RELIABILITY OF NON-NORMALIZED AND NORMALIZED INTEGRATED EMG DURING MAXIMAL ISOMETRIC CONTRACTIONS IN FEMALES

The purpose of this investigation was to examine the test-retest relia bility of non-normalized (absolute or raw units of mV . s) and normali zed (percentage ratio) scores using integrated electromyography (IEMG) in voluntary maximal isometric contractions. Bipolar surface electrod es on the vastus medialis (VM) and vastus lateralis (VL) muscles were used to record IEMG (mV . s) on two occasions, 2-8 days apart. While p ositioned supine, 20 healthy young women (mean age 24 +/- 2 yr) perfor med: (a) maximal voluntary unilateral quadriceps setting (QS) (i.e. is ometric knee extension with the knee in 0 degrees) with the ankle join t in a neutral position and the ankle musculature relaxed, and (b) max imal unilateral QS with the ankle joint in maximal dorsiflexion and th e ankle dorsiflexors maximally contracted (QSD). The QS exercise was u sed to normalize IEMG (QSD : QS ratio for each of the two muscle heads ) and the VM muscle was also used to normalize IEMG to the other head of the vasti (VL:VM ratio for each exercise). Reliability coefficients were excellent for test-retest reliability of non-normalized IEMG (mV . s) and for IEMG normalized to another muscle: (intraclass correlati on coefficients (ICCs)>0.86). However, IEMG normalized to another exer cise was characterized by poor reliability (ICCs <0.34), even when det ermined as the reliability of data averaged over two occasions. Regard less of whether absolute or normalized IEMG was used, 95% confidence i ntervals were wide, suggesting that precise, interday prediction of an individual's performance using the present protocol is questionnable. Copyright (C) 1996 Elsevier Science Ltd.