Abstract
ABSTRACTPatients suffering from glycogen storage disease V (McArdle disease) were shown to have higher surface electrical activity in their skeletal muscles when exercising at the same intensity as their healthy counterparts, indicating more muscle fibre recruitment. To explain this phenomenon, this study investigated whether muscle fibre type is shifted towards a predominance in type I fibres as a consequence of the disease. Muscle biopsies from the Biceps brachii (BB) (n = 9) or Vastus lateralis (VL) (n = 8) were collected over a 13-year period from male and female patients diagnosed with McArdle disease, analysed for myosin heavy chain (MHC) isoform content using SDS-PAGE, and compared to healthy controls (BB: n = 3; VL: n = 10). All three isoforms were expressed and no difference in isoform expression in VL was found between the McArdle patients and healthy controls (MHC I: 33±19% vs. 43±7%; MHC IIa: 52±9% vs. 40±7%; MHC IIx: 15±18% vs. 17±9%). Similarly, the BB isoform content was also not different between the two groups (MHC I: 33±14% vs. 30±11%; MHC IIa: 46±17% vs. 39±5%; MHC IIx: 21±13% vs. 31±14%). In conclusion, fibre type distribution does not seem to explain the higher surface EMG in McArdle patients. Future studies need to investigate muscle fibre size and contractility of McArdle patients.
Highlights
McArdle patients suffer from glycogen storage disease V and have limited endogenous glycogen for use during exercise
Many McArdle patients avoid exercise, or are advised that exercise is contra-indicated for their condition, which may inadvertently decrease their quality of life
A recent study found that patients suffering from McArdle disease produced less force, fatigued faster, and surprisingly recorded almost three times as much surface electrical activity in their skeletal muscles compared to healthy controls exercising at the same intensity (Rae et al, 2010)
Summary
McArdle patients suffer from glycogen storage disease V and have limited endogenous glycogen for use during exercise. They find exercise difficult and fatigue quickly, presumably since they initially rely on blood glucose from exogenous sources for fuel. Some evidence exist that muscle fibre type correlates with EMG activity in vitro, it is still unclear whether this holds true in vivo (Farina, 2008; Kupa et al, 1995; von Tscharner and Nigg, 2008). Rae et al (Rae et al, 2010) suggested that this excessive muscle recruitment might be attributed to altered contractile properties of the diseased muscle, perhaps compounding the exercise intolerance experienced by McArdle patients
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
