Improving The Power Phase of the Pedal Stroke in Cycling
17 Sep 2018
Knowledge is power, and in the sport of cycling having a good understanding of your pedal stroke biomechanics and muscle function will allow you to pedal more efficiently, with more power, and tailor your strength and conditioning program to strengthening the right muscles in the right way. In this blog I will explore the power phase of your pedal stroke.
Let us start by breaking down the pedal stroke into various phases. I have seen this be done many different ways however, the best and most useful way I have come across is the following;
Image: Four stages of the pedal stroke
These 4 stages align more appropriately with joint forces, joint range of motion and muscle activation as they occur in cycling. This, therefore, allows us to better describe and analyse the pedal stroke and implement injury prevention and management strategies when needed.
E = extension or power phase. Let’s discuss which muscles work, and when, during this phase.
If looking at the pedal stroke as a clock face the extension (power) phase starts at 11 o’clock and finishes at approximately 5 o’clock. Or, if looking at the pedal cycle as a 3600 circle (with 00/3600 top dead centre and 6 o’clock 1800). This phase runs from 3000 through to 1400
The extension phase is the most important segment of the pedal stroke and is the region in which over 90% of the propulsion force is generated in cycling.
Image: Red circle = power produced during the extension or power phase of the pedal stroke. Blue line = Peak power occurring around 1100
One of the big differences between pro and amateur cyclists is the angle at which peak power is achieved. Pros will usually hit peak power around 1100 (blue line in image above) whereas amateur cyclists will take a little longer, peaking around 1200-1300 (or if you are anything like me 1400!). Reaching peak power earlier allows a greater range of the pedal stroke to be held at this higher power
Hitting peak power later in the cycle means you have used a lot of the pedal stroke to get there and now have the less range available.
The gluteus maximus muscle together with adductor magnus (see below) are the main contributors that enable powerful hip extension whilst the quadriceps produce knee extension. All these muscles work together extending the leg and generating significant force down into the pedal and crank during he initial phase of the pedal stroke, top dead centre (00) to 900-1100
Image: Adductor Magnus.
The soleus (the short power generating calf muscle) will slightly plantarflex the ankle (pointing toes down) contributing to power production (akin to performing a calf raise) however, it has a larger role in resisting opposing reaction forces at the pedal, preventing the heel from dropping and creating a rigid lever (stiff foot) for optimal transference of power into the crank.
Tip: a weak calf can be a major reason for heel drop and loss of power during this phase.
Image: Pedal at 3 o’clock position (900). Red line = external forces pushing the toes up and heel down. Blue line = force produced buy the calf muscles to counteract external forces (red line) pushing the toes down and keeping the heel from dropping.
Long muscles which cross two joints such as; the hamstrings, adductors (groin muscles) and the gastrocnemius (the other calf muscle) are thought to have more of a role in coordinating movement of the leg, ensuing a smooth action and controlling the direction of the force applied to the pedal.
The hamstrings and groin muscles will control the knee and hip, preventing excessive medial-lateral and rotational movements, whilst the gastrocnemius will position the foot on the pedal ensuring power generated from above is efficiently and effectively transferred in to the pedal and crank.
The gluteus maximus and adductor magnus should activate at top dead centre (00 or 12 o’clock) and remain active all way through to bottom dead centre. Together with the hamstrings, these hip extensors continue to produce power and ensure optimal transition from the extension phase into the bottom phase of the pedal stroke.
Image: Exercises such as a barbell hip thrust can strengthen both gluteus maximus and adductor magnus
In contrast, the quads should activate before the top of the pedal stroke (around 11 o’clock) to continue hip flexion and begin to extend the knee, driving the shin and foot across the top of the pedal stroke and through to the early power phase, reaching maximum force production at around 360 (approx. 2 o’clock). However, as opposed to the power producing hip muscles (gluteus maximus and adductor magnus), it is vital that activation of the quads reduce significantly at 900 (3 o’clock) and stop altogether at and end of the extension phase (1200 or 4 o’clock). The reason for this will be detailed in the next phase – Bottom Phase.
In summary, the power phase of pedal stroke is more than just your quads pushing hard from 11 o’clock to 5 o’clock. Many other muscles contribute power including the gluteus maximus and adductor magnus. Other leg muscles provide stability and control to allow the power muscles to do their job.
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