Just like the anatomy of a track cyclist, the subject matter at hand requires several units in a bachelor’s degree and several more for postgraduate studies. I’ll just share with you the essentials of cycling physiology. Physiology in a track cyclist is similar to that of a road cyclist after all everyone shares the same human anatomy.
When it comes to measuring cycling performance, sports medicine specialists, and sports physiologists turn to several parameters. In published studies, one of the most important and widely used is the Gross mechanical efficiency. So what is Gross mechanical efficiency? It can be summarized as follows:
1. ratio of mechanical work performed to energy expended metabolically
2. energy expended internally is determined via indirect calorimetry from analysis of expired gasses; 1 liter of O2 uptake = 20.9 kJ (Watts per liter is referred to as“economy”)
3. efficiency has a high positive correlation with % of slow-twitch (Type I) fibers present in the working muscles
4. efficiency is not determined by pedaling technique, in fact, elite riders produce more power simply by ‘stomping’ harder (exerting greater downstroke force) rather than pedaling more smoothly or pulling up
5. efficiency is more “rigid” (resistant to training) than VO2max and lactate threshold, but can be improved through longer rides that fatigue Type I fibers, causing Type IIb fibers to be “called up,” fatigue, and be converted to Type IIa, which behave more nearly like Type I
So then let’s discuss the energy systems utilized in cycling.
1. the majority of energy supply during any single event over 75 seconds is from aerobic sources
2. in three 30 second bouts of maximal exercise, each separated by complete recovery, most of the energy utilized by the third bout came from aerobic metabolism. This is even more pronounced in continuous exercise, such as a road race,where intensity is much lower and there recovery in between sprints is incomplete.
3. the extent to which limited anaerobic energy reserves are taxed (and blood lactate is produced) depends on how much and often lactate threshold is exceeded, therefore, the higher it is, the less they are called on, and the more available they will be when needed
4. in the context of any road (i.e., endurance) event, how quickly one recovers from short, intense efforts is actually more reflective of aerobic, not anaerobic fitness, since a) 100% of ATP resynthesis within fatigued muscle occurs via aerobic metabolism, and b) the rate of ATP resynthesis is correlated with mitochondrial respiratory capacity
5. road racing categories and time trial performance both correlate much more highly with sustainable threshold power than with anaerobic capacity or sprinting power
Body Mass and Cycling:
1. Power output scales with body mass raised to the 0.67 power. In other words, expressing power output as W/kg0.67 accounts for differences in body mass.
2. The power requirement to ride at a given velocity on flat terrain increases with body mass raised to the 0.32 power. In other words, expressing the power requirement as W/kg0.32 accounts for differences in body mass.
3. The power required to climb hills (of sufficient steepness) increases with body mass raised to the 1.00 power. In other words, expressing the power requirement as W/kg accounts for differences in body mass.
4. Combining facts #1 and #2 explains why larger riders tend to do better on level terrain: power output goes up more rapidly with body mass than does the power requirement (i.e., 0.67 > 0.32).
5. Combining facts #1 and #3 explains why smaller riders tend to do better going uphill: power output doesn’t go up as quickly with body mass as power requirement (i.e., 0.67 < 1.00).
6. Although there are, to some extent, “horses for courses,” individuals with a very wide range of body sizes can be equally competitive as a result of variations in terrain, as well as the effects of drafting.
Determinants of Endurance Performance
1. Performance in endurance events (>3 minutes) has 3 determinants:
a. maximal oxygen uptake (VO2max) – sets the upper limit of steady-state energy output
b. lactate threshold – determines the percentage of VO2max that can be utilized on a prolonged basis
c. gross mechanical efficiency – relationship of work output to energy expended
2. VO2max is largely (though not entirely) determined by genetics, but lactate threshold depends on muscular factors such as capillary and mitochondrial density, which associate with years of specific training of sufficient intensity and volume. Gross mechanical efficiency is directly proportional to the % of Type I (slow-twitch) muscle fibers present in the working muscles.
Always remember: Cycling is an aerobic sport!