Intramuscular pressure, EMG and blood flow during low‐level prolonged static contraction in man

Abstract

Seven men performed one-legged isometric knee-extension at 5% MVC for 1 h. Intramuscular pressure increased with contraction from its resting value of 14 (2-31) mmHg. Some intramuscular pressure recordings stayed at an almost constant level through the 1 h contraction, but most recordings showed large fluctuations from resting values up to 90 mmHg. The overall mean intramuscular pressure was twice the resting value. In some cases, EMG recordings confirmed that the changes in intramuscular pressure were related to alternating recruitment of various parts of the knee-extensors. Blood flow in the femoral vein increased within 3 min of 5% MVC to a level of 1.58 (1.25-2.22) 1 min-1 and no significant changes occurred during the 1 h contraction. In two subjects blood flow was measured also in the recovery period, and this decreased almost immediately when the muscle relaxed. It is concluded that during low-level static contractions, the blood supply to the exercising muscle is maintained at a sufficiently high level, and that the alternating recruitment of muscle fibres may result in a heterogeneously distributed blood flow within the contracting muscle. Despite this the muscle was fatigued after the 1 h at 5% MVC. The rating of perceived exertion (RPE) increased from 1.9 (1-3) at the beginning to 4.5 (2-8) at the end of contraction, and MVC was decreased by 12% after the contraction.

One-year randomized controlled trial with different physical-activity programs to reduce musculoskeletal symptoms in the neck and shoulders among office workers

“…The remaining 549 participants were randomly allocated to three intervention groups. A sample size of approximately 180 participants per intervention (allowing for a 10% loss to follow-up) was needed for 80% power to detect a 10% change in muscle strength (20). With a 10% change in muscle strength, there was a high likelihood that there would be a detectable impact on musculoskeletal symptoms in the neck and shoulder area.…”

An Exploration of the Effects of Cycle Time and Force Variations on Muscle Fatigue during Submaximal Intermittent Isometric Exertions

“…This could mean that some motor units are active even at these low metabolic rates, which could result in them fatiguing prematurely (VØllestad, 1997). While the landmark study by Rohmert (1960) concluded that fatigue would not be induced with muscle exertions of less than 15% of maximum force, findings by Sjøgaard et al (1986) indicated this threshold force to only be 5% of maximum.…”

“…RPE, a good indicator of perceptual fatigue (Iridiastadi & Nussbaum, 2006;Enoka & Duchateau, 2008), significantly increased, while maximal voluntary force production significantly decreased over time, which is also indicative of localized muscle fatigue (LMF) (Bigland-Ritchie & Woods, 1984;Garland et al, 1994;Enoka & Duchateau, 2008). The increase in EMG amplitude is often used to estimate muscle fatigue under sub-maximal isometric conditions since it infers an increased recruitment of motor units as a result of LMF (SjØgaard et al, 1986;Hermans & Spaepen, 1997;Hunter & Enoka, 2003;Chang et al, 2016). In the current study, EMG(RMS) only increased significantly for the 10-40%max force conditions, while the 0-50%max force conditions remained unchanged.…”

“…Intermittent force exertions varying between 0 to 50% max force would provide insight into fatigue development under a condition were complete muscle relaxation is allowed, while conditions using force levels varying between 10% and 40% would provide some insight into the effects of a constant underlying contraction that may prevent blood flow thus inhibiting recovery. Rohmert (1973) stated that an isometric exertion of 15% MVIE could be held indefinitely, while Sjøgaard et al (1986) found that only 5% muscle activation was the lowest level of activation that could produce fatigue. The minimum underlying static component of 10% was hence selected as the half-way exertion between these two values.…”

“…Prolonged static exertions have been widely studied for the development of LMF (e.g., Rohmert, 1960;Gamet & Maton, 1989;Hunter & Enoka, 2003), and the relationship between the endurance time and isometric level of muscle effort is well established. Such exertions are known to result in the fastest onset and greatest development of muscle fatigue, compared to dynamic or intermittent exertions at similar force levels (Bigland-Ritchie & Woods, 1984;SjØgaard et al, 1986;Jonsson, 1988;Masuda et al, 1999;Iridastadi & Nussbaum, 2006). One major factor contributing to fatigue during such sustained static exertions is that blood flow to the working muscle is reduced due to increased intramuscular pressure, thereby decreasing the oxygen and substrate supply to the muscle, while preventing metabolite removal (Sahlin et al, 1998).…”