Inclusion Criteria:  on HD for longer than 6 months under the permission of their nephrologist adequately dialyzed (most recent Kt/V > 1.2) and stable during dialysis in the past 3 months  Exclusion Criteria:  occurrence of hyperkalemia in the past 3 months comorbid medical, physical, and mental conditions that contraindicate exercise unstable cardiac conditions (eg, unstable angina, heart failure or symptomatic severe aortic stenosis, etc.) disabling orthopedic and neuromuscular diseases