EMG SIGNAL AMPLITUDE NORMALIZATION TECHNIQUE IN STRETCH-SHORTENING CYCLE MOVEMENTS

Analysis of functional movements using surface electromyography (EMG) often involves recording both eccentric and concentric muscle activity during a stretch-shorten cycle (SSC). The techniques used for amplitu de normalization are varied and are independent of the type of muscle activity involved. The purpose of this study was: (i) to determine the effect of 11 amplitude normalization techniques on the coefficient of variation (CV) during the eccentric and concentric phases of the SSC; and (ii) to establish the effect of the normalization techniques on t he EMG signal under variable load and velocity. The EMG signal of the biceps brachii of eight normal subjects was recorded under four SSC co nditions and three levels of isometric contraction. The 11 derived nor malization values were total rms, mean rms and peak rms (100 ms time c onstant) for the isometric contractions and the mean rms and peak rms values of the ensemble values for each set of isotonic contractions. N ormalization using maximal voluntary isometric contractions (MVIC), ir respective of rms processing (total, mean or peak), demonstrated great er CV above the raw data for both muscle actions. Mean ensemble values and submaximal isometric recordings reduced the CV of concentric data . No amplitude normalization technique reduced the CV for eccentric da ta under loaded conditions. An ANOVA demonstrated significant (P<0.01) main effects for load and velocity on concentric raw data and an inte raction (P<0.05) for raw eccentric data. No significant effects were d emonstrated for changes in velocity when the data were normalized usin g mean rms values. The reduction of the CV should not be at the expens e of true biological variance and current normalization techniques poo rly serve the analysis of eccentric muscle activity during the SSC.