Effect Of Locomotor Training On Skeletal Muscle Size In Individuals With Incomplete Spinal Cord Injury

Abstract

More than 50% of all spinal cord injuries (SCI) in humans are incomplete and several studies report the potential for neuromuscular plasticity and motor recovery with training in this patient population. In specific, locomotor training using a body weight support and treadmill modality with manual assistance (LT) has shown promise in improving the ambulatory capacity of persons with incomplete SCI (ISCI). However the mechanisms underlying motor-training induced recovery following ISCI are not well known. PURPOSE To assess the effect of LT on the lower limb skeletal muscle morphology of individuals with ISCI. METHODS a) Subjects: 8 individuals with ISCI (40±12years old, 2 females, 11±4 months post-ISCI, ASIA classification: C(4)/D) underwent 45 sessions of step training on the treadmill (start with 40% BWS, 5/week, 20 min/session) followed by overground walking. b) MRI: Three-dimensional trans-axial images (256±128 matrix, TR=300 ms, TE=35ms) of the more involved lower limb were collected in a 1.5T magnet using an extremity (for calf muscles; n=8) or body coil (for quadriceps muscles; n=5) before and after completion of LT. Maximal cross sectional area (CSA) of the soleus, gastrocnemius, tibialis anterior and quadriceps muscles were calculated using custom designed software. c) Statistical Analysis: One tailed paired t-tests were used to compare CSA values at baseline and after 45 sessions of LT. Significance was set at 0.05. RESULTS The maximal CSA (mean±se) before and after training was 19.93±1.02cm2 vs. 21.61±1.42cm2 for the soleus, 10.28±0.98cm2 vs. 11.75±1.03cm2 for the medialgastrocnemius (MG), 6.08±0.80cm2 vs 6.72±0.74cm2 for the lateral-gastrocnemius (LG), 6.87±0.41cm2 vs 7.12±0.35cm2 for the tibialis anterior (TA) and 49.15±3.26cm2 vs 51.70±1.39cm2 for the quadriceps muscles respectively. The soleus, MG and LG muscles hypertrophied by 8% (p=0.040), 14% (p = 0.008) and 11% (p = 0.047) respectively, while increases in the quadriceps and tibialis anterior muscles with training failed to reach statistical significance (p <0.05). CONCLUSIONS Our findings show selective hypertrophy of the plantarflexors over the dorsiflexor and quadriceps muscles with LT. The observed muscle specific response to LT may be attributed to differences in loading patterns among muscle groups. Dietz et. al also reported a selective increase in the EMG amplitude in the gastrocnemius muscles compared to the tibialis anterior after locomotor training. Collectively, our data provide evidence that lower extremity muscle hypertrophy contributes to motortraining induced recovery. Supported by NIH RO1 (HD37645-01)/ NIH K01HDO1348-01/VA BRRC-VARRND F2182C