title: Gradual increase in leg oxygen uptake during repeated submaximal contractions in humans.
abstract: We examine whether muscle oxygen consumption (VO2) increases gradually during repeated submaximal isometric contractions. Six subjects made two-legged isometric quadriceps contractions at 30% maximal voluntary contraction for 6 s with 4 s of rest between until exhaustion (58 +/- 8 min). Blood samples were taken from the femoral vein and artery, and blood velocity was recorded by ultrasound-Doppler technique in the femoral artery. Blood flow was calculated from velocity and artery diameter values. Leg VO2 increased sixfold within the 1st min of exercise. A further doubling of the VO2 was seen during the remainder of the exercise, reaching 307 +/- 22 ml/min at exhaustion. This latter increase was due to a 54% increase in blood flow and a 34% increase in oxygen extraction. After 20 min of recovery VO2 was still 75% higher than preexercise values. The results show a twofold increase in energy demand of the working muscle during repeated constant-force isometric contractions. The increased energy cost of contraction is probably localized at the cellular level, and it parallels fatigue determined as decreased force-generating capacity.
authors.affiliation: Department of Physiology, National Institute of Occupational Health, Oslo, Norway.
authors.forename: N K
authors.initials: NK
authors.lastname: Vøllestad
authors.forename: J
authors.initials: J
authors.lastname: Wesche
authors.forename: O M
authors.initials: OM
authors.lastname: Sejersted
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000328:Adult; D001783:Blood Flow Velocity; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology; D005221:Fatigue / Q000503:physiopathology; D005260:Female; D005263:Femoral Artery / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007866:Leg; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000098:blood supply / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption
chemical_list: D000255:Adenosine Triphosphate; D010100:Oxygen