Forces During the Recovery Phase - Pulling Up
The experiments described indicate that the energetics of cycling are affected by the mechanics of the recovery phase. This leads to a second issue, that is, whether cyclists pull up during this phase. When asked, most cyclists' response to a question regarding the direction of force application during the recovery phase is usually unequivocal. They say they definitely pull up. This seems contrary to most of the data reported in the literature and general response of the elite riders whose data we have seen so far. The force-measuring pedal shown earlier (see Figure 5 [photo of a lab pedal with toeclips and some kind of a strain gauge]) is obviously ideal to investigate this question....

When our measurements determine that the pedal is unloaded, the riders are actually pulling up to some degree. To unload the pedal during the recovery phase, they must overcome two forces, the first is the weight of the leg that gravity is pulling down against the pedal. The second is a force resulting from inertial effects - the tendency of the limb mass to resist the motion of the pedal. This second force would be present even in the absence of gravity. Our definition of pulling up is when the rider overcomes both of these forces and then applies more force so that an upward force is actually acting on the pedal.

In all of our studies of steady-state riding of the elite 4,000-m pursuit team and of recreational riders, we found only a few examples of pulling up. Some cyclists did exhibit unloading of the pedals during the latter portion of the recovery phase (315° to 360°) but rarely did they pull up. Typically, the pull-up forces, when they existed, were small and applied over a short duration.

These data are certainly contrary to the expressed opinion in a number of magazines [1986] suggesting that pulling up on the pedals could result in a 30% increase of efficiency. If changes in economy of riding were to be that large, surely the elite cyclist woudl pull up. Because no evidence supports the popular claims, we must question whey riders in laboratory experiments do not pull up. The literature on this issue has been specific and reproducible over a number of years and in different laboratories. Hoes, Binkhorst, Smeekes-Kuyl, and Vissers (1968), Gregor (1976), and Lafortune, Cavanagh, Valiant, and Burke (1983) have reported the absence of pull-up forces in the recovery phase. The one condition common to all of these investigations is that the riding is similar to high-speed riding on the level, it does not replicate sprint or climbing hills. The situation regarding pull up will change during these events.

We have conducted one experiment involving low inertial load. In this case, had the cyclist stopped pedaling, the cycle would also have stopped rapidly. As we can see in Figure 16, the subjects (recreational cyclists) did pull up between positions 15 and 20 with forces that reached a maximum of approximately 70N (15 lbs). In fact, they did not exert negative torques, even in positions 10 through 14, where most riders tend to show negative torques (see Figure 4 [Not displayed here])....