Maintaining Balanced Exertion Through Cadence and Gearing Selection

posted Aug 10, 2012, 11:07 AM by Donald Vescio   [ updated Aug 10, 2012, 11:30 AM ]
A good amount has been written on cycling and cadence, with many coaches and athletes assuming that higher pedal cadences (+90 RPM) are better than lower cadences.  Lance Armstrong's Tour successes often have been seen as predicated on his higher than average cadence selection, and a review of the hour record on the track indicates that almost all record holders pedaled in cadences in excess of 100 RPM.  Most professional cyclists will race at cadences between 90 and 105 RPM, and cadences in excess of 150 RPM are not uncommon in some events on the track.  Based on all of this observational data, it's easy to assume that one should ride in cadences greater than 90 RPM if one wants to be competitively successful.

But before we look at cadence specifically, it might be useful to describe how we generate power on a bike, which is directly tied to the cadences and gearing that we select.  Basic terminologies as applied to cycling:

1.  Strength: the amount of downward force or energy that  is applied to the pedals

2.  Torque: the ability to rotate the pedal/crank (strength is the limiter of torque)

3.  Power: the application of strength over time

4.  Speed: the register of power over distance

Power is delivered to the bike as follows:

1.  Pushing forward through the top-center of the pedal stroke

2.  Pressing down on the pedal on the down stroke

3.  Pulling back through the bottom-center of the pedal stroke

4.  Unweighting the pedal on the upstroke

Most elite cyclists focus almost all of their strength on pressing hard on the pedal during the down stroke, while trying to minimize the weight of the foot and leg on the upstroke.  In other words, elite cyclists don't apply force smoothly throughout their pedal stroke--they do not pedal circles, but rather they stomp down hard for a limited portion of their pedal stroke, while trying to reduce loss on the remaining portion of their cycle.  To go fast, they "stomp" down on their pedals.

Above is a representation of how force is distributed in a pedal stroke.  Note that the larger the arrow, the greater the force.  According to Broker, cycling power is the product of instantaneous crank torque and instantaneous crank angular velocity; what this means is that for a given average power at a given average RPM, instantaneous power (the power of a given moment) will fluctuate significantly through each pedal revolution.

Okay--now that we have some basic concepts out of the way, let's take a look at a simple way of describing power as applied to cycling:

power = force x angular velocity

A more expanded form of this description might look like this:

power =  ability to push really hard on the pedals x the ability to spin the pedals rapidly in a circle

Here's an easy way to think about all of this--in order to ride, say, 25 mph, a rider may need to generate an average power of 250 watts (power on a bike is measured in watts).  To achieve this average power that will enable the realization of this target average speed, I have two basic options:

1.  I can push down really hard on the pedals when I'm in a big gear (this emphasizes the force side of the power equation, which is tied to physical strength)

2.  I can spin my pedals really fast when I'm in a bigger gear (this emphasizes fitness)

Cycling cadence has a specific metabolic cost.  Athletes who are very fit and who have a high VO2 value have greater metabolic capacity than those who are less trained or who are less genetically gifted.  In practical terms, higher cadences generally result in higher heart and respiratory rates, which carry a high metabolic cost.  The fitter one is, and the higher one's VO2, the greater metabolic cost that can be carried.  Lance Armstrong's success was in part tied to his high sustained cadences, which were possible due to his tremendous aerobic capacity (think: he had a large metabolic bank account).

A low cadence carries an increased cost of muscular fatigue.  Pushing down really hard on the pedals while in a big gear requires a considerable amount of strength in one's quadriceps, hamstrings, and gluteus maximus; the cost, here, is muscular fatigue, which is the failure of muscular strength.   All riders are predisposed to cadences that average above or below the ideal 90 RPM marker--and this is perfectly okay.  In fact, the most recent thought is that a cyclist should simply self-select his or her cadence and not worry about cadence as an absolute value in itself--just let your body decide what is the most effective cadence for a given effort.

This is not to say that riders should ignore their cadence--far from it.  Rather, one should be attentive to cadence in relationship to its impact on one's perceived exertion.  Sounds complicated?  It really isn't.  We know that

1. That pushing down hard in a big gear results in a slow cadence that taxes the strength of our legs;

2.  That spinning a small gear results in a fast cadence that taxes our heart and respiration rates.

So, if you're in a race and you find that your heart rate is drifting up and your breathing is becoming quick, you can slow down a bit to recover (which never is good for one's performance!), OR you can shift to a bigger gear and decrease your cadence, which will shift greater emphasis to the force/strength side of the power equation, enabling your heart and respiratory rates to decrease.  Similarly, if you're in a race and your legs are getting tired and heavy, shift to a smaller gear and increase your cadence, which shifts emphasis to the part of the power equation that privileges fitness over muscular strength.

Successful cyclists will adjust their cadences and gearing not only to meet the challenge of changing terrain, but also as a way to balance out the various stresses placed on their muscular strength and overall fitness during the course of an event.    

Next Discussion: the myth of pedaling in circles.