyond BMI, activity level predicts longevity.  If your primary focus is on the health benefits of running you not need worry too much about those few extra pounds.

That extra six-pack may not shorten your life, but will it lengthen your run?  Popular opinion asserts a gain in weight means an increase in run time.  Many runners lament about the burden of carrying those stubborn extra ten pounds.  Some races even offer Clydesdale and Filly divisions for so-called heftier runners (usually 200 pounds+ for men and 150+ pounds for women), in addition to the typical age-graded categories.  Science supports this contention.  As a general rule, thinner is faster, so long as you lose bad weight (e.g. excess fat), not good weight (e.g. lean muscle mass or water).  It probably goes without saying, but as a public service message should be said anyway – less is not always more.  A BMI <18.5 and your risk becoming weaker and slower, not stronger and speedier (I will save you from my long-winded rant about this arbitrary BMI cut-off).  If you do have pounds to spare though, dropping a bit of weight – allegedly, even in the absence of additional training – should result in quicker race times. 

How much faster?  A healthy runner will race about 2 seconds per mile faster for every pound lost.  As your weight decreases your V02 max increases, allowing you to run farther and faster before oxygen debt (the point at which the demands outpace your ability to use oxygen to produce energy).  Not to mention that running feels easier, so you can train harder by increasing pace and distance which will also lead to faster race times.  At first glance two seconds doesn’t sound like much, but those seconds can really add up over a distance.

This table from Runner’s World provides an estimate of race time improvement with a drop in excess pounds and the associated changes in maximal aerobic capacity.  Caution: the following numbers may increase desire for weight loss.

Interested in how fast you would be if you were 25 years old and skinny (skinny = 110/142 pounds for females/males)?  Check out the Flyer Handicap Calculator.  It takes your current race times and using an algorithm computes your age/weight equivalency performance.  If I was 25 again (that sounds like a movie) I would finish a marathon a whopping 12 minutes sooner!  Egads, to be young(er) again.  With this nifty calculator you can compare yourself to running comrades of different ages/weights/genders.  All things equal, you may be surprised by who is  fastest.  Hours of fun.  And regret.

Sadly, I can’t turn back that age clock.  My 12 minutes speedier 25 year old self is a long gone.  But few of us would shed tears bidding adieu to a bonus pound or two.

Title Reference:  Larry Williams – Bony Moronie.  Released as a single.  1957.  Cover versions released by  Dr. Feelgood (1974), John Lennon (1975), and The Who (1994), to name a few.