The advance in reaction time research by employing electromyography technique that has made it possible to divide the reaction time (RT) into the motor (MT) and premotor (PMT) have resulted in new findings. The present research we conducted to examine the effect of response complexity and limb weight change on electromyography records of simple and discriminative RT of young and elderly men. The participants included 14 young and 14 older adults. They performed arm flexion with or without added weight to a target at 60 cm distance away upon hearing simple or discriminative signals. The results of ANOVA-repeated measures indicated that there was a significant main effect for the three factors including the number of stimuli (p=0/001), the limb weight (p=0/001) and response complexity (p=0/001) on PMT. It was concluded that the variables that have affected RT have also effect on the PMT but may not affect MT. These delay in activating the involved muscles to prevent fall is the result of elderly people increased age and overweight.