Lower-extremity muscle cross-sectional area after incomplete spinal cord injury

Muscle after spinal cord injury

The morphological and contractile changes of muscles below the level of the lesion after spinal cord injury (SCI) are dramatic. In humans with SCI, a fiber-type transformation away from type I begins 4-7 months post-SCI and reaches a new steady state with predominantly fast glycolytic IIX fibers years after the injury. There is a progressive drop in the proportion of slow myosin heavy chain (MHC) isoform fibers and a rise in the proportion of fibers that coexpress both the fast and slow MHC isoforms. The oxidative enzymatic activity starts to decline after the first few months post-SCI. Muscles from individuals with chronic SCI show less resistance to fatigue, and the speed-related contractile properties change, becoming faster. These findings are also present in animals. Future studies should longitudinally examine changes in muscles from early SCI until steady state is reached in order to determine optimal training protocols for maintaining skeletal muscle after paralysis.

The length-tension relationship of human dorsiflexor and plantarflexor muscles after spinal cord injury

STUDY DESIGN

A cross-sectional design.

OBJECTIVES

To examine the length-tension relationship of dorsiflexion (DF) and plantarflexion (PF) muscle groups in seven individuals with chronic spinal cord injury (SCI; C2-T7; age 43+/-10.1 years) and compare it with a group of age and sex-matched able-bodied (AB) controls.

SETTING

McMaster University, Hamilton, ON, Canada.

METHODS

Isometric single twitch properties, 0.5-s tetanic contractions (SCI) and maximal voluntary contractions (AB) were measured at nine joint angles from 20 degrees DF to 20 degrees PF.

RESULTS

In the DF muscles, peak-evoked twitch (PT) torque occurred at 20 degrees PF for SCI (3.4+/-1.1 N m) and AB (3.8+/-1.4 N m) with no difference in peak torque between groups, whereas peak summated force occurred at 10 degrees PF in AB and 20 degrees PF in SCI (P<0.01). In the PF muscles, PT torque occurred at 15 degrees DF in AB (18.6+/-2.6 N m) and at 5 degrees DF (6.8+/-3.3 N m; P<0.01) in SCI, and peak-summated force occurred at 15 degrees DF in AB. The SCI group did not show any change in PF peak-summated force with varying joint angles. Rates of contraction and relaxation were not different between the two groups.

CONCLUSIONS

The results suggest a significant change in the length-tension relationship of the PF muscles after SCI, but no change in the DF muscle group. Rehabilitation programs should focus on maintaining PF muscle length in order to optimize muscle strength and function after SCI.

Combined effects of acrobatic exercise and magnetic stimulation on the functional recovery after spinal cord lesions

The objective of the study was to determine whether physical exercise combined with epidural spinal cord magnetic stimulation could improve recovery after injury of the spinal cord. Spinal cord lesioning in mice resulted in reduced locomotor function and negatively affected the muscle strength tested in vitro. Acrobatic exercise attenuated the behavioral effects of spinal cord injury. The exposure to magnetic fields facilitated further this improvement. The progress in behavioral recovery was correlated with reduced muscle degeneration and enhanced muscle contraction. The acrobatic exercise combined with stimulation with magnetic fields significantly facilitates behavioral recovery and muscle physiology in mice following spinal cord injury.

Non-invasive assessment of lower extremity muscle composition after incomplete spinal cord injury

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

(1) To quantify intramyocellular lipid (IMCL) content of the soleus muscle. (2) To assess the T(2) relaxation rates in the lower extremity skeletal muscles in persons with incomplete spinal cord injury (SCI).

SETTING

Academic Institution, Florida.

METHODS

Eight subjects (42+/-10 years old; 70+/-12 kg; 176+/-10 cm) with chronic (17+/-9 months post injury) motor SCI (C4-T12; ASIA C or D) and eight matched healthy controls were tested. Localized unsuppressed proton spectroscopy (H-MRS) was performed to estimate total lipid content and individual lipid components; IMCL and extramyocellular lipid (EMCL) from the soleus muscle. T(2)-weighted imaging of lower extremity muscles yielded muscle T(2) rates.

RESULTS

The IMCL content of the soleus muscle was 3.3 times higher in the patient group as compared to controls (P=0.002; 0.0401 (0.0234-0.0849) versus 0.0123 (0.0090-0.0175)). Similarly, EMCL measures were 4.5 times higher as compared to the controls (P=0.002). Significant differences were observed in the T(2) relaxation times of the soleus and gastrocnemius muscles (P<0.05).

CONCLUSION

The increased levels of IMCL might interfere with the glucose uptake in skeletal muscle; potentially predisposing persons with incomplete SCI to the development of peripheral insulin resistance. Marked elevations in the T(2) relaxation times of the locomotor muscles are reflective of an altered muscle composition.

A longitudinal study of skeletal muscle following spinal cord injury and locomotor training

STUDY DESIGN

Experimental rat model of spinal cord contusion injury (contusion SCI).

OBJECTIVE

The objectives of this study were (1) to characterize the longitudinal changes in rat lower hindlimb muscle morphology following contusion SCI by using magnetic resonance imaging and (2) to determine the therapeutic potential of two types of locomotor training, treadmill and cycling.

SETTING

University research setting.

METHODS

After moderate midthoracic contusion SCI, Sprague-Dawley rats were assigned to either treadmill training, cycle training or an untrained group. Lower hindlimb muscle size was examined prior to SCI and at 1-, 2-, 4-, 8-, and 12-week post injury.

RESULTS

Following contusion SCI, we observed significant atrophy in all rat hindlimb muscles with the posterior muscles (triceps surae and flexor digitorum) showing greater atrophy than the anterior muscles (tibialis anterior and extensor digitorum). The greatest amount of atrophy was measured at 2-week post injury (range from 11 to 26%), and spontaneous recovery in muscle size was observed by 4 weeks post-SCI. Both cycling and treadmill training halted the atrophic process and accelerated the rate of recovery. The therapeutic influence of both training interventions was observed within 1 week of training and no significant difference was noted between the two interventions, except in the tibialis anterior muscle. Finally, a positive correlation was found between locomotor functional scores and hindlimb muscle size following SCI.

CONCLUSIONS

Both treadmill and cycle training diminish the extent of atrophy and facilitate muscle plasticity after contusion SCI.

Locomotor training and muscle function after incomplete spinal cord injury: case series

BACKGROUND/OBJECTIVE

To determine whether 9 weeks of locomotor training (LT) results in changes in muscle strength and alterations in muscle size and activation after chronic incomplete spinal cord injury (SCI).

STUDY DESIGN

Longitudinal prospective case series.

METHODS

Five individuals with chronic incomplete SCI completed 9 weeks of LT. Peak isometric torque, torque developed within the initial 200 milliseconds of contraction (Torque 200), average rate of torque development (ARTD), and voluntary activation deficits were determined using isokinetic dynamometry for the knee-extensor (KE) and plantar-flexor (PF) muscle groups before and after LT. Maximum muscle cross-sectional area (CSA) was measured prior to and after LT.

RESULTS

Locomotor training resulted in improved peak torque production in all participants, with the largest increases in the more-involved PF (43.9% +/- 20.0%), followed by the more-involved KE (21.1% +/- 12.3%). Even larger improvements were realized in Torque 200 and ARTD (indices of explosive torque), after LT. In particular, the largest improvements were realized in the Torque 200 measures of the PF muscle group. Improvements in torque production were associated with enhanced voluntary activation in both the KE and ankle PF muscles and an increase in the maximal CSA of the ankle PF muscles.

CONCLUSION

Nine weeks of LT resulted in positive alterations in the KE and PF muscle groups that included an increase in muscle size, improved voluntary activation, and an improved ability to generate both peak and explosive torque about the knee and ankle joints.