Fatty acid kinetics and carbohydrate metabolism during electrical exercise in spinal cord-injured humans

The interaction of macronutrients and body composition among individuals with chronic spinal cord injury

Changes in body composition and dietary intake occur following spinal cord injury (SCI). The Geometric Framework for Nutrition (GFN) is a tool that allows the examination of the complex relationships between multiple nutrition factors and health parameters within a single model. This study aimed to utilize the GFN to examine the associations between self-reported macronutrient intakes and body composition in persons with chronic SCI. Forty-eight individuals with chronic SCI were recruited. Participants completed and returned 3- or 5-day self-reported dietary recall sheets. Dietary intake of macronutrients (fats, proteins, and carbohydrates) were analysed. Anthropometric measures (circumferences), dual-energy x-ray absorptiometry (DXA), and magnetic resonance imaging (MRI) were used to assess whlole-body composition. Associations between all circumference measures and carbohydrates were observed. Among MRI measures, only significant associations between subcutaneous adipose tissue and protein x carbohydrate as well as carbohydrates alone were identified. Carbohydrates were negatively associated with several measures of fat mass as measured by DXA. Overall, carbohydrates appear to play an important role in body composition among individuals with SCI. Higher carbohydrate intake was associated with lower fat mass. Additional research is needed to determine how carbohydrate intake influences body composition and cardiometabolic health after SCI.

Selective Myostatin Inhibition Spares Sublesional Muscle Mass and Myopenia-Related Dysfunction after Severe Spinal Cord Contusion in Mice

Clinically relevant myopenia accompanies spinal cord injury (SCI), and compromises function, metabolism, body composition, and health. Myostatin, a transforming growth factor (TGF)β family member, is a key negative regulator of skeletal muscle mass. We investigated inhibition of myostatin signaling using systemic delivery of a highly selective monoclonal antibody - muSRK-015P (40 mg/kg) - that blocks release of active growth factor from the latent form of myostatin. Adult female mice (C57BL/6) were subjected to a severe SCI (65 kdyn) at T9 and were then immediately and 1 week later administered test articles: muSRK-015P (40 mg/kg) or control (vehicle or IgG). A sham control group (laminectomy only) was included. At euthanasia, (2 weeks post-SCI) muSRK-015P preserved whole body lean mass and sublesional gastrocnemius and soleus mass. muSRK-015P-treated mice with SCI also had significantly attenuated myofiber atrophy, lipid infiltration, and loss of slow-oxidative phenotype in soleus muscle. These outcomes were accompanied by significantly improved sublesional motor function and muscle force production at 1 and 2 weeks post-SCI. At 2 weeks post-SCI, lean mass was significantly decreased in SCI-IgG mice, but was not different in SCI-muSRK-015P mice than in sham controls. Total energy expenditure (kCal/day) at 2 weeks post-SCI was lower in SCI-immunoglobulin (Ig)G mice, but not different in SCI-muSRK-015P mice than in sham controls. We conclude that in a randomized, blinded, and controlled study in mice, myostatin inhibition using muSRK-015P had broad effects on physical, metabolic, and functional outcomes when compared with IgG control treated SCI animals. These findings may identify a useful, targeted therapeutic strategy for treating post-SCI myopenia and related sequelae in humans.

Effects of functional electrical stimulation on muscle health after spinal cord injury

Spinal cord injury is a devastating condition interrupting voluntary movement and motor control. In response to unloading, skeletal muscle undergoes numerous adaptations, including rapid and profound atrophy, intramuscular fat accumulation, impaired muscular glucose metabolism and decreased force generation and muscle performance. Functional electrical stimulation (FES) involves electrically stimulating affected muscles to contract in a coordinated manner to create a functional movement or task. Effects of FES-cycling, rowing and resistance training on muscle health are described here. Briefly, FES-cycling and resistance training may slow muscle atrophy or facilitate muscle hypertrophy, and all modalities benefit muscle composition and performance to some extent. These interventions show promise as future rehabilitative tools after spinal cord injury.

Neither Postabsorptive Resting Nor Postprandial Fat Oxidation Are Related to Peak Fat Oxidation in Men With Chronic Paraplegia

The peak rate of fat oxidation (PFO) achieved during a graded exercise test is an important indicator of metabolic health. In healthy individuals, there is a significant positive association between PFO and total daily fat oxidation (FO). However, conditions resulting in metabolic dysfunction may cause a disconnect between PFO and non-exercise FO. Ten adult men with chronic thoracic spinal cord injury (SCI) completed a graded arm exercise test. On a separate day following an overnight fast (≥ 10 h), they rested for 60 min before ingesting a liquid mixed meal (600 kcal; 35% fat, 50% carbohydrate, 15% protein). Expired gases were collected and indirect calorimetry data used to determine FO at rest, before and after feeding, and during the graded exercise test. Participants had “good” cardiorespiratory fitness (VO_2peak: 19.2 ± 5.2 ml/kg/min) based on normative reference values for SCI. There was a strong positive correlation between PFO (0.30 ± 0.08 g/min) and VO_2peak (r = 0.86, p = 0.002). Additionally, postabsorptive FO at rest was significantly and positively correlated with postprandial peak FO (r = 0.77, p = 0.01). However, PFO was not significantly associated with postabsorptive FO at rest (0.08 ± 0.02 g/min; p = 0.97), postprandial peak FO (0.10 ± 0.03 g/min; p = 0.43), or incremental area under the curve postprandial FO (p = 0.22). It may be advantageous to assess both postabsorptive FO at rest and PFO in those with SCI to gain a more complete picture of their metabolic flexibility and long-term metabolic health.

Neuromuscular electrical stimulation resistance training enhances oxygen uptake and ventilatory efficiency independent of mitochondrial complexes after spinal cord injury: a randomized clinical trial

The purpose of the study was to determine whether neuromuscular electrical stimulation resistance training (NMES-RT)-evoked muscle hypertrophy is accompanied by increased V̇o₂ peak, ventilatory efficiency, and mitochondrial respiration in individuals with chronic spinal cord injury (SCI). Thirty-three men and women with chronic, predominantly traumatic SCI were randomized to either NMES-RT (n = 20) or passive movement training (PMT; n = 13). Functional electrical stimulation-lower extremity cycling (FES-LEC) was used to test the leg V̇o₂ peak, V̇E/V̇co₂ ratio, and substrate utilization pre- and postintervention. Magnetic resonance imaging was used to measure muscle cross-sectional area (CSA). Finally, muscle biopsy was performed to measure mitochondrial complexes and respiration. The NMES-RT group showed a significant increase in postintervention V̇o₂ peak compared with baseline (ΔV̇o₂ = 14%, P < 0.01) with no changes in the PMT group (ΔV̇o₂ = 1.6%, P = 0.47). Similarly, thigh (ΔCSA_thigh = 19%) and knee extensor (ΔCSA_knee = 30.4%, P < 0.01) CSAs increased following NMES-RT but not after PMT. The changes in thigh and knee extensor muscle CSAs were positively related with the change in V̇o₂ peak. Neither NMES-RT nor PMT changed mitochondrial complex tissue levels; however, changes in peak V̇o₂ were related to complex I. In conclusion, in persons with SCI, NMES-RT-induced skeletal muscle hypertrophy was accompanied by increased peak V̇o₂ consumption which may partially be explained by enhanced activity of mitochondrial complex I.NEW & NOTEWORTHY Leg oxygen uptake (V̇o₂) and ventilatory efficiency (V̇E/V̇co₂ ratio) were measured during functional electrical stimulation cycling testing following 12-16 wk of either electrically evoked resistance training or passive movement training, and the respiration of mitochondrial complexes. Resistance training increased thigh muscle area and leg V̇o₂ peak but decreased V̇E/V̇co₂ ratio without changes in mitochondrial complex levels. Leg V̇o₂ peak was associated with muscle hypertrophy and mitochondrial respiration of complex I following training.

Substrate metabolism during recovery from circuit resistance exercise in persons with spinal cord injury

INTRODUCTION

Whole body energy expenditure and lipid oxidation (Lox) are upregulated during and after exercise. Persons with spinal cord injury (SCI) generally have a blunted ability to utilize fat during exercise, but it is unknown if their substrate partitioning is affected during recovery from exercise.

PURPOSE

To determine the effect of a single session of upper body circuit resistance exercise (CRE) on energy expenditure and Lox during exercise recovery in persons with and without SCI.

METHODS

Twenty four persons (3 groups; 7 male and 1 female per group) without paralysis (neurologically intact; N) or with chronic (≥ 1 yr) paraplegia (P) or tetraplegia (T) participated. Energy expenditure and substrate partitioning were assessed via indirect calorimetry before, during, and three times after (up to 120 min after) a single session of CRE, or time-matched seated control (CON).

RESULTS

During CRE, all groups experienced a similar relative increase in oxygen consumption (49 ± 13, 55 ± 11, and 48 ± 15% VO_2peak for N, P, and T, respectively). The Post_0-120 energy expenditure was greater following CRE vs. CON (P < 0.01) and independent of injury characteristics (10.6, 22.6, and 14.3% higher than CON for N, P, and T; P = 0.21). The absolute increase in Lox above CON during recovery was similar for N, P, and T (5.74 ± 2.81, 6.62 ± 3.10, and 4.50 ± 3.91 g, respectively; P = 0.45).

CONCLUSIONS

Energy expenditure and lipid utilization was increased similarly following circuit exercise in persons without and with spinal cord injury in a manner independent of level of injury.

Exercise Interventions Targeting Obesity in Persons With Spinal Cord Injury

Spinal cord injury (SCI) results in an array of cardiometabolic complications, with obesity being the most common component risk of cardiometabolic disease (CMD) in this population. Recent Consortium for Spinal Cord Medicine Clinical Practice Guidelines for CMD in SCI recommend physical exercise as a primary treatment strategy for the management of CMD in SCI. However, the high prevalence of obesity in SCI and the pleiotropic nature of this body habitus warrant strategies for tailoring exercise to specifically target obesity. In general, exercise for obesity management should aim primarily to induce a negative energy balance and secondarily to increase the use of fat as a fuel source. In persons with SCI, reductions in the muscle mass that can be recruited during activity limit the capacity for exercise to induce a calorie deficit. Furthermore, the available musculature exhibits a decreased oxidative capacity, limiting the utilization of fat during exercise. These constraints must be considered when designing exercise interventions for obesity management in SCI. Certain forms of exercise have a greater therapeutic potential in this population partly due to impacts on metabolism during recovery from exercise and at rest. In this article, we propose that exercise for obesity in SCI should target large muscle groups and aim to induce hypertrophy to increase total energy expenditure response to training. Furthermore, although carbohydrate reliance will be high during activity, certain forms of exercise might induce meaningful postexercise shifts in the use of fat as a fuel. General activity in this population is important for many components of health, but low energy cost of daily activities and limitations in upper body volitional exercise mean that exercise interventions targeting utilization and hypertrophy of large muscle groups will likely be required for obesity management.

Low-Dose Testosterone and Evoked Resistance Exercise after Spinal Cord Injury on Cardio-Metabolic Risk Factors: An Open-Label Randomized Clinical Trial

The purpose of the work is to investigate the effects of low-dose testosterone replacement therapy (TRT) and evoked resistance training (RT) on body composition and metabolic variables after spinal cord injury (SCI). Twenty-two individuals with chronic motor complete SCI (ages 18-50 years) were randomly assigned to either TRT+RT (n = 11) or TRT (n = 11) for 16 weeks following a 4 -week delayed entry period. TRT+RT men underwent twice weekly progressive RT using electrical stimulation with ankle weights. TRT was administered via testosterone patches (2-6 mg/day). Body composition was tested using anthropometrics, dual energy x-ray absorptiometry, and magnetic resonance imaging. After an overnight fast, basal metabolic rate (BMR), lipid panel, serum testosterone, adiponectin, inflammatory and anabolic biomarkers (insulin-like growth factor-1 and insulin-like growth factor-binding protein 3 [IGFBP-3]), glucose effectiveness (Sg), and insulin sensitivity (Si) were measured. Total body lean mass (LM; 2.7 kg, p < 0.0001), whole muscle (p < 0.0001), and whole muscle knee extensor cross-sectional areas (CSAs; p < 0.0001) increased in the TRT+RT group, with no changes in the TRT group. Visceral adiposity decreased (p = 0.049) in the TRT group, with a trend in the TRT+RT (p = 0.07) group. There was a trend (p = 0.050) of a 14-17% increase in BMR following TRT+RT. Sg showed a trend (p = 0.07) to improvement by 28.5-31.5% following both interventions. IGFBP-3 increased (p = 0.0001) while IL-6 decreased (p = 0.039) following both interventions, and TRT+RT suppressed adiponectin (p = 0.024). TRT+RT resulted in an increase in LM and whole thigh and knee extensor muscle CSAs, with an increase in BMR and suppressed adiponectin. Low-dose TRT may mediate modest effects on visceral adipose tissue, Sg, IGFBP-3, and IL-6, independent of changes in LM.

Retained differentiation capacity of human skeletal muscle satellite cells from spinal cord-injured individuals

Despite the well‐known role of satellite cells in skeletal muscle plasticity, the effect of spinal cord injury on their function in humans remains unknown. We determined whether spinal cord injury affects the intrinsic ability of satellite cells to differentiate and produce metabolically healthy myotubes. We obtained vastus lateralis biopsies from eight spinal cord‐injured and six able‐bodied individuals. Satellite cells were isolated, grown and differentiated in vitro. Gene expression was measured by quantitative PCR. Abundance of differentiation markers and regulatory proteins was determined by Western blotting. Protein synthesis and fatty acid oxidation were measured by radioactive tracer‐based assays. Activated satellite cells (myoblasts) and differentiated myotubes derived from skeletal muscle of able‐bodied and spinal cord‐injured individuals expressed similar (P > 0.05) mRNA levels of myogenic regulatory factors. Myogenic differentiation factor 1 expression was higher in myoblasts from spinal cord‐injured individuals. Desmin and myogenin protein content was increased upon differentiation in both groups, while myotubes from spinal cord‐injured individuals contained more type I and II myosin heavy chain. Phosphorylated and total protein levels of Akt‐mechanistic target of rapamycin and forkhead box protein O signalling axes and protein synthesis rate in myotubes were similar (P > 0.05) between groups. Additionally, fatty acid oxidation of myotubes from spinal cord‐injured individuals was unchanged (P > 0.05) compared to able‐bodied controls. Our results indicate that the intrinsic differentiation capacity of satellite cells and metabolic characteristics of myotubes are preserved following spinal cord injury. This may inform potential interventions targeting satellite cell activation to alleviate skeletal muscle atrophy.

Skeletal muscle hypertrophy and attenuation of cardio-metabolic risk factors (SHARC) using functional electrical stimulation-lower extremity cycling in persons with spinal cord injury: study protocol for a randomized clinical trial

Background

Persons with spinal cord injury (SCI) are at heightened risks of developing unfavorable cardiometabolic consequences due to physical inactivity. Functional electrical stimulation (FES) and surface neuromuscular electrical stimulation (NMES)-resistance training (RT) have emerged as effective rehabilitation methods that can exercise muscles below the level of injury and attenuate cardio-metabolic risk factors. Our aims are to determine the impact of 12 weeks of NMES + 12 weeks of FES-lower extremity cycling (LEC) compared to 12 weeks of passive movement + 12 weeks of FES-LEC on: (1) oxygen uptake (VO₂), insulin sensitivity, and glucose disposal in adults with SCI; (2) skeletal muscle size, intramuscular fat (IMF), and visceral adipose tissue (VAT); and (3) protein expression of energy metabolism, protein molecules involved in insulin signaling, muscle hypertrophy, and oxygen uptake and electron transport chain (ETC) activities.

Methods/Design

Forty-eight persons aged 18–65 years with chronic (> 1 year) SCI/D (AIS A-C) at the C5-L2 levels, equally sub-grouped by cervical or sub-cervical injury levels and time since injury, will be randomized into either the NMES + FES group or Passive + FES (control group). The NMES + FES group will undergo 12 weeks of evoked RT using twice-weekly NMES and ankle weights followed by twice-weekly progressive FES-LEC for an additional 12 weeks. The control group will undergo 12 weeks of passive movement followed by 12 weeks of progressive FES-LEC. Measurements will be performed at baseline (B; week 0), post-intervention 1 (P1; week 13), and post-intervention 2 (P2; week 25), and will include: VO₂ measurements, insulin sensitivity, and glucose effectiveness using intravenous glucose tolerance test; magnetic resonance imaging to measure muscle, IMF, and VAT areas; muscle biopsy to measure protein expression and intracellular signaling; and mitochondrial ETC function.

Discussion

Training through NMES + RT may evoke muscle hypertrophy and positively impact oxygen uptake, insulin sensitivity, and glucose effectiveness. This may result in beneficial outcomes on metabolic activity, body composition profile, mitochondrial ETC, and intracellular signaling related to insulin action and muscle hypertrophy. In the future, NMES-RT may be added to FES-LEC to improve the workloads achieved in the rehabilitation of persons with SCI and further decrease muscle wasting and cardio-metabolic risks.

Trial registration

ClinicalTrials.gov, NCT02660073. Registered on 21 Jan 2016.

Influence of upper-body continuous, resistance or high-intensity interval training (CRIT) on postprandial responses in persons with spinal cord injury: study protocol for a randomised controlled trial

Background

Chronic spinal cord injury (SCI) increases morbidity and mortality associated with cardiometabolic diseases, secondary to increases in central adiposity, hyperlipidaemia and impaired glucose tolerance. While upper-body Moderate Intensity Continuous Training (MICT) improves cardiorespiratory fitness, its effects on cardiometabolic component risks in adults with SCI appear relatively modest. The aim of this study is to assess the acute effects of Continuous Resistance Training (CRT), High Intensity Interval Training (HIIT), MICT and rest (CON) on fasting and postprandial systemic biomarkers and substrate utilisation.

Methods

Eleven healthy, chronic SCI (> 1 year, ASIA A-C) men will be recruited. Following preliminary testing, each will complete four experimental conditions, where they will report to the laboratory following an ~ 10-h overnight fast. A venous blood sample will be drawn and expired gases collected to estimate resting metabolic rate (RMR). In order to ensure an isocaloric exercise challenge, each will complete CRT first, with the remaining three conditions presented in randomised order: (1) CRT, ~ 45 min of resistance manoeuvres (weight lifting) interspersed with low-resistance, high-speed arm-crank exercise; (2) CON, seated rest; (3) MICT, ~ 45 min constant arm-crank exercise at a resistance equivalent to 30–40% peak power output (PPO) and; (4) HIIT, ~ 35 min arm-crank exercise with the resistance alternating every 2 min between 10% PPO and 70% PPO. After each ~ 45-min condition, participants will ingest a 2510-kJ liquid test meal (35% fat, 50% carbohydrate, 15% protein). Venous blood and expired gas samples will be collected at the end of exercise and at regular intervals for 120 min post meal.

Discussion

This study should establish the acute effects of different forms of exercise on fasting and postprandial responses in chronic SCI male patients. Measures of glucose clearance, insulin sensitivity, lipid and inflammatory biomarker concentrations will be assessed and changes in whole-body substrate oxidation estimated from expired gases.

Trial registration

ClinicalTrials.gov, ID: NCT03545867. Retrospectively registered on 1 June 2018. 

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3583-1) contains supplementary material, which is available to authorized users.

Altered oxidative stress and antioxidant defence in skeletal muscle during the first year following spinal cord injury

Oxidative stress promotes protein degradation and apoptosis in skeletal muscle undergoing atrophy. We aimed to determine whether spinal cord injury leads to changes in oxidative stress, antioxidant capacity, and apoptotic signaling in human skeletal muscle during the first year after spinal cord injury. Vastus lateralis biopsies were obtained from seven individuals 1, 3, and 12 months after spinal cord injury and from seven able-bodied controls. Protein content of enzymes involved in reactive oxygen species production and detoxification, and apoptotic signaling were analyzed by western blot. Protein carbonylation and 4-hydroxynonenal protein adducts were measured as markers of oxidative damage. Glutathione content was determined fluorometrically. Protein content of NADPH oxidase 2, xanthine oxidase, and pro-caspase-3 was increased at 1 and 3 months after spinal cord injury compared to able-bodied controls. Furthermore, total and reduced glutathione content was increased at 1 and 3 months after spinal cord injury. Conversely, mitochondrial complexes and superoxide dismutase 2 protein content were decreased 12 months after spinal cord injury compared to able-bodied controls. In conclusion, we provide indirect evidence of increased reactive oxygen species production and increased apoptotic signaling at 1 and 3 months after spinal cord injury. Concomitant increases in glutathione antioxidant defences may reflect adaptations poised to maintain redox homeostasis in skeletal muscle following spinal cord injury.

Lactate production without hypoxia in skeletal muscle during electrical cycling: Crossover study of femoral venous-arterial differences in healthy volunteers

BACKGROUND

Aim of the study was to compare metabolic response of leg skeletal muscle during functional electrical stimulation-driven unloaded cycling (FES) to that seen during volitional supine cycling.

METHODS

Fourteen healthy volunteers were exposed in random order to supine cycling, either volitional (10-25-50 W, 10 min) or FES assisted (unloaded, 10 min) in a crossover design. Whole body and leg muscle metabolism were assessed by indirect calorimetry with concomitant repeated measurements of femoral venous-arterial differences of blood gases, glucose, lactate and amino acids.

RESULTS

Unloaded FES cycling, but not volitional exercise, led to a significant increase in across-leg lactate production (from -1.1±2.1 to 5.5±7.4 mmol/min, p<0.001) and mild elevation of arterial lactate (from 1.8±0.7 to 2.5±0.8 mM). This occurred without widening of across-leg veno-arterial (VA) O2 and CO2 gaps. Femoral SvO2 difference was directly proportional to VA difference of lactate (R2 = 0.60, p = 0.002). Across-leg glucose uptake did not change with either type of exercise. Systemic oxygen consumption increased with FES cycling to similarly to 25W volitional exercise (138±29% resp. 124±23% of baseline). There was a net uptake of branched-chain amino acids and net release of Alanine from skeletal muscle, which were unaltered by either type of exercise.

CONCLUSIONS

Unloaded FES cycling, but not volitional exercise causes significant lactate production without hypoxia in skeletal muscle. This phenomenon can be significant in vulnerable patients' groups.

Exercise and Health-Related Risks of Physical Deconditioning After Spinal Cord Injury

A sedentary lifestyle occurring soon after spinal cord injury (SCI) may be in contrast to a preinjury history of active physical engagement and is thereafter associated with profound physical deconditioning sustained throughout the lifespan. This physical deconditioning contributes in varying degrees to lifelong medical complications, including accelerated cardiovascular disease, insulin resistance, osteopenia, and visceral obesity. Unlike persons without disability for whom exercise is readily available and easily accomplished, exercise options for persons with SCI are more limited. Depending on the level of injury, the metabolic responses to acute exercise may also be less robust than those accompanying exercise in persons without disability, the training benefits more difficult to achieve, and the risks of ill-considered exercise both greater and potentially irreversible. For exercise to ultimately promote benefit and not impose additional impairment, an understanding of exercise opportunities and risks if exercise is undertaken by those with SCI is important. The following monograph will thus address common medical challenges experienced by persons with SCI and typical modes and benefits of voluntary exercise conditioning.

Associations of the trunk skeletal musculature and dietary intake to biomarkers of cardiometabolic health after spinal cord injury

PURPOSE

Skeletal muscle atrophy and poor dietary habits may contribute to increased adiposity and impaired metabolic health after spinal cord injury (SCI). The relative association of trunk muscle cross-sectional areas (CSA) versus dietary habits to central adiposity and impaired metabolic health after SCI remains unclear.

METHODS

Twenty-two men with motor complete SCI completed five-day dietary recalls for 4 weeks. Trunk muscle CSAs as well as visceral and subcutaneous adipose tissue (VAT and SAT, respectively) were quantified using magnetic resonance imaging. Basal metabolic rate (BMR), glucose effectiveness, insulin sensitivity and lipid profile were measured after overnight fast.

RESULTS

Antero-lateral trunk muscle (r = -0·79, P < 0·001) and posterior trunk muscle (r = -0·56, P = 0·008) CSAs normalized to total trunk CSA were negatively related to VAT. Antero-lateral trunk muscle ratio (TMR) was positively related to BMR (r = 0·54, P = 0·01), and posterior TMR was positively related to peak oxygen uptake (VO2 peak; r = 0·71, P = 0·003). After accounting for total TMR as a co-variate, total fat (r = 0·47, P = 0·04) and protein (r = 0·61, P = 0·004) intakes were positively related to fasting insulin levels.

CONCLUSION

Trunk muscle CSAs normalized to total trunk CSA were negatively associated with central adiposity. Both trunk muscles and dietary macro-nutrients are related to markers of metabolic health. The study highlights the significance of developing an exercise intervention with a healthy dietary regimen to attenuate the development of central adiposity associated metabolic disorders after SCI.

Paradigms of Lower Extremity Electrical Stimulation Training After Spinal Cord Injury

Skeletal muscle atrophy, increased adiposity and reduced physical activity are key changes observed after spinal cord injury (SCI) and are associated with numerous cardiometabolic health consequences. These changes are likely to increase the risk of developing chronic secondary conditions and impact the quality of life in persons with SCI. Surface neuromuscular electrical stimulation evoked resistance training (NMES-RT) was developed as a strategy to attenuate the process of skeletal muscle atrophy, decrease ectopic adiposity, improve insulin sensitivity and enhance mitochondrial capacity. However, NMES-RT is limited to only a single muscle group. Involving multiple muscle groups of the lower extremities may maximize the health benefits of training. Functional electrical stimulation-lower extremity cycling (FES-LEC) allows for the activation of 6 muscle groups, which is likely to evoke greater metabolic and cardiovascular adaptation. Appropriate knowledge of the stimulation parameters is key to maximizing the outcomes of electrical stimulation training in persons with SCI. Adopting strategies for long-term use of NMES-RT and FES-LEC during rehabilitation may maintain the integrity of the musculoskeletal system, a pre-requisite for clinical trials aiming to restore walking after injury. The current manuscript presents a combined protocol using NMES-RT prior to FES-LEC. We hypothesize that muscles conditioned for 12 weeks prior to cycling will be capable of generating greater power, cycle against higher resistance and result in greater adaptation in persons with SCI.

Physiological and lipid profile response to acute exercise at different intensities in individuals with spinal cord injury

STUDY DESIGN

Experimental and cross-sectional study.

OBJECTIVE

To assess the immediate effect of exercise on heart rate (HR), oxygen uptake (VO₂), pulmonary ventilation (PV), oxygen pulse (OP), glucose and lipids of wheelchair basketball players with spinal cord injury (SCI).

SETTING

Center of Studies in Psychobiology and Exercise-São Paulo, Brazil.

METHODS

In all, nine wheelchair basketball players with SCI and nine able-bodied controls (C) performed three exercise sessions at different intensities: ventilatory threshold 1 (VT1), 15% below VT1 and 15% above VT1 with a duration of ~24-34 min. HR, VO₂, PV, OP, glucose and lipids were analyzed.

RESULTS

VO_2, PV and OP were significantly lower in the players with SCI compared to C during the same intensity exercise sessions. However, the individuals with SCIs demonstrated increases in HR, PV and OP at similar rates to C. Triglycerides of the SCI group were elevated 30 min after the exercise session at VT1 compared to values before the exercise session (P=0.017); this elevation was not observed in group C. For the exercise sessions 15% above VT1, only glucose (P=0.040) and low-density lipoprotein (P=0.012) 30 min after the exercise were elevated in the SCI group compared to group C.

CONCLUSION

We conclude that the SCI group demonstrated increases in HR, PV and OP but not VO₂ with increased intensity of exercise at similar rates as in group C.

Effects of Testosterone and Evoked Resistance Exercise after Spinal Cord Injury (TEREX-SCI): study protocol for a randomised controlled trial

INTRODUCTION

Individuals with spinal cord injury (SCI) are at a lifelong risk of obesity and chronic metabolic disorders including insulin resistance and dyslipidemia. Within a few weeks of injury, there is a significant decline in whole body fat-free mass, particularly lower extremity skeletal muscle mass, and subsequent increase in fat mass (FM). This is accompanied by a decrease in anabolic hormones including testosterone. Testosterone replacement therapy (TRT) has been shown to increase skeletal muscle mass and improve metabolic profile. Additionally, resistance training (RT) has been shown to increase lean mass and reduce metabolic disturbances in SCI and other clinical populations.

METHODS AND ANALYSIS

26 individuals with chronic, motor complete SCI between 18 and 50 years old were randomly assigned to a RT+TRT group (n=13) or a TRT group (n=13). 22 participants completed the initial 16-week training phase of the study and 4 participants withdrew. 12 participants of the 22 completed 16 weeks of detraining. The TRT was provided via transdermal testosterone patches (4-6 mg/day). The RT+TRT group had 16 weeks of supervised unilateral progressive RT using surface neuromuscular electrical stimulation with ankle weights. This study will investigate the effects of evoked RT+TRT or TRT alone on body composition (muscle cross-sectional area, visceral adipose tissue, %FM) and metabolic profile (glucose and lipid metabolism) in individuals with motor complete SCI. Findings from this study may help in designing exercise therapies to alleviate the deterioration in body composition after SCI and decrease the incidence of metabolic disorders in this clinical population.

ETHICS AND DISSEMINATION

The study is currently approved by the McGuire VA Medical Center and Virginia Commonwealth University. All participants read and signed approved consent forms. Results will be submitted to peer-reviewed journals and presented at national and international conferences.

TRIAL REGISTRATION NUMBER

Pre-result, NCT01652040.

Acute Responses of Functional Electrical Stimulation Cycling on the Ventilation-to-CO2 Production Ratio and Substrate Utilization After Spinal Cord Injury

BACKGROUND

Ventilation-to-carbon dioxide ratio is comparable with peak oxygen uptake in the prognosis of cardiovascular disorders. Currently, there are no established indices to determine the submaximal effects of functional electrical stimulation on cardiovascular performance in persons with spinal cord injury.

OBJECTIVE

To determine the effects of an acute bout of functional electrical stimulation-lower extremity cycling on ventilation, carbon dioxide production, ventilation-to-carbon dioxide ratio, and substrate utilization in people with motor complete spinal cord injury.

DESIGN

Observational cross-sectional design.

SETTING

Clinical laboratory setting.

PARTICIPANTS

Ten individuals with motor complete spinal cord injury.

METHODS

Participants were allowed to cycle until fatigue. The effects of functional electrical stimulation on ventilation, carbon dioxide production, ventilation-to-carbon dioxide ratio, and substrate utilization were measured with a portable metabolic cart (COSMED K4b2). Body composition was determined with bioelectrical impedance.

RESULTS

Resting and warm-up ventilation were 8.15 ± 3.5 L/min and 8.15 ± 2.8 L/min, respectively. Functional electrical stimulation increased ventilation significantly (14.5 ± 6.4 L/min), which remained significantly elevated (13.3 ± 4.3 L/min) during the recovery period. During resting and warm-up phases, the ventilation-to-carbon dioxide ratios were 41 ± 4.8 and 38 ± 5.4, respectively. Functional electrical stimulation decreased the ventilation-to-carbon dioxide ratio significantly to 31.5 ± 4, which remained significantly reduced during the recovery period (34.4 ± 3). Functional electrical stimulation relied primarily on carbohydrate utilization (188 ± 160 g/day to 574 ± 324 g/day; P = .001) with no changes in fat utilization (77.5 ± 28 g/day to 93.5 ± 133.6 g/day; P = .7) from resting to exercise periods. Significant relationships were noted between carbohydrate utilization during functional electrical stimulation and carbon dioxide (r = 0.98; P = .00010) production. The percentage whole body fat-free mass was negatively related to the exercise ventilation-to-carbon ratio (r = -0.66; P = .045).

CONCLUSIONS

An acute bout of functional electrical stimulation resulted in a significant drop in the ventilation-to-carbon ratio, accompanied with a reliance on carbohydrate utilization and a diminished capacity to utilize fat as a substrate. Fat-free mass may be associated with a decrease in ventilation to carbon dioxide ratio and an increase in carbohydrate utilization in persons with spinal cord injury.

Exercise and the Regulation of Adipose Tissue Metabolism

Adipose tissue is a major regulator of metabolism in health and disease. The prominent roles of adipose tissue are to sequester fatty acids in times of energy excess and to release fatty acids via the process of lipolysis during times of high-energy demand, such as exercise. The fatty acids released during lipolysis are utilized by skeletal muscle to produce adenosine triphosphate to prevent fatigue during prolonged exercise. Lipolysis is controlled by a complex interplay between neuro-humoral regulators, intracellular signaling networks, phosphorylation events involving protein kinase A, translocation of proteins within the cell, and protein-protein interactions. Herein, we describe in detail the cellular and molecular regulation of lipolysis and how these processes are altered by acute exercise. We also explore the processes that underpin adipocyte adaptation to endurance exercise training, with particular focus on epigenetic modifications, control by microRNAs and mitochondrial adaptations. Finally, we examine recent literature describing how exercise might influence the conversion of traditional white adipose tissue to high energy-consuming "brown-like" adipocytes and the implications that this has on whole-body energy balance.

Frequency of Dietary Recalls, Nutritional Assessment, and Body Composition Assessment in Men With Chronic Spinal Cord Injury

OBJECTIVES

To assess different frequencies of dietary recalls while evaluating caloric intake and the percentage of macronutrients in men with spinal cord injury (SCI) and to examine the relations between caloric intake or percentage of macronutrients and assessment of whole and regional body composition using dual-energy x-ray absorptiometry.

DESIGN

Cross-sectional and longitudinal.

SETTING

Laboratory and hospital.

PARTICIPANTS

Men with chronic (>1 y postinjury) motor complete SCI (N=16).

INTERVENTIONS

Participants were asked to turn in a 5-day dietary recall on a weekly basis for 4 weeks. The averages of 5-, 3-, and 1-day dietary recalls for caloric intake and percentage of macronutrients (carbohydrates, fat, protein) were calculated. Body composition was evaluated using whole-body dual-energy x-ray absorptiometry. After overnight fast, basal metabolic rate (BMR) was evaluated using indirect calorimetry and total energy expenditure (TEE) was estimated.

MAIN OUTCOME MEASURES

Caloric intake, percentage of macronutrients, BMR, and body composition.

RESULTS

Caloric intake and percentage of macronutrients were not different after using 5-, 3-, and 1-day dietary recalls (P>.05). Caloric intake was significantly lower than TEE (P<.05). The percentage of fat accounted for 29% to 34% of the whole and regional body fat mass (P=.037 and P=.022). The percentage of carbohydrates was positively related to the percentage of whole-body lean mass (r=.54; P=.037) and negatively related to the percentage of fat mass.

CONCLUSIONS

The frequency of dietary recalls does not vary while evaluating caloric intake and macronutrients. Total caloric intake was significantly lower than the measured BMR and TEE. Percentages of dietary fat and carbohydrates are related to changes in body composition after SCI.

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.

Effects of circuit resistance training and timely protein supplementation on exercise-induced fat oxidation in tetraplegic adults

BACKGROUND

Substrate utilization during exercise in persons with spinal cord injury (SCI) remains poorly defined.

PURPOSE

To investigate effects of circuit resistance training (CRT) and timing of protein supplementation (PS) on fuel utilization in persons with tetraplegia.

METHODS

Eleven individuals with chronic tetraplegia underwent 6 months of CRT 3 times weekly. Five randomly assigned participants received immediate PS (iPS) administered in split doses prior to and following all exercise sessions. Other participants consumed a matched dose of PS that was delayed until 24 hours post-exercise (dPS). Participants underwent a maximal graded exercise test (GXT) to volitional exhaustion at 4 conditioning time points: 3 months before (-3mo), at the beginning of (0mo), 3 months into (3mo), and 6 months following (6mo) the CRT conditioning program. Respiratory measures were continuously obtained throughout the GXT via open-circuit spirometry. Fuel utilization and energy expenditure were computed from the respiratory data.

RESULTS

The differences in changes in substrate utilization between the PS groups were not significant as determined by the interaction of PS group and conditioning time point, F (3, 27) = 2.32, P = .098, η(2) P = .205. Maximal absolute fat oxidation did not change significantly from 0 to 6mo (mean difference, 0.014 ± 0.031 g/min; P = .170), and fat oxidation remained low never exceeding an average of 0.10 ± 0.09 g/min for any given exercise intensity.

CONCLUSION

Maximum fat utilization during exercise and fat utilization at matched exercise intensities were not increased in persons with tetraplegia, independent of PS, and levels of fat oxidation remained low after training.

Heavy reliance on carbohydrate across a wide range of exercise intensities during voluntary arm ergometry in persons with paraplegia

CONTEXT/OBJECTIVE

To describe and compare substrate oxidation and partitioning during voluntary arm ergometry in individuals with paraplegia and non-disabled individuals over a wide range of exercise intensities.

DESIGN

Cross-sectional study.

SETTING

Clinical research facility.

PARTICIPANTS

Ten apparently healthy, sedentary men with paraplegia and seven healthy, non-disabled subjects.

INTERVENTIONS

Rest and continuous progressive voluntary arm ergometry between 30 and 80% of peak aerobic capacity (VO2peak).

OUTCOME MEASURES

Total energy expenditure and whole body rates of fat and carbohydrate oxidation.

RESULTS

A maximal whole body fat oxidation (WBFO) rate of 0.13 ± 0.07 g/minute was reached at 41 ± 9% VO2peak for subjects with paraplegia, although carbohydrate became the predominant fuel source during exercise exceeding an intensity of 30-40% VO2peak. Both the maximal WBFO rate (0.06 ± 0.04 g/minute) and the intensity at which it occurred (13 ± 3% VO2peak) were significantly lower for the non-disabled subjects than those with paraplegia.

CONCLUSION

Sedentary individuals with paraplegia are more capable of oxidizing fat during voluntary arm ergometry than non-disabled individuals perhaps due to local adaptations of upper body skeletal muscle used for daily locomotion. However, carbohydrate is the predominant fuel source oxidized across a wide range of intensities during voluntary arm ergometry in those with paraplegia, while WBFO is limited and maximally achieved at low exercise intensities compared to that achieved by able-bodied individuals during leg ergometry. These findings may partially explain the diminished rates of fat loss imposed by acute bouts of physical activity in those with paraplegia.

Physical activity and exercise in the regulation of human adipose tissue physiology

Physical activity and exercise are key components of energy expenditure and therefore of energy balance. Changes in energy balance alter fat mass. It is therefore reasonable to ask: What are the links between physical activity and adipose tissue function? There are many complexities. Physical activity is a multifaceted behavior of which exercise is just one component. Physical activity influences adipose tissue both acutely and in the longer term. A single bout of exercise stimulates adipose tissue blood flow and fat mobilization, resulting in delivery of fatty acids to skeletal muscles at a rate well-matched to metabolic requirements, except perhaps in vigorous intensity exercise. The stimuli include adrenergic and other circulating factors. There is a period following an exercise bout when fatty acids are directed away from adipose tissue to other tissues such as skeletal muscle, reducing dietary fat storage in adipose. With chronic exercise (training), there are changes in adipose tissue physiology, particularly an enhanced fat mobilization during acute exercise. It is difficult, however, to distinguish chronic "structural" changes from those associated with the last exercise bout. In addition, it is difficult to distinguish between the effects of training per se and negative energy balance. Epidemiological observations support the idea that physically active people have relatively low fat mass, and intervention studies tend to show that exercise training reduces fat mass. A much-discussed effect of exercise versus calorie restriction in preferentially reducing visceral fat is not borne out by meta-analyses. We conclude that, in addition to the regulation of fat mass, physical activity may contribute to metabolic health through beneficial dynamic changes within adipose tissue in response to each activity bout.

Human investigations into the exercise pressor reflex

During exercise, neural input from skeletal muscles reflexly maintains or elevates blood pressure (BP) despite a maybe fivefold increase in vascular conductance. This exercise pressor reflex is illustrated by similar heart rate (HR) and BP responses to electrically induced and voluntary exercise. The importance of the exercise pressor reflex for tight cardiovascular regulation during dynamic exercise is supported by studies using pharmacological blockade of lower limb muscle afferent nerves. These experiments show attenuation of the increase in BP and cardiac output when exercise is performed with attenuated neural feedback. Additionally, there is no BP response to electrically induced exercise with paralysing epidural anaesthesia or when similar exercise is evoked in paraplegic patients. Furthermore, BP decreases when electrically induced exercise is carried out in tetraplegic patients. The lack of an increase in BP during exercise with paralysed legs manifests, although electrical stimulation of muscles enhances lactate release and reduces muscle glycogen. Thus, the exercise pressor reflex enhances sympathetic activity and maintains perfusion pressure by restraining abdominal blood flow, while brain, skin and muscle blood flow may also become affected because the reflex 'resets' arterial baroreceptor modulation of vascular conductance, making BP the primarily regulated cardiovascular variable during exercise.

Substrate metabolism during exercise in the spinal cord injured

The primary aim of the study was to examine substrate metabolism during combined passive and active exercise in individuals with spinal cord injury (SCI). Nine men and women with SCI (mean age 40.6 +/- 3.4 years) completed two trials of submaximal exercise 1 week apart. Two maintained a complete injury and seven had an incomplete injury. Level of injury ranged from thoracic (T4-T6 and T10) to cervical (four C5-C6 and three C6-C7 injuries). During two bouts separated by 1 week, subjects completed two 30 min sessions of active lower-body and passive upper-body exercise, during which heart rate (HR) and gas exchange data were continuously assessed. One-way analysis of variance with repeated measures was used to examine differences in all variables over time. Results demonstrated significant increases (P < 0.05) in HR and oxygen uptake (VO(2)) from rest to exercise. Respiratory exchange ratio (RER) significantly increased (P < 0.05) during exercise from 0.85 +/- 0.02 at rest to 0.95 +/- 0.01 at the highest cadence, reflecting increasing reliance on carbohydrate from 50.0 to 83.0% of energy metabolism. Data demonstrate a large reliance on carbohydrate utilization during 30 min of exercise in persons with SCI, with reduced contribution of lipid as exercise intensity was increased. Strategies to reduce carbohydrate utilization and increase lipid oxidation in this population should be addressed.

Effects of chronic spinal cord injury on body weight and body composition in rats fed a standard chow diet

The inability to maintain body weight within prescribed ranges occurs in a significant portion of the human spinal cord injury (SCI) population. Using a rodent model of long-term high thoracic (spinal level T3) spinal cord transection (TX), we aimed to identify derangements in body weight, body composition, plasma insulin, glucose tolerance, and metabolic function, as measured by uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT). Sixteen weeks after SCI, body weights of injured female rats stabilized and were significantly lower than surgical control animals. At the same time point, SCI rats had a significantly lower whole body fat:lean tissue mass ratio than controls, as measured indirectly by NMR. Despite lower body weight and fat mass, the cumulative consumption of standard laboratory chow (4.0 kcal/g) and mean energy intake (kcal.day(-1).100 g body wt(-1)) of chronic SCI rats was significantly more than controls. Glucose tolerance tests indicated a significant enhancement in glucose handling in 16-wk SCI rats, which were coupled with lower serum insulin levels. The post mortem weight of gonadal and retroperitoneal fat pads was significantly reduced after SCI and IBAT displayed significantly lower real-time PCR expression of UCP1 mRNA. The reduced fat mass and IBAT UCP1 mRNA expression are contraindicative of the cumulative caloric intake by the SCI rats. The prolonged postinjury loss of body weight, including fat mass, is not due to hypophagia but possibly to permanent changes in gastrointestinal transit and absorption, as well as whole body homeostatic mechanisms.

Higher glucose uptake in paralysed spastic leg

BACKGROUND

Insulin resistance and diabetes mellitus have been reported in the spinal cord injured (SCI). The group exhibits risk factors, as decreased physical activity, as well as episodes of stimulation of sympathetic nervous system below the level of lesion known to stimulate lipolysis, which in turn could induce insulin resistance. However, data are inconsistent, which might indicate the presence of protective mechanisms.

OBJECTIVE

To investigate the glucose uptake in spastic paralysed SCI legs compared to able-bodied. To investigate regional differences between glucose handling in the arm and leg.

STUDY DESIGN

Experimental controlled study.

SETTINGS

Institution of Clinical Neuroscience and Physiology, Spinal Injures Unit, Sahlgrens University Hospital, Goteborg, Sweden.

METHODS

Nine SCI subjects (2 C7, 7 T1-T4 ASIA A: 8, ASIA B: 1) were compared to 10 weight- and age-matched controls. Plasma flow in arm and leg was analysed by venous occlusion strain gauge plethysmography, and plasma derived from artery and veins in the arm and leg was analysed for glucose, insulin and lactate during fasting resting conditions.

RESULTS

Glucose uptake was higher in SCI legs compared to controls. There was no difference in insulin uptake or lactate production. Plasma flow was higher in SCI legs compared to controls. Controls showed a higher glucose uptake and lactate production in arm than leg.

CONCLUSIONS

Spasticity may counteract the risk of diabetes by inducing an insulin-independent glucose uptake. The regional difference in metabolism in able-bodied make it hazardous to do generalizations to whole body metabolism from arm or leg measurements.

Nutrient supplementation post ambulation in persons with incomplete spinal cord injuries: a randomized, double-blinded, placebo-controlled case series

OBJECTIVE

To examine effects of protein-carbohydrate intake on ambulation performance in persons with incomplete spinal cord injury (SCI).

DESIGN

Double-blinded treatment with washout and placebo crossover.

SETTING

Academic medical center.

PARTICIPANTS

Three subjects aged 34 to 43 years with incomplete SCI at C5-T4.

INTERVENTIONS

Subjects walked to fatigue on 5 consecutive days. On fatigue, participants consumed 48g of vanilla-flavored whey and 1g/kg of body weight of carbohydrate (CH(2)O). Weekend rest followed, and the process was repeated. A 2-week washout was interposed and the process repeated using 48g of vanilla-flavored soy.

MAIN OUTCOME MEASURES

Oxygen consumed (Vo(2); in L/min), carbon dioxide evolved (Vco(2)), respiratory exchange ratio (RER: Vco(2)/Vo(2)), time (in minutes), and distance walked (in meters) were recorded. Caloric expenditure was computed as Vo(2) by time by 21kJ/L (5kcal/L) of oxygen consumed. Data were averaged across the final 2 ambulation sessions for each testing condition.

RESULTS

Despite slow ambulation velocities (range, .11-.34m/s), RERs near or above unity reflected reliance on CH(2)O fuel substrates. Average ambulation time to fatigue was 17.8% longer; distance walked 37.9% longer, and energy expenditure 12.2% greater with the whey and CH(2)O supplement than with the soy drink.

CONCLUSIONS

Whey and CH(2)O ingestion after fatiguing ambulation enhanced ensuing ambulation by increasing ambulation distance, time, and caloric expenditure in persons with incomplete SCI.

Increasing blood flow before exercise in spinal cord-injured individuals does not alter muscle fatigue

Previous studies have shown increased fatigue in paralyzed muscle of spinal cord-injured (SCI) patients (Castro M, Apple D Jr, Hillegass E, and Dudley GA. Eur J Appl Physiol 80: 373-378, 1999; Gerrits H, Hopman MTE, Sargeant A, and de Haan A. Clin Physiol 21: 105-113, 2001). Our purpose was to determine whether the increased muscle fatigue could be due to a delayed rise in blood flow at the onset of exercise in SCI individuals. Isometric electrical stimulation was used to induce fatigue in the quadriceps femoris muscle of seven male, chronic (>1 yr postinjury), complete (American Spinal Injury Association, category A) SCI subjects. Cuff occlusion was used to elevate blood flow before electrical stimulation, and the magnitude of fatigue was compared with a control condition of electrical stimulation without prior cuff occlusion. Blood flow was measured in the femoral artery by Doppler ultrasound. Prior cuff occlusion increased blood flow in the first 30 s of stimulation compared with the No-Cuff condition (1,350 vs. 680 ml/min, respectively; P < 0.001), although blood flow at the end of stimulation was the same between conditions (1,260 ± 140 vs. 1,160 ± 370 ml/min, Cuff and No-Cuff condition, respectively; P = 0.511). Muscle fatigue was not significantly different between prior cuff occlusion and the control condition (32 ± 13 vs. 35 ± 10%; P = 0.670). In conclusion, increased muscle fatigue in SCI individuals is not associated with the prolonged time for blood flow to increase at the onset of exercise.