Inclusion Criteria:  adult (age≥18) with stable ESRD; receiving≥3 months HD; receiving HD more than 5 times every two weeks; volunteer for participating in this investigation.  Exclusion Criteria:  are unable to do walk on one's own (severe musculoskeletal pain at rest or with minimal activity precluding walking or stationary cycling; unable to sit, stand or walk unassisted, walking devices such as cane or walker allowed); have shortness of breath at rest or with activities of daily living (NYHA Class IV); have mental disease, disturbance of consciousness and couldn't cooperate with this investigation.