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Functional Electrical Stimulation

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Table 6: FES Studies Examining Muscle Function and Morphology

Author Year; Country
Score
Research Design
Total Sample Size
MethodsOutcomes
FES-assisted cycling
 

 

 

 

 

 

Ralston et al. 2013

Australia

RCT

Level 1

PEDro=8

N=14

Population: 14 individuals; average age 25y; motor complete lesions between C4 and T10; AIS A, B; 118 days post injury

 

Treatment: Participants were randomized to an experimental phase followed by a control phase or vice versa, with a 1-week washout period in between. The experimental phase involved FES cycling four times a week for two weeks and the control phase involved standard rehabilitation for two weeks.

 

Outcome Measures: Primary outcome-urine output (mL/hr); Secondary outcomes- lower limb circumference, and spasticity using the Ashworth Scale, and the Patient Reported Impact of Spasticity Measure (PRISM). Participants were also asked open-ended questions to explore their perceptions about treatment effectiveness.

1.     The mean between-group differences (95% CI) for lower limb swelling, spasticity (Ashworth), and PRISM were –0.1 cm (–1.5 to 1.2), –1.9 points (–4.9 to 1.2) and –5 points (–13 to 2), respectively. (Significant differences between groups were not reported).

2.     All point estimates of treatment effects favored FES cycling.

Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- and post-intervention data

 

Kuhn et al. 2014

Germany

Clinical Cohort Study

Level 2

N= 30

 

 

 

 

 

 

Kuhn et al. 2014

Germany

Clinical Cohort Study

Level 2

N= 30

Population: 30 individuals; average age 44 ± 15.5y; motor complete and incomplete spinal cord injuries in the cervical, lumbar, and thoracic regions; AIS A = 10, B = 3, C = 15, D = 2; 0-122 months post injury

 

Treatment: During the 4-week study period, all patients received eight 20min FES interventions at the beginning and end of each week. At every intervention, circumferential measurement and spasticity testing before and after FES cycling (pretest/post-test) were performed. Ultrasound, walking tests, and manual muscle test were only performed at the beginning of week 1 (T1) and at the end of week 4.

 

Outcome Measures: Circumferential measurement, muscular ultrasound measurement, spasticity measured by MAS, Walking (6 Minute Walk, TUG).

1.     An increase in the circumference of the cross-sectional area of 15.3% on the left and of 17% on the right m. rectus femoris could be observed in group AIS A + B after 4 weeks of treatment

2.     AIS C + D group, the circumference of the left m. rectus femoris increased by 25% and that of the right m. rectus femoris by 21% (for all, P < 0.05).

3.     For the 5 patients with partial walking ability at the start of the study, the mean 6-MWT distance significantly increased from 62.3±135.3 to 94.3±167.1 m throughout the study (P = 0.03) and the time for TUG was reduced from 11.7±21.9 to 10.1±18.1 s (P = 0.5)

Duffell et al. 2008;

UK

Prospective Controlled Trial

Level 2

N=11

Population: 11 participants with complete SCI, level of injury T3-T9, mean (SD) 10.7(2.1) YPI; 10 untrained AB controls, mean (SD) age 30.6(3.2) yrs

 

Treatment: FES cycling, up to 1hr/day, 5 days/week for 1 year

 

Outcome Measures: Maximal quadriceps torque; quadriceps fatigue resistance; power output (PO).

1.     The maximal quadriceps torque increased significantly throughout training in SCI participants (+399% at 3 months, +673% at 12), but remained significantly less than that of AB controls (mean (SD) 107.0(17.9) vs. 341.0(28.6)).

2.     Quadriceps fatigue resistance (76.7 (2.0)% force loss after 3 min at baseline, compared to 30.3(4.6)% after 12 months) and peak power output (+177%) improved significantly after training.

Baldi et al. 1998;

USA
PEDro=5
RCT

Level 2
N=26

Population: 26 males and females; age 25-28 yrs; traumatic motor complete; cervical or thoracic lesion level; 15 wks post-injury

 

Treatment: Random assignment to 3-6 months of 1) FES-assisted cycle ergometry (n=8), 30 min, 3X/week; 2) PES-assisted isometric exercise group (n=8) (same muscle groups as FES group) for 1 hr, 5X/week or 3) control group (n=9) with no stimulation.

 

Outcome Measures: lower limb lean body mass.

1.     Lean body mass increased with FES-cycling at all regions and declined for control and PES group.

2.     Lower limb lean mass and and gluteal lean mass were both significantly greater than the baseline after 6 months (p<.05)

3.     Controls lost an average of 6.1%, 10.1%, 12.4% after 3 months and 9.5%, 21.4%, 26.8% after 6 months in total body lean mass, lower limb lean mass and gluteal lean mass, respectively.

Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- and post-intervention data

 

 

 

 

 

 

Deley et al. 2015

USA

Pre-Post

Level 4

N=10

Population: 10 individuals- 8m/2f; average age 34 ± 4.0y; years post injury 9.8 ± 2.7y; level of lesion between C5 and T12; 9 AIS A & 1 AIS B

 

Treatment: Each participant underwent 2 testing sessions separated by at least 24h. During each testing session, isometric muscle torque was measured under 2 sequential electrical stimulation train patterns. Individuals underwent either CFT or VFT patterns until target torque was no longer produced and then switched immediately to the other pattern.

 

Outcome Measures: Isometric muscle torque, CFT (constant frequency train) pattern, VFT (variable frequency train) pattern.

1.     CFT needed significantly less stimulus activity than VFT in order to generate 50% maximal force (p<.05).

2.     These findings suggest that for the same initial forces the VFT pattern is less fatiguing than CFT and that when combining train types, and thus VFT should be used first.

 

 

 

 

 

Gibbons et al. 2014

United Kingdom

Post Test

Level 4

N= 8

Population: 8 participants- 4 males and 4 females; chronic complete and incomplete tetraplegia; injuries between C4 and C7, 5 AIS A, 1 AIS B, 2 AIS C; mean age= 30.5 ± 11.4y; years post injury= 8.4 ± 4.2y

 

Treatment: Participants completed a progressive FES-assisted training program building to three continuous 30-min FES-R sessions per week at 60–80% of their predetermined peak power output. Thereafter, rowing performance was monitored for 12 months.

 

Outcome Measures: Number and type of FES-training sessions required before achieving 30-min continuous FES-R, FES-R average power output (POav) pre and post 12 months training, participant feedback of perceived benefits.

1.     All participants were able to continuously FES-row for 30 min after completing 13±7 FES-R training sessions.

2.     Each individual POav during 30 min FES-R increased over 12 months FES-training.

3.     FES-R was found safe and well tolerated in this group of individuals with tetraplegia.

 

 

 

 

 

Gorgey et al. 2015

USA
Pre-Post

Level 4

N= 7

Population: 7 males; motor complete SCI; RT + diet group: average age= 35 ± 10y, years post injury 15 ± 9y, level of lesion between C5 and C7; Diet control group: mean age= 29 ± 4y; years post injury= 4 ± 2y

 

Treatment: Seven men with motor complete SCI were randomly assigned to a resistance training plus diet (RT + diet) group (n = 4) or a diet control group (n = 3). Participants in the RT + diet group were enrolled in a 12-week leg extension weight-lifting program via surface NMES of the knee extensor muscle group. The length of mid-thigh intermuscular fascia and the patellar tendon CSA were measured using MRI.

 

Outcome Measures: Length of mid-thigh intermuscular fascia and the patellar tendon CSA

1.     The length of the mid-thigh intermuscular fascia increased by 19% and 23% in the right (P = .029) and left (P = .015) legs, respectively, with no changes in the diet control group.

2.     Positive relationships were noted between skeletal muscle CSAs of the whole thigh (r = 0.77, P = .041) and knee extensors (r = 0.76, P = .048) and intermuscular fascial length.

 

 

Fornusek et al. 2013;

Australia

Pre-post

Level 4

N=8

 

Population: 8 participants with chronic SCI; mean (SD) age: 39 (14); C7-T11; 7 AIS A, 1 AIS C.

 

Treatment: 6 weeks (3 days/wk) of training on an isokinetic FES cycle ergometer. For each participant, 1 leg was randomly allocated to cycling at 10 rpm (LOW) for 30 min/day and the other cycling at 50rpm (HIGH) for 30 min/day.

 

Outcome Measures: lower limb circumference (distal and middle position of each thigh); electrically evoked quadriceps muscle torque during isometric contraction

1.      The intervention significantly increased thigh girth in both LOW and HIGH groups. At midthigh, girth increases induced by LOW (6.6% (1.2%)) were significantly greater than those by HIGH (3.6%(0.8%)).

2.      LOW (87%) produced greater gains in electrically evoked isometric torque than HIGH (20%) after training.

 

Thrasher et al. 2013;

USA

Pre-post

Level 4

N=11

Population: 11 participants with SCI (8M, 3F); 22-57 yrs; 8-95 months post-injury.

 

Treatment: 40 sessions of FES-LCE at a rate of 3 sessions/wk for 13 weeks. Continuous exercise was performed at a pedal cadence of 45RPM against a constant resistance for up to 60 minutes.

 

Outcome Measures: Mean power output; knee extension torque; Fatigue Index.

1.   Participants demonstrated significant increases in mean power output (9.0 to 20.3W), peak isometric knee extension torque (3.8 to 16.9 Nm), and sustainable isometric knee extension torque (4.9 to 14.4 Nm) after FES-LCE training.

2.   Participants with incomplete motor impairment demonstrated a decrease in Fatigue Index and improved mean power output more than those with complete motor impairment.

 

Reichenfelser et al. 2012;

Austria

Pre-post

Level 4

N=23

Population: 23 participants with SCI (20M 3F); mean(SD) age=40(14); mean(SD) DOI: 9(7) months; 7 tetraplegic, 16 paraplegic.

 

Treatment: All participants underwent a mean(SD) of 18(14) training sessions on an instrumented tricycle combined with functional electrical stimulation.

 

Outcome Measures: Power output; Modified Ashworth Test.

1.   Power output test showed a monthly increase in power output of 4.4W (SD 13.7) at 30rpm and 18.2W (SD 23.9) at 60 rpm.

 

Haapala et al. 2008;

USA

Pre-Post

Level 4

N=6

Population: 6 SCI participants, between 20-50yrs old, complete and incomplete injury at or below C4, with previous FES cycle ergometry experience.

 

Treatment: FES-LCE, progressive cycling (resistance) protocol with increasing resistance, as well as prolonged, submaximal cycling for 30min.

 

Outcome Measures: Power output for ankle (APO), knee (KPO), and hip (HPO), HR

1.     4 participants successfully completed both protocols.

2.     Initial and final APO for progressive protocol was lower than the submaximal protocol, but was not significantly different. There was no significant change in APO in the progressive protocol. APO significantly declined with time in the submaximal protocol.

3.     The initial KPO were similar for both progressive and submaximal protocols. There was no significant change in KPO during the progressive protocol. KPO significantly declined with time in the submaximal protocol.

4.     HPO for progressive protocol increased significantly with resistance. HPO for the submaximal protocol varied over time but displayed a gradual decrease overall.

5.     HR was initially similar for both protocols. HR for submaximal cycling increased significantly with time. There were no significant changes in HR during the progressive protocol.

Liu et al. 2007;

Taiwan

Pre-post

Level 4

N=18

Population: 18 males and females; age 26-61 yrs; AIS B-D; C3-L1 lesion level; 1-9 yrs post-injury

 

Treatment: FES cycling exercises three times a week for 8 weeks; 30 minutes/session

 

Outcome Measures: Muscle peak torque of knee flexors and extensors

1.     Significant increase in mean thigh girth after 4 weeks

2.     Significant increase in peak torque of bilateral knee flexors and right knee extensors

3.     Strength gains in AIS D > AIS C > AIS B

Crameri et al. 2002; Denmark
Pre-postLevel 4
N=6
Population: 5 males, 1 female; age 28-43 yrs; complete; T4-T12 lesion level; >8 yrs post-injury

 

Treatment: FES leg cycle ergometry training, 3 – 30 min/week for 10 weeks.

Outcome Measures: Incremental exercise leg test to muscle fatigue (total work output), histological assessment, myosin heavy chain (contractile protein) (MHC), citrate synthase (a mitochondrial enzyme) and hexokinase (enzyme needed to produce muscle glycogen).

1.     Total work performed increased after training.

2.     Paralysed vastus lateralis muscle was altered with increased type IIA fibres, decreased type IIX fibres, decreased MHC IIx and increased MHC IIA.

3.     Total mean fibre cross-sectional area increase of 129%, significantly increased cross-sectional area of type IIA and IIX fibres.

4.     Increased number of capillaries surrounding each fibre.

5.     Increase in citrate synthase and hexokinase activity.

Gerrits et al. 2000;

UK
Pre-post

Level 4
N=7

Population: 7 males; age 28-61 yrs; AIS A and B; C5-T8 lesion level; 1-27 yrs post-injury

 

Treatment: FES leg cycle ergometry training, 3 – 30 minutes sessions/week for 6 weeks.

Outcome Measures: Thigh girth, work output, contractile speed and fatigue resistance characteristics, including half relaxation time (½ Rt) and degree of fusion of electrically stimulated isometric contractions.

1.     Increase in work output as training progressed.

2.     More fatigue-resistant: decreased force decrement during quadriceps fatiguing stimulations.

3.     No change in contractile speed (using maximal rate of rise force) but half relaxation time decreased and there was significantly less fusion.

4.     Decrease in force responses at low stimulation frequencies, indicating less fusion and more relaxation.

5.     No change in thigh circumference.

Koskinen et al. 2000;

Finland
Pre-post

Level 4
N=10

Population: 10 males and females; age 27-45 yrs; complete; tetraplegic and paraplegic

 

Treatment: 18-month FES-assisted cycling ergometry (First training period: 30 min, 3X/week, 1 year; Second training period: 1X/week, 6 months).

Outcome Measures: Muscle morphology and protein measurement (type IV collagen, total collagen, muscle proteins).

1.     Total collagen content (as indicated by hydroxyproline concentration) was increased with first training period and second training period and even more so compared to able-bodied controls. No difference in Type IV collagen content between groups.

2.     This result combined with the changes seen with the other muscle proteins suggest accelerated type IV collagen turnover in skeletal muscle.

Scremin et al. 1999;

USA
Pre-post

Level 4
N=13

Population: 13 males; age 24-46 yrs; AIS A; C5-L1 lesion level; 2-19 yrs post-injury.

 

Treatment: A 3-phase, FES-assisted cycle ergometry exercise program leading to FES-induced cycling for 30 minutes. Average program was 2.3X/week for 52.8 weeks.

 

Outcome Measures: CT-scan of legs to assess muscle cross-sectional area and proportion of muscle and adipose tissue collected (pre-test, midpoint and post-test).

1.     Increase in cross-sectional area of: rectus femoris, sartorius, adductor magnus-hamstrings, vastus lateralis, vastus medialis-intermedius. No change in cross-sectional area of adductor longus and gracilis muscles.

2.     No correlations between total number of sessions and magnitude of muscle hypertrophy.

3.     Significant increases in the muscle/adipose tissue ratio, muscle tissue in the thigh and leg but no changes in the adipose tissue.

 

 

 

 

Yasar et al. 2015;

Turkey

Prospective single-arm study

Pre-Post

Level 4

N= 10

 

 

 

 

Population: 10 males and females with incomplete SCI that can ambulate more than 10m independently or with an assistive device

 

Treatment: The participants underwent 1-h FES cycling sessions three times a week for 16 weeks.

 

Outcome Measures: Total motor score, the Functional Independence Measure (FIM) score, the Modified Ashworth Scale for knee spasticity, temporal spatial gait parameters and oxygen consumption rate during walking.

1.     There were statistically significant improvements in total motor scores, the FIM scores and spasticity level at the 6-month follow-up (P<0.01).

2.     The changes in gait parameters reached no significant level (P>0.05).

3.     Oxygen consumption rate of the patients showed significant reduction at only 6 months compared with baseline (P<0.01).

 

 

 

 

Estigoni et al. 2014

Malaysia

Pre-Post

Level 4

N=8

 

Population: 8 males; age 45.6 ± 15.7y; complete or incomplete spinal cord lesions between C7 and T11, AIS A to C; 10.5 ± 6 y post injury

 

Treatment: All participants had their quadriceps muscles group stimulated during three sessions of isometric contractions separated by 5 min of recovery. The eEMG signals, as well as the produced torque, were synchronously acquired during the contractions and during short FES bursts applied during the recovery intervals.

 

Outcome Measures:  A commercial muscle dynamometer (Biodex Medical Systems) was used to measure isometric torque evoked from the electrically stimulated quadriceps. A custom-made, computerized evoked EMG acquisition system (the UniSyd e2MG) was utilized to control the stimulator and synchronize myoelectric signals with the torque outputs from the muscle dynamometer.

1.     After the first onset of neurostimulation during c1, while PtpA and Area curves were still increasing towards their maximal values, the muscle-evoked torque was already in decline for these SCI participants.

2.     Both m-waves and torque presented fast recovery during the first 20 s (b11–b12), which gradually reduced from b12 through b14. Still, the ratio m-wave × torque was fairly constant in r1with high R2PtpA also maintained a tight linear relationship with Torque during r2, with R2 between 0.96 and 0.99 for all legs

FES-assisted Stand or Gait Training
 

 

 

 

 

 

 

Kapadia et al. 2014

Canada

RCT

PEDro=5

Level 2

N= 27

Population: 27 individuals; traumatic (>18 months) and incomplete chronic spinal cord lesions between C2 and T12, AIS C and D.

 

Treatment: 45 minutes of therapy per session, 3 days per week, for 16 weeks (48 sessions in total). Outcome measures were assessed at baseline, 4 months, 6 months, and 12 months post baseline.

 

Outcome Measures:  Gait Measures- 6 Minute Walk, 10 Meter Walk, Assistive Device Score (ADS), Walking Mobility Scale (WMS); Balance & Mobility Measure- Time Up and Go Test (TUG); Functional Measures- Spinal Cord Independence Measure (SCIM), Functional Independence Measure (FIM); Spasticity Measure- Modified Ashworth Scale (MAS), Pendulum Test

1.     Spinal cord independence measure (SCIM) mobility sub-score significantly improved over time for the intervention group (p<.01) but not for the control group the control group (baseline/12 months: 17.27/21.33 vs. 19.09/17.36, respectively).

2.     On all other outcome measures the intervention and control groups had similar improvements.

3.     Walking speed, endurance, and balance during ambulation all improved upon completion of therapy and the majority of participants retained these gains at long-term follow-ups.

Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- to post-intervention data and pre-intervention to retention/follow-up data

Carvalho de Abreu et al. 2008, 2009;

Brazil

Prospective Controlled Trial
Level 2

N = 15

Population: 15 complete chronic participants with tetraplegia; injury level C4-C7; mean (SD) age 31.95(8.01) yrs with intact lower motor neurons, divided into gait training (n=8) and control (n=7) groups

 

Treatment: Partial body-weight supported treadmill gait training with NMES, for 2 – 20min session every week for 6 months; control group performed conventional physiotherapy, and gait training without NMES for 6 months

 

Outcome Measures: Cross-sectional area (CSA) of quadriceps, muscle hypertrophy.

1.     After gait training there was a significant increase in quadriceps mean (SD) CSA (49.81(9.36) cm2 vs. 57.33 (10.32) cm2), whereas there was no significant difference in the control group.

2.     No significant differences in muscle mass after 6 months, but the NMES group increased by 7.7%, and the control group decreased by 11.4%.

 

Kern et al. 2010a;

Austria

Pre-post

Level 4

N=25

 

Population: 20 males, 5 females; 22 thoracic SCI, 3 lumbar SCI; all with complete conus/cauda equina lesions

 

Treatment: Home-based functional electric stimulation (hb-FES) 30 minutes/muscle group (gluteus, thighs, and lower leg muscles), 5 days/week for two years. Stimulation was composed of long duration biphasic impulses five days a week and was adjusted every 12 weeks following assessment by a physiatrist.

 

Outcome Measures: Muscle cross-sectional area (CSA), knee extension torque, vastus lateralis muscle composition.

 

1.      Cross-sectional area of the quadriceps muscles significantly increased from mean (SD) 28.2 (8.1) to 38.1(12.7) cm2.

2.       Cross-sectional area of the hamstrings increased from 26.8(8.4) to 30.7(9.8) cm2.

3.       Mean diameter of vastus lateralis muscle fibers increased from 16.6(14.3) to 29.1(23.3) µm, and showed structural improvement.

4.       Maximum knee torque with ES increased from 0.8(1.3) to 10.3(8.1) Nm after 2 years.

5.       At the end of the two years, 5/20 of patients were able to perform FES-assisted standing and parallel-bars supported stepping-in-place.

 

 

Kern et al. 2010b;

Austria

Pre-post

Level 4

N=25

 

Population: 20 males, 5 females; 22 thoracic SCI, 3 lumbar SCI; all with complete conus/cauda equina lesions

 

Treatment: Home-based functional electrical stimulation training of the vastus lateralis 5 days/week for 2 years.  Long duration, high intensity biphasic simulation impulses adjusted according to excitability produced by daily hb-FES over a period of one year, eventually accompanied by daily standing-up exercises

 

Outcome Measures: Quadriceps muscle mass, force, and structure

 

1.       Mean muscle torque after 1 year of daily FES training increased from mean(SD) 0.8(1.3) to 7.21(7.18) Nm.

2.       After 2 years, mean fiber size diameter significantly increased from 15.5(11.4) to 30.1(21.3) μm, with a shift toward larger muscle fibers. Muscle atrophy was delayed or reduced in both patients less than 1 year post-injury and in those over a year.

3.       After the year of training, 20% of participants became able to stand, with 44% improving 1 functional class, 20% improving 2 functional classes, and 4% improving 3 functional classes.

Possover et al. 2010; Switzerland

Pre-post

Level 4

N=3

 

Population: 3 thoracic patients; all presenting with spasms/spasticity of the lower limbs, and bladder spasms

 

Treatment: Stimulation by electrodes to the sciatic and pudendal nerves and one double extradural Brindley-Finetech electrode bilaterally to the sacral nerve roots S3 and S4.

 

Outcome Measures: Spasticity and motion of the legs.

1.       Contraction of the quadriceps was obtained with optimal pulse widths between 8-20μs and permitted stable standing and alternative locomotion.

2.       At the post-operative follow-up points of 9, 6 and 3 months all patients reported optimal control of lower extremity spasticity with an increase in muscle mass.

 

Kern et al. 2005;

Austria
Pre-post

Level 4
N=9

Population: 1 female, 8 males; age 20-49 yrs; complete traumatic conus cauda equina lesions; > 0.8 yrs post-injury.

 

Treatment: Progressive PES to FES program for quadriceps to FES-assisted standing (n=4 trained ³ 2.4 years); untrained controls (n=5).

Outcome Measures: Muscle biopsy of vastus lateralis (mean fiber diameter, % area covered by muscle fibers, adipocytes, connective tissue).

1.     Overall mean fiber diameter of trained group was increased vs untrained group and also had similar values to normal sedentary adults.

1.    Proportion of total cross-sectional area covered by muscle fibers increased with training whereas the area covered by adipocytes and connective tissue significantly decreased.

 

 

 

 

 

Sharif et al. 2014

Canada

Pre-Post

Level 4

N= 6

Population: 6 individuals- 3 males and 3 females; Level of injury C5 to L4; All AIS D; mean age= 60.5 ± 13.2y; years post injury= 9.3 ± 12.0y

 

Treatment: The exercise protocol consisted of 12 weeks of FES-ambulation, with the RT600 (Restorative Therapies, Baltimore, MD), at a frequency of 3 times per week.

 

Outcome Measures: Locomotor function was assessed via the Walking Index for Spinal Cord Injury II (WISCI II), the 6-minute walk test (6MWT), the 10-meter walk test (10MWT), and the body-weight support required during training. HRQOL was assessed via the Short Form-36, the Perceived Stress Scale, and the Center of Epidemiological Studies for Depression scale.

1.     Participants showed significant improvements in the 6MWT (223 ± 141.5 to 297.7 ± 164.5 m, P=.03) and the required body weight support (55.3% ± 12.6% to 14.7% ± 23.2%; P = .03) following the training program.

2.     Four participants showed improvements on the WISCI II.

3.     Participants also showed a decrease in the Short Form-36 pain score and an increase in the overall mental health score.

Man on power wheelchair using a seated cycling machine while using FES

Discussion

In general, all studies reviewed involving FES produced beneficial results on muscle functions such as strength and endurance or muscle structure such as increased muscle size (i.e., reduced muscle atrophy). FES may have additional benefits over PES alone. In particular, the study by Baldi et al. (1998) should be highlighted as it was the only randomized, controlled trial (n=26) which compared FES (cycle ergometry exercise), PES (isometric exercise) and an untrained control group. These investigators assessed lean body mass in 3 distinct body areas (i.e. total body, lower limb, gluteal) as a marker of muscle atrophy in recently injured (approximately 10 weeks) individuals with motor complete SCI. Their results demonstrate that the FES-assisted cycling program is effective in reducing atrophy and resulted in relative increases in lean body mass in all areas after 3 and 6 months of participation. The PES-assisted isometric exercise group also reduced muscle atrophy but had intermediate results between FES and no treatment (their control group actually lost lean mass).

[su_spoiler title=”Effect Size Forest Plots of RCTs with Available Data” style=”fancy”][su_row]Click on the image to enlarge[/su_row]

[su_lightbox type=”image” src=”/wp-content/uploads/Forest_LLimb_Baldi_1998.gif”][image_with_animation image_url=”/wp-content/uploads/Forest_LLimb_Baldi_1998.gif” alt=”Effect size SMD forest plot for Baldi et al. 1998, functional electrical stimulation (FES) cycle ergometry”][/su_lightbox]

[/su_spoiler]

Reversal of muscle atrophy also appears feasible in more longstanding complete or motor-complete SCI (i.e. > 2 years post-injury) as shown by increases in muscle cross-sectional area and the muscle/adipose tissue ratio using FES-cycling (Crameri et al., 2002; Scremin et al., 1999). In chronic SCI, fatigability is also a key issue due to changes in muscle fiber composition. Fornusek et al. (2013) proposed that lower FES cycling cadences may therefore be more beneficial as slower cycling could mitigate the onset of fatigue and allow greater muscle force production. Indeed, in a recent pilot study using each participant as their control, Fornusek et al (2013) provided preliminary evidence that a lower FES cycling cadence compared to a higher cadence (10 rpm vs. 50 rpm) could be more effective at improving muscle hypertrophy and isometric strength.

NMES may also be used to strengthen the atrophied muscles to some extent prior to FES (Kern et al., 2005; Kern et al., 2010a; Kern et al., 2010b) and in some cases, FES is not possible unless NMES is first used. Kern et al. (2005) used a progressive NMES – FES program for quadriceps building eventually leading to FES-assisted standing in people with longstanding complete cauda equina injuries (>1.2 years post-injury). These investigators demonstrated increases to the overall mean fiber diameter and the proportion of total cross-sectional area covered by muscle fibers with training as compared to an untrained group. Later studies showed that FES had similar results in a larger group of participants (Kern et al., 2010a, Kern et al., 2010b). However, the feasibility of providing life-long stimulation therapy to participants with denervation injuries is uncertain.

There was one null finding associated with muscle atrophy in that Gerrits et al. (2000) employed a relatively shorter program of 6 weeks of FES-assisted cycling exercise in people with longstanding motor complete SCI (> 1 year post-injury) and found no change in muscle size. These non-significant results might be due to the relative insensitivity of the measure of thigh circumference, especially with the short intervention period and the absence of a control group for comparison purposes.

In addition to improving muscle properties, FES-cycling can improve work output and endurance (Crameri et al., 2002; Gerrits et al., 2000). For example, Gerrits et al. (2000) used a short (6 weeks) pre-post trial of FES-assisted cycling intervention in people with motor complete SCI and found an increased resistance to fatigue in the quadriceps muscle and greater work output.

Some mechanistic investigations have been conducted which help to explain some of these adaptations to muscle morphology and function with ongoing electrical stimulation exercise programs. For example, using FES-assisted cycling, Koskinen et al. (2000) demonstrated an increase in total collagen content as well as up- and down-regulation of proteins consistent with muscle-building activity. Others have noted an adaptive response to FES-assisted cycling exercise that serves to limit or alter the shift in the oxidative properties or fibre type composition of muscles that typically occurs following SCI (Crameri et al., 2002).

Conclusion

There is level 2 evidence (Baldi et al. 1998) that FES-assisted cycling exercise prevents and reverses lower limb muscle atrophy in individuals with recent (~10 weeks post-injury) motor complete SCI and to a greater extent than PES.

There is level 4 evidence (Scremin et al. 1999; Crameri et al. 2002) that FES may partially reverse the lower limb muscle atrophy found in individuals with long-standing (>1 year post-injury) motor complete SCI.

There is level 4 evidence (Gerrits et al. 2000) that FES-assisted cycle exercise may increase lower limb muscular endurance.

  • FES-assisted exercise is beneficial in preventing and restoring lower limb muscle atrophy as well as improving lower limb muscle strength and endurance in SCI.