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

A key objective of sports biomechanics is to improve performance while reducing the incidence of injury. Knowledge of the biomechanics of cycling benefits recreational, competitive and rehabilitating cyclists and physiotherapists.

The aim of biomechanics applied to cycling is to improve the cyclist’s interaction with the bicycle, with the aim of ensuring the comfort of the position (posture) and the efficiency (of pedaling).

In fact the practical purpose of biomechanics applied to cycling is to create products and services derived from scientific research that are valid for achieving the comfort (posture) and the efficiency (pedaling).

Clinical Implications

The global bicycle market size was valued at USD 54.44 billion in 2020.

The number of people opting for bicycling as a form of leisure is anticipated to grow. Bicycles are a convenient form of exercise to ensure a healthy life, free from obesity and other disorders.

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.

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 eg cyclist's palsy, cyclist's neck

Phases of Cycling/Pedalling

There are 2 main phases of the pedal cycle;

1. Power phase: From 12 o'clock till 6, phase where all the force is generally generated to propel the bike forward.
2. Recovery phase. From 6 back to 12 o'clock

• 12 o'clock, this is known as Top Dead Centre (TDC).
• 6 o'clock is known as Bottom Dead Centre (BDC).

Have a look at this video (2 minutes) to learn to pedal like a pro based on leg biomechanics.

Anatomy of Cycling

The primary power-producing muscles used for cycling include the quadriceps, hamstrings, and gluteals. The calf muscles, abdominals, and erector spinae, in conjunction with upper body muscles, are used for stability when riding a bike.

See the 30 second animation below.

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

The Power Phase of the Cyclist's Pedal Stroke

From the top of the pedal stroke, a cyclist utilizes their hip extensors (gluteus maximus muscle) which initiates the Power Phase of the pedal stroke until point at 3 on a clock face

From the point of 3 to 5 on the clock face the knee extensors activate: vastus lateralis and vastus medialis. Many cyclists associate this point with generating the most force for their pedal stroke; this is particularly prominent while climbing out of the saddle on steep gradients.

Due to the position on the bike, rectus femoris can become shortened leading to anterior hip pain, also with rectus femoris shortening the compressive forces around the patella increase causing discomfort. See cyclist's knee.

From positions 5 to 6, plantar flexion occurs, thanks to the gastrocnemius which causes the toes to point outwards. The gastrocnemius and soleus's main role is to stabilise the lower leg to enable an efficient transition of the force generated by the upper leg to the pedal.

Recovery Phase of the Cyclists’ Pedal Stroke

The transition from 6 o'clock back up to 12 o'clock 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.

From 6 to 8, the Tibialis Anterior draws the toe upwards towards the shin. (dorsiflexion)

From 8 to 10, hamstrings (Semimembranosus, Semitendinosus and Biceps Femoris) pull the heel upwards towards the buttocks. Note: 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.

From 10 to 12, the hip flexors of the Iliacus and Psoas finish off the pedal stroke.

Trunk, Back and Arm

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.

Joints of the Lower Limb and their Role in Cycling

• The pelvis is the start of the lower limb complex. The ischial tuberosities (sit bones) are located here are the origin role for the hamstrings.
• The hip during cycling allows for and guides hip flexion, extension and small degree of rotation.
• The knee 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 ankle allows for dorsiflexion and plantarflexion in cycling.
• The foot 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.

Bike Fit

Correct positioning is critical for successful performance and injury prevention. A correctly fitted bike can prevent many of the overuse injuries that occur from faulty biomechanics (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.

Jaw Clenching

The jaw clenching facial expression can be considered an important factor for estimating the intensity of effort.

• Frowning and jaw clenching muscle activity reflects the perception of effort during incremental workload cycling.
• EMG activity of the masseter muscle is strongly and positively correlated with RPE, HR and lower limb EMG activity during incremental workload cycling.