Dr. Andreacci 05.575 FL 2011 EXCESS POST‐EXERCISE OXYGEN CONSUMPTION (EPOC) REFERENCES: Exercise Physiology: Energy, Nutrition, and Human Performance (5th ed.). W. McArdle, F. Katch, and V. Katch. Lippincott Williams & Wilkins: Philadelphia, PA. 2001, and Exercise Physiology: Human Bioenergetics and Its Applications (3nd ed.). G. Brooks, T. Fahey, T. White, and K. Baldwin. Mayfield: Mountain View, CA. 2000. INTRODUCTION: Submaximal exercise is performed at an intensity (i.e. workload) below the subject’s maximal oxygen consumption (VO2max). While the intensity of submax exercise may vary greatly between individuals, it may be further defined as a workload where aerobic metabolism provides almost all energy required for muscle contraction. Oxygen consumption (VO2) rises exponentially during the first minutes of submax exercise generally reaching a plateau within 3‐4 minutes. It then remains relatively stable for the duration of exercise if intensity is constant. The terms steady‐state or steady‐rate are used to describe this plateau in VO2 during exercise. Steady‐state reflects a balance between energy required by the working muscles and ATP production, primarily by aerobic metabolism. Lactic acid is produced at a slow enough rate during steady‐state exercise that it is either oxidized or reconverted to glucose in the liver (Cori Cycle). Thus, under steady‐state metabolic conditions blood lactate does not accumulate and exercise could theoretically progress indefinitely. Regardless of exercise intensity, at the onset of exercise there is an immediate need for additional energy above resting level. Oxygen consumption (VO2) does not increase instantaneously to steady‐state and therefore aerobic metabolism contributes very little energy early in the exercise bout. The lag in VO2 at the beginning of exercise is primarily due to the delay in circulatory delivery of oxygen to the mitochondria of working muscles. Therefore, the intramuscular anaerobic energy systems (i.e. ATP‐CP, glycolysis) provide the energy required until steady‐state oxygen consumption is reached within a few minutes. This delay in aerobic energy production at the onset of all exercise is known as the oxygen deficit. It may be defined as the difference between the total oxygen consumed during exercise and the total that would have been consumed had steady‐state aerobic metabolism been reached from the start. Moderate‐to‐heavy aerobic exercise requires a longer time to reach steady‐state, which creates a larger oxygen deficit than less‐intense exercise. Following exercise, oxygen consumption (VO2) declines but remains elevated above pre‐
exercise resting levels. The elevated aerobic metabolism in recovery restores the body to its pre‐exercise condition. The length of time that VO2 remains elevated is dependent upon the intensity and duration of the exercise, the fitness of the individual, and other factors. The amount of oxygen consumed during recovery that is above resting levels is called excess post‐
1 Dr. Andreacci 05.575 FL 2011 exercise oxygen consumption (EPOC). The magnitude of EPOC approximates the size of the oxygen deficit at the beginning of exercise. Recovery VO2 generally precedes rapidly decreasing by about 50% over each 30‐second period until reaching pre‐exercise level. The rate of VO2 decrease after exercise follows an exponential curve consisting of two primary components. During the initial phase of recovery, VO2 decreases very rapidly (fast component) which is followed by a slower rate of decline (slow component), until pre‐exercise VO2 values are attained. The fast component is indicative of the energy required to replenish the ATP and CP stored in muscle and for the resynthesis of a small portion of lactate to glucose. Approximately 70% of intramuscular ATP and CP are restored in 30‐seconds, while 100% replenishment is attained within 3 minutes post‐exercise. The slow component is comprised of several factors including: (1) *reduction of elevated body temperature, (2) restoration of hemoglobin and myoglobin oxygen stores, (3) elevated cardiorespiratory function (heart & respiratory muscle), (4) redistribution of ions within muscle (Na‐K pump), and (5) residual effects of thermogenic hormones (e.g. epinephrine, norepinephrine). Each of these factors contributes to elevated VO2 levels, which may remain elevated up to 60‐minutes post‐exercise. EQUIPMENT: - Monarch Cycle Ergometer/Treadmill - Open‐Circuit Metabolic Cart - Polar Heart Rate Monitor PROCEDURES/TEST PROTOCOL: Select a subject to exercise at 2 submaximal workloads: a low intensity (i.e. 1kg @ 60 rpm) and a moderate intensity (i.e. 2kg @ 60 rpm). The testing protocol is as follows: Minute 0:00‐ 5:00 Obtain Resting VO2 Minute 5:01‐ XX:00 First Exercise Bout Minute XX:01‐XX:00 Recovery Period Minute XX:01‐XX:00 Second Exercise Bout Minute XX:01‐XX:00 Recovery Period * Record HR at the end of every minute. 2 Dr. Andreacci 05.575 FL 2011 1. Obtain subject data (height, weight, age, and training status) and fit subject with Polar HR monitor. 2. Identify an individual to record HR every minute of the test and record (i.e. Table 2). 3. Adjust the cycle seat height such that the subject almost extends the leg at the bottom of the revolution. 4. Obtain a 2‐minute pre‐exercise gas sample with the subject sitting on the cycle ergometer at rest. This will establish the subject’s resting VO2. 5. Instruct the subject to cycle at 60 rpm and locate the rpm on the cycle’s display. 6. Have the subject pedal for 5‐minutes at a resistance of 1 kg. This represents a workload of 360 kgm (60 rpm * 1kg * 6 m/rev). Record HR at end of each minute of exercise. 7. Following 5‐minutes of exercise have the subject stop pedaling and remain sitting on the cycle. Obtain a 5‐minute recovery measurement of VO2. Record HR each minute of recovery. 8. Set the resistance to 2 kg and have the subject pedal for 5‐minutes. This represents a workload of 720 kgm (60 rpm * 2kg * 6 m/rev). Record HR. 9. Obtain a second 5‐minute recovery measurement before removing the open‐circuit mouthpiece. Record HR. 10. Collect a copy of the computer print‐out containing VO2 data for the testing protocol. Use print‐out to complete Tables 2 & 4 of laboratory packet. DATA: TABLE 1: SUBJECT CHARACTERISTICS
Subject 1 Gender Age (yrs) Height (in) Weight (lbs) FFM (lbs) NA Please Check One: _____Trained _____Untrained 3 Dr. Andreacci 05.575 EXAMPLE of TABLE 2: Workload 1 HR Time (b/min) (min) Resting 1:00 2:00 3:00 4:00 5:00 Exercise 1:00 1kg 2:00 3:00 4:00 5:00 6:00 7:00 8:00 Rest 1:00 2:00 3:00 4:00 5:00 Example TABLE 3: Workload 2 FL 2011 VO2 (L/min) Exercise 2kg Rest Time (min) 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 1:00 2:00 3:00 4:00 5:00 HR (b/min) VO2 (L/min) CALCULATIONS: 4 Dr. Andreacci 05.575 FL 2011 1. Perform the necessary calculations to determine resting and steady‐state VO2, oxygen deficit, and EPOC. See sample calculation below. SAMPLE CALCULATION: Workload #1 The following data were collected from a single 8‐minute exercise bout on a treadmill, preceded by a 5‐minute resting observation and followed by a 5‐minute recovery period. The treadmill speed was set at 3.5 mph. Time (min) Resting 1:00 2:00 3:00 4:00 5:00 0.41 0.40 0.34 0.42 0.43 Average the 1st 2‐minutes to get the Resting VO2 (0.40 L/min) Exercise 0.93 1.24 1.23 1.24 1.21 1.24 1.31 1.29 Average the VO2 over the last 3 min of the exercise bout to obtain steady‐state VO2. (1.26 L/min). 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 1:00 2:00 3:00 4:00 5:00 0.99 0.51 0.48 0.46 0.56 Recovery VO2 (l/min) Total exercise VO2 = add VO2 for minutes 1‐8 = 9.69 Liters Total post‐exercise VO2 (add VO2 for minutes 8‐12) = 3.00 Liters. 5 Dr. Andreacci 05.575 FL 2011 SAMPLE CALCULATION CONTINUED: 1) Oxygen cost of steady‐state exercise: ‐ Steady‐state VO2 * length of exercise = 1.26lLmin * 8 min = 10.08 L = 9.69 L 2) Total exercise oxygen consumption (VO2) 3) OXYGEN DEFICIT (#1 minus #2) = 0.39 L 4) Total post‐exercise VO2 = 3.00 L = 2.00 L = 1.00 L 5) Resting oxygen cost ‐ Resting VO2 * recovery time = .40 L/min * 5 min 6) EPOC (#4 minus #5) RESULTS: TABLE 4: RESULTS 1kg 2kg Oxygen Deficit (L) Steady‐state VO2 (L/min) *Get From Calculations Workload EPOC (L) 6 Dr. Andreacci 05.575 FL 2011 PLOT Create the following graphs for both of the exercise intensities: Please be creative VO2 vs. Time HR vs. Time RER vs. Time VE vs. Time QUESTIONS 1. What is responsible for the oxygen deficit observed during the onset of exercise? 2. Discuss the role that exercise intensity had on excess post‐exercise oxygen consumption. 3. How does training state (i.e. trained, untrained) affect an individuals ability to achieve steady‐state? 4. How does the recovery from steady‐state exercise (i.e. sub‐maximal) differ from non steady‐state exercise (i.e. maximal)? 5. Did the physiological responses reach a steady state during cycle exercise? Was this true at both power outputs? If not, which power output did not reach a steady state? What are some reasons why this may have occurred? Hint: define ‘steady state!’ 6. Which energy fuel substrate is being utilized during rest and during each test condition? Why? 7. What was the subjects HR intensity for each exercise workload (total exercise)? 7