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

Assessing the efficacy of duration and intensity prescription for physical activity in mitigating cardiometabolic risk after spinal cord injury

PURPOSE OF REVIEW

Spinal cord injury (SCI) heightens susceptibility to cardiometabolic risk (CMR), predisposing individuals to cardiovascular disease. This monograph aims to assess the optimal duration and intensity of physical activity (PA) for managing CMR factors, particularly obesity, after SCI and provide modality-specific PA durations for optimal energy expenditure.

RECENT FINDINGS

PA guidelines recommend at least 150 min/week of moderate-intensity activity. However, non-SCI literature supports the effectiveness of engaging in vigorous-intensity PA (≥6 METs) and dedicating 250-300 min/week (≈2000 kcal/week) to reduce CMR factors. Engaging in this volume of PA has shown a dose-response relationship, wherein increased activity results in decreased obesity and other CMR factors in persons without SCI.

SUMMARY

To optimize cardiometabolic health, individuals with SCI require a longer duration and higher intensity of PA to achieve energy expenditures comparable to individuals without SCI. Therefore, individuals with SCI who can engage in or approach vigorous-intensity PA should prioritize doing so for at least 150 min/wk. At the same time, those unable to reach such intensities should engage in at least 250-300 min/week of PA at a challenging yet comfortable intensity, aiming to achieve an optimal intensity level based on their abilities. Given the potential to decrease CMR after SCI, increasing PA duration and intensity merits careful consideration in future SCI PA directives.

Effects of two different paradigms of electrical stimulation exercise on cardio-metabolic risk factors after spinal cord injury. A randomized clinical trial

Objective

To examine the combined effects of neuromuscular electrical stimulation-resistance training (NMES-RT) and functional electrical stimulation-lower extremity cycling (FES-LEC) compared to passive movement training (PMT) and FES-LEC in adults with SCI on (1) oxygen uptake (VO2), insulin sensitivity and glucose disposal in adults with SCI; (2) Metabolic and inflammatory biomarkers; (3) skeletal muscle, intramuscular fat (IMF) and visceral adipose tissue (VAT) cross-sectional areas (CSAs).

Materials and methods

Thirty-three participants with chronic SCI (AIS A-C) were randomized to 24 weeks of NMES-RT + FES or PMT + FES. The NMES-RT + FES group underwent 12 weeks of evoked surface NMES-RT using ankle weights followed by an additional 12 weeks of progressive FES-LEC. The control group, PMT + FES performed 12 weeks of passive leg extension movements followed by an additional 12 weeks of FES-LEC. Measurements were performed at baseline (BL; week 0), post-intervention 1 (P1; week 13) and post-intervention 2 (P2; week 25) and included FES-VO2 measurements, insulin sensitivity and glucose effectiveness using the intravenous glucose tolerance test; anthropometrics and whole and regional body composition assessment using dual energy x-ray absorptiometry (DXA) and magnetic resonance imaging to measure muscle, IMF and VAT CSAs.

Results

Twenty-seven participants completed both phases of the study. NMES-RT + FES group showed a trend of a greater VO2 peak in P1 [p = 0.08; but not in P2 (p = 0.25)] compared to PMT + FES. There was a time effect of both groups in leg VO2 peak. Neither intervention elicited significant changes in insulin, glucose, or inflammatory biomarkers. There were modest changes in leg lean mass following PMT + FES group. Robust hypertrophy of whole thigh muscle CSA, absolute thigh muscle CSA and knee extensor CSA were noted in the NMES-RT + FES group compared to PMT + FES at P1. PMT + FES resulted in muscle hypertrophy at P2. NMES-RT + FES resulted in a decrease in total VAT CSA at P1.

Conclusion

NMES-RT yielded a greater peak leg VO2 and decrease in total VAT compared to PMT. The addition of 12 weeks of FES-LEC in both groups modestly impacted leg VO2 peak. The addition of FES-LEC to NMES-RT did not yield additional increases in muscle CSA, suggesting a ceiling effect on signaling pathways following NMES-RT.

Clinical trial registration

identifier NCT02660073.

Similar fat and carbohydrate oxidation in response to arm cycling exercise in persons with spinal cord injury versus able-bodied

CONTEXT

Persons with spinal cord injury (SCI) present with low fat oxidation that is associated with poor cardiometabolic health. This study compared changes in fat and carbohydrate (CHO) oxidation during moderate intensity continuous exercise in persons with SCI and able-bodied adults (AB).

DESIGN

Repeated measures, within-subjects study.

SETTING

University laboratory in San Diego, CA.

PARTICIPANTS

Nine men and women with SCI (age and time since injury = 32 ± 11 yr and 7 ± 6 yr) and 10 AB adults (age = 25 ± 8 yr).

INTERVENTIONS

To assess peak oxygen uptake (VO₂peak) and peak power output (PPO), participants performed progressive arm ergometry to volitional exhaustion. Subsequently, they completed 25 min of continuous exercise at 45%PPO.

OUTCOME MEASURES

Respiratory exchange ratio (RER), fat and CHO oxidation, and blood lactate concentration (BLa) were assessed.

RESULTS

Data showed a similar RER (P = 0.98) during exercise in SCI (0.97 ± 0.04) versus AB (0.97 ± 0.03) reflecting high CHO use and no differences in BLa (3.5 ± 1.1 and 3.0 ± 0.9 vs. mM, P = 0.56) or fat and CHO oxidation between groups (P > 0.05). However, participants with SCI exercised at a higher relative intensity (P < 0.01, 84 ± 7 vs. 75 ± 7%HRpeak) versus AB.

CONCLUSION

Data confirm high reliance on CHO during arm ergometry in persons with SCI. To better compare substrate utilization to AB adults, we recommend that exercise be prescribed according to peak heart rate due to differences in cardiorespiratory fitness between groups.

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.

Assessment of mitochondrial respiratory capacity using minimally invasive and noninvasive techniques in persons with spinal cord injury

Purpose

Muscle biopsies are the gold standard to assess mitochondrial respiration; however, biopsies are not always a feasible approach in persons with spinal cord injury (SCI). Peripheral blood mononuclear cells (PBMCs) and near-infrared spectroscopy (NIRS) may alternatively be predictive of mitochondrial respiration. The purpose of the study was to evaluate whether mitochondrial respiration of PBMCs and NIRS are predictive of respiration of permeabilized muscle fibers after SCI.

Methods

Twenty-two individuals with chronic complete and incomplete motor SCI between 18–65 years old were recruited to participate in the current trial. Using high-resolution respirometry, mitochondrial respiratory capacity was measured for PBMCs and muscle fibers of the vastus lateralis oxidizing complex I, II, and IV substrates. NIRS was used to assess mitochondrial capacity of the vastus lateralis with serial cuff occlusions and electrical stimulation.

Results

Positive relationships were observed between PBMC and permeabilized muscle fibers for mitochondrial complex IV (r = 0.86, P < 0.0001). Bland-Altman displayed agreement for complex IV (MD = 0.18, LOA = -0.86 to 1.21), between PBMCs and permeabilized muscles fibers. No significant relationships were observed between NIRS mitochondrial capacity and respiration in permeabilized muscle fibers.

Conclusions

This is the first study to explore and support the agreement of less invasive clinical techniques for assessing mitochondrial respiratory capacity in individuals with SCI. The findings will assist in the application of PBMCs as a viable alternative for assessing mitochondrial health in persons with SCI in future clinical studies.

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.

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.

Energy Expenditure, Cardiorespiratory Fitness, and Body Composition Following Arm Cycling or Functional Electrical Stimulation Exercises in Spinal Cord Injury: A 16-Week Randomized Controlled Trial

Background: Physical deconditioning and inactivity following spinal cord injury (SCI) are associated with multiple cardiometabolic risks. To mitigate cardiometabolic risk, exercise is recommended, but it is poorly established whether arm cycling exercise (ACE) or functional electrical stimulation (FES) leg cycling yields superior benefits. Objectives: To determine the adaptations of 16 weeks of FES cycling and ACE on exercise energy expenditure (EEE), cardiorespiratory fitness (CRF), and obesity after SCI. Methods: Thirteen physically untrained individuals were randomly assigned to FES (n = 6) or ACE (n = 7) exercise 5 days/week for 16 weeks. Pre- and post-intervention EEE, peak oxygen consumption (absolute and relative VO2Peak), and work were assessed using indirect calorimetry, while body composition was measured by dual-energy x-ray absorptiometry. Results: Main effects were found for peak power (p < .001), absolute (p = .046) and relative (p = .042) VO2Peak, and peak work (p = .013). Compared to baseline, the ACE group increased in EEE (+85%, p = .002), peak power (+307%, p < .001), VO2Peak (absolute +21%, relative +22%, p ≤ .024), peak work (19% increase, p = .003), and total body fat decreased (-6%, p = .05). The FES group showed a decrease in percentage body fat mass (-5%, p = .008). The ACE group had higher EEE (p = .008), peak power (p < .001), and relative VO2Peak (p = .025) compared to postintervention values in the FES group. Conclusion: In the current study, ACE induced greater increases in EEE and CRF, whereas ACE and FES showed similar results on body fat. Exercise promotional efforts targeting persons with SCI should use both FES and ACE to reduce sedentary behavior and to optimize different health parameters after SCI.

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.

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.

Anthropometric cutoffs and associations with visceral adiposity and metabolic biomarkers after spinal cord injury

Background/Objectives

To examine associations of different anthropometric measurements of central adiposity to visceral adipose tissue (measured via multi-axial magnetic resonance imaging; MRI) and cardiometabolic disease risk factors in men with spinal cord injury (SCI). Additionally, to determine population-specific seated/supine waist and abdominal circumference cutoffs, which may identify men at increased risk of cardiometabolic disease.

Participants/Methods

Twenty-two men with chronic SCI underwent MRI scans, anthropometric measurements along with assessments of various cardiometabolic risk biomarkers. Pearson/part (accounting for age as a covariate) correlation coefficients were calculated to determine the associations between study variables. Abdominal and waist circumference cutoffs were extrapolated using the slope of linear regression equations.

Results

Seated/supine abdominal and waist circumferences were (P < 0.01) associated with MRI visceral fat cross-sectional area (VAT_CSA), VAT volume and CSA:Total_CSA. Low density lipoprotein, non-high-density lipoprotein and total cholesterol were positively associated with seated/supine abdominal and waist circumferences after controlling for age; r = 0.50–0.61, r = 0.46–0.58, r = 0.52–0.58, P < 0.05, respectively. Tumor necrosis factor alpha was associated with seated/supine abdominal and waist circumferences after accounting for age; r = 0.49–0.51 and r = 0.48–0.56, P < 0.05 respectively. The population-specific cutoffs were 86.5cm and 88.3cm for supine waist and abdominal circumferences, respectively, as well as 89cm and 101cm for seated waist and abdominal circumferences, respectively. After dichotomizing VAT_CSA (< or ≥ 100cm²), peak oxygen uptake, triglycerides, insulin sensitivity and glycated hemoglobin were different (P < 0.05) between groups. After dichotomizing (< or ≥ 86.5cm) supine waist circumference, VAT_CSA, triglycerides and insulin sensitivity were different (P < 0.05) between groups.

Conclusions

Seated/supine circumferences are associated with both central adiposity and biomarkers of cardiometabolic disease risk in persons with SCI. Population-specific cutoffs are proposed herein to identify central adiposity and potential cardiometabolic disease risk after SCI.

Plasma adiponectin levels are correlated with body composition, metabolic profiles, and mitochondrial markers in individuals with chronic spinal cord injury

STUDY DESIGN

Cross-sectional design.

OBJECTIVES

This study examined the relationships between circulating adiponectin levels, body composition, metabolic profile, and measures of skeletal muscle mitochondrial enzyme activity and biogenesis.

SETTINGS

Clinical Research in a Medical Center.

METHODS

Plasma adiponectin was quantified in 19 individuals with chronic spinal cord injury (SCI). Body composition was evaluated by dual x-ray absorptiometry and magnetic resonance imaging. Metabolic profile was assessed by basal metabolic rate (BMR), oxygen uptake (VO₂), and intravenous glucose tolerance testing. Mitochondrial enzyme activity of skeletal muscle was obtained by spectrophotometric assays and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and 5' AMP-activated protein kinase (AMPK) protein expression was assessed by Western blots.

RESULTS

Adiponectin was negatively related to both total and regional fat mass and positively related to lean mass and muscle mass. Furthermore, there were positive relationships between adiponectin and BMR (r = 0.52, P = 0.02) and VO₂ (r = 0.73, P = 0.01). Furthermore, adiponectin was positively related to citrate synthase (r = 0.68, P = 0.002) and complex III activity (r = 0.57, P = 0.02). The relationships between adiponectin and body composition remained significant after accounting for age. The relationships between adiponectin, metabolic profile, and markers of mitochondria mass and activity were influenced by age.

CONCLUSIONS

The study demonstrated that adiponectin is closely related to body composition and metabolic profile in persons with SCI and further supports mechanistic studies suggesting that adiponectin may stimulate mitochondrial biogenesis.

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.

Skeletal muscle mitochondrial mass is linked to lipid and metabolic profile in individuals with spinal cord injury

PURPOSE

Changes in metabolism and body composition after spinal cord injury (SCI) predispose individuals to obesity, type II diabetes, and cardiovascular disease. A link between lean mass and skeletal muscle mitochondrial mass has been reported but it is unknown how skeletal muscle mitochondrial mass and activity impact metabolic health. This study examined the relationship between skeletal muscle mitochondrial mass, activity and metabolic profile in individuals with chronic SCI.

METHODS

Twenty-two men with motor complete SCI participated in the study. Citrate synthase (CS) and complex III (CIII) activity was measured in vastus lateralis biopsies. Metabolic profile was assessed by intravenous glucose tolerance test, basal metabolic rate (BMR), maximum oxygen uptake (VO₂ peak) and blood lipid profile.

RESULTS

Skeletal muscle CS activity was negatively related to the cholesterol:high density lipoprotein cholesterol (HDL-C) ratio and triglycerides (r = -0.60, p = 0.009; r = -0.64, p = 0.004, respectively). CS activity was positively related to insulin sensitivity and BMR (r = 0.67, p = 0.006; r = 0.64, p = 0.005, respectively). Similar relationships were found for CIII and metabolic profile, but not CIII normalized to CS. Many of the relationships between CS and metabolism remained significant when age, level of injury, or time since injury were accounted for. They also remained significant when CS activity was normalized to total lean mass.

CONCLUSIONS

These results suggest that an increase in skeletal muscle mitochondrial mass is associated with improved metabolic health independent of age, level of injury, or time since injury in individuals with chronic SCI. This highlights the importance of maintaining and improving mitochondrial health in individuals with SCI.

Abundance in proteins expressed after functional electrical stimulation cycling or arm cycling ergometry training in persons with chronic spinal cord injury

STUDY DESIGN

Longitudinal design.

OBJECTIVES

The study determined the effects of two forms of exercise training on the abundance of two proteins, (glucose transporter-4 [GLUT-4], adenosine monophosphate kinase [AMPK]) involved in glucose utilization and the transcriptional coactivator that regulates the genes involved in energy metabolism and mitochondrial biogenesis (peroxisome proliferator-activated receptor (PPAR) coactivator 1 alpha [PGC-1α]), in muscles in men with chronic motor-complete spinal cord injury (SCI).

SETTINGS

Clinical trial at a Medical Center.

METHODS

Nine men with chronic motor-complete SCI participated in functional electrical stimulation lower extremity cycling (FES-LEC; n = 4) or arm cycling ergometer (arm-cycling ergometer [ACE]; n = 5) 5 days/week for 16 weeks. Whole body composition was measured by dual energy X-ray absorptiometry. An intravenous glucose tolerance test was performed to measure glucose effectiveness (Sg) and insulin sensitivity (Si). Muscle biopsies of the right vastus lateralis (VL) and triceps muscles were collected one week prior to and post the exercise training intervention.

RESULTS

Neither training intervention altered body composition or carbohydrate metabolism. GLUT-4 increased by 3.8 fold in the VL after FES training and increased 0.6 fold in the triceps after ACE training. PGC-1α increased by 2.3 fold in the VL after FES training and 3.8 fold in the triceps after ACE training. AMPK increased by 3.4 fold in the VL after FES training and in the triceps after ACE training.

CONCLUSION

FES-LEC and ACE training were associated with greater protein expressions in the trained muscles by effectively influencing the abundance of GLUT-4, AMPK and PGC-1α. Thus, FES-LEC training of paralyzed muscle can modulate protein expression similar to that of trained and innervated muscle.