Cycling Biomechanics

Original Editor - Michelle Lee

Top Contributors - Michelle Lee, Lucinda hampton, Evan Thomas, Wanda van Niekerk, Kim Jackson, Vidya Acharya, Laura Ritchie, Scott Buxton, Naomi O'Reilly and WikiSysop

Introduction

Cycling was initially invented by Baron Carl von Drais in 1817, but not as we know it. This was a machine which initially 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 velocipede. This was solely used by the male population at the time of invention. The velocipede 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 propelled by pedals at the feet. This was the first conventional bicycle, and since then and up until the current day the bicycle 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 phase between the 2 is known as the Power Phase where all the force is generally generated to propel the bike forward. Have a look at this video to see a clear explanation of TDC and BDC.

The transition from BDC back up to 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. Have a look a the video below and then have a read of the text below.

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  ilium, ischium, pubis, coccyx, and sacrum bones. The ischial tuberosities (also referred to at the sitting bones) are located here and play an important role for the hamstrings, as this is where all three originate. 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 multi-directional movement. During cycling the hip allows for and guides hip flexion, 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 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 sesamoid 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 relevance is the ankle. This joint allows for dorsiflexion and plantarflexion in cycling, which allows for a term known as 'ankleing' where the foot moves from a dorsiflexed position to a plantarflexed position through the bottom of the pedal stroke before returning back to a dorsiflexed position.

The foot has many small joints but primarily this is where the force that is generated from the lower limb complex is transferred to the pedal. Irregular amounts of force 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 approximately 3 o'clock in the pedal cycle the quadriceps kick in to take the knee from its flexed position to an extended position at BDC.

The rectus femoris is one of the four quadriceps muscles, but the only one to cross both the hip and knee joint, giving it dual responsibility of hip flexion and knee extension. The quadriceps work in close partnership with the gluteals (maximus), these are two large powerful groups of muscles 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 cause patella femoral pain. This is due to the rectus femoris leading into the patella tendon and attaching onto the tibial tuberosity, 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, therefore compressing the origin of the hamstrings. The hamstrings main role in cycling is to assist knee flexion up through the back part of the pedal stroke but they also play an important part in stabilising the knee through BDC.

Further down the chain into the lower leg the gastrocnemius and soleus haven't been found to add much power to the pedal stroke but their main role is to stabilise the lower leg to enable an efficient transition of the force generated by the upper leg to the pedal.

Then as we come back up the other side of the pedal cycle the hamstrings kick in to help flex the knee to bring it back up to TDC, and when enough knee flexion and hip flexion is achieved the hip flexors start to work again to bring the leg up to true TDC to start the cycle again.

Trunk, Back and Arm

There is more to cycling than the movement of the lower limbs. The trunk and back play an important role in stabilising the spine and maintaining posture. There are many muscles within the back but to name a few: Multifidi and the quadratus lumborum are a couple of the main stabilisers of the spine when undergoing lateral and rotational movements, such as right leg enters the power phase whilst the left side of the spine stabilises and vice versa. The erector spinae muscles also play an important part in maintaining a stable posture whilst on the bike.

Abdominal muscles such as the rectus abdominus help to maintain stability as does the obliques. The obliques similarly to the back muscles will help stabilise a contralateral limb movement. As we move up the spine toward the shoulders, the latissimus dorsi and trapezius muscles enable the rider to fix their upper body onto the handlebars. The upper body has a role in stabilising contralateral torque, so as the right leg pushes down the left arm anchors to the handle bars and pulls up.

Similarly with the feet, the hands can undergo sustained amount of pressure so vascularity and nerves can become injured, most commonly the ulna nerve (cyclist's palsy) followed by the median nerve.

Bike Fit

A correctly fitted bike can prevent many of the overuse injuries that occur from poor position. It also means you can get the more comfort and can ride better and faster. The correct position varies from person to person, depending on factors like age, style of riding, and physical attributes like flexibility and anatomical variants.

The video below gives a basic bike fit instruction. The key elements outlined being saddle height, saddle layback and handlebar reach.