Exercise and Metabolism How fit are you?

Rest to Exercise What changes must take place in skeletal muscle at the beginning of exercise to provide the necessary energy to continue movement? Increase demand for: –O2–O2 –ATP

During Exercise ATP consumption increases up to 25 times than at rest ATP needed for muscle contractions –ATP-PC system –Glycolysis –Aerobic pathway

O 2 Deficit The lag in O 2 uptake at the beginning of exercise. This means initial ATP production must be anaerobic

The Oxygen Deficit

Trained vs. Untrained Subjects O 2 Deficit Trained athletes have lower oxygen deficit. –aerobic ATP production begins sooner Due to: –Better-developed aerobic capacity –Cardiovascular or muscular adaptations –Results in less production of lactic acid »Lactic Acid = fatigue

Trained vs. Untrained

In Summary  In the transition from rest to light or moderate exercise, oxygen uptake increases rapidly, generally reaching a steady state within one to four minutes.  The term oxygen deficit applies to the lag in oxygen uptake in the beginning of exercise.  The failure of oxygen uptake to increase instantly at the beginning of exercise suggests that anaerobic pathways contribute to the overall production on ATP early in exercise. After a steady state is reached, the body’s ATP requirement is met via aerobic metabolism.

Recovery from Exercise Oxygen uptake remains elevated after exercise and into recovery Metabolism remains elevated –Increased body temp

O 2 Debt Definition: the excess oxygen consumption, above rest, following exercise AV Hill –“to repay the oxygen deficit that occurs at exercise onset”

O 2 Debt

Divided into 2 portions: Rapid Portion –2-3 minutes post exercise Slow Portion –Greater than 30 minutes post exercise

Rapid Portion of O 2 Debt First 20% Steep decline in O 2 uptake following exercise Due to: –Resynthesis of creatine phosphate in muscle –Replenishment of muscle and blood O 2 stores

Slow Portion 80% Slow decline in O 2 consumption after exercise Due to: –Elevated heart rate and breathing  energy need –Elevated body temperature  metabolic rate –Need to supply O 2 to respiratory muscles for breathing

Excess Post Exercise O 2 Consumption EPOC / O 2 Debt Many scientists use these terms interchangeably EPOC is greater following higher intensity exercise

Oxygen Deficit and EPOC Light vs. Heavy Exercise

Factors Contributing to EPOC

O 2 Consumption During Exercise Maximal oxygen consumption = VO 2 max The maximal capacity to transport and use oxygen during exercise. Considered by many exercise scientists to be the most valid measurement of cardiovascular fitness.

Factors Influencing VO 2 Max: 1.Ability of cardiorespiratory system to deliver oxygen to the muscle 2.Muscle’s ability produce ATP aerobically 3.Genetics 4.Exercise training 5.Cardiovascular Disease 6.Age –VO 2 max decreases with age

VO 2 and Exercise Intensity Low intensity –Fast walking –30% VO 2 max Moderate intensity –Jogging –50 – 80% High intensity –Sprinting –85 – 150%

Examples of VO 2 max Healthy person –20ml/kg/min Olympic Athlete –>80ml/kg/min Heart Failure/ Transplant –<14ml/kg/min

Lactate Threshold The point during exercise at which lactic acid starts to accumulate in the blood Lactic Acid is produced faster than it can be removed Reflects the intensity of exercise »Lactic Acid = fatigue

Training and Lactate Threshold LT can be increased with training. –Trained athletes have a higher LT Interval training takes advantage of the body being able to recover from LT. –LA produced by the muscles is removed without it building up. –Reduces fatigue

Training and Lactate Threshold A useful tool in training for racing and endurance sports Long distance activity: work just below lactate threshold –long distance running –cycling, rowing –swimming –cross country skiing

Fuel Sources During Exercise Carbohydrates –Blood sugar –Glycogen Fats –FFA –Triglycerides How do you know what fuel you are using?

Respiratory Exchange Ratio RER Used to estimate fuel use during exercise –Carbohydrate vs. Fat –Done non invasively –Metabolic Analysis Carbs and Fat utilize different amounts of O 2 and produce different amounts of CO 2. Measure respiratory gasses during exercise.

C 16 H 32 O O 2  16 CO H 2 O VCO 2 VO 2 = R = 16 CO 2 23 O 2 = 0.70 VCO 2 VO 2 R = RER for Fats = 0.70

VCO 2 VO 2 = R = 6 CO 2 6 O 2 = 1.00 C 6 H 12 O O 2  6 CO H 2 O RER for Carbs = 1.00

Respiratory Exchange Ratio CO 2 / O 2 Fat oxidation requires more oxygen than carbohydrate Carbohydrates contain more oxygen than fat

R Value High R –More carbohydrates Low R –More fat

R value of –50% comes from fat –50% comes from carbohydrate

Estimation of Fuel Utilization During Exercise

Fuel Sources The source that is used is determined by exercise intensity Intense exercise utilizes carbs Low intensity exercise utilizes fats

Rate of Fat Metabolism at Different Exercise Intensities

“Crossover” Concept

Is Low-Intensity Exercise Best for Burning Fat? At low exercise intensities (~20% VO 2 max) –Fuel source is about 60% from fat –However, total energy expended is low Total fat usage is also low

Is Low-Intensity Exercise Best for Burning Fat? At higher exercise intensities (~50% VO 2 max) –Lower contribution of fat as fuel source (about 40%) from fat –Total energy expended is higher Total fat usage is also higher

“Fats burn in the flame of carbohydrates” Carbs are needed to introduce fats into the cell. Glycogen stores can be depleted during exercise. Is Low-Intensity Exercise Best for Burning Fat?

Prolonged Exercise (over 2 hrs) May deplete muscle glycogen stores No products to send through the Krebs Cycle No production of ATP Result: fatigue

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Discussion Questions How can elite marathoners run 26.2 miles at a pace of 5 minutes per mile, yet very few can run just 1 mile in 4 minutes? Is it important for weight lifters and sprinters to have a high capacity to consume oxygen? From an exercise perspective, what are some advantages of having different sources of potential energy for synthesizing ATP

Influence of Exercise Intensity on Muscle Fuel Source

quiz 1.At rest ATP is produced by ….aerobic 2.Tf factors contributing to o2 debt include resynthesis or creatine phosphate and body temp. t 3.The upward drift in o2 uptake during exercise is due to ….increasing body temperature 4.Tf maximal o2 uptake provides and overall assesment of exercise capability and is reduced in patients with cardio pulmonary disease. T

Crossover happens because… 1.Fast muscle fibers prefer glycolysis 2.Increasing levels of epinephrine The rise in epinephrine increases muscle glycogen breakdown Increased lactate production inhibits fat metabolism

Factors Governing Fuel Selection Sources of Carbohydrate During Exercise Blood glucose –From liver (glycogen to glucose) –Primary source during low-intensity exercise –Important during long-duration exercise As muscle glycogen levels decline Muscle glycogen –Primary source during high-intensity exercise –Supplies much of the carbohydrate in the first hour of exercise

Factors Governing Fuel Selection Sources of Fat During Exercise Muscle stores of Triglycerides –Primary source of fat during higher intensity exercise Plasma FFA –From adipose tissue –Enters Krebs cycle –Source of fat during low-intensity exercise –Becomes more important as muscle triglyceride levels decline in long-duration exercise

Work rate can still increase, even though there is no increase in O 2 consumption

Calculate VO 2 max VO 2 max = cardiac output X arterial/venus oxygen difference at peak exercise Cardiac output- the amount blood pumped by the heart Arterio venus oxygen difference – the difference in oxygen between the arteries and veins.

Lactate Threshold & Stats Blood samples taken during exercise Untrained person achieves threshold at % VO 2 max Trained person –Threshold at 65-80%VO 2 max Elite athletes –80-90 % of VO 2 max

In Summary  Oxygen uptake increases in a linear fashion during incremental exercise until VO 2 max is reached.  The point at which blood lactic acid rises systematically during graded exercise is termed the lactate threshold or anaerobic threshold.  The lactate threshold has practical uses such as in performance prediction and as a marker of training intensity.

Factors Governing Fuel Selection Shift From Carbohydrate to Fat Metabolism During Prolonged Exercise Figure 4.13