CoursesPhysiologyMuscular systemSkeletal muscleExercise and muscle performance

Exercise and muscle performance

Learning objectives:

After completing this study unit, you will be able to:

Describe the mechanisms that contribute to fatigue.
Compare and contrast endurance and resistance training.
Discuss the effects of muscle atrophy.

Introduction

Physical training induces structural and metabolic adaptations that enhance skeletal muscle performance. Conversely, prolonged inactivity can lead to atrophy and reduced performance.

Exercise induces short-term responses and long-term adaptations.
Acute responses to training and exercise include fatigue, a reversible decline in a muscle's ability to maintain the intended force output. Fatigue can be classified as:

Central fatigue: occurs in the central nervous system and decreases voluntary muscle activation
Peripheral fatigue: occurs at the muscle level and decreases muscle contraction force primarily due to failure of excitation-contraction coupling or crossbridge cycling

In the long term, exercise induces structural and biochemical remodeling of existing muscle cells that improve performance. Specifically:

Endurance training: increases mitochondrial density and vascularization of Type I muscle fibers, improving their oxidative catabolism
Resistance training: induces hypertrophy (more myofibrils, larger fiber diameter), enhancing muscle tension generation in Type II fibers

The opposite adaptation, muscle atrophy that hinders performance, often occur due to:

Physical inactivity: loss of myofibrils and less efficient oxidative catabolism reduce both endurance and strength
Older age (sarcopenia): preferential loss of faster fibers, replaced with non-contractile connective and adipose tissue. It is exacerbated by sedentary behaviour, but physical activity can attenuate its progression.

Explore concepts

Fatigue

Acutely, exercise can cause central and peripheral fatigue.

Training and disuse

Resistance training, endurance training and physical inactivity induce long-term muscle fiber adaptations.

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Test your knowledge about exercise and muscle performance with this quiz!

Summary

Key points about exercise and muscle performance
Training and exercise	Acute effects: fatigue, unbalanced homeostasis; decrease performance Long-term adaptations: structure and metabolism; improve performance
Fatigue	Central: nervous system, lower voluntary muscle activation Includes psychophysiological mechanisms that increase effort, neurotransmitter imbalances, reflex modulation Peripheral: muscle, impaired mechanical force production Can be due to glycogen depletion, accumulation of ADP and Pᵢ, ion imbalances (H⁺, K⁺)
Excess postexercise oxygen consumption	Increased rate of breathing to: i) dissipate heat; ii) introduce oxygen to restore muscle ATP reserves; iii) expel CO₂ to restore blood pH
Training	Endurance training: lower loads, more repetitions; increases Type I fiber vascularization and mitochondrial density; improves oxidative catabolism Resistance training: higher loads, fewer repetitions; hypertrophy of Type II fibers; improves force generation
Physical inactivity	Disuse: muscle atrophy, reduced strength and endurance
Aging	Sarcopenia: atrophy of Type II fibers; exacerbated by physical inactivity, can be attenuated by exercise