Work Capacity Evaluation: Assessment of physiological capacities in relation to job requirements. It is usually done by measuring certain physiological (e.g., circulatory and respiratory) variables during a gradually increasing workload until specific limitations occur with respect to those variables.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.Work: Productive or purposeful activities.Return to Work: Resumption of normal work routine following a hiatus or period of absence due to injury, disability, or other reasons.Physical Exertion: Expenditure of energy during PHYSICAL ACTIVITY. Intensity of exertion may be measured by rate of OXYGEN CONSUMPTION; HEAT produced, or HEART RATE. Perceived exertion, a psychological measure of exertion, is included.Phosphofructokinase-1, Muscle Type: An allosteric enzyme that regulates glycolysis by catalyzing the transfer of a phosphate group from ATP to fructose-6-phosphate to yield fructose-1,6-bisphosphate. In humans, PHOSPHOFRUCTOKINASE-1 in muscle exists as the homotetramer of M subunits. Defects in this muscle enzyme cause GLYCOGEN STORAGE DISEASE TYPE VII, also known as Tarui's disease.Oxygen Consumption: The rate at which oxygen is used by a tissue; microliters of oxygen STPD used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (Stedman, 25th ed, p346)Nurses' Aides: Allied health personnel who assist the professional nurse in routine duties.Physical Endurance: The time span between the beginning of physical activity by an individual and the termination because of exhaustion.