Volitional and evoked strength are outcomes often used in both adults and children. However, the reliability of these measurements is sparse. Emerging reliability studies utilize a robust analysis, which includes “consistency” of scores and “stability” of group means. This study aimed to assess the reliability of volitional and evoked muscle strength outcomes of the knee extensors in boys and men. Twelve boys and twelve men participated in the study. Participants completed ten maximal isometric knee extensions (MVCs) on three separate days. On days two and three, quadriceps muscle belly stimulation was introduced in the 6th-10th MVC. The stability of group means was determined through a repeated measures Analysis of Variance (ANOVA) model, while consistency was determined through a fully nested ANOVA model. High reliability was observed in both, men and boys in volitional torque production, as reflected by the ICCs (Men R = 0.97 and 0.98, boys R = 0.91 and 0.92) and true score variance. The group means were stable in both, men and boys, especially in 1st-5th MVC. Twitch amplitudes were stable across days and demonstrated good reliability, as reflected by high ICCs (Pre-MVC twitch:​ men R = 0.78 and 0.83, boys R = 0.98 and 0.99;​ post-MVC twitch:​ men R = 0.84 and 0.85, boys R= 0.98 and 0.99), and true score variance. PAP demonstrated acceptable reliability in both boys and men, although it was lower compared to the other outcomes. PAP in the 1st-5th MVCs in men showed low reliability, while PAP in the 6th-10th MVCs showed high reliability in men and boys, as reflected by the high true score variance, ICC, and stable means. The results support using volitional torque and evoked outcomes in adults and children. Future research could examine the reliability of other evoked variables and different volitional exercise protocols.