Rocuronium block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. There have been several studies reported positive relationship between muscle mass and amount of neuromuscular junction. The purpose of this study is to find relationship between muscle mass and muscle relaxation time.

Rocuronium block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. There have been several studies reported positive relationship between muscle mass and amount of neuromuscular junction. Until now, dose of rocuronium has been judged by patient's weight and height. However, height and weight do not represent exact muscle mass. The purpose of this study is to find relationship between muscle mass and muscle relaxation time. Measurement of muscle mass will be obtained using bioelectrical impedence analysis.

Inclusion Criteria:

• All patient who undergo general anesthesia.
• Male; weight 70-75kg , height 170-175cm
• Female; weight 53-58kg , height 158-163cm

Exclusion Criteria:

• Liver and kidney disease
• Any types of muscle disorder.
• Metal materials or pacemaker in body