Pedalling Technique: why pedalling fast is more efficient

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Elsewhere we have explained 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 newly published paper 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 pedalling.
我们已经在其他文章里面说明过了，自行车手不管是在山路还是平地，快速蹬踏（大约80-85rpm）比慢速蹬踏的时候效率要高。一份最新发表的文章表明，这和快收缩肌纤维在低频率大力量蹬踏时候的肝糖快速耗尽有关系。

To determine the actual effects of slow and fast pedalling on leg muscle cells, scientists at the University of Wisconsin and the University of Wyoming recently asked eight experienced cyclists to cycle at an intensity of 85% VO2max for 30 minutes under two different conditions. In one case, the cyclists pedalled at 50 rpm while using a high gear. In the second case, the athletes pedalled in a low gear at 100 rpm. They were travelling at identical speeds in the two instances, so the athletes’ 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.
为了检验慢速和快速蹬踏对腿部肌肉细胞的实际效果，美国威斯康星大学和怀俄明大学的科学家们找来了8位有经验的单车手，分别在两种条件下，用他们最大耗氧量（VO2max）85%的强度骑行30分钟。一组车手用高齿比以50rpm的踏频骑行。另一组车手用低齿比以100rpm的转速骑行。在两种情况下，他们的速度完全相同。因此50rpm踏频的车手腿部肌肉的收缩是需要非常用力的，而100rpm踏频的车手蹬踏用力相对轻松，但是频率更高。结果显示，两组运动员的氧气消耗水平几乎相同，心跳和呼吸频率、总体的做功效率、血液的乳酸水平也几乎相同。

However, the 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 cells lost comparable amounts of glycogen at 50 and 100 rpm, but fast-twitch cells lost almost 50% of their glycogen at 50 rpm and only 33% 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 pedalling probably explains why slow pedalling is less efficient than faster cadences of 80-85 rpm. Basically, as the fast fibres quickly deplete their glycogen during slow, high-strength pedalling, 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.
然而，以50rpm骑行的车手分解肌肉里面的碳水化合物的速度更快，而用100rpm频率骑行的车手则更多的依赖于脂肪。50rpm时更快速的肝糖消耗仅存在于快收缩肌肉细胞。慢收缩肌肉细胞在50rpm和100rpm时消耗的肝糖量相等。但是快收缩肌肉细胞在50rpm时肝糖损失了大约50%，而在100rpm时损失了仅33%，虽然锻炼的回合只持续了30分钟。在低速、大力蹬踏时快收缩肌肉细胞里面碳水化合物的快速消耗可能解释了为什么低踏频没有80-85rpm的高踏频有效率。基本上由于快收缩肌纤维在低速、大力蹬踏的时候快速消耗了肝糖，他们的收缩会变得相对无力，所以更多的肌肉细胞会被调动起来以保持同样的速度，结果就是更多的氧气消耗和更低的效率。

Admittedly, this scenario – in which slow pedalling preferentially pulls the glycogen out of fast-twitch muscle cells – may sound a little odd to you! Fortunately, the paradox isn’t really too troubling; after all, slow pedalling 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 required to move the bike along rapidly.
在这个例子里面，低踏频更容易消耗快收缩肌肉里面的肝糖，也许听起来比较奇怪。其实这并不矛盾，因为低踏频是和高齿比和大力蹬踏联系在一起的，而高踏频是和低齿比和轻松的肌肉收缩相联系的。因为快收缩肌肉比慢收缩肌肉更有力，快收缩肌肉在低速的情况下工作，需要更多的肌肉力量来推动单车前进。

On the other hand, ‘fast’ pedalling 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 pedalling 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 brethren!
另一方面，80-100rpm的蹬踏频率对于慢收缩肌肉是不困难的。慢收缩肌肉每分钟可以收缩80-100次，可以轻松的应付低齿比所需要的力量。威斯康星-怀俄明研究的另一个看似矛盾之处就是高踏频导致更高的脂肪消耗。最大的脂肪燃烧通常是和低频率的运动联系在一起的。100rpm之所以有更高的脂肪分解是因为慢收缩肌肉细胞在处理高转速低力量的收缩。慢收缩肌肉相比快收缩肌肉而言是更好的脂肪燃烧机！

Fortunately, there’s a bottom line to all this: during training and competition, cyclists should attempt to use fast pedalling rates of 80-85 rpm, both on the flat and on inclines. Compared to slower cadences, the higher pedalling speeds are more economical and burn more fat during exercise. Ultimately, the high pedalling rates also preserve greater amounts of glycogen in fast-twitch muscle fibres, leading to more explosive ‘kicks’ to the finish line in the closing moments of races.
幸运的是，我们只要记住要点：在训练和比赛的时候，不管是平地和上坡，车手应该用80-85rpm的快速踏频。相对于慢速的踏频，更高的踏频更经济，可以燃烧更多的脂肪。最后，高速的踏频也可以在快收缩肌肉纤维里面保存更多的肝糖，这样在比赛的终点可以有更大的爆发力。

(‘The Effect of Pedalling Frequency on Glycogen-Depletion Rates in Type I and Type II Quadriceps Muscles during Submaximal Cycling Exercise’, European Journal of Applied Physiology, vol. 65, pp. 360-364, 1992)

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