Muscle fiber types fall into three main categories; slow-twitch (type-I), glycolytic fast-twitch (type-IIx) or oxidative fast-twitch (type-IIa). Slow-twitch fibers are recruited to lift lighter loads and have very little capacity for increasing size. The type-IIa and IIx fibers are characterized as fast twitch; they produce the highest levels of force but are recruited only during maximum lifts with very heavy weight. Fast-twitch fibers are capable of dramatic growth responses from training. Therefore, bodybuilders must lift heavy (high loads, low reps) to stand a chance of making decent gains in the gym.
A recent study has shown that depleting the fast twitch fibers utilizes more calories during recovery. This extra energy cost during recovery may be yet another reason why Max-OT training is so effective at burning calories and promoting a lean physique. Additionally, this research showed that depleting the slow twitch muscle fibers of glycogen (with prolonged endurance exercise and fasting) enabled greater recruitment of the fast twitch fibers during a subsequent bout of exercise. However, the application of this information is limited for bodybuilders.
Based on this information, the editors of one muscle magazine recently recommended that bodybuilders should perform 60-90 minutes of cardio exercise and then go perform intense weight lifting. Only follow this stupid advice if you want a physique like Pee-wee Herman. Be careful where you obtain your bodybuilding advice.
Med Sci Sports Exerc
