Quick questions on Physiological adaptations to training: HSC PDHPE Core 2

The average untrained adult has a resting heart rate around 70-80 beats per minute. Trained endurance athletes can have resting heart rates in the 40s or even 30s. Resting heart rate decreases with training because the heart muscle (specifically the left ventricle) gets stronger and pumps more blood per beat, so it needs fewer beats per minute to circulate the same blood volume at rest.

Stroke volume is the volume of blood ejected from the left ventricle per heartbeat. An untrained adult averages around 70 mL per beat at rest; a trained endurance athlete can hit 100 mL or more.

VO2 max is the maximum rate at which the body can take up and use oxygen. It is the gold-standard measure of aerobic fitness and is expressed in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min).

Lung capacity itself (total lung volume) does not change much with training - it is largely determined by genetics, body size, and age. What does change is the efficiency of gas exchange: stronger respiratory muscles (intercostals, diaphragm), more efficient breathing pattern, and improved oxygen and carbon dioxide diffusion at the alveolar-capillary membrane.

Haemoglobin is the iron-containing protein in red blood cells that binds oxygen. Total haemoglobin mass increases with aerobic training, especially when training includes time at altitude (real or simulated). This increases the oxygen-carrying capacity of the blood and is one of the key reasons VO2 max improves with training.

Hypertrophy is the increase in muscle cross-sectional area, primarily driven by an increase in the size of individual muscle fibres (rather than an increase in fibre number). The driver is mechanical loading sustained over weeks to months.

Slow-twitch (Type I) fibres are aerobic-dominant: high mitochondrial density, lots of capillaries, fatigue-resistant. They adapt to aerobic training by increasing mitochondrial number and size, capillary density, and myoglobin content. They get better at oxidising fat and glucose aerobically.