What is the expected development for an infant when placed prone at 4 months?

At 4 months of age, infants typically exhibit an increased ability to control their head and upper body when they are placed in a prone position. One of the expected developments at this stage is the ability to raise their head up to about 90 degrees. This milestone reflects advances in neck strength and overall muscle coordination, which are essential for later skills such as rolling over, sitting, and crawling.

When placed prone, a healthy 4-month-old will not lie flat without movement, as they are becoming increasingly active and engaged with their environment. While some infants may begin to push up on their arms or roll over, these abilities tend to develop more fully a bit later. Thus, raising the head to a 90-degree angle is the hallmark achievement expected at this age, marking a significant step in their physical development.