Recently, fatigability and muscle oxygen consumption (mVO 2 ) during sustained isometric contractions were found to be less at shorter (30° knee angle; 0°= full extension) compared to longer knee extensor muscle lengths (90°) 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 Wndings could be accounted for by a knee angle-and a muscle-dependent activation respectively. On two experimental days rectiWed 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° 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°, maximal mVO 2 was reached signiWcantly 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° (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°. At 10%MTC at all knee angles, maximal mVO 2 of the RF occurred signiWcantly later (28.8 § 36.0 s) and showed a signiWcantly 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 »60% lower oxygen consumption at 30°, but the later increase in RFmVO 2 seemed to be caused by a less strong activation of the RF.

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