There is an ever increasing attention being paid to the role of proximal issues in the development of lower limb injuries. This most recent publication from Medicine & Science in Sports & Exercise adds to the knowledge base:
Neuromotor Control of Gluteal Muscles in Runners with Achilles Tendinopathy
Smith, Melinda M.; Honeywill, Conor; Wyndow, Narelle; Crossley, Kay M.; Creaby, Mark W.
Medicine & Science in Sports & Exercise: 10 October 2013
Purpose: The purpose of this study was to compare the neuromotor control of the Gluteus Medius (GMED) and Gluteus Maximus (GMAX) muscles in runners with Achilles tendinopathy to that of healthy controls.
Methods: Fourteen male runners with Achilles tendinopathy and nineteen healthy male runners (Control) ran over-ground whilst electromyography of GMED and GMAX was recorded. Three temporal variables were identified via visual inspection of EMG data: (i) onset of muscle activity (onset), (ii) offset of muscle activity (offset), and (iii) duration of muscle activity (duration). A multivariate analysis of covariance with between subject factor of group (Achilles tendinopathy, Control) and variables of onset, offset, and duration was performed for each muscle. Age, weight and height were included as covariates and alpha level set at 0.05.
Results: The Achilles tendinopathy group demonstrated a delay in the activation of the GMED relative to heel strike (p < 0.001) and a shorter duration of activation (p < 0.001) compared to that of the Control group. GMED offset time relative to heel strike was not different between the groups (p = 0.063). For GMAX the Achilles tendinopathy group demonstrated a delay in its onset (p = 0.008), a shorter duration of activation (p = 0.002), and earlier offset (p < 0.001) compared to the Control group.
Conclusion: This study provides preliminary evidence of altered neuromotor control of the GMED and GMAX muscles in male runners with Achilles tendinopathy. Whilst further prospective studies are required to discern the causal nature of this relationship, this study highlights the importance of considering neuromotor control of the gluteal muscles in the assessment and management of patients with Achilles tendinopathy.
Essentially what these authors found was that the in the group with the achilles tendinopathy that:
- Gluteus Medius had a delay in onset; shorter duration of activity; but offset was the same as the control group.
- Gluteus Maximus had a delay in onset; shorter duration of activity; and an earlier offset than the control group.
As with any case control study the selection of the control group is crucial. In a previous study I commented on, the selection of the control group was probably enough to be fatal to that study, but in the case of the above study the characteristics of the two groups were much better matched with only a slight differences in ages (p=0.04).
The biggest proviso with this study is the good old chicken or egg scenario. This was a case control study and not a prospective study. This study presents two equally plausible mechanisms:
- The presence of the symptoms of the Achilles tendinopathy altered the gait and caused the findings with the gluteal muscles
- The findings with the gluteal muscles caused a gait problem that was the risk factor and helped increase the load in the achilles tendon
It is not possible from the study design to say if it is one or the other or both. That does not mean that we should not consider gluteal function as part of the assessment of achilles tendinopathy. Even if it is a chicken or egg, the dysfunction is present and there is a potential that it should be dealt with. What is now needed is a prospective risk factor study on this and a clinical trial.
As always, I go where the evidence takes me until convinced otherwise, and this evidence suggests that we probably need to start considering what is happening with glutes in Achilles tendinopathy.