The plantar interossei are small, deep muscles in the sole of your foot. They sit between the metatarsal bones, which are the long bones that run from your midfoot to your toes. Most people have three plantar interossei, associated with toes 3, 4, and 5. Each one starts from the side of a metatarsal and attaches into the base of its toe and into the tendon system that helps move the toe.
Their main job is toe control. They pull toes 3 to 5 inward toward the second toe, which is the reference line for toe motion. They also help flex the metatarsophalangeal joints, the knuckle joints where the toes meet the foot, and they assist the toe tendons in keeping the smaller toe joints straighter during push off. They are supplied by the lateral plantar nerve, a branch of the tibial nerve.
In training and daily movement, these muscles act like stabilizers for the front of the foot. When you walk, run, jump, or lift, the ball of the foot must stay organized so force transfers cleanly into the ground. The plantar interossei help prevent the toes from drifting or splaying too much, and they contribute to supporting the transverse arch across the forefoot. If they are weak or poorly coordinated, you may feel less steady in squats, lunges, or sprints, and you may overload the plantar fascia, the metatarsals, or the big toe by compensating.
You can encourage them by practicing controlled toe alignment, barefoot balance on safe surfaces, gentle toe squeezing toward the second toe, and slow calf raises while keeping a tripod foot contact at the heel, base of the big toe, and base of the little toe.