A cartwheel is performed mainly in which plane and about which axis?

Frontal plane, sagittal (anteroposterior) axis

Transverse plane, longitudinal axis

Frontal plane, longitudinal axis

Frontal plane, sagittal (anteroposterior) axis

Which joint of the body is a saddle joint?

The carpometacarpal joint of the thumb

Which statements about muscle attachments and actions are correct? Select all that apply.

The triceps brachii inserts on the olecranon and extends the elbow

The gastrocnemius inserts on the calcaneus through the Achilles tendon

The triceps brachii inserts on the olecranon and extends the elbow

The gastrocnemius inserts on the calcaneus through the Achilles tendon

Assertion (A): Most levers in the human body are third-class levers. Reason (R): Third-class levers have a mechanical advantage greater than 1 and so save muscular effort. Choose the correct option.

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Kinematics differs from kinetics in that kinematics

describes motion (displacement, velocity, acceleration, angles) without regard to the forces causing it

Why are children given shorter, lighter bats and rackets than adults?

A shorter, lighter implement reduces the resistance arm and moment of inertia, so a weaker child can swing it with control

Rules forbid children from using long levers

A shorter implement turns a third-class lever into a second-class lever

A shorter implement always produces a faster ball speed for any player

A shorter, lighter implement reduces the resistance arm and moment of inertia, so a weaker child can swing it with control

Kinesiology and Biomechanics I: Meaning and Modern Trends, the Planes and Axes of the Human Body, Joints and their Movements, the Origin, Insertion, Action and Leverage of the Principal Muscles Used in Sports, and Mechanical Advantage and the Applications of Levers in Sports

Unit III is the mechanics of human movement. This chapter lays its anatomical foundation: what kinesiology and biomechanics are and how modern tools have changed them; the three planes and three axes in which every sporting movement can be described; the classes of joint and the movements each allows; the attachments, actions and leverage of the muscles that matter most in sport; and the three classes of lever, with mechanical advantage worked as effort arm divided by resistance arm. The platform's physics chapters teach levers and torque as physics; here they are applied to the body and to sports equipment.

1. Kinesiology, biomechanics and modern trends

Kinesiology (from the Greek kinesis, movement) is the study of human movement; in the narrower, classical sense used in this unit it is the study of movement from the standpoint of anatomy and mechanics: which joints move, which muscles act, and how. Biomechanics applies the principles of mechanics to living bodies. It has two branches: kinematics, which describes motion (displacement, velocity, acceleration, angles and timing) without regard to its causes, and kinetics, which studies the forces and torques that cause motion (gravity, ground reaction force, friction, muscle force, air and water resistance). Both are divided into linear and angular. Statics deals with bodies at rest or in equilibrium, and dynamics with bodies in motion.

The purposes of sports biomechanics are to improve technique and performance, to prevent injury, to design better equipment and facilities, and to support teaching and rehabilitation. Modern trends have transformed it from film and hand-drawn stick figures into a data science: high-speed video and three-dimensional motion capture with reflective markers, and increasingly markerless systems using computer vision; force platforms that measure ground reaction forces; electromyography (EMG) that records muscle activity; wearable inertial sensors, GPS units and pressure insoles that take the laboratory onto the field; computer modelling and simulation of techniques; and machine learning applied to large sets of movement data. Ball-tracking systems in cricket and tennis and video review in football are biomechanics and kinematics put to officiating.

2. Planes and axes of the human body

Movements are described from the anatomical position: standing upright, facing forward, arms at the sides with palms facing forward. Three imaginary planes pass through the body at right angles, and each movement occurs in a plane and about an axis perpendicular to it. The sagittal (median) plane divides the body into right and left; movement in it occurs about the frontal (transverse or mediolateral) axis, which runs from side to side: flexion and extension, as in running, a forward somersault, a biceps curl or kicking a ball. The frontal (coronal) plane divides the body into front and back; movement in it occurs about the sagittal (anteroposterior) axis, which runs from front to back: abduction, adduction and lateral flexion, as in a cartwheel or a jumping jack. The transverse (horizontal) plane divides the body into upper and lower parts; movement in it occurs about the longitudinal (vertical) axis: rotation, as in a pirouette, the turn of a discus thrower or a golf swing's trunk rotation.

Plane	Axis	Movements	Sporting example
Sagittal	Frontal (mediolateral)	Flexion, extension, dorsiflexion, plantar flexion	Running, forward somersault, squat, kicking
Frontal	Sagittal (anteroposterior)	Abduction, adduction, lateral flexion, inversion, eversion	Cartwheel, jumping jack, side-step
Transverse	Longitudinal (vertical)	Medial and lateral rotation, pronation, supination, horizontal abduction and adduction	Pirouette, discus turn, full twist in diving

⚠️ The axis is named differently from the plane

Movement in the sagittal plane turns about the frontal axis, and movement in the frontal plane about the sagittal axis. The names cross over because each axis is perpendicular to its plane. Only the transverse plane pairs with an axis of a different name altogether, the longitudinal.

3. Joints and their movements

Joints are classified by structure and by movement. Fibrous joints (synarthroses), such as the sutures of the skull, are immovable. Cartilaginous joints (amphiarthroses), such as the intervertebral discs and the pubic symphysis, are slightly movable. Synovial joints (diarthroses) are freely movable and are the joints of sport: the bone ends are covered with articular cartilage and enclosed in a capsule lined by synovial membrane, which secretes lubricating synovial fluid, and ligaments reinforce the capsule. Synovial joints are subdivided by the shape of their surfaces, which determines the movements and number of axes they allow.

Synovial joint type	Axes	Movements	Examples
Ball and socket	Three (multiaxial)	Flexion, extension, abduction, adduction, rotation, circumduction	Shoulder, hip
Hinge	One (uniaxial)	Flexion and extension	Elbow (humero-ulnar), ankle, interphalangeal joints; the knee is a modified hinge
Pivot	One (uniaxial)	Rotation	Atlanto-axial joint (turning the head), proximal radio-ulnar joint
Condyloid (ellipsoid)	Two (biaxial)	Flexion, extension, abduction, adduction	Wrist (radiocarpal), knuckles
Saddle	Two (biaxial)	Flexion, extension, abduction, adduction, opposition	Carpometacarpal joint of the thumb
Gliding (plane)	Non-axial	Sliding	Intercarpal and intertarsal joints

The principal movement terms are flexion (decreasing the angle between segments) and extension (increasing it; hyperextension beyond the anatomical position); abduction (away from the midline) and adduction (towards it); medial and lateral rotation; circumduction, the circular, cone-shaped movement combining flexion, abduction, extension and adduction; pronation and supination of the forearm (palm down and palm up); dorsiflexion and plantar flexion at the ankle (toes up and pointing the toes); inversion and eversion of the foot (sole inward and outward); and elevation, depression, protraction and retraction of the shoulder girdle. Range of motion depends on the shape of the joint surfaces, ligaments and capsule, muscle bulk and extensibility, and training.

4. Origin, insertion, action and leverage of the principal muscles

A muscle's origin is its attachment to the more stable bone, usually proximal, and its insertion its attachment to the bone it moves, usually distal; when it contracts it pulls the insertion towards the origin. Its action follows from the line of pull relative to the joint axis, and its leverage from how far from the joint it inserts. In a concentric contraction the muscle shortens (lifting); in an eccentric contraction it lengthens under tension (lowering, landing, braking); in an isometric contraction it produces force without changing length (holding a plank).

Muscle	Origin	Insertion	Main action	Sporting use
Biceps brachii	Short head: coracoid process; long head: supraglenoid tubercle of the scapula	Radial tuberosity	Elbow flexion, forearm supination	Pull-up, rowing, lifting
Triceps brachii	Infraglenoid tubercle and back of the humerus	Olecranon process of the ulna	Elbow extension	Push-up, shot put, throwing
Deltoid	Clavicle, acromion and spine of the scapula	Deltoid tuberosity of the humerus	Shoulder abduction (middle fibres)	Overhead lifts, serving
Pectoralis major	Clavicle, sternum and costal cartilages	Lateral lip of the bicipital groove of the humerus	Horizontal adduction, medial rotation	Bench press, forehand, discus
Latissimus dorsi	Lower thoracic and lumbar spine, iliac crest	Bicipital groove of the humerus	Shoulder extension, adduction, medial rotation	Swimming pull, pull-up
Rectus abdominis	Pubic crest and symphysis	Xiphoid process and costal cartilages 5–7	Trunk flexion	Sit-up, pike
Gluteus maximus	Ilium, sacrum and coccyx	Gluteal tuberosity and iliotibial band	Hip extension, lateral rotation	Sprinting, jumping, climbing
Iliopsoas	Lumbar vertebrae and iliac fossa	Lesser trochanter of the femur	Hip flexion	Knee drive in sprinting, kicking
Quadriceps femoris	Rectus femoris: anterior inferior iliac spine; vasti: femur	Tibial tuberosity via the patella and patellar ligament	Knee extension (rectus femoris also flexes the hip)	Jumping, kicking, squatting
Hamstrings	Ischial tuberosity (biceps femoris short head: femur)	Tibia and fibula	Knee flexion, hip extension	Sprinting; commonly strained in sprinters
Gastrocnemius	Medial and lateral condyles of the femur	Calcaneus via the Achilles tendon	Plantar flexion, knee flexion	Take-off, sprinting, jumping

5. Levers and mechanical advantage in sport

A lever is a rigid bar that turns about a fixed point, the fulcrum (axis), when a force is applied. It has three elements: the fulcrum, the effort (force) and the resistance (load). The effort arm (force arm) is the perpendicular distance from the fulcrum to the line of the effort, and the resistance arm (load arm) the perpendicular distance from the fulcrum to the line of the resistance. In the body, bones are the bars, joints are the fulcrums, muscles supply the effort and the weight of the segment plus any object held is the resistance. Levers are classified by the arrangement of the three.

Class	Arrangement	Mechanical advantage	Body example	Other example
First	Fulcrum between effort and resistance (E–F–R)	Greater than, equal to or less than 1	Nodding the head at the atlanto-occipital joint; triceps extending the elbow	Seesaw, crowbar, scissors
Second	Resistance between fulcrum and effort (F–R–E)	Always greater than 1	Rising on the toes: fulcrum at the ball of the foot, body weight through the ankle, calf muscles pulling on the heel	Wheelbarrow, nutcracker
Third	Effort between fulcrum and resistance (F–E–R)	Always less than 1	Biceps flexing the elbow; most limb movements	Tweezers; a bat, racket or hockey stick swung from the hands

Mechanical advantage (MA) = effort arm ÷ resistance arm, which for a lever in balance equals resistance ÷ effort. An MA above 1 means that less effort than resistance is needed, a force advantage; an MA below 1 means that more effort is needed, but the resistance end moves farther and faster than the point where effort is applied, a speed and range-of-motion advantage. The biceps inserts about 4–5 cm from the elbow while the hand is about 30–35 cm away, so the muscle must pull with several times the weight held, but the hand moves several times faster than the insertion. Most levers in the body are third class because sport needs speed at the end of the limb more than force.

Worked example: a forearm holds a 40 N ball in the hand, 32 cm from the elbow; the biceps inserts 4 cm from the elbow. MA = 4 ÷ 32 = 0.125, and the biceps force needed to hold the ball (ignoring the weight of the forearm) is 40 × 32 ÷ 4 = 320 N, eight times the load. In sport, levers are lengthened to gain speed: a longer bat, racket or golf club, or a straight arm at release, increases the resistance arm and the linear speed of the striking end for a given angular speed, provided the performer is strong enough to swing it; beginners and children are given shorter, lighter implements because they cannot. Shortening a lever makes it easier to move: a sprinter tucks the heel close to the buttock during the recovery swing so that the leg comes through quickly.

🧠 FRE — the middle letter tells the class

Write F, R, E for the element in the middle: Fulcrum in the middle is first class, Resistance in the middle is second class, Effort in the middle is third class. Second class always gives force (MA above 1); third class always gives speed (MA below 1).

Key takeaways

Kinesiology studies movement anatomically and mechanically; biomechanics divides into kinematics (describing motion) and kinetics (its causes), each linear and angular.
Sagittal-plane movements (flexion, extension) turn about the frontal axis, frontal-plane movements (abduction, adduction) about the sagittal axis, and transverse-plane rotations about the longitudinal axis.
Synovial joints are ball and socket (shoulder, hip), hinge (elbow), pivot (atlanto-axial), condyloid (wrist), saddle (thumb) and gliding (intercarpal).
A muscle pulls its insertion towards its origin; the biceps inserts on the radial tuberosity, the triceps on the olecranon and the gastrocnemius on the calcaneus via the Achilles tendon.
Mechanical advantage = effort arm ÷ resistance arm; second-class levers always exceed 1, third-class levers are always below 1 and trade force for speed, which is why most body levers are third class.

Practice questions (10)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

The biceps inserts 4 cm from the elbow joint and a ball is held in the hand 32 cm from the elbow. What is the mechanical advantage of this lever? Type the number as a decimal.
Numerical answer — type the value.
Show answer
Answer: 0.125
MA = effort arm ÷ resistance arm = 4 ÷ 32 = 0.125, less than 1, as it always is for a third-class lever. Dividing the other way gives 8, which is the ratio of muscle force to load, not the mechanical advantage.
In the same arm, the ball in the hand weighs 40 N. Ignoring the weight of the forearm, what force in newtons must the biceps exert to hold the forearm horizontal? Type the number.
Numerical answer — type the value.
Show answer
Answer: 320
For balance, effort × effort arm = resistance × resistance arm, so effort = 40 × 32 ÷ 4 = 320 N, eight times the load. This is the price the body pays for the speed advantage of a third-class lever.
A cartwheel is performed mainly in which plane and about which axis?
1. Transverse plane, longitudinal axis
2. Sagittal plane, frontal axis
3. Frontal plane, longitudinal axis
4. Frontal plane, sagittal (anteroposterior) axis
Show answer
Answer: D — Frontal plane, sagittal (anteroposterior) axis
A cartwheel turns sideways, in the frontal plane, about an axis running from front to back, the sagittal axis. A forward somersault would be sagittal plane and frontal axis, and a pirouette transverse plane and longitudinal axis.
Rising onto the toes, with the fulcrum at the ball of the foot, body weight acting through the ankle and the calf muscles pulling on the heel, is an example of a
1. pulley system with no lever
2. first-class lever
3. third-class lever
4. second-class lever
Show answer
Answer: D — second-class lever
The resistance (body weight at the ankle) lies between the fulcrum (ball of the foot) and the effort (Achilles tendon at the heel), the F–R–E arrangement of a second-class lever, whose mechanical advantage is always above 1.
Which joint of the body is a saddle joint?
1. The radiocarpal (wrist) joint
2. The carpometacarpal joint of the thumb
3. The hip joint
4. The atlanto-axial joint
Show answer
Answer: B — The carpometacarpal joint of the thumb
The thumb's carpometacarpal joint is the classic saddle joint, allowing opposition. The atlanto-axial joint is a pivot, the hip a ball and socket, and the wrist's radiocarpal joint a condyloid joint.
Which statements about muscle attachments and actions are correct? Select all that apply.
1. The triceps brachii inserts on the olecranon and extends the elbow
2. The gastrocnemius inserts on the calcaneus through the Achilles tendon
3. The iliopsoas extends the hip
4. The hamstrings extend the knee
Show answer
Answer: A — The triceps brachii inserts on the olecranon and extends the elbow; B — The gastrocnemius inserts on the calcaneus through the Achilles tendon
The gastrocnemius reaches the heel via the Achilles tendon, and the triceps extends the elbow from its olecranon insertion. The hamstrings flex the knee and extend the hip, and the iliopsoas flexes the hip.
Assertion (A): Most levers in the human body are third-class levers. Reason (R): Third-class levers have a mechanical advantage greater than 1 and so save muscular effort. Choose the correct option.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: C — A is true, but R is false
A is true: most limb movements, such as elbow flexion by the biceps, are third class. R is false: a third-class lever always has a mechanical advantage below 1; it costs extra force and gains speed and range at the end of the limb.
Kinematics differs from kinetics in that kinematics
1. deals only with bodies at rest
2. describes motion (displacement, velocity, acceleration, angles) without regard to the forces causing it
3. studies the forces and torques that cause motion
4. deals only with angular motion
Show answer
Answer: B — describes motion (displacement, velocity, acceleration, angles) without regard to the forces causing it
Kinematics describes motion; kinetics explains it through forces and torques. Both have linear and angular forms, and bodies at rest are the province of statics.
Why are children given shorter, lighter bats and rackets than adults?
1. Rules forbid children from using long levers
2. A shorter implement turns a third-class lever into a second-class lever
3. A shorter implement always produces a faster ball speed for any player
4. A shorter, lighter implement reduces the resistance arm and moment of inertia, so a weaker child can swing it with control
Show answer
Answer: D — A shorter, lighter implement reduces the resistance arm and moment of inertia, so a weaker child can swing it with control
A long lever gives more end speed only if the performer can swing it; a shorter, lighter implement is easier to control for a weaker child. Shortening does not change the class of lever, which depends on the arrangement of fulcrum, effort and resistance.
Which of the following movements take place in the transverse plane about the longitudinal axis? Select all that apply.
1. The turn of a discus thrower
2. A forward roll
3. A pirouette in dance
4. Forearm pronation
Show answer
Answer: A — The turn of a discus thrower; C — A pirouette in dance; D — Forearm pronation
Rotations such as the discus turn, a pirouette and forearm pronation occur in the transverse plane about the longitudinal axis. A forward roll is flexion in the sagittal plane about the frontal axis.