What is the expected progression of muscle tone in infancy?

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Infancy begins with a flexion-dominant tone. Newborns tend to hold their arms and legs tucked in with the joints flexed, fists clenched, and a curled posture. This flexor bias provides a protected, compact position and supports early reflexes and stabilization. As the nervous system matures and infants gain head control, trunk stability, and the ability to sit and move against gravity, extensor muscles become more active. This gradual shift toward more extension allows antigravity control and the progression through typical milestones such as propping, rolling, sitting, and standing. So the expected pattern is flexion dominates first, then extension develops as age-appropriate motor control emerges.