Excessive skeletal muscle recruitment during strenuous exercise in McArdle patients.
We compared the cardiorespiratory response and muscle recruitment [as determined by electromyography (EMG)] of 37 McArdle patients [19 males, 37.4 ± 2.8 years, body mass index (BMI): 25.1 ± 4.7 kg m(-2)] and 33 healthy controls (18 males, 36.4 ± 10.0 years, BMI: 25.7 ± 3.8 kg m(-2)) during cycle-ergometer exercise (an incremental test to exhaustion and a 12-min submaximal constant workload test). We obtained cardiorespiratory [oxygen uptake and heart rate (HR)] and EMG data (rectus femoris and vastus lateralis muscles). During the incremental test, the patients exhibited the expected hyperkinetic cardiovascular response shown by a marked increase in the slope of the HR:Power relationship (p < 0.001). Throughout the incremental test and at the point of fatigue, the patients produced significantly less power than the controls (peak power output: 67 ± 21 vs. 214 ± 56 watts respectively, p < 0.001), yet they demonstrated significantly higher levels of muscle activity for a given absolute power. During the constant workload test, patients displayed higher levels of EMG activity than the controls during the second half of the test, despite a lower power production (34 ± 13 vs. 94 ± 29 watts respectively, p < 0.001). In conclusion, since the McArdle patients required more motor unit recruitment for a given power output, our data suggest that the state of contractility of their muscles is reduced compared with healthy people. Excessive muscle recruitment for a given load could be one of the mechanisms explaining the exercise intolerance of these patients.
Rae
Dale E
DE
UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Newlands, Cape Town, South Africa. Dale.Rae@uct.ac.za
Noakes
Timothy D
TD
San Juan
Alejandro F
AF
Pérez
Margarita
M
Nogales-Gadea
Gisela
G
Ruiz
Jonatan R
JR
Morán
María
M
Martín
Miguel A
MA
Andreu
Antoni L
AL
Arenas
Joaquín
J
Lucia
Alejandro
A
D000328:Adult; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006012:Glycogen Storage Disease Type V / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000502:physiology