What is exercise physiology? Sport types and the body
Physiology is how the body works. Exercise physiology looks at how the heart, lungs, muscles and other systems respond to activity, both right away (acute responses) and after weeks of training (chronic adaptations).
Classifying physical activity
- Competitive (matches, races with rules and results) vs leisure / recreational (for fun and health).
- Outdoor and adventure activities: hiking, orienteering, cycling, climbing.
- Individual (athletics, swimming), team (football, hockey, kabaddi), racket / net (badminton), combat (judo).
- By energy demand: aerobic (long, steady: marathon) vs anaerobic (short, intense: sprint, weightlifting); most team games are mixed.
Muscles, bones and how they respond to exercise
Skeleton
The skeleton gives support, protection, movement (bones are levers), makes blood cells and stores minerals. Bone types: long (femur), short (wrist bones), flat (skull, ribs), irregular (vertebrae), sesamoid (kneecap).
Muscle
Skeletal muscle can contract, extend, is elastic and responds to nerve signals (excitable). Muscles work in pairs: the agonist pulls while the antagonist relaxes (biceps and triceps). Slow-twitch fibres resist fatigue (endurance); fast-twitch fibres are powerful but tire quickly (sprint).
Effects of exercise
- During exercise: more blood flows to muscles, muscle temperature rises, lactate may build up, fatigue sets in.
- After training: muscles grow larger (hypertrophy), more capillaries and mitochondria, stronger tendons, denser bones, better posture and coordination.
Heart, lungs and blood during exercise
The circulatory system (heart, blood vessels, blood) carries oxygen and glucose to muscles and takes away CO₂ and heat. The respiratory system (airways, lungs, alveoli) brings oxygen in and takes CO₂ out.
- Heart rate (HR): beats per minute. Rest ≈ 60–80; it rises with intensity. Maximum HR ≈ 220 − age.
- Stroke volume (SV): blood pumped per beat (≈ 70 mL at rest, up to 120+ mL in exercise).
- Cardiac output (Q) = HR × SV.
- Breathing: rate rises from ≈ 12 to 40+ breaths per minute and each breath gets deeper (tidal volume ↑). Minute ventilation = rate × tidal volume.
- VO₂ max: the most oxygen your body can use per minute; a key measure of aerobic fitness.
After exercise, HR and breathing stay high for a while to repay the oxygen debt (EPOC). A fast recovery is a sign of good fitness.
Energy systems: ATP-PC, anaerobic and aerobic
Muscles can only use ATP for energy, and they store very little. Three systems remake it:
- ATP-PC (phosphocreatine): very fast, no oxygen, lasts about 10 s. 100 m sprint, a jump, a throw.
- Anaerobic glycolysis (lactic acid system): breaks glucose without oxygen; fast, lasts up to about 2 min; makes lactate and H⁺ that cause the burning feeling and fatigue. 400 m run.
- Aerobic system: uses oxygen to break glucose and fat fully into CO₂ and water. Slower but lasts for hours. Marathon, long cycling. Glucose + oxygen → CO₂ + water + lots of ATP.
All three always work together; the activity decides which one leads.
Physiological factors behind fitness
- Strength: muscle size, fibre type, nerve signals.
- Speed: fast-twitch fibres, reaction time, ATP-PC stores.
- Endurance: VO₂ max, capillaries, slow-twitch fibres, heart size.
- Flexibility: joint structure, muscle elasticity, warm muscles.
Biomechanics, sports medicine and ageing
Biomechanics
Biomechanics applies physics to movement: levers (bones and joints), force and Newton's laws (push the ground back, you move forward), centre of gravity and balance (lower stance = more stable), and projectiles (best throw angle, spin).
Sports medicine
Sports medicine prevents and treats injuries. Prevent: warm-up, cool-down, correct technique, rest, safe equipment and hydration. First aid for sprains and strains: RICE (Rest, Ice, Compression, Elevation).
Ageing
With age: maximum HR and VO₂ max fall, muscle mass and strength drop, bones lose density, joints stiffen and reaction time slows. Regular exercise slows all of these and lowers the risk of heart disease, diabetes and falls.
Try it at home
Find your pulse on your wrist. Count beats for 15 s and multiply by 4: this is your resting HR. Do 60 seconds of fast stepping or skipping and measure again. Then measure every minute until you are back to resting. How many minutes did recovery take?
Key formulas and definitions
- Cardiac output Q = heart rate × stroke volume
- Maximum heart rate ≈ 220 − age (beats/min)
- Minute ventilation = breathing rate × tidal volume
- Heart rate from pulse: beats in 15 s × 4
- Aerobic: glucose + oxygen → carbon dioxide + water + energy (ATP)
- Anaerobic: glucose → lactate + a little energy (ATP)
Worked examples
1. At rest HR = 72 bpm and SV = 70 mL. Find cardiac output in L/min.
Q = 72 × 70 = 5040 mL/min = 5.04 L/min.
2. A 16-year-old wants to train at 70% of maximum heart rate. What heart rate should she aim for?
Max HR ≈ 220 − 16 = 204 bpm. 70% of 204 = 0.70 × 204 ≈ 143 bpm.
3. During a run Q = 20 L/min and HR = 160 bpm. Find the stroke volume.
SV = Q ÷ HR = 20 000 mL ÷ 160 = 125 mL per beat.
4. Which energy system leads in: a long jump, a 400 m race, a 10 km run?
Long jump: ATP-PC (under 10 s). 400 m (about 50–60 s): anaerobic glycolysis. 10 km: aerobic.
5. Breathing rate 30 breaths/min, tidal volume 2 L. Find minute ventilation.
30 × 2 = 60 L/min.
6. Why does a trained athlete have a lower resting heart rate?
Training makes the heart muscle stronger, so stroke volume rises. The same cardiac output (≈ 5 L/min) needs fewer beats: 5000 ÷ 90 mL ≈ 56 bpm.
Common mistakes
- Thinking the aerobic system switches on only after 2 minutes. All three systems work together; only the main one changes.
- Saying lactic acid causes next-day soreness. Next-day soreness (DOMS) is from tiny muscle damage; lactate clears within about an hour.
- Forgetting units in Q = HR × SV: mL/beat × beats/min = mL/min; divide by 1000 for L/min.
- Believing exercise is unsafe for older people. Suitable exercise slows ageing effects and is strongly recommended.