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Metabolism changes in single human fibres during brief maximal exercise
C Karatzaferi1, A de Haan, W van Mechelen
1Neuromuscular Research Group, Manchester Metropolitan University, Alsager, UK. ck@itsa.ucsf.edu
Experimental Physiology
|July 27, 2001
Summary
Maximal exercise rapidly depletes phosphocreatine (PCr) in all human skeletal muscle fiber types. Type II fibers expressing the IIX myosin heavy chain isoform experience the greatest metabolic stress, indicated by reduced ATP levels.
Area of Science:
- Exercise Physiology
- Skeletal Muscle Metabolism
- Biochemistry
Background:
- Understanding energy metabolism in human skeletal muscle is crucial for optimizing athletic performance and understanding fatigue.
- High-energy phosphate compounds, such as adenosine triphosphate (ATP) and phosphocreatine (PCr), are vital for muscle contraction.
- Different human skeletal muscle fiber types (Type I, IIA, IIAx, IIXa) possess distinct metabolic characteristics.
Purpose of the Study:
- To investigate the changes in high-energy phosphate levels in single human skeletal muscle fibers immediately after 10 seconds of maximal dynamic exercise.
- To determine if specific myosin heavy chain (MyHC) isoforms influence the metabolic response to brief, intense exercise.
Main Methods:
- Muscle biopsies were obtained from the vastus lateralis of two volunteers at rest and immediately post-exercise.
- Single muscle fibers were dissected and categorized based on their MyHC isoform content (Type I, IIA, IIAx, IIXa).
- High-performance liquid chromatography (HPLC) was used to analyze ATP, inosine monophosphate (IMP), PCr, and creatine levels in fiber fragments.
Main Results:
- PCr content decreased significantly (P < 0.01) in all fiber types after 10s of maximal exercise (approx. 46-62% reduction).
- ATP levels declined only in Type II fibers, with the most pronounced reductions observed in IIAx and IIXa fibers.
- IMP accumulation was significant in IIAx and IIXa fibers, reaching mean values of 16 and 18 mmol/(kg dry mass), respectively.
Conclusions:
- Brief maximal dynamic exercise induces substantial PCr depletion across all human skeletal muscle fiber types.
- Type II fibers, particularly those expressing the IIX MyHC isoform (IIAx and IIXa), are subjected to the greatest metabolic stress during such exercise, evidenced by significant ATP decline.
- These findings highlight the differential metabolic demands placed on various muscle fiber types during high-intensity, short-duration physical activity.