title: Is the blood flow response to a single contraction determined by work performed?
abstract: Nine healthy volunteers performed a series of single handgrip isometric contractions to test the hypothesis that the blood flow response to a contraction is determined solely by the tension-time index (isometric analog of work). Contractions were performed in duplicate at 15, 30, and 60% of maximal voluntary contraction (MVC) at durations of 0.5, 1, and 2 s. Forearm blood flow (FBF) was measured beat by beat by using Doppler ultrasound. Peak FBF responded in a graded fashion to graded increases in peak tension with contraction time held constant (35, 56, and 90 ml/min for 15, 30, and 60% MVC for 1 s, respectively). When tension was kept constant, peak FBF responded in a graded fashion to graded increases in duration (77, 90, and 97 ml/min for 60% MVC for 0.5, 1, and 2 s). With a constant tension-time index, peak FBF responded in a graded fashion to graded increases in peak tension (48, 56, and 77 ml/min for 15% MVC/2 s, 30% MVC/1 s, and 60% MVC/0.5 s). Similar trends were also observed for total postcontraction hyperemia. Blood flow increased regardless of whether the change in tension-time index was accomplished by an increase in tension or duration of contraction. However, with a constant tension-time index, the change in blood flow was related to the peak tension developed. Our results suggest that the blood flow response to a single muscle contraction is not determined solely by the work performed (tension-time index) but also by the number of muscle fibers recruited.
authors.affiliation: Medical College of Wisconsin, Veterans Affairs Medical Center, Anesthesia Research 151, 5000 W. National Ave., Milwaukee, WI 53295, USA.
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Hamann
authors.forename: John B
authors.initials: JB
authors.lastname: Buckwalter
authors.forename: Philip S
authors.initials: PS
authors.lastname: Clifford
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure; D001827:Body Height; D001835:Body Weight; D004576:Electromyography; D005260:Female; D018737:Hand Strength; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D013314:Stress, Mechanical