Carb wisdom - Triathlon Week

sfricks · 03-07-2006, 05:31 AM

Here's an article I picked up and thought I'd share...

Dr. Gabe Mirkin's Fitness and Health E-Zine
March 5, 2006

Low-Carbohydrate Diet Slows Time Trial

A recent study from South Africa shows that eating a
low-carbohydrate diet slows extended sprint performance of
cyclists (Journal of Applied Physiology, January 2006).
Competitive bicycle racers ate a high fat or high-carbohydrate
diet for six days followed by a high-carbohydrate diet for one day
and completed time trials on their bikes. Then they ate the
opposite diet for six days followed by a high carbohydrate diet for
one day and repeated their time trial. Diets did not affect their
times or power output for 100 kilometers (62 miles), but the high
fat diet slowed their sprint performance over one kilometer (0.6
miles.)
Muscles get their energy from sugar and fat stored in
muscles or from the bloodstream. The limiting factor in how fast
an endurance athlete can exercise is the time it takes to transport
oxygen from the blood in the lungs to the muscles. Muscles
require far more oxygen to burn fat than to burn sugar for energy.
So when a muscle runs out of its stored sugar, called glycogen,
it becomes less efficient, hurts, is difficult to co-ordinate and
slows you down.
Many previous studies show that it doesn’t make any
difference what an trained endurance athlete eats on the week
before competition because the muscles of trained athletes store
the most glycogen when they reduce training for several days,
regardless of what they eat. Any sprint that takes less than 50
seconds is not affected by diet, because you can work up to 50
seconds anaerobically, without requiring additional oxygen. This
study shows that a high-fat diet before extended sprinting hurts
performance. A high fat diet causes muscles to burn a higher
percentage of fat. Using fat for energy requires more oxygen
than carbohydrates do, and how fast you can sprint 0.6 miles on
a bicycle is limited by how rapidly you can deliver oxygen to
muscles. Restricting carbohydrates before a sprint taking more
than 50 seconds increases oxygen needs which slows you down.