Purpose <p>Cross-sectional studies indicate that sprint performance is strongly associated with leg-muscle strength, however there is no consensus on which muscles to strengthen to maximize running speed. The purpose of this study was to quantify and rank the sensitivity of maximum sprinting speed to changes in the strengths of individual leg muscles.</p> Methods <p>A full-body musculoskeletal model was combined with dynamic optimization theory to predict the effects of muscle strengthening on maximum sprinting speed.</p> Results <p>Maximum sprinting speed was most sensitive to a change in hip muscle strength: a 10% increase in hip strength increased maximum sprinting speed by 2.59% compared with 1.02% and 0.33% for the same change in ankle and knee strength, respectively. A 10% increase in hip strength increased step frequency by 2.24% and step length by just 0.4%. When muscles were grouped according to their anatomical function (e.g., flexors vs extensors), maximum sprinting speed was most sensitive to changes in hip-flexor strength: a 10% increase in hip-flexor strength increased maximum sprinting speed by 1.40% compared with 1.12% and 0.77% for the hip adductors and ankle plantarflexors, respectively. When individual muscles were strengthened in isolation, maximum sprinting speed was most sensitive to a change in iliopsoas strength: a 10% increase in iliopsoas strength increased maximum sprinting speed by 1.07% compared with 0.54, 0.44, 0.44 and 0.36% for adductor longus, adductor magnus, soleus, and gluteus maximus, respectively. Maximum sprinting speed was relatively insensitive (&lt;1%) to changes in vasti and hamstring strength. Running speed was maximized by prioritizing step frequency over step length.</p> Conclusion <p>Strength training programs designed to maximize sprinting speed should focus on the hip flexors (iliopsoas) and hip adductors (adductor longus/magnus). Strengthening vasti, gluteus maximus, and hamstring will improve sprinting speed only marginally.</p>