The aim of this study was to determine whether the first sensation of stretching (ROM_FSS) may predict the maximum range of motion (ROM_MAX) in male (N = 37) and female (N = 32) volunteer subjects, and to assess the reliability of the ROM perceived by subjects in relation to a pre-determined ROM (ROM_50%). Subjects attempted three experimental sessions with 48 hours between sessions 1 and 2 and 28 days between sessions 1 and 3. Within each session, five trials were performed with isokinetic equipment to assess posterior thigh muscle flexibility. The results revealed a strong and significant correlation between ROM_MAX and ROM_FSS for both sexes, females (r = 0.96, p < 0.001, R² = 0.92) and males (r = 0.91, p < 0.001; R² = 0.82). The accuracy of the model verified by the standard error of estimate (SEE) was high in the equations proposed for both female (SEE = 4.53%) and male (SEE = 5.45%). Our results revealed that ROM_FSS may predict the ROM_MAX for both male and female subjects. The ROM_FSS may contribute to the development of evaluation methods that do not subject the individuals to conditions that may include unnecessary risk of injury and is well suited to monitor the training process of stretching exercises with submaximal loads.