Muscle Fibers and Endurance Quiz

Muscle Adaptation to Exercise

• Muscle strength is defined as the amount of force a muscle can produce.
• Maximal contractile force is influenced by muscle size (3-4 kg/cm2).
• Muscle power is the amount of work a muscle performs in a period of time (kg-m/min).
• Power is the ability to generate force quickly (combination of strength and speed).
• Muscle performance is limited without power.
• Muscle endurance is the ability of muscles to sustain repeated contractions against resistance for a period of time.
• Endurance depends on energy stored (glycogen) in the muscle.
• Types of muscle endurance include dynamic (repeated contraction/relaxation) and static (sustained contraction).

Physiological Effects of Strength Training

• Strength training increases muscle mass and fiber size.
• It enhances motor unit utilization and coordination.
• Strength training increases the strength of tendons, ligaments, and bones.
• It improves fuel storage and blood supply to muscles.
• Strength training can improve blood fat levels and biochemical processes.

Benefits of Muscular Strength and Endurance

• Improved performance of physical activities.
• Prevention of injury.
• Improved body composition.
• Enhanced self-image and quality of life.
• Improved muscle and bone health with aging.
• Prevention and management of chronic disease.

Effect of Training on Muscles and Muscle Performance (Maximal Resistance Training)

• 6 maximal muscle contractions x 3 sets x 1 week increases muscle strength without muscle fatigue.
• Muscles function under no load also. (Note: The chart shows how muscle strength increases over time with resistance training).

Muscle Hypertrophy

• Training causes muscle hypertrophy (30-60%).
• The increase is due to increased diameter of muscle fibers, and possibly some increase in number of fibers.

Changes in the Hypertrophied Muscle Fiber

• Aerobic and anaerobic metabolisms increase.
• Myofibrils increase.
• Mitochondrial enzymes increase (120%).
• ATP and phosphocreatine increase.
• Stored glycogen increases (50%).
• Stored triglycerides increase (75-100%).
• Oxidative metabolic efficiency improves.

Muscle Fibers

Slow-twitch Fibers

• Fatigue-resistant.
• Contract less rapidly and forcefully than fast-twitch fibers.
• Rely primarily on oxidative energy systems.

Fast-twitch Fibers

• Contract rapidly and forcefully.
• Fatigue more quickly than slow-twitch fibers.
• Rely more on non-oxidative energy systems.

Slow-Twitch vs. Fast-Twitch Muscle Fibers

• Slow-twitch muscles are for prolonged muscle activity (e.g., soleus muscle in lower leg for standing), providing endurance and strength of contraction for minutes to hours.
• Fast-twitch muscles are for forceful and rapid contraction (e.g., gastrocnemius muscle used for jumping), providing maximal power in very short periods.

Respiration in Exercise

• Oxygen consumption and pulmonary ventilation increase about 20-fold between resting and maximal exercise intensity. (Note: The graph shows this relationship).

Cardiovascular System in Exercise

• Work output, oxygen consumption, and cardiac output are directly related.
• Muscle work increases oxygen consumption, which in turn dilates muscle blood vessels to increase venous return and cardiac output.

Effect of Training on Heart Hypertrophy and Cardiac Output

• Training increases cardiac output (COP) by about 40% compared to untrained individuals.
• Heart chambers of marathoners enlarge by about 40% compared with non-trained individuals.
• Heart size is larger in marathoners than in normal people.

Cardiac Output in Exercise

• Cardiac output increases from 5 L/min to 30 L/min.
• Stroke volume increases from 105 to 162 ml (about 50%).
• Heart rate increases from 50 to 185 beats/min (about 270%).
• Heart rate increase contributes more significantly to increased cardiac output compared to stroke volume increase.

Body Heat in Exercise

• Almost all the energy released by the body is converted into body heat.
• Remaining energy is converted to heat.

Heat Stroke

• During endurance training, body temperature may rise to 37°C to 40°C.
• Hot and humid conditions can cause temperatures to reach 41°C to 42°C.
• High temperature is destructive to tissue cells (especially brain cells).
• Symptoms include body weakness, exhaustion, headache, dizziness, nausea, sweating, confusion, uncontrolled gait, collapse, and unconsciousness.
• Symptoms may lead to death.

Treatment of Heatstroke

• Remove all clothing.
• Maintain a spray or continuously sponge the body with cool water.
• Blow air over the body with a fan.
• Physicians prefer total cooling measures.

References

• Textbook of Physiology by Guyton & Hall, 11th edition.
• Review of Medical Physiology by Ganong, 24th edition.

Test your knowledge on muscle fibers, oxidative metabolism, and endurance. This quiz covers key concepts related to muscle performance, training effects, and the distinctions between muscle power and strength. Perfect for students studying exercise physiology or fitness enthusiasts looking to deepen their understanding.