by Doug Rennie, Portland Velo's own "Health & Fitness Guru"
There's one question I am continually asked at rides:
"Doug, how'd you ever come by such a set of guns? How can we get arms like yours?"
Well, in some future Fit Bit, I'll share with all of you my Secret Biceps-Building workouts.
But not this time. Sorry, brothers and sisters, but this month it's all about, you know, becoming better on your bike.
I'm sure you've all heard, ad nauseum, that Fast Pedaling Makes You A More Efficient Bike Rider. It's been well-established in a bushel of studies that cyclists are usually more efficient on both hills and flat terrain when they crank it quickly rather than at slower cadences. Now we're not talking here about whirling away like some rabid hamster on crack. No, we're talking 80-85 rpm, something in that range.
Well, here's more proof for you sassy Big Gear Grinders: a pair of recent studies 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 compare 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 (pretty damn hard, but well below Croak City levels) under two different conditions. In one case the cyclists pedaled their bikes at 50 revolutions per minute (rpm) while using a high gear (Owwwwwww!!!). In the second case, the athletes (this would be the wise ones) spun away in a low gear at 100 rpm.
To really nail this thing down, both groups were traveling at identical speeds, so their leg-muscle contractions were "quite forceful" (gee, yuh think?) at 50 rpm and moderate - but more frequent - at 100 rpm.
Now, here's the shocker: Riders' 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.
But.
The Big Gear 50-rpm-ers broke down the carbohydrate in their muscles at a greater rate, 
while the 100 rpm cadence flipped one of those physiologoical switches that produced a greater reliance on fat. The greater glycogen depletion at 50 rpm occurred only in fast-twitch (speed/power) muscle cells. Slow-twitch (endurance/stamina) muscle cells lost about the same amounts of their glycogen at both 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.
How come?
Because as the fast-twitch fibres quickly deplete their glycogen during slow, high-strength pedaling, their contractions (gradually and inevitably; all you have experienced this kind of power drain) 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, hard 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 big gears and high muscle force, while fast cadences are associated with low gears and (relatively) easy muscle contractions. So, since fast-twitch fibres are more powerful than slow-twitch cells, the fast twitchers get the immediate call to arms at slow cadences because 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 burning even though max fat burning is usually linked with slow-paced efforts. Still, the higher fat burn rate at 100 rpm DID OCCUR because the slow-twitch cells handled the fast-paced, low-muscle force contractions. And, as you know, slow-twitch fibres are much better fat-burners than their fast-twitch partners.
Confused?
Welll, fortunately, there's a bottom line to all this: 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.
So now you know. To ride faster, longer without muscle meltdown spin, don't struggle. And make a few more withdrawals from your Adipose Tissue Bank as a bonus.
Until next month – pedal fast, not hard.
~Doug