The flexor hallucis longus is a long muscle in the lower leg that allows the big toe to bend.
Structure and position in the body
The flexor hallucis longus belongs to the group of deep calf muscles. It originates at the back of the fibula, which is the medical name for the calf bone. From there, the muscle runs as a strong tendon behind the inner ankle bone and down to the underside of the big toe. It travels from the lower leg through what is called the tarsal tunnel at the ankle joint and ends at the sole of the foot.
What does this muscle do?
The main job of the flexor hallucis longus is to bend the big toe downwards, towards the sole of the foot. This is especially important when rolling the foot during walking, running, or jumping. The muscle also helps to stabilise the arch of the foot and spread body weight evenly. It is also active when standing on tiptoe.
Importance in everyday life
Without this muscle, it would be impossible to press the big toe firmly downwards. This becomes most noticeable when pushing off from the ground, for example when running fast or jumping. The flexor hallucis longus also plays a role in balance, as it supports the arch of the foot and helps provide a steady stance.
When problems occur
Injuries or overuse of this muscle are seen most often in sports such as ballet, gymnastics, or athletics, where the toes and ankle joint are put under a great deal of strain. Typical complaints range from pain in the sole of the foot or around the inner ankle to reduced movement in the big toe. In rare cases, a condition called tenosynovitis can develop, where the tendon of the muscle becomes irritated or inflamed.
Role in medical reports
In medical letters or findings, the term flexor hallucis longus usually appears in connection with injuries, tendon problems, or imaging investigations such as an MRI scan. These reports describe whether the tendon is intact, whether inflammation is present, or whether there is a tear. This muscle may also be mentioned during foot surgery, for example when its tendon is used to reconstruct other structures.
The flexor hallucis longus is therefore a key muscle for the movement and stability of the big toe and the whole foot. Without it, many everyday movements would be very difficult.
