Limits to exercise tolerance Flashcards
(19 cards)
Define fatigue
The inability to maintain power output or force during repeated muscle contractions.
Define exercise performance
The ability to maintain a specific speed or power output.
( Vo2 max)
Define exercise capacity
The total duration or distance an individual can sustain before exhaustion.
State 3 reasons for fatigue
- Hyperthermia in the heat which reduces your central drive and motivation, muscle damage and central fatigue - moderate domain
- Glycogen depletion - heavy domain
- Depletion of finite energy stores and the accumulation of fatiguing metabolites e.g. lactic acid - severe
Why is VO2 max the key indicator of endurance performance
- VO2max (maximal oxygen uptake) is the maximal rate of oxygen consumption during exercise.
- Higher VO2max is associated with better endurance performance and greater work capacity.
Reasons why lungs are not the limiting factor in your Vo2 max
Large alveolar area
Ventilation increases more than oxygen uptake does - suggesting a greater ca-pacity to ventilate our lungs
Partial pressure is maintained even at VO2 max
Reasons why the lungs are a limiting factor in Vo2 max
Oxygen levels decline as the intensity of exercise increases, suggests that the lungs may be a limiting factor to VO2
Relative hypoventilation as a limitation, people with a higher ventilation rate for given O2 uptake have a higher oxygen saturation
Mechanical constraints to breathing- narrow airways will limit the flow of oxygen into the lungs
Changing the density of air we breathe in is a good way to test if lung function is a limiting factor to VO2
- Less dense air (altitude) means we fatigue quicker
Haemoglobin saturation is the amount of haemoglobin that is bound to oxygen
Higher the partial pressure in the higher the haemoglobin saturation
What is a pulmonary oedema
- Swelling in the lungs
- Can be damaging
- This happens when the gap increases which means the oxygen & CO2 will take longer to transfer
What is red blood cell transit time
the amount of time it takes for the red blood cell to pass through capillaries
- Longer the transit time the more time for gaseous exchange and the longer the transit time the less time for gaseous exchange
How does the alveoli capillary change during exercise
- Breathing effort increases dramatically during exercise (from 10 L/min at rest to 250 L/min!).
- Respiratory muscles compete for blood flow, potentially limiting leg muscle oxygenation.
- Respiratory muscle fatigue occurs during intense endurance exercise, affecting performance.
What is the respiratory muscle metaboreflex
- When respiratory muscles fatigue, blood flow is redirected away from the legs.
- This can cause premature fatigue in leg muscles.
Conclusion: Respiratory muscle fatigue may limit high-intensity endurance exercise.
How does cardiac output limit exercise tolerance
- Cardiac output (Q) is the most important determinant of VO2max.
- Differences in stroke volume explain most inter-individual variations in VO2max.
- Plasma volume expansion increases stroke volume, leading to early improvements in VO2max with training.
Conclusion: Heart function (not lungs or muscles) is the primary limiter of VO2max in most people.
How does fuel depletion limit exercise tolerance
o Muscle glycogen stores are critical for prolonged endurance performance.
o Low muscle glycogen correlates with early fatigue.
How does lactate threshold limit exercise tolerance
o The higher the % of VO2max sustainable without excess lactate, the better the endurance performance.
o Even if two athletes have the same VO2max, the one with a higher lactate threshold will outperform the other.
How does exercise economy limit exercise tolerance
Runners with more efficient movement patterns require less oxygen for the same speed.
How does muscle glycogen effect endurance
- High glycogen levels increase endurance time.
- Carbohydrate (CHO) intake during exercise delays fatigue
How does muscle glycogen as a signalling
Glycogen is stored in different muscle compartments:
1. Subsarcolemmal (near cell membrane).
2. Intermyofibrillar (between muscle fibres).
3. Intermyofibrillar (inside muscle fibres, most critical for contraction).
Intermyofibrillar glycogen depletion is most associated with fatigue.
Why are carbs the preferred fuel for endurance exercise
- CHO is more oxygen-efficient than fat.
- Glycogen depletion leads to increased reliance on fat oxidation, which is slower and less efficient.
CHO ingestion extends endurance performance by maintaining high glycogen stores.
How does mental fatigue effect exercise tolerance
- Differences in cardiac output(via stroke volume) largely explain differences in maximal oxygen uptake
- VO2 max is a measure of potential- the proportion of VO2 max that is sustainable and efficiency will then determine performance speed/power
