Back and hip extensor muscle function during therapeutic exercises

Background: Therapeutic exercises are widely used in the treatment of low b ack problems. Clinical knowledge about targeting the load in these exercise s, however, is insufficient. This study assessed the L2 and L5 level parasp inal and gluteus maximus muscle activities in different therapeutic exercis es. Intramuscular and surface electromyography (EMG) measurements were obta ined to study whether surface EMG measurements can be used in the assessmen t of multifidus muscle function. Methods: Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age vol unteered for the study. The subjects performed 18 different therapeutic exe rcises. During the exercises paraspinal EMG was recorded using fine wire an d surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary contraction [MVC]) during ea ch task were determined. Results: The correlations between the average intramuscular and surface act ivities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exercise s were below 50% and 25% of MVC, respectively. At the L5 level, the multifi dus peak and average EMG amplitudes (% MVC) were higher in women than in me n, whereas no significant difference was found at the L2 level. In women, t he normalized multifidus EMG amplitude was higher at the L5 level than at t he L2 level, whereas no significant difference was found in men. In both se xes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle. Conclusion: Surface EMG measurements may be used in the assessment of multi fidus muscle function. Simple therapeutic exercises are effective in activa ting the lumbar paraspinal muscles. (C) 1999 by the American Congress of Re habilitation Medicine and the American Academy of Physical Medicine and Reh abilitation.