that the body responds to the instability of the ball to remain balanced, engaging many more muscles (so-called “unstable training”). Those muscles become stronger over time to keep balance. Some dumbbell exercises, such as dumbbell fly can be performed on a ball. Ball exercises are popular among runners. Most frequently, the core body muscles; the abdominal muscles and back muscles are the focus of exercise ball fitness programs. Using an unstable surface recruits more muscle units without increasing the total load. The greatest benefit of moving an exercise onto an unstable surface is achieving a greater activation of the core musculature, exercises such as curl-up or push-up performed on an exercise ball. An unstable surface increases activation of the rectus abdominis muscles (abdominals) and allows for greater activity per exercise when compared to a stable surface. Exercises such as a curl-up on an exercise ball yields a greater amount of electromyographic (EMG) activity (electrical activity produced by muscles) compared to exercises on a stable platform. Performing standard exercises, such as a push-up, on an unstable surface can be used to increase activation of core trunk stabilizers and in turn provide increased trunk strength and greater resistance to injury. Other uses There is no scientific evidence of benefits from sitting without additional exercises. This large plastic ball, known as a "birth ball", can also be used during labour to aid the descent of the fetal head into the pelvis. Sitting in an upright position will also aid fetal positioning and is more comfortable for the woman. Sitting on the ball with arms placed on a bed, table or otherwise sturdy object for support and gently rocking the hips may help with the contractions and aid the natural physiological process of birth. However, using the ball as an alternative to normal seating (such as in the office) is not recommended. See also List of inflatable manufactured goods Medicine ball Pilates reformer Bibliography References Exercise equipment Balls Inflatable manufactured goods 1963 introductions Italian inventions