PED 291 - Chapter 5 Notes

Energy for a 100 meter dash, or a 25 meter swim are supplied by ATP phosphocreatine stored within muscles. These are termed phosphagens.

How many phosphagens stored influence the ability to generate all out energy for brief (5-8 seconds) durations. REMEMBER: CREATINE KINASE, AN ENZYME WHICH TRIGGERS CREATINE TO RESYNTHSIZE ATP, REGULATES THE ROLE OF PHOSPHAGEN BREAKDOWN IN THE MUSCLES.

What kind of exercises are we talking about?

A lineman blocking a sled, pushing a car out of the snow bank while the driver pushes on the gas, swimming as fast as you can to the other end. During intense exercise, intramuscularly stored glycogen provides the energy source to make ADP.

Long duration sports have other energy sources. These are the breakdown of food: carbohydrates, fat, and protein macronutrients. This more aerobic process also recharges phosphates.

Lactate (lactic acid) is formed during anaerobic glycogenolysis: when glycogen stored in muscles provides the energy source to make ADP.

Short intense exercises (running 400 meters for 60 seconds) when active muscles cannot meet the additional energy demands for oxygen.

Without oxygen: pyruvate (figure 4.10, from chapter 4) converts to lactate so ATP can be continuously made to finish the high intensity exercise. (This is crucial during a 400 meter dash, hockey and soccer competitions). If to much lactate builds up, fatigue and pain set in.

Lactate can build at times of rest, but it’s usually removed at the same rate.

Aerobic training produces changes in cells that increase rates of lactate removal (it's called cellular oxidation). The accumulation in tissues usually occurs more as the level of exercise intensity increases. (Lactate in the blood goes up as lack of oxygen increases).

Page 126 ...figure 5.1 shows significant levels of increased lactate at about 55% aerobic metabolism for a HEALTHY UNTRAINED MALE. As training increases, lactate does not increase until higher percentages of aerobic metabolism take place.

The blood lactate threshold (point of abrupt increase in blood lactate) for an athlete usually takes place at about 75% aerobic metabolism due to an increase in mitochondria size and the concentrations of enzymes involved in aerobic metabolism increases, thus the cells can generate ATP aerobically by breaking down fatty acids.

This happens due to:

Endurance training also provides the following:

The capacity to generate high lactate levels during exercise enhances power output for short durations and increase more with sprint and power training. Well trained athletes generate up to 30 % more lactate than untrained ones.

Why do we want to generate lactate?

Lactate shuffling- lactate circulates to other muscle fibers to convert to pyruvate (which converts to a substance called acetyl coA for entry into the Krebs cycle for aerobic energy metabolism).

Muscle is a major site of lactate production and removal (cool down after exercise by slowly jogging, not sitting down) after the workout.

The chart on page 129 looks at the amount of oxygen consumed during a 20 minute run:

Oxygen use at the beginning of exercise (the first minute or so) is far below the steady rate, even though oxygen requirement is steady all the way throughout (figure 5.2) Why?

Because at the start of exercise ATP provides the muscles energy requirement without the need for oxygen.

Oxygen deficit- the difference between total oxygen consumed during exercise (sprinting), and the amount that would have occurred should the exercise been at a steady rate (jog).

Where does the energy come from during the deficit?

Anaerobic energy transfer

The energy supply of anaerobic and aerobic energy systems does not get put into work by switching from one to the other. They usually transfer smoothly from anaerobic to aerobic.

A trained person has a smaller oxygen deficit, which means:

Why do they have a smaller oxygen deficit?

2 types of muscle fibers

The contraction speed of slow twitch is about half as fast as fast twitch.

What requires a combination of fibers for athletic performance? A basketball game, 800 meter run, soccer game.

Every person has a different fiber make up in muscles and these fibers can be specifically trained.

If I want someone to run a better 200 meter dash: a good workout would be running 150 meters 8 times with 2 minutes rest in between (rebuild the ATP). Intensity and duration determine what anaerobic or aerobic systems and metabolic processes (burning fat for example during a long run) are going to be utilized.

A long run (aerobic activity) utilizes fat as the primary fuel source. If the intensity kicks up (interval running: every other lap is a fast one) the liver increases glucose release to active muscles.

A sprint (anaerobic activity) utilizes glycogen as the dominant carbohydrate energy source.

An intermediate activity, like an 800 meter run, uses about 50% from aerobic processes, and the rest from anaerobic. Intensity and duration determine the energy system used during exercise.

During the higher intensity exercise, the liver releases more glucose to active muscle. Glycogen is the energy system used during early stages of exercise, but when it depletes from the muscles and liver, triglycerides and fatty free acids enters the metabolic mix for ATP production.

In maximum anaerobic effort, like a 200 meter dash, carbohydrate is the sole contributor to ATP production (due to glycolysis).

A world class miler will run with more intensity than most of us would, so his predominant energy source may be carbohydrate, although he/she is probably receiving about half of their energy through the aerobic system. By about the 6 minute mark of exercise, 90% of our energy comes from aerobic glycolysis.

Bonking- the inability to continue exercising due to severe depletion of liver and muscle glycogen (remember they store this)

After exercise is over the body does not return immeadiately to resting levels:

Recovery from exercise can be active (slow jog), or passive (sitting). Be aware that active helps remove lactic acid.

People exercising at or below 60 percent of max oxygen uptake usually don't accumulate much lactic acid. How can some people work well above and still not build up lactic acid?

By exercising at an exhausting intensity for 3-5 minutes, or an all out exercise for about 8 seconds. Then they would let their body recover and do it again.

Examples: Interval training for 400 meter runners: practicing 6  400meter dashes at 80% of their maximum heart rate, with 5 minutes of recovery.

Example 2: run a mile in 6 minutes: rest for 8 minutes and repeat.

Example 3: if you can do 40 sit-ups in 2 minutes: do sets of 6 sit-ups in 10 seconds, rest 20 seconds, and repeat 10 times. (This is called the E to R method: exercise to rest).