Amputation to the lower extremity is a life-changing event. Approximately 2 million Americans live with limb loss, with \~45% of losses occurring from traumatic mechanisms. After the injury has healed and a prosthetic limb is fitted, the long-term care for amputees typically focuses on maintenance of the prosthesis fit and optimizing physical function. Even with high-quality prostheses, amputation permanently impacts biomechanical symmetry of gait. After unilateral transtibial or transfemoral amputation, skeletal muscle atrophy occurs in the lower extremity and back. Asymmetric gait causes mechanical stresses at lumbar spine, and loss of muscle mass and strength, all of which exaggerate gait aberrations. As a result, chronic low back pain (LBP) can develop. LBP is a common, but often unaddressed, secondary complication in over half of the unilateral amputee population.

Lower extremity amputees face numerous physical and emotional challenges after their injuries. Performing ambulatory activities are more physically demanding with an amputation than without. The psychological stress levels are often high after an amputation, contributing to activity avoidance and limiting participation in load-bearing activities. LBP independently contributes to costly health burdens such as addiction to pain medicine, depression and lifestyle diseases and LBP erodes physical and mental quality of life (QOL). Pain is also related to skeletal muscle atrophy in the low back. The combination of an amputation injury and LBP may amplify ambulation-related limitations and further deteriorate QOL. Unilateral lower extremity amputees who suffer from chronic LBP therefore may therefore experience greater walking limitations, physical activity avoidance and physiological changes to skeletal muscle, strength and perceived QOL than people with back pain or amputation alone.

Long-term care for amputees requires a team of physicians, prostheticians, therapists and other specialists. Patients often travel long distances to receive their care. Patients with limited resources may not be able to maintain a long-term relationship with therapists due to cost restrictions. Home-based interventions that target LBP could substantially impact the secondary disease burden and help restore QOL in the amputee population. In the general population, evidence indicates that consistently-performed muscle strengthening activity is associated with significantly lower odds of developing back pain in men and women. Resistance exercise is effective for lumbar muscle strength gains, functional gains in ambulation and movement and for improving both physical and mental aspects of QOL. Resistance training benefits in strength, motor skills, and many aspects of quality of life (both functional and psychosocial) are seen throughout several different demographics; from young adults to the elderly.

Current clinical paradigms to treat general LBP include referral to physical therapy for strengthening exercise programs. For amputees, challenges to receiving therapeutic care include travel distance, and financial limitations for exercise facility memberships or therapy copayments. Patients may not be able to sustain and therapy gains over the long-term when therapy benefits run out. Thus, exercise to treat LBP in amputees must be accessible, low or no cost and sustainable. A significant deficit in the clinical literature is that the study team does not know the effectiveness of home-based resistance training on different chronic musculoskeletal pains in amputees. Moreover, the mechanisms that may contribute to effectiveness of strength training on pain relief in amputees are not clear. The problem is therefore multifaceted: 1) amputees experience permanent anatomic changes that impact load-bearing activity, back pain and QOL; 2) chronic LBP treatment is not often a focus for the long-term management of the unilateral lower extremity amputee; 3) chronic LBP can develop in amputees as a consequence of asymmetric movement patterns, lumbar muscle atrophy and low muscle strength, but the relative contribution of each to pain severity is not known. These evidence gaps are significant barriers to the optimization of care for this special population by clinical teams who care for these individuals, and for determination of pain responders with strengthening exercise.