The investigators are examining: 1) whether the three treatment regimens are significantly more efficacious than standard HEP alone in improving lower extremity muscle strength, physical activity, mobility, pain, and quality of life; 2) lower extremity muscle strength, physical activity, mobility, pain, and quality of life differ significantly across the 4 time periods; 3) is there an interaction between treatment and time in relation to lower extremity muscle strength, physical activity, mobility, pain, and quality of life.