When do children start to run in a “stiff” manner?

Children typically start to run in a "stiff" manner around 16 to 18 months of age. At this stage of development, toddlers are still refining their motor skills and coordination. Their muscles and joints are not fully developed, which can lead to a more rigid running style, as they are trying to balance and control their movements.

During this period, children often exhibit a somewhat upright posture and limited knee bend, and their arms may not be swinging freely. This stiffness is part of their natural progression as they transition from walking to running. Over time, as children gain strength, balance, and coordination, their running style becomes more fluid and relaxed, typically occurring as they approach the age of 2 to 3 years.