He is doing a special exercise to train his longissimus thoracis muscle.

After the exam was over, he was relieved.

I cannot know the thoughts buried deep inside her heart.

He acknowledged his mistake and self-reflected by placing his hand on his chest.

He admitted his mistake and decided to deeply self-reflect.

I was filled with his kindness.

His kindness made me have a lump in my throat.

The semispinalis thoracis muscle is a deep muscle in the back that supports movement from the neck to the waist.

The multifidus thoracis muscle is a part of the back muscles, mainly involved in stabilizing the spine.

He started exercises to strengthen his sternocleidomastoid muscle.