Applied anatomy and physiology

Welcome to Applied Anatomy and Physiology!

Ever wondered why your heart beats faster before a race even starts, or why your muscles burn during a sprint? This chapter is all about the "inner engine" of the athlete. We are going to look at how your heart, lungs, and muscles work together to keep you moving, and how sport actually changes your body for the better. Don't worry if some of the science seems heavy at first—we'll break it down into bite-sized pieces with plenty of sporting examples!

1. The Cardiovascular System: The Body's Delivery Service

Think of your cardiovascular system as a high-speed delivery network. It picks up oxygen from the lungs and "parcels" of energy from your food, delivering them to the working muscles while taking away "trash" like Carbon Dioxide (\(CO_{2}\)).

Health vs. Fitness

Health is about being free from disease. Regular sport helps prevent Heart Disease, High Blood Pressure, and Strokes by keeping your "pipes" (arteries) clear of Cholesterol. Fitness is how well your body handles exercise. A trained individual will have a much higher Cardiac Output (the total amount of blood pumped per minute) during maximal exercise than an untrained individual.

How the Heart is Regulated

Your heart doesn't just speed up by accident. It is controlled by three main factors:

1. Neural: Your Sympathetic Nervous System acts like an "accelerator pedal" to speed up the heart, while the Parasympathetic Nervous System acts like a "brake" to slow it down.
2. Hormonal: Adrenaline is released, causing an Anticipatory Rise (your heart rate goes up just thinking about the race!).
3. Chemical: Receptors detect changes in your blood.

Meet the Receptors (The Body's Sensors)

Chemoreceptors: Detect a rise in \(CO_{2}\) and acidity.
Proprioceptors: Detect movement in your joints and muscles.
Baroreceptors: Detect changes in blood pressure.

Redistributing Blood: The Vascular Shunt

When you exercise, your muscles need more blood, but you only have so much to go around! Your body uses the Vascular Shunt Mechanism:
- Vasodilation: Blood vessels to the muscles widen (get bigger) to let more blood in.
- Vasoconstriction: Blood vessels to non-essential organs (like your stomach) narrow to "steal" that blood for the muscles.

Oxygen Transport and the Bohr Shift

Oxygen travels in the blood attached to Haemoglobin and is stored in the muscles by Myoglobin. During exercise, your muscles get hotter and more acidic. This causes the Oxyhaemoglobin Dissociation Curve to shift to the right. This is called the Bohr Shift.
Analogy: Imagine Haemoglobin is a taxi. The Bohr Shift is like the taxi driver realizing the passenger (Oxygen) is late for a meeting and letting them out exactly where they need to be much faster!

Quick Review: The Cardiovascular System

- Cardiac Output (\(Q\)) = Stroke Volume (\(SV\)) \(\times\) Heart Rate (\(HR\)).
- Starling’s Law: The more the heart fills with blood during exercise, the harder it contracts (like stretching a rubber band).
- Cardiovascular Drift: After 20+ mins of exercise in the heat, your HR rises even if intensity stays the same because you are sweating out fluid.

2. The Respiratory System: The Gas Exchange

The goal here is simple: get Oxygen (\(O_{2}\)) in and Carbon Dioxide (\(CO_{2}\)) out.

Lung Volumes

You need to know how much air is moving in and out:

- Tidal Volume: Normal breath in and out.
- Inspiratory Reserve Volume: The extra air you can force in (deep breath).
- Expiratory Reserve Volume: The extra air you can force out.
- Residual Volume: The air that stays in your lungs so they don't collapse.
- Minute Ventilation (\(VE\)): Total air breathed per minute (\(VE = Tidal Volume \times Frequency\)).

Gas Exchange: Diffusion and Partial Pressures

Gases always move from an area of High Pressure to Low Pressure. In the lungs (alveoli), there is a high partial pressure of \(O_{2}\), so it "pushes" itself into the blood. At the muscle, \(CO_{2}\) pressure is high, so it "pushes" itself into the blood to be taken away.

Common Mistake to Avoid: Don't confuse breathing (Ventilation) with Gas Exchange (Diffusion). Ventilation is moving air into the lungs; Diffusion is moving the gases into the blood.

3. The Neuromuscular System: Power and Control

This is how your brain tells your muscles to move.

Muscle Fibre Types

Type I (Slow Twitch): Like a marathon runner. They don't have much power, but they can go for hours without getting tired.
Type IIa (Fast Oxidative Glycolytic): A mix. Good for a 400m or 800m run.
Type IIx (Fast Glycolytic): Like a 100m sprinter. Massive power, but they tire out in seconds.

Recruiting Muscle Fibres

Your brain uses Motor Units to control muscles.
- All or None Law: A motor unit either fires 100% or not at all.
- Spatial Summation: Using more motor units at the same time for more strength.
- Wave Summation/Tetanic Contraction: Sending signals so fast that the muscle doesn't have time to relax, creating a smooth, powerful movement.

PNF Stretching (Proprioceptive Neuromuscular Facilitation)

This is a clever way to "trick" your nervous system into letting your muscles stretch further. It uses Muscle Spindles (which stop over-stretching) and the Golgi Tendon Organ (which causes the muscle to relax if the tension is too high) to increase flexibility.

4. Musculo-Skeletal System and Movement Analysis

To analyze movement, we look at Planes (the lines we move along) and Axes (the imaginary pins we rotate around).

The Big Three Movements

1. Sagittal Plane / Transverse Axis: Forward and backward movements like a somersault or a bicep curl (Flexion/Extension).
2. Frontal Plane / Sagittal Axis: Side-to-side movements like a star jump (Adduction/Abduction).
3. Transverse Plane / Longitudinal Axis: Twisting movements like a discus throw or a full twist in trampolining.

Muscle Contractions

Isotonic Concentric: Muscle shortens under tension (e.g., upwards phase of a bicep curl).
Isotonic Eccentric: Muscle lengthens under tension (e.g., lowering the weight in a controlled way).
Isometric: Muscle stays the same length (e.g., a "plank" or holding a rugby scrum position).

5. Energy Systems: Fueling the Fire

Your body needs ATP (Adenosine Triphosphate) to move. We have three ways to get it:

The Anaerobic Systems (No Oxygen)

1. ATP-PC System: Uses Phosphocreatine. Lasts 5–10 seconds. Great for a shot put or a 100m sprint start.
2. Anaerobic Glycolytic System: Breaks down glycogen. Lasts 10–90 seconds. Produces Lactic Acid. Think of a 400m sprint. If you go too hard, you hit OBLA (Onset of Blood Lactate Accumulation) and your muscles "burn."

The Aerobic System (With Oxygen)

This is for long-duration stuff like a 5000m run. It involves Glycolysis, the Kreb’s Cycle, and the Electron Transport Chain. It even uses Beta Oxidation to turn fat into energy!

Energy Continuum

Most sports aren't just one system. A football player uses the Aerobic system to jog around for 90 minutes but uses the ATP-PC system for a sudden 5-meter sprint to the ball. This mix is called the Energy Continuum.

Recovery: EPOC

After exercise, you keep breathing hard. This is Excess Post-exercise Oxygen Consumption (EPOC). Your body is "paying back" the Oxygen Deficit you created at the start. It's busy clearing out lactic acid and restoring your ATP/PC stores.

Key Takeaway: Energy Systems

Speed/Power = ATP-PC.
High intensity but longer = Lactic Acid/Glycolytic.
Long duration/Low intensity = Aerobic.

Final Encouragement: You've made it through the "engine room" of PE! Understanding how these systems interact is the secret to explaining why athletes perform the way they do. Keep reviewing the definitions and try to apply them the next time you're watching a match or working out!