Skeletal muscle tension, flow, pressure, and EMG during sustained isometric contractions in humans

Abstract

In five healthy males sustained isometric torques during elbow flexion, knee extension, and plantar flexion correlated positively with intramuscular tissue pressure (MTP) in the range 0-80% of the maximal voluntary contraction (MVC). During passive compression of the muscle at rest 133-Xenon muscle clearance stopped when MTP reached diastolic arterial pressure (DAP) indicating that the muscle vascular bed was occluded. However, during sustained contraction this relation between DAP, flow and MTP was not seen. In two cases 133-Xenon clearance from M. soleus did not stop in spite of an 80% maximal contraction and MTP stayed below DAP. In other cases MTP would reach as high as 240 mm Hg before clearance was zero. In the deeper parts of the muscles MTP during contraction was increased in relation to the more superficial parts. The means values for the % MVC that would stop MBF varied between 50 and 64% MVC for the investigated muscles. Mean rectified EMG (MEMG) showed a high correlation to MTP during sustained exhaustive contractions: When MEMG was kept constant MTP also remained constant while the exerted force decreased; when force was kept constant both MEMG and MTP increased in parallel. This demonstrated that muscle tissue compliance is decreasing during fatigue. Muscle ischemia occurring during sustained isometric contractions is partly due to the developed MTP, where especially the MTP around the veins in the deeper parts of the muscle can be considered of importance. However, ischemia is also affected by muscle fiber texture and anatomical distorsion of tissues.

Blood flow and muscle oxygenation during low, moderate, and maximal sustained isometric contractions

“…In a variety of muscle groups (e.g., elbow flexors, knee extensors, plantar flexors, and dorsiflexors), data collected indirectly using isotope clearance (22), VOP (25), or fMRI (31) suggest that the IMP generated during isometric exercise will occlude MBF at a relative contraction strength of 50 -65% MVC (60% MVC in the dorsiflexors of young males; Ref. 31).…”

“…IMP is positively related to contraction intensity (22,24); thus, it is held that there is a critical force threshold beyond which mechanical pressure will occlude MBF (24,25,29,30) and below which flow will be affected to varying degrees depending on the contraction intensity and anatomical location (compartmental pressure). Results obtained using a variety of techniques suggest that complete occlusion of MBF and perfusion occur at 50 -60% of maximal voluntary contraction (MVC) force (13,22,25,31). However, relatively few studies have recorded MBF directly during a sustained isometric effort, and the degree to which perfusion is compromised by high-intensity contraction remains uncertain.…”

Cardiorespiratory Response to Dynamic and Static Leg Press Exercise in Humans

“…It was reported that the mean % MVC that would stop muscle blood flow is 50% MVC in the musculus rectus femoris and 64% MVC in the musuclus vastus lateralis (Sadamoto, 1983). Shepard (1983) suggested that isometric contractions that develop less than 15% to 30% MVC, depending on the muscle groups, produce moderate increase in blood flow during contractions.…”

Measurement of blood flow in the human Achilles tendon <i>in vivo</i>

“…Previous studies demonstrated that the blood flow in the muscles decreased towards or below the resting level at higher intensities, since intramuscular pressure is positively related to contraction intensity 14,15) . We recently reported that blood volume and oxygen saturation in human tendons could be determined using a laser oxygenation monitor 16) .…”