Swimming efficiency and neck musculature activity
The pattern of cervical muscle use drives spinal alignment and shoulder girdle alignment in swimmers for similar reasons that it can distort upright posture.
Neck muscle misuse can be due to tissue shortening or weakening, generally both.
The scalene muscles of the neck are involved in higher intensity exercise to increase lung capacity but also deviate the neck from optimal if other muscles do not counterbalance their effects.
Excess scalene activity is very common. In the freestyle stroke it leads to counterproductive sinking into the water, reduced freedome of neck rotation and naturally increases drag effects. It also tends to interfere with optimal scapula positioning.
Both the endurance and strength of the deep neck flexors is an important counterbalance to scalene muscle activity. If you’re tending to sink into the water as a session progresses, these muscles or the hip extensor muscles may need work on their length, strength or endurance.