Transcript Fatigue
Fatigue Dr. Afaf A.M. Shaheen L e c t u re N O . , 1 2 RHS 322 Outlines and objectives of the lecture Definition of fatigue Types of fatigue a) Muscle (local) fatigue Theories of local Fatigue b) Cardiopulmonary (general) fatigue Threshold for fatigue Factors that influence fatigue Recovery from Exercise Changes that occur in muscle during recovery Fatigue Fatigue is a complex phenomenon that affects muscle performance and must be considered in a resistance training program. Fatigue has a variety of definitions that are based on the type of fatigue being addressed. • Muscle (local) fatigue 1 2 • Cardiopulmonary (general) fatigue a) Muscle (local) fatigue. Most relevant to resistance exercise, it is the phenomenon of skeletal muscle fatigue. Muscle (local) fatigue : the diminished response of muscle to a repeated stimulus—is reflected in a progressive decrement in the amplitude of motor unit potentials. This occurs during exercise when a muscle repeatedly contracts statically or dynamically against an imposed load. a) Muscle (local) fatigue . Cont., This acute physiological response to exercise is normal and reversible. It is characterized by a gradual decline in the force-producing capacity of the neuromuscular system, that is, a temporary state of exhaustion (failure), leading to a decrease in muscle strength. a) Muscle (local) fatigue . Cont., The diminished response of the muscle is caused by a combination of factors, which include: 1. Disturbances in the contractile mechanism of the muscle itself because of a decrease in energy stores, insufficient oxygen, and a build-up of H 2. Inhibitory (protective) influences from the central nervous system 3. Possibly a decrease in the conduction of impulses at the myoneural junction, particularly in fast-twitch fibers. a) Muscle (local) fatigue . Cont., The fiber-type distribution of a muscle, which can be divided into two broad categories (type I and type II), affects how resistant it is to fatigue. Muscle Fiber Types and Resistance to Fatigue Characteristics Type I Type IIA Type IIB Resistance to fatigue Capillary density High Intermediate Low High High Low Aerobic Aerobic Anerobic Diameter Small Intermediate Large Twitch rate Slow Fast Fast Maximum muscle shortening velocity Slow Fast Fast Energy system Because different muscles are composed of varying proportions of tonic and phasic fibers, their function becomes specialized. A heavy distribution of type I (tonic) fibers is found in postural muscles, which allows muscles e.g. soleus to sustain a low level of tension for extended periods of time to hold the body erect against gravity or stabilize against repetitive loads. On the other end of the fatigue spectrum, muscles with a large distribution of type IIB (phasic) fibers, e.g. gastrocnemius or biceps brachii, produce a great burst of tension to enable a person to lift the entire body weight or to lift, lower, push, or pull a heavy load but fatigue quickly. Signs and Symptoms of Muscle Fatigue 1 • An uncomfortable sensation in the muscle, even pain and cramping 2 • Tremulousness in the contracting muscle 3 • Active movements jerky, not smooth Signs and Symptoms of Muscle Fatigue 3 • Inability to complete the movement pattern through the full range of available motion during dynamic exercise against the same level of resistance 4 • Use of substitute motions—that is, incorrect movement patterns—to complete the movement pattern 5,6 • Inability to continue low-intensity physical activity • Decline in peak torque during isokinetic testing When these signs and symptoms develop during resistance exercise, decrease the load on the exercising muscle or stop the exercise and shift to another muscle group to allow time for the fatigued muscle to rest and recover…. Origins of Localized Muscle Fatigue Accumulation Theory of Fatigue: Fatigue results from an accumulation of certain by-products produced as a result of metabolic processes associated with the mechanisms of muscular contraction Origins of Localized Muscle Fatigue Accumulation Theory of Fatigue: Lactic Acid and free H+ K+ NH3 • Decreases membrane excitability • Decreases Ca++ affinity for Tropopin • Decreases the release of Ca++ • Obstructs glycolyses • Inhibits Aerobic Metabolism Origins of Localized Muscle Fatigue Depletion Theory of Fatigue: Fatigue results from the depletion of metabolites necessary for energy production Glucose ADP or CP ATP Oxygen Reaction Enzymes b)Cardiopulmonary (general) fatigue It is the diminished response of an individual (the entire body) as the result of prolonged physical activity, such as walking, jogging, cycling, or repetitive lifting or digging. It is related to the body’s ability to use oxygen efficiently. Cardiopulmonary fatigue associated with endurance training is probably caused by a combination of the following factors. blood sugar (glucose) levels factors Depletion of potassium, especially in the elderly patient glycogen stores in muscle and liver Threshold for fatigue Threshold for fatigue is the level of exercise that cannot be sustained indefinitely A patient’s threshold for fatigue could be noted as the length of time a contraction is maintained or the number of repetitions of an exercise that initially can be performed. Factors that influence fatigue Factors that influence fatigue are diverse. 1. A patient’s health status, 2. diet, or lifestyle (sedentary or active) all influence fatigue. In patients with neuromuscular, cardiopulmonary, oncologic, inflammatory, or psychological disorders, the onset of fatigue is often abnormal Recovery from Exercise Adequate time for recovery from fatiguing exercise must be built into every resistance training program. This applies to both intra-session and intersession recovery. After vigorous exercise, the body must be given time to restore itself to a state that existed prior to the exhaustive exercise. Recovery from acute exercise, where the force-producing capacity of muscle returns to 90% to 95% of the pre exercise capacity, usually takes 3 to 4 minutes, with the greatest proportion of recovery occurring in the first minute. Changes that occur in muscle during recovery are: 1. Oxygen stores are replenished in muscles. 2. Energy stores are replenished. Decrease in blood sugar (glucose) levels 3. Lactic acid is removed from skeletal muscle and blood within approximately 1 hour after exercise. 4. Glycogen is replaced over several days. Focus on Evidence It has been known for some time that if light exercise is performed during the recovery period (active recovery), recovery from exercise occurs more rapidly than with total rest (passive recovery).Faster recovery with light exercise is probably the result of neural as well as circulatory influences.