Efficiency? The Metabolic and Mechanical Considerations

Many times, discussions about pedaling technique start with “what is most efficient”. Depending on who you are speaking with or what research you are viewing, efficiency can be defined differently.

Metabolic Efficiency

To an exercise physiologist, efficiency is defined as the cost for the amount of work performed. The cost is often measured in METs (the metabolic equivalent). This is a measurement of the energy demands of exercise. The work is measured as power (or watts / joules). Using an ergometer (bike) and metabolic testing equipment, we can determine how much energy it takes to do a certain amount of work.

Piston vs. Smooth/Circular Pedaling

Numerous debates are still going on concerning which is most efficient: (1) solely pushing down (piston) or (2) pulling up, over, down and back (circular). Research has shown that there is little to no difference in energy cost with either pedaling style (when riders are setup correctly and using proper form).

Does this make sense?

Absolutely. Plainly speaking, pushing down on the pedals uses your glutes (butt) and quadriceps muscles. The rest of the pedal stroke uses the hamstrings (pulling back), hip flexors (pulling up) and calves (stabilizers). Whether you are using predominantly one set of muscles or spreading the work over multiple muscles is going to require the same amount of overall energy (More on muscle usage in Part 2).

Here is a grossly simplified example:

If you use 100% Quadriceps vs. 70% Quadriceps / 30% Hip Flexors, the total is still going to equal 100%. The energy cost is going to be the same. The body just uses a little less of one muscle and supplements another.

Since there is no difference in the energy requirement, one could conclude that their is no benefit to one pedaling style over another. But is metabolic efficiency the best or only way to determine this? Are there other considerations? The answer is yes. Read on.

Mechanical Efficiency

Biomechanists and Kinesiologists look at efficiency through another lens. They are concerned with the mechanical movement and the forces that are being applied to joints and muscles. The physiologist will say “it doesn’t have to look pretty, it just has to be metabolically efficient”. The biomechanist and kinesiologist cringe at someone bouncing, mashing and muscling a bike in an attempt to produce power because they understand that the muscles and joints are being abused in the process.

A piston style of pedaling will place all of the force of the pedal stroke on the knee during the down-stroke. Since no other muscles are being used with this style of pedaling, all of the force needs to be generated during the down-stroke. This places a considerable amount of stress on the knees, more specifically, the patella tendon/ligament. Now if you consider that you will pedal an average of 10,000 rotations per hour, that is quite a bit of concentrated stress on the joint, connective tissues and muscles that act at the knee.

This touches on an issue biomechanists and kinesiologists have with current research: Most, if not all, of the studies that were conducted only required cyclists to ride at high intensities for less than an hour. The effects of mechanical inefficiency generally occur when attempting to maintain moderate to high intensity beyond an hour. These effects would impact endurance, fatigue and the ability to sustain consistent power output. Since cycling is an endurance sport, and many of us ride longer than an hour most of the time, the current research is not replicating the true demands of our sport. Additionally, the longterm effects of mechanical inefficiency can lead to over-use injuries due to the repetitive stress on the knee joint (more on this in Part 8).

In Summary

Efficiency may not be the best method (or term) to use when trying to examine the benefits of piston vs. circular/smooth pedaling style. There are metabolic and mechanical factors that need to be considered. Cutting-edge research is looking into the neurological stress on the body during exercise. It will be interesting to see how new discoveries in this area enlighten our current understanding of how the body works and responds to the stress of exercise.

Next we will dive deeper into which muscles power which part of the pedal stroke. We will also consider whether using a certain muscle or muscle group is effective or ineffective in generating power.

As a coach and educator, the issue of pedaling technique comes up quite a bit.  I’ve been participating in a number of forums of cycling enthusiasts, instructors and sports scientists and the topic of “proper” or “efficient” pedal stoke is still being heavily debated.  What I’ve found is that most of what is being presented is correct.  Even when there are opposing arguments.  How can this be? There are the physiologists, the biomechanists, cycling coaches, indoor cycling instructors and strength and conditioning coaches all contributing to the theories and referring to various research.  After a number of weeks of frustration, attempting to participate and sift through the myriad of seeming controversy, I stumbled on the issue.  The variables and applications surrounding pedal stoke are so plentiful that it is difficult to explain all of the aspects of the technique in a simple statement or even a short paragraph.  I found myself plunging into verbose responses trying to explain and simplify the concepts.  The short, simple responses given by others would be correct within a single application, but would be incorrect when attempted to define the entire realm of pedaling biomechanics.

As the saying goes “More often, the simpler we make a complex topic, the more incorrect we become”.

So where do we go from here?  The goal of this multi-part article is to present the numerous issues and applications of pedaling dynamics in context.  Hopefully, this will allow us to understand ALL of the elements that contribute to this vast topic.  We will also put some definition to various terms so we are all speaking the same language.  As coaches, instructors and cyclists, we will be able to confidently approach our training and teaching with a well-rounded (pun not intended), holistic approach to the topic.

Here is what we will cover:

-          Part 1: Efficiency? The Metabolic and Mechanical Considerations

-          Part 2: Which Muscles and When are they Effective

-          Part 3: What are these variables you speak of?

-          Part 4: In Context – Does this only apply for Racers?

-          Part 5: In Context – Climbing (Seated and Standing)

-          Part 6: In Context – Explosive & Sustained Power

-          Part 7: In Context – Special Applications (e.g. Track Cycling)

-          Part 8: From the Lab: Over-use Injuries and Rehabilitation

-          Part 9: Is There a Benefit to Developing Pedal Technique and Leg Speed

-          Part 10: Finally, What Should We Teach?

Our goal is to present this complex topic in small, digestible chunks.  Considering the need for this information and the confusion surrounding the topic, we will attempt to post all of the parts of this article within the next 2-3 weeks.  That is the goal anyway.  Please feel free to contact us if you have questions or comments.  These are deeply appreciated.