APK3110_Ch13_Training+Adaptations_Aerobic_Anaerobic_ (Fall 2025) PDF

PHYSIOLOGY OF TRAINING: EFFECTS OF AEROBIC AND ANAEROBIC TRAINING Chapter 13  Lecture Outline Principles of training. Endurance training and VO2 max. Why does exercise training improve VO2 max? Endurance training: effects on performance and homeostasis. Endurance trainin...

PHYSIOLOGY OF TRAINING: EFFECTS OF AEROBIC AND ANAEROBIC TRAINING Chapter 13  Lecture Outline Principles of training. Endurance training and VO2 max. Why does exercise training improve VO2 max? Endurance training: effects on performance and homeostasis. Endurance training: links between muscle and systemic physiology. Detraining following endurance training. Muscle adaptations to anaerobic exercise training.  Principles of Training Overload For a training effect to occur, a system or tissue must be challenged with an intensity, duration, or frequency of exercise to which it is unaccustomed. Over time, the tissue or system adapts to this increased load. Specificity Training effect is specific to: Muscle fibers recruited during exercise Energy system involved (aerobic vs. anaerobic) Velocity of contraction Type of contraction (eccentric, concentric, isometric) Reversibility Gains are lost when overload is removed Endurance Training and VO2 Max Maximal oxygen uptake (VO2 max): also called maximal aerobic power Maximal capacity of the body to transport and use oxygen during dynamic exercise using large muscle groups (i.e., legs). Training to increase VO2 max Large muscle groups, dynamic activity 20–60 min, ≥3 times/week, ≥50% VO2 max Expected increases in VO2 max after 2-3 months of endurance training Average = 15-20% As low as 2–3% increase in those with high initial VO2 max Requires higher training intensity (>70% VO2 max) As high as 50% increase in those with low initial VO2 max Requires relatively low training intensity (40–50% VO2 max) Impact of Genetics on VO2 Max and Exercise Training Response (A Closer Look 13.1) Heritability (genetics) Determines approximately 50% of VO2 max in sedentary adults. Genetics also plays key role in determining the training response. Average improvement in VO2 max is 15 to 20%. Low responders improve VO2 max by 2 to 3%. High responders can improve VO2 max by approximately 50% with rigorous training. Large variations in training adaptations reveal that heritability of training adaptations is approximately 47%. Range of VO2 Max Values in the Population Why Does Training Improve VO2 Max? VO2 max is defined by the Fick equation: VO2 max = maximal cardiac output × a-vO2 difference. Differences in VO2 max between individuals. Primarily due to differences in SV max. Exercise-induced improvements in VO2 max. Short duration training (~4 months); Increase in stroke volume is dominant factor in increasing VO2 max. Longer duration training (~32 months); Both stroke volume and a-vO2 increase to improve VO2 max. Factors Influencing Stroke Volume with Training SV = EDV - ESV Increased maximal stroke volume  Preload (EDV)  Plasma volume  Venous return  Ventricular volume  Afterload (total peripheral resistance)  sympathetic vasoconstriction  maximal muscle blood flow  Contractility Changes occur rapidly 6-day training program (2hr/day at 65% of VO2max) resulted in 7% ↑ in VO2max due to: 11% ↑ in plasma volume 10% ↑ in stroke volume  Arteriovenous O2 Difference a-vO2 max ↑ in a-vO2 difference in response to endurance training due to increased O2 extraction from the blood Improved ability of the muscle to extract oxygen from the blood due to  Capillary density Slows rate of blood flow to allow time for O2 diffusion to take place ↓ diffusion distance to the mitochondria  Mitochondrial number Factors Causing Increased VO2 Max Check your understanding The ______________ principle reveals that for a training effect to occur, a system or tissue must be challenged with an intensity, duration, or frequency of exercise to which it is unaccustomed. Over time, the tissue or system adapts to this increased load. The ________________ principle refers to the fact that fitness gains are lost when training is stopped. The principle of ________________ relates to the fact that the training effect is limited to the muscle fibers involved in the activity. In addition, the muscle fiber adaptation is driven by the type of activity. Check your understanding ▪ In healthy, sedentary subjects, the training-induced improvements in V̇O2 max that occur following short-term training (i.e., ~4 months) are due to increases in ____________________________. ▪ However, the training-induced improvements in V̇O2 max that occur following long duration training (i.e., ~32 months) are the result of both increases in ___________________________(but not heart rate) and an increase in the ___________________________________. ▪ The training-induced increase in maximal stroke volume is due to both an increase in ____________ and a decrease in ____________. Check your understanding ▪ The increased preload is primarily due to an increase in _____________________________ and an increase in plasma ____________. ▪ The decreased afterload is due to a ____________ in the arteriolar constriction in the trained muscles, _______________ maximal muscle blood flow with no change in the mean arterial blood pressure. ▪ The training–induced increase in the a-v̄ O2 difference is due to an increase in the ____________ of the trained muscles, which is needed to accept the increase in maximal muscle blood flow. ▪ The greater capillary density allows for a slow red blood cell transit time through the muscle, providing enough time for _________ diffusion from the capillary into the muscle fiber. Endurance training: effects on performance and homeostasis The ability to continue prolonged, submaximal work is dependent on the maintenance of homeostasis during the activity Maintenance of homeostasis in response to endurance training is reached by: More rapid transition from rest to steady-state Reduced reliance on liver and muscle glycogen stores Cardiovascular and thermoregulatory adaptations Many of these adaptations are due to structural and biochemical changes in skeletal muscle Some of the initial metabolic adaptations are due to neural/hormonal changes  Endurance Training-Induced Changes in Fiber Type and Capillarity ▪ Fast-to-slow shift in muscle fiber type ↓ in fast myosin and ↑ in slow myosin This means can perform more work with less ATP use (i.e., ↑ mechanical efficiency which can improve endurance performance) Extent of change determined by exercise intensity and duration and years of endurance training Extremely high aerobic capacity in elite athletes is likely due to genetics ▪ Increased number of capillaries Enhanced diffusion of oxygen and substrate delivery to muscle fibers Increased removal of metabolic waste  Endurance Training Increases Mitochondrial Content in Skeletal Muscle Fibers Endurance training ↑ mitochondrial volume in muscle fibers. Results in improved oxidative capacity and ability to utilize fat as fuel. Training also increases mitochondrial turnover (that is, breakdown of damaged mitochondria and replacement with healthy mitochondria). Muscle mitochondrial volume can increase quickly (within first 5 days of training) Can ↑ 50–100% within first 6 weeks Depends on intensity and duration of training  Endurance Training Reduces the O2 Deficit Energy requirement can be met by oxidative ATP production at the onset of exercise Faster rise in VO2 curve, and steady state is reached earlier Oxygen deficit is lower following training ▪Results in: Less lactate and H+ formation Less PC depletion Less disruption in homeostasis  Biochemical Adaptations and the Plasma Glucose Concentration Plasma glucose is the primary fuel of the nervous system. Endurance training helps maintain blood glucose during prolonged submaximal exercise by ↑ fat utilization and sparing of plasma glucose and muscle glycogen  Endurance training increases fat metabolism during exercise ↑ Transport of FFA into the muscle ↑ capillary density ↑ fatty acid binding protein and fatty acid translocase ↑ Transport of FFA from the cytoplasm to the mitochondria ↑ mitochondrial number/size →↑mitochondria membrane surface area ↑ fat transporting enzymes carnitine palmitoyltransferase I and fatty acid translocase ↑ Mitochondrial oxidation of FFA ↑ enzymes of -oxidation ↑ rate of acetyl-CoA formation High citrate level inhibits PFK and glycolysis Endurance Training Improves Muscle Antioxidant Capacity ▪ Free radicals are chemical molecules that contain an unpaired electron in their outer orbital which makes them highly reactive ▪ Can damage proteins, membranes and DNA ▪ Free radicals are produced by contracting muscles ▪ Can disturb cellular homeostasis, damage muscle contractile proteins and contribute to muscle fatigue during prolonged endurance events. ▪ Cells contain molecules that neutralize free radicals (i.e., antioxidants) ▪ Endogenous and exogenous (from diet) ▪ Training increases endogenous antioxidants Protects against oxidative damage and fatigue Exercise Training Improves Acid-base Balance During Exercise Less PFK = less glycolysis Less glycolysis = less pyruvate Less pyruvate = less lactate The “H” form of LDH has less affinity for pyruvate Enhanced shuttling of H+ to the ETC LDH pyruvate + NADH lactate + NAD  Check your understanding Endurance training improves the ability of muscle fibers to maintain ___________ during prolonged exercise. Regular bouts of endurance training result in a ___________________ in muscle fiber types and ↑ the number of _________ surrounding the trained muscle fibers. Endurance exercise also ↑ _______________ volume in the exercised muscles. The combination of the ↑ in the density of capillaries and mitochondrial volume in the muscle fiber ↑ the capacity to transport ____________________________ from the plasma → cytoplasm → mitochondria. The ↑ in the enzymes of beta oxidation ↑ the rate of formation of ____________ from FFA for oxidation in the Krebs cycle. This ↑ in fat oxidation in endurance- trained muscle spares liver and muscle ____________ and plasma __________. Check your understanding Endurance training increases endogenous _________________ in trained muscles, and these changes protect muscle fibers against _________________ mediated damage and fatigue during prolonged endurance exercise. Endurance training results in less disruption of the blood pH during submaximal work because endurance-trained muscles produce less _____________ and _____________.  Links Between Muscle and Systemic Physiology Muscle biochemical adaptations to training influence the systemic response to exercise: Sympathetic nervous system ( E/NE) Cardiorespiratory system ( HR,  ventilation) Due to: Reduction in “feedback” from muscle chemoreceptors Receptors increase their firing rate in proportion to changes in metabolites produced (i.e., metabolic rate). Reduced number of motor units recruited reduced “feedforward” input from higher brain centers (central command) with endurance training, biochemical/structural adaptations in skeletal muscles make them more efficient, needing less muscle to do same amount of work. Demonstrated in one-leg training studies that there is lack of transfer of training effect to untrained leg Check your understanding The _______________ changes in muscle due to endurance training influence the heart rate and ventilatory responses to exercise. The reduction in “feedback” from ________________ in the trained muscle and a decreased need to recruit ________________to accomplish an exercise task result in reduced sympathetic nervous system, heart rate, and ventilation responses to submaximal exercise. Endurance exercise training also reduces ___________________ during submaximal exercise that results in a lower heart rate and ventilatory response during exercise.  Detraining and VO2 Max ▪ Rapid decrease in VO2 max  ~8% within 12 days;  20% after 84 days ▪ Initial decrease (12 days) due to  SV max ▪  SV max Rapid loss of plasma volume ▪ Later decrease due to  a-v O2 max ▪  Maximal a-v O2 difference  Mitochondria but capillary density unchanged  Oxidative capacity of muscle ▪ Slow to fast fiber type shift:  Type IIa fibers and  type IIx fibers  Time Course of Training/Detraining Mitochondrial Changes Training Mitochondria double with 5 weeks of training Detraining About 50% of the ↑ in mitochondrial content lost after 1 week of detraining Majority of adaptations lost within 2 weeks of detraining It took 3 to 4 weeks of retraining to regain the adaptations lost in the first week of detraining Check your understanding After exercise ________________, V̇O2 max begins to decline quickly and can decrease by ~8% within 12 days after cessation of training, and declines by almost 20% following 84 days of detraining. The decrease in V̇O2 max with cessation of training is due to a decrease in both _______________________ and _______________________, the reverse of what happens with training. Exercise performance during submaximal exercise tasks also declines rapidly in response to detraining, due primarily to a decrease in the ___________________ in muscle fibers.  Muscle Adaptations to Anaerobic Exercise Training Anaerobic exercise Refers to short-duration (i.e., 10-30 seconds) all-out effort which is also referred to as “sprint training” Recruits both type I and II muscle fibers to perform the exercise During exercise lasting 10 seconds or less, the energy is primarily supplied by ATP-PC system During exercise lasting 20-30 seconds, 80% of energy needed is provided anaerobically whereas remaining 20% is provided aerobically Anaerobic training increases performance 4-10 weeks of sprint training can increase peak anaerobic power by 3- 25% across individuals  Muscle Adaptations to Anaerobic Exercise Training Anaerobic training increases performance Sprint training improves muscle buffering capacity by increasing intracellular buffers and hydrogen ion transporters Sprint training also results in hypertrophy of type II muscle fibers and elevates enzymes involved in the ATP-PC system and glycolysis Check your understanding Muscle adaptations that occur in response to sprint training vary depending upon the ___________ of exercise. Short-duration (10–30 seconds) sprint exercise training results in increased _____________________, increases in the _____________________, and an improved ability to generate ________ via anaerobic energy systems.