Sarcopenia: clinical evaluation, biological markers and other evaluation tools.

Sarcopenia is characterized by a lower skeletal muscle quantity, higher fat accumulation in the muscle, lower muscle strength, and lower physical performance. The most commonly used, low cost and accessible methods to assess skeletal muscle mass include dual energy X-ray absorptiometry (DEXA), anthropometry and bioelectrical impedance analysis (BIA). Magnetic resonance imaging (MRI), computerized tomography (CT) and creatinine excretion are the most specific golden standards for assessing muscle mass or cross sectional muscle area. Other available measures include peripheral quantitative computerized tomography (pQCT), ultrasound and neutron activation. Skeletal muscle strength is another important component for the assessment of sarcopenia and muscle quality. Several methods are available for the measurement of muscle strength which include simple dynamometers to measure isometric strength and the most complex isokinetic strength measures of power and torque. Standardized physical performance measures complement the measures of muscle mass for the assessment of sarcopenia. A clinical definition of sarcopenia ought to use methods of assessment that are valid, reliable, specific to skeletal muscle, predictive of future health events, non-invasive, practical, low cost and widely accessible.