Understanding Muscle Contraction Types, Strength, and Fatigue
Types of Muscle Contraction
Isotonic Contractions
Isotonic contractions occur when muscle fibers contract and change length. They are divided into two types:
Concentric Contractions
A concentric contraction happens when a muscle develops enough tension to overcome resistance, causing it to shorten and move a body part against that resistance.
Eccentric Contractions
An eccentric contraction occurs when the resistance is greater than the tension exerted by the muscle, causing the muscle to lengthen under tension.
Isometric Contraction
In an isometric contraction, the muscle remains at a constant length, either shortened or lengthened, while maintaining static tension. This generates a static contraction without changes in muscle length.
Auzotonic Contractions
Auzotonic contractions combine isometric and isotonic contractions. The isotonic component is accentuated at the beginning of the contraction, while the isometric component is further accentuated at the end.
Isokinetic Contractions
An isokinetic contraction is defined as a maximal contraction at a constant speed throughout the range of motion.
Muscle Strength and Power
Muscular Strength
Muscular strength is a physical capacity representing the neuromuscular ability to overcome internal and external resistance through static (isometric) or dynamic muscle contractions.
Muscle Power
Muscle power is determined by the force of muscle contraction, the distance of contraction, and the number of contractions per minute.
Fast and Slow Muscle Fibers
Characteristics of Fast Fibers
- High levels of ATPase
- Great force of contraction
- Extensive sarcoplasmic reticulum for rapid calcium release
- Large amounts of glycolytic enzymes
- Decreased blood supply
- Lower number of mitochondria
- Secondary oxidative metabolism
Characteristics of Slow Fibers
- Presence of oxygen and more fat deposits
- Smaller innervated fibers
- More blood vessels and systems to provide extra oxygen
- Increased amount of myoglobin (iron-protein similar to hemoglobin)
- Reddish appearance (giving the name “red muscle”)
Muscle Fatigue
Muscle fatigue is a decrease in the maximum throughput capacity in response to training loads. It can lead to injuries and should be prevented by coaches and athletes.
Causes of Muscle Fatigue
Causes include excessive physical work beyond tolerance limits, either through large volumes or heavy loads, and insufficient rest periods.
Role of Lactate in Fatigue
Lactate is a metabolic intermediate that increases during high-intensity exercise due to high glycolytic activity. ATP production is associated with lactate ion generation, reducing the cell’s pH. Increased lactate levels, dependent on fiber type, can contribute to fatigue.
Skeletal Muscle
Skeletal muscles are striated muscles attached to the skeleton, consisting of elongated cells or fibers with peripheral nuclei. The organization of actin and myosin proteins gives them a striated appearance under a microscope. They facilitate movement and maintain bone-joint union through contraction.
Diagnostic Procedures
Biopsy
A biopsy is a diagnostic procedure involving the removal of a tissue sample for microscopic examination. It is often used for accurate cancer diagnosis.
Electromyography (EMG)
Electromyography is a medical diagnostic technique involving a neurophysiological study of bioelectric muscular activity. Small, low-voltage electrodes are inserted into the muscle to measure the response and connectivity between different electrodes.