Muscle Performance & Force Exertion

• Muscle performance has 3 components: Muscle strength, power, and endurance

Muscle Strength

• The maximum force that a muscle or muscle group can exert during a contraction
• The ability to exert force at any speed

Power

• Is the rate of performing muscle contractions over a distance for a specific period of time.
• Power is generally associated with high speeds of movement
• Power is required for many functional tasks

Endurance

• The ability of the muscle or muscle group to sustain contractions repeatedly or over for a certain period of time

Resistance Training Terminology

• Isometric Muscle Action is static and is produced mm tension is created without a change in muscle length
• Isotonic Muscle Action is a dynamic change in mm length.
• Concentric mm action is when mm shortens during activity.
• Eccentric muscle action is when mm lengthens during activity.

Principles

• Overload Principle is where, to improve muscle performance, there must be a challenge to performing at a greater level
• The application of the overload principle includes intensity of resistance exercise, volume of exercise, and context of the underlying pathology
• Specific Adaptation to Imposed Demands (SAID) principle includes the extension of Wolff's law, specificity of training and transfer of training
• Reversibility principle includes detraining

Muscle Structure

• Muscles are composed of thousands of cells called muscle fibers
• Each muscle fiber is covered by the endomysium
• Fascicles are bundles of muscle fibers, and are covered by the perimysium
• Bundles of fascicles make up the muscle
• The muscle is covered by the epimysium
• Muscle fiber cells do not run the length of the entire muscle
• Connective tissue coverings are necessary to transmit contractile forces
• Myofibrils are threads of proteins, and are enclosed in the sarcolemma
• Each myofibril contains smaller threads called myofilaments
• Myofilaments are protein molecules
• Myofilaments are composed of Actin (thin filiment) and Myosin (thick filiment)
• Force is obtained by the contraction of different motor units a few at a time, in rapid succession so the tension is a tetanic nature rather than a twitching one

Motor unit

• Composed of a motor neuron, its axon and all of the muscle fibers which it innervates
• The number of muscle fibers/motor unit varies from 5-100
• Muscles requiring a fine degree of control have a smaller number of fibers/neuron than large postural muscles
• Motor units fire in an “all or none fashion"
• Increasing strength of a contraction is accomplished by increasing the number of activated motor units
• Contraction strength is also affected by the frequency of stimulation
• During wave summation, the fiber is stimulated many consecutive times with each contraction adding to the force, increasing contraction strength ,and the new contraction starts before the previous one ends

Muscle Contractions

• Muscle twitch is the response to a quick stimulation
• Includes quick contraction & relaxation
• Tetany is where the frequency of contractions/twitches increase, allowing no relaxation between
• Muscle contraction increases smoothly up to a point of maximum strength
• Weak contraction uses only 1-2 motor units to contract 2-3 times/second
• Units take turns contracting, so tetany occurs
• Strong contraction uses a greater number of motor units which are recruited and fire more frequently

Muscle Force

• Cross Sectional Area (CSA) is the larger the CSA of a muscle, the more tension is produced during a max contraction

Adaptations of muscle

• Two changes occur to muscle due to resistance training: adaptation of the muscle, and the extent to which the motor unit can activate the muscle
• Hypertrophy of muscle fibers increases the cross sectional area
• The increase is caused by increased synthesis of actin and myosin
• Untrained individuals can make significant strength gains in just a few days of resistance training through “learning" how to use their muscles

Muscle Loss

• Adults who do not strength train lose 5-7 lbs of muscle every decade
• Only muscle training maintains muscle mass and strength during the mid-life years
• Immobilization leads to atrophy
• Can be reversed with resistance training
• Muscle loss is accompanied by a decrease in metabolic rate
• Adults have a 2-5% reduction in metabolic rate every decade
• Regular exercise training in adulthood can help decrease loss of metabolic rate
• Adding 3 lbs of muscle mass increases metabolic rate by 7% and daily caloric needs by 15%
• Progressive resistance training stimulates increases in bone mineral density
• Progressive resistance training is commonly done in programs for osteoarthritis
• Exercises should involve many muscle groups

Glucose Metabolism

• 4 months of resistance training increased glucose uptake by 23%
• Exercise programs, including resistance training, are beneficial to decrease DM II onset

Training Principles

• Dosage: increasing intensity or amount of weight, changing sets and repetitions, decreasing rest periods, and changing frequency of exercise
• Mode: the method of exercise (use of weights, tubing, etc.)
• Repetitions: is the Number of times an exercise that is repeated
• A set is performance of an exercise for a number of repetitions followed by a rest break or a different exercise
• Frequency: is how often the exercises are performed
• Rest Interval is Generally from 1-3 minutes
• Increase in training load that leads to an adaptation in muscle is overload
• An increased training load challenges an individual's current level of fitness, a response by the body occurs as an adaptation to the stimulus of the training load
• Example: increase in muscle strength
• Intensity is the amount of effort of training
• It may be expressed through change in HR, BP, or by the patient stating how hard the effort is
• Rutherford and Jones(1986) showed that a ~170% increase in training weights resulted in a ~10% increase in isometric MVC force
• Volume: is the amount of training
• The Nature of the training will determine the training effect
• For example, swimming to prepare for a marathon would not be a good idea
• While cross training you may improve performance in one area by training in another mode
• Cross training benefits are mostly physiological, not performance based
• Overtraining results when training loads are too demanding on an individual's ability to adapt
• Overtraining results in fatigue, substitute patterns, and injury
• Delayed Onset Muscle Soreness (DOMS) is due to microscopic tearing
• DOMS is NOT Lactic Acid related
• DOMS develops 24-28 hours after exercise and resolves within a week
• Eccentric exercise causes more DOMS than concentric
• DOMS Can be reduced by performing warmup and cool down exercises

Resistive Exercise

• Indications: muscle weakness or paralysis, increase bone density, to improve aerobic capacity, and to improve pliability and strength of other connective tissue
• Contraindications: pain, inflammation, severe cardiopulmonary disease, loss of joint integrity
• Precautions: valsalva, substitution, overwork (weakness), Overtraining (fatigue), muscle soreness and acute DOMS, and pathological fracture