Alternate Muscle Activity Of Four Synergists In Quadriceps Femoris During Low-level Sustained Contraction

Alternate muscle activity between synergist muscles has been demonstrated during low-level sustained contractions [≤5% of maximal voluntary contraction (MVC) force]. To determine the functional significance of the alternate muscle activity, the association between the frequency of alternate muscle activity during a low-level sustained knee extension and the reduction in knee extension MVC force was studied. Forty-one healthy subjects performed a sustained knee extension at 2.5% MVC force for 1 h. Before and after the sustained knee extension, MVC force was measured. The surface electromyogram was recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles. The frequency of alternate muscle activity for RF-VL, RF-VM, and VL-VM pairs was determined during the sustained contraction. The frequency of alternate muscle activity ranged from 4 to 11 times/h for RF-VL (7.0 ± 2.0 times/h) and RF-VM (7.0 ± 1.9 times/h) pairs, but it was only 0 to 2 times/h for the VL-VM pair (0.5 ± 0.7 times/h). MVC force after the sustained contraction decreased by 14% ( P < 0.01) from 573.6 ± 145.2 N to 483.3 ± 130.5 N. The amount of reduction in MVC force was negatively correlated with the frequency of alternate muscle activity for the RF-VL and RF-VM pairs ( P < 0.001 and r = 0.65 for both) but not for the VL-VM pair. The results demonstrate that subjects with more frequent alternate muscle activity experience less muscle fatigue. We conclude that the alternate muscle activity between synergist muscles attenuates muscle fatigue.

Download Full-text

Local blood circulation among knee extensor synergists in relation to alternate muscle activity during low-level sustained contraction

Journal of Applied Physiology ◽

10.1152/japplphysiol.00671.2002 ◽

2003 ◽

Vol 95 (1) ◽

pp. 49-56 ◽

Cited By ~ 22

Author(s):

Motoki Kouzaki ◽

Minoru Shinohara ◽

Kei Masani ◽

Masanobu Tachi ◽

Hiroaki Kanehisa ◽

...

Keyword(s):

Blood Volume ◽

Muscle Activity ◽

Cross Correlation ◽

Near Infrared ◽

Time Lag ◽

Knee Extensor ◽

Local Circulation ◽

Sustained Contraction ◽

Low Level ◽

Cross Correlation Analysis

The relation between local circulation and alternate muscle activity among knee extensor synergists was determined during low-level sustained knee extension at 2.5% of maximal voluntary contraction for 60 min in seven subjects. Blood volume of rectus femoris (RF) and vastus lateralis (VL) was assessed by using near-infrared spectroscopy. Surface electromyogram (EMG) was recorded from RF, VL, and vastus medialis (VM). Alternate muscle activity was observed between RF and either VL or VM. Cross-correlation analysis was used to investigate the relation between blood volume and integrated EMG (iEMG) sequences throughout the task. One negative peak in the cross-correlation function was seen between the iEMG and blood volume with time lag of 30–60 s, indicating that muscle activity increases (or decreases) with the decrease (or increase) in local circulation with the corresponding time lag. Two cases in the emergence of alternate muscle activities, i.e., an increase in the EMG of RF accompanied by a decline of EMG in VL ( case I) and vice versa ( case II) were further analyzed. The time lag between iEMG and blood volume was longer in case I than that in case II. These results were statistically significant in the RF but not in the VL. It is concluded that even during low-level sustained contraction, local circulation is modulated by the alternate muscle activity of knee extensor synergists, and a negative correlation between the muscle activity and blood volume sequences was found in only RF but not in VL.

Download Full-text

Alternate muscle activity observed between knee extensor synergists during low-level sustained contractions

Journal of Applied Physiology ◽

10.1152/japplphysiol.00764.2001 ◽

2002 ◽

Vol 93 (2) ◽

pp. 675-684 ◽

Cited By ~ 68

Author(s):

Motoki Kouzaki ◽

Minoru Shinohara ◽

Kei Masani ◽

Hiroaki Kanehisa ◽

Tetsuo Fukunaga

Keyword(s):

Muscle Activity ◽

Vastus Lateralis ◽

Force Production ◽

Knee Extensor ◽

Rectus Femoris ◽

Quadriceps Muscle ◽

Knee Extension ◽

Voluntary Contraction ◽

Low Level ◽

Integrated Emg

To determine quantitatively the features of alternate muscle activity between knee extensor synergists during low-level prolonged contraction, a surface electromyogram (EMG) was recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) in 11 subjects during isometric knee extension exercise at 2.5% of maximal voluntary contraction (MVC) for 60 min ( experiment 1). Furthermore, to examine the relation between alternate muscle activity and contraction levels, six of the subjects also performed sustained knee extension at 5.0, 7.5, and 10.0% of MVC ( experiment 2). Alternate muscle activity among the three muscles was assessed by quantitative analysis on the basis of the rate of integrated EMG sequences. In experiment 1, the number of alternations was significantly higher between RF and either VL or VM than between VL and VM. Moreover, the frequency of alternate muscle activity increased with time. In experiment 2, alternating muscle activity was found during contractions at 2.5 and 5.0% of MVC, although not at 7.5 and 10.0% of MVC, and the number of alternations was higher at 2.5 than at 5.0% of MVC. Thus the findings of the present study demonstrated that alternate muscle activity in the quadriceps muscle 1) appears only between biarticular RF muscle and monoarticular vasti muscles (VL and VM), and its frequency of alternations progressively increases with time, and 2) emerges under sustained contraction with force production levels ≤5.0% of MVC.

Download Full-text