Musculoskeletal adaptations in chronic spinal cord injury: effects of long-term soleus electrical stimulation training

Developing and Investigating a Nanovibration Intervention for the Prevention/Reversal of Bone Loss Following Spinal Cord Injury

Osteoporosis disrupts the fine-tuned balance between bone formation and resorption, leading to reductions in bone quantity and quality and ultimately increasing fracture risk. Prevention and treatment of osteoporotic fractures is essential for reductions in mortality, morbidity, and the economic burden, particularly considering the aging global population. Extreme bone loss that mimics time-accelerated osteoporosis develops in the paralyzed limbs following complete spinal cord injury (SCI). In vitro nanoscale vibration (1 kHz, 30 or 90 nm amplitude) has been shown to drive differentiation of mesenchymal stem cells toward osteoblast-like phenotypes, enhancing osteogenesis and inhibiting osteoclastogenesis simultaneously. Here, we develop and characterize a wearable device designed to deliver and monitor continuous nanoamplitude vibration to the hindlimb long bones of rats with complete SCI. We investigate whether a clinically feasible dose of nanovibration (two 2 h/day, 5 days/week for 6 weeks) is effective at reversing the established SCI-induced osteoporosis. Laser interferometry and finite element analysis confirmed transmission of nanovibration into the bone, and microcomputed tomography and serum bone formation and resorption markers assessed effectiveness. The intervention did not reverse SCI-induced osteoporosis. However, serum analysis indicated an elevated concentration of the bone formation marker procollagen type 1 N-terminal propeptide (P1NP) in rats receiving 40 nm amplitude nanovibration, suggesting increased synthesis of type 1 collagen, the major organic component of bone. Therefore, enhanced doses of nanovibrational stimulus may yet prove beneficial in attenuating/reversing osteoporosis, particularly in less severe forms of osteoporosis.

Low-frequency electrically induced exercise after spinal cord injury: Physiologic challenge to skeletal muscle and feasibility for long-term use

CONTEXT

Skeletal muscle has traditionally been considered a "force generator": necessary for purposes of locomotion, but expendable for non-ambulators who use wheelchairs, such as people with a spinal cord injury (SCI). Active skeletal muscle plays an indispensable role in regulating systemic metabolic functions, even in people with paralysis, but because of severe osteoporosis, high tetanic muscle forces induced with high frequency electrical stimulation may be risky for some individuals. The purpose of this study was to compare the physiologic muscle properties incurred by two low force/low frequency repetitive stimulation protocols (1 and 3 Hz); and, to assess the acceptability of each protocol among people with SCI.

METHODS

Ten individuals with chronic SCI (12.9 years) and 11 individuals without SCI (NonSCI) participated in the study. Participants received either 1 or 3 Hz stimulation to the quadriceps muscle on Day 1, then the converse on Day 2. Each session consisted of 1000 stimulus pulses.

RESULTS

The initial and maximum forces were similar for the 1 and 3 Hz frequencies. The fatigue index (FI) for SCI and NonSCI groups were lower (P < 0.007) for 3 Hz than for 1 Hz (0.34 ± 0.17 versus 0.65 ± 0.16 and 0.72 ± 0.14 versus 0.87 ± 0.07, respectively).

CONCLUSION

The 3 Hz stimulation offered the greatest physiological challenge and was perceived as more acceptable for long term use among people with SCI.

Impaired Glucose Tolerance and Visceral Adipose Tissue Thickness among Lean and Non-Lean People with and without Spinal Cord Injury

After spinal cord injury (SCI), multiple adaptations occur that influence metabolic health and life quality. Prolonged sitting and inactivity predispose people with SCI to body composition changes, such as increased visceral adipose tissue (VAT) thickness, which is often associated with impaired glucose tolerance. Our goal is to understand whether VAT is an index of leanness, and, secondarily, whether mobility methods influence glucose tolerance for people living with SCI. A total of 15 people with SCI and 20 people without SCI had fasting oral glucose tolerance tests (OGTT) and VAT thickness (leanness) measured during a single session. Glucose was 51% and 67% greater for individuals with SCI relative to those without SCI after 60 and 120 min of an OGTT (p < 0.001). Glucose area under the curve (AUC) was 28%, 34%, and 60% higher for non-lean people with SCI than lean people with SCI and non-lean and lean people without SCI, respectively (p = 0.05, p = 0.009, p < 0.001). VAT was associated with glucose AUC (R2 = 0.23, p = 0.004). Taken together, these findings suggest that leanness, as estimated from VAT, may be an important consideration when developing rehabilitation programs to influence metabolism among people with SCI.

The Pathophysiology, Identification and Management of Fracture Risk, Sublesional Osteoporosis and Fracture among Adults with Spinal Cord Injury

BACKGROUND

The prevention of lower extremity fractures and fracture-related morbidity and mortality is a critical component of health services for adults living with chronic spinal cord injury (SCI).

METHODS

Established best practices and guideline recommendations are articulated in recent international consensus documents from the International Society of Clinical Densitometry, the Paralyzed Veterans of America Consortium for Spinal Cord Medicine and the Orthopedic Trauma Association.

RESULTS

This review is a synthesis of the aforementioned consensus documents, which highlight the pathophysiology of lower extremity bone mineral density (BMD) decline after acute SCI. The role and actions treating clinicians should take to screen, diagnose and initiate the appropriate treatment of established low bone mass/osteoporosis of the hip, distal femur or proximal tibia regions associated with moderate or high fracture risk or diagnose and manage a lower extremity fracture among adults with chronic SCI are articulated. Guidance regarding the prescription of dietary calcium, vitamin D supplements, rehabilitation interventions (passive standing, functional electrical stimulation (FES) or neuromuscular electrical stimulation (NMES)) to modify bone mass and/or anti-resorptive drug therapy (Alendronate, Denosumab, or Zoledronic Acid) is provided. In the event of lower extremity fracture, the need for timely orthopedic consultation for fracture diagnosis and interprofessional care following definitive fracture management to prevent health complications (venous thromboembolism, pressure injury, and autonomic dysreflexia) and rehabilitation interventions to return the individual to his/her pre-fracture functional abilities is emphasized.

CONCLUSIONS

Interprofessional care teams should use recent consensus publications to drive sustained practice change to mitigate fracture incidence and fracture-related morbidity and mortality among adults with chronic SCI.

Effects of a combined progressive resistance training and functional electrical stimulation-evoked cycling exercise on lower limb muscle strength of individuals with incomplete spinal cord injury: A randomized controlled study

Objectives

This study was conducted to investigate the effects of combined progressive resistance training (PRT) and functional electrical stimulation-evoked leg cycling exercise (FES-LCE) on isometric peak torque and muscle volume in individuals with incomplete spinal cord injury.

Patients and methods

In the single-blind, randomized controlled trial performed between April 2015 and August 2016, 28 participants were randomized between two exercise interventions (FES-LCE+PRT and FES-LCE alone), and training was conducted over 12 weeks. The isometric muscle peak torque and muscle volume for both lower limbs were measured at the baseline and after 6 and 12 weeks. Linear mixed-model analysis of variance was performed to test the effects of FES-LCE+PRT versus FES-LCE on each outcome measure over time via an intention-to-treat analysis.

Results

Twenty-three participants (18 males, 5 females; mean age: 33.4±9.7 years; range 21 to 50 years) completed study (10 in the FES-LCE+PRT group, and 13 in the FES-LCE group). The 12-week pre-and posttraining change for left hamstrings' muscle peak torque in the FES-LCE+PRT group (mean difference=4.5±7.9 Nm, 45% change, p<0.05) was consistently higher than that in the FES-LCE group (mean difference=2.4±10.3 Nm, 4% change; p<0.018). The improvement in the right quadriceps muscle's peak torque of the FES-LCE+PRT group (mean difference=19±7.6 Nm, 31% change, p<0.05) was more significant compared to the FES-LCE group. The left muscle volume showed a remarkable increase after 12 weeks in the FES-LCE+PRT group (mean difference=0.3±9.3 L, 7% change, p<0.05).

Conclusion

The combination of PRT and FES-LCE was better in improving lower limb muscle strength and volume in chronic incomplete individuals with spinal cord injury.

Effects of Electrical Stimulation Training on Body Composition Parameters After Spinal Cord Injury: A Systematic Review

OBJECTIVE

To determine the effects of neuromuscular electrical stimulation (NMES) or functional electrical stimulation (FES), or both, training on different body composition parameters in individuals with spinal cord injury.

DATA SOURCES

Three independent reviewers searched PubMed, Web of Science, Scopus, Cochrane Central, and Virtual Health Library until March 2020.

STUDY SELECTION

Studies were included if they applied NMES/FES on the lower limb muscles after spinal cord injury, reported stimulation parameters (frequency, pulse duration, and amplitude of current), and body composition parameters, which included muscle cross-sectional area (CSA), fat-free mass, lean mass (LM), fat mass, visceral adipose tissue, and intramuscular fat.

DATA SYNTHESIS

A total of 46 studies were included in the final analysis with a total sample size of 414 subjects. NMES loading exercise and FES cycling exercise were commonly used for training. Increases in muscle CSA ranged from 5.7-75%, with an average of 26% (n=33). Fifteen studies reported changes (both increase and decrease) in LM or fat-free mas ranged from -4% to 35%, with an average of less than 5%. Changes in fat mass (n=10) were modest. The effect on ectopic adipose tissue is inconclusive, with 2 studies showing an average reduction in intramuscular fat by 9.9%. Stimulation parameters ranged from 200-1000 μs for pulse duration, 2-60 Hz for the frequency, and 10-200 mA in amplitude. Finally, increase in weekly training volumes after NMES loading exercise resulted in a remarkable increase in percentage changes in LM or muscle CSA.

CONCLUSIONS

NMES/FES is an effective rehabilitation strategy for muscle hypertrophy and increasing LM. Weekly training volumes are associated with muscle hypertrophy after NMES loading exercise. Furthermore, positive muscle adaptations occur despite the applied stimulation parameters. Finally, the included studies reported wide range of stimulation parameters without reporting rationale for such selection.

The Effects of Exercise and Activity-Based Physical Therapy on Bone after Spinal Cord Injury

Spinal cord injury (SCI) produces paralysis and a unique form of neurogenic disuse osteoporosis that dramatically increases fracture risk at the distal femur and proximal tibia. This bone loss is driven by heightened bone resorption and near-absent bone formation during the acute post-SCI recovery phase and by a more traditional high-turnover osteopenia that emerges more chronically, which is likely influenced by the continual neural impairment and musculoskeletal unloading. These observations have stimulated interest in specialized exercise or activity-based physical therapy (ABPT) modalities (e.g., neuromuscular or functional electrical stimulation cycling, rowing, or resistance training, as well as other standing, walking, or partial weight-bearing interventions) that reload the paralyzed limbs and promote muscle recovery and use-dependent neuroplasticity. However, only sparse and relatively inconsistent evidence supports the ability of these physical rehabilitation regimens to influence bone metabolism or to increase bone mineral density (BMD) at the most fracture-prone sites in persons with severe SCI. This review discusses the pathophysiology and cellular/molecular mechanisms that influence bone loss after SCI, describes studies evaluating bone turnover and BMD responses to ABPTs during acute versus chronic SCI, identifies factors that may impact the bone responses to ABPT, and provides recommendations to optimize ABPTs for bone recovery.

Genomic and Epigenomic Evaluation of Electrically Induced Exercise in People With Spinal Cord Injury: Application to Precision Rehabilitation

OBJECTIVE

Physical therapists develop patient-centered exercise prescriptions to help overcome the physical, emotional, psychosocial, and environmental stressors that undermine a person's health. Optimally prescribing muscle activity for people with disability, such as a spinal cord injury, is challenging because of their loss of volitional movement control and the deterioration of their underlying skeletal systems. This report summarizes spinal cord injury-specific factors that should be considered in patient-centered, precision prescription of muscle activity for people with spinal cord injury. This report also presents a muscle genomic and epigenomic analysis to examine the regulation of the proliferator-activated receptor γ coactivator 1α (PGC-1α) (oxidative) and myostatin (hypertrophy) signaling pathways in skeletal muscle during low-frequency (lower-force) electrically induced exercise versus higher-frequency (higher-force) electrically induced exercise under constant muscle recruitment (intensity).

METHODS

Seventeen people with spinal cord injury participated in 1 or more unilateral electrically induced exercise sessions using a lower-force (1-, 3-, or 5-Hz) or higher-force (20-Hz) protocol. Three hours after the exercise session, percutaneous muscle biopsies were performed on exercised and nonexercised muscles for genomic and epigenomic analysis.

RESULTS

We found that low-frequency (low-force) electrically induced exercise significantly increased the expression of PGC-1α and decreased the expression of myostatin, consistent with the expression changes observed with high-frequency (higher-force) electrically induced exercise. Further, we found that low-frequency (lower-force) electrically induced exercise significantly demethylated, or epigenetically promoted, the PGC-1α signaling pathway. A global epigenetic analysis showed that >70 pathways were regulated with low-frequency (lower-force) electrically induced exercise.

CONCLUSION

These novel results support the notion that low-frequency (low-force) electrically induced exercise may offer a more precise rehabilitation strategy for people with chronic paralysis and severe osteoporosis. Future clinical trials are warranted to explore whether low-frequency (lower-force) electrically induced exercise training affects the overall health of people with chronic spinal cord injury.

Osteoporosis after spinal cord injury: aetiology, effects and therapeutic approaches

Osteoporosis is a long-term consequence of spinal cord injury (SCI) that leads to a high risk of fragility fractures. The fracture rate in people with SCI is twice that of the general population. At least 50% of these fractures are associated with clinical complications such as infections. This review article presents key features of osteoporosis after SCI, starting with its aetiology, a description of temporal and spatial changes in the long bones and the subsequent fragility fractures. It then describes the physical and pharmacological approaches that have been used to attenuate the bone loss. Bone loss after SCI has been found to be highly site-specific and characterised by large inter-variability and site-specific changes. The assessment of the available interventions is limited by the quality of the studies and the lack of information on their effect on fractures, but this evaluation suggests that current approaches do not appear to be effective. More studies are required to identify factors influencing rate and magnitude of bone loss following SCI. In addition, it is important to test these interventions at the sites that are most prone to fracture, using detailed imaging techniques, and to associate bone changes with fracture risk. In summary, bone loss following SCI presents a substantial clinical problem. Identification of at-risk individuals and development of more effective interventions are urgently required to reduce this burden.

Tibiofemoral forces during FES rowing in individuals with spinal cord injury

The purpose of this study is to determine the tibiofemoral forces during functional electrical stimulation (FES) rowing in individuals with spinal cord injury (SCI). We analysed the motion of five participants with SCI during FES rowing, with simultaneous measurements of (i) three-dimensional marker trajectories, (ii) foot reaction forces (FRFs), (iii) ergometer handle forces, and (iv) timestamps for electrical stimulation of the quadriceps and hamstrings muscles. We created full-body musculoskeletal models in OpenSim to determine subject-specific tibiofemoral forces during FES rowing. The peak magnitudes of tibiofemoral forces averaged over five participants with SCI were 2.43 ± 0.39 BW and 2.25 ± 0.71 BW for the left and right legs, respectively. The peak magnitudes of FRFs were 0.19 ± 0.04 BW in each leg. The peak magnitude of handle forces was 0.47 ± 0.19 BW. Peak tibiofemoral force was associated with peak FRF (magnitudes, R² = 0.56, p = 0.013) and peak handle force (magnitudes, R² = 0.54, p = 0.016). The ratios of peak magnitude of tibiofemoral force to peak magnitude of FRF were 12.9 ± 1.9 (left) and 11.6 ± 2.4 (right), and to peak magnitude of handle force were 5.7 ± 2.3 (left) and 4.9 ± 0.9 (right). This work lays the foundation for developing a direct exercise intensity metric for bone mechanical stimulus at the knee during rehabilitation exercises. Clinical Significance: Knowledge of tibiofemoral forces from exercises such as FES rowing may provide clinicians the ability to personalize rehabilitation protocols to ensure that an SCI patient is receiving the minimum dose of mechanical stimulus necessary to maintain bone health.

Epidural stimulation for cardiovascular function increases lower limb lean mass in individuals with chronic motor complete spinal cord injury

NEW FINDINGS

What is the central question of this study? Spinal cord injury results in paralysis and deleterious neuromuscular and autonomic adaptations. Lumbosacral epidural stimulation can modulate motor and/or autonomic functions. Does long-term epidural stimulation for normalizing cardiovascular function affect leg muscle properties? What is the main finding and its importance? Leg lean mass increased after long-term epidural stimulation for cardiovascular function, which was applied in the sitting position and did not activate the leg muscles. Leg muscle strength and fatigue resistance, assessed in a subgroup of individuals, also increased. These adaptations might support interventions for motor recovery and warrant further mechanistic investigation.

ABSTRACT

Chronic motor complete spinal cord injury (SCI) results in paralysis and deleterious neuromuscular and autonomic adaptations. Paralysed muscles demonstrate atrophy, loss of force and increased fatigability. Also, SCI-induced autonomic impairment results in persistently low resting blood pressure and heart rate, among other features. We previously reported that spinal cord epidural stimulation (scES) optimized for cardiovascular (CV) function (CV-scES), which is applied in sitting position and does not activate the leg muscles, can maintain systolic blood pressure within a normotensive range during quiet sitting and during orthostatic stress. In the present study, dual-energy X-ray absorptiometry collected from six individuals with chronic clinically motor complete SCI demonstrated that 88 ± 11 sessions of CV-scES (7 days week^-1 ; 2 h day^-1 in four individuals and 5 h day^-1 in two individuals) over a period of ∼6 months significantly increased lower limb lean mass (by 0.67 ± 0.39 kg or 9.4 ± 8.1%; P < 0.001). Additionally, muscle strength and fatigability data elicited by neuromuscular electrical stimulation in three of these individuals demonstrated a general increase (57 ± 117%) in maximal torque output (between 2 and 44 N m in 14 of the 17 muscle groups tested overall) and torque-time integral during intermittent, fatiguing contractions (63 ± 71%; between 7 and 230% in 16 of the 17 muscle groups tested overall). In contrast, whole-body mass and composition did not change significantly. In conclusion, long-term use of CV-scES can have a significant impact on lower limb muscle properties after chronic motor complete SCI.

Optimizing Neuromuscular Electrical Stimulation Pulse Width and Amplitude to Promote Central Activation in Individuals With Severe Spinal Cord Injury

Neuromuscular electrical stimulation (NMES) is one of the most effective treatments for counteracting the deleterious skeletal muscle adaptations that occur after spinal cord injury (SCI). Additionally, previous findings suggest that NMES can activate motor units via both peripheral and central mechanisms; however, this NMES-promoted central activation is not well understood. In this study, we aimed at investigating the effects of NMES on central activation in 10 individuals with motor complete SCI, focusing on understanding how to optimize NMES pulse width and amplitude for promoting central activation in this population. To this end, we used NMES to generate isometric contractions of the knee extensors and ankle plantarflexors while electromyographic (EMG) activity was recorded from the vastus lateralis and gastrocnemius medialis, respectively. We used EMG activity that persisted after the termination of NMES delivery (post-NMES) as a neurophysiological marker to assess central activation and explored differences in post-NMES EMG activity promoted by 500 and 1,000 μs pulse width NMES. Additionally, we explored the relationships between post-NMES EMG amplitude, torque output, and stimulation amplitude. Our results show that the higher pulse width (1,000 μs) demonstrated a greater effect on central activation as quantified by more frequent occurrences of post-NMES EMG activity (p = 0.002) and a 3.551 μV higher EMG amplitude (p = 0.003) when controlling for the torque output generated by 500 and 1,000 μs pulse width NMES. Importantly, we also found that the interplay among central activation, stimulation amplitude, and muscle torque output differs across SCI individuals, conceivably because of the individual-specific characteristics of the cord lesion and following plasticity of the spinal circuitry. These results suggest that NMES can be optimized to promote central activation, which may lead to novel opportunities for motor function recovery after SCI.

Bone Mineral Density Testing in Spinal Cord Injury: 2019 ISCD Official Position

Spinal cord injury (SCI) causes rapid osteoporosis that is most severe below the level of injury. More than half of those with motor complete SCI will experience an osteoporotic fracture at some point following their injury, with most fractures occurring at the distal femur and proximal tibia. These fractures have devastating consequences, including delayed union or nonunion, cellulitis, skin breakdown, lower extremity amputation, and premature death. Maintaining skeletal integrity and preventing fractures is imperative following SCI to fully benefit from future advances in paralysis cure research and robotic-exoskeletons, brain computer interfaces and other evolving technologies. Clinical care has been previously limited by the lack of consensus derived guidelines or standards regarding dual-energy X-ray absorptiometry-based diagnosis of osteoporosis, fracture risk prediction, or monitoring response to therapies. The International Society of Clinical Densitometry convened a task force to establish Official Positions for bone density assessment by dual-energy X-ray absorptiometry in individuals with SCI of traumatic or nontraumatic etiology. This task force conducted a series of systematic reviews to guide the development of evidence-based position statements that were reviewed by an expert panel at the 2019 Position Development Conference in Kuala Lumpur, Malaysia. The resulting the International Society of Clinical Densitometry Official Positions are intended to inform clinical care and guide the diagnosis of osteoporosis as well as fracture risk management of osteoporosis following SCI.

Hybrid stimulation enhances torque as a function of muscle fusion in human paralyzed and non-paralyzed skeletal muscle

OBJECTIVE

After spinal cord injury (SCI), hybrid stimulation patterns that interpose paired-pulse doublets over a constant-frequency background may enhance the metabolic "work" (muscle torque) performed by paralyzed muscle. This study examined the effect of background stimulation frequency on the torque contribution of the doublet before and after fatigue.

DESIGN

Cross-sectional study.

SETTING

Research laboratory in an academic medical center.

PARTICIPANTS

Five men with chronic sensory and motor-complete SCI and ten non-SCI controls (6 males, 4 females). SCI subjects were recruited from a long-term study of unilateral plantar-flexor training; both limbs were tested for the present study.

INTERVENTIONS

Subjects underwent plantar flexor stimulation at 5, 7, 9, and 12 Hz. The four background frequencies were overlaid with 6 ms doublets delivered at the start, middle, or at both the start and middle of each train. The 5 Hz and 12 Hz frequencies were analyzed after fatigue.

OUTCOME MEASURES

Mean torque, peak torque, torque fusion index, doublet torque.

RESULTS

Trains with doublets at both the start and middle yielded the most consistent enhancement of torque (all P < 0.028). Torque contribution of the doublet was greatest at low stimulus frequencies (all P < 0.016). The low relative fusion of untrained paralyzed muscle preserved the efficacy of the doublet even during fatigue.

CONCLUSION

Hybrid stimulus trains may be an effective way to increase contractile work in paralyzed muscle, even after fatigue. They may be useful for rehabilitation strategies designed to enhance the metabolic work performed by paralyzed skeletal muscle.

Advanced weight-bearing mat exercises combined with functional electrical stimulation to improve the ability of wheelchair-dependent people with spinal cord injury to transfer and attain independence in activities of daily living: a randomized controlled trial

STUDY DESIGN

Randomized controlled trial.

OBJECTIVE

To determine the effects of advanced weight-bearing mat exercises (AWMEs) with/without functional electrical stimulation (FES) of the quadriceps and gastrocnemius muscles on the ability of wheelchair-dependent people with spinal cord injury (SCI) to transfer and attain independence in activities of daily living (ADLs).

SETTING

An outpatient clinic, Iran.

METHODS

People with traumatic chronic paraplegia (N = 16) were randomly allocated to three groups. The exercise group (EX; N = 5) performed AWMEs of quadruped unilateral reaching and tall-kneeling for 24 weeks (3 days/week). Sessions were increased from 10 min to 54 min over the 24-week period. The exercise-FES group (EX + FES; N = 5) performed AWMEs simultaneously with FES of the quadriceps and gastrocnemius muscles. The control group performed no exercise and no FES (N = 6). The primary outcomes were the total Spinal Cord Independence Measure-III (SCIM-III) to reflect independence with ADL, and the sum of the four SCIM-III transfer items to reflect ability to transfer. There were six other outcomes.

RESULTS

The mean (95% CI) between-group differences of the four transfer items of the SCIM-III for the EX vs. control group was 1.8 points (0.2-3.4), and for the EX + FES vs. control group was 2 points (0.4-3.6). The equivalent differences for the total SCIM-III scores were 2.7 points (-0.6-6.0) and 4.1 points (0.8-7.4), respectively. There were no significant between-group differences for any other outcomes.

CONCLUSIONS

Advanced weight-bearing mat exercises improve the ability of wheelchair-dependent people with SCI to transfer and attain independence in ADL.

Combination Therapy With Zoledronic Acid and FES-Row Training Mitigates Bone Loss in Paralyzed Legs: Results of a Randomized Comparative Clinical Trial

Spinal cord injury (SCI) results in rapid, severe osteoporosis and an increased risk of lower extremity fractures. Despite the medical complications associated with these fractures, there is no standard of care to prevent osteoporotic fractures following SCI. Functional electrical stimulation- (FES-) assisted rowing is a promising intervention to improve bone health in SCI because of its ability to generate a muscular contraction in conjunction with mechanical loading of the lower extremity long bones. Combination therapy consisting of FES-rowing plus zoledronic acid (ZA) may be a superior treatment via inhibition of bone resorption and stimulation of new bone formation. We studied participants enrolled in a randomized clinical trial comparing FES-rowing alone with FES-rowing plus ZA to improve bone health in SCI. Volumetric CT scans at the distal femur and proximal tibial metaphyses were performed. Bone geometric properties (cortical thickness index [CTI], cortical compressive strength index [CSI], buckling ratio [BR], bending strength index) and mineral (cortical bone volume [CBV], cortical bone mineral density, cortical bone mineral content) indices were determined. In models adjusting for baseline values, we found that the CBV (p = 0.05 to 0.006), the CTI (p = 0.009), and the BR (p = 0.001) at both the distal femoral and proximal tibial metaphyses were greater in the ZA plus rowing group compared with the rowing-only group. Similarly, there was a significant positive association between the total rowing work completed and the BR at the proximal tibia (p = 0.05). A subgroup analysis of the rowing-only arm showed that gains in the CSI at the tibial metaphysis varied in a dose-dependent fashion based on the total amount of exercise performed (p = 0.009). These findings demonstrate that the osteogenic response to FES-rowing is dose-dependent. Combination therapy with ZA and FES-row training has therapeutic potential to improve bone quality, and perhaps reduce fracture risk at the most common fracture site following SCI. © 2019 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Submaximal Marker for Investigating Peak Muscle Torque Using Neuromuscular Electrical Stimulation after Paralysis

Spinal cord injury (SCI) results in deleterious skeletal muscle adaptations, such as relevant atrophy and loss of force. In particular, the relevant loss of lower-limb force-generating capacity may limit functional mobility even if neuronal control was sufficient. Currently, methods of assessing maximal force-generating capacity using neuromuscular electrical stimulation (NMES) are limited in individuals who cannot tolerate higher stimulation amplitudes, such as those with residual sensation and those at risk of fracture. In this study, we examined the relationship between NMES amplitude and muscle torque exerted (recruitment curve) in order to determine whether maximal torque output can be characterized by a submaximal marker. Recruitment curves for knee extensors, knee flexors, and ankle plantarflexors were recorded from 30 individuals with motor complete SCI. NMES was delivered starting with an amplitude of 5 mA, and increasing by 5 mA for every subsequent stimulation until either the participant requested to stop the stimulation or the maximum stimulation amplitude (140 mA) was reached. Significant correlations between peak slope of the recruitment curve and peak torque for all muscle groups were found (knee extensors, r = 0.75; p < 0.0001; knee flexors, r = 0.68; p < 0.0001; ankle plantarflexors, r = 0.91; p < 0.0001), indicating that muscles that show greater peak slope of the recruitment curve tend to generate a greater peak torque. This suggests that peak slope, which was achieved at an average stimulation intensity (55.0 mA) that was 43% smaller than that corresponding to peak torque (97.4 mA), may be used as a submaximal marker for characterizing maximal torque output in individuals with SCI.

Interval training elicits higher enjoyment versus moderate exercise in persons with spinal cord injury

BACKGROUND

High intensity interval training (HIIT) is a robust and time-efficient approach to improve multiple health indices including maximal oxygen uptake (VO2max). Despite the intense nature of HIIT, data in untrained adults report greater enjoyment of HIIT versus continuous exercise (CEX). However, this has yet to be investigated in persons with spinal cord injury (SCI).

OBJECTIVE

To examine differences in enjoyment in response to CEX and HIIT in persons with SCI.

DESIGN

Repeated measures, within-subjects design.

SETTING

University laboratory in San Diego, CA.

PARTICIPANTS

Nine habitually active men and women (age = 33.3 ± 10.5 years) with chronic SCI.

INTERVENTION

Participants performed progressive arm ergometry to volitional exhaustion to determine VO2peak. During subsequent sessions, they completed CEX, sprint interval training (SIT), or HIIT in randomized order.

OUTCOME MEASURES

Physical activity enjoyment (PACES), affect, rating of perceived exertion (RPE), VO2, and blood lactate concentration (BLa) were measured.

RESULTS

Despite a higher VO2, RPE, and BLa consequent with HIIT and SIT (P < 0.05), PACES was significantly higher (P = 0.03) in response to HIIT (107.4 ± 13.4) and SIT (103.7 ± 12.5) compared to CEX (81.6 ± 25.4). Fifty-five percent of participants preferred HIIT and 45% preferred SIT, with none identifying CEX as their preferred exercise mode.

CONCLUSION

Compared to CEX, brief sessions of submaximal or supramaximal interval training elicit higher enjoyment despite higher metabolic strain. The long-term efficacy and feasibility of HIIT in this population should be explored considering that it is not viewed as more aversive than CEX.

In Vivo Assessment of Mitochondrial Dysfunction in Clinical Populations Using Near-Infrared Spectroscopy

The ability to sustain submaximal exercise is largely dependent on the oxidative capacity of mitochondria within skeletal muscle, and impairments in oxidative metabolism have been implicated in many neurologic and cardiovascular pathologies. Here we review studies which have demonstrated the utility of Near-infrared spectroscopy (NIRS) as a method of evaluating of skeletal muscle mitochondrial dysfunction in clinical human populations. NIRS has been previously used to noninvasively measure tissue oxygen saturation, but recent studies have demonstrated the utility of NIRS as a method of evaluating skeletal muscle oxidative capacity using post-exercise recovery kinetics of oxygen metabolism. In comparison to historical methods of measuring muscle metabolic dysfunction in vivo, NIRS provides a more versatile and economical method of evaluating mitochondrial oxidative capacity in humans. These advantages generate great potential for the clinical applicability of NIRS as a means of evaluating muscle dysfunction in clinical populations.

A feasibility pilot using telehealth videoconference monitoring of home-based NMES resistance training in persons with spinal cord injury

INTRODUCTION

The objective of the study was to investigate the feasibility and initial efficacy of telehealth communication in conjunction with surface neuromuscular electrical stimulation (NMES) resistance training (RT) to induce muscle hypertrophy.

MATERIALS AND METHODS

This was a home-based setting of within-subject control design of trained vs controlled limbs. Five men with chronic (>1 year postinjury) motor-complete spinal cord injury (SCI) participated in a twice-weekly telehealth videoconference program using home-based NMES-RT for 8 weeks. Stimulation was applied to the knee extensor muscle group of the trained leg, while the untrained leg served as a control. Participants received real-time feedback to ensure a proper setup of electrodes and stimulator to monitor subject safety throughout the entire training session. Magnetic resonance imaging was used to measure cross-sectional areas (CSAs) and intramuscular fat (IMF) of the whole thigh and individual muscle groups. Average two-way travel time, distance traveled in miles and total cost of gas per mile were calculated.

RESULTS

Participants had 100% compliance. Trained whole and absolute knee extensor muscle CSA increased by 13% (P=0.002) and 18% (P=0.0002), with no changes in the controlled limb. Absolute knee flexor and adductor CSAs increased by 3% (P=0.02) and 13% (P=0.0001), respectively. Absolute whole thigh and knee extensor IMF CSAs decreased significantly in the trained limb by 14% (P=0.01) and 36% (P=0.0005), respectively, with no changes in controlled limb.

DISCUSSION

The pilot work documented that using telehealth communication is a safe, feasible and potentially cost-reducing approach for monitoring home-based NMES-RT in persons with chronic SCI. All trained muscles showed detectable muscle hypertrophy with concomitant decrease in ectopic adipose tissue.

Evidence-based prevention and treatment of osteoporosis after spinal cord injury: a systematic review

PURPOSE

Spinal cord injury (SCI) results in accelerated bone mineral density (BMD) loss and disorganization of trabecular bone architecture. The mechanisms underlying post-SCI osteoporosis are complex and different from other types of osteoporosis. Findings of studies investigating efficacy of pharmacological or rehabilitative interventions in SCI-related osteoporosis are controversial. The aim of this study was to review the literature pertaining to prevention and evidence-based treatments of SCI-related osteoporosis.

METHODS

In this systematic review, MEDLINE, EMBASE, PubMed, and the Cochrane Library were used to identify papers from 1946 to December 31, 2015. The search strategy involved the following keywords: spinal cord injury, osteoporosis, and bone loss.

RESULTS

Finally, 56 studies were included according to the inclusion criteria. Only 16 randomized controlled trials (involving 368 patients) were found. We found following evidences for effectiveness of bisphosphonates in prevention of BMD loss in acute SCI: very low-quality evidence for clodronate and etidronate, low-quality evidence for alendronate, and moderate-quality evidence for zoledronic acid. Low-quality evidence showed no effectiveness for tiludronate. In chronic SCI cases, we found low-quality evidence for effectiveness of vitamin D₃ analogs combined with 1-alpha vitamin D₂. However, low-quality inconsistent evidence exists for alendronate. For non-pharmacologic interventions, very low-quality evidence exists for effectiveness of standing with or without treadmill walking in acute SCI. Other low-quality evidences indicated that electrical stimulation, tilt-table standing, and ultrasound provide no significant effects. Very low-quality evidence did not show any benefit for low-intensity (3 days per week) cycling with functional electrical stimulator in chronic SCI.

CONCLUSIONS

No recommendations can be made from this review, regarding overall low quality of evidence as a result of high risk of bias, low sample size in most of the studies, and notable heterogeneity in type of intervention, outcome measurement, and duration of treatment. Therefore, future high-quality RCT studies with higher sample sizes and more homogeneity are strongly recommended to provide high-quality evidence and make applicable recommendations for prevention and treatment of SCI-related bone loss.

Bone loss at the distal femur and proximal tibia in persons with spinal cord injury: imaging approaches, risk of fracture, and potential treatment options

Persons with spinal cord injury (SCI) undergo immediate unloading of the skeleton and, as a result, have severe bone loss below the level of lesion associated with increased risk of long-bone fractures. The pattern of bone loss in individuals with SCI differs from other forms of secondary osteoporosis because the skeleton above the level of lesion remains unaffected, while marked bone loss occurs in the regions of neurological impairment. Striking demineralization of the trabecular epiphyses of the distal femur (supracondylar) and proximal tibia occurs, with the knee region being highly vulnerable to fracture because many accidents occur while sitting in a wheelchair, making the knee region the first point of contact to any applied force. To quantify bone mineral density (BMD) at the knee, dual energy x-ray absorptiometry (DXA) and/or computed tomography (CT) bone densitometry are routinely employed in the clinical and research settings. A detailed review of imaging methods to acquire and quantify BMD at the distal femur and proximal tibia has not been performed to date but, if available, would serve as a reference for clinicians and researchers. This article will discuss the risk of fracture at the knee in persons with SCI, imaging methods to acquire and quantify BMD at the distal femur and proximal tibia, and treatment options available for prophylaxis against or reversal of osteoporosis in individuals with SCI.

Bone architecture adaptations after spinal cord injury: impact of long-term vibration of a constrained lower limb

SUMMARY

This study examined the effect of a controlled dose of vibration upon bone density and architecture in people with spinal cord injury (who eventually develop severe osteoporosis). Very sensitive computed tomography (CT) imaging revealed no effect of vibration after 12 months, but other doses of vibration may still be useful to test.

INTRODUCTION

The purposes of this report were to determine the effect of a controlled dose of vibratory mechanical input upon individual trabecular bone regions in people with chronic spinal cord injury (SCI) and to examine the longitudinal bone architecture changes in both the acute and chronic state of SCI.

METHODS

Participants with SCI received unilateral vibration of the constrained lower limb segment while sitting in a wheelchair (0.6g, 30 Hz, 20 min, three times weekly). The opposite limb served as a control. Bone mineral density (BMD) and trabecular micro-architecture were measured with high-resolution multi-detector CT. For comparison, one participant was studied from the acute (0.14 year) to the chronic state (2.7 years).

RESULTS

Twelve months of vibration training did not yield adaptations of BMD or trabecular micro-architecture for the distal tibia or the distal femur. BMD and trabecular network length continued to decline at several distal femur sub-regions, contrary to previous reports suggesting a "steady state" of bone in chronic SCI. In the participant followed from acute to chronic SCI, BMD and architecture decline varied systematically across different anatomical segments of the tibia and femur.

CONCLUSIONS

This study supports that vibration training, using this study's dose parameters, is not an effective anti-osteoporosis intervention for people with chronic SCI. Using a high-spatial-resolution CT methodology and segmental analysis, we illustrate novel longitudinal changes in bone that occur after spinal cord injury.

Reactions of the rat musculoskeletal system to compressive spinal cord injury (SCI) and whole body vibration (WBV) therapy

Traumatic spinal cord injury (SCI) causes a loss of locomotor function with associated compromise of the musculo-skeletal system. Whole body vibration (WBV) is a potential therapy following SCI, but little is known about its effects on the musculo-skeletal system. Here, we examined locomotor recovery and the musculo-skeletal system after thoracic (T7-9) compression SCI in adult rats. Daily WBV was started at 1, 7, 14 and 28 days after injury (WBV1-WBV28 respectively) and continued over a 12-week post-injury period. Intact rats, rats with SCI but no WBV (sham-treated) and a group that received passive flexion and extension (PFE) of their hind limbs served as controls. Compared to sham-treated rats, neither WBV nor PFE improved motor function. Only WBV14 and PFE improved body support. In line with earlier studies we failed to detect signs of soleus muscle atrophy (weight, cross sectional diameter, total amount of fibers, mean fiber diameter) or bone loss in the femur (length, weight, bone mineral density). One possible explanation is that, despite of injury extent, the preservation of some axons in the white matter, in combination with quadripedal locomotion, may provide sufficient trophic and neuronal support for the musculoskeletal system.

Chinese tuina downregulates the elevated levels of tissue plasminogen activator in sciatic nerve injured Sprague-Dawley rats

OBJECTIVE

To elucidate the mechanism of Chinese tuina in treating sciatic nerve crush injury, and to detect the levels of tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1), which is thought to play an important role in nerve regeneration.

METHODS

Thirty-two adult male Sprague-Dawley rats were subjected to sciatic nerve crush injury and 16 rats (sham-operated group) went through a sham operation. Control group was given no treatment while tuina group received tuina therapy since day 7 post-surgery. Tuina treatment was performed once a day and lasted for 20 days. The sciatic functional index was examined every 5 days during the treatment session. The rats' gastrocnemius muscles were evaluated for changes in mass and immunohistochemistry techniques were performed to detect the levels of tPA and PAI-1.

RESULTS

Tuina therapy improved the motor function of sciatic nerve injured rats (P<0.05), however, it did not increase muscle volume (P<0.05). Tuina downregulated the levels of tPA and PAI-1 (P<0.05).

CONCLUSIONS

The present study implies that tuina treatment could accelerate rehabilitation of peripheral nerve injury.

Evaluation of serum myostatin and sclerostin levels in chronic spinal cord injured patients

STUDY DESIGN

Case-control study.

OBJECTIVES

To assess serum myostatin levels, bone mineral density (BMD), appendicular skeletal muscle mass (ASMM) and serum sclerostin levels in chronic spinal cord injured (SCI) patients and healthy controls.

SETTING

SCI centre in Italy.

METHODS

Blood samples, whole-body bioelectrical impedance analysis and BMD measurement with the ultrasound technique at the calcaneus level were taken from patients suffering from chronic SCI (both motor complete and incomplete) and healthy control subjects.

RESULTS

A total of 28 SCI patients and 15 healthy controls were enrolled. Serum myostatin levels were statistically higher (P<0.01) in SCI patients compared with healthy controls. Similar results were found comparing both the motor complete and the motor incomplete SCI subgroups to healthy controls. Serum sclerostin was significantly higher in patients with SCI compared with healthy controls (P<0.01). BMD, stiffness and mean T-score values in SCI patients were significantly lower than those in healthy controls. Serum myostatin concentrations in the motor complete SCI subgroups correlated only with serum sclerostin levels (r(2)=0.42; P=0.001) and ASMM (r(2)=0.70; P=0.002) but not in healthy controls.

DISCUSSION

Serum myostatin and serum sclerostin are significantly higher in chronic SCI patients compared with healthy controls. They are potential biomarkers of muscle and bone modifications after SCI. This is the first study reporting an increase in serum myostatin in patients suffering from chronic SCI and a correlation with ASMM.

The effect of low-magnitude whole body vibration on bone density and microstructure in men and women with chronic motor complete paraplegia

OBJECTIVE

To examine the effect of low-magnitude whole body vibration on bone density and microstructure in women and men with chronic motor complete paraplegia.

METHODS

We studied nine subjects (four women and five men) with motor complete paraplegia of 2 years duration or more, age 20-50 years. Subjects were instructed to stand on a low-magnitude vibration plate within a standing frame for 20 minutes per day, 5 days a week, and for 6 months. Bone density at the proximal femur by dual-energy X-ray absorptiometry and bone microstructure at the distal tibia by high-resolution peripheral quantitative computed tomography were assessed at four timepoints over 12 months (baseline, at 3 months and 6 months while on intervention, and after 6 months off intervention).

RESULTS

Standing on the low-magnitude vibration plate with a standing frame was well tolerated by participants. However, most subjects did not show an improvement in bone density or microstructure after 6 months of intervention, or any relevant changes 6 months following the discontinuation of the low-magnitude vibration.

CONCLUSION

We were unable to identify an improvement in either bone density or microstructure following 6 months use of a low-magnitude vibration plate in women or men with chronic motor complete paraplegia. Longer duration of use may be necessary, or it is possible that this intervention is of limited benefit following chronic spinal cord injury.

The effects of electrical stimulation on body composition and metabolic profile after spinal cord injury--Part II

Diet and exercise are cornerstones in the management of obesity and associated metabolic complications, including insulin resistance, type 2 diabetes, and disturbances in the lipid profile. However, the role of exercise in managing body composition adaptations and metabolic disorders after spinal cord injury (SCI) is not well established. The current review summarizes evidence about the efficacy of using neuromuscular electrical stimulation or functional electrical stimulation in exercising the paralytic lower extremities to improve body composition and metabolic profile after SCI. There are a number of trials that investigated the effects on muscle cross-sectional area, fat-free mass, and glucose/lipid metabolism. The duration of the intervention in these trials varied from 6 weeks to 24 months. Training frequency ranged from 2 to 5 days/week. Most studies documented significant increases in muscle size but no noticeable changes in adipose tissue. While increases in skeletal muscle size after twice weekly training were greater than those trials that used 3 or 5 days/week, other factors such as differences in the training mode, i.e. resistance versus cycling exercise and pattern of muscle activation may be responsible for this observation. Loading to evoke muscle hypertrophy is a key component in neuromuscular training after SCI. The overall effects on lean mass were modest and did not exceed 10% and the effects of training on trunk or pelvic muscles remain unestablished. Most studies reported improvement in glucose metabolism with the enhancement of insulin sensitivity being the major factor following training. The effect on lipid profile is unclear and warrants further investigation.

Whole-Body Electromyostimulation to Fight Osteopenia in Elderly Females: The Randomized Controlled Training and Electrostimulation Trial (TEST-III)

Whole-body electromyostimulation (WB-EMS) has been shown to be effective in increasing muscle strength and mass in elderly women. Because of the interaction of muscles and bones, these adaptions might be related to changes in bone parameters. 76 community-living osteopenic women 70 years and older were randomly assigned to either a WB-EMS group (n = 38) or a control group (CG: n = 38). The WB-EMS group performed 3 sessions every 14 days for one year while the CG performed gymnastics containing identical exercises without EMS. Primary study endpoints were bone mineral density (BMD) at lumbar spine (LS) and total hip (thip) as assessed by DXA. After 54 weeks of intervention, borderline nonsignificant intergroup differences were determined for LS-BMD (WB-EMS: 0.6 ± 2.5% versus CG -0.7 ± 2.5%, P = .051) but not for thip-BMD (WB-EMS: -1.1 ± 1.9% versus CG: -0.8 ± 2.3%, P = .771). With respect to secondary endpoints, there was a gain in lean body mass (LBM) of 1.5% (P = .006) and an increase in grip strength of 8.4% (P = .000) in the WB-EMS group compared to CG. WB-EMS effects on bone are less pronounced than previously reported effects on muscle mass. However, for subjects unable or unwilling to perform intense exercise programs, WB-EMS may be an option for maintaining BMD at the LS.

Method to Reduce Muscle Fatigue During Transcutaneous Neuromuscular Electrical Stimulation in Major Knee and Ankle Muscle Groups

BACKGROUND

A critical limitation with transcutaneous neuromuscular electrical stimulation as a rehabilitative approach is the rapid onset of muscle fatigue during repeated contractions. We have developed a method called spatially distributed sequential stimulation (SDSS) to reduce muscle fatigue by distributing the center of electrical field over a wide area within a single stimulation site, using an array of surface electrodes.

OBJECTIVE

To extend the previous findings and to prove feasibility of the method by exploring the fatigue-reducing ability of SDSS for lower limb muscle groups in the able-bodied population, as well as in individuals with spinal cord injury (SCI).

METHODS

SDSS was delivered through 4 active electrodes applied to the knee extensors and flexors, plantarflexors, and dorsiflexors, sending a stimulation pulse to each electrode one after another with 90° phase shift between successive electrodes. Isometric ankle torque was measured during fatiguing stimulations using SDSS and conventional single active electrode stimulation lasting 2 minutes.

RESULTS

We demonstrated greater fatigue-reducing ability of SDSS compared with the conventional protocol, as revealed by larger values of fatigue index and/or torque peak mean in all muscles except knee flexors of able-bodied individuals, and in all muscles tested in individuals with SCI.

CONCLUSIONS

Our study has revealed improvements in fatigue tolerance during transcutaneous neuromuscular electrical stimulation using SDSS, a stimulation strategy that alternates activation of subcompartments of muscles. The SDSS protocol can provide greater stimulation times with less decrement in mechanical output compared with the conventional protocol.

A minimal dose of electrically induced muscle activity regulates distinct gene signaling pathways in humans with spinal cord injury

Paralysis after a spinal cord injury (SCI) induces physiological adaptations that compromise the musculoskeletal and metabolic systems. Unlike non-SCI individuals, people with spinal cord injury experience minimal muscle activity which compromises optimal glucose utilization and metabolic control. Acute or chronic muscle activity, induced through electrical stimulation, may regulate key genes that enhance oxidative metabolism in paralyzed muscle. We investigated the short and long term effects of electrically induced exercise on mRNA expression of human paralyzed muscle. We developed an exercise dose that activated the muscle for only 0.6% of the day. The short term effects were assessed 3 hours after a single dose of exercise, while the long term effects were assessed after training 5 days per week for at least one year (adherence 81%). We found a single dose of exercise regulated 117 biological pathways as compared to 35 pathways after one year of training. A single dose of electrical stimulation increased the mRNA expression of transcriptional, translational, and enzyme regulators of metabolism important to shift muscle toward an oxidative phenotype (PGC-1α, NR4A3, IFRD1, ABRA, PDK4). However, chronic training increased the mRNA expression of specific metabolic pathway genes (BRP44, BRP44L, SDHB, ACADVL), mitochondrial fission and fusion genes (MFF, MFN1, MFN2), and slow muscle fiber genes (MYH6, MYH7, MYL3, MYL2). These findings support that a dose of electrical stimulation (∼10 minutes/day) regulates metabolic gene signaling pathways in human paralyzed muscle. Regulating these pathways early after SCI may contribute to reducing diabetes in people with longstanding paralysis from SCI.

Neuronal involvement in muscular atrophy

The innervation of skeletal myofibers exerts a crucial influence on the maintenance of muscle tone and normal operation. Consequently, denervated myofibers manifest atrophy, which is preceded by an increase in sarcolemma permeability. Recently, de novo expression of hemichannels (HCs) formed by connexins (Cxs) and other none selective channels, including P2X7 receptors (P2X7Rs), and transient receptor potential, sub-family V, member 2 (TRPV2) channels was demonstrated in denervated fast skeletal muscles. The denervation-induced atrophy was drastically reduced in denervated muscles deficient in Cxs 43 and 45. Nonetheless, the transduction mechanism by which the nerve represses the expression of the above mentioned non-selective channels remains unknown. The paracrine action of extracellular signaling molecules including ATP, neurotrophic factors (i.e., brain-derived neurotrophic factor (BDNF)), agrin/LDL receptor-related protein 4 (Lrp4)/muscle-specific receptor kinase (MuSK) and acetylcholine (Ach) are among the possible signals for repression for connexin expression. This review discusses the possible role of relevant factors in maintaining the normal functioning of fast skeletal muscles and suppression of connexin hemichannel expression.

Osteoporosis in individuals with spinal cord injury

The pathophysiology, clinical considerations, and relevant experimental findings with regard to osteoporosis in individuals with spinal cord injury (SCI) will be discussed. The bone loss that occurs acutely after more neurologically motor complete SCI is unique for its sublesional skeletal distribution and rate, at certain skeletal sites approaching 1% of bone mineral density per week, and its resistance to currently available treatments. The areas of high bone loss include the distal femur, proximal tibia, and more distal boney sites. Evidence from a study performed in monozygotic twins discordant for SCI indicates that sublesional bone loss in the twin with SCI increases for several decades, strongly suggesting that the heightened net bone loss after SCI may persist for an extended period of time. The increased frequency of fragility fracture after paralysis will be discussed, and a few risk factors for such fractures after SCI will be examined. Because vitamin D deficiency, regardless of disability, is a relevant consideration for bone health, as well as an easily reversible condition, the increased prevalence of and treatment target values for vitamin D in this deficiency state in the SCI population will be reviewed. Pharmacological and mechanical approaches to preserving bone integrity in persons with acute and chronic SCI will be reviewed, with emphasis placed on efficacy and practicality. Emerging osteoanabolic agents that improve functioning of WNT/β-catenin signaling after paralysis will be introduced as therapeutic interventions that may hold promise.

Improving the Efficiency of Electrical Stimulation Activities After Spinal Cord Injury

In order to enhance spinal cord injury (SCI) rehabilitation programs using neuromuscular electrical stimulation (NMES) and functional electrical stimulation (FES) it is important to examine the manner in which muscle fibers are recruited and the dose-response relationship. A review of the literature suggests that premature force decline and early fatigue with NMES and FES activities may be alleviated with decreased current frequency and increased current intensity. Dose-response relationships with NMES and FES are dependent on the goals of interest as reversing muscle atrophy can be achieved with activities 2-3 times per week for 6 or more weeks while increasing bone mass is more limited and requires more intense activity with greater exercise frequency and duration, e.g., 3-5 days per week for at least 6-12 months. The best known protocol to elicit neurological improvement is massed practice activities-based restorative therapies (ABRT) (3-5 h per day for several weeks).

High bone density masks architectural deficiencies in an individual with spinal cord injury

Context Spinal cord injury (SCI) causes a decline of bone mineral density (BMD) in the paralyzed extremities via the gradual degradation and resorption of trabecular elements. Clinical tools that report BMD may not offer insight into trabecular architecture flaws that could affect bone's ability to withstand loading. We present a case of a woman with a 30-year history of SCI and abnormally high distal femur BMD. Findings Peripheral quantitative-computed tomography-based BMD for this subject was ∼20% higher than previously published non-SCI values. Computed tomography (CT) revealed evidence of sclerotic bone deposition in the trabecular envelope, most likely due to glucocorticoid-induced osteonecrosis. Volumetric topologic analysis of trabecular architecture indicated that the majority of the bone mineral was organized into thick, plate-like structures rather than a multi-branched trabecular network. Visual analysis of the CT stack confirmed that the sclerotic bone regions were continuous with the cortex at only a handful of points. Conclusions Conventional clinical BMD analysis could have led to erroneous assumptions about this subject's bone quality. CT-based analysis revealed that this subject's high BMD masked underlying architectural flaws. For patients who received prolonged glucocorticoid therapy, excessively high BMD should be viewed with caution. The ability of this subject's bone to resist fracture is, in our view, extremely suspect. A better understanding of the mechanical competency of this very dense, but architecturally flawed bone would be desirable before this subject engaged in activities that load the limbs.

H-reflexes reduce fatigue of evoked contractions after spinal cord injury

INTRODUCTION

Neuromuscular electrical stimulation (NMES) over a muscle belly (mNMES) generates contractions predominantly through M-waves, while NMES over a nerve trunk (nNMES) can generate contractions through H-reflexes in people who are neurologically intact. We tested whether the differences between mNMES and nNMES are present in people with chronic motor-complete spinal cord injury and, if so, whether they influence contraction fatigue.

METHODS

Plantar-flexion torque and soleus electromyography were recorded from 8 participants. Fatigue protocols were delivered using mNMES and nNMES on separate days.

RESULTS

nNMES generated contractions that fatigued less than mNMES. Torque decreased the least when nNMES generated contractions, at least partly through H-reflexes (n = 4 participants; 39% decrease), and torque decreased the most when contractions were generated through M-waves, regardless of NMES site (nNMES 71% decrease, n = 4; mNMES, 73% decrease, n = 8).

CONCLUSIONS

nNMES generates contractions that fatigue less than mNMES, but only when H-reflexes contribute to the evoked contractions.

Low force contractions induce fatigue consistent with muscle mRNA expression in people with spinal cord injury

Spinal cord injury (SCI) is associated with muscle atrophy, transformation of muscle fibers to a fast fatigable phenotype, metabolic inflexibility (diabetes), and neurogenic osteoporosis. Electrical stimulation of paralyzed muscle may mitigate muscle metabolic abnormalities after SCI, but there is a risk for a fracture to the osteoporotic skeletal system. The goal of this study was to determine if low force stimulation (3 Hz) causes fatigue of chronically paralyzed muscle consistent with selected muscle gene expression profiles. We tested 29 subjects, nine with a SCI and 20 without and SCI, during low force fatigue protocol. Three SCI and three non-SCI subjects were muscle biopsied for gene and protein expression analysis. The fatigue index (FI) was 0.21 ± 0.27 and 0.91 ± 0.01 for the SCI and non-SCI groups, respectively, supporting that the low force protocol physiologically fatigued the chronically paralyzed muscle. The post fatigue potentiation index (PI) for the SCI group was increased to 1.60 ± 0.06 (P <0.001), while the non-SCI group was 1.26 ± 0.02 supporting that calcium handling was compromised with the low force stimulation. The mRNA expression from genes that regulate atrophy and fast properties (MSTN, ANKRD1, MYH8, and MYCBP2) was up regulated, while genes that regulate oxidative and slow muscle properties (MYL3, SDHB, PDK2, and RyR1) were repressed in the chronic SCI muscle. MSTN, ANKRD1, MYH8, MYCBP2 gene expression was also repressed 3 h after the low force stimulation protocol. Taken together, these findings support that a low force single twitch activation protocol induces paralyzed muscle fatigue and subsequent gene regulation. These findings suggest that training with a low force protocol may elicit skeletal muscle adaptations in people with SCI.

Electrical stimulation modulates Wnt signaling and regulates genes for the motor endplate and calcium binding in muscle of rats with spinal cord transection

BACKGROUND

Spinal cord injury (SCI) results in muscle atrophy and a shift of slow oxidative to fast glycolytic fibers. Electrical stimulation (ES) at least partially restores muscle mass and fiber type distribution. The objective of this study was to was to characterize the early molecular adaptations that occur in rat soleus muscle after initiating isometric resistance exercise by ES for one hour per day for 1, 3 or 7 days when ES was begun 16 weeks after SCI. Additionally, changes in mRNA levels after ES were compared with those induced in soleus at the same time points after gastrocnemius tenotomy (GA).

RESULTS

ES increased expression of Hey1 and Pitx2 suggesting increased Notch and Wnt signaling, respectively, but did not normalize RCAN1.4, a measure of calcineurin/NFAT signaling, or PGC-1ß mRNA levels. ES increased PGC-1α expression but not that of slow myofibrillar genes. Microarray analysis showed that after ES, genes coding for calcium binding proteins and nicotinic acetylcholine receptors were increased, and the expression of genes involved in blood vessel formation and morphogenesis was altered. Of the 165 genes altered by ES only 16 were also differentially expressed after GA, of which 12 were altered in the same direction by ES and GA. In contrast to ES, GA induced expression of genes related to oxidative phosphorylation.

CONCLUSIONS

Notch and Wnt signaling may be involved in ES-induced increases in the mass of paralyzed muscle. Molecular adaptations of paralyzed soleus to resistance exercise are delayed or defective compared to normally innervated muscle.

The effects of aging and electrical stimulation exercise on bone after spinal cord injury

Age related bone loss predisposes adults to osteoporosis. This is especially true for individuals with spinal cord injury (SCI). The effects of decreased bone loading with older age and paralysis significantly contribute to decreased bone mass and increased risk for fragility fractures. Loading bone via volitional muscle contractions or by using electrical stimulation are common methods for helping to prevent and/or decrease bone loss. However the effectiveness and safety of electrical stimulation activities remain unclear. The purpose of this review is to investigate the factors associated with aging and osteoporosis after SCI, the accuracy of bone measurement, the effects of various forms of bone loading activities with a focus on electrical stimulation activities and the safety of physical exercise with a focus on electrical stimulation cycling. Osteoporosis remains a disabling and costly condition for older adults and for those with paralysis. Both dual energy x-ray absorptiometry and peripheral quantitative computed tomography are valuable techniques for measuring bone mineral density (BMD) with the latter having the ability to differentiate trabecular and cortical bone. Physical activities have shown to be beneficial for increasing BMD however, the extent of the benefits related to aging and paralysis remain undetermined. Electrical stimulation activities administered appropriately are assumed safe due to thousands of documented safe FES cycling sessions. However, specific documentation is needed to verify safety and to development formal guidelines for optimal use.

Electroacupuncture and Acupuncture Promote the Rat's Transected Median Nerve Regeneration

Background. Acupuncture and electroacupuncture treatments of damaged nerves may aid nerve regeneration related to hindlimb function, but the effects on the forelimb-related median nerve were not known. Methods. A gap was made in the median nerve of each rat by suturing the stumps into silicone rubber tubes. The influences of acupuncture and electroacupuncture treatments on transected median nerve regeneration were evaluated from morphological, electrophysiological, and functional angles. Results. Morphologically, the group receiving acupuncture and electroacupuncture treatments had larger total nerve area and blood vessel number compared with the controls. Electrophysiologically, the group receiving electroacupuncture had significantly larger amplitude and larger area of the evoked muscle action potentials compared with the controls. Functionally, the acupuncture and electroacupuncture treatments enhanced the injured paw's ability to regain its grasping power and resulted in a faster efficiency to a new bilateral balance. Conclusion. Our findings provide multiapproach evidence of the efficacy of acupuncture and electroacupuncture treatments to the regeneration of median nerve. Indeed, acupuncture and electroacupuncture appear to have positive effects on the regeneration processes. This platform is beneficial to further study the clinical application of acupuncture and electroacupuncture alternative treatments on nerve-injured patients.

High dose compressive loads attenuate bone mineral loss in humans with spinal cord injury

People with spinal cord injury (SCI) lose bone and muscle integrity after their injury. Early doses of stress, applied through electrically induced muscle contractions, preserved bone density at high-risk sites. Appropriately prescribed stress early after the injury may be an important consideration to prevent bone loss after SCI.

INTRODUCTION

Skeletal muscle force can deliver high compressive loads to bones of people with spinal cord injury (SCI). The effective osteogenic dose of load for the distal femur, a chief site of fracture, is unknown. The purpose of this study is to compare three doses of bone compressive loads at the distal femur in individuals with complete SCI who receive a novel stand training intervention.

METHODS

Seven participants performed unilateral quadriceps stimulation in supported stance [150% body weight (BW) compressive load-"High Dose" while opposite leg received 40% BW-"Low Dose"]. Five participants stood passively without applying quadriceps electrical stimulation to either leg (40% BW load-"Low Dose"). Fifteen participants performed no standing (0% BW load-"Untrained") and 14 individuals without SCI provided normative data. Participants underwent bone mineral density (BMD) assessment between one and six times over a 3-year training protocol.

RESULTS

BMD for the High Dose group significantly exceeded BMD for both the Low Dose and the Untrained groups (p < 0.05). No significant difference existed between the Low Dose and Untrained groups (p > 0.05), indicating that BMD for participants performing passive stance did not differ from individuals who performed no standing. High-resolution CT imaging of one High Dose participant revealed 86% higher BMD and 67% higher trabecular width in the High Dose limb.

CONCLUSION

Over 3 years of training, 150% BW compressive load in upright stance significantly attenuated BMD decline when compared to passive standing or to no standing. High-resolution CT indicated that trabecular architecture was preserved by the 150% BW dose of load.

Prior heat stress effects fatigue recovery of the elbow flexor muscles

INTRODUCTION

Long-lasting alterations in hormones, neurotransmitters, and stress proteins after hyperthermia may be responsible for the impairment in motor performance during muscle fatigue.

METHODS

Subjects (n = 25) performed a maximal intermittent fatigue task of elbow flexion after sitting in either 73° or 26°C to examine the effects of prior heat stress on fatigue mechanisms.

RESULTS

The heat stress increased the tympanic and rectal temperatures by 2.3° and 0.82°C, respectively, but there was full recovery prior to the fatigue task. Although prior heat stress had no effects on fatigue-related changes in volitional torque, electromyographic (EMG) activity, torque relaxation rate, motor evoked potential (MEP) size, and silent period (SP) duration, prior heat stress acutely increased the pre-fatigue relaxation rate and chronically prevented long-duration fatigue (P < 0.05).

CONCLUSIONS

These findings indicate that prior passive heat stress alone does not alter voluntary activation during fatigue, but prior heat stress and exercise produce longer-term protection against long-duration fatigue.

Low-frequency H-reflex depression in trained human soleus after spinal cord injury

After spinal cord injury (SCI), widespread reorganization occurs within spinal reflex systems. Regular muscle activity may influence reorganization of spinal circuitry after SCI. The purpose of this study is to investigate the effects of long-term soleus training on H-reflex depression in humans after SCI. Seven subjects with acute (<7 weeks) SCI (AC group) underwent testing of H-reflex depression at several frequencies of repetitive stimulation. Eight subjects (including 3 from AC) stimulated one soleus muscle daily, leaving the other leg as an untrained within-subject control. Trained limb H-reflexes were assessed during year 1 (TR1) and year 2 (TR2) of training. Untrained limbs were tested during year 2 (UN). H-reflex amplitude was lower at 1, 2 and 5 Hz than at 0.1 or 0.2 Hz (p<0.05). The pattern of depression differed between AC and UN (p<0.05), but not between TR2 and UN (p>0.05) despite significant adaptations in torque and fatigue resistance (p<0.05). Three subjects who began training very early after SCI retained H-reflex post activation depression, suggesting that early intervention of daily muscular activity may be important.

Effects of cycling and/or electrical stimulation on bone mineral density in children with spinal cord injury

STUDY DESIGN

Randomized clinical trial.

OBJECTIVES

To determine the effect of cycling and/or electrical stimulation on hip and knee bone mineral density (BMD) in children with spinal cord injury (SCI).

SETTING

Children's hospital specializing in pediatric SCI.

METHODS

A total of 30 children, aged 5-13 years, with chronic SCI were randomized to one of three interventions: functional electrical stimulation cycling (FESC), passive cycling (PC), and non-cycling, electrically stimulated exercise (ES). Each group exercised for 1 h, three times per week for 6 months at home. The hip, distal femur and proximal tibia BMD were examined via dual-energy X-ray absorptiometry (DXA) pre- and post-intervention.

RESULTS

In all, 28 children completed data collection. The FESC group exhibited increases in hip, distal femur and proximal tibia BMD of 32.4, 6.62 and 10.3%, respectively. The PC group exhibited increases at the hip (29.2%), but no change at the distal femur (1.5%) or proximal tibia (-1.0%). The ES group had no change at the hip (-0.24%) and distal femur (3.3%), but a loss at the proximal tibia (-7.06%). There were no differences between groups or within groups over time. Significant negative correlations were found between baseline BMD and the amount of BMD change.

CONCLUSION

Although not achieving statistical significance, hip BMD changes observed were greater than the reported 0.9-10% gains after exercise for children with and without disability. Thus, cycling with and without electrical stimulation may be beneficial for skeletal health in pediatric SCI, but further research is needed with a larger sample size.

Enhancing muscle force and femur compressive loads via feedback-controlled stimulation of paralyzed quadriceps in humans

OBJECTIVE

To compare paralyzed quadriceps force properties and femur compressive loads in an upright functional task during conventional constant-frequency stimulation and force feedback-modulated stimulation.

DESIGN

Crossover trial.

SETTING

Research laboratory.

PARTICIPANTS

Subjects (N=13; 12 men, 1 woman) with motor-complete spinal cord injury.

INTERVENTIONS

Subjects performed 2 bouts of 60 isometric quadriceps contractions while supported in a standing frame. On separate days, subjects received constant-frequency stimulation at 20Hz (CONST) or frequency-modulated stimulation triggered by a change in force (FDBCK). During FDBCK, a computer algorithm responded to each 10% reduction in force with a 20% increase in stimulation frequency.

MAIN OUTCOME MEASURES

A biomechanical model was used to derive compressive loads on the femur, with a target starting dose of load equal to 1.5 times body weight.

RESULTS

Peak quadriceps force and fatigue index were higher for FDBCK than CONST (P<.05). Within-train force decline was greater during FDBCK bouts, but mean force remained above CONST values (P<.05). As fatigue developed during repetitive stimulation, FDBCK was superior to CONST for maintenance of femur compressive loads (P<.05).

CONCLUSIONS

Feedback-modulated stimulation in electrically activated stance is a viable method to maximize the physiologic performance of paralyzed quadriceps muscle. Compared with CONST, FDBCK yielded compressive loads that were closer to a targeted dose of stress with known osteogenic potential. Optimization of muscle force with FDBCK may be a useful tactic for future training-based antiosteoporosis protocols.