Inclusion Criteria:  18 years or older Able to ambulate independently without the use of aids (i.e., walking cane) Able to walk at least 10 minutes continuously without stopping History of diagnosed peripheral artery disease. For Amputees: History lower limb unilateral transtibial or transfemoral amputation.  Exclusion Criteria:  Inability to give informed consent neurological disorder that affects gait two or more falls within the previous 12 months currently pregnant (or intend to become pregnant while participating in study) history of any condition where fatiguing contractions or resisted leg contractions are contraindicated blood clots in the leg, or any condition in which compression of the thigh or transient ischemia is contraindicated (e.g. open wounds in the leg). history of hypertension history of heart failure Head injury within the previous 6 months Seizure disorder Adverse reaction to ultrasound gel History of thrombosis History of sickle cell trait