Muscular evolution in humans refers to the adaptations of the muscular system from early ancestors to modern humans. Humans are predisposed to develop muscle mass because early humans depended on strength for hunting and survival. Although modern humans rely less on muscle for everyday survival, muscle development can be as rapid—or faster—thanks to improved training techniques and greater knowledge of anatomy.

DNA and anthropological data indicate that modern humans (Homo sapiens) are primates and descendants of ape-like species. All species of the genus Homo are extinct except modern humans, who are thought to have evolved from australopithecine ancestors in East Africa. The development of modern humans has taken place over roughly 300,000 years, and unique adaptations resulted from the ecological pressures Homo sapiens faced. Largely due to ecological and behavioral factors, the human muscular system differs significantly from that of our early primate ancestors. As with other evolutionary changes, the muscular system evolved to increase survivability. Because muscles, ligaments, and tendons are distributed throughout the body and support many functions, our behavior and choices are shaped in part by our physical capabilities. It is believed that our ancestors' original habitat was not on the ground but in the trees. We developed new habits that eventually allowed us to thrive on the ground, such as changes in diet, food gathering, energy expenditure, social interactions, and responses to predators. Life in the canopy offered a food supply similar to that of herbivores: leaves, fruits, and berries—mostly low-protein foods that did not require much energy to find. However, when available, meat was also consumed. At that time our ancestors had not yet switched to full-time bipedalism, so searching for food on the ground was impractical because it involved too much energy and risk. The canopy also lacked the predators found on the ground, against which our chimp-like ancestors would have been poor defenders. As they became bipedal, they began to live in groups that used weapons to fend off predators and hunt prey; running became a key aspect of survival. Even so, it is the development of the brain that guided the evolution of human muscle function and structure. Skull, neck, and head structures reflect these changes. It is suspected that H. sapiens' ancestors did not initially forage on the forest floor; instead they migrated from the trees for various reasons. In that environment they survived on a diet high in plant matter, with some insects and small amounts of meat. Early human ancestors were not formidable compared with dominant mammals such as large cats, but improvements in hunting, gathering, and brain development allowed them to add high-calorie foods like meat to their diet. Analyses of jaws and skulls indicate they had larger, stronger jaw muscles and larger posterior molars, consistent with a diet that included substantial amounts of fruit and plants.

Reliance on higher-calorie foods grew as bipedalism proved less efficient and climbing tall trees became more energetically costly. Early ancestors also had more muscles connecting the skull, neck, and shoulders—similar to apes—which gave their neck and skull a more downward appearance like that of non-human primates. Reduction of these muscles allowed the head to be held in a more upright position and enabled the occipitofrontalis (forehead) to play a greater role in facial expression.

As humans became taller after adopting bipedalism, the back muscles around the base of the tailbone and hips lengthened and body mass increased, further reducing the ability to climb. Early human ancestors had a tail where the modern coccyx (tailbone) is located. This aided balance in the trees but lost importance as bipedalism was adopted. Arms became relatively shorter compared with the legs, better suited for carrying objects and manipulating tools rather than climbing and swinging. The Homo sapiens lineage developed an opposable thumb, enabling many new manual functions. Forearm muscles and their tendons transmit force to the hands and fingers, allowing fine manipulation and greater strength. Overall, upper-body muscles adapted to activities that concentrate force in the hands and arms, such as holding, throwing, lifting, carrying while running to escape danger, hunting, and constructing shelters. The shift to full-time bipedalism in our ancestors is the primary reason for adaptations in muscle structure and function, especially in the lower body.