Typically there is a strong correlation between the mechanical measurement of applied force and the measurement of muscle activation by electromyography. History Müller and Hettinger In the 1950s, German scientists Dr. Erich Albert Müller and Theodor Hettinger "observed that contractions involving less than about one third of maximum strength do not train the muscle. If the contraction of a muscle exceeds one third of its maximum strength, its mass grows and hence also its strength". The study at the Max Planck Institute consisted of over 200 experiments over a ten-year period. Theodor Hettinger published his book Physiology of Strength. They both developed a training program based on isometrics exercise. In the 1960s, professor James A. Baley put isometrics to the test with a class of 104 college students at the University of Connecticut to study the results on tests measuring increases in strength, endurance, coordination, and agility. The original article showed significant gains after a 4 week program of isometric exercises. Isometric exercises were first brought to the modern American public's attention in the early days of physical culture, the precursor to bodybuilding. Many bodybuilders had incorporated isometric exercises into their training regimens. Medical uses Isometric exercises can also be used at the bedside to differentiate various heart murmurs; the murmur of mitral regurgitation gets louder as compared to the quieter murmur of aortic stenosis. They can also be used to prevent disuse syndrome in a limb that has been immobilized by a cast following a fracture. Isometric exercises are recommended in case of injury. The exercises help maintain strength and promote recovery. NASA studies NASA has researched the use of isometrics in preventing muscle atrophy experienced by astronauts as a result of living in a zero gravity environment. Isometrics, muscle lengthening and muscle shortening exercises were studied and compared. The outcome showed that while all three exercise types promoted muscle growth, isometrics failed to prevent a decrease in the amount of contractile proteins found in the muscle tissue. The result was muscle degradation at a molecular level. As contractile proteins are what cause muscles to contract and give them their physical strength, NASA concluded that isometrics may not be the best way for astronauts to maintain muscle tissue. See also Isometric exercise device Physical exercise Physical fitness Power training Strength training Supercompensation Weight training References Further reading Ilse Buck, Gesund und schlank durch Isometrik, Auflage. Goldmann, München 1976, ().