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The principal demand on the body during cycling is on the lower extremities as they are responsible for producing a majority of the energy imparted to the bike. As a result the legs, due to high reactive forces between the foot and pedal, experience high loads on the joints. These loads may adversely affect joint tissues and contribute to overuse injuries, e.g. knee pain. The mechanical link between the leg and the bike is the shoe/pedal interface. This transmission site, by design, can either create smooth transfer of energy or abnormally high repetitive loads which are potentially injurious to the body. Incidence of lower extremity injury in cycling is high, and historically biomechanical analyses of this activity have focused their attention on either the rider or the bike, but not the link between the two. Recently, pedal designs have changed in response to complaints of sore knees with the development of pedals allowing varying degrees of float. This form of transmission is intended to enhance power transfer from rider to bike as well as minimise trauma to the legs by permitting the foot to rotate during the pedalling cycle in a toe-in/heel-out or heel-in/toe-out movement pattern. Recent evidence suggests this type of pedal design does reduce trauma and maintains power output. This article reviews common lower extremity overuse injuries and biomechanical factors during the pedalling cycle with the primary focus on the shoe/pedal interface. We will summarise information available on lower extremity kinematics and kinetics as well as recent data specifically related to shoe/pedal interface kinetics, evaluation of different pedal types-specifically comparison between clipless 'fixed' and clipless 'float' systems-and discuss their resultant effect on lower extremity dynamics and their implications for injury.

In response to the popularity of clipless bicycle pedals with float designs, an instrumented force pedal system with multicompatibility for different shoe/pedal interfaces is presented. A dual piezoelectric element pedal has been modified for use with popular clipless pedal interfaces. The dual transducer arrangement permits measurement of three components of uniaxial load, location of the applied load, and calculation of the moment Mz about an axis through the position of the applied load and orthogonal to the pedal surface. Quantification of lower extremity kinetics using float feature pedals and the investigation of the pathomechanics of lower extremity cycling overuse injuries, especially knee injuries, is warranted. Qualitative descriptions of lower extremity pathomechanics related to overuse injuries have suggested that foot constraint may induce undesirable knee kinematics and kinetics. The instrumented force pedal system described here permits a comparison between pedal kinematics and kinetics of popular shoe/pedal interfaces with varying degrees of float allowance.