No / The purpose of this article is determining if and how the kinematic relationship between adjacent body segments changes when an individual’s gait pattern is experimentally manipulated can yield insight into the robustness of the kinematic coupling across the associated joint(s). The aim of this study was to assess the effects on the kinematic coupling between the forefoot, rearfoot and shank during ground contact of running with alteration in foot strike pattern. Twelve subjects ran over-ground using three different foot strike patterns (heel strike, forefoot strike, toe running). Kinematic data were collected of the forefoot, rearfoot and shank, which were modelled as rigid segments. Coupling at the ankle-complex and midfoot joints was assessed using cross-correlation and vector coding techniques. In general good coupling was found between rearfoot frontal plane motion and transverse plane shank rotation regardless of foot strike pattern. Forefoot motion was also strongly coupled with rearfoot frontal plane motion. Subtle differences were noted in the amount of rearfoot eversion transferred into shank internal rotation in the first 10–15% of stance during heel strike running compared to forefoot and toe running, and this was accompanied by small alterations in forefoot kinematics. These findings indicate that during ground contact in running there is strong coupling between the rearfoot and shank via the action of the joints in the ankle-complex. In addition, there was good coupling of both sagittal and transverse plane forefoot with rearfoot frontal plane motion via the action of the midfoot joints.

There has been much debate on the benefits of a forefoot versus rearfoot strike pattern in distance running in terms of performance and injury prevalence. Shock attenuation occurs more prominently in soft tissues at impact in forefoot runners compared to the passive skeletal loading in rearfoot runners. Recent studies indicate that a forefoot strike pattern may not be maintainable over long distance efforts. Therefore, this study tested the hypothesis that habitual forefoot runners could not maintain their strike pattern throughout a prolonged, intensive run. Fourteen forefoot runners ran to voluntary exhaustion on an instrumented force treadmill (average run duration: 15.4±2.2 minutes). Kinematic and kinetic data were sampled each minute at 200Hz and 1000Hz, respectively. Ankle plantar-flexor torque was measured during pre- and post-run isometric contractions, during which electromyographic activity was measured in the soleus, lateral, and medial gastrocnemius. Loading rate (49.95±14.83 to 57.40±22.53 BW*s-1, p=0.0311) and impact peak (1.35±0.43 to 1.50±0.51, p=0.0207) increased significantly throughout the run. Both peak knee flexion (-33.93±3.67º to -36.21±3.48º, p=<0.0000) and sagittal ankle angle at touchdown (-11.83±5.33º to -9.33±6.29º, p =0.0202) increased significantly. Ankle torque decreased significantly from pre- to post-run (120.57±33.57 to 110.76±32.91 Nm, p = 0.0154). This was accompanied by a decrease in medial and lateral gastrocnemius integrated electromyographic activity (iEMG) (p=0.0387 and 0.0186, respectively). The results indicated that there were significant changes in landing mechanics in the habitual forefoot runners with increased levels of exertion, as they shifted towards strike patterns more similar to rearfoot runners throughout the run. These changes are in line with metabolic findings of other studies. There is increased eccentric loading of the ankle plantar-flexor muscles at touchdown in forefoot runners that may contribute to a decreased torque output by the end of the run. The decline in iEMG may indicate altered central drive of the system and a decline in the impact attenuation ability of the triceps surae, leading to the changes exhibited up the kinematic chain. These findings suggest that while forefoot strike patterns are good for speed, the onset of fatigue may affect the ability to maintain this pattern during a prolonged, intensive effort.

One possible solution to common running related injuries is to transition runners from a rearfoot strike during initial contact to a midfoot strike. Natural rearfoot strike runners were studied to see if a modified elliptical trainer could be used to alter their running pattern to that of a midfoot strike runner. Their results were compared to subjects who ran on a non-modified elliptical trainer. After training on the modified elliptical trainer, subjects demonstrated a decrease in foot angle at initial contact when attempting to run with a midfoot strike. Training did not affect all kinetic metrics or stride frequency. However, the kinematic change suggests that there may be an impact on running energetics. Training on the modified elliptical trainer resulted in improved midfoot strike kinematics in natural rearstrike runners when they attempted run in a midfoot strike pattern.

The main goal of the project was to compare how the Achilles tendon is affected while running with traditional shoes, minimalistic shoes and barefoot. Displacement and strain were calculated both for different shoes and for different foot strike patterns. The calculations were done with a speckle tracking algorithm and displacement was calculated for three different depths in the tendon: deep layer, mid layer and superficial layer. The goal was also to conduct this analysis after a review of the algorithm used. The review of the algorithm focused on the size of the region of interest, kernel size and frequency. Literature study showed that it is more common to use a smaller kernel size, but the same shape. The region of interest was chosen depending on the size of the tendon. Displacement and strain in the Achilles tendon was calculated for seven subjects and the result did not show any difference in amount of mean deformation due to different shoe types or foot strike patterns. It was a small sample group but the result indicated a difference in peak displacement between deep and superficial layer depending on different shoe types and foot strike patterns. The difference in peak displacement between deep and superficial layer was lowest when running barefoot, larger when running with minimalistic shoes and greatest when running with traditional shoes. This result was only achieved when running with rear foot strike pattern. When running with fore foot strike pattern the difference in peak displacement between layers did not change with different conditions. In all conditions the difference in peak displacement between the layers was greater when running with rear foot strike pattern than when running with front foot strike pattern. The deep layer displaced more than the superficial layer (p&lt;0.01) for all conditions and foot strike patterns.