Kicks

Side kick (yoko-geri / yop chagi)

Names by art: Taekwondo: yop chagi 옆차기 · Karate: yoko-geri kekomi 横蹴り蹴込み · Savate: chassé latéral · Kung fu: ce chuai 側踹

In the side kick the heel drives in a straight line, with hip, knee and heel aligned behind it. That alignment is the whole point: a study of elite taekwon-do athletes found that far more of the body’s mass took part in the side kick than in the turning kick, and the impact force was higher.

⚠ Train with an instructor. Learn and practise this technique only under a qualified instructor, on a suitable surface and with a cooperative partner. This page explains; it does not replace a teacher.

Diagram 1. Hip, knee and heel on one line (dashed) behind the force F. The blue line marks where peak speed was reached in a case study: at 82% of full leg extension (Wąsik, 2011).

F: force through the heel
CM: centre of mass
82%: fraction of full leg length

Step by step

Turn side-on to the target and bring the knee of the kicking leg up across the body (chamber), foot pulled back.
Pivot the supporting foot so its heel points towards the target.
Drive the heel out in a straight line, extending hip and knee together; the edge or the heel of the foot leads.
At impact, hip, knee and heel are in one line; the trunk leans away but the head looks at the target.
Pull back to the chamber before putting the foot down.

Common errors

Toes pointing up: the kick becomes a weak front kick turned sideways.
Bending at the waist so the hips stay behind — the line breaks and less mass goes into the target.
Not pivoting the supporting foot, which twists the supporting knee.
Kicking with the toes instead of the heel or the outer edge of the foot.

Biomechanics: what the body does

Main muscles

Gluteus maximus and medius (hip extension and abduction), quadriceps, tensor fasciae latae; trunk lateral flexors (obliques, quadratus lumborum) hold the line; the supporting leg works isometrically.

Joints

Hip (abduction and extension), knee (extension), ankle (dorsiflexion, so the heel leads); supporting ankle and hip rotate during the pivot.

Kinetic chain

In a case study of one black belt, knee speed during the lift almost fully predicted foot speed (r = 0.97), and the total kick time depended on that knee speed (r = 0.75) (Wąsik, 2011). The chamber is not a pause: it is where the speed starts.

Base and balance

A narrow base, one foot. The trunk leans away as a counterweight; because the force goes straight back along the leg into the hip, a well-aligned kick also pushes the kicker backwards — the supporting leg must resist it.

Physics and maths

F̄ · Δt = m_ef · Δv

With similar foot speeds, the kick with more effective mass behind it delivers more impulse.

F_1→2 = −F_2→1

Newton’s third law (1 = foot, 2 = target): the target pushes back on the heel with the same force, along the line of the leg.

What studies measured

Góra et al., 2025: 5 elite female ITF taekwon-do athletes (64.2 ± 5.8 kg), 100 kicks. Side kick mean peak force 1770 N versus 1379 N for the turning kick (p < 0.01). Effective mass ≈ 85% of body mass for the side kick and ≈ 18% for the turning kick; segment accelerations showed the opposite trend.
Wąsik, 2011: case study, one male black belt, four side kicks as used in board breaking. Knee vs foot speed r = 0.97; total time vs knee speed r = 0.75; maximum speed at 82% of full leg length.

Our calculation from cited data
With 64.2 kg mean body mass (Góra et al., 2025): 85% ≈ 54.6 kg behind the side kick versus 18% ≈ 11.6 kg behind the turning kick — almost five times more mass. The force was only about 1.28 times higher (1770 / 1379), because the turning kick moves its smaller mass faster.

A case study of one athlete (Wąsik, 2011) shows a pattern, not a rule for everybody.

Diagram 2. Mean peak impact force in five elite female ITF athletes, 100 kicks in total (Góra et al., 2025).

N: newtons

Numbers come from the cited studies, with their sample and conditions. They describe those athletes in that laboratory, not every practitioner.

Comparison across arts

The straight, heel-first line is common to all; height, surface and purpose vary.

Art	Surface	Height / style	Typical use
Taekwondo (yop chagi)	Heel or blade of the foot	Mid to high	Stopping an advance; breaking (ITF)
Karate (yoko-geri kekomi)	Heel / edge (sokuto)	Mostly mid-level thrust; keage is the snapping version	Kata and kihon; counters
Savate (chassé latéral)	Sole of the shoe	Low to high, very fast	Keeping distance; stop-kicks

Safety

Never kick a partner’s knee from the side — the joint does not bend that way. In training, target the body with protection.
Practise the alignment slowly against a wall or a heavy bag before adding speed.
Warm up the hip abductors and the lower back.

Train with an instructor. Learn and practise this technique only under a qualified instructor, on a suitable surface and with a cooperative partner. This page explains; it does not replace a teacher.

Taekwondo Karate Savate Kung Fu Kickboxing

Straight punch (reverse punch / cross) Front kick (mae-geri / teep / ap chagi) Roundhouse kick (mawashi-geri / dollyo chagi / Thai kick) Breakfalls (ukemi) Major outer reap (o-soto-gari) Shoulder throw (seoi-nage) Rear naked choke (mata-leão / hadaka-jime) Cross armlock (juji-gatame / armbar)

Sports science bibliography Code of Honour Glossary

Sources

Tomasz Góra, Jacek Wąsik, Dariusz Mosler & Dorota Ortenburger (2025). Relationship of kinetic and somatic variables to kicking strength in female taekwon-do athletes. Acta of Bioengineering and Biomechanics 27(1). DOI 10.37190/abb-02592-2025-02
Jacek Wąsik (2011). Kinematic analysis of the side kick in Taekwon-do. Acta of Bioengineering and Biomechanics 13(4), 71–75. pubmed.ncbi.nlm.nih.gov/22339376/
Joseph Hamill, Kathleen M. Knutzen & Timothy R. Derrick (2015). Biomechanical Basis of Human Movement (4th ed.). Wolters Kluwer. ISBN 9781451177305

Cite / use this content

You may quote short excerpts with a visible link to this page. Suggested citation:

Wabukan (2026). “Side kick (yoko-geri / yop chagi)”. https://wabukan.com/manual/pontape-lateral (accessed 2026-10-30).

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