title: Knee extensor muscle oxygen consumption in relation to muscle activation.
abstract: Recently, fatigability and muscle oxygen consumption (mVO(2)) during sustained isometric contractions were found to be less at shorter (30 degrees knee angle; 0 degrees = full extension) compared to longer knee extensor muscle lengths (90 degrees ) and, at low torques, less in the rectus femoris (RF) muscle than in the vastus lateralis and medialis. In the present study we hypothesized that these findings could be accounted for by a knee angle- and a muscle-dependent activation respectively. On two experimental days rectified surface EMG (rsEMG) was obtained as a measure of muscle activation in nine healthy young males. In addition, on day 1 maximal torque capacity (MTC) was carefully determined using superimposed nerve stimulation on brief high intensity contractions (> 70%MVC) at 30, 60 and 90 degrees knee angles. On day 2, subjects performed longer lasting isometric contractions (10-70%MTC) while mVO(2) was measured using near-infrared spectroscopy (NIRS). At 30 degrees , maximal mVO(2) was reached significantly later (11.0 s +/- 6.5 s) and was 57.9 +/- 8.3% less (average +/- SD, across intensities and muscles) than mVO(2) at 60 and 90 degrees (p < 0.05). However, rsEMG was on average only 18.0 +/- 11.8% (p = 0.062) less at the start of the contraction at 30 degrees . At 10%MTC at all knee angles, maximal mVO(2) of the RF occurred significantly later (28.8 +/- 36.0 s) and showed a significantly smaller increase in rsEMG compared to both vasti. In conclusion, it is unlikely that the tendency for less intense muscle activation could fully account for the approximately 60% lower oxygen consumption at 30 degrees , but the later increase in RFmVO(2) seemed to be caused by a less strong activation of the RF.
authors.affiliation: Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081, BT, Amsterdam, The Netherlands. Ronald.Kooistra@fbw.vu.nl
authors.forename: R D
authors.initials: RD
authors.lastname: Kooistra
authors.forename: M E
authors.initials: ME
authors.lastname: Blaauboer
authors.forename: J R
authors.initials: JR
authors.lastname: Born
authors.forename: C J
authors.initials: CJ
authors.lastname: de Ruiter
authors.forename: A
authors.initials: A
authors.lastname: de Haan
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D019415:Torque