BACKGROUND: Normalization in surface electromyography (SEMG) has been the object of numerous investigations.
OBJECTIVE: The purpose of this study was to evaluate the reliability of normalized SEMG amplitude, as well as the reliability of different normalization coefficients during isokinetic upper-body strength assessment.
METHODS: Thirteen male subjects performed a maximal isokinetic elbow flexion test and test-retest separated by 5 to 7 days. Three normalization coefficients were extracted from the tests: 1) mean value of the rectified SEMG signal (Mean
$_{Task}$
); 2) peak value of the rectified SEMG signal (Peak
$_{Task}$
); 3) maximal value of the rectified SEMG signal of the peak torque repetition(Isokinetic-spec
$_{MVC}$
). These normalization coefficients, as well as the root mean square value (RMS) of the signal before and after normalization by described coefficients (RMS-Mean
$_{Task}$
; RMS-Peak
$_{Task}$
; RMS-Isokinetic-spec
$_{MVC$
) were evaluated in terms of absolute and relative reliability.
RESULTS: None of the normalization coefficients presented acceptable levels of absolute reliability (bias range in limits of agreement greater than 27%). However Mean
$_{Task}$
and Isokinetic-spec
$_{MVC}$
presented good levels of relative reliability (ICC > 0.80). RMS-Mean
$_{Task}$
was the only amplitude parameter that demonstrated satisfactory indices of absolute (bias range lower than 5% and CV < 1.50%) and relative (ICC > 0.80) reliability.
CONCLUSIONS: Normalizing SEMG amplitude by Mean
$_{Task}$
is a reasonable strategy to reduce day-to-day amplitude discrepancies during isokinetic upper-body strength assessment.
