The Muscle's You Use (and the ones you forgot about)

Cycling is one of the most popular forms of aerobic exercise for individuals all across the world. Some use it as training for other sports while others devote their lives to racing and improving their speed and efficiency. Many people tend to fall under the assumption that cycling only works the cardiovascular system, this is far from the reality however. The act of simply carrying out one rotation of the pedals uses muscles from all over the body, many of which we typically don’t think about. To break this down let's take a look at the major groups on the body.

The first group that probably comes to mind when talking about cycling are the leg muscles. These include the quads(primary power producers), hamstrings(power/knee stability), glutes(power/stability) and calves(aids in ankle stability). Next are the abdominals and erector spinae (runs parallel to the spine), which help stabilize the torso. And last but not least are the upper body muscles, these include the triceps, latissimus dorsi, and the pectorals which all aid in supporting body weight and even generating power (by pulling on the handle bars). All these groups work together to deliver output to the pedals, for example if a rider is swinging the bike from side to side in a sprint both the core and arms must be engaged to transfer that power effectively (Cannon et al., 2007). A more stable platform will yield better power transfer, and help limit energy loss to motion not directly aiding in power delivery. Let’s dive deeper into each muscle group to see why we should be paying more attention to them.

The Quads are made up of four thigh muscles of which the vastus lateralis, vastus medialis and vastus intermedius are the primary power producers. All these muscles fire from the top of the pedal stroke to the bottom.

The Hamstrings are most active from the six o’clock to nine o’clock position of the pedal stroke. Although the quads generate the bulk of the power in the pedal stroke, the hamstrings still contribute a decent amount of overall power output. Moreover, they aid with knee stability when the leg is fully extended. Activating the hamstrings will slightly increase power, reduce the load on the quads, and help smooth power delivery (i.e., pedal in circles).

The Glutes can be broken down into the gluteus maximus and the gluteus medius. The gluteus maximus can help add additional power throughout the pedal stroke, while the gluteus medius and minimus stabilize the hips and also aid with regulating outward rotation of the thigh. This is key for helping reduce common knee injuries as you will see if you read the “Common injuries and how to solve them” Blog post. Glute activation is also highly dependent on your bike fit and past activity history, but it is a key muscle to work on and incorporate into the pedal stroke. Glute activation exercises like band work can help form a connection between brain and muscle and lead to a more stable knee.

There is typically a dead spot around both the twelve and six o’clock positions where power transfer is limited due to the angle of the cranks. You can see this in Figure 1. Thus breaking the pedal stroke down into the two main portions. There is the “power phase” or “down stroke” and the “recovery phase” or “upstroke” where, the first of which is where the crank travels from twelve to six and where the quads typically dominate as the primary muscle group (So et al., 2005). The second phase is where the hamstrings activate as they help to pull the pedal back up to the top of the stroke. To engage in a more efficient pedal stroke, riders should focus on trying to pedal in circles instead of disjointedly pushing and then pulling, which isolates muscle groups and can put undue pressure on the knee. When looking at the power being produced from the thigh muscles it becomes easy to see how muscle activation patterns can be responsible for the occurrence of overuse injuries. “Over the crank cycle, uniarticular hip and knee extensor muscles provide 55% of the propulsive energy, even though 27% of the amount they produce in the downstroke is absorbed in the upstroke. Only 44% of the energy produced by these muscles during downstroke is delivered to the crank directly. The other 56% is delivered to the limb segments, and then transferred to the crank by the ankle plantar flexors. The plantar flexors, especially soleus, also prevent knee hyperextension, by slowing the knee extension being produced during downstroke by the other muscles, including hamstrings” (Raasch et al., 1997). This transfer of power down the shanks is what makes cycling so much more than just a cardiovascular exercise. The muscles in the leg are undergoing strong contractions and during the “recovery phase” they are still helping stabilize other muscles and joints. Other studies like those done by Cannon et al., have found that manipulating the flexion or extension of various joints can play a big role in oxygen uptake and efficiency. In their study they specifically looked at the differences between self selected dorsi or plantar flexion of the foot and predetermined angles. They were able to determine that the acute effects in the slight change in the angle of the foot lead to greater muscle activation of the gastrocnemius lateralis and lower mechanical efficiency.

Citations

• Cannon, D. T., Kolkhorst, F. W., & Cipriani, D. J. (2007). Effect of pedaling technique on muscle activity and cycling efficiency. European Journal of Applied Physiology, 99(6), 659–664. https://doi.org/10.1007/s00421-006-0391-6

• Raasch, C. C., Zajac, F. E., Ma, B., & Levine, W. S. (1997). Muscle coordination of maximum-speed pedaling. Journal of Biomechanics, 30(6), 595–602. https://doi.org/10.1016/S0021-9290(96)00188-1

• So, R. C. H., Ng, J. K.-F., & Ng, G. Y. F. (2005). Muscle recruitment pattern in cycling: A review. Physical Therapy in Sport, 6(2), 89–96. https://doi.org/10.1016/j.ptsp.2005.02.004