The NICHD recommends «tummy time» and «changing the direction the baby lies in the crib from one week to the next» and to «avoid too much time in car seats, carriers, bouncers etc.» The other risk of too little tummy time and too much time in carriers and
similar equipment is tight neck muscles (the medical term is torticollis) which
tilts the baby's
head to one side and turns it to the opposite side.
This involves using muscles
similar to when you have to stand up straight — they include the abdominals, gluteus maximus, and even the neck flexors that prevent the
head from
tilting back.