Importance of physical and sports exercise – Physical Exercises and Health (Senior 4 Physical Education) | Ganzaa

Physical Exercises and Health

Lessons

Senior 4 · Physical Education

Physical Exercises and Health

4 lessons

Lesson 4 of 4

Importance of physical and sports exercise

25 min

Streets without cars

On the first and third Sunday of every month, some of Kigali's main roads close to motor vehicles in the early morning. Thousands of people walk, jog, cycle and join group aerobics on them. This is Car Free Day, a mass-sport event run by the City of Kigali and its partners since 2016. Its stated aim is health: to build a habit of sport that prevents non-communicable diseases (NCDs) such as heart disease, stroke and diabetes, and to keep the city's air clean. Health workers from the Rwanda Biomedical Centre (RBC) and the Rwanda NCD Alliance offer free check-ups there, such as blood pressure, blood glucose and body mass index.

Why would a city close its roads for exercise? This lesson brings together what you learned in the last three lessons to answer that question, measures your own activity against the World Health Organization (WHO) guidelines, and shows how to use, and when not to use, the body mass index.

Definition

Physical activity: any movement of the body by the skeletal muscles that uses energy, including walking to school, farming and housework. Exercise: planned, repeated physical activity done to improve or keep fitness. Sport: organised, competitive physical activity played to rules.

Moderate-intensity activity: activity that raises the heart rate and breathing, during which you can still talk but not sing (brisk walking). Vigorous-intensity activity: activity that makes you breathe hard, so you can say only a few words (running, a football match).

Sedentary behaviour: time spent sitting or lying with very low energy use while awake, such as watching screens.

Non-communicable disease (NCD): a disease that does not pass from person to person, such as heart disease, stroke, type 2 diabetes and many cancers.

Body mass index (BMI): $\text{BMI} = \frac{m}{h^{2}}$ , with mass $m$ in kilograms and height $h$ in metres, in $\mathrm{kg\,m^{-2}}$ .

Why exercise matters: four kinds of benefit

Area	Benefits
Physical health	Stronger heart and lungs; healthy blood pressure and blood sugar; strong bones and muscles; a healthy body weight; lower risk of heart disease, stroke, type 2 diabetes and some cancers later in life
Mental health and learning	Better mood and less anxiety and depression; better sleep; better attention, memory and thinking, which WHO lists among the benefits for young people
Social	Friendship, teamwork, fair play and respect for rules; a sense of belonging to a team, school or community
Economic	Fewer days lost to illness; lower health-care costs. WHO estimates that if inactivity does not fall, new cases of preventable disease will cost health systems about US$ 300 billion worldwide between 2020 and 2030

How much is enough? The WHO 2020 guidelines

Age	Aerobic activity	Strength	Sitting
5 to 17 years	An average of at least 60 minutes a day of moderate-to-vigorous activity, mostly aerobic, across the week; vigorous activity on at least 3 days a week	Muscle- and bone-strengthening activity on at least 3 days a week	Limit sedentary time, especially recreational screen time
18 to 64 years	150 to 300 minutes a week of moderate activity, or 75 to 150 minutes of vigorous activity, or an equivalent mix	Muscle-strengthening activity on at least 2 days a week	Limit sedentary time; replace it with any activity

WHO reported in 2024 that about 80% of adolescents and 31% of adults worldwide do not meet these levels. Any amount of activity is better than none.

Umutoni, a Senior 4 pupil, kept a log of her activity for one week:

Worked example 1: does Umutoni meet the guideline?

Total for the week: $75 + 40 + 90 + 35 + 70 + 120 + 20 = 450\,\text{min}$
Daily average: $\frac{450}{7} = 64.3\,\text{min per day}$ This is above 60, so she meets the aerobic guideline on average, even though four days are below 60 minutes.
Vigorous activity: Monday, Wednesday, Friday and Saturday, so 4 days; the guideline asks for at least 3. ✔
Strength: she must check that on at least 3 days her activity loads her muscles and bones, for example jumping, push-ups or squats in PE.

Advice. Her weak days are Tuesday, Thursday and Sunday. A 25-minute jog or skipping session on two of them would lift her average to about $\frac{500}{7} \approx 71$ minutes a day and make it less dependent on Saturday's football.

Using BMI, and its limits

BMI is a quick screening number for adults. WHO classes an adult BMI of 25 or more as overweight and 30 or more as obese; below 18.5 is underweight. For children and adolescents aged 5 to 19, the adult cut-offs do not apply: a young person's BMI must be compared with the WHO growth reference for their sex and age (overweight is more than 1 standard deviation above the median, obesity more than 2). BMI also cannot tell muscle from fat: a heavily muscled athlete can have a "high" BMI and be very healthy.

Worked example 2: two BMI calculations, two different rules

Mr Gatete, a 34-year-old teacher, has mass 82 kg and height 1.75 m: $\text{BMI} = \frac{82}{1.75^{2}} = \frac{82}{3.0625} = 26.8\,\mathrm{kg\,m^{-2}}$ As an adult, 26.8 is in the overweight range (25 to 29.9). Brisk walking for 30 minutes on 5 days (150 minutes a week) would meet the adult guideline.
Ishimwe, aged 16, has mass 52 kg and height 1.68 m: $\text{BMI} = \frac{52}{1.68^{2}} = \frac{52}{2.8224} = 18.4\,\mathrm{kg\,m^{-2}}$ It would be wrong to call him "underweight" from the adult table. At 16 his BMI must be read on the WHO BMI-for-age chart for boys; many healthy, still-growing teenagers have values like this.

Video: "How playing sports benefits your body ... and your brain" by Leah Lagos and Jaspal Ricky Singh, TED-Ed. Watch for the effects of regular exercise on the heart, the brain and mood.

Tip

Remember "60 a day, 3 to strengthen". Ages 5 to 17: an average of 60 minutes of moderate-to-vigorous activity a day, with vigorous and strengthening activity on at least 3 days a week.

Warning

Common mistakes. Applying the adult BMI cut-offs to pupils under 19. Forgetting to square the height in BMI. Thinking only sport counts: walking to school and active work count too. Counting a whole PE lesson as activity when much of it was spent standing and waiting: count only the active minutes.

✦

Practice

Distinguish between physical activity, exercise and sport, with an example of each.
Give one physical, one mental, one social and one economic benefit of regular exercise.
State the WHO 2020 recommendation for aerobic activity for people aged 5 to 17.
A pupil is active for 30, 45, 0, 60, 20, 90 and 40 minutes on the seven days of a week. Calculate the daily average and say whether she meets the guideline.
Calculate the BMI of an adult with mass 70 kg and height 1.60 m, and classify it.
Explain why the same BMI value can mean different things for a 15-year-old and a 40-year-old.
A rugby player has a BMI of 31. Evaluate the claim that he must be unhealthy.
Suggest two ways your school could help more pupils meet the WHO guideline, and say which guideline each helps with.

Show answersHide answers

Physical activity: any movement using energy (walking to market). Exercise: planned activity for fitness (a 20-minute jog). Sport: organised competitive activity with rules (a volleyball match).
For example: lower blood pressure; better mood or sleep; friendships and teamwork; fewer days lost to illness.
An average of at least 60 minutes a day of moderate-to-vigorous, mostly aerobic activity across the week, with vigorous activity and muscle- and bone-strengthening activity on at least 3 days a week.
Total = 285 min; 285 ÷ 7 = 40.7 min a day, below 60: she does not meet it.
70 ÷ 1.60² = 70 ÷ 2.56 = 27.3 kg m⁻²: overweight for an adult.
Adult cut-offs (25, 30) apply to the 40-year-old. For the 15-year-old, BMI changes normally with growth, so it must be compared with the WHO BMI-for-age reference for his or her sex and age.
Not necessarily true. BMI cannot separate muscle from fat; a rugby player carries a lot of muscle. Waist size, body-fat measures and fitness tests give a better picture.
For example: active breaks or a morning run (aerobic minutes); a strength circuit in PE three times a week (muscle and bone); clubs after school (vigorous activity); walking or cycling to school (daily minutes).

Quick check

Remember

Exercise brings physical, mental, social and economic benefits and lowers the risk of NCDs.
WHO 2020, ages 5 to 17: an average of 60 minutes a day of moderate-to-vigorous activity; vigorous and strengthening activity on 3 days a week; less screen time.
$\text{BMI} = \frac{m}{h^{2}}$ . Adult cut-offs: 25 overweight, 30 obese. Under 19, use WHO BMI-for-age charts.
Kigali's Car Free Day, on the first and third Sunday of each month, is mass sport for health.

1Streets without cars

2Why exercise matters: four kinds of benefit

3How much is enough? The WHO 2020 guidelines

4Using BMI, and its limits

Streets without cars

Why exercise matters: four kinds of benefit

How much is enough? The WHO 2020 guidelines

Using BMI, and its limits