Lecture 11: Exercise Thresholds

What is a threshold?

is the amount, level, or limit, at which something happens or changes

What is the utilization of a given energy system is dependent on?

• Rate of energy demand (Magnitude & Timeline)

• Substrate availability

• Local (in the mitochondria) oxygen supply

What is the rate of energy demand?

It takes time for aerobic system to supply energy

Aerobic energy is pretty slow (low rate)

What is substrate availability?

It takes time for aerobic system to supply energy

Aerobic energy is pretty slow (low rate)

ATP+PCr run out

What is local oxygen supply?

mits on O2 supply will limit aerobic performance

Within the body oxygen (at any given time) can be?

• In the lungs

• Bound to hemoglobin within the blood

• Bound to myoglobin in the muscle

• In the mitochondria

Where does oxygen need to present in order to be consumed?

(aerobic metabolism), it has to be present in the mitochondria of the working muscle.

• Oxygen in the lungs or blood does the exerciser no good

• Oxygen bound to myoglobin in non-active muscles does the exerciser no good

If oxygen is not present or present in sufficient amounts, then?

the muscle must utilize anaerobic sources

-Even at intensities less than VO2max, the local muscle can have insufficient oxygen supply for aerobic metabolism

Total energy is the sum of?

• Aerobic contribution

• Anaerobic contribution

Oxygen deficit can be brief?

quickly resolved deficiencies in oxygen supply:

• At onset of exercise or increase in intensity

• Small, brief, local

Oxygen deficit can be sustained?

deficiency in oxygen supply so anaerobic has to supplement energy supply

• Larger, sustained and accumulating, becomes systemic • Balance between lactate (and H+ ):

• Production

• Clearance

What are the two metabolic " boundaries" ?

Threshold 1: • The intensity at which blood lactate can be maintained at resting levels

• Threshold 2: • The intensity at which lactate production within muscle may be stabilized in blood

What is lactic acid clearance?

H+ : cleaned up using bicarbonate buffering: Bicarbonate (HCO3 - ) combines with H+ to form water and carbon dioxide:

How is lactate converted back into pyruvate?

• In muscle of origin

• In the blood

• Transported by blood to other muscles

• Transported by blood to liver

Where can the clearance of lactate and H+ occur?

• The muscle of origin

• The blood

Threshold 1?

- Aerobic Threshold

-Lactate Threshold -Lactate Threshold 1

-Ventilatory Threshold 1

- Gas Exchange Threshold

Threshold 2?

- Anaerobic Threshold

- Critical Power

- Lactate Threshold 2

-Ventilatory Threshold 2

- Respiratory Compensation Point

-Maximum Lactate Steady State (MLSS)

-Onset of Blood Lactate Accumulation (OBLA)

What is predicting performance?

Threshold intensity describes maximum sustainable intensity during sustained exercise

What is prescribing training intensity?

Understanding intensity domains can be used to inform training zones

• In general:

• Higher intensity training is shorter in duration and requires greater recovery

• Lower intensity training is longer in duration but requires shorter recovery