Long-term adaptation to electrically induced cycle training in severe spinal cord injured individuals

Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

Control of leg-powered paraplegic cycling using stimulation of the lumbo-sacral anterior spinal nerve roots

We investigated leg-powered cycling in a recumbent tricycle for a paraplegic using functional electrical stimulation (FES) with the lumbo-sacral anterior root stimulator implant (LARSI). A female complete T9 paraplegic had a stimulator for the anterior L2 to S2 spinal roots (bilaterally) implanted in 1994. She was provided with equipment for daily FES cycling exercise at home. The cycling controller applies a pattern of stimulation in each of 16 crank angle phases. A 7-bit shaft encoder measures the crank angle with adequate precision. Each pattern was originally chosen to give the greatest propulsive force in that position when there was no motion. However, dynamically, some reduction in co-contraction is needed; also the patterns are applied with a preset advance time. Maximal power is obtained with an advance of 250 ms, which compensates for muscle response delay and accommodates changes in cadence (from about 25 to 85 rpm). With this system, she has cycled 1.2 km at a time on gently undulating road. We found that spinal root stimulation gives sufficient control over the muscles in the legs to produce a fluid cycling gait. We propose that root stimulation for leg cycling exercise may be a practicable and valuable function for paraplegics following spinal cord injury.

Differential fatigue of paralyzed thenar muscles by stimuli of different intensities

Muscles paralyzed by injury or disease fatigue excessively when stimulated. This study examined whether the first few paralyzed thenar motor units recruited by electrical stimulation of the median nerve were more fatigue resistant than the total thenar motor unit population. The paralyzed thenar muscles of four subjects with chronic cervical spinal cord injury were fatigued by a 2-min intermittent 40-HZ protocol on 2 days. One experiment involved submaximal stimulation, the other supramaximal stimulation. These stimuli resulted in activation of part and all of the thenar muscles, respectively. Relative force loss, force-time integral decline, and slowing of half-relaxation time were always significantly less when only part rather than all of the muscles was fatigued. The part of the paralyzed muscles that was activated was also relatively fatigue resistant compared with control single thenar motor units. Thus, a reversal of recruitment order from fatigable to fatigue-resistant units cannot explain the extreme fatigability of paralyzed muscles. Use of submaximal stimulation during functional electrical stimulation may therefore help to reduce muscle fatigue because it recruits the more fatigue-resistant units.

Effects of training on contractile properties of paralyzed quadriceps muscle

Effects of two different training regimens on the contractile properties of the quadriceps muscle were studied in six individuals with spinal cord injury. Each subject had both limbs trained with the two regimens, consisting of stimulation with low frequencies (LF) at 10 HZ or high frequencies (HF) at 50 HZ; one limb of each subject was stimulated with the LF protocol and the other with the HF regimen. Twelve weeks of daily training increased tetanic tension by approximately 20%, which was not significantly different between training regimens. Interestingly, after HF but not LF training, the unusual high forces at the low frequency range of the force-frequency relationship decreased, possibly due to a reduced activation per impulse. After LF but not HF training, force oscillation amplitudes declined (by 33%) as relaxation tended to slow, which may have opposed possible effects of reduced activation as seen after HF training. Finally, fatigue resistance also increased rapidly after LF training (by 43%) but not after HF training. These results indicate that different types of training may selectively change different aspects of function in disused muscles.

Improved glucose tolerance and insulin sensitivity after electrical stimulation-assisted cycling in people with spinal cord injury

DESIGN

Longitudinal training.

OBJECTIVES

The purpose was to determine the effect of electrical stimulation (ES)-assisted cycling (30 min/day, 3 days/week for 8 weeks) on glucose tolerance and insulin sensitivity in people with spinal cord injury (SCI).

SETTING

The Steadward Centre, Alberta, Canada.

METHODS

Seven participants with motor complete SCI (five males and two females aged 30 to 53 years, injured 3-40 years, C5-T10) underwent 2-h oral glucose tolerance tests (OGTT, n=7) and hyperglycaemic clamp tests (n=3) before and after 8 weeks of training with ES-assisted cycling.

RESULTS

Results indicated that subjects' glucose level were significantly lower at 2 h OGTT following 8 weeks of training (122.4+/-10 vs 139.9+/-16, P=0.014). Two-hour hyperglycaemic clamps tests showed improvement in all three people for glucose utilisation and in two of three people for insulin sensitivity.

CONCLUSIONS

These results suggested that exercise with ES-assisted cycling is beneficial for the prevention and treatment of Type 2 diabetes mellitus in people with SCI.

SPONSORSHIP

Supported by Alberta Paraplegic Foundation, Therapeutic Alliance.

Insulin action and long-term electrically induced training in individuals with spinal cord injuries

PURPOSE

Individuals with spinal cord injuries (SCI) have an increased prevalence of insulin resistance and type 2 diabetes mellitus. In able-bodied individuals, training with large muscle groups increases insulin sensitivity and may prevent type 2 diabetes mellitus. However, individuals with SCI cannot voluntarily recruit major muscle groups, but by functional electrical stimulation (FES) they can now perform ergometer bicycle training.

METHODS

Ten subjects with SCI (35 +/- 2 yr (mean +/- SE), 73 +/- 5 kg, level of lesion C6--Th4, time since injury: 12 +/- 2 yr) performed 1 yr of FES cycling (30 min x d(-1), 3 d x wk(-1) (intensive training)). Seven subjects continued 6 months with reduced training (1 d x wk(-1) (reduced training)). A sequential, hyperinsulinemic (50 mU x min(-1) x m(-2) (step 1) and 480 mU x min(-1) x m(-2) (step 2)), euglycemic clamp, an oral glucose tolerance test (OGTT), and determination of GLUT 4 transporter protein in muscle biopsies were performed before and after training.

RESULTS

Insulin-stimulated glucose uptake rates increased after intensive training (from 4.9 +/- 0.5 mg x min(-1) x kg(-1) to 6.2 +/- 0.6 mg x min(-1) x kg(-1) (P < 0.008) (step 1) and from 9.0 +/- 0.8 mg x min(-1) x kg(-1) to 10.6 +/- 0.8 mg x min(-1) x kg(-1) (P = 0.103) (step 2)). With the reduction in training, insulin sensitivity decreased to a similar level as before training (P > 0.05). GLUT 4 increased by 105% after intense training and decreased again with the training reduction. The subjects had impaired glucose tolerance before and after training, and neither glucose tolerance nor insulin responses to OGTT were significantly altered by training.

CONCLUSIONS

Electrically induced bicycle training, performed three times per week increases insulin sensitivity and GLUT 4 content in skeletal muscle in subjects with SCI. A reduction in training to once per week is not sufficient to maintain these effects. FES training may have a role in the prevention of the insulin resistance syndrome in persons with SCI.

Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury

OBJECTIVE

To test whether a short period of training leads to adaptations in the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with spinal cord injury (SCI).

DESIGN

Before-after trial.

SETTING

Rehabilitation center, academic medical center.

PARTICIPANTS

Nine men with spinal cord lesions.

INTERVENTION

Six weeks of cycling using a functional electrically stimulated leg cycle ergometer (FES-LCE).

MAIN OUTCOME MEASURES

Longitudinal images and simultaneous velocity spectra were measured in the common carotid (CA) and femoral (FA) arteries using quantitative duplex Doppler ultrasound examination. Arterial diameters, peak systolic inflow volumes (PSIVs), mean inflow volumes (MIVs), and a velocity index (VI), representing the peripheral resistance, were obtained at rest. PSIVs and VI were obtained during 3 minutes of hyperemia following 20 minutes of FA occlusion.

RESULTS

Training resulted in significant increases in diameter (p < .01), PSIVs (p < .01), and MIVs (p < .05), and reduced VI (p < .01) of the FA, whereas values in the CA remained unchanged. Postocclusive hyperemic responses were augmented, indicated by significantly higher PSIVs (p <.01) and a trend toward lower VI.

CONCLUSION

Six weeks of FES-LCE training increased the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with SCI.

Temperature responses to electrically induced cycling in spinal cord injured persons

PURPOSE

The purpose of the study was to investigate the core temperature responses to the induction of electrical exercise and to clarify whether an increase in temperature could be responsible for some of the observed reactions to acute and repeated exposure to electrical muscle stimulation.

METHODS

The paralyzed thigh and gluteal muscles were stimulated electrically with surface electrodes in seven persons with transection of the spinal cord. By this means, they were able to pedal a lower extremity ergometer at 50 revolutions per minute for 30 min. Skin surface, esophageal (Tes), rectal (Tre), and muscle temperature in m. quadriceps were measured with thermocouples.

RESULTS

The average rate of oxygen consumption was 0.91 +/- 0.16 L.min-1, and the heart rate after 20 min was 123 +/- 9 bpm during the electrically induced exercise. The involuntary, induced exercise led to increases in core temperature, whereas skin surface temperature was the same before and after exercise. Average Tes and Tre both rose 0.7 degrees C from, respectively, 36.6 +/- 0.2 and 36.9 +/- 0.1 degrees C, and muscle temperature increased even more: 2.9 degrees C from 33.9 +/- 0.3 degrees C.

CONCLUSION

It is suggested that these increased temperatures may act as stimuli, directly or, through resulting release of humoral factors, and elicit the changes in heart rate, as well as the previously observed adaptive changes after electrically induced exercise, e.g., in muscle fiber size, and capillarization.

Electrical stimulation influences mineral formation of osteoblast-like cells in vitro

The aim of the present study was to assess the structure of newly formed mineral crystals after electrical stimulation of osteoblast-like cells in vitro. Pulsed electrical stimulation was coupled capacitively or semi-capacitively to primary osteoblast-like cells derived from bovine metacarpals. Computer calculations revealed that the chosen input signal (saw-tooth, 100 V, 63 ms width, 16 Hz repetition rate) generated a short pulsed voltage drop of 100 microV (capacitive coupled mode) and of 350 microV (semi-capacitive coupled mode) across the cell-matrix layer. Stimulated cultures showed an enhanced mineral formation compared to the non stimulated controls. In cultures exposed to capacitively coupled electric fields and in control cultures nodules and mineralized globules were found. Nodules with a diameter of less than 200 nm covered the cell surface, whereas mineral globules with a diameter of up to 700 nm formed characteristic mineral deposits in the vicinity of the cells similar to biomineral formations occurring in mineralizing tissues. In contrast, large rod-shaped crystals were found in cultures stimulated by semi-capacitive coupled electric fields, indicating a non-physiological precipitation process. In conclusion, osteoblasts in culture are sensitive to electrical stimulation resulting in an enhancement of the biomineralization process.

Reproducibility of contractile properties of the human paralysed and non-paralysed quadriceps muscle

This study assessed the reproducibility of electrically evoked, isometric quadriceps contractile properties in eight people with spinal cord injury (SCI) and eight able-bodied (AB) individuals. Over all, the pooled coefficients of variation (CVps) in the SCI group were significantly lower (ranging from 0.03 to 0.15) than in the AB group (ranging from 0.08 to 0.21) (P<0.05). Furthermore, in all subjects, the variability of force production increased as stimulation frequency decreased (P<0.01). In subjects with SCI, variables of contractile speed are clearly less reproducible than tetanic tension or resistance to fatigue. Contractile properties of quadriceps muscles of SCI subjects were significantly different from that of AB subjects. Muscles of people with SCI were less fatigue resistant (P<0.05) and produced force-frequency relationships that were shifted to the left, compared with AB controls (P<.01). In addition, fusion of force responses resulting from 10 Hz stimulation was reduced (P<.05) and speed of contraction (but not relaxation) was increased (P<0.05), indicating an increased contractile speed in paralysed muscles compared with non-paralysed muscles. These results correspond with an expected predominance of fast glycolytic muscle fibres in paralysed muscles. It is concluded that quadriceps dynamometry is a useful technique to study muscle function in non-paralysed as well as in paralysed muscles. Furthermore, these techniques can be reliably used, for example, to assess therapeutic interventions on paralysed muscles provided that expected differences in relative tetanic tension and fatigue resistance are larger than approximately 5% and differences in contractile speed are larger than approximately 15%.

Cycling Exercise and Fetal Spinal Cord Transplantation Act Synergistically on Atrophied Muscle following Chronic Spinal Cord Injury in Rats

The potential of two interventions, alone or in combination, to restore chronic spinal cord transection-induced changes in skeletal muscles of adult Sprague-Dawley rats was studied. Hind limb skeletal muscles were examined in the following groups of animals: rats with a complete spinal cord transection (Tx) for 8 weeks; Tx with a 4-week delay before initiation of a 4-week motor-assisted cycling exercise (Ex) program; Tx with a 4-week delay before transplantation (Tp) of fetal spinal cord tissue into the lesion cavity; Tx with a 4-week delay before Tp and Ex; and uninjured control animals. Muscle mass, muscle to body mass ratios, and mean myofiber cross-sectional areas were significantly reduced 8 weeks after transection. Whereas transplantation of fetal spinal cord tissue did not reverse this atrophy and exercise alone had only a modest effect in restoring lost muscle mass, the combination of exercise and transplantation significantly increased muscle mass, muscle to body mass ratios, and mean myofiber cross-sectional areas in both soleus and plantaris muscles. Spinal cord injury (SCI) also caused changes in myosin heavy chain (MyHC) expression toward faster isoforms in both soleus and plantaris and increased soleus myofiber succinate dehydrogenase (SDH) activity. Combined exercise and transplantation led to a change in the expression of the fastest MyHC isoform in soleus but had no effect in the plantaris. Exercise alone and in combination with transplantation reduced SDH activity to control levels in the soleus. These results suggest a synergistic action of exercise and transplantation of fetal spinal cord tissue on skeletal muscle properties following SCI, even after an extended post-injury period before intervention.

Type IV collagen and its degradation in paralyzed human muscle: effect of functional electrical stimulation

The purpose of this study was to evaluate the effects of spinal cord injury (SCI) and functional electrical stimulation (FES) of paralyzed muscles on type IV collagen content and proteins involving its degradation, which is initiated by matrix metalloproteinase (MMP)-2 and -9 and regulated by their tissue inhibitors (TIMPs)-2 and -1. Ten SCI subjects participated in an 18-month program of functional electrical stimulation (FES) of their leg muscles. Needle biopsies were taken from the vastus lateralis muscle before and at various times during the training period, and from able-bodied controls. Type IV collagen concentration was unaltered. ProMMP-2 level of SCI subjects before the training period tended to be higher than able-bodied controls and was significantly above the control level after FES. MMP-9 concentration was unchanged. The results suggest accelerated type IV collagen turnover in skeletal muscle of SCI individuals especially after FES as a part of adaptive process of the muscle.

Myosin heavy chain isoform and ubiquitin protease mRNA expression after passive leg cycling in persons with spinal cord injury

OBJECTIVE

To determine the effects of passive leg cycling exercise on myosin heavy chain (MHC) isoform and ubiquitin (UBI) protease mRNA expression in patients with spinal cord injury (SCI).

STUDY DESIGN

Case series.

INTERVENTION

Eight SCI subjects (5 men, 3 women) participated in a 12-week exercise program involving the Psycle ergometer. Training occurred 2 days a week at 75% of each subject's maximum heart rate. Anthropometric measures (body weight, thigh girth, and body mass index) and muscle biopsy specimens were obtained before and after training. Analyses were performed to determine the mRNA expression of types I, IIa, and IIx MHC, as well as UBI, a UBI-conjugating enzyme (E2), and 20S proteasome (20S).

RESULTS

Despite small increases, paired t tests (p < .05) to assess changes from pretraining to posttraining failed to locate significant differences for the three anthropometric measures. For mRNA expression, there were significant increases in expression of MHC types IIa and IIx and significant decreases in expression for UBI, E2, and 20S.

CONCLUSION

Exercise using passive leg cycling increases the expression of fast MHC isoforms while concomitantly decreasing proteolytic activity associated with muscle degradation, thus helping to possibly ameliorate muscle atrophy in patients with SCI.

High expression of MHC I in the tibialis anterior muscle of a paraplegic patient

A long-term paraplegic man presented exclusively (>99%) myosin heavy chain I (MHC I) in the tibialis anterior muscle (TA). This was coupled to a slow speed of contraction, a high resistance to fatigue, and a rapid resynthesis of phosphocreatine after an electrically evoked fatiguing contraction when compared with the TA muscles of 9 other paraplegic individuals. In contrast, the MHC composition of his vastus lateralis, gastrocnemius, and soleus muscles was that expected of a muscle from a spinal cord injured individual. This information may be of clinical importance in terms of the expected morphological and functional adaptations of skeletal muscle to different types of electrical stimulation therapy.

Functional electrical stimulation exercise increases GLUT-1 and GLUT-4 in paralyzed skeletal muscle

The study purpose was to determine the effect of functional electrical stimulation (FES)-leg cycle ergometer training (30 minutes on 3 d/wk for 8 weeks) on the GLUT-1 and GLUT-4 content of paralyzed skeletal muscle. Biopsy samples of vastus lateralis muscle were obtained pre- and post-training from five individuals with motor-complete spinal cord injury ([SCI] four men and one woman aged 31 to 50 years, 3 to 25 years postinjury involving C5-T8). Western blot analysis indicated that GLUT-1 increased by 52% and GLUT-4 increased by 72% with training (P < .05). This coincided with an increase in the muscle oxidative capacity as indicated by a 56% increase in citrate synthase (CS) activity (P < .05) and an improvement in the insulin sensitivity index as determined from oral glucose tolerance tests (P < .05). It is concluded that FES endurance training is effective to increase glucose transporter protein levels in paralyzed skeletal muscle of individuals with SCI.

Salbutamol effect in spinal cord injured individuals undergoing functional electrical stimulation training

OBJECTIVE

Preliminary study to investigate possible changes in skeletal muscle morphology and function, as well as hormonal and metabolic effects, after treatment with a selective beta2-adrenergic receptor agonist.

DESIGN

Double-blind, placebo-controlled trial.

PARTICIPANTS

Three individuals with spinal cord injury (SCI).

INTERVENTION

Two-week treatment with salbutamol (2mg) or placebo (ascorbic acid, 50mg) twice a day. Program of functional electronic stimulation (FES) cycling for 30 minutes twice a week.

MAIN OUTCOME MEASURES

Body weight, three measures of leg circumference (gluteal furrow, one third of subischial height up from tibial-femoral joint space, and minimum circumference above the knee), muscle fiber area, and total work output per session.

RESULTS

There were increases in body weight (2.30 +/- .70kg), leg circumferences (gluteal furrow 1.70 +/- .27cm, one third subischial height 1.53 +/- 1.65cm, minimum circumference above the knee .43 +/- .04cm), and muscle (vastus lateralis) cross-sectional area (1,374 +/- 493 to 2,446 +/- 1,177microm2) after salbutamol treatment, whereas quadriceps muscle contractile function was not modified. Total work output during FES cycling sessions was increased more during salbutamol treatment (64%) compared with training alone (27%). Salbutamol treatment was associated with a large decrease in skeletal muscle beta-adrenergic receptor density.

CONCLUSION

Although some side effects were noted, these results suggest that a short treatment with the beta2-adrenergic receptor agonist salbutamol during a training program with FES cycling could be beneficial in patients with SCI.

Contractile properties of the quadriceps muscle in individuals with spinal cord injury

Selected contractile properties and fatigability of the quadriceps muscle were studied in seven spinal cord-injured (SCI) and 13 able-bodied control (control) individuals. The SCI muscles demonstrated faster rates of contraction and relaxation than did control muscles and extremely large force oscillation amplitudes in the 10-Hz signal (65 +/- 22% in SCI versus 23 +/- 8% in controls). In addition, force loss and slowing of relaxation following repeated fatiguing contractions were greater in SCI compared with controls. The faster contractile properties and greater fatigability of the SCI muscles are in agreement with a characteristic predominance of fast glycolytic muscle fibers. Unexpectedly, the SCI muscles exhibited a force-frequency relationship shifted to the left, most likely as the result of relatively large twitch amplitudes. The results indicate that the contractile properties of large human locomotory muscles can be characterized using the approach described and that the transformation to faster properties consequent upon changes in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles.

Cardiorespiratory responses to arm cranking and electrical stimulation leg cycling in people with paraplegia

PURPOSE

The purpose of this study was to assess the cardiorespiratory responses during arm exercise with and without concurrent electrical stimulation-induced leg cycling in people with paraplegia.

METHODS

On separate days, 10 subjects with spinal cord injuries (T5-T12) performed either arm cranking (ACE), or simultaneous arm cranking + electrical stimulation-induced leg cycling (ACE+ES-LCE) graded exercise tests.

RESULTS

During submaximal, steady-state exercise, ACE+ES-LCE elicited significantly higher VO2, (by 0.25-0.28 L x min(-1)) stroke volume (by 13 mL), and VE(BTPS) (by 9.4 L x min(-1)) compared with ACE alone. In contrast, there were no significant differences of submaximal HR, cardiac output, or power output between the exercise modes. At maximal exercise, ACE+ES-LCE elicited significantly higher VO2 (by 0.23 L x min(-1)) compared with ACE alone, but there were no differences in power output, HR, or VE(BTPS).

CONCLUSIONS

These results demonstrate that during submaximal or maximal exercise there was a greater metabolic stress elicited during ACE+ES-LCE compared with during ACE alone. The higher stroke volume observed during submaximal ACE+ES-LCE, in the absence of any difference in HR, implied a reduced venous pooling and higher cardiac volume loading during ACE+ES-LCE. These results suggest that training incorporating ACE+ES-LCE may be more effective in improving aerobic fitness in people with paraplegia than ACE alone.

Exercise-induced overexpression of key regulatory proteins involved in glucose uptake and metabolism in tetraplegic persons: molecular mechanism for improved glucose homeostasis

Complete spinal cord lesion leads to profound metabolic abnormalities and striking changes in muscle morphology. Here we assess the effects of electrically stimulated leg cycling (ESLC) on whole body insulin sensitivity, skeletal muscle glucose metabolism, and muscle fiber morphology in five tetraplegic subjects with complete C5-C7 lesions. Physical training (seven ESLC sessions/wk for 8 wk) increased whole body insulin-stimulated glucose uptake by 33+/-13%, concomitant with a 2.1-fold increase in insulin-stimulated (100 microU/ml) 3-O-methylglucose transport in isolated vastus lateralis muscle. Physical training led to a marked increase in protein expression of GLUT4 (378+/-85%), glycogen synthase (526+/-146%), and hexokinase II (204+/-47%) in vastus lateralis muscle, whereas phosphofructokinase expression (282+/-97%) was not significantly changed. Hexokinase II activity was significantly increased, whereas activity of phosphofructokinase, glycogen synthase, and citrate synthase was not changed after training. Muscle fiber type distribution and fiber area were markedly altered compared to able-bodied subjects before ESLC training, with no change noted in either parameter after ECSL training. In conclusion, muscle contraction improves insulin action on whole body and cellular glucose uptake in cervical cord-injured persons through a major increase in protein expression of key genes involved in the regulation of glucose metabolism. Furthermore, improvements in insulin action on glucose metabolism are independent of changes in muscle fiber type distribution.

Bone fracture during electrical stimulation of the quadriceps in a spinal cord injured subject

We report a fracture through the lateral femoral condyle of a paraplegic subject caused by electrical stimulation (ES). The subject was a 50-year-old man who 4 years earlier had sustained a complete spinal cord injury (SCI) at level T6. The fracture occurred during ES-induced measurement of maximal isometric torque of the quadriceps with the knee flexed at an angle of 90 degrees. ES was delivered through surface electrodes with biphasic square wave pulses from a constant current stimulator. The torque was calculated to be 93Nm, corresponding to 20.8kg at the ankle. The regional bone mineral density of the entire lower extremities was .83g/cm2, corresponding to 60% of sex- and age-matched able-bodied reference values. Several factors are suspected to have contributed to the fracture: maximal ES in combination with a muscle spasm, severe osteoporosis, increased muscular strength induced by regular ES cycling (twice a week), and testing position with the knee locked in 90 degrees flexion. The risk of fracture as well as various precautions are discussed and should be taken into consideration in future studies.