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Acute Responses vs Chronic Adaptations Acute responses to training involve how the body responds to one bout of exercise. Chronic physiological adaptations to training mark how the body responds over time to the stress of repeated exercise bouts.
Key Points Acute Responses to Exercise w Control environmental factors such as temperature, humidity, light, and noise. w Account for diurnal cycles, menstrual cycles, and sleep patterns. w Use ergometers to measure physical work in standardized conditions. w Match the mode of testing to the type of activity the subject usually performs.
Basic Training Principles Individuality—Consider the specific needs and abilities of the individual. Specificity—Stress the physiological systems critical for the specific sport. Disuse—Include a program to maintain fitness. Progressive overload—Increase the training stimulus as the body adapts. Hard/easy—Alternate high-intensity with low-intensity workouts. Periodization—Cycle specificity, intensity, and volume of training.
Measuring Muscular Performance Strength—the maximal force a muscle or muscle group can generate. Power—the product of strength and the speed of movement. Muscular endurance—the capacity to sustain repeated muscle actions.
Muscular Endurance w Can be evaluated by noting the number of repetitions you can perform at a given percentage of your 1-RM w Is increased through gains in muscular strength w Is increased through changes in local metabolic and circulatory function
Key Points Terminology w Muscular strength is the maximal amount of force a muscle or group of muscles can generate. w Muscular power is the product of strength and speed of the movement. w Though two individuals can lift the same amount of weight, if one can lift it faster, she is generating more power than the other. w Muscular endurance is the ability of a muscle to sustain repeated muscle actions or a single static action.
Did You Know…? Resistance training programs can produce a 25% to 100% improvement in strength within 3 to 6 months.
Results of Resistance Training w Increased muscle size (hypertrophy). w Alterations of neural control of trained muscle. w Studies show strength gains can be achieved without changes in muscle size, but not without neural adaptations.
Possible Neural Factors of Strength Gains w Recruitment of additional motor units for greater force production w Counteraction of autogenic inhibition allowing greater force production w Reduction of coactivation of agonist and antagonist muscles w Changes in the discharge rates of motor units w Changes in the neuromuscular junction
Muscle Hypertrophy Transient—pumping up of muscle during a single exercise bout due to fluid accumulation from the blood plasma into the interstitial spaces of the muscle. Chronic—increase of muscle size after long-term resistance training due to changes in muscle fiber number (fiber hyperplasia) or muscle fiber size (fiber hypertrophy).
Fiber Hypertrophy w The numbers of myofibrils and actin and myosin filaments increase, resulting in more cross-bridges. w Muscle protein synthesis increases during the postexercise period. w Testosterone plays a role in promoting muscle growth. w Training at higher intensities appears to cause greater fiber hypertrophy than training at lower intensities.
Fiber Hyperplasia w Muscle fibers split in half with intense weight training. w Each half then increases to the size of the parent fiber. w Satellite cells may also be involved in skeletal muscle fiber generation. w It has been clearly shown to occur in animal models; only a few studies show this occurs in humans too.
Neural Activation and Fiber Hypertrophy w Early gains in strength appear to be more influenced by neural factors. w Long-term strength increases are largely the result of muscle fiber hypertrophy.
w Chronic muscle hypertrophy results from long-term training and is caused by structural changes in the muscle. (continued) Key Points Resistance Training w Neural adaptations always accompany strength gains from resistance training; hypertrophy may or may not be present. w Transient hypertrophy results from short-term increases in muscle size due to fluid in the muscle.
Key Points Resistance Training w Muscle hypertrophy is most clearly due to increases in fiber size, but also may be due to increases in the number of fibers. w Muscle atrophy occurs when muscles are inactive; however, a planned reduction in training can maintain muscle size and strength for a period of time. w A muscle fiber type can take on characteristics of the opposite type in response to training. Cross-innervation or chronic stimulation of fibers may convert one fiber type into another fiber type.
Aerobic vs Anaerobic Training Aerobic (endurance) training leads to w Improved blood flow, and w Increased capacity of muscle fibers to generate ATP. Anaerobic training leads to w Increased muscular strength, and w Increased tolerance for acid-base imbalances during highly intense effort.
. w Improved submaximal aerobic endurance and VO2max Adaptations to Aerobic Training w Muscular changes in fiber size, blood and oxygen supply, and efficiency of functioning w Improved efficiency of energy production w The magnitude of these changes depend on genetic factors
w Increased number of capillaries supplying the muscles which likely is an important factor that allows increase in VO2max . Muscular Adaptations w Increased cross-sectional area of ST fibers w Small transition of FTb to FTa fibers, but there can also be a small transition of FT to ST fibers w Increased myoglobin content of muscle by 75% to 80% (allowing muscle to store more oxygen) w Increased number, size, and oxidative enzyme activity of mitochondria
CAPILLARIZATION IN MUSCLES Untrained Trained
Adaptations Affecting Energy Sources w Trained muscles store more glycogen and triglycerides than untrained muscles. w FFAs are better mobilized and more accessible to trained muscles. w Muscles’ ability to oxidize fat increases with training. w Muscles’ increased reliance on fat stores conserves glycogen during prolonged exercise.
. . QO2 vs VO2max . QO2 measures the maximal respiratory or oxidative capacity of muscle. . VO2max measures the body's maximal oxygen uptake.
. . QO2 AND VO2MAX WITH TRAINING
w Myoglobin (which stores oxygen) content increases in muscle by about 75% to 80% with aerobic training. (continued) Key Points Adaptations to Aerobic Training w Aerobic training stresses ST fibers more than FT fibers and causes ST fibers to increase in size. w Prolonged aerobic training may cause FTb fibers to take on characteristics of FTa fibers, and in some cases a small percentage of ST fibers become FT fibers. w The number of capillaries supplying each muscle fiber increases with training.
Key Points Adaptations to Aerobic Training w Aerobic training increases the number and size of mitochondria and the activities of oxidative enzymes. w Endurance-trained muscle stores more glycogen and triglyceride than untrained muscle. w Increased fat availability and capacity to oxidize fat lead to increased use of fat as an energy source, sparing glycogen.
Volume w Frequency of exercise bouts w Duration of each exercise bout Intensity w Interval training w Continuous training Aerobic Training Considerations
w Athletes who train with progressively greater volumes eventually reach a maximal level of improvement beyond which additional training volume will not improve endurance or VO2max. . Training Volume w Volume is the load of training in each training session and over a given period of time. w Adaptations to given volumes vary from individual to individual. w An ideal aerobic training volume appears to be equivalent to an energy expenditure of about 5,000 to 6,000 kcal per week.
. TRAINING VOLUME AND VO2MAX
Training Intensity w Muscular adaptations are specific to the speed as well as duration of training. w Athletes who incorporate high-intensity speed training show more performance improvements than athletes who perform only long, slow, low-intensity training. w Aerobic intervals are repeated, fast-paced, brief exercise bouts followed by short rests. w Continuous training involves one continuous, high-intensity exercise bout.
Key Points Training the Aerobic System w Ideal aerobic training volume is equivalent to a caloric expenditure of 5,000 to 6,000 kcal per week. w To perform at higher intensities, athletes must train at higher intensities. w Aerobic interval training—repeated bouts of short, high-intensity performance followed by short rest periods—and continuous training—one prolonged, high-intensity bout—both generate aerobic benefits.
Selected Muscle Enzyme Activities (mmol g min ) for Untrained, Anaerobically Trained, and Aerobically Trained Men . . -1 -1 Anaerobically Aerobically Untrained trained trained Aerobic enzymesOxidative systemSuccinate dehydrogenase 8.1 8.0 20.8Malate dehydrogenase 45.5 46.0 65.5Carnitine palmityl transferase 1.5 1.5 2.3 Anaerobic enzymesATP-PCr systemCreatine kinase 609.0 702.0 589.0Myokinase 309.0 350.0 297.0Glycolytic systemPhosphorylase 5.3 5.8 3.7Phosphofructokinase 19.9 29.2 18.9Lactate dehydrogenase 766.0 811.0 621.0 a a a a a a a a Denotes a significant difference from the untrained value.
Major Cardiovascular Functions w Delivery (e.g., oxygen and nutrients) w Removal (e.g., carbon dioxide and waste products) w Transportation (e.g., hormones) w Maintenance (e.g., body temperature, pH) w Prevention (e.g., infection—immune function)
Myocardium—Cardiac Muscle w Thickness varies directly with stress placed on chamber walls. w Left ventricle is the most powerful of chambers and thus, the largest. w With vigorous exercise, the left ventricle size increases. w Due to intercalated disks—impulses travel quickly in cardiac muscle allowing rapid contraction.
Extrinsic Control of the Heart w Parasympathetic nervous system acts through the vagus nerve to decrease heart rate and force of contraction (predominates at rest—vagal tone). w Sympathetic nervous system is stimulated by stress to increase heart rate and force of contraction. w Epinephrine and norepinephrine—released due to sympathetic stimulation—increase heart rate.
Did You Know…? Resting heart rates in adults tend to be between 60 and 85 beats/min. However, extended endurance training can lower resting heart rate to 35 beats/min or less. This lower heart rate is thought to be due to decreased intrinsic heart rate and increased parasympathetic stimulation.
Did You Know…? The decrease in resting heart rate that occurs as an adaptation to endurance training is different from pathological bradycardia, an abnormal disturbance in the resting heart rate.
w Cardiac tissue has its own conduction system through which it initiates its own pulse without neural or hormonal control. (continued) Key Points Structure and Function of the Cardiovascular System w The two atria receive blood into the heart; the two ventricles send blood from the heart to the rest of the body. w The left ventricle has a thicker myocardium due to hypertrophy resulting from the resistance against which it must contract.
Key Points Structure and Function of the Cardiovascular System w The pacemaker of the heart is the SA node; it establishes heart rate and coordinates conduction. w The autonomic nervous system or the endocrine system can alter heart rate and contraction strength. w An ECG records the heart's electrical function and can be used to detect cardiac disorders.
Stroke Volume (SV) w Volume of blood pumped per contraction w End-diastolic volume (EDV)—volume of blood in ventricle before contraction w End-systolic volume (ESV)—volume of blood in ventricle after contraction w SV = EDV – ESV . Cardiac Output (Q) w Total volume of blood pumped by the ventricle per minute . w Q = HR ´ SV Stroke Volume and Cardiac Output
Ejection Fraction (EF) w Proportion of blood pumped out of the left ventricle each beat w EF = SV/EDV w Averages 60% at rest
Vascular System w Arteries w Arterioles w Capillaries w Venules w Veins
Blood Distribution w Matched to overall metabolic demands w Autoregulation—arterioles within organs or tissues dilate or constrict in response to the local chemical environment w Extrinsic neural control—sympathetic nerves within walls of vessels are stimulated causing vessels to constrict w Determined by the balance between mean arterial pressure and total peripheral resistance
Blood Pressure w Systolic blood pressure (SBP) is the highest pressure and diastolic blood pressure (DBP) is the lowest pressure w Mean arterial pressure (MAP)—average pressure exerted by the blood as it travels through arteries w MAP = DBP + [0.333 ´ (SBP – DBP)] w Blood vessel constriction increases blood pressure; dilation reduces blood pressure