During the stance phase of running, the foot is exposed to ground reaction forces in the vertical, mediolateral and anteroposterior directions. These forces will have a marked effect on the motion of the foot and lower limb. At heel strike, a vertical impact peak occupies approximately the first 20 – 30ms of stance. This phase of absorption is referred to as passive because it is not controlled by muscle activity and it is thought that passive structures are used to absorb energy. In the normal heel-toe runner this vertical impact force is applied lateral to the subtalar joint axis and posterior to the ankle joint axis, and results in a pronatory moment at the subtalar joint. During the initial contact phase of gait the ground reaction force has medial and posterior components as the shoe is stopped by the ground.

 After the passive phase, active absorption starts as muscles become the primary controllers of ground reaction forces.  During the foot flat phase of gait a substantial peak in vertical ground reaction force is seen and the mediolateral force is in a lateral direction. At this phase of stance the centre of pressure is lateral to the subtalar joint which when combined with the lateral shear force produces a pronatory moment at the subtalar joint.  When the anteroposterior force reverses and becomes propulsive, the vertical force reduces and the mediolateral force also reverses to a medial direction. The center of pressure now moves to the medial side of the subtalar joint axis, which produces a supinatory moment at the subtalar joint ( Hamill & Knutzen, 1995). 

Theory and Practice

This biomechanical sequence has some controversial aspects and varies a great deal due to the individual patients strength, flexibility, training and general skeletal structures. Possibly what is becoming more controversial is how these observable kinematic movements are created.  For many years it has been theorized that foot pronation and supination is the primary cause of lower limb movement dysfunction and impairment and may lead to injuries. However contempory research is struggling to confirm this view.  While some researchers suggest that foot control of the lower limb is normal for some patients, other studies report that this theory is incorrect. 

Stacoff et al (2000) highlighted concerns about this foot centred control of the lower limb when they tested kinematic changes in running with varying degrees of arch and heel control, essentially controlling foot pronation. Their results showed non-significant and highly variable effects from this intervention and changes of only 2 degrees of eversion were noted in rear foot. However a significant change was seen if tibial rotation which should not of happened if kinematic changes of the foot were needed to alter the more proximal lower limb  structures. Essentially tibial function was altered but foot function was not changed by medial foot control.  This tibial rotation change may have been caused by a sensory change in the foot that caused a change in the muscle activity in the pelvic, femoral or tibial regions. 

This possibility was given scientific plausibility by a study by Belchamber et al (2000) when they tested lower limb power flows while running and walking. This power flow technique will show whether a kinematic movement is being passively driven by ground reaction forces, by the proximal end of the segment or the distal end of the segment, ie. is the foot driving the hip or is the hip driving the foot? This study showed that lower limb kinematics are firstly driven by ground reaction forces in the absorption phase of running gait and then primarily at the proximal end of the lower limb. In some subjects a small period of distal segment control was noted which may provide an opportunity for foot control to positively assist lower limb stability. 

These studies have great relevance to rehabilitation oriented gait assessment because we must ensure that our approach to biomechanical analysis has the ability to see more than simple kinematics but must have some capacity to assess where it is best to change function to reduce stress in the injured body part. I believe that an integrated muscle balance and observation gait assessment will achieve this result.  This is the approach that we will cover in the Gait Assessment and Correction Workshop.  With a total body approach to injury treatment and rehabilitation the right level of stability training and passive support can be directed to the appropriate region of the lower limb.

References

Belchamber, T., & van den Bogert, A. (2000). Contribution of proximal and distal moments to axial tibial rotation while walking and running. Journal of Biomechanics, 33(11), 1397-1403.

Hamill, J., & Knutzen, K. (1995). Biomechanical Basis of Human Movement. (pp. 244-257 398-402). United States of America: Lippcott Williams Wilkins.

Lafortune, M., Valiant, G., & McLean, B. (2000). Biomechanics of Running. In J. Hawley (Ed.), Running (pp. 28-43). London: Blackwell Science.

Stacoff, A., Reinschmidt, C., Nigg, B., van den Bogert, A., Lundberg, A., Denoth, J., (2000). Effects of foot orthoses on skeletal motion during running. Clinical Biomechanics, 15, 54-64.