Human Physiology: Heart Function

Resting Heart Rate

• Resting heart rate (RHR) is the number of heartbeats per minute when at rest.
• Trained athletes have lower RHR than untrained individuals due to a more efficient cardiovascular system and higher stroke volume.
• RHR can decrease by 1 bpm per week of training for sedentary individuals. Highly trained endurance athletes can have a RHR below 40 bpm.
• Lower RHR leads to faster recovery and reduced fatigue/injury risk.

Stroke Volume (SV)

• SV is the amount of blood ejected by the left ventricle during one contraction, measured in mL/beat.
• Endurance training increases SV, particularly during maximal exercise.
• Training causes the left ventricle to fill more efficiently during diastole.
• Increased SV leads to better oxygen delivery to working muscles and improved performance.

Cardiac Output (CO)

• CO is the amount of blood pumped by the heart per minute (L/min).
• CO = stroke volume x heart rate.
• Untrained athletes have a CO of 15-20 L/min, while trained athletes' CO is 20-25 L/min.
• Trained athletes may have a slightly lower maximal heart rate (MHR) than untrained athletes, but achieve higher CO through increased stroke volume, not heart rate.
• CO naturally decreases with age.

Oxygen Uptake

• Muscles use more oxygen during exercise.
• Maximal oxygen uptake (VO2 max) is the best indicator of cardiorespiratory endurance.
• High VO2 max signifies an efficient oxygen delivery system and superior endurance performance.
• Measured in mL/kg/min.
• High-intensity aerobic training can significantly improve VO2 max within 8-12 weeks.

Lung Capacity

• Lung capacity is the maximum amount of air the lungs can hold, roughly 6L in males and slightly less in females.
• Lung volume changes minimally with training.
• Vital capacity (amount of air expelled after maximum inspiration) increases slightly.
• Residual volume (air not expelled) decreases slightly.
• Tidal volume (normal breath volume) remains unchanged with training, but increases at maximum exercise levels.

Haemoglobin Level

• Haemoglobin is a protein in red blood cells that binds and transports oxygen.
• Women generally have lower haemoglobin levels and VO2 max than men.
• Training and high-altitude training increase haemoglobin levels, boosting oxygen-carrying capacity.

Muscle Hypertrophy

• Hypertrophy is muscle growth caused by increases in muscle cell size.
• Resistance training causes muscle hypertrophy, while muscle atrophy occurs with lack of stimulation.
• Training must follow the principles of overload and specificity to encourage hypertrophy.

Effect on Fast and Slow Twitch Muscle Fibres

• Slow-twitch (red) fibres: Contract slowly, used for endurance activities like marathons. Efficient in using oxygen to generate energy (ATP).
• Fast-twitch (white) fibres: Contract quickly, used for explosive movements. Fatigue rapidly.
• FTa (intermediate fast-twitch fibres): Produce high output for longer periods using both aerobic and anaerobic metabolism.
• FTb (fast-twitch fibres): Use solely anaerobic sources for energy, enabling explosive actions.
• Training increases tolerance to lactic acid in fast-twitch fibres and extends the duration of anaerobic performance.
• Endurance activities lead to some hypertrophy in slow-twitch fibres.

This quiz covers key concepts related to resting heart rate, stroke volume, and cardiac output. Explore how these cardiovascular parameters are influenced by training and how they affect athletic performance. Test your knowledge on how heart function contributes to overall fitness and recovery.