A previous study found that, during exercise, McArdle patients had much greater electrical activity within their muscles compared to healthy individuals. The authors of that study argued that more muscle fibres are being activated to compensate for the weakness associated with this disease. Besides the fact that McArdle patients lack phosphorylase, very little is actually known about the functional components of their muscle fibres, such as muscle fibre type, muscle fibre size and the contractility of the fibres. In order to answer whether McArdle patients have an altered muscle fibre type (which could lead to less force production and hence, weakness), we performed a relative muscle fibre type analyses (Kohn et al., 2014).
To our surprise, there was no difference in the fibre type composition of McArdle patients’ muscle and that of healthy controls (see graph below). We were able to show this in both the Biceps brachii and Vastus lateralis muscles. To further explain the weakness that McArdle patients experience, we analysed the cross-sectional areas of the various fibre types (Henning et al., 2016). Again, there was no difference between fibre size of healthy individuals and that of McArdle patients in both the arm and leg muscles.
We therefore concluded that fibre type and fibre size is not compromised or altered as a result of this disorder.
What are we doing next?
We are currently awaiting muscle biopsies from our Spanish collaborators to determine the fibre contractile properties from McArdle patients and comparing it to that from healthy individuals.
★ Franclo Henning (PhD candidate, University of Cape Town)
★ Alejandro Lucia (European University of Madrid, Spain)
★ Miguel A. Martín (Hospital 12 de Octubre, Spain)
★ Tomas Pinós (Universitat Autónoma de Barcelona, Spain)
★ Juan Carlos Rubio (Hospital 12 de Octubre, Spain)
★ Alfredo Santala (Universidad Pablo de Olavide, Spain)
★ Jo Wilmshurst (Red Cross Children’s Hospital, Cape Town)
Past students on this project
★ Carol Cunninghame