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VO2 and Cardiorespiratory Responses

Oxygen uptake/consumption (VO2) during constant-load exercise reflects aerobic metabolism contributions; VO2 increases rapidly at the onset and plateaus during steady-state exercise.

Resting VO2

Not 0 because the body requires oxygen for basic metabolic functions.

VO2 steady state

VO2 steady state is the plateau in oxygen uptake during prolonged submaximal exercise when energy demands are met aerobically.

O2 deficit

Lag in oxygen uptake at the start of exercise, reflecting initial anaerobic energy contributions.

EPOC

Excess post-exercise oxygen consumption, representing recovery processes like replenishing energy stores and clearing lactate.

Exercise intensity and VO2

Higher exercise intensity increases O2 deficit, elevates steady-state VO2, and prolongs EPOC.

VO2max

Maximum oxygen uptake during intense exercise, representing aerobic capacity; average values are ~40-50 mL/kg/min for men and ~30-40 mL/kg/min for women, with endurance athletes having the highest values due to sport-specific demands.

VO2max equation

Determined by cardiac output (heart rate × stroke volume) and a-vO2 difference.

Stroke volume

Increases with exercise intensity up to ~40-60% of VO2max and is higher after aerobic training.

Heart rate

Heart rate increases linearly with intensity and decreases at rest after aerobic training.

a-vO2 difference

a-vO2 difference, the oxygen extraction by tissues, increases with exercise intensity and is higher after training.

Blood flow distribution

Blood flow shifts from visceral organs to working muscles during exercise due to vasodilation and vasoconstriction controlled by sympathetic activity.

Ventilation

Increases linearly with intensity until the ventilatory threshold, after which it rises disproportionately due to increased CO2 production.

Skeletal muscle fiber types

The three types are slow-twitch (Type I), fast-twitch A (Type IIa), and fast-twitch B (Type IIx), which differ in contraction speed, force, and fatigability due to structural and metabolic properties.

Fiber recruitment and intensity

Muscle fibers are recruited according to the size principle, with smaller slow-twitch fibers recruited first and larger fast-twitch fibers recruited as intensity increases.

Athletic specialization

Endurance athletes typically have a higher percentage of Type I fibers, while power/speed athletes have more Type II fibers.

Carbohydrate intake

Carbohydrate intake during training accelerates muscle glycogen recovery, improves time-to-fatigue, and sustains performance.

Carbohydrate loading

Carbohydrate loading increases muscle glycogen stores and benefits endurance events lasting longer than 90 minutes.

Post-exercise carbohydrates

Consuming carbohydrates immediately after exercise enhances glycogen recovery compared to delayed intake.

Sweating

Sweat rates average 0.5-2.0 L/hour and help regulate body temperature by dissipating heat.

Carbohydrate consumption and performance

Consuming carbohydrates during exercise benefits activities lasting over 60 minutes by maintaining blood glucose and delaying fatigue.

Protein RDA

The RDA for protein is 0.8 g/kg/day for the general population, while active individuals require 1.2-2.0 g/kg/day.

Muscle protein balance

Muscle protein balance depends on synthesis vs. breakdown, which are enhanced by dietary protein and resistance training.

Sprint/strength adaptations

Sprint/strength training increases ATP, CP, glycogen stores, anaerobic enzymes, and muscle fiber size.

Endurance adaptations

Endurance training increases mitochondrial and capillary density, aerobic enzymes, and fat utilization.

Lactate threshold

Endurance training raises the lactate threshold, allowing higher exercise intensity without fatigue.

Resistance training effects

Early strength gains come from neural adaptations, while long-term gains result from muscle hypertrophy.

Fiber type changes

Training can shift fibers from Type IIx to IIa but not from Type I to Type II.

Specificity

Training adaptations are specific to the exercise type, intensity, and muscle groups used.

Overload

Progressive overload is achieved by increasing training intensity, duration, or frequency.

Individualization

Training must be tailored to individual needs, even for athletes at similar levels.

Reversibility

Fitness declines without training, but maintaining some activity reduces losses.

Periodization

Training is structured into cycles to optimize performance at key times.

Overtraining

Excessive stress causing performance declines, mitigated by recovery and monitoring.

ACSM guidelines

For health, adults should engage in 150 minutes of moderate or 75 minutes of vigorous exercise weekly.

Strength training types

Static involves no movement, dynamic uses full ranges of motion, and isokinetic maintains constant speed.

Resistance training goals

Strength requires high weights and low reps; endurance uses low weights and high reps; power involves moderate weights and explosive reps.

Circuit training

Combines strength and endurance exercises in one session.

DOMS

Peaks 24-72 hours post-exercise and lessens with repeated activity.

Aging and performance

VO2max and strength decline with age, influenced by reduced physical activity and muscle loss.

VO2max and aging

VO2max declines ~10% per decade, but regular exercise slows this loss.

Anaerobic capacity and strength with age

Both decrease due to neuromuscular changes, affecting function.

Physical activity and mortality

Physical activity reduces all-cause mortality and disease risks like CVD and cancer.

Exercise and disease risk

Moderate exercise significantly lowers disease risks, with benefits increasing at higher levels.

Inactivity vs. other risks

Physical inactivity rivals smoking and hypertension in its contribution to CVD due to its high prevalence and risk ratio.