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° 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.

Knee angle-dependent oxygen consumption of human quadriceps muscles during maximal voluntary and electrically evoked contractions

“…Since potentiation may lead to constant force output despite a decline in motor unit Wring rate (Klein et al 2001), a muscle length-dependent potentiation could allow for a slower increase in muscle activation at extended compared with Xexed knee angles during constant force production. This less intense muscle activation could delay the recruitment of larger motor units which may account for the lower mVO 2 and lower fatigability found at extended knee angles Kooistra et al 2006). However, at submaximal contraction intensities (10-70% of the maximal torque capacity [MTC]) the lower muscle activation at extended knee angles, which was inferred from changes in surface EMG, could only partially account for the lower mVO 2 found at extended knee angles (Kooistra et al 2006).…”

“…This less intense muscle activation could delay the recruitment of larger motor units which may account for the lower mVO 2 and lower fatigability found at extended knee angles Kooistra et al 2006). However, at submaximal contraction intensities (10-70% of the maximal torque capacity [MTC]) the lower muscle activation at extended knee angles, which was inferred from changes in surface EMG, could only partially account for the lower mVO 2 found at extended knee angles (Kooistra et al 2006). However, because it is likely that the position of surface electrodes relative to the muscle changes with changing knee angle and because surface EMG was normalised to the values obtained during MVC and maximal voluntary activation may diVer (see below) across knee angles , it is hazardous to interpret diVerences in surface EMG during submaximal contractions in terms of knee angle dependent diVerences in neural activation.…”

“…This probably contributed to the greater endurance found at extended knee angles in the past (Kooistra et al 2005;Ng et al 1994). The lower mVO 2 at extended knee angles was accompanied by a somewhat smaller increase in surface EMG during the contraction, suggesting a smaller increase in neural activation, possibly due to a greater potentiation at shorter muscle lengths (Kooistra et al 2006). Potentiation, the enhancement of contractile response by prior activation, is greater at short compared to long muscle lengths in rats (Rassier et al 1997;Rijkelijkhuizen et al 2005).…”

Function of a large biarticular hip and knee extensor during walking and running in guinea fowl (Numida meleagris)

“…EMG amplitude has been used for many years (Inman et al, 1952;Bigland and Lippold, 1954) over the years has focused on whether EMG amplitude correlates with muscle force, mechanical power output and metabolic rate (Bigland-Ritchie and Woods, 1976;De Luca, 1997;Kooistra et al, 2006;Disselhorst-Klug et al, 2009). Studies with isolated muscle (Woledge et al, 1985;DeHaan et al, 1989;Beltman et al, 2004;Trinh and Syme, 2007) and in vivo studies (Bigland and Lippold, 1954;Bigland-Ritchie and Woods, 1976;Aura and Komi, 1986;Takarada et al, 1997) predict that the relationship between active fiber volume, as estimated by EMG intensity, and all these variables will vary with the mechanical state of the muscle, including fiber length and shortening velocity.…”

Comparison of oxygenation kinetics measured by different placements of the NIRS probe during sustained isometric gripping

“…It is possible to approximately calculate the change of oxygenation hemoglobin/myoglobin with a modification of the Beer-Lambert law due to the fact that the near-infrared light-absorption differs in response to the hemoglobin/myoglobin oxygenation [4,5]. This has recently been used not only to measure oxygenation kinetics, but also to predict the oxygen consumption of an active muscle with an arterial/veinous occlusion method [5][6][7][8]. Of all the various NIRS instruments, the NIRO-300 (Hamamatsu Photonics, Japan) has confirmed the validity of oxygen saturation measurements and their reliability in vivo by a simulation experiment using a phantom tissue [5,9].…”