The effects of foot structure, footwear and technique on knee joint loads in over ground running

Research is yet to consider the influence of forefoot structure on forefoot pronation, its interaction with footwear and the ramifications for knee joint loading when performing endurance running (ER). This thesis investigated the relationships between forefoot structure, forefoot pronation, footwear choice, running technique and knee joint loading. Chapter four examined the measurement error of ER kinematics and kinetics within a test session, between sessions on the same day and between two days. Absolute measurement error for all kinematic and kinetic comparisons were ≤7.62° and ≤0.59 Nm·Kg-1 respectively. Results were used to assess habituation to novel footwear conditions and calculate sample size in subsequent studies. Using data from chapter four, chapter five investigated time to habituate in novel running conditions (barefoot, minimal and maximally-cushioned footwear) in a sample of recreational runners. Twentyone minutes was sufficient to establish consistent hip, knee and ankle sagittal plane kinematics, where variability was less than or equal to previously established within-session data. Post habituation, chapter six investigated associations between foot structure, forefoot pronation and peak-knee adduction moment, and the effect of running condition on forefoot pronation. Hallux angle and phalange width accounted for 35% of variance in forefoot pronation (P = 0.029). Results also showed forefoot pronation was significantly associated (P < 0.05) with peak-knee adduction moment (r = -0.57, r = -0.77, r = -0.61, for barefoot, minimal and structured-cushioned shoes, respectively). A medial translation in the centre of pressure was not associated with increased forefoot pronation. Footwear also influenced forefoot pronation. Minimal footwear had greater forefoot pronation compared to barefoot (P = 0.042) and the structured-cushioned condition (P = 0.001). Chapter seven examined the effects of footwear on lower-limb kinematics and kinetics. Compared to barefoot and minimal shoes, a more extended knee and dorsiflexed ankle at initial contact, increased peak-knee flexion moment, and reduced the peak-dorsiflexion moment were observed in maximally-cushioned shoes. An extended lower limb follows previous work that suggests insulation of mechanoreceptors would encourage a running technique that projects the foot more anteriorly to reduce ground contacts for a given distance. These kinematic changes also suggested overstride would increase as participants change from barefoot to maximally-cushioned footwear. Subsequently, chapter eight investigated the effects of footwear on overstride and its association with peak-knee adduction moment. Changing from maximally cushioned, to minimal shoes or barefoot, reduced overstride relative to the hip, whereas overstride relative to the knee decreased from maximally cushioned to barefoot only. Results also showed moderate to strong positive correlations between overstride and peak-knee adduction moment in all running conditions. Findings suggest footwear influences overstride, overstride was associated with peak-knee adduction moment, and reducing overstride might reduce peak-knee adduction moment, a variable associated with injury. Following observed relationships in chapter eight, chapter nine attempted to reduce peak-knee adduction moment. Twelve recreational endurance runners performed either a 30-minute run, or 30 minutes of gait retraining. The intervention had a primary focus on reducing overstride following the reported relationship between overstride and peak-knee adduction moment. Controlling for baseline measures, there was no significant difference between overstride, trunk lean and subsequently peakknee adduction moment. The lack of difference was attributed to the short duration and the acute nature of the coaching session. Similar investigations over a longer period of time are warranted. Collectively, phalange width and hallux angle contributed to forefoot pronation, and forefoot pronation was associated with peak-knee adduction moment when running, a measure associated with injury. This suggests those with compromised forefoot structure, might be at risk of injury, particularly when attempting to run barefoot or in minimal shoes that lack support. As participants changed from barefoot to minimal to maximally-cushioned footwear overstride increased, with medium to strong positive correlations for overstride and peak-knee adduction moment. This suggests runners with a large overstride are likely to be exposed to increased peak-knee adduction moment and potentially injury, and reduced overstride might present a means to reduce injury.