EHS 385: Exercise Metabolism I Notes

🏃‍♀ Exercise Metabolism: Fueling Your Body's Movement

Basically, this is all about how your body produces and uses energy when you exercise. Exercise puts a big demand on your body's energy systems. In fact, it can increase your energy expenditure by a lot!

🫁 VO2: Measuring Aerobic Fitness

VO2VO2​ is a measure of how much oxygen your body uses. It's an index of how your body produces ATP, which is the energy currency for cells.

  • Incremental Exercise Test: This test steadily increases exercise intensity to measure your VO2VO2​.

  • At Rest: When you're resting, almost all of your energy comes from aerobic metabolism (using oxygen).

  • Rapid ATP Production: When you exercise, your body needs to produce ATP very quickly.

🔄 Rest-to-Exercise Transition: Getting Started

When you go from rest to exercise, several things happen:

  • Initial Metabolic Responses: Initially, your body uses the ATP-PC system (phosphocreatine) and glycolysis (breaking down glucose) for quick energy. These systems are effective for a short time. "ATP-PC and glycolysis are very effective, but only for a short period."

  • Oxygen Consumption Lag: Your oxygen consumption doesn't immediately increase to meet the demand. Anaerobic metabolism (without oxygen) helps to bridge the gap. "O2 consumption does not increase instantaneously; anaerobic metabolism does some of the 'heavy lifting' first."

⏳ Oxygen Deficit, Steady State, and EPOC: Catching Up and Recovering

  • Oxygen Deficit: This is the "missing" oxygen at the beginning of exercise because your body can't immediately deliver oxygen fast enough. "O2O2​ deficit - the amount of O2O2​"missing" in the first few minutes of exercise."

  • Steady State: After a few minutes (3-4 minutes), your oxygen uptake levels off, and your body is meeting its energy needs primarily through aerobic metabolism. "Steady State occurs when aerobic and anaerobic pathways produce enough ATP needed for submaximal activity"

  • EPOC (Excess Post-exercise Oxygen Consumption): This is the extra oxygen your body uses after exercise to recover. We need to address issues from earlier energy decisions made while reaching steady state, and this happens during the EPOC period.

💪 Metabolic Responses to Exercise: Duration and Intensity

  • Short, Intense Exercise: Your body relies heavily on the ATP-PC system. Anything over 45 seconds will use a combination of the three energy systems.

  • Prolonged Exercise: For longer, moderate-intensity exercise, your body can usually maintain a steady state of oxygen uptake. The exceptions are: Hot/Humid environments and continuous exercise at a high work rate (>75% VO2VO2​max).

📈 Incremental Exercise: Pushing Your Limits

  • Graded Exercise Tests (GXTs): These tests gradually increase the intensity of exercise to assess your fitness and cardiac health. The intensity increases until you can't maintain the power output or reach volitional fatigue!

  • VO2max: This is the maximum rate at which your body can use oxygen during exercise. "VO2VO2​max is the best indicator of cardiovascular fitness and endurance potential, but it is not an indicator of performance."