Magnesium supports normal muscle function, including the contraction and relaxation of major muscle groups such as the calves. If blood levels of magnesium are low, magnesium is withdrawn from the muscles, causing them to stiffen up or contract. Magnesium is essential for many cellular functions, particularly for the normal functioning of muscle and nerve tissue. Blackmores Bio Magnesium contains co-factors that support the absorption and utilization of magnesium. For example, vitamin B6 supports the action of magnesium in many of the body's enzyme systems, and the two nutrients work together to support the healthy functioning of the female reproductive system and help maintain a healthy menstrual cycle.