Obesity — Causes, Effects and Links to Performance

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.

---

What Is Obesity?

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.

---

Causes of Obesity

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

---

Effects of Obesity on Sporting Performance

This is a crucial section for AQA GCSE PE. Obesity negatively affects multiple components of fitness, limiting sporting performance in several ways.

1. Limits Stamina (Cardiovascular Endurance)

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.

2. Limits Flexibility

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.

3. Limits Agility

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.

4. Limits Speed and Power