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Obesity is one of the most significant health issues facing the UK today, and it is a key topic for AQA GCSE PE. This lesson covers the causes of obesity, its effects on physical and mental health, and crucially, how it affects sporting performance. You must be able to explain these effects in detail and link them to the components of fitness.
Obesity is a condition in which a person has an excessively high proportion of body fat. It is typically measured using the Body Mass Index (BMI).
| BMI Category | BMI Range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 and above |
However, BMI has limitations — it does not distinguish between muscle mass and fat mass. A muscular rugby player might have a high BMI but not be obese. For this reason, other measures such as waist circumference and skinfold tests are also used.
Exam Tip: If asked to evaluate BMI as a measure of obesity, always mention that it does not account for muscle mass. A weightlifter with very low body fat could be classified as "obese" by BMI alone. This is a very common exam question.
Obesity occurs when a person consistently takes in more energy (calories) than they expend — a positive energy balance over a prolonged period.
| Cause | Detail |
|---|---|
| Overeating | Consuming too many calories, particularly from high-fat and high-sugar foods |
| Sedentary lifestyle | Not enough physical activity to burn the calories consumed |
| Poor diet quality | Reliance on processed food, fast food and sugary drinks |
| Genetics | Some people are genetically predisposed to store fat more easily |
| Medical conditions | Conditions like hypothyroidism can contribute to weight gain |
| Socio-economic factors | Healthier food is often more expensive; lower-income areas may have fewer exercise options |
| Psychological factors | Comfort eating in response to stress, anxiety or depression |
| Portion sizes | Portion sizes have increased significantly over the decades |
This is a crucial section for AQA GCSE PE. Obesity negatively affects multiple components of fitness, limiting sporting performance in several ways.
| Effect | Explanation |
|---|---|
| Greater body mass to move | An obese person must work harder to move their larger body, requiring more energy and oxygen |
| Heart under more strain | The heart must pump harder to supply blood to a larger body mass |
| Faster fatigue | The cardiovascular system reaches its limit sooner, leading to earlier exhaustion |
| Reduced aerobic capacity | Excess fat does not contribute to movement but still requires blood supply, reducing oxygen available for working muscles |
Impact on sport: An obese person would struggle in endurance activities such as long-distance running, swimming, football or hockey, where sustained cardiovascular effort is required.
| Effect | Explanation |
|---|---|
| Excess body fat restricts movement | Fat deposits around joints physically limit the range of movement |
| Reduced joint mobility | Additional weight puts strain on joints, reducing their ability to move freely |
| Difficulty performing certain movements | Bending, twisting and stretching are all harder with excess body fat |
Impact on sport: Reduced flexibility affects sports like gymnastics, martial arts, swimming strokes and any activity requiring a full range of movement.
| Effect | Explanation |
|---|---|
| Slower change of direction | Greater body mass requires more force to stop, start and change direction |
| Reduced balance | A higher centre of mass and wider body shape make balance changes more difficult |
| Increased momentum | Heavier bodies carry more momentum, making quick direction changes harder |
Impact on sport: Agility is essential in sports like tennis, badminton, football, basketball and netball, where quick changes of direction are required.
| Effect | Explanation |
|---|---|
| Lower power-to-weight ratio | Excess fat adds weight without contributing any force — the same muscles must now move a heavier body |
| Reduced acceleration | More force is needed to accelerate a greater mass (Newton's Second Law: F = ma) |
| Reduced maximum speed | The additional weight creates more friction and resistance, limiting top speed |
Impact on sport: Speed and power are essential in sprinting, jumping, throwing and most team sports. An obese athlete would be significantly disadvantaged.
| Health Condition | How Obesity Increases the Risk |
|---|---|
| Coronary heart disease (CHD) | Excess fat increases cholesterol, leading to fatty deposits in coronary arteries |
| Type 2 diabetes | Excess fat causes insulin resistance, leading to high blood sugar |
| High blood pressure (hypertension) | The heart must work harder to pump blood through a larger body |
| High cholesterol | Obesity raises LDL ("bad") cholesterol and lowers HDL ("good") cholesterol |
| Stroke | Hypertension and atherosclerosis increase the risk of blood clots in the brain |
| Some cancers | Obesity is linked to increased risk of bowel, breast and kidney cancers |
| Joint problems (osteoarthritis) | Excess weight puts strain on weight-bearing joints (knees, hips, ankles) |
| Breathing difficulties | Fat around the chest and abdomen restricts lung expansion |
| Mental Health Effect | Detail |
|---|---|
| Depression | Negative body image, reduced physical ability and social stigma can lead to depression |
| Low self-esteem | Feeling unhappy with appearance and physical limitations |
| Loss of confidence | Struggling with everyday tasks and exercise reduces confidence |
| Anxiety | Fear of judgement, especially in sporting or social settings |
| Social withdrawal | Embarrassment and low confidence may lead to avoiding social situations |
| Social Health Effect | Detail |
|---|---|
| Inability to socialise through sport | Physical limitations prevent participation in many activities |
| Social isolation | Low confidence and mobility issues may prevent people from leaving the house |
| Difficulty with employment | Obesity may limit the types of work a person can do, especially physical roles |
| Stigma and discrimination | Obese individuals may face prejudice and discrimination |
| Reduced quality of life | The combined physical, mental and social effects significantly reduce overall wellbeing |
Obesity, like a sedentary lifestyle, can create a self-reinforcing cycle:
graph TD
A[Obesity] --> B[Exercise is harder and more uncomfortable]
B --> C[Person avoids exercise]
C --> D[Energy expenditure decreases]
D --> E[Further weight gain]
E --> A
A --> F[Low self-esteem and depression]
F --> G[Comfort eating]
G --> E
style A fill:#ffcdd2,stroke:#c62828
style E fill:#ffcdd2,stroke:#c62828
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