VO2 Max Lab Write-Up



Corinne MagoonKinesiology 323Spring 2014VO2max Lab Write-upVO2 max is a measure of the body’s maximal capacity to transport and utilize oxygen during prolonged exercise and represents the point at which an increase in workload does not result in an increase in VO2 (Powers 76). During exercise, the demand for ATP in the working skeletal muscle leads to an increased demand for oxygen, ultimately leading to increased respiratory and cardiovascular output. By measuring the ratio of oxygen to carbon dioxide in the air inhaled compared to that of the sample exhaled, it is possible to calculate approximately how much oxygen was used in the body for aerobic energy production; therefore, oxygen consumption can be used as an index for aerobic ATP production (Powers 69). During prolonged exercise VO2 increases linearly in relation to workload until VO2max is reached (Powers 76). Because VO2 is dependent on cardiac output and the difference between arterial and venous blood concentrations of oxygen, it is considered a good indicator of overall cardiovascular and respiratory fitness (Powers 76, Lab ). Trained athletes generally have a higher VO2max than an untrained individual because aerobic ATP production begins earlier during exercise (Powers 70). In order to understand the concept of VO2max more clearly, on February 6, 2014, as a group of eight students, we measured a 65.9 kilogram subject’s VO2max while running using the Bruce Treadmill Test Protocol on a motor-driven treadmill. The subject ran through five stages of the Bruce Treadmill Test Protocol, with each increase in stage resulting in a higher speed and incline than the previous stage. Two group members adjusted the speed and incline of the treadmill at the beginning of each stage. A subject monitor was available to manage the mouth piece and make sure the subject was comfortable. One group member acted as a heart rate monitor to give heart rate measurements at each stage. Three group members worked together to collect gas samples and take measurements from the metabolic cart. A Rudolph one-way breathing valve was used with gas bags and a 120 liter Collins spirometer to collect gas samples of exhaled oxygen and carbon dioxide; samples were analyzed using a Parvomedics metabolic cart at the end of each sampling session. Prior to beginning exercise a one-minute resting gas sample was collected while the subject was seated to determine a base VO2. In order to obtain the most accurate measure of oxygen consumption, the subject was allowed to reach steady state before each sample. We took one minute air samples during the final minute of each of the first three stages, and in order to avoid overfilling the Collins, a thirty second sample was taken during the final thirty seconds of the fourth and fifth three-minute stages. The ambient temperature of the lab was twenty three degrees Celsius and the barometric pressure was 756 mmHg. Due to the fact that the air we measured from the Collins contained moisture, we used a KSTPD conversion factor of 0.89 to find the volume of air exhaled at standard temperature and pressure without the partial pressure of water in the air. After converting the VESTPS of 96.7 L/min to a VESTPD of 86.1 L/min we are able to calculate the subject’s VO2max by finding the product of VESTPD and the ratio of oxygen and carbon dioxide in inhaled and exhaled air.VO2 (y axis) against Bruce Protocol Stage on treadmill. VO2max was 0.12 L/min at rest and increased to 0.30, 1.43, 2.45, 2.95, and 3.33 L/min for stages one through five respectively. HR (y axis) against Stage. The subject’s resting heart rate was measured at 65 and rose steadily to 108, 134, 173, 178, and 188 bpm for stages one through five respectively. RER vs Stage. RER was 0.56 at rest and increased to 0.58, 0.67, 0.79, 0.87, 1.01 VCO2/VO2 in stages one through five respectively. VO2 vs HR. As heart rate increases, VO2max increases as well in a linear fashion. CHO ox & fat ox vs stage. Fat oxidation increased through the third stage and began to decrease; carbohydrate oxidation increased consistently throughout the five stages. %CHO & %fat vs stage. Fat oxidation was 100% in the first stage and decreased steadily throughout the five stages. Carbohydrate did the opposite, and increased as the five stages progressed. DiscussionAt lower workloads VO2 is linearly related to workload. Do these results imply a causal relationship between VO2 and work?There is a causal relationship between workload and VO2 in that an increase in workload leads to an increase in VO2 until the point of volitional fatigue. As workload increases, the mitochondria of the working skeletal muscle must produce more ATP. An increase in aerobic ATP production during prolonged exercise requires an increase in oxygen delivery to the muscle via the cardiovascular system. With VO2 being dependent on cardiac output as well as the difference between arterial and venous oxygen concentration, increased oxygen delivery and utilization increases VO2 (Lecture 33). Discuss the physiological significance of the leveling off of VO2, while workload continues to increase. Each stage in the Bruce protocol is at a higher speed and incline than the previous stage; with this increase in intensity, the workload and amount of energy required of the body increases as well. As the working muscles require larger amounts of ATP to continue the action, the cardiovascular system is required to move more oxygen to the working muscles to maintain ATP production in the mitochondria. If the subject was able to run through another stage, we might see the VO2 max reach a plateau, because the cardiovascular system has reached its capacity for oxygen transport. An increase in workload will result in an increase in VO2 up to a certain point, but there is a volume at which oxygen transport and utilization cannot be increased any higher; at this point we see VO2max plateau while workload may increase. Given the graph, what causes R to increase rapidly at point A? Respiratory exchange ratio measures the ratio of volume of carbon dioxide output to the volume of oxygen used (Powers 79). Due to the fact that fat and carbohydrates require different amounts of oxygen to be oxidized, RER is often used to estimate what substrate the muscles are using to produce ATP. Because fat oxidation requires more oxygen than carbohydrate oxidation, a higher RER would represent more carbohydrate oxidation than fat oxidation (Powers 79). Describe the relationship between heart rate and workload. Why does the heart respond this way?VO2 max is dependent on cardiac output, which is dependent on both stroke volume and heart rate. As the demand for ATP in the working muscle increases, the demand for oxygen transportation by the cardiovascular system increases as well. As more oxygen needs to be delivered to the working muscle, the cardiovascular system increases both stroke volume and heart rate to deliver a large amount of blood. The Frank-Starling law states that an increase in end diastolic blood volume leads to stretching of cardiac muscle fibers causing the muscles of the heart to contract harder, as a result increasing stroke volume (Frank-Starling Relationship). Why does the absolute amount of CHO and fat change w/ increasing exercise intensity? Why does the percent contribution of each substrate change w/ increasing exercise intensity? During the first few minutes of exercise, the majority of ATP is produced by anaerobic metabolism, oxidizing primarily fat. Prolonged exercise brings about increased blood levels of epinephrine, which subsequently increases phosphorylase activity (Powers 80) causing breakdown of muscle glycogen and increased lactate production. Due to the increased availability of muscle glycogen, the body transitions from oxidizing fat to producing ATP primarily by oxidizing carbohydrate. As it requires more oxygen to metabolize fat than it does to metabolize carbohydrates, it becomes more efficient to use oxygen for carbohydrate metabolism during prolonged exercise. Prolonged exercise may also require a large number of fast-twitch muscle fibers, which metabolize carbohydrates more efficiently than fats due to their lack of lipolytic enzymes.Resources:Dr. Azevedo. Exercise Physiology Lecture Notes Spring 2014. Exercise Physiology Lab Manual, Spring 2014. Powers, Howley. Exercise Physiology: Theory and Application to Fitness and Performance, 8th edition. McGraw Hill, 2012. R. Moss, D. Fitzsimons. Frank-Starling Relationship: Long on Importance, Short on Mechanism. American Heart Association; Circulation Research, 2002; 90:11-13. ................
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