NIT enhanced the peak force response to low-frequency electrical stimulation , as follows : maximal twitch ( NIT , 149 41 N , vs PLA , 138 37 N ; P = 0.008 ; effect size , r ( ES ) = 0.56 ) and submaximal 1 - to 20-Hz contractions ( 5 % -10 % , ES = 0.53-0 .63 ) .