Energy and Exercise

Vocabulary terms: Aerobic – requiring the presence of oxygen Anaerobic – without oxygen Fast-twitch fibers – fibers that are large in diameter, contain densely packed myofibrils, large glycogen reserves, relatively few mitochondria. They produce rapid and powerful contractions of relatively brief duration. Slow-twitch fibers – fibers that are ½ the diameter of fast fibers and take 3x as long to contract after stimulation. Specializations such as abundant mitochondria and extensive capillary supply and high concentrations of myoglobin, enable slow fibers to continue contracting for extended periods. Intermediate-twitch fibers – very similar to fast fibers but have a greater resistance to fatigue. Oxygen debt – the amount of extra oxygen required by muscle tissue to oxidize lactic acid and replenish depleted ATP and phosphocreatine following vigorous exercise. Glycolysis – the anaerobic cytoplasmic breakdown of glucose into lactic acid by way of pyruvic acid, with a net gain of 2 ATP molecules.

Vocabulary Terms continued.... Lactic acid – a compound produced from pyruvic acid under anaerobic conditions (glycolysis). Lactic acid causes pH changes, and muscle fibers respond poorly to stimulation. Heat production/heat loss – muscular activity generates substantial amounts of heat. Dehydration synthesis (catabolic process), such as the breakdown of glycogen or the reactions of glycolysis, a muscle fiber captures only a portion of the released energy. The rest is released as heat through the skin (integumentary system). Muscle fatigue – an active skeletal muscle is said to be fatigued when it can no longer continue to perform at the required level of activity. Muscle fatigue is cumulative – the effects become more pronounced as more neurons and muscle fibers are affected. Recovery period – a period of time in which muscle fibers are returned to normal, preexertion levels. (Note: moderate activity may take several hours for recovery. Sustained activity at higher levels, complete recovery can take a week.) Force – the maximum amount of tension produced by a particular muscle or muscle group. Endurance – the amount of time during which the individual can perform a particular activity. Two major factors determine the performance capabilities of any skeletal muscle: 1) types of muscle fibers in the muscle, and 2) physical conditioning or training.