Skeletal muscle is enclosed by a surrounding band of fibrous tissue called the fascia. Within the fascia and between the muscle fibers – the interstitium, free fluid and solid materials (consisting of collagen fibers) exist. For certain muscle manoeuvres and/or conditions these materials exert a pressure called the intramuscular pressure – IMP. If the IMP exceeds a certain limit local circulation will be disturbed, thus stressing the importance of measuring IMP in clinical situations. But IMP is also used for experimental settings.
Measuring IMP is an invasive procedure that involves insertion of a catheter or tube into the muscle of interest. Most often the intramuscular tube is joined to an extension tube that is connected to an external sensing device (transducer).
Factors affecting IMP
Increases in IMP occur during muscle contraction, during external compression, when the muscle is volume loaded due to intra- or extracellular swelling, or when the muscle is passively stretched. Increases in IMP are additive by a combination of these factors.
Applications of IMP measurements
Measurements of IMP are used clinically in the assessment of acute and chronic compartment syndrome. IMP is also used for research purposes as an estimate of muscle load for ergonomic studies, as a corollary to muscle blood flow, and as an estimator of contraction force