Why fast pedaling makes cyclists more efficient.
(Reproduced
with the kind permission of Peak Performance Newsletter)
RECENTLY we reported that cyclists are usually
more efficient on both hills and flat terrain when they pedal
quickly (at about 80-85 rpm) rather than at slower cadences. Now,
a new study suggests that the greater efficiency may be related
to the rapid rate at which glycogen is depleted in fast-twitch
muscle fibres during slow, high-force pedaling.
To determine the actual effects of slow and fast pedaling on leg-muscle
cells, scientists at the University of Wisconsin and the University
of Wyoming asked eight experienced cyclists to cycle at an intensity
of 85% V02max for 30 minutes under two different conditions. In
one case the cyclists pedaled their bikes at 50 revolutions per
minute (rpm) while using a high gear. In the second case, the
athletes pedaled in a low gear at 100 rpm. The athletes were traveling
at identical speeds in the two instances, so their leg-muscle
contractions were quite forceful at 50 rpm and moderate - but
more frequent - at 100 rpm.
As it turned out, the athletes' oxygen consumption rates were
nearly identical in the two cases, and heart and breathing rates,
total rate of power production, and blood lactate levels were
also similar. However, athletes broke down the carbohydrate in
their muscles at a greater rate when the 50 rpm strategy was used,
while the 100 rpm cadence produced a greater reliance on 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 per cent of their glycogen at 50 rpm and only 33 per
cent 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 fibres 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 fibres
are more powerful than slow-twitch cells, the fast twitchers 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
fibres are much better fat-burners than their fast-twitch neighbours.
Fortunately, there's a bottom line to all this: during training
and competition, cyclists should attempt to use fast pedaling
rates of 80-85 rpm, both on the flat and on inclines. Compared
to slower cadences, the higher pedaling speeds are more economical
and burn more fat during exercise. Ultimately, the high pedaling
rates also preserve greater amounts of glycogen in fast-twitch
muscle fibres, leading to more explosive 'kicks' to the finish
line in closing moments of races. (European Journal of Applied
Physiology, 1992)
This kind of information is available on a regular basis in the
monthly Peak Performance
Newsletter online or in print |
