Cycling

For Patients

The Principle

A movement that is harmless once can cause trouble if it is repeated often enough and always in exactly the same way.

Variety protects joints. A machine that fixes the path removes the variety.

So the thing to adjust is usually the machine rather than the person.

At the Knee

On a bike the body weight is on the saddle, so the knee carries far less than it does when walking.

The knee moves through the same arc roughly eighty times a minute, which is thousands of repetitions an hour.

The pedals and cleats fix where the foot can be, so the knee cannot choose a slightly different path.

Saddle height sets how much the knee bends, and it is the single most important setting. 3.12.3 covers kneecap pressures.

Clinical Relevance

Cycling knee pain is usually a setup problem, and a bike fit is a reasonable first step.

Pain at the front of the knee often means the saddle is too low. Pain at the back often means it is too high.

Cycling is often recommended after knee injury precisely because the loads are low.

No injury rates are given on this page, because no source was available to check them against.

For Medical Students

The Principle

Cycling inverts the usual sporting risk profile: the load per repetition is low and the repetition count is extreme.

That makes the knee's problem one of accumulated cycles in a fixed kinematic path rather than of peak force.

A fixed path is the key feature, because it removes the small variations that spread loading across tissue.

At the Knee

Pedalling cadence of 80 to 90 revolutions per minute gives around five thousand knee flexion cycles an hour per limb.

The knee is largely unloaded by body weight, and the force comes from the quadriceps against pedal resistance.

Patellofemoral load rises as knee flexion increases, so a low saddle raises it throughout the stroke. 3.12.3 covers pressure.

A high saddle extends the knee more and increases reach at the bottom of the stroke, which loads the posterior structures and the hamstring insertion.

Cleat position and rotational float determine whether the tibia can find its own rotation or is held. 3.2.3 covers internal rotation.

What Changes It

Saddle height, which is the dominant variable for knee flexion range.

Saddle fore and aft position, which changes the knee's position over the pedal axle.

Cleat rotation and float, which govern transverse plane freedom.

Gear selection and cadence, since a low cadence in a high gear raises force per repetition.

Training volume and its rate of change.

Clinical Relevance

Take a bike setup history, since the setup is the exposure here.

Anterior knee pain suggests excessive flexion, commonly a low saddle. Posterior pain suggests excessive extension.

Lateral pain suggests iliotibial band friction, often related to cleat position. 3.11.1 covers the band.

Avoid quoting injury rates, which this page does not, because no source was available.

MRCS Level

The Principle

Cycling is the clearest case in this chapter where the intervention is engineering rather than biology.

The bike is adjustable in several axes and the rider is not, so the efficient move is to change the machine.

That is a different clinical posture from every other sport here, where the advice is about the athlete.

At the Knee

Patellofemoral joint reaction force in cycling is modest in absolute terms and is applied many thousands of times per session.

Saddle height determines peak knee flexion, and lowering it raises patellofemoral force across the whole stroke. 3.12.2 covers contact areas.

Excessive saddle height produces posterior knee pain and hamstring insertional symptoms, and causes pelvic rocking.

Restricted cleat float can impose a tibial rotation the knee does not choose, which is implicated in medial and lateral pain. 3.2.9 covers coupled motion.

Cycling is used therapeutically after knee injury and arthroplasty precisely because of this profile. 3.14.12 covers that gait.

What Changes It

Saddle height, fore and aft, and cleat position, which are the adjustable axes.

Cadence and gear, which trade force against repetition at a given power.

Crank length, which alters the flexion range at the top of the stroke.

Bilateral asymmetry, which a fixed bilateral machine makes visible.

Volume and its rate of change, as in all repetition dominated sports.

How It Is Measured

Motion capture based bike fitting, which measures joint angles through the stroke and is commercially available. 3.16.7 covers capture.

Instrumented pedals, which give force and its direction through the stroke.

Static fit measurements, which are what most riders receive and are a poorer proxy.

Modelled patellofemoral force from pedal force and kinematics. 3.16.4 covers modelling.

Cycling has better availability of individual biomechanical measurement than any other sport here, because the fitting industry supplies it.

Clinical Relevance

Refer for a dynamic bike fit rather than adjusting by rule of thumb, since the measurement is available in this sport.

Map the site of pain onto the likely setup fault before investigating the knee.

Allow cleat float unless there is a reason to restrict it, since a held rotation has no escape.

Recommend cycling as rehabilitation on the mechanical grounds given here. Section 8 covers the programmes.

Weigh the rider's age, physiology, comorbidities, knee demand, psychological state and their own ideas, concerns and expectations, since a fit changes a position the rider may have held for years.