Energy Systems

Some basic truisms: 1. All energy systems are “on” at all times, relative contributions of each one will change: 2. As intensity , energy supplied by CHO  3. As duration , energy supplied by fat . 4. As glycogen , energy supplied by protein . 5. Training  fat use at any given intensity. 6. Heat, cold, altitude, other stress  CHO use. 7. Effects of diet  as exercise intensity 

SPRINT (10 seconds of maximal exercise) HUMAN ENERGY SYSTEMS ADENOSINE TRIPHOSPHATE (ATP) PHOSPHO- CREATINE (PCr) GLYCOLYSIS (ANAEROBIC; CHO BREAKDOWN) KREBS CYCLE (AEROBIC; CHO, FAT, AND PROTEIN BREAKDOWN) SPRINT (10 seconds of maximal exercise)

HUMAN ENERGY SYSTEMS 800 METER RUN (50 seconds) ADENOSINE TRIPHOSPHATE (ATP) PHOSPHO- CREATINE (PCr) GLYCOLYSIS (ANAEROBIC; CHO BREAKDOWN) KREBS CYCLE (AEROBIC; CHO, FAT, AND PROTEIN BREAKDOWN) 800 METER RUN (50 seconds)

MARATHON 2.5 hours of exercise HUMAN ENERGY SYSTEMS ADENOSINE TRIPHOSPHATE (ATP) PHOSPHO- CREATINE (PCr) GLYCOLYSIS (ANAEROBIC; CHO BREAKDOWN) KREBS CYCLE (AEROBIC; CHO, FAT, AND PROTEIN BREAKDOWN) MARATHON 2.5 hours of exercise

Some basic truisms: 1. All energy systems are “on” at all times, relative contributions of each one will change: 2. As intensity , energy supplied by CHO  3. As duration , energy supplied by fat . 4. As glycogen , energy supplied by protein . 5. Training  fat use at any given intensity. 6. Heat, cold, altitude, other stress  CHO use. 7. Effects of diet  as exercise intensity 

As exercise gets harder, the % energy from 40 60 80 100 % energy from CHO % energy from FAT 40 30 20 10 increasing intensity of exercise As exercise gets harder, the % energy from oxidation of CHO goes UP sharply while the % energy from fat goes DOWN

Exercise Intensity & Fuel Source 100 80 60 FAT (% Total Kcal) CHO 40 20 25% MAX 85% MAX

Misinterpretation The graph on the previous slide indicates that if you exercise at very low intensity levels (25% MAX) you will burn a great deal more fat for energy However, at the end of the day, body weight is determined by how many TOTAL calories were ingested vs. how many TOTAL calories were expended Consider the next slide which is the same exercise scenario now expressed in absolute (calorie) terms

Exercise Intensity & Fuel Source 600 500 400 FAT (kcal) 300 CHO 200 100 25% MAX 85% MAX

Some basic truisms: 1. All energy systems are “on” at all times, relative contributions of each one will change: 2. As intensity , energy supplied by CHO  3. As duration , energy supplied by fat . 4. As glycogen , energy supplied by protein . 5. Training  fat use at any given intensity. 6. Heat, cold, altitude, other stress  CHO use. 7. Effects of diet  as exercise intensity 

%CHO & FAT Use in Exercise 90 % FAT being used 80 70 60 50 %CHO & FAT Use in Exercise 40 30 20 % CHO being used 10 30 60 90 120 Exercise Time (min)

WHY does the % of energy from CHO go down as the exercise duration gets longer? Glycogen supplies getting low: remember that use of glycogen is related to how much you have. rate of glycogen use amount of glycogen remaining

So, as exercise progresses, the use of glycogen lessens and use of fat goes up. What happens to intensity? When glycogen supplies become very low, it is no longer possible to provide enough glycogen to sustain high intensity exercise. How does that make you feel?

Inability to maintain a high exercise intensity when muscle glycogen supplies get low is called “bonking”, “hitting the wall”, “going down in flames” and other colorful expressions.

So, there is always a trade-off between exercise intensity and duration: High intensity (fast, hard) requires a lot of glycogen so duration has to be short Low-intensity (slow, easy) requires little glycogen so duration can be long What can you do to improve ability to maintain a higher intensity for a longer period of time?

Some basic truisms: 1. All energy systems are “on” at all times, relative contributions of each one will change: 2. As intensity , energy supplied by CHO  3. As duration , energy supplied by fat . 4. As glycogen , energy supplied by protein . 5. Training  fat use at any given intensity. 6. Heat, cold, altitude, other stress  CHO use. 7. Effects of diet  as exercise intensity 