The ability to rapidly accelerate and reach maximal sprinting velocity is paramount to success in running-based sports. However, there is a lack of scientific literature examining the muscular determinants of overground sprint acceleration and maximal velocity in athletes. The purpose of this study was to 1) identify the spatial patterns of lower limb muscle volumes and peak cross-sectional areas in sub-elite rugby league athletes who were affiliated with a National Rugby League (NRL) club; and 2) identify if spatial differences in normalised muscle volumes and peak cross-sectionals area were associated with 10-m sprint times, 30-m sprint times and peak sprint velocity. Nineteen male under-20 rugby league athletes (mean ± SD, age, 19.2 ± 0.7 years; height, 180.7 ± 5.6 cm; mass, 89.9 ± 10.0 kg) from a single NRL club, performed a series of 30-m sprints in order to derive 10-m sprint times, 30-m sprint times and peak sprint velocity. Magnetic Resonance (MR) imaging was used to calculate the normalised muscle volumes and peak cross-sectional areas of the gluteus maximus (GMAX), medius (GMED) and minimus (GMIN), tensor fascia latae (TFL), sartorius (SART), iliopsoas (ILIOP), gracilis (GR), adductor magnus, longus and brevis (ADD), rectus femoris (RF), vastus lateralis (VL), vastus intermedius (VI), vastus medialis (VM), semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BFLH), biceps femoris short head (BFSH), soleus (SOL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL). Stepwise linear regression models were used to determine the extent to which sprint performance was explained by muscle morphology. The results revealed that variation in 10-m sprint times was best explained by ADD peak CSA (r2 = 0.582, p = 0.005) and TFL and VI normalised volume (r2 = 0.570, p = 0.026). Variation in 30-m sprint times were best explained by ADD, VI and VM peak CSA (r2 = 0.751, p = 0.030) and ILIOP and TFL normalised muscle volumes (r2 = 0.672, p = 0.021). Variation in peak sprint velocity was best explained by GMIN and GL peak CSA (r2 = 0.445, p = 0.029) and ILIOP, GL, RECF and ADD normalised muscle volume (r2 = 0.820, p = 0.035). The findings of this study demonstrate that sub-elite male rugby league athletes display non-uniform patterns of lower limb muscle size and suggest the possibility that preferential hypertrophy of the proximal hip- and knee-spanning muscles may have important implications for improving sprint acceleration and maximal velocity performance.