Energy Systems for Exercise

Energy Sources From Food: – CHO = 4 kcal – Fat = 9 kcal – Protein = 4 kcal For Exercise: ATP  ADP + P + energy (for muscle contraction)

Adenosine Triphosphate Energy-carrying molecule found in the cells of all living things. ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes. Cells require chemical energy for three general types of tasks: to drive metabolic reactions that would not occur automatically; to transport needed substances across membranes; and to do mechanical work, such as moving muscles.

Methods of Supplying ATP For Energy Stored ATP + PC (Creatine Phosphate) or ATP-PC Anaerobic metabolism/ glycolysis/lactic acid system Aerobic metabolism

ATP-PC System Short duration (<10 secs) anaerobic Uses stored ATP Strength/power movements Replenishes rapidly

The ATP-PC system Active at the beginning of all forms of activities Especially important in high intensity exercises like weight lifting that require short bursts of energy. The source of fuel for the ATP-PC system is ATP and PC that is stored in the muscles. Only a small quantity can be stored, so this energy source is only effective for activities that last ten seconds or less.

Glycolysis Breakdown of carbohydrates for fuel Fuel stored in the muscle as glycogen / delivered to the muscle as blood glucose Glycolysis can produce fuel for 30 seconds to a minute for moderate heavy resistance training

Fast (Anaerobic) Glycolysis (The lactic acid system) Fast glycolysis is used when oxygen is in short supply. Fast glycolysis results in the formation of lactic acid An increase in lactic acid in the muscle can involve muscular fatigue and ultimately cessation of exercise.

Active Recovery from Exercise (Cool down) Facilitates lactate removal because of: – increased perfusion of blood through the liver and heart – increased blood flow in muscles because muscle tissue oxidizes lactate

Slow (Aerobic) glycolysis (The aerobic system) Slow glycolysis is used if there is enough oxygen to allow a continuous supply of fuel. The byproduct of this form of glycolysis is pyruvate, which is not converted to lactic acid but is transported elsewhere. Pyruvate is eventually dissipated as sweat/urine

Aerobic/Oxidative System Supplies energy to the muscle through the use of continuous oxygen transport. System works at rest and during very low intensity exercise such as walking This form of energy primarily utilizes fats (70%) and carbohydrates (30%) as fuel sources, but as intensity is increased there is a switch in substrate majority from fats to carbohydrates

Oxygen Uptake During Aerobic Exercise Increases sharply at onset Levels off within a few minutes if pace is constant (steady state) Oxygen demand met by supply

Maximal Oxygen Uptake (VO 2 max ) The region where oxygen uptake plateaus and does not increase despite an additional increase in exercise intensity.

Difference between oxygen consumed during exercise and amount that would have been consumed had a steady rate, aerobic metabolism occurred at onset of exercise. Oxygen Deficit

Order of energy production Initial energy comes form ATP stored in muscles about 2 seconds Then the ATP-PC system about 10 seconds Then the Lactic acid system about 1 minute Then the Aerobic system 1minute onwards

The Energy-Time Continuum As the work time increases, the percentage of energy contributed by the aerobic system increases.

Blood Lactate Threshold Exercise intensity at the point of lactate buildup. Predicts aerobic exercise performance. Untrained ~ 55% of VO 2 max. Trained ~ 75% of VO 2 max.