Physiological Response to Submaximal Contractions of the Paravertebral Muscles

The aim was to evaluate paravertebral EMG (electromyography) and intramuscular pressure as indicators of force development and to evaluate the relationship of tissue oxygenation with intramuscular pressure and force development during brief and prolonged paravertebral muscle contractions. Brief (30 s) trunk extensions were performed at 5, 20, 40, 60 and 80% maximal voluntary contraction (MVC). Prolonged contraction (3 min) were performed at 20% MVC. The RMS-amplitudes of the paravertebral EMG and the intramuscular pressure measured at L4 level increased with greater force development in a curva-linear manner. A significant decrease in the oxygenation of the lumbar vertebral muscle in response to muscle contraction was found at an initial level of 20 %MVC. This corresponded to a paravertebral intramuscular pressure of 30–40 mmHg. However, during the prolonged trunk extension, no further decrease in the tissue oxygenation was found compared to the tissue oxygenation level at the end of the brief contractions, indicating that homeostatic adjustments over time were sufficient to maintain paravertebral muscle oxygenation levels.