Participants are stratified by initial comfortable walking speed (moderate >0.5 m/sec; severe <= 0.5 m/sec) and randomized to one of four exercise pairs: 1) body-weight supported treadmill training (BWST) and locomotor-based strength training (resistive cycling task, LBST), 2) BWST and LE muscle-specific strength training (MSST), 3) BWST and upper extremity ergometry (SHAM), and 4) LBST and SHAM. Training will occur 4 times per week for 6 weeks (24 total sessions). Exercise type in each exercise pair is alternated daily.