Superficial Back Muscles: The top layer of the back muscles whose function is to move the SCAPULA. This group of muscles consists of the trapezius, latissimus dorsi, rhomboid major, rhomboid minor and levator scapulae.Back: The rear surface of an upright primate from the shoulders to the hip, or the dorsal surface of tetrapods.Intermediate Back Muscles: Two muscles, the serratus posterior superior and serratus posterior inferior, located in between the deep and the superficial back muscle layers. Their function is to control THORAX movement.Back Muscles: Musculature of the BACK.Lumbosacral Region: Region of the back including the LUMBAR VERTEBRAE, SACRUM, and nearby structures.Low Back Pain: Acute or chronic pain in the lumbar or sacral regions, which may be associated with musculo-ligamentous SPRAINS AND STRAINS; INTERVERTEBRAL DISK DISPLACEMENT; and other conditions.Muscle, Skeletal: A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles.Muscle Fatigue: A state arrived at through prolonged and strong contraction of a muscle. Studies in athletes during prolonged submaximal exercise have shown that muscle fatigue increases in almost direct proportion to the rate of muscle glycogen depletion. Muscle fatigue in short-term maximal exercise is associated with oxygen lack and an increased level of blood and muscle lactic acid, and an accompanying increase in hydrogen-ion concentration in the exercised muscle.Muscles: Contractile tissue that produces movement in animals.Electromyography: Recording of the changes in electric potential of muscle by means of surface or needle electrodes.