The reason that the issue is important is that most biomechanical studies and clinical assessments are done when runners are fresh and not fatigued. When they are fresh, they may not display what are assumed to be risk factors for an injury that they may display when they are fatigued. Obviously, the later part of every run and race is done in a fatigued state!
Which clearly shows why we need to know more about fatigue and how it affects the forces associated with running, so I was initially pleased to see this turn up in my alerts (…until I read it ☺):
Navicular Drop Before and After Fatigue of the Ankle Invertor Muscles
Fredrick Anthony Gardin, PhD, ATC, CSCS; David Middlemas, EdD, ATC; Jennifer L. Williams,
ATC; Steven Leigh, PhD; and Rob R. Horn, PhD
International Journal of Athletic Therapy & Training Nov 2013
Context: Navicular drop is widely believed to be an indicator of elevated susceptibility to pronation-related injuries, which may be increased by fatigue in the muscles that dynamically support the medial longitudinal arch.
Objective: The purpose of this study was to evaluate navicular drop before and after fatigue of the ankle invertor muscles among individuals with different foot types. Participants: 20 male and 16 female recreationally active, college-age volunteers (20.03 ± 1.48 years of age).
Methods: Navicular drop was measured before and after inducing fatigue in the ankle invertor muscles. Participants’ foot types were
classified as high-arch, neutral, or low-arch.
Results: There was no interaction between foot type and trial, and no main effect for trial. A main effect for foot type was significant (p = .001). Intra-class correlation coefficients for prefatigue and postfatigue measurements indicated good internal consistency.
Our findings failed to provide any evidence to support the existence of a relationship between ankle invertor muscle fatigue and static measurements of change in navicular height from a sitting to standing position.
Basically they measured the changes in the height of the navicular when relaxed and weightbearing; then fatigued the invertor muscles then then measured the changes in navicular height again.
Anyone see the problem? What were they thinking? The invertor muscles do not even fire or work during static stance, so what is the point of measuring what fatigue in those muscles do to navicular height? Of course its not going to have any effect. Stick an EMG needle into those muscles and you can see that. Stand up barefoot, are your ankle invertors working? The invertor muscles only work during dynamic function or when there are perturbations to balance during static stance.
If there was ever the Nobel Ig Prize equivalent for biomechanics research, this study would be nominated.
As always, I go where the evidence takes me until convinced otherwise.