14.17
Exercise and Muscle Performance
Exercise induces a range of adaptations in muscle tissue, depending on the type and duration of activity. Such physical training can be broadly catego…
Physical training has two broad types—muscle-strengthening endurance exercises and muscle-enlarging resistance exercises.
Endurance exercises such as running, swimming, or cycling use slow muscle fibers for low-force and repetitive movements.
After exhausting the sarcoplasmic reserves of carbohydrates, lipids, and proteins for aerobic respiration, the slow fibers start drawing nutrients from the circulating blood to support contractions.
Regular endurance training stimulates extensive angiogenesis that increases oxygen supply to the muscle fibers, gradually building stamina and allowing extended activity without fatigue.
In contrast, resistance exercises such as weightlifting, sprinting, or jumping require more strength than stamina and utilize fast fibers.
The initial contractions of fast fibers rely on ATP and creatine phosphate reserves, moving on to the anaerobic breakdown of glycogen for these power-intensive muscle contractions.
Consistent resistance training helps to change muscle size by enlargement of cells. It also builds strength by converting the fast oxidative muscle fibers to the fast glycolytic type.
Additionally, tendons undergo strengthening to support muscles while contracting against high-resistance forces, further adding to overall muscle mass.
View the full transcript and gain access to JoVE Core videos
Q1: What is the difference between endurance and resistance exercises?
Endurance exercises like running, swimming, or cycling use slow muscle fibers for repetitive, low-force movements and build stamina. Resistance exercises such as weightlifting, sprinting, or jumping engage fast muscle fibers and require more strength than endurance. Endurance training increases oxygen supply through angiogenesis, while resistance training enlarges muscle cells and builds strength.
Q2: How do slow muscle fibers adapt to endurance training?
Regular endurance training stimulates angiogenesis, increasing capillaries around muscle fibers and oxygen supply. Slow fibers develop more mitochondria and synthesize additional myoglobin, enhancing aerobic metabolism efficiency. These adaptations gradually build stamina and allow extended activity without fatigue by enabling muscles to draw nutrients from circulating blood.
Q3: What energy systems do fast muscle fibers use during resistance exercise?
Fast muscle fibers initially rely on ATP and creatine phosphate reserves during resistance exercise. When these reserves deplete, fibers shift to anaerobic breakdown of glycogen for power-intensive contractions. This energy system supports the high-force, short-duration movements characteristic of weightlifting, sprinting, and jumping.
Q4: How does consistent resistance training change muscle composition?
Consistent resistance training enlarges individual muscle cells, increasing overall muscle mass and strength. Training converts fast oxidative muscle fibers to the fast glycolytic type, optimizing them for power output. Tendons also strengthen to support muscles contracting against high-resistance forces, contributing to increased muscle mass and performance.
Q5: Can fast glycolytic fibers transform into fast oxidative fibers?
Yes, regular endurance exercise can cause fast glycolytic fibers to transform into fast oxidative fibers, though the transformation is not total or straightforward. The extent of fiber type changes varies significantly between individuals and depends on training intensity, duration, and genetic predisposition, making responses to endurance training highly individual.
Q6: How much muscle mass can resistance training build in a year?
Just a few minutes of high-intensity resistance exercise every other day can lead to a 50% increase in muscle mass within a year, even for someone not particularly strong. This additional bulk primarily results from increased size of individual muscle fibers, particularly the fast glycolytic variety, rather than an increase in the overall number of fibers.
Q7: What metabolic changes occur in muscle fibers during endurance training?
Endurance training increases the number of capillaries and mitochondria within muscle fibers and stimulates myoglobin synthesis. These changes make muscles more efficient in aerobic metabolism, particularly in slow oxidative fibers. The result is greater endurance, strength, and resistance to fatigue as muscles become better equipped to utilize oxygen and circulating nutrients.