Biomechanics is the study of movement, more specifically, the movement (technique) involved in a strength exercise, or in execution of a sports skill. It deals mainly with physical factors such as speed, mass, acceleration, levers, force, and the physical functions of the movement. Some think of biomechanics as the science of movement based on principles derived from physics and anatomy. It explains the “why” and “how” of a movement and strategies to improve it through scientifically-based modificatio

1. Concentric Strength. In a concentric contraction the muscles shorten and produce movement. Concentric strength is sometimes known as overcoming strength. In other words, when the muscle contracts, it overcomes the resistance and puts the object or your body into motion.

2. Eccentric Strength. In an eccentric contraction (often known as a yielding contraction), the muscle lengthens (stretches back to its original length) as it contracts. The more the muscle lengthens or the faster it is stretched the greater the tension that is developed. The eccentric contraction plays a very important role in controlling and stopping movement and in preparing the muscles for an explosive type contraction.

3. Isometric Strength. In an isometric contraction you exhibit strength, but there is no movement of the limbs. The muscle develops tension and there is some shortening of the muscle fibers and tendon, but there is no limb or body movement.

When executing a strength exercise, all three muscle contraction regimes are involved. As you perform a movement, the main muscles (agonists) undergo a concentric contraction while the opposing antagonist muscles undergo an eccentric contraction. The adjacent joints and parts of the body that are not in use are stabilized via the isometric contraction. Thus, all three muscle contraction regimes are in operation at the same time, each with a very important purpose.

A muscle can contract with different amounts of force and in different ways to produce different types of movement. This includes:

1. A sustained force movement in which there are continuous muscle contractions to keep moving a weight. In other words, force is applied by the prime muscles involved throughout the ROM.

2. Ballistic movement in which there is inertial movement after an explosive or quick, maximum force contraction. Usually there is pre-tensing of the muscle in the eccentric contraction so that the muscle can contract concentrically with maximum speed and quickness.

3. Guided movement occurs when both the agonist and the antagonist contract to control the movement. Guided movement is seen most often in fine skills such as when you are writing or when you must move the limb through a specific movement pattern.

4. Dynamic balance movements occur when there are constant agonist-antagonist muscle contractions to maintain a certain position or posture.

Also known as dorsi flexion, or the movement of the toe area of the foot toward the shin. In this action there is a combination of inversion at the subtalar joint and dorsiflexion at the ankle joint when executing ankle joint flexion. In dorsi flexion(raising the toe area of the foot toward the shin), the tibialis anterior, extensor digitorum longus, and peroneus tertius muscles are the major muscles involved. The toe raise exercise involves dorsi flexion.

The two movements of the foot in the subtalar joint are not true ankle joint movements but are usually referred to as ankle movements. They are inversion and eversion, which take place between the talus (ankle bone), the navicular (tarsal bone), and the calcaneus (heel bone). In inversion, also known as adduction or supination, the sole of the foot is turned inward and upward. In eversion the foot is turned outward and downward, that is, the toe area of the foot is pointed outward. These movements are an important part of the pushing-off actions required by athletes in many sports. Development of the muscles involved in eversion and inversion helps prevent ankle sprains. In running, pronation and supination respectively are the terms most commonly used for these actions.

In knee extension (the opposite of flexion) the shin moves away from the thigh (or vice versa) and the leg is straightened. When the knee is fully extended, the knee joint is locked in place and no rotation is possible. However, when the knee is flexed, the lower leg can be rotated in or out, but the range of movement is small. Rotation is used most often in the movement of pushing off and turning the body in a different direction. The quadriceps muscle group includes the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius muscles, which extend the knee. The Knee Extension (Leg Extension) exercise involves knee joint extension.

Movement of the thigh forward is called hip flexion. When you are in a standing position, flexion occurs when the leg is raised forward and upward approximately 45° without the pelvic girdle also rotating to increase ROM. When the leg is bent the ROM is increased, and the mass of the abdominal wall then stop hip joint flexion. The major muscles involved in hip joint flexion are the psoas, iliacus, pectineus, and rectus femoris. The Hip Flexion exercise can be done on a hip flexion machine or with active cords.

Hip Extension is the reverse of hip flexion. In this action the leg is brought down and back to the anatomical straight-line body position from a hip-flexed position. When the leg is in line with the body, it is stopped in its movement by the tension of the ligaments that cross the front of the hips and the psoas and iliacus muscles. The major muscles involved in hip joint extension are the hamstring muscle group and the gluteus maximus. The Hip Extension exercise can be done on a hip extension machine or with active cords.

In hip joint abduction(the opposite of hip joint adduction) the leg is moved from the midline out toward the side of the body. The usual range of motion is approximately 45 degrees. The exact amount depends on the tightness of the opposing muscles, tendons and ligaments. If the leg is raised higher the pelvis will have to go into motion to increase the ROM. The gluteus medius is the major muscle involved in hip joint abduction. The Hip Abduction exercise can be done on a hip abduction machine or with active cords.

In exercises such as the squat and lunge there is a combination of knee joint extension and hip joint extension. The muscles involved therefore are the muscles involved in knee extension and hip extension.

Extension is the return from a position of flexion to the anatomical position. It is the opposite of flexion. Going beyond the anatomical position (bending backward) is called hyperextension. Two sets of muscles are involved in extension of the spine: a deep spinal group and a superficial spinal group. The back raise exercise involves extension of the spine.

Shoulder (shoulder girdle) rotation, is a twisting action around the long axis of the spinal column. In this movement the shoulders (or hips) are in motion. Shoulder rotation can also occur with the axis in the left or right side of the body. Twisting exercises such as the standing twist or Russian twist involve shoulder (shoulder girdle) rotation.

Shoulder joint flexion is movement of the arm upward and in front of the body. The anterior deltoid, the pectoralis major (upper portion), and the coracobrachialis are the major muscles involved in shoulder joint flexion. The front arm raise exercise involves shoulder joint flexion.

Shoulder joint adduction is movement of the arm sideward and downward towards the body. The major muscles involved in shoulder joint adduction are the latissimus dorsi, the teres major, and the lower pectoralis major. The pronated wide grip variant of the lat pulldown exercise involves in shoulder joint adduction.

Shoulder joint horizontal adduction is movement of the arm horizontally towards the front of the body. In this action, also known as horizontal flexion, the major muscles are the pectoralis major, the coracobrachialis, and the anterior deltoid. The dumbbell fly (butterfly) exercise involves shoulder joint horizontal adduction.

Shoulder joint lateral rotation is rotation of the humerus outward. In this action the major muscles involved are the infraspinatus and the teres minor.

It is possible to elevate and depress the shoulder girdle. In this case the entire shoulder girdle (clavicle and scapula) is raised upward in an action called shoulder girdle elevation; lowering the shoulder girdle is called shoulder girdle depression. In the shoulder shrug exercise there is elevation of the clavicle and scapula, which involves the upper trapezius, levator scapulae, and rhomboids. In this action the shoulder girdle is raised directly upward (vertically).

In elbow joint extension the forearm moves away from the upper arm in an arm-straightening action. The reverse action, in which the upper arm moves away from the forearm, is also possible. This is seen in the lowering phase of a pull-up or chin-up. Only one major muscle is involved in elbow joint extension - the triceps brachii, which is a large muscle that covers the entire back side of the upper arm. The triceps pushdown exercise involves elbow joint extension.

Only two actions are possible in the radio-ulnar joint: supination and pronation. In pronation the forearm is rotated so that the hand is turned palm down. The pronator teres and the pronator quadratus muscles are involved in pronation. The exercise that most effectively develops the supinator and pronator muscles is supination and pronation with the Strength Bar.

The opposite movement of wrist joint flexion is wrist joint extension-hyperextension, in which the back of the hand moves toward the posterior surface of the forearm. The extensor carpi radialis longus and brevis and the extensor carpi ulnaris are involved in wrist joint extension-hyperextension. In this action the back of your hand moves toward your forearm from a wrist flexed position. The reverse wrist curl exercise involves wrist joint extension.

The opposite of wrist adduction is abduction, also known as radial flexion, in which the thumb side of the hand moves away from the body when the arm is in the anatomical position. In this the thumb side of the hand moves toward the forearm while the hand remains in line with the forearm. In radial flexion (hand abduction), the flexor carpi radialis and the extensor carpi radialis longus and brevis are involved. In this action the thumb side of the hand moves toward the forearm.

There are compound exercises that involve movements in both the should and elbow joint. The bench press exercise involves shoulder joint horizontal flexion (adduction) and elbow extension. The overhead press (military press) exercise involves shoulder joint flexion and elbow extension. The chin-up (supinated or neutral grip) exercise involves shoulder joint extension and elbow joint flexion.

The hamstring muscle group includes the semitendinosus, semimembranosus, and the biceps femoris. These muscles flex the knee.

The abdominal muscles include the rectus abdominis and the internal and external obliques. They are involved in spinal flexion and twisting.

The triceps brachii is the arm extensor muscle. It is a large muscle that covers the entire back side of the upper arm. It is divided into three sections, known as the lateral (outer) head, medial (middle) head, and long (inner) head.

The wrist extensors (Extensor carpi radialis longus, Extensor carpi radialis brevis and Extensor carpi ulnaris) are located on the back of the forearm, i.e., on the back of the hand side of the forearm.