Cycling Biomechanics

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Introduction

Cycling was initially invented by Baron Carl von Drais in 1817, but not as we know it. This was a machine which intailly had two wheels that were connected by a wooden plank with a rudder device for steering. It involved people running along the ground whilst sitting down; giving them the name of a 'running machine' (in all senses) or a velocipied. This was solely used by the male population at the time of invention. The velocipied then made a huge design development in the 1860's at the Michaux factory in Paris. They added leaver arms to the front wheel which were prepelled by pedals at the feet. This was the first conventional bicycle, and since then and up until the current day the bicyle has made great design and technological advances. 

A survey in 2014 estimated that over 43% of the United Kingdom population have or have access to a bike and 8% of the population aged 5 and above cycled 3 or more times a week.  With such a large amount of people cycling, whether it be professional, recreational or for commuting this increase the chance of developing an injury, so it is time we understood the biomechanics of cycling. 

3 Points of Contact

There are 3 points of contact in cycling. Meaning 3 points of the body that make contact with the bike:

• Pelvis on the saddle
• Hand on the handlebars
• Foot on the pedal 

Something to be aware of is that these areas can undergo sustained amounts of pressure and compression which can cause numbness, pain and weakness. 

Phases of Cycling / Pedaling

There are 2 main phases of the pedal cycle; the power phase and the recovery phase. If you imagine the pedal cycle as a clock face and you start with the pedal at 12 o'clock, this is known as Top Dead Centre (TDC). The pedal is then pushed down from 12 until 6 o'clock, this position is known as Bottom Dead Centre (BDC). The pahse between the 2 is known as the Power Phase where all the force is generally generated to propell the bike forward. 

The transition from BDC back upto TDC is known as the Recovery Phase. Now not all of the muscles just switch of during this phase, it just is not as active as the Power Phase.

If you look at the image you can see what muscles are working at which points during the pedal cycle.

Anatomy of Cycling

There are many components that are working whilst cycling this is not just a sport of the lower limbs. Below the areas of anatomy have been broken down to provide more detail on what is happening and when. 

Joints of the Lower Limb and their Role in Cycling

The pelvis is the start of the lower limb complex, and is compromised of the ischium and the ilium. The ischial tuberosities (also referred to at the sitting bones) are located here and play an important roll for the hamstrings, as this is where all three origionate.The hip is also an important anatomical feature as this is a large 'ball and socket' type joint, which allows for a large degree of multidirectional movement. During cycling the hip allows for and guides hip felxion, extension and small degree of rotation. Further down the lower limb complex the knee is found. This 'hinge' joint acts as a lever to the femur, as as the femur is the longest bone in the body this can create large amounts of torque. This is where the patella plays a vital role, as it acts as a fulcrum and enables the force from the upper leg to be transferred to the lower leg. The patella is a seasamoid bone that sits within the patella tendon and connects the quadriceps to the tibial tuberosity. The patella glides in the intercondylar fossa of the femur. 

Moving down the lower limb complex the next main joint of relavance is the ankle. This joint allows for dorsi-flexion and plantar-flexion in cycling, which allows for a term known as 'ankleing' where the foot moves from a dorsi-flexed position to a plantar-flexed position through the bottom of the pedal stroke before returning back to a dorsi-flexed position. 

The foot has many small joints but primarily this is where the force that is generated from the lower limb complex is transfered to the pedal. Irregular amounts of fource or compression running through the foot can result in neural pain and tissue damage from compression.  

Muscles of the Lower Limb and their Role in Cycling

The initiation of the pedal cycle starts with the gluteals, taking the hip from a flexed position at TDC through the power phase to an extended position. Then at approximatley 3 o'clock in the pedal cycle the quadriceps kick in to take the knee from it's flexed position to an extended position at BDC.

The rectus femoris is one of the four quadricep muscles, but the only one to cross both the hip and knee joint, giving it duel responsibility of hip flexion and knee extension. The quadriceps work in close partnership with the gluteals (maximus), these are two large powerful groups of mucles produce the greatest amount of torque in cycling. Due to the position on the bike, muscles such as the rectus femoris can become shortened leading to anterior hip pain, but also commonly patella femoral pain. This is due to the rectus femoris leading into the patella tendon and attatching onto the tibial tiberosity, so if this muscle becomes shortened it can increase the the compressive forces around the patella, causing discomfort.  

The main role of the hamstrings is knee flexion but they also assist hip extension. During cycling depending on the position that is adopted by the cyclist if on an upright bike, the ischial tuberosities may take most of the load through the saddle. 

References

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