Human muscles attach to the skeleton via tendons and enable movement. It is important to understand of which muscles attach where, and the movements they create. Here we explain the major muscles of the human body as well as muscle structure and how they contract.
Structure of skeletal muscle
Skeletal muscle is made up of a number of different parts. Muscles are made up of bundles of muscle fibres called fasciculi. Each muscle fibre is made up of a number of myofibrils. Each myofibril is made up of proteins called actin and myosin.
Read more on the structure of skeletal muscle.
How muscles contract
Muscles contract in different ways depending on the type of movement at the joint. For example, a concentric muscle contraction is when the muscle being contracted shortens. An eccentric muscle contraction is when the muscle lengthens whilst contracting. Sliding filament theory describes at a molecular level how muscles contract.
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Foot and ankle muscles
The major muscles of the foot and ankle are the gastrocnemius & Soleus (calf muscles), peroneus brevis, peroneus longus, tibialis posterior, tibialis anterior, flexor hallucis longus, flexor digitorum longus, extensor hallucis longus and the extensor digitorum longus.
The movements generated at the foot and lower leg are plantar flexion (foot points down), dorsi flexion (foot points up), eversion (foot rolls in) and inversion (foot rolls out like an ankle sprain).
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Knee joint muscles
The major muscles of the knee joint are the quadriceps at the front of the thigh, the hamstrings at the back. The quadriceps muscle group consists of the rectus femoris, vastus medialis, vastus intermedius & vastus lateralis. The hamstring muscles are the biceps femoris, semitendinosus and semimenbranosus. In addition, the gastrocnemius, popliteus, sartorius and gracilis also aid movement of the knee joint.
Movements available at the knee joint are knee flexion (bending), knee extension (straightening) and a small amount of rotation.
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Hip, groin and pelvic muscles
The hip and pelvic muscles include the Rectus femoris, Iliopsoas (hip flexors), Adductor longus, Adductor magnus, Gracilis, Adductor brevis (adductor muscles), Gluteus maximus, Gluteus medius (gluteal muscles) and the Biceps femoris. These muscles enable flexion (thigh forwards and upwards), hip extension (thigh downwards and backwards), abduction (out to the side), adduction (inwards) and rotation.
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Trunk and spine muscles
The spine consists of 24 vertibrae, 7 cervical (neck), 12 thoracic (chest), 5 lumbar (lower back), 5 fused bones of the sacrum and 4 fused bones in the coccyx or tailbone. The main muscles involved in moving the spine and neck are the rectus abdominus, internal and external obliques, quadratus lumborum, multifidus, sternocleidomastoid and errector spinae.
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Shoulder joint muscles
The muscles of the shoulder joint are the subscapularis, infraspinatus, teres minor, teres major, latissimus dorsi, pectoralis major and deltoid. Together these are known as the rotator cuff muscles. They work closely with the shoulder girdle muscles to stabilize and move the shoulder.
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Elbow joint muscles
The muscles at the elbow joint include Triceps brachii, Biceps brachii, Brachialis, Brachioradialis, Pronator teres, Anconeus, Supinator and the Pronator quadratus. Many of the elbow joint muscles also cross the wrist joint as well. Movements at the elbow joint are flexion and extension, with pronation and supination of the forearm.
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Wrist and hand joint muscles
Wrist and hand muscles include Extensor carpi radialis brevis, Extensor carpi radialis longus, Extensor carpi ulnaris, Extensor digitorum, Extensor pollicis longus, Felxor carpi radialis, Flexor carpi ulnaris, Flexor digitorum superficialis and Flexor pollicis longus.
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Shoulder girdle muscles
Shoulder girdle consists of the clavicle (collar bone) and the scapula (shoulder blade) which generally move together as a unit. Only the clavicle connects directly to the rest of the skeleton at the sternum bone. It is really only the scapula which moves from action of the muscles. The muscles of the shoulder girdle are serratus anterior, pectoralis minor, levator scapulae, rhomboids and trapezius.
Read more on shoulder girdle muscles.