Cycling Biomechanics

NJD Sports Injury Clinic

Cycling Biomechanics

Based in the North West of England, we offer a unique and comprehensive BIKEFIT PACKAGE (Testimonials).  Our unique Bikefit Package is designed to improve your cycling biomechanics (pedalling symmetry). Poor pedalling symmetry predisposes the cyclist to overuse injuries, knees especially, and can result in power loss. A crucial part of cycling biomechanics (pedalling symmetry) is the area we like to refer to as the Foot/Pedal interface which includes (foot type, foot alignment, leg alignment, leg-length differences, shoe design, shoe insert type and design, pedal and cleat system and cleat position).

Consequently, unlike many Bikefitting sources, we allocate considerable amounts of time and effort during the Bikefit process towards correcting common problems associated with the Foot/Pedal interface. Often neglected by many Bikefitter, the foot/pedal interface is arguably the 'cornerstone' of effective Bikefitting.

We always recommend our unique Bikefit Package rather than a simply stand-alone Bikefit. The reason is our Pre-Bike Musculoskeletal Screening enables us to identify problems at the foot/pedal interface, many of which can only be found through head-to-toe musculoskeletal screening.

 

The Foot / Pedal Interface - crucial areas to consider

Leg Alignment Foot Alignment Shoe, Pedal & Cleat  Design Cleat Position Cycling Insert

 

Foot/pedal interface

The foot/pedal interface is arguably the 'cornerstone' of effective bikefitting. The foot/pedal interface dictates how effectively pedal forces are transmitted down to the cranks, and potentially, how deleterious forces are transmitted upwards through the kinetic-chain. Problems at the foot/pedal interface can cause potential power-loss and overuse injury. Overuse injuries are likely to occur at the weakest link in the kinetic-chain e.g. knee, hip, pelvis, lower back and neck.

 

The slightest amount of misalignment can reduce power output

From the conception of the bicycle in the 19th century through to the modern-day race cycle, cycling has been a marriage between man machine. Cycling is very repetitive; during 1 hour of cycling, a rider may average up to 5,000 pedal revolutions. The slightest amount of misalignment, whether it be anatomical, biomechanical, mechanical or otherwise, at the foot/pedal interface (forefoot tilt) can lead to injury and reduced performance - measured as power output in our own research.
 

 

Modern carbon equipment exacerbates alignment and forefoot problems

  Rigid carbon wheelsets

While never alluded to in the literature, it’s highly likely modern technology exacerbates the problem of foot dysfunction. Carbon frames, wheels, cranks, pedals and shoes have all advanced and become significantly stronger and stiffer. However, the human foot remains unchanged. Jarboe and Quesda (2003) demonstrated that carbon-fiber shoes are 42% stiffer in longitudinal bending and 550% stiffer in three-point bending compared with plastic cycling shoes.  As a direct consequent, there is little scope for any flex, thus energy cannot dissipate.

       
      Rigid carbon soled shoes

The combination of rapid technological advancements in carbon components and ever-increasing levels of strength enable the rider to transfer more power to the pedal, thus placing greater loads / pressure on the structures of the foot. Increased forefoot pressures cause forefoot problems and  cause the foot to collapse inwardly, which in turn increases pronation (24-26).

Rationale

Efficient, injury free cycling relies on rider symmetry throughout the entire pedal revolution. Strength and balance in the muscles situated in and around the pelvis are prerequisite to symmetry and paramount to efficient cycling, whether road, track or mountain biking. Symmetry represents a stable, level pelvis, with minimal pelvic motion (no rocking) and sound core stability. Similarly, there should be minimal sideways movement of the knee when pedalling. Excessive aberrant motion of the knee means the knee must travel further than is necessary through each pedal revolution - as depicted in the image by red arrows. This extra, but unwanted knee motion constitutes wasted energy and is potentially destructive on the structures of the kinetic-chain (foot, ankle, knee, hip, back and neck).
 

Power loss

Our own unique research carried out in 2010 at Manchester Metropolitan University found a strong correlation between power output and cyclists with varying amounts of forefoot varus. Interestingly, those with the highest levels of forefoot varus demonstrated increased mean peak power outputs of approximately 10% while performing 30 second maximum anaerobic effort. Considering the high prevalence of forefoot varus (87%) found amongst cyclists, these findings may have implications across the cycling population. In summary, cyclists presenting with higher levels of forefoot varus potentially have the most to gain.

                      Abnormal knee motion

What is the cause of asymmetry?

The foot/pedal interface is the mechanical link between the leg and the cycle, and consequently, the point at which asymmetry most often arises. Less than (<) 10% of the population has a neutral foot (2-5). When translated into cycling terms, < 10% of cyclists have a perfect foot position when placed on the pedal (5,6). Reduced cycling performance and overuse injuries, particularly knee related, are frequently linked to the anatomic structure of the foot (i.e. excessive pronation). This is because the structure and function of the foot dictate how effectively pedal forces are transmitted via the foot/pedal interface down to the cranks, and potentially, how deleterious forces are transmitted up the kinetic-chain – impacting on the knee, hip, pelvis, lower back and neck. During one hour of cycling, a rider may average up to 5,000 pedal revolutions. The smallest amount of misalignment at the foot/pedal interface, whether anatomic, biomechanical or mechanically related, creates asymmetry – which often leads to overuse injury and impaired performance. In support of these claims, studies demonstrate excessive foot pronation can compromise core and pelvic stability and/or create postural issues (7-14).

Case Study      

   Anatomic LLD of 30mm

Leg-length differences (LLD)  can be clased as either anatomic or functional.  Anatomical differences are true LLDs, and represent an actual anatomic shortening of one or more of the bones of the lower extremity. Whereas, functional LLD are not  true leg-length differences. Functional LLD are often associated with muscular weakness or inflexibility at the pelvis or foot and ankle complex.

Studies have demonstrated the prevalence of anatomic LLD affect approximately 90% of the population (15,16). We use a battery of tests to establish LLD. The image on the left shows a cylist with an anatomic LLD of approximately 30mm. The image on the right shows how we  built-up the shoe to compensate.

    Built-up shoe 15mm

What is pronation?

Pronation is when the foot rolls inwards and is considered a normal and necessary motion for efficient gait. Excessive pronation is when the foot rolls in too far, which can result in knee problems (17-22), pelvic and core problems (7-14), and reduced cycling performance (23-26). Excessive pronation can be unilateral (one foot) or bilateral (both feet).

       Forefoot varus

Forefoot varus and tibial varum are considered to be the two most common causes of excessive pronation. Forefoot varus is a forefoot-rearfoot alignment problem; the 1st MTP joint (big toe) is elevated from the pedal with the rearfoot in a neutral position - image on the left. Tibial varum (bowlegged) is represented by the natural bowing of the lower third of the tibia - image on the right. Both these two conditions necessitate the foot to roll inwards to enable effective contact with the pedal surface. The greater the levels of forefoot varus and/or tibial varum, the greater the level of pronation.

        Tibial varum

The evolution of clipless pedal systems

In 1984, the French-based ski binding manufacturer (Look) first tested a rigid float-less clipless pedal with the help of professional cyclist Bernard Hinault. This clipless system was introduced to the market in 1986. However, this rigid float-less system placed undesirable stress on the knees. In 1987, Jean Beyl invented the Time pedal system, known as Bioperformance, which allowed free rotational float and some lateral motion of the foot. At first the Bioperformance system received much criticism from competing pedal manufactures, alleged claims of power loss due to float were proved incorrect after research studies demonstrated otherwise. Professional cyclist quickly adopted the system, and subsequently most manufactures modified their pedal systems to include varying degrees of rotational float (37).
 

Some riders need more float

Self-centering

Most modern-day clipless pedal systems (e.g. Shimano, Time, and Look) use spring loaded devices which employ a self-centering mechanism which allows varying degrees of rotational motion (typically 4° to 8°) against increasing resistance. This design system brings the shoe back to the preset neutral alignment.  We believe self-centering pedal systems are suitable for the majority of riders, i.e, riders with small amounts of anatomical or biomechanical misalignment. However, in a minority of cases where a rider presents with greater levels of misalignment a system with more rotational float may be required.  Speedplay pedal offers 0° to 15° of free float rotational motion. Speedplay can offer two benefits; more rotational float, and free float – meaning the foot does not have to work against spring loaded resistance.

Free rotational float

 

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