肌肉與運動

Exercise that is relatively low intensity but long duration (popularly called "aerobic exercise"), such as running or swimming, produces increases in the number of mitochondria in the fibers that are recruited in this type of activity. In addition, the number of capillaries around these fibers also increases. All these changes lead to an increase in the capacity for endurance activity with a minimum of fatigue. (Surprisingly, fiber diameter decreases slightly, and thus there is a small decrease in the maximal strength of muscles as a result of endurance training.) As we will see in later chapters, endurance exercise produces changes not only skeletal muscles but also in the respiratory and circulatory systems, changes that improve the delivery of oxygen and fuel molecules to the muscle.

The structure of actin and myosin filaments

Myofibrils

Image: https://www.britannica.com

In contrast, short-duration, high-intensity exercise (popularly called "strength training"), such as weight lifting, affects primarily the fast-glycolytic fibers, which are recruited during strong contractions. These fibers undergo an increase in fiber diameter (hypertrophy) due to increased synthesis of actin and myosin filaments, which form more myofibrils. In addition, glycolytic activity is increased by increasing the synthesis of glycolytic enzymes. The result of such high-intensity exercise is an increase in the strength of the muscle and bulging muscles of a conditioned weight lifter. Such muscles, although very powerful, have little capacity for endurance, and they fatigue rapidly.

Widmaier, E.P., & Raff, H. (2008). Vander’s Human Physiology: The Mechanisms of Body Function. New York, NY: McGraw-Hill.

Fast-glycolytic fibers have relatively fast contractions and primarily use anaerobic glycolysis.

bulging: swollen with contents

Enhancing cardiovascular fitness can lead to substantial health benefits. High-intensity interval training (HIT) is an efficient way to develop cardiovascular fitness, yet comparisons between this type of training and traditional endurance training are equivocal.

equivocal: uncertain as an indication or sign

Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.

VO2max: maximal oxygen consumption

Milanović, Z. (2015). Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Springer Link, 45, 1469–1481.

Growth in cell numbers is limited to the prenatal and immediately postnatal period, with the animals and man being born with or soon reaching their full complement of muscle cells.

Pearson, A. M. (1990). Muscle growth and exercise. Critical Reviews in Food Science and Nutrition, 29(3), 167-196. https://www.tandfonline.com/doi/abs/10.1080/10408399009527522

complement: the full quantity, number, or assortment needed or included