One of the shortcomings of a lot of biomechanical laboratory testing is that it is done on runners who are fresh and not fatigued. A number of studies have shown how foot function is different at, for example, the beginning of a marathon vs what it is at the end of a marathon. While this is not close to pointing to a fatal flaw in the research done on fresh participants, it does need to be taken into account when considering what the foot does, as it is probably more often fatigued than not when running. Clinically, when we assess runners, they are fresh and not fatigued. Little or nothing is known about the injury impact risks of that fatigue.
Some of the previous research has shown:
- Elena Escamilla-Martinez et al showed an increase in the Foot Posture Index of 2 points after running for 60 mins at 3.3 m/sec on a treadmil (more pronation for those not familiar with the Foot Posture Index)
- Willems et al reported an increases in the loading of the forefoot, midfoot and medial heel were noted and decreases in loading of the lateral toes after a 20kn run
- Alfuth and Rosenbaum found no effects after a 10 km run on plantar pressure distribution and peak forces.
- Stolwijk et al reported an increased heel loading and decreased function of the toes and a change of walking pattern with less roll-off after several days of walking almost 200km
- Schleee et al found that the values of maximum pronation velocity showed a significant increase after a 45 min treadmill run
- Karagounis et al found increases in in the peak pressure and impulse values under the forefoot and toe regions
- Bisiaux and Moretto found a significant decrease in pressure peak and the relative impulse under the heel and the midfoot along with significant increase in pressure peak and relative impulse under the forefoot were observed 30min after the run
- Nagel et al reported after a marathon that there was increased peak pressure under the metatarsal heads after the race indicates a load shift from the toes to the metatarsal heads
- Headlee et al showed a 10.0+/-3.8mm of navicular drop at baseline and 11.8+/-3.8mm after fatigue of the intrinsic muscles
- Chang-Ryeol Lee et al found that after 75 isotonic contractions of the intrinsic foot muscles there were increases in plantar pressure parameters indicting more pronation of the subtalar joint
- Coventry et al reported that after fatigue was induced there was no significant change in shock attenuation throughout the body. Hip and knee flexion increased and ankle plantarflexion decreased at touchdown with fatigue. Hip joint work increased and ankle work decreased.
- Vie et ak reported increased eversion after running
- Dierks et al reported that after fatigue that there were no differences were observed for knee flexion, hip internal rotation, or any joint timing relationship. Based on these results, runners demonstrated subtle changes in kinematics in the exerted state, most notably for eversion. However, runners were able to maintain joint timing throughout the leg, which may have been a function of the knee.
- Milgrom et al showed increase strain in the tibia after fatigue.
The most recent study just published on this is:
The effects of prolonged running on foot posture: a repeated measures study of half marathon runners using the foot posture index and navicular height
Emma Cowley and Jonathan Marsden
Journal of Foot and Ankle Research 2013, 6:20 doi:10.1186/1757-1146-6-20
Different foot postures are associated with alterations in foot function, kinetics and the subsequent occurrence of injury. Little is known about changes in foot posture following prolonged weightbearing exercise. This study aimed to identify changes in foot posture after running a half marathon.
Foot posture was measured using the Foot Posture Index (FPI-6) and navicular height in thirty volunteer participants before and after running a half marathon. FPI-6 scores were converted to Rasch logit values and means compared for these and navicular height using an ANOVA.
There was a 5 mm drop in navicular height in both feet when measured after the half marathon (P < 0.05). The FPI-6 showed a side x time interaction with an increase in score indicating a more ‘pronated’ position in the left foot of + 2 [Rasch value + 1.7] but no change in the right foot (+ 0.4 [+ 0.76]) following the half marathon.
The apparent differences between the FPI-6 and navicular height on the right foot may be because the FPI-6 takes soft tissue contour changes into consideration whilst the navicular height focuses on skeletal changes. The changes in foot posture towards a more pronated position may have implications for foot function, and therefore risk of injury; shoe fit and comfort and also the effect of therapeutic orthoses worn during prolonged running.
Quite clearly fatigue affects a number of parameters, many of which are commonly assumed to be associated with increased risk for injury. A 5mm change in navicular drop reported by these authors after a half marathon does seem like a lot. I wonder what it would have been after a marathon?
As always, I go where the evidence takes me.
Cowley, E., & Marsden, J. (2013). The effects of prolonged running on foot posture: a repeated measures study of half marathon runners using the foot posture index and navicular height Journal of Foot and Ankle Research, 6 (1) DOI: 10.1186/1757-1146-6-20