Isometric back muscle endurance: an EMG study on the criterion validity of the Ito test

The validity of the Sorensen test as a measure for back muscle endurance is controversial due to a possible impact of hip extensor muscles. The aim of this study was to investigate the criterion validity of an alternative test (Ito test) compared to the Sorensen test. Both procedures were performed by 29 healthy subjects (11 women) for 5s and until exhaustion (randomized order). EMG activity was measured from 3 lumbar back and 3 hip extensor muscles. Muscular involvement in test positions was calculated as percentage of maximal voluntary contraction (MVC). Muscle fatigue was determined by the normalized regression coefficient of the median frequencies of the EMG power spectrum (NMF(slope)). Prediction of holding time by NMF(slope) values was investigated using regression analysis. In the test positions, the hamstring muscles were activated to a higher MVC percentage in the Sorensen than in the Ito test, while the iliocostalis muscle was less activated. Similarly, the iliocostalis (p=0.006) and the multifidi muscles (p=0.03) significantly contributed to predict holding time in the Ito test, whereas the multifidi muscles (p=0.001) and the semitendinosus muscle (p=0.046) did so in the Sorensen test. The results of this study indicate that the Ito test might present a valuable alternative for testing back muscle endurance in LBP patients.