Do you ever consider how hard your ankles are working to hold you in a steady position? Most people don't give this much thought, but the ankle is actually a very important part of standing and moving.

Control of movement depends on information that comes to the ankle from the skin, muscles, and surrounding joints. In order to move, the ankle must know the speed and direction of motion. Without this important information, the ankle is more likely to be injured. To keep balance, the ankle must be able to tell what position the joint is in. The ankle is an important link between the ground, gravity, and center of balance.

Injuring the ankle can change the joint's sense of position and motion. The technical name for this "position sense" is proprioception. Researchers wanted to know whether there's anything that can alter proprioception. Perhaps changes in proprioception make the ankle prone to injury.

What about the effects of fatigue? Does intense physical activity change the joint's sense of position? In other words, are athletes more likely to injure their ankles after working or competing hard enough to affect the proprioceptive system?

A small study of eight men looked at this question. Proprioception was measured by placing one foot and ankle in a position and asking the person to match that position with the other foot and ankle. Differences in ankle position can be accurately measured with today's advanced technology.

Before measuring position sense, the foot was fatigued by strapping it to a footplate and working it. Muscle contractions at a load equal to 70 percent of the maximum contraction capacity were done until the foot was fatigued. Electromyographic (EMG) measures were taken to document the fatigue.

Results showed that fatigue affected position accuracy. When the foot was fatigued, there were larger errors in matching movement and position between feet. The two areas of movement that were the most affected were large movements bending the ankle up and small movements bending the ankle down.

Fatigue seems to affect the ankle's ability to detect its position. This may contribute to ankle injuries after periods of intense exercise or competition. It may also have an effect on other joints, such as the knee. The knee depends on the ankle for stability and support. If fatigue alters the ankle's sense of position, then decreased ankle proprioception may also contribute to knee injuries.