Learn which muscles govern movement in the body

The skeletal muscles can be divided into three groups (figure 2.5):

Muscles governing movement of the upper extremitiesMuscles governing moment of the trunk and spine (including breathing musculature)Muscles governing movement of the lower extremities
Muscles of the human body: (a) front and (b) back view.

The muscles of the upper extremity comprise the muscles around the shoulder or pectoral girdle as well as the muscles of the glenohumeral (shoulder) joint and of the elbow and wrist. These muscles are active in all pressing and pulling movements of the upper body:

Shoulder or pectoral girdleTrapeziusRhomboideusLatissimus dorsiPectoralsDeltoidsBicepsBrachialisTriceps

The muscles of the spine and trunk produce movement of the spine and hips and contribute to ventilation. This covers extension, flexion, lateral flexion, reduction and rotation along the full length of the spine. Additionally, the diaphragm is the principal ventilation muscle, but muscles between the ribs can expand the thorax for heavy or deep breathing and the transversus abdominis muscles assist in establishing thoracic pressure during Valsalva manoeuvres. Valsalva manoeuvres are initiated reflexively, when external moments are applied to the torso. They consist of simultaneous contraction of the transversus and the obliques and sometimes the diaphragm, similar to a forced exhalation but against closed airways. Together these muscle actions increase intrathoracic and intra-abdominal pressure, stiffening the trunk and thereby reducing shear forces across the spine (Hill and Butler 1991).

Functionally, the muscles in the trunk are often divided into the inner unit and the outer unit. The inner unit includes the muscles that do not produce macroscopic movement but instead stabilise the vertebrae and sacroiliac joint during movement, whereas the outer unit produces the movements of the spine and hip. The inner unit consists of tonic muscles such as the transversus abdominis, the posterior fibres of the obliquus internus abdominis, the diaphragm, the pelvic floor muscles, the multifidus and the lumbar portions of the longissimus and iliocostalis (part of the erector spinae). These muscle co-contract in virtually all standing or sitting movements and most lying movements prior to other muscles firing in order to provide spinal rigidity, ensuring efficient force transfer. The outer unit consists of the obliquus externus, obliquus internus, erector spinae, latissimus dorsi, gluteal muscles, quadratus lumborum, adductors and hamstrings. Following are phasic muscles that can produce movement with great power and ROM, fulfilling tasks of vastly different mechanical and metabolic requirements:

Rectus abdominisObliques (internal and external)Transversus abdominisErector spinaeQuadratus lumborum

The muscles of the lower extremity comprise the muscles around the hip, pelvis, knees and ankles. Together these muscles perform all movements in the movement chains of the lower body:

Gluteal musclesQuadricepsHamstringsAdductorsPsoas complex (hip flexors)Triceps surae (calf muscles)
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