Abduction Moving away from the midline.
Accessory muscles of breathing Muscles that attach to the ribcage and thorax that can be used to augment the action of the diaphragm for inhalation and exhalation. These include the rhomboids, pectorals, quadratus lumborum, sternocleidomastoid, and intercostals (among others).
Active insufficiency A condition in which a muscle is shortened or lengthened to a point where it can no longer effectively move a joint. For example, in Kurmasana the hips are fully flexed and so the psoas muscle is shortened to a point where it cannot effectively flex the hips further. At such times, other parts of the body must be used for leverage, such as the arms under the knees.
Adduction Moving toward the midline.
Agonist The muscle that contracts to produce a certain action about a joint (sometimes referred to as the prime mover). For example, the brachialis contracts to flex the elbow joint.
Alveoli Sac-like spherical structures with thin membrane-like walls through which gas exchange occurs in the lungs.
Anatomy The study of the structure of living things. Musculoskeletal anatomy studies the bones, ligaments, muscles, and tendons.
Antagonist The muscle that opposes the action of the agonist muscle and produces the opposite action about a joint. For example, the hamstrings are the antagonists to the quadriceps for extending the knee.
Anteversion Tilting forward.
Aponeurosis A fibrous thickening of fascia that forms the attachment for muscles. For example, the abdominal muscles attach to the linea alba, an aponeurotic thickening at the front of the abdomen.
Appendicular skeleton Composed of the shoulder (pectoral girdle) and upper extremities and pelvis and lower extremities.
Asana Sanskrit term for body position in yoga (yogasana).
Autonomic nervous system Part of the nervous system that functions largely unconsciously to control breathing, heart rate, blood pressure, digestion, perspiration, and other functions. It is divided into the sympathetic (fight or flight) and parasympathetic (rest and digest) nervous systems.
Axial skeleton Composed of the skull, spine, and ribcage.
Bandha Sanskrit term referring to binding, locking, or stabilizing. Co-activating muscle groups can be used to form bandhas in yoga postures.
Biomechanics The application of mechanical physics to the body. For example, contracting the biceps flexes the elbow joint.
Carpals The bones of the wrist, including the scaphoid, lunate, triquetrum, hamate, capitate, trapezoid, and trapezium.
Center of gravity The center of an object’s weight distribution and at which point an object is in balance.
Center of gravity projection An extension of the force of gravity downward and away from the body. For example, in Warrior III the center of gravity is projected out through the arms and the back leg, balancing the pose.
Chakra Wheel-like centers or concentrations of energy within the subtle body. They may correspond to collections of nerves such as the lumbosacral plexus (for the first and second chakras).
Closed chain contraction/movement The origin of the muscle moves and the insertion remains stationary. For example, the psoas contracts to flex the trunk in Trikonasana.
Co-contraction/co-activation Simultaneously contracting agonist and antagonist muscles to stabilize a joint. For example, co-activating the peroneus longus and brevis and the tibialis posterior muscles stabilizes the ankle joint.
Core muscles Composed of the transversus abdominis, internal and external obliques, rectus abdominis, erector spinae, psoas, gluteus maximus, and pelvic diaphragm.
Drishti Sanskrit term for focus of vision or gaze.
Eccentric contraction The muscle generates tension (contracts) while lengthening.
Erector spinae The group of three deep back muscles that run parallel to the spinal column, including the spinalis, longissimus, and iliocostalis muscles.
Eversion Rotating the sole of the foot (via the ankle) away from the midline of the body. This is associated with pronation (internal rotation) of the forefoot.
Extension Joint movement that increases space and distance between skeletal segments, bringing them farther apart.
Facilitated stretching A powerful method of stretching in which the muscle is first taken out to its full length and then contracted for several moments. This stimulates the Golgi tendon organ and produces the “relaxation response,” causing the muscle to relax and lengthen. It is also known as PNF.
Fascia Connective tissue that surrounds, separates, and binds muscles to each other. This can also form an aponeurosis for muscle attachment.
Flexion Joint movement that decreases space between skeletal segments and draws them closer together.
Floating ribs Five pairs of ribs that articulate posteriorly with the vertebrae and attach to the costal cartilage anteriorly.
Forefoot The region of the foot distal to the midfoot. It is composed of the metatarsal and phalangeal bones (and their corresponding joints). Motion includes toe flexion and extension and deepening of the foot arches.
Glenohumeral joint Ball and socket synovial joint where the head (ball) of the humerus articulates with the glenoid fossa (socket) of the scapula.
Golgi tendon organ A sensory receptor located at the muscle-tendon junction that detects changes in tension. This information is conveyed to the central nervous system, which then signals the muscle to relax, providing “slack” in the muscle. This protects against the tendon being torn from the bone. The Golgi tendon organ is central to PNF or facilitated stretching.
Hindfoot Typically refers to the calcaneous and talus bones. The joint for the hindfoot is the subtalar joint, which is responsible for everting and inverting the foot. For example, the hindfoot is inverted in the back leg in Warrior I.
Iliotibial tract Fibrous fascial structure that runs on the outside of the thigh and blends into the lateral portion of the knee capsule. This forms the attachment for the tensor fascia lata and part of the gluteus maximus muscles.
Impingement Narrowing or encroachment of the space between two bones. It can cause inflammation and pain. For example, a nerve root can become impinged by a herniated intervertebral disc. You can also have impingement between the humeral head and the acromion, causing pain in the shoulder.
Insertion The distal site where a muscle attaches to a bone (via a tendon), usually farther from the midline of the body and more mobile than the muscle origin at its opposite end.
Inversion Rotating the sole of the foot towards the midline of the body (turning it inward). This is associated with supination (external rotation) of the forefoot.
Isometric contraction The muscle generates tension but does not shorten, and the bones do not move.
Isotonic contraction The muscle shortens while maintaining constant tension through a range of motion.
Kriya Sanskrit term for action or activity.
Leverage Creating a mechanical advantage based on the length of the lever. For example, placing the hand on the outside of the foot in Parivrtta Trikonasana uses the length of the arm for leverage to turn the body.
Line of action A line through which forces act or are directed within the body. For example, there is a line of action extending from the tips of the fingers to the heel in Utthita Parsvakonasana.
Metacarpals The intermediate region of the hand between the carpus (wrist) and the fingers, i.e., the five bones of the palms of the hands.
Midfoot The intermediate region of the foot between the hindfoot and forefoot. It is composed of the navicular, the cuboid, and three cuneiform bones. Motion includes contribution to supination and pronation of the forefoot.
Mudra Sanskrit term for seal; similar to a bandha. It is often performed with the hands by bringing the fingertips together in a specific way. Other mudras are created by combining bandhas throughout the body.
Muscle spindle A sensory receptor within the muscle belly that detects changes in length and tension in the muscle. This information is conveyed to the central nervous system which can then signal the muscle to contract to resist stretching. This reflex protects against tearing the muscle.
Open chain contraction/movement The insertion of the muscle moves and the origin remains stationary. For example, the deltoids contract to lift the arms in Warrior II.
Origin The proximal site where a muscle attaches to a bone (via a tendon), usually closer to the midline of the body and less mobile than the muscle insertion on the bone at its opposite end.
Parivrtta Revolving, twisted, or turning version of a pose. For example, Parivrtta Trikonasana is the revolving version of Trikonasana (Triangle Pose).
Pelvic girdle The ilium, ischium, pubic bones, and pubic symphysis.
Physiology The study of the functional processes of living things. Most physiological processes take place unconsciously but can be influenced by the conscious mind. Examples include breathing and facilitated stretching.
PNF Proprioceptive neuromuscular facilitation. Also known as facilitated stretching. (See facilitated stretching.)
Posterior kinetic chain Composed of a group of interconnecting ligaments, tendons, and muscles on the back of the body. Includes the hamstrings, gluteus maximus, erector spinae, trapezius, latissimus, and posterior deltoids.
Pranayama Yogic art of controlling the breath.
Prime mover The muscle that contracts to directly produce a desired movement. For example, the quadriceps contracts to extend the knee joint. The term is sometimes used interchangeably with ‘agonist muscle.’
Radial deviation Tilting the hand toward the index-finger side or away from the midline of the body.
Reciprocal inhibition A phenomenon whereby the brain signals an agonist muscle to contract, and a simultaneous inhibitory signal is sent to the antagonist muscle, causing it to relax. This physiological process takes place unconsciously.
Retroversion Tilting backward.
Rotation Joint movement around a longitudinal axis. For example, we externally rotate the humerus bones (longitudinal axis) to turn the palms to face up in Savasana.
Scapulohumeral rhythm Simultaneous movements at the glenohumeral and scapulothoracic joints that function together to abduct and flex the shoulders. For example, scapulohumeral rhythm takes place when we raise the arms overhead in Urdhva Hastasana.
Shoulder girdle The clavicles and scapulae.
Synergist A muscle that assists and fine-tunes the action of the agonist or prime mover. It can be used to produce the same action, although generally not as efficiently. For example, the pectineus muscle synergizes the psoas in flexing the hip joint.
True ribs Seven pairs of ribs that articulate posteriorly with the vertebrae and anteriorly with the sternum.
Ulnar deviation Tilting the hand toward the little-finger side or midline of the body.