Physical performance is mainly assessed in terms of gait speed, chair rise capacity, and balance skills, and assessments are often carried out on the lower limbs. Such physical performance is largely influenced by the strength of the quadriceps and hamstrings muscles. Flexibility of the hamstrings is important because quadriceps muscle activity influences the hip flexion angle. Therefore, hamstring flexibility is essential to improve physical performance. In this study, Myofascial Release (MFR) was applied to the hamstrings to evaluate its effects. MFR on the hamstrings was performed on 17 young adults. Physical function and physical performance were measured before, immediately after, and 5 days after the MFR intervention: finger floor distance (FFD), range of motion (ROM) of the straight leg raising test (SLR), standing long jump (SLJ), squat jump (SJ), functional reach test (FRT), comfortable walking speeds (C-walking speed), and maximum walking speeds (M-walking speed). The results of the analysis show a significant increase in FFD (−2.6 ± 8.9 vs. 0.4 ± 9.4 vs. 2.4 ± 8.9, p < 0.01), SLJ (185.6 ± 44.5 vs. 185.0 ± 41.8 vs. 196.6 ± 40.1, p < 0.01), and M-walking speed (2.9 ± 0.6 vs. 3.0 ± 0.6 vs. 3.3 ± 0.6, p < 0.01). This study has shown that MFR for hamstrings not only improves flexibility but also increases M-walking speed and physical performance of the SLJ. As MFR is safe and does not involve joint movement, it may be useful for maintaining and improving performance and flexibility during inactivity and for stretching before exercise.