Background: The aim of the study was to estimate differences in bioelectrical activity between rectus femoris (RF) and vastus medialis (VM) muscles of each lower limb. Material/Methods: 29 female and 18 male adult subjects participated in the study. Each subject performed the following quadriceps contractions with each lower limb: concentric, isometric, eccentric and 30-sec. long maximal voluntary isometric contraction. 3 parameters were obtained in surface electromyography (SEMG): mean RMS amplitude (RMS), mean percentage value of maximal voluntary contraction (%MVC) and mean frequency (MF). Results: RF occurred to have a lower percentage activity (-28.43%) and absolute amplitude (- 36.57%) value than VM during all three basic forms of contraction against gravity. Except the RMS values for concentric contraction, all the mentioned parameters were significantly different. In contrast, RF had a higher MF rate than VM. Differences were at the mean level of 22.57% for all activities. Conclusions: There are no differences in SEMG of quadriceps muscle between both lower limbs. VM and RF differ from each other in RMS, %MVC and MF during all types of studied contractions.