What is posture?
Posture is the position you keep your body in when you stand, sit, lie down or move. Good posture puts the least strain on muscles and joints.
The line of gravity
Hang a string with a small weight (a plumb line). Stand sideways next to it. In good posture these five points are on the line: ear, shoulder, hip, knee, ankle.
The S-shaped spine
The spine has 33 small bones called vertebrae. Seen from the side it has three curves:
- Neck (cervical) curve bends forward.
- Upper-back (thoracic) curve bends backward.
- Lower-back (lumbar) curve bends forward.
These curves spread the body's weight and soften shocks when you walk, run and jump, like a spring. From the front, a healthy spine looks straight.
Posture faults: kyphosis, lordosis, flat back, scoliosis, text neck
A posture fault is a habit or shape that moves the body away from the line of gravity. Mild faults come from habits and weak or tight muscles. Serious ones need a doctor.
- Kyphosis (round back): the upper back curves too much; shoulders and head move forward.
- Lordosis (hollow back): the lower back curves in too much; belly and bottom stick out.
- Flat back: the lower-back curve is lost; the spine absorbs shocks badly.
- Scoliosis: the spine bends sideways in a C or S. One shoulder or hip looks higher.
- Forward head (text neck): the head sits in front of the shoulders, often from phones.
Other faults seen in PE checks: knock knees (knees touch, ankles apart), bow legs (knees apart) and flat feet (no arch).
Why faults happen
Long sitting, heavy one-sided bags, soft sagging mattresses, screens below eye level, weak core and back muscles, fast growth in the teen years, and sometimes birth or illness.
Correcting faults: exercise programmes for each body part
Correction works on one idea: stretch the tight side, strengthen the weak side. Analytic exercises train one body segment at a time (neck, shoulders, back, abdomen, hips, legs).
| Fault | Stretch | Strengthen |
|---|---|---|
| Round back | chest (doorway stretch) | upper back: shoulder-blade squeeze, rowing |
| Hollow back | hip front and lower back | abdomen: plank, curl-ups |
| Flat back | back of thigh | back extensors: superman, bridge |
| Text neck | chest and front neck | chin tucks, upper back |
| Mild scoliosis | as advised | symmetric core work; doctor's plan |
Types of programmes
- Stretching: hold each stretch 20 to 30 seconds, no bouncing.
- Aerobic gymnastics: rhythmic moves to music, 20 to 40 minutes, for heart and lungs.
- Light-resistance work: elastic bands, light dumbbells, medicine balls, your own body weight; 2 to 3 sets of 10 to 15 slow repeats.
- Bodybuilding-type and adapted programmes: muscle strength for each segment; teens use light loads and perfect form; programmes are adapted for anyone with a health need.
Equipment: mats, wall bars, benches, Swiss balls, bands, dumbbells. Routines can be done indoors (gym, home) or outdoors (park, track), and as leisure-time fitness 3 to 5 times a week.
Measuring physical development and body functions
Physical development indicators show how a body grows. Height, body mass, chest size, arm span and BMI (body mass in kg / height in m squared) are compared with charts for the same age and sex, because girls and boys grow at different times.
Body functions at rest and after effort
| Value | At rest (teen) | Right after hard effort |
|---|---|---|
| Heart rate | 60 to 100 beats/min | up to about 220 minus age |
| Breathing rate | 12 to 20 breaths/min | 30 to 50 breaths/min |
| Blood pressure | about 110/70 mmHg | top number rises |
Recovery: count your pulse 1, 2 and 3 minutes after effort. A fitter body returns to its resting value faster.
How much activity?
Global health guidance: children and teens about 60 minutes of moderate to vigorous activity a day, with muscle- and bone-strengthening work 3 days a week; adults 150 to 300 minutes a week. Each sport shapes the body in its own way: swimmers build wide shoulders, runners light legs. Balance it with work for the other body parts.
Try it: the wall test and your posture diary
- Stand with heels, bottom, upper back and head touching a wall.
- Slide a hand into the gap behind your lower back. About one flat hand fits = normal. A fist fits = possible hollow back. No gap = possible flat back.
- If your head cannot touch the wall without lifting the chin, you may have a forward head.
- Ask a friend to check from behind: are both shoulders and both hips level?
- For one week, write how many hours you sit and look down at screens. Then try the 20-minute rule: every 20 minutes, stand up and roll your shoulders.
Then open the 3D (last step) and match your result to a posture.
Key formulas and definitions
- Good posture line: ear - shoulder - hip - knee - ankle in one vertical line
- BMI = body mass (kg) / height (m)²
- Maximum heart rate ≈ 220 - age
- Correction rule: stretch the tight side + strengthen the weak side
- Neck load ≈ 5 kg (0°), 12 kg (15°), 18 kg (30°), 22 kg (45°), 27 kg (60°)
Worked examples
1. Riya is 1.60 m tall and has a mass of 51.2 kg. Find her BMI and say what it means.
BMI = 51.2 / (1.60 × 1.60) = 51.2 / 2.56 = 20. For a teen this is compared with an age-and-sex chart; 20 is in the healthy range for most 15-17 year olds.
2. Arjun's resting pulse is 72 beats/min. After a 400 m run it is 168. After 1 min it is 120, after 3 min 84. What does this show?
The heart rate rose by 96 beats/min during effort. It fell by 48 in the first minute and is only 12 above rest after 3 minutes. Fast recovery shows good fitness.
3. A student stands sideways. The ear and shoulder are 6 cm in front of the hip line, and the upper back looks rounded. Name the fault and plan two exercises.
Round back (kyphosis) with forward head. Stretch the tight chest (doorway stretch, 3 × 30 s). Strengthen the weak upper back (shoulder-blade squeeze 10 × 5 s, band rowing 3 × 12). Add chin tucks for the neck.
4. How old is a person whose maximum heart rate is about 204 beats/min? What is 70% of it?
220 - age = 204, so age = 16. 70% of 204 = 0.7 × 204 ≈ 143 beats/min, a good target for steady aerobic training.
Common mistakes
- Thinking a perfect spine is straight from the side. It has three natural curves; only from the front should it look straight.
- Pulling the shoulders far back and pushing the chest out like a soldier. That causes a hollow back; posture should be relaxed and tall.
- Doing only strength work. Correction needs both: stretch the tight muscles and strengthen the weak ones.
- Ignoring a big sideways curve or pain. Mild faults can be fixed with exercise; scoliosis or pain needs a doctor.