title: Relationship between performance at different exercise intensities and skeletal muscle characteristics.
abstract: The hypothesis investigated whether exercise performance over a broad range of intensities is determined by specific skeletal muscle characteristics. Seven subjects performed 8-10 exhaustive cycle trials at different workloads, ranging from 150 to 700 W (150 min to 20 s). No relationships between the performance times at high and low workloads were observed. A relationship (P < 0.05) was noticed between the percentage of fast-twitch x fibers and the exercise time at 579 ± 21 W (∼30 s; r(2) = 0.88). Capillary-to-fiber-ratio (r(2): 0.58-0.85) was related (P < 0.05) to exercise time at work intensities ranging from 395 to 270 W (2.5-21 min). Capillary density was correlated (r(2) = 0.68; P < 0.05) with the net rate of plasma K(+) accumulation during an ∼3-min bout and was estimated to explain 50-80% (P < 0.05) of the total variance observed in exercise performances lasting ∼30 s to 3 min. The Na(+)-K(+) pump β(1)-subunit expression was found to account for 13-34% (P < 0.05) during exhaustive exercise of ∼1-4 min. In conclusion, exercise performance at different intensities is related to specific physiological variables. A large distribution of fast-twitch x fibers may play a role during very intense efforts, i.e., ∼30 s. Muscle capillaries and the Na(+)-K(+) pump β(1)-subunit seem to be important determinants for performance during exhaustive high-intensity exercises lasting between 30 s and 4 min.
authors: Dept. of Exercise and Sport Sciences, Section of Human Physiology, August Krogh Bldg., Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark.
authors: F Marcello
authors: FM
authors: Iaia
authors: Jorge
authors: J
authors: Perez-Gomez
authors: Martin
authors: M
authors: Thomassen
authors: Nikolai B
authors: NB
authors: Nordsborg
authors: Ylva
authors: Y
authors: Hellsten
authors: Jens
authors: J
authors: Bangsbo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling; D015415:Biomarkers / Q000097:blood; D001706:Biopsy; D002196:Capillaries / Q000502:physiology; D004734:Energy Metabolism; D015444:Exercise; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D010101:Oxygen Consumption; D010807:Physical Endurance; D011188:Potassium / Q000097:blood; D012044:Regression Analysis; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013647:Task Performance and Analysis; D013997:Time Factors; D055815:Young Adult
chemical_list: C503551:ATP1B1 protein, human; D015415:Biomarkers; D019344:Lactic Acid; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium