Changes in foot and shank coupling due to alterations in foot strike pattern during running
Introduction
During running (along with other forms of locomotion) the foot is the site at which external forces are applied to the body. Since the foot transfers these forces to the lower limb, the accompanying kinematic relationship between the foot and lower limb has been suggested as a potential mechanism for overuse injuries of the lower extremity (Powers et al., 2002). For instance, the subtalar joint is oriented in such a manner that frontal plane motion of the foot is transferred up the kinetic chain as transverse shank rotation (Hicks, 1953, Inman et al., 1981). Thus prolonged or excessive foot motion causing increased transverse plane motion of the lower extremity may result in non-optimal loading of bone and/or soft tissue. In an attempt to determine how these injuries develop a wealth of research has examined the kinematic coupling between the foot and lower leg (for review see DeLeo et al., 2004). Historically, research investigating this coupling mechanism has focused on the relationship between the rearfoot and shank (ankle-complex joint). Recent research, however, suggests that including the distal joints of the foot can be valuable in fully understanding the coupling mechanisms between the foot and lower limb (Eslami et al., 2007, Pohl et al., 2006, Pohl et al., 2007). It is therefore pertinent to assess motion of the foot using a multi-segment modelling approach (Carson et al., 2001, Leardini et al., 2007, MacWilliams et al., 2003, Myers et al., 2004).
A typical approach in investigating the kinematic coupling relationship between the rearfoot and shank is to determine differences in the coupling relationship across different subgroups of the population (Nawoczenski et al., 1998), or study changes in the coupling relationship when rearfoot motion is altered via an in-shoe orthotic/change in shoe construction (Stacoff et al., 2001, Williams et al., 2003). A feature of such research is that quite often the differences found in joint kinematics are small and inter-subject variability can be of a similar magnitude to the group differences. This, considered along with measurement error and skin movement artefact, may partly explain the equivocal findings in the literature concerning segmental coupling.
An alternative approach in understanding the coupling relationship between the segments of the foot and lower limb, is to substantially alter the kinematics of one of the segments of interest and observe its influence on the adjacent segment. This can be achieved using experimental manipulation to greatly alter an individual’s normal gait pattern. By comparing substantially different gait patterns, the coupling relationship between adjacent foot and lower limb segments can be measured with greater validity than otherwise might have been the case. This approach also has the advantage of assessing the robustness of this coupling relationship across different activities. We have recently used such an approach to determine the effects of altering step width (Pohl et al., 2006), speed and mode of gait (Pohl et al., 2007) on foot and lower limb coupling. In the present study we continue this theme by investigating how foot and lower limb coupling during running is affected by variations in how the foot initially makes contact with the ground.
It has been shown that rearfoot motion during early stance in running is affected by foot strike pattern (Stackhouse et al., 2004, Stacoff et al., 1989). In these studies it was reported that when touchdown was made with the forefoot, rearfoot eversion excursion was substantially lower than when a rearfoot touchdown occurred. Interestingly, an increased amount of forefoot eversion was also evident during heel strike running compared to forefoot strike running (Stacoff et al., 1989). In a later study, it was demonstrated that forefoot kinematics in forefoot strike running were influenced by whether subjects touched the ground with their heel or not following initial contact (Stacoff et al., 1991).
In the present study we extend this earlier work by using a multi-segment modelling approach to determine how alterations in foot-strike pattern during running affect the kinematic coupling between the forefoot, rearfoot and shank. It was postulated that if the shank and forefoot were kinematically coupled with the rearfoot via the joints of the ankle-complex (includes the talocrural and subtalar joints) and midfoot, respectively, then any alterations in rearfoot motion induced by foot-strike pattern changes, would in turn alter shank and forefoot kinematics. Further, it was postulated that the robustness of coupling found at the ankle-complex and midfoot joints would be demonstrated by the degree to which changes in rearfoot motion altered kinematics at the shank and forefoot, respectively.
Section snippets
Subjects
Twelve subjects (six males, six females; mean (SD) age, 21.3 (1.9) years; body mass, 67.5 (13.1) kg; and height, 1.74 (0.09) m) volunteered to participate. Inclusion criteria were that subjects were currently engaging in at least 2 h per week of exercise involving running, had been free from injury of the lower extremity in the last six months, had no obvious anatomical malalignment and did not wear foot orthotics. The study was approved by the institutional ethics committee, and written informed
Results
For each foot strike condition the main affect of repetition (across the 5 trials) was non significant (P > 0.05). This indicated there were no learning or fatigue effects between trials and thus that any differences between conditions were due to the manipulation of foot-strike pattern.
Rearfoot and shank kinematic coupling
It was postulated that manipulation of foot strike pattern would induce changes in rearfoot eversion kinematics, and depending on how such changes affected the kinematics of the shank and forefoot, this would highlight the robustness of coupling found at the ankle-complex and midfoot joints, respectively. When subjects were asked to run with a heel foot strike pattern (HFS) both peak rearfoot eversion and eversion excursion were significantly different from the forefoot strike (FFS) and toe
Conclusions
Good kinematic coupling was found between rearfoot eversion/inversion and shank internal/external rotation regardless of foot-strike pattern. Forefoot sagittal and transverse planar movements were also strongly coupled with rearfoot frontal plane motion in all foot-strike conditions. Some subtle differences were noted in the amount of rearfoot eversion transferred into shank internal rotation in the first 10–15% of stance during HFS running. Forefoot kinematics in all three planes were also
Acknowledgements
John Buckley is supported by an RCUK Academic Fellowship (Research Councils, UK). The authors gratefully acknowledge the help of Neil Messenger, Elliot Messenger, David Snape and Chandra Lloyd for their assistance with the project.
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Data collected during M.B. Pohl’s time as a member of the Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK.