Sports Physiology Flashcards
What are the two major types of energy sources used for muscle activity?
Aerobic and anaerobic
Describe the difference in terms of recruitment and efficiency of aerobic vs. anaerobic sources of energy
In general, anaerobic pathways are very rapid acting and have a maximal rate of production that is very fast. However the EFFICIENCY of energy (ATP) production isn’t as high as aerobic which is able to be sustained for several minutes-hours. Aerobic pathways have their take much longer to turn on and have a slower rate of ATP production.
How long can muscles operate without any oxygen?
Muscles are only able to operate for 3-4 minutes without oxygen. For any activity that exceeds this length, there needs to be oxygen present. This is because muscle glycogen stores run out very quickly in the absence of oxygen, hence preserving and increasing glycogen stores is a crucial aspect of sports training (glycogen loading)
What are the two major types/classes of exercise?
Long duration (eg. marathon) and rapid duration at maximal force (eg. sprint).
What types of energy sources are likely to be used in a marathon/endurance event?
During a endurance events, the muscles are continually working and energy is required for the whole time (require aerobic pathways to work). In a marathon, even aerobic glycogen is likely to run out and this is when fatty acids become available. However when this happens the run rate is reduced to half (a phenomenon called ‘hitting the wall’).
What types of energy sources are likely to be used in short duration/high power events?
These forms of exercise only last several seconds-minutes and muscles are able to work entirely aerobically.
The limitations on short duration events are NOT the same as the limitations on long duration.
What are the limits on short duration?
Blood flow to the muscles ceases when the force exceeds more than 50% of the maximal voluntary contraction.
Thus the cardiac output and oxygen delivery to the muscles isn’t important in short duration/high power events. It is also known that VO2 max is not important (because you can hold your breath during a 100 metre sprint without affecting performance).
The key to this type of event is developing the greatest muscle cross sectional area (HYPERTROPHY to allow more recruitment of contractile units).
The limitations on short duration events are NOT the same as the limitations on long duration. What are the limits on long duration?
Any exercise that lasts for more than a few minutes requires oxygen supply to the muscles. The capacity to use oxygen is determined by the VO2 max
Define VO2 max
The maximal or optimal amount of oxygen uptake per minute that the heart, lungs and muscles can effectively use during exercise. It is also called “aerobic capacity” In general, the higher the VO2 max, the higher the performance ability
What determines VO2 max?
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Cardiac Output: governs the amount of blood and hence oxygen is delivered to the tissues which in turn is a product
- Stroke Volume (blood volume and dehydration)
- Heart Rate
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Oxygen Saturation of Blood
- Determined by Hb and Blood count
- Determined also by Partial Pressure of Atmospheric Oxygen
Cardiac Output is dramatically increased in exercise. How is this achieved in athletes?
- Increasing heartrate
- Increasing end diastolic volume (ventricular filling and thus increasing SV).
Thus these two components impact on VO2max
What adaptations are made in the cardiovascular system of atheletes to maximise the efficiency of cardiac output?
When HR exceeds 180 beats/min even the CO starts to drop (decreased filling time). Athletes have lower resting heart rates implying that their stroke volume has been enhanced likely due to hypertrophy and thus tachieve high CO with lower HRs. However this is limited by laplace’s law and the coronary artery supply.
The EDV is set by central venous pressure and the size of the heart. It increases to increase cardiac output (and maximise the VO2 max). In order to this, there needs to be an increase in central venous pressure and/or increase in sympathetic vasoconstriction.
The ESV needs to be minimal to allow for optimal oxygen delivery around the body. It is determined by contractility of the heart (which is set by the intracellular calcium). It is achieved by the sympathetic nervous system and intrinsic control of the heart.
What is the “break point”?
Ventilation increases in proportion to the level of exercise (work) being performed. This relationship is linear until a ‘break point’ is reached.
This is at approximately 70% of the VO2 max. and signals that ventilation begins to exceed performance (hyperventilation occurs).
[This correlates with the lactic acid threshold where anaerobic glycolysis begins to occur]
Respiratory Rate is not a major limitation to VO2 max.
Is diffusion capacity a limitation?
Diffusion is the ability for oxygen to get from the air into the bloodstream. Measuring diffusion is complex but a good indicator is arterial PO2. Measuring the arterial PO2 during exercise shows that it doesn’t (it actualy rises).
The rise is most likely due to hyperventilation. Hyperventilation also causes PCO2 to decrease although arterial pH decreases (due to lactic acidosis).
However past a certain point there is a fall in the arterial PO2 (fall in diffusion). Due to increase in CO through the lungs and less time for diffusion to occur).
What is muscle fatigue?
The decline of force or power produced by a muscle during repeated contractions.
It is known that some muscles (the heart, respiratory muscles and postural muscles) never fatigue. These have large oxidative capacities such that their demand never exceeds their supply - they utilise slow muscle fibres. Thus fatigue must be linked to amount of energy available.
