Sceptically Fit

23/10/2011

Cycling fast preserves glycogen and burns fat.

Filed under: Exercise — Sceptically Me @ 00:45

A new study has found that cycling by pedalling fast is more efficient than cycling at a slower cadence but greater force (ie a higher gear). Oxygen consumption, heart and breathing rates and blood lactate levels were very similar between both sets of cyclists. The key difference was that cyclists pedalling at the faster rate had a higher utilisation of fat.

The greater glycogen depletion at 50 rpm occurred only in fast-twitch muscle cells. Slow-twitch muscle cells lost comparable amounts of their glycogen at 50 and 100 rpm, but fast-twitch cells lost almost 50 percent of their glycogen at 50 rpm and only 33 percent at 100 rpm, even though the exercise bouts lasted for 30 minutes in each case.

This rapid loss of carbohydrate in the fast-twitch cells during slow, high-force pedaling probably explains why slow pedaling is less efficient than faster cadences of 80-85 rpm.

Basically, as the fast fibers quickly deplete their glycogen during slow, high-strength pedaling, their contractions become less forceful, so more muscle cells must be activated to maintain a particular speed. This activation of a larger number of muscle cells then leads to higher oxygen consumption rates and reduced economy.

This scenario, in which slow pedaling pulls the glycogen out of fast-twitch muscle cells, may sound paradoxical but it isn’t; after all, slow pedaling rates are linked with high gears and elevated muscle forces, while fast cadences are associated with low gears and easy muscle contractions.

Since fast-twitch fibers are more powerful than slow-twitch cells, the fast-twitch fibers swing into action at slow cadences, when high muscular forces are needed to move the bicycle along rapidly.

On the other hand, “fast” pedaling rates of 80-100 rpm are not too hot for the slow-twitch cells to handle. Slow-twitch cells can contract 80-100 times per minute and can easily cope with the forces required to pedal in low gear.

Another possible paradox in the Wisconsin/Wyoming research was that fast pedaling led to greater fat oxidation, even though maximal fat burning is usually linked with slow-paced efforts.

Basically, the higher fat degradation at 100 rpm occurred because the slow-twitch cells handled the fast-paced, low-force contractions. Slow-twitch fibers are much better fat-burners than their fast-twitch neighbors.

 

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