Custom formed orthoses in cycling

Abstract

To assess the effects of currently used prescribed in-shoe custom foot orthoses (CFOs) on a number of biomechanical variables during the power phase of cycling, including: hip adduction, knee abduction and tibial internal rotation. Before and after cross-over study recording subjects’ biomechanical variables with and without their CFOs. Twelve competitive cyclists, currently using prescribed in-shoe CFOs, performed two exercise bouts on a stationary trainer, with 3-dimensional data recorded on an 8 camera Vicon Mx system. 2-way ANOVA statistical analysis of Null vs Orthotic condition, and left leg vs right leg. No systematic effects from the CFOs were seen. A trend towards reduced tibial internal rotation range of movement was found (P < 0.072). Significant subject-specific effects from the CFOs were seen (P < 0.05). Three distinct patterns of knee movement were observed. All subjects had significant left to right leg differences. CFOs do not produce systematic effects on cycling biomechanics. Significant subject-specific biomechanical effects can be produced by CFOs utilizing rearfoot and/or forefoot wedges. An individualised approach to orthotic prescription, and attention to the forefoot–rearfoot relationship, is recommended.

Introduction

Overuse knee injuries in cycling are one of the most common complaints of cyclists.1, 2, 3 There are several factors which contribute to knee injuries in cyclists: extrinsic (bike size and set-up, training load and type) and intrinsic (lower limb alignment, lower limb biomechanics) risks, forming a complex interplay which can result in knee pain.1, 2, 4 Injury causes loss of training and potentially poor performance. A more linear cycling pattern is suggested to offer greater efficiency, reducing injury risk2, 5 and improving performance.⁶ The use of external wedges and orthotics have been shown to alter the frontal plane motion of the knee,⁷ tibial internal rotation,8, 9 and affect muscle activation patterns during the power phase of the cycle stroke.⁸ Subject-specific responses vary which limits the statistical significance of these studies, but subjective improvements are consistently reported in cyclists with knee pain.⁹ Similar results have been found in research with custom foot orthoses (CFOs) in runners, with variable biomechanical effects despite significant subjective improvements.10, 11, 12 Recent evidence supports an immediate and sustained effect from CFOs on lower limb mechanics in running. In particular, alterations in rearfoot and forefoot kinetics and kinematics, and tibial internal rotation through the coupling effect of the subtalar joint, are reported.13, 14, 15

Francis¹⁶ hypothesised that understanding the coupling relationship at the subtalar joint is crucial in appreciating overuse knee injury risk in cyclists. Tibial internal rotation is required during ankle plantar flexion of a locked foot, such as in the power phase of cycling, with increased tibial rotation required to accommodate any forefoot varus or rearfoot valgus malalignment.16, 17 Similar models have been proposed in running.13, 18 Compensatory hip adduction helps dissipate tissue tension at the knee, but increases knee abduction and the Q angle, known risk factors for anterior knee pain.1, 2, 5 This “malaligned syndrome” for cyclists, subtalar pronation, tibial internal rotation, knee abduction and hip adduction forcing the knee closer to the bicycle, coincides with peak power development at the knee, potentially increasing tissue stress and development of overuse injury.16, 18, 19 Bailey et al.⁵ found support for the injury mechanism proposed by Francis¹⁶ in their study on coronal plane knee movement, where cyclists with current or previous knee injury displayed a more medially placed knee, with increased knee abduction, during the power phase of the pedal cycle. Evidence exists for external wedging and in-shoe orthotics being capable of altering lower limb mechanics in cyclists,7, 8, 9 and thus potentially limiting injury risk, but no research to date found by the authors has assessed cyclists already using in-shoe orthotics for their effects on lower limb mechanics.

The aim of our study is to determine if and how CFOs currently used by cyclists alter the mechanics of the lower limb during the power phase of the pedal stroke, including: hip adduction; knee abduction; range (degrees) of tibial rotation; and relative knee position to the bike from top dead centre to bottom dead centre. Our research seeks to address previous studies’ limitations by analyzing both left and right legs over ten consecutive revolutions in cyclists currently using CFOs specific for cycling, and comparing that to cycling without their CFOs. This differs from previous research in this area, where orthotics and/or wedges were provided for the cyclists for the research period, with no knowledge if the cyclists continued using the supports following the research period.7, 8, 9