Primary means of motion Works in combination with the skeletal system and the nervous system Movement occurs when a nerve stimulates a muscle to contract. Muscle fibers shorten and pull on attached bones to produce movement.
Skeletal muscles are made up of many muscle fibers held in place by connective tissue (fascia). Muscle fibers are made up of myofibrils (protein filaments) composed of a series of repeating segments called sarcomeres. Sarcomeres, made up of thick (myosin) and thin (actin) myofilaments, are the functional contracting unit of skeletal muscle.
Sliding filament model ◦ If sufficient energy is present, cross- bridges are formed and the myosin pulls the actin toward the center, thereby shortening the sarcomere and the muscle fiber itself. ◦ See the video this week on the Sliding Filament Theory
Nerves are made up of neurons (nerve cells) A motor unit is made up of one motor neuron and all of the muscle cells it innervates. The number of muscle cells a motor neuron innervates depends on the precision and accuracy required of that muscle.
Skeletal fibers can be divided into categories based on how quickly they contract. ◦ Slow-twitch muscle fibers (also called slow oxidative or type I muscle fibers) As the name implies, slow-twitch fibers contract more slowly than fast-twitch fibers. They have lower force outputs, but are more efficient and fatigue-resistant than fast-twitch fibers. ◦ Fast-twitch muscle fibers (also called type II muscle fibers) are further subdivided into fast-glycolytic (type IIx) and fast-oxidative glycolytic (type IIa) fibers. Type IIx have a limited capacity for aerobic metabolism, and fatigue more easily than slow-twitch fibers. They have considerable anaerobic capacity, and are the largest and fastest, and are capable of producing the most force, of all the skeletal muscle fibers. Type IIa muscle fibers possess speed, fatigue, and force-production capabilities somewhere between type I and type IIx fibers. For this reason, type IIa fibers are also called intermediate fibers.
Muscle Fiber Types This chart is similar to Table 4.1 page 46 The following table compares the three types of muscle fiber using the relative terms low, medium, and high. Type I Type IIa Type IIx Speed of Low Medium High contraction Force capacity Low Medium High Fatigue resistance High Medium Low Mitochondrial High Medium Low content Size Low Medium High Efficiency High Medium Low Aerobic capacity High Medium Low Anaerobic Low Medium High capacity
In a third-class lever, the motive force has a short lever arm and the resistance has a long lever arm. Motive force muscles are at a mechanical disadvantage. ◦ Muscles typically attach near the joint, creating a short lever arm and, as a result, it requires relative high forces to lift even small weights. Application to training: ◦ Assuming a client is lifting the same amount of weight, he or she can create more resistance by moving the weight farther from the working joint, or less resistance by moving it closer to the working joint.
Concentric contraction ◦ Muscle acts as the motive force and shortens as it create tension. ◦ Motion is created by the muscle contraction. Eccentric contraction ◦ Muscle acts as the resistive force and lengthens as it creates tension. ◦ External force exceeds the contractive force generated by the muscle. ◦ Motion is controlled (slowed) by the muscle contraction.
Research suggests DOMS is caused by tissue injury from excessive mechanical force, particularly eccentric force, exerted on muscle and connective tissue. Generally appears 24–48 hours after strenuous exercise Attempt to reduce DOMS by starting at a low intensity and progressing slowly through the first few weeks while minimizing eccentric actions.
Maximal force that can be exerted in a single effort Priority in sports that require a weighted object to be lifted, carried or thrown. Directly related to muscle cross-sectional area. Resistance training can increase the number of fibers recruited for work.
Rate of doing work Relationship of strength and velocity Usually, the shorter the duration of the activity, the greater the power needed
The ability to sustain submax contractions Muscular power – Ability to repeatedly perform a skill with adequate speed. Table 4.2 (page 53) ◦ Strength-Endurance Continuum diagram
Reaction time ◦ Time elapsed from the stimulus until movement starts Quickness ◦ Reaction time plus the power of initial movement Speed ◦ Final velocity attained
Dynamic ◦ Ability to maintain equilibrium during vigorous movements. Static ◦ Ability to maintain equilibrium in a stationary position. Task specific – need to practice specific balance needed.
Range of motion through which joints are able to move Influenced by ◦ Joint design ◦ Tendons, muscles and ligaments ◦ Gender ◦ Habitual use ◦ Stretching
Sport Specific Athletes should have slightly more range of motion than their sport requires. Flexibility can sacrifice joint stability For most sports a moderate degree of flexibility is adequate.
Ability to change speed and direction rapidly with precision. Practicing movements enhances agility ◦ Learning movements ◦ Reduced cognitive processing time ◦ Training specific muscle fibers ◦ Develops power specific to skill