Insulin is a polypeptide hormone, a molecular chain of amino acids-secreted by the beta-cells of the pancreas. Although generally associated with carbohydrate metabolism, insulin also has potent anabolic effects in muscle. Past research showed that it produced its anabolic effects by
promoting amino acid transport into muscle cells. Other studies pointed to an anticatabolic action, in which insulin retarded the degradation of muscle amino acids. Most of these observations were indirect, however. Few studies actually took a "live action" view of insulin metabolism
To remedy this discrepancy, researchers from the University of Texas, Galveston, recently used two methods that allowed them to view precisely how insulin does its thing in muscle. They reported their results in a HISS issue of the Journal of Clinical Investigation.
After infusing insulin into the thighs of six healthy male subjects, the scientists found that insulin directly increased muscle protein synthesis. In contrast, the rate of protein breakdown, or catabolism, didn't significantly change alter the insulin was administered. As for amino
acid transport, some aminos were affected, while others weren't. For example, insulin speeded the entry of lysine and alanine into muscle more than it did leucine. Transport of another amino acid, phenylalanine, wasn't affected at all.
In terms of muscle protein breakdown, insulin only comes into play when low levels of amino acids exist. At that time muscle protein breakdown is orchestrated by cell organelles called lysosomes. Under conditions of high amino acid availability, the primary degrading mechanism
involves an ATP-independent system consisting of a special protein called ubiquitin that isn't affected by insulin.
Thus, insulin appears to exert its anabolic actions by selectively increasing amino acid entry into muscle while also directly turning on muscle protein synthesis. Even so, exogenous insulin-that is, insulin introduced from or produced outside the body-can be dangerous, and its use
should he strictly reserved for diabetics. You can manipulate your own insulin by consuming carbohydrates and protein within one hour after a workout. Another method is to take supplements that increase insulin effectiveness, such as chromium. Vanadyl sulfate may exert its actions
by mimicking the metabolic effects of insulin.
Electric Muscle Stimulation
The use of electrical muscle stimulation, or EMS, remains controversial, though intriguing. Past studies show that EMS can increase muscular strength but only isometrically. This means that EMS will increase strength only in the joint positions where it's applied, similarly to the
effect of straight isometric exercise. Isometric exercise is characterized by static exercise that doesn't involve movement.
The most effective use of EMS is in physical therapy by electrically stimulating muscles made immobile through injury, EMS can prevent excessive muscle atrophy that would otherwise occur. This both speeds recovery and allows a more rapid return to previous strength levels, also have
value during extended space missions. Under conditions of low gravity both muscle and bone tissue degenerate. Sending a proper dose of electrical current through those tissues may prevent the negative effects.
Since most research involving EMS has used isometric protocols, a group of Swedish and Finnish scientists wondered what would happen if it were applied during dynamic or full-range exercise. To find out, they recruited seven healthy male physical education students. The men did
electrically induced one-leg extensions three times a week for 60 minutes for a month.
EMS reverses the usual pattern of muscle fiber recruitment. With normal isotonic exercise, such as weight training, the brain first recruits slow- twitch, or endurance, fibers, gradually involving faster growing fast-twitch fibers, depending on how much weight is used and the level
of intensity. In contrast, EMS cuts to the chase by directly activating the fast-twitch fibers. While it would seem that this should increase muscular size most studies don't bear this out.
The new study reported here likewise found that EMS preferentially recruited fast-twitch fibers, but it also showed no size increases. Even so, the EMS-trained leg produced a whopping 82 percent increase in muscular endurance. Since no aerobic enzyme changes occurred in the involved
muscles, the researchers attributed the increase in muscular endurance to neural adaptation. Another surprise included a minor crossover effect of increased endurance in the untrained thigh.
The scientists conducting the study suggested that the amount of electrical voltage applied may have been too low to promote muscle hypertrophy hut was enough to induce a large-scale endurance increase- Although the voltage applied may have been of low intensity, it apparently was
enough to cause some damage to muscle connective tissue, as shown by increased activity of an enzyme involved in muscle collagen synthesis.