ONE-YEAR REPRODUCIBILITY AND STABILITY OF THE SIGNAL AMPLITUDE RATIO AND OTHER VARIABLES OF THE ELECTROMYOGRAM - TEST-RETEST OF A SHOULDER FORWARD FLEXION TEST IN FEMALE WORKERS WITH NECK AND SHOULDER PROBLEMS

We have studied 23 women with neck and shoulder problems in a car fact ory with 1-year interval. Our main aim Tvas to investigate the reprodu cibility and stability of the tension pattern. Ln addition, the mean f requency (MNF) of the power spectrum and the signal amplitude (RMS) of the surface electromyograph (EMG) of the trapezius, deltoid and infra spinatus muscles and mechanical output were determined throughout 100 maximal isokinetic shoulder forward flexions. The signal amplitude rat io (SAR) was calculated as the ratio between the signal amplitude of t he EMG of the passive relaxation and the active flexion part of each c ontraction cycle. The SAR variable can be reproduced (r = 0.47-0.76) w ith a 1-year interval. There was a significantly lower SAR of the trap ezius at the second test, which might have been due to lower work pace at the factory. The longitudinal patterns of SAR throughout the two t ests were similar at both tests. There were significant correlations b etween tests for 18 out of 22 EMG variables, even though the correlati ons were generally lower than for SAR (initial MNF: r = 0.39-0.48; MNF endurance level: r = 0.55-0.83; RMS (%): 0.08-0.46). Peak torque had better reproducibility than work. In conclusion, SAR has a long-term r eproducibility equal to or better than other EMG and biomechanical var iables. The present results indicate that SAR has potential to measure unnecessary muscle tension in intervention studies and to identify in dividual movement patterns.