Chapter 8 8 Aerobic Fitness: Stamina and Efficiency C H A P T E R

Objectives This chapter will help you do the following: Understand the terms aerobic and anaerobic Determine the meaning of aerobic exercise and aerobic fitness Experience the concept of exercise intensity and the lactate thresholds Differentiate between aerobic and anaerobic effort Understand the factors that influence aerobic fitness Define the effects of aerobic training Understand how systematic exercise (training) stimulates changes in muscle fibers, respiration and oxygen transport, blood volume, the heart and circulation, the endocrine system, fat metabolism and body composition, and bones, ligaments, and tendons Understand the specificity of training and its importance for the design of effective programs

Definitions Aerobic In the presence of oxygen Anaerobic In the absence oxygen

Aerobic Exercise Oxygen used to convert fat and CHO to ATP Low to moderate intensity Higher energy yield Slower energy yield “Fat burn” zone (use caution)

Anaerobic Exercise No oxygen necessary to convert CHO to ATP Moderate to high intensity Immediate, short bursts of exercise Lower energy yield Faster energy yield “Cardio zone” Symptoms Lactate versus hydrogen ions

Fat Involved in energy production Low-intensity and long-duration physical activity –Train muscles to use fat more efficiently –Performance implications ~130 ATP per fat molecule Stored in unlimited quantities in the human body

Carbohydrate Involved in energy production High-intensity and long-duration physical activity Preferred energy source during exercise and physical activity 2 ATP molecules via anaerobic pathways 38 ATP molecules via aerobic pathways Stored in small quantities in the human body

Muscle Fiber Types Slow oxidative Efficiently use oxygen Fast oxidative glycolytic Faster contracting that can work with or without oxygen Fast glycolytic Short, intense contractions that use muscle glycogen

Figure 8.1 Lactate Thresholds

Levels of Exercise Intensity

Aerobic Fitness Maximal oxygen uptake and utilization –VO 2 max or VO 2 peak Collect all expired gases Increase intensity –Graded exercise test (GXT) Continue to volitional exhaustion Marker of fitness –Use some caution here; genetics, age, training –Newer, more appropriate measures of fitness

Absolute Versus Relative Fitness Absolute = L/min –Larger people tend to have higher numbers. –Can be used to assess performance in non-weight- bearing activities. Relative = ml/kg/min –Relative to body weight to eliminate influence of body size. –Can be used to assess performance in weight- bearing activities.

Factors Influencing Aerobic Fitness: Heredity Heredity –47 percent of variability in VO 2 peak –At least 50 percent of variability in maximal power –Maternal DNA –Mitochondrial DNA = 60 percent of inherited component –LT1 very trainable—80 percent variance (continued)

Factors Influencing Aerobic Fitness: Heredity (continued) Respiratory Cardiovascular Heart size RBC and Hb Percent of SO and FOG fibers Mitochondria ALL MOM! (continued)

Factors Influencing Aerobic Fitness: Heredity (continued) Ability of muscle to be trained –Improvements in fitness 5 percent in some, others 30 percent Physique Body composition

Factors Influencing Aerobic Fitness: Training Improvements in VO 2 peak –Most people can improve 20 to 25 percent. –If you start training harder right now, 20 to 25 percent gain. Improved function –Respiratory, cardiovascular, blood volume, and changes in fiber type (continued)

Factors Influencing Aerobic Fitness: Training (continued) Increased fat utilization –More mitochondria, more enzymes –Reduced fat storage –Reduced fat in blood –Insulin more efficient –Reduced risk of cancer Long duration = improved LT1 High density = improved LT2

Factors Influencing Aerobic Fitness: Sex No difference before puberty Males have 10 to 20 percent higher aerobic fitness ~10 percent reduced performance –Why? Hemoglobin Muscle mass Body fat

Factors Influencing Aerobic Fitness: Age ~10 percent decline in sedentary people regardless of starting point ~5 percent decline in active people ~2 percent decline in highly fit people Start at any age for improvement

Factors Influencing Aerobic Fitness: Body Fat Calculated by body weight –4 L/min for a 100 kg person = 40 ml/kg/min –4 L/min for a 90 kg person = 44.4 ml/kg/min With training at 20 percent improvement –53 ml/kg/min

Factors Influencing Aerobic Fitness: Activity Years of training can be lost in 12 weeks Three weeks bed rest = ~30 percent decline Good news: You’ll gain it back!

Relative Fitness Aerobic fitness is doing the best with what you have. Relative fitness is the percent of maximal aerobic capacity you can maintain. More fit people can sustain a higher percentage of max. You can define this by comparing LT1 or LT2 to maximal aerobic capacity. The closer either of these values are to max, the more effective your training has been.

Terms Cardiovascular Cardiorespiratory Aerobic fitness Aerobic fitness is the most appropriate term in explaining the adaptations are occurring. The target of aerobic training is muscle!

Training Effect on Muscle Training increases the concentration of aerobic enzymes needed for the metabolic breakdown of carbohydrate and fat to produce energy in the form of ATP. Training increases the size and number (volume) of mitochondria, which produce energy aerobically (with oxygen). Training increases the ability of the muscle to use fat as a source of energy. (continued)

Training increases the size of the fibers used. Long, slow training improves the oxidative capabilities of slow oxidative fibers. High-intensity training enhances the capabilities of fast oxidative glycolytic fibers. Training increases the storage of muscle glycogen. Training Effect on Muscle (continued) (continued)

Training Effect on Muscle (continued) Training increases the supply of intramuscular fat. Training increases the myoglobin (a compound that carries oxygen from the cell membrane to the mitochondria) in muscle fibers. Training increases the number of capillaries serving muscle fibers.

Respiratory Improvements No increase in lung size. Efficiency of breathing muscles improves. Reduces residual lung volume. Chronic lifetime physical activity reduces the increase in residual lung volume with aging. Improved tidal volume (deeper breathing). In general: The respiratory system is overbuilt and is not a limiting factor for aerobic fitness or performance.

Blood Volume Blood volume may increase 5 to 10 percent. –Normal blood volume is about 5 L. –May increase to 5.5 or even 5.75 L. Hemoglobin concentration initially decreases slightly, but then will increase from about 45 to 50 percent to up to 56+ percent. These changes may account for up to 47 percent of the improvements in VO 2 max.

Heart and Circulation Long-term aerobic training increases the volume of the left ventricle (left ventricle hypertrophy). –The heart muscle (myocardium) increases strength to maintain pressure in the enlarged (fit) heart. –This results in an increased stroke volume and a decreased HR at rest. Heart muscle becomes trained (increases in aerobic enzymes, fat oxidation, vascularity, and mitochondria). Better distribution of blood. Muscle capillary density increases.

Nervous System Efficiency of movement Improved economy Improved motor control in CNS Improved learning both during physical activity, after physical activity, and in more physically fit individuals

Endocrine System The system of glands whose secretions—hormones—are distributed by circulation. Hormonal responses to training: Adjustments in hormonal response Increased sensitivity to certain hormones Important metabolic adjustments: –Catecholamines –Cortisol –Thyroxin –Insulin and glucagon –Non-insulin glucose uptake

Fat Metabolism Aerobically trained muscles derive a higher percentage of energy via fat metabolism at all intensities of exercise from rest to high intensity. This conserves carbohydrate stores. Trained individuals mobilize fat better.

Other Effects of Training Reductions in stored adipose tissue –Increased fat burning during all hours –Increased metabolic rate even when not exercising This is more true with higher intensity aerobic training. Stronger bones, ligaments, and tendons

Specificity of Training The muscles used during any activity will adapt to that specific stimulus. Other types of training may be necessary to avoid boredom, injury, or muscle imbalances. Concentrate training on the movements, muscle fibers, metabolic pathways, supply, and support systems you intend to use in an activity.

Summary Aerobic fitness is the ability to take in, transport, and use oxygen in the body. LT1 is a good indicator of performance during long-duration races. LT2 is a good indicator of performance during events lasting less than 30 minutes. Heredity, training, age, sex, and body fat all influence training adaptations. Many systems in the body are affected by aerobic training, but skeletal muscle is the primary target. Choose an activity you enjoy or want to improve for specific adaptations.