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.
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A Quick Note on “Circular” or “Smooth” Pedaling Technique Smooth or circular pedaling technique is often confused with trying to apply the same or consistent amount of force around the entire pedal stroke (360 degrees). A brief glance at the different sizes and strengths of the leg muscles that propel the pedals (glutes, quads, calves, hamstrings and hip flexors) should indicate that this is virtually impossible. For example, the hamstrings would be hard pressed to attempt to generate the same amount of power during the bottom of the pedal stroke as the quads can produce on the down-stroke. So what is a smooth pedal stroke referring to? A smooth pedal stroke refers to the “smooth” transition between the different quadrants (down, back, up and top). Muscles are engaging at various strengths throughout the 360 degrees to maintain a fluid “circular” movement. |
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).
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Going Deep Force needs to be applied to produce velocity. This is the force-velocity relationship. If you only push down on the pedals (piston), force will only be applied to the down-stoke. Thus, the bike will only be accelerating (increasing velocity) during the down-stroke. So what is happening during the top and bottom of the pedal stroke? Well, applying Newton’s second law, without force, the bike will be decelerating at the top and bottom of the pedal stroke. Now we know that the physiologists have proved there is little to no difference in energy needed to pedal using a piston vs. circular technique, so why is this significant? Hold on to your seats…we’re going in… Leg muscle contraction when pedaling is concentric. Basically, the muscles shorten to move the bones (levers) that move the pedals. On the contrary, an eccentric contraction occurs when the muscle resists force (or the movement of the bones) causing the muscles to lengthen. If you only push down on the pedals, the bike will be decelerating at the top and bottom of the stroke. This means you will be pushing against a pedal that is decelerating. Your muscles will have to resist and reverse this deceleration to re-accelerate the pedals again. Remember, 10,000 rotations per hour. Those thousands of eccentric contractions will place additional stress on the muscles causing fatigue. Circular pedaling technique maintains force around the entire pedal stroke which reduces the fatiguing effects of repetitive eccentric contractions due to deceleration (re-acceleration). |
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.
