He is doing special exercises to strengthen his superior rectus muscle.

He is doing special exercises to strengthen the lateral rectus muscle.

He is doing a special exercise to strengthen his inferior rectus muscle.

He is doing special exercises to strengthen his medial rectus muscle.

The rectus capitis anterior muscle is part of the neck muscles, helping to bend the head forward.

He did a somersault in the park.

His words held a double surprise, like 'isseki-rokuto'.

The rectus capitis lateralis muscle is part of the neck muscles, and it helps to move the head sideways.

The rectus capitis posterior major muscle is a part of the neck muscles, and it helps in the action of pulling the head backwards.

The rectus capitis posterior minor muscle is a part of the neck muscles, and it helps tilt the head backwards.