Not all muscles involved in ambulation re- spond equally to body weightsupported (BWS) treadmill training in patients with incomplete spinal cord injury (SCI), according to research from the University of Florida.
One of several related studies from the Florida group, presented in June at the annual meeting of the American College of Sports Medicine (ACSM), found that BWS locomotor training was associated with statistically significant hypertrophy of the plantar flexor muscles, but not the dorsiflexor or quadriceps muscles. In that study, 8 patients with incomplete SCI (C5-C6) underwent 9 weeks of locomotor training--five 20-minute sessions per week--starting on a treadmill with 40% BWS and progressing to overground walking depending on the patient's status. Researchers used 1.5T MRI to assess the maximal cross-sectional area (CSA) of the soleus, gastrocnemius, tibialis anterior, and quadriceps at the beginning and end of the 9-week period.
Maximal CSA increased by 14% in the medial gastrocnemius, 11% in the lateral gastrocnemius, and 8% in the soleus, but did not increase significantly in the quadriceps or tibialis anterior. "The hypertrophic stimulus of the locomotor training appears to be specific for a few muscles. We believe that maybe combinations of therapies, including strengthening exercises and/or electrical stimulation, will evoke a global hypertrophy of the other lower limb muscles," said Prithvi K. Shah, a graduate student in the department of rehabilitation sciences at the university, who presented the findings at the ACSM meeting.
Not coincidentally, the Florida group also is investigating the effects of more conventional resistance training in patients with incomplete SCI; another study presented at the ACSM meeting suggests that this type of training can improve isometric torque in the knee extensors and the plantar flexors. That study involved 3 patients with incomplete SCI (C5-T4) who completed 12 weeks (30 sessions) of resistance training designed specifically to target the patients' impairments. This training included typical resistance exercises (leg press, leg extension, leg curl, hip flexion, hip extension, calf raises) 2 or 3 times per week, plus plyometric jump training twice a week.
On completion of the 12-week program, torque production had improved by 46% in the knee extensors and 52% in the plantar flexors, compared with baseline levels. Further analysis, slated to be presented in September at the annual meeting of the American Paraplegia Society, revealed that time to peak torque decreased significantly in the plantar flexors but not in the knee extensors (Table).
Perhaps most telling, self-selected gait speed by the end of the training program had improved from 0.77 to 1.01 m/s and maximum gait speed had increased from 1.08 to 1.45 m/s, compared with baseline levels. Further study is required to determine the extent to which the improvements in velocity are related to the improvements in strength, said Chris Gregory, PhD, PT, a research associate in the department of physical therapy at the university, who also presented the findings at the ACSM meeting.
"Cause-and-effect relationships are extremely tough to establish," Gregory said. "In addition, the greatest strength gains did not necessarily result in the greatest improvements in gait speed. At some point, strength may not be the limiting factor, but we don't know where that would be or if we approached that threshold in our study."
Similarly, Shah and colleagues do not yet know how the muscle hypertrophy they observed with locomotor training contributes to ambulatory recovery. The researchers assessed ambulatory recovery in terms of gait speed, functional independence, and scores on the Walking Index for Spinal Cord Injury. Although those data are still being analyzed and have not yet been publicly reported, the early results are encouraging, if not necessarily conclusive. *