Physical Activity: Cardiovascular Health and Fitness

Neuromuscular Electrical Stimulation (NMES) Training

Neuromuscular electrical stimulation (NMES), delivered transcutaneously via electrodes placed on the skin over the target muscles, can be used to evoke muscle contractions. Devices have been constructed so that NMES can be used as a form of exercise. One common approach is NMES leg cycling, often known as functional electrical stimulation (FES) cycling. For practical purposes, we will use the common nomenclature “FES” when describing certain NMES approaches (such as “FES leg cycling”, “FES rowing”, etc) and the term “NMES” for others (such as “NMES resistance training”) despite the fact that all approaches use NMES technology. In this approach, a computer controls the phasic cycling activation of different leg muscle groups so that contractions are coordinated to power a leg cycle. Other approaches can be used, such as pairing NMES with resistance exercise movements (such as knee extension). It should be noted that some investigators have used low-intensity/high-volume NMES approach where the muscle is tonically activated with a low level of stimulation that is sustained for a prolonged period of time. This approach will not be covered in this chapter.

Author Year

Country
Research Design

Score
Total Sample Size

 Methods

Outcome
Functional Electrical Stimulation Leg Cycling Exercise (FES-LCE)

Gorgey et al. (2017)

USA

RCT

PEDro=5

N=9

Population: 9 SCI participants. SCI: C8-T10, AIS A (n=8) AIS B (n=1), AIS C=0.

Arm Cycling Exercise (ACE) (n=5): age 41±13yr, Time since injury (TSI): 11±9yr.

FES-LEC (n=4): age 37±7yr, TSI: 7±5yr.

Intervention: 16 weeks FES-LCE or ACE, 5 sessions / week. ACE: 10 min warmup, followed by 40 min of training, 10 min cool-down. Workload adjusted to maintain a peak heart rate (HR) at 75% of HRpeak. FES-LCE: cycling on ERGYS 2 with bilateral stimulation of the quadriceps, hamstrings, and gluteal muscles. Muscles stimulated at 60 Hz with current amplitude (140 mA) necessary to complete 40 min cycling at 50 RPM, progressively greater resistance over training.

Outcome Measures: Systolic and diastolic blood pressure, HR (rest and peak)

·         Resting systolic and diastolic blood pressures did not change following either ACE or FES-LES training

·         No changes to resting HR or HRpeak following ACE or FES-LCE training

Berry et al. (2012)

UK

Longitudinal study

N=11

Population: 11 SCI participants (2 female). Age 41.8±7.6 yrs. SCI: T3-T9, TSI ≥ 2 yrs, all AIS A.

Intervention: 12 months, home-based progressive FES-LCE program. Up to 5, 60-minute sessions / wk.

Outcome Measures: Stimulation cost, oxygen cost, efficiency, and markers of anaerobic metabolism before and after 6 and 12 months of training, during constant work-rate tests.

·         No significant change to oxygen cost and efficiency.

·         Total stimulation cost and blood lactate values reduced overall.

 

Berry et al. (2008)

UK

Pre-Post

N=11

Population: 12 SCI participants (2 female). SCI: 73-T12, AIS A (motor and sensory complete)

Intervention: 52 weeks (1 year) FES-LCE, 236 sessions.

Outcome Measures: Heart rate, O2 pulse, power output.

·         ↑ to HRpeak (13%) and peak O2 pulse after 6 months.

·         Significant improvements to peak power output after 3 months and 6 months.

Zbogar et al. (2008)

Canada

Pre-Post

N=4

Population: 4 SCI participants, all female. Age 19-51, lesion level C4-T7

Intervention: 12 weeks LES-LCE. 30-minute sessions, 3 session / week.

Outcome Measures: Large and small artery compliance

·         No significant change in large artery compliance

·         ↑ small artery compliance after training ~63% ↑ (range 4.2 + 1.8 to 6.9 + 3.2 mL/mmHg-1 × 100).

Janssen & Pringle (2008)

The Netherlands

Pre-Post

N=12

Population: 12 male SCI participants, 6 tetraplegia and 6 paraplegia; 4 experienced and 8 novice with FES-LCE. Age 36±16 yrs, SCI: C4-T11, TSI: 11±9 yrs.

Intervention: 6 weeks “modified” FES-LCE involving modified muscle activation and ITP design. 2-3 sessions / wk (total 18 sessions). In each session participants accumulated 25-30 mins of exercise, intervals of 5-10 mins exercise with 5 min rest. Applied progressive overload of duration and resistance.

Outcome Measures: Heart rate; power output; oxygen uptake (VO2peak); minute ventilation (VE); stroke volume and cardiac output via impedance cardiography

·         ↑ HRpeak (+16%) and power output (+57%) after training

·         ↑ VO2peak (+29%) and VEpeak (+19%).

·         No change to stroke volume of cardiac output

·         No significant differences with training when looking solely at tetra, para, experienced or novice separately

Hopman et al. (2002)

The Netherlands

Pre-Post

N=9

Population: 9 males with SCI. Age 40.7±7.2 yrs. SCI: T4-T12, AIS-A, TSI 12.8±7.6 yrs (range 1-22 yrs).

**note data from 3 participants omitted due to their medications, final n=6**

Intervention: 6 weeks FES-LCE training with electrodes placed over hamstring, gluteal, and quadriceps muscles. 30 mins per session, 3 session / wk

Outcome Measures: Mean arterial pressure (MAP), resting femoral artery (FA) blood flow

·         “↑” in workload from 4±5 to 16±14 kJ (no statistics provided) during training

·         No change in MAP

·          ↑ resting femoral artery blood flow: Peak systolic blood flow 1330±550 to 1710±490 mL/min, mean blood flow from 270±120 to 370±160 mL/min

·        Calculated vascular resistance ↓ by 30% after 6 weeks of training (no statistics)

Gerrits et al. (2001)

The Netherlands

Pre-Post

N=9

 

Population: 9 males with SCI. Age mean 39.2 yrs, range 26-61. SCI: C4-T8, 4 cervical and 5 thoracic; 5 AIS-A, 3 AIS-B, 1 AIS-C;TSI: mean 11.1 yrs, range 2-27.

Intervention: 6 weeks FES-LCE ergometry (LCE), 3 sessions / wk. Sessions were 30 minutes exercise with electrodes on hamstrings, glutes and quadriceps, target 50 RPM.

Outcome Measures: Common carotid artery (CA) and femoral artery (FA) diameters, inflow volumes (peak systolic, PSIV; mean, MIV) and velocity index (VI; representing peripheral resistance) via longitudinal imaging and Doppler velocity spectra

·         Average work output over the first 3 sessions vs last 3 ↑ (4 ±5 kJ to 16±14 kJ, p<0.01)

·         No change HR and systolic BP

·         ↑ FA diameter (pre-training 7.5±1.5 mm vs. post-raining 8.1±1.5 mm), no change CA diameter.

·         FA VI ↓ from 1.24±0.11 to 1.14±0.12 (p<0.01) but VI was unchanged in CA

·         Significant ↑ to resting inflow volumes in the FA (PSIV 1330 ± 550 to 1710 ± 490 mL/min and MIV 270 ± 120 to 370 ± 160 mL/min), ↑ in CA not significant

·         ↑ hyperaemic response to occlusion post-training.

Hjeltnes et al. (1997)

Norway

Pre-Post

N=5

Population: 5 males with SCI. Age 35±3 yrs. SCI: C5-C7 AIS-A except one AIS-A/B, TSI: 10.2±3.4 yrs.

Intervention: 8 weeks FES-LCE “full” training phase preceded by 2 weeks “run-in” period for adaptation. Full training was 7 sessions / week (once per day for 3 days, twice per day for 2 days).

Outcome Measures: peak oxygen uptake (VO2peak) and workload, pulmonary function (vital capacity, VC; forced expiratory volume (FEV); total lung capacity (TLC); lung diffusion capacity (DLCO).

·         VO2peak ↑ (70%) during FES-LCE but unchanged during ACE.

·         VO2peak during FES-LCE became similar to peak values during ACE post-training

·         No changes to pulmonary measures (VC, FEV, DLCO, TLC or RV) after training

Barstow et al. (1996)

USA

Pre-Post

N=9

Population: 9 males with SCI. Age 34.4 ± 5.6 yrs. SCI: 2 tetraplegia, 7 paraplegia, all AIS-A,TSI: 10.1 ± 4.1 yrs.

Intervention: FES-LCE, minimum 24 sessions, 30 mins per session, minimum of 24 sessions. Sessions averaged 2.1±0.4/week. Increasing work rate as tolerated

Outcome Measures: Work rate, VO2peak, oxygen pulse measured during incremental and constant work rate tests on cycle ergometer

·         Training significantly ↑ VO2peak (10.9%), peak work rate (46.5%), and peak oxygen pulse (12.6%).

·         No change in HRpeak

·         Improved (faster) VO2 and VE kinetics post-training

Faghri et al. (1992)

USA

Pre-Post

N=13

Population: 13 participants with SCI (3 female). Age 30.5 ±5 yrs. SCI: 6 paraplegia (5 complete, AIS A-B, T5-T10), 7 tetraplegia (all AIS-B to D, C4-T5), TSI 8 ± 4 yrs.

Intervention: 12 weeks FES-LCE, total 36 sessions. All started at 0W in first three sessions, load ↑ when possible.

Outcome Measures: Stroke volume (SV) and cardiac output (Q) assessed with impedance cardiography; blood pressure (SBP, DBP, MAP), HR; VO2peak and peak PO; ventilation (VE), arterio-venous difference of oxygen (a-VO2), and respiratory exchange ratio (RER). Assessed at rest and during 5 mins FES-LCE at 0W “submaximal” work.

·         Both para and quad improved continuous exercising PO (no stats), similar improvements between groups

·         No change in VO2, a-VO2 diff, RER or VE responses to submaximal exercise

·         ↑ HR and SBP in quad; ↓BP, DBP and MAP in para

·         Across all participants, during submax exercise ↓ HR and BP but ↑ SV and Q (↑ Q was most notable in the para group)

 

Hooker et al. (1992)

USA

Pre-Post

N=18

 

Population: 18 participants with SCI (1 female). Age: 30.6 ± 0.45 yrs (SE). SCI: 10 quadriplegia (C5-C7; 2 complete), 8 paraplegia (T4-T11; 6 complete), TSI: 6.1 ± 0.25 yrs (SE).

Intervention: FES-LCE. Total of 36 sessions completed over 13.6 ± 0.9 weeks (~2.7 sessions per week), 10-30 minutes per session.

Outcome Measures: VO2peak, power output (PO), and ventilation (VE) assessed with metabolic cart. Estimations of cardiac output (Q) and stroke volume (SV) with impedance cardiography. Blood pressure, total peripheral resistance (TPR) and HR also reported.

·         ↑ POpeak and VO2peak, and peak VE and HR responses to peak FES-LCE, no change during ACE test.

·         ↑ peak Q response due to ↑ HR peak, and reduced TPR response during FES-LCE

·         No change in responses of SV, MAP or a-VO2 difference during FES-LCE or ACE

·         No changes pre-post training in any measures during ACE testing.

Hooker et al. (1995)

USA

Pre-Post Test

N=8

Population: 8 males with SCI. Age  36 ± 5.4yr. SCI: two C5-C7, six T4-L1, all Frankel Class A, TSI: 9.8 ± 4.0 yrs.

Intervention: 19 weeks FES-LCE (called “NMES leg cycling”), minimum 24 (38 ± 17) 30-minute sessions. NMES was applied to the quadriceps, gluteal and hamstring muscles. Phase I: duration started at 10-15min and progressively ↑ until they could perform 30 minutes of continuous cycling. 2 session per week, 7 weeks. Phase II: resistance on the cycle was progressively ↑.

Outcome Measures: Work rate, VO2, heart rate, pulmonary ventilation and respiratory exchange rate.

·         For the graded cycle ergometer test to fatigue, there was a significant ↑ in VO2 after training (p=0.04), but when calculated per kilogram of body weight, this difference was no longer significant (p=0.07). All other outcomes did not significantly change after training.

·         During steady rate cycle test, ↓ respiratory exchange rate after training (p<0.05), but no other significant changes

Ragnarsson (1988)

USA

Pre-Post

N=19 Study I,

N=11 Study II

Population: Study I: 19 participants with SCI (3 female). Age 19-47 yrs. SCI: paraplegia=7, quadriplegia=12, TSI 2-17 yrs.

Study II: 11 participants with SCI (4 female). Age 18-54 yrs. SCI: paraplegia=4, quadriplegia=7, TSI 7months – 11yrs.

Intervention (same for both Study I and II). Phase I: quadriceps stimulation with dynamic knee extensions against increasing resistance, 3 sessions / week for 4 weeks. Phase II: 12 weeks FES-LCE, 15-30 minutes / session, 3 sessions / week

Outcome Measures: VO2peak, peak work rate, heart rate and blood pressure

·         Most showed an ↑ in strength and endurance.

·         During arm-crank ergometer stress tests VO2peak ↑ non-significantly (14.9%) after training

Pollack et al. (1989)

USA

Pre-Post

N=11d

Population: 11 participants with SCI (4 female), age 18-54 yrs. SCI: C4-C6 and T2-T6, motor-complete, TSI: 6–132 months.

Intervention: 3 phase program over 13–28wk. Phase I: quadriceps stimulation (knee extension); Phase II: FES leg cycle with 0–1 kp resistance; Phase III: loaded FES leg cycle, 3 d/wk, 3 wk.

Outcome Measures: VO2peak, endurance time, heart rate (HR), blood pressure (BP), ventilation (VE) and tidal volume (VT)

·         No change in any resting measures

·         ↑ endurance time (288%), VO2peak (95.9%), and peak HR (16.8%)

·         ↓ diastolic BP response (31.5%) with training, no change systolic BP response

·         ↑ VEpeak, but no significant changes to VTpeak or breathing frequency

 
Functional Electrical Stimulation Ambulation – PARASTEP® 1

Nash et al. (1997)

USA

Pre-Post

N=12

Population: 12 participants with SCI (1 female). Age 28 ± 7.2 yrs. SCI: T4-T11, TSI: 3.9 ± 3.1 yrs.

Intervention: 12 weeks PARASTEP ambulation training (FES of lower extremities with rolling walker), total  32 sessions.

Outcome measures: Common femoral artery (CFA) diameter and flow velocity profiles assessed with Doppler ultrasound at rest and after 5 min thigh occlusion: flow-velocity integral (FVI), cross sectional area (CSA), inflow volume (IV), pulse volume (PV= CSA*FVI), peak systolic velocity (PSV), arterial inflow volume (AIV)

·         Significant effects of training for resting CSA, HR, FVI, PV and AIV; no change in PSV

·         33% ↑ in FA CSA (p<0.001) and ↓ HR by 7 bpm (p<0.05)

·         ↑ resting FVI and PV by 26% and 67% respectively (p<0.05, p=0.001)

·         ↑ resting AIV 417 to 650 ml/min (p<0.01)

·         AIV response 1 minute post-occlusion ↑ 78.2% in absolute magnitude and 17.4% when expressed as % change from baseline. After 1 min though no differences pre- vs post-training

Jacobs et al. (1997)

USA

Pre-Post

N=15

Population: 15 participants with SCI (3 female). Age: 28.2 ± 6.8 yrs, range 21.1-45.2 yrs. SCI: T4-T11, all paraplegia AIS-A, TSI 3.7 ± 3.0 yrs range 7-8.8 yrs.

Intervention: 32 sessions of Parastep ® 1 functional neuromuscular stimulation ambulation training. 3 sessions / week. Typically, three walking trials were completed during each training session. Participants chose ambulation pace and duration.

Outcome measures: heart rate (HR), peak VO2.

·         Lowered HR throughout sub-peak levels of arm ergometry post-training

·         ↑ VO2peak from 20.0 ± 3.3 mL/kg/min to 23.0 ±3.6 mL/kg/min post-training
FES Hybrid Leg-Cycling Ergometry with Voluntary Arm Crank (FES-LCE+ACE)

Bakkum et al. (2015)

Netherlands

RCT

PEDro=6

N=19

 

 

Population: 19 participants with SCI (1 female). SCI: C2-L2, TSI: >10 years.

Intervention: 16 weeks, participants randomized to FES-LCE+ACE (n=9) or ACE alone (n=10). 32 sessions, 18-32 minutes per session (↑ across program). Interval training protocol.

Outcome Measures: Systolic and diastolic blood pressure are only cardiorespiratory measures, all others are metabolic.

·         Lowered diastolic blood pressure

 

 

 

 

 

Brurok et al. (2011)

Norway

Pre-Post

N=6

Population: 6 men with SCI in stable neurologic recovery (5 participants – paraplegic AIS A, 1 participant – tetraplegic AIS A).

Intervention: 8 weeks FES-LCE+ACE, aerobic high-intensity hybrid exercise training, 3 session per week. Training preceded by a 7 week control period of regular daily activity. Peak tests were performed at three different time points: 1, baseline; 2, control; and 3, post-training.

Outcome measures: Peak stroke volume (SV) during hybrid cycling and VO2peak during FES-LCE+ACE, arm cycle ergometry (ACE), and FES-LCE

 ·         Between the control and post training test, ↑ in VO2peak (25.3%) during FES-LCE+ARM, and VO2peak during ACE (25.9%) and FES-LCE (25.8%).

Gurney et al. (1998)

USA

Pre-Post

N=6

Population: 6 males with SCI. Ages 23-41 yrs. SCI: C4-T10, 4 paraplegia, 2 tetraplegia, TSI 5–24 yrs.

Intervention: Phase I: FES-LCE, 3 sessions / week for 6 weeks.

Phase II: FES-LCE+ACE, 3 session / week for 6 weeks.

Phase III: 8 weeks detraining.

Outcome Measures: VO2peak, submaximal and maximal HR.

·         ↑ VO2peak (81.7%) and workload with FES-LCE+ARM.

·         After detraining period, POpeak returned to baseline; VO2peak remained higher.

Mutton et al. (1997)

USA

Pre-Post

N=11

Population: 11 males with SCI. Mean age 35.6 yrs. SCI: C5-6 to T12-L1, all AIS A, TSI mean 9.7 yrs.

Intervention: Phase I: progressive FES-LCE to 30min of exercise;

Phase II: ~35 sessions of FES-LCE; Phase III: ~41 sessions, 30 mins each of combined FES-LCE+ACE.

Outcome Measures: VO2peak and submaximal physiological parameters (VO2, HR, blood lactate).

 ·         ↑ VO2peak (13%) and POpeak (28%) during graded hybrid testing, but not during graded ACE or graded FES-LCE testing alone.

Krauss et al. (1993)

USA

Pre-Post

N=8

Population: 8 participants with SCI (1 female). Age 32 ± 2 yrs. SCI: 7 paraplegia, 1 tetraplegia, TPI: 13 ± 2 yrs.

Intervention: Phase I: FES-LCE, 6 weeks, 3 sessions / week.

Phase II: FES-LCE+ACE for 6 weeks.

Outcome Measures: VO2peak, HR, workload, peak lactate.

·         After Phase I, ↑ VO2peak during ACE (21.9%) and FES-LCE (62.7%).

·         After Phase II, ↑VO2peak during FES-LCE+ACE by 13.7%.

·         HRpeak only ↑ with training during FES-LCE.
FES Rowing (FES-ROW)

Wheeler et al. (2002)

Canada

Pre-Post

N=6

Population: 6 with SCI (sex not defined, likely all male): 5 paraplegia (AIS-A, T4-12) and 1 quadriplegia (AIS-C, C7), TSI 13.8 ± 11.6 yrs. Age 42.5 ± 17.9 yrs

Intervention: 12 weeks FES-ROW (quadriceps) at 70%–75%VO2peak, 30 mins per session, 3 sessions / week.

Outcome Measures: VO2peak, peak O2 pulse and total rowing distance during arm-only rowing, FES bilateral lower-extremity flexion and extension (LFES) and hybrid exercise (FES-ROW).

·         Post-training during FES-ROW: ↑ rowing distance (25%, p<0.02), VO2peak (11.2%, p<0.001), and peak oxygen pulse (11.4%, p<0.01).

·         HRpeak response to hybrid training was unchanged, but HRpeak with LFES ↑ (p<0.01)

 

Solinsky et al. (2020)

USA

Pre-Post

N=40

Population: 40 participants with SCI (6 female). Age 34.1 ± 12.4cyrs. SCI: C1-T1=21, T2-L5=18 Unknown=1; AIS A=19, AIS B=8, AIS C=5, AIS D=2, AIS Unknown=6; TSI 41.4 ± 87.4 months.

Intervention: 6 months FES-ROW. Goal of 2-3 sessions / week at a goal > 75% HRmax. Individuals averaged 42.1 ± 22.0 min of FES rowing per week, 1.69 sessions per week.

Outcome Measures: VO2peak, Cardiometabolic Disease (CMD) indicators

·         ↑ VO2peak p<0.001

 

Jeon et al. (2010)

Canada

Pre-Post

N=6

Population: 6 male participants with paraplegia. SCI: T4-T5 and T10, age 48.6 ± 6.0 y.

Intervention: 12 weeks of FES-ROW 3-4 sessions per week (600–800 kcal per week).

Outcome measures: VO2peak (plus metabolic markers)

·         ↑ VO2peak from 21.4 ± 1.2 to 23.1 ± 0.8 mL/kg/min (P = 0.048).

 

Gibbons et al. (2016)

UK

Observational and

Pre-Post

N=14

 

Population: Study-1: FES-untrained (FES-UT) males (n=3): Age 38 ± 14 yrs; C4=1, T6-8=2; AIS A. FES-untrained (FES-UT) females (n=3): Age 33 ± 1 yrs; C6-7=2, T10=1; AIS A=2, AIS B=1. FES-trained (FES-T; n=3): Age 42 ± 15 yrs (males); C6=1, T2-T4=2; AIS A.

Study-2: FES-naïve (n=5, 4 females): C4-6=3, T6-10=2; AIS A.

Intervention: Study-1. Cross-sectional study. Resting cardiac ultrasound assessment then incremental arm crank exercise (ACE) test. Study-2. Progressive structured FES-ROW training with two conditioning phases to ↑ quadriceps fatigue resistance and force-generating characteristics and a third intervention phase for 8 weeks.

Outcome Measures: cardiac ultrasound, VO2peak, work rate

·         Study-1. VO2peak during ACE was not different between FES-UT and FES-T.

·         Left ventricular internal diameter diastole (LVIDd), end-diastolic volume (EDV), relative EDV (REDV), end-systolic volume (ESV), and relative ESV (RESV) were lower in FES-UT females, and LVIDd was lower in FES-UT males, compared to FES-T

·         Relative wall thickness diastole (RWTd) was higher in FES-UT vs FES-T

·         Early to late diastole ratio (E/A), early septal myocardial tissue velocity diastole (E’) and early to late septal tissue velocity diastole ratio (E’/A’) was lower and early LV relaxation diastole to early septal myocardial tissue velocity diastole ratio (E/E’) was higher in FES-UT compared with FES-T

·         Stroke volume (SV) and cardiac output (Q) were lower and resting HR was higher in FES-UT compared to FES-T

·         No differences in blood pressure between groups

·         Study-2. Individual ACE VO2peak and POpeak ↑ with training, and FES-ROW VO2peak and POpeak ↑ during Phase-3

·         ↑ LVIDd, EDV, REDV, ESV and left ventricular mass training and ↓ RWTd

·         ↑ Early LV relaxation diastole (E), E/A, E’, E’/A’ and flow propagation velocity (FPV) ↑ with training ↓ LV relaxation diastole (A), late diastole tissue velocity (A’) and E/E’

·         SV, ejection fraction (EF) and Q ↑ with training

Qiu et al. (2016)

USA

Pre-Post

N=12

Population: 12 participants with SCI (1 female). Age 33.3 ± 3.8 yrs. SCI: T2-C4=12; TPI 8.3 ± 3.3 yrs

Intervention: FES-ROW. Training 3 times / week and only advanced to FES-RT when 30 min of full knee extension was achieved. All participants underwent the FES-RT 3 sessions / week for 6 months, goal of reaching an exercise intensity of 75-85% of HRpeak for 30 continuous minutes. Outcome measures: aerobic capacity (VO2peak), peak ventilation (VEpeak), peak tidal volume (VTpeak), peak breathing frequency (BFpeak), peak espiratory exchange ratio (RERpeak), peak heart rate (HRpeak), oxygen uptake efficiency slope (OUES).

·         ↑ VO2peak on average by 12% with 6 months of FES-RT, from 15.3 ± 1.5 to 17.1 ± 1.6 mL/kg−1/min−1 (p=0.02), and 28% ↑ in peak wattage (34.6 ± 4.4 versus 44.4 ± 5.7 W, p<0.01).

·         Average VEpeak did tend to be higher after FES-RT (37.5+ 4.4 versus 40.7 + 3.0 L/min−1, p=0.09), but an ↑ was demonstrated in only 7 individuals.

·         No change RERpeak and HRpeak.

·         Average OUES was higher after 6 months of FES-RT (1.24 ± 0.11 versus 1.38 ± 0.12, p<0.05).

Kim et al. (2014)

Korea

Pre-Post

N=12

 

Population: 12 participants with SCI (2 female). Age 36 ± 12 yr. SCI: L1-C6; AIS A=7, B=1, C=4; TSI 11.4 ± 5.8 yr.

Intervention: 6 weeks FES-ROW, 42.5 minutes / session, 5 session / week. 5 min warm-up, 32.5 min exercise (6 bouts of 5 minutes exercise 30s rest), and 5 min cool-down. During exercise aimed to maintain HR >70% of peak HR. Outcome measures were assessed at baseline and 6wk.

Outcome Measures: peak oxygen consumption during ACE test

 ·         No significant change in peak oxygen consumption.

 

 

Taylor et al. (2014)

United States

Pre-Post

N=14

 

 

Population: 14 SCI individuals (1 female). Age 39.2  ± 3.3 yrs. SCI: T3-T11, AIS-A, TSI 9.7 ± 2.6 years

Intervention: First, variable period of FES ‘strength training’ (3-5 days per week until repetitive knee extension could be achieved for 30 mins). Then FES-ROW 3 days per week, consisting of multiple intervals of FES rowing interspersed with intervals of 3-5 mins arms-only rowing for total of 30 mins per session). Once they could complete 10 mins continuously of rowing, did lab-based RT 3 days per week for 6 months.

Outcome Measures: peak minute ventilation, peak aerobic capacity. Note that initial peak graded exercise tests were performed when muscle strength and endurance allowed for continuous FES-ROW >10 mins (range 2-6 weeks). Outcome tests were graded FES-ROW

·         ↑ VO2peak (19.6±6.0 ml/kg/min to 21.4±6.6, p=0.02), VE peak (54.1±13.5 L/min to 60.3±13.5 L/min, p=0.01),

·         No change HRpeak or power output (p=0.07)

·         Pre-training, significant correlation between LOI and VO2peak (adj r2=0.50, p<0.01), and LOI and VEpeak (adj r2=0.38, p=0.01)

·         Post-training, relationship between VO2peak and LOI was non-significant, while correlation between VEpeak and LOI remained (adj r2=0.58, p=0.001)

 

Vivodtzev et al (2020)

USA

RCT

PEDro=3

N=9

 Population: NIV: Mean age: 42.8yr; Level of injury: C1-T1=5, T2-T3=1; Level of severity: AIS A=3, AIS C=3; Mean time since injury: 13.7yr. Sham: Mean age: 31yr; Level of injury: C1-T1=2, T2-T3=1; Level of severity: AIS A=1, AIS B=1, AIS C=1; Mean time since injury: 11.3yr.
Intervention: Ventilatory support during whole-body FES rowing. All participants had training adaptations plateauing for more than 6 months before enrolling the study. After baseline assessment participants continued training with randomly assigned non-invasive ventilation (NIV: n=6) or sham (n=3) for 3mo.
Outcome Measures: oxygen uptake efficiency slope (OUES)

1.      Training with NIV ↑ OUES compared to baseline (4.1 ± 1.1 versus. 3.4 ± 1.0, i.e., +20 ± 12%, p<0.05) and sham (p=0.01), thus illustrating an ↑ in the ability to uptake oxygen.

↑ OUES result also seen when no NIV during test, this suggests improved cardiopulmonary reserve

Vivodtzev etl al (2020)

USA

RCT

PEDro=7

N=19

 

 Population: Mean age: 39.13yr; Level of injury: C4-T8=19; Level of severity: AIS A=8.5, AIS B=3.5, AIS C=7; Mean time since injury: 12.2yr.
Intervention: Acute ventilatory support in the form of non-invasive ventilation (NIV) during whole-body rowing. All patients were familiar with functional electrical stimulation (FES) rowing and had plateaued in their training-related ↑ in aerobic capacities. Patients performed two FES-rowing peak exercise tests with NIV or without.
Outcome Measures: oxygen uptake efficiency slope (OUES).

1.      NIV ↑ the exercise tidal volume (peak, 1.50±0.31 L versus 1.36±0.34 L; p<0.05) and reduced breathing frequency (peak, 35±7 beats/min versus 38±6 beats/min; p<0.05) compared with the sham test, leading to no change in alveolar ventilation but a trend toward ↑ oxygen uptake efficiency (p=0.06).

2.      In those who reached peak oxygen consumption (VO2peak) criteria (n=13), NIV failed to significantly ↑ VO2peak (1.73±0.66 L/min versus 1.78±0.59 L/min); however, the range of responses revealed a correlation between changes in peak alveolar ventilation and VO2peak (r=0.89; p<0.05).

Those with higher level injuries and shorter time since injury exhibited the greatest ↑ in VO2peak.
Neuromuscular Electrical Stimulation Resistance Training (NMES-RT)

 

Carty et al. (2012)

Ireland

Prospective cohort

N=14

Population: Participants with T2-T11 SCI (3 female); 11 AIS A, 3 AIS B; age 45.08 ± 7.92; TSI 11.22 ±11.23 yrs.

Intervention: 8 weeks NMES, 1 hour 5 times / week. Four electrodes were placed bilaterally on the quadriceps and hamstrings muscle groups, and subtetanic contractions were elicited using a neuromuscular electrical stimulation device. Participants ↑ the stimulation intensity on an incremental wheelchair exercise test of increasing speed and incline as quickly as tolerable to bring them to the desired training intensity as recorded on the Borg scale of rating of perceived exertion (RPE) (between 13 and 15 on RPE).

Outcome Measures: Incremental treadmill wheelchair propulsion exercise test with simultaneous cardiopulmonary gas exchange analysis to determine VO2peak and HRpeak.

·         ↑ VO2peak and HRpeak between baseline and follow-up was observed. Changes in VO2peak ranged from -1.1% to 57.2%.

·         No difference in the mean VO2peak change between the 2 groups based on the level of injury (above T6, T6 and below).

Stoner et al. (2007)

USA

Pre-Post

N=5

Population: 5 males with SCI. Age 35.6 ± 4.9 yrs. SCI: C5-T10, AIS A, TSI 13.4 ± 6.5 yr.

Intervention: 18 weeks NMES, 2 session / week. Quadriceps femoris muscle group of both legs were trained with 4×10 repetitions of unilateral, dynamic knee extensions

Outcomes measures: FMD and resting diameter and arterial range of the posterior tibial artery.

 ·         FMD improved from 0.08 ± 0.11 (2.7%) to 0.18 ± 0.15 (6.6%) and arterial range improved from 0.36 ± 0.28 mm to 0.94 ± 0.40 mm. Resting diameter did not change.

Sabatier et al. (2006)

USA

Pre-Post

N=5

Population: 5 males with SCI. Age 35.6 ± 4.9 yrs, AIS A, TSI 13.4 ± 6.5 yrs

Intervention: 18 weeks home-based NMES, twice per week.

Outcome Measures: Femoral artery diameter and blood flow, weight lifted, muscle mass, and muscle fatigue.

·         ↑ weight lifted and muscle mass and a ↓ in muscle fatigue.

·         There was no change in femoral artery diameter with training.

·         Resting, reactive hyperaemia, and exercise blood flow did not change significantly with training.

Discussion

Fourteen studies have used FES leg cycling exercise (FES-LCE) as a training intervention with cardiorespiratory outcomes, ranging in duration from 6 weeks to 52 weeks. A single RCT study by Gorgey et al. (Gorgey, Graham et al. 2017) compared the efficacy of 16 weeks of FES-LCE versus arm-cycle ergometry (ACE) training. These authors reported that peak oxygen uptake was not significantly changed in either of the intervention groups nor was resting heart rate or blood pressure. By contrast, of the single-cohort longitudinal studies, most reported concurrent improvements to both VO2peak and POpeak (or endurance time) during or following FES-LEC training. Of those that examined ventilatory parameters, only two out of six noted increased peak ventilation during graded stress tests (Janssen & Pringle 2008; Pollack et al. 1989), and Hjeltnes et al (Hjeltnes et al. 1997) did not observe any changes to resting lung volumes after training. Seven of the FES-LEC studies assessed blood pressure or arterial parameters. While resting blood pressure seems largely unchanged with training (four studies including an RCT), both Pollack (Pollack et al. 1989) and Faghri (Faghri et al. 1992) observed lower blood pressure responses to exercise, indicating positive cardiovascular adaptations with FES-LEC training. This is further supported by findings from Hopman (Hopman et al. 2002) and Zbogar (Zbogar et al. 2008) indicating favourable vascular adaptations. Furthermore, most studies reporting on heart rate (HR) data found increased peak or submaximal exercising HR, though the RCT from Gorgey (Gorgey, Graham et al. 2017) did not see significant changes to HRpeak.

Of twelve studies involving hybrid FES training, five used hybrid FES that combines FES-LEC with voluntary arm cycling exercise (FES-LEC+ACE), and seven involved FES-rowing training. There was a single RCT by Bakkum (Bakkum et al. 2015) which compared FES-LCE+ACE versus ACE, though this study did not include cardiorespiratory data related to oxygen uptake or exercise performance, and otherwise only saw some reductions in resting diastolic blood pressure following the 16-week intervention. All studies but one reported improvements to VO2peak in the ranges of ~10-100%, not only in FES-hybrid modalities but in some cases translating to other modalities like ACE alone and/or FES-LCE alone (Brurok et al. 2011; Gibbons et al. 2016; Krauss et al. 1993). Most often the improvements in oxygen uptake were accompanied by greater POpeak during graded stress tests. The only study that didn’t see improved VO2peak was Kim (Kim et al. 2014) whose training duration was a relatively short 6 weeks and did otherwise report improved muscular strength. In contrast to findings from the FES-LCE studies, all hybrid FES studies reporting on ventilation found increases in peak ventilation responses during graded stress tests. Two studies assessing cardiac structure and function also noted increased cardiac output. Of note, Gibbons et al. (Gibbons et al. 2016) performed detailed echocardiographic assessments in participants following FES-ROW training, and observed augmented heart mass, dimensions, and improved ejection and filling function. Finally, two of the studies noted increased peak HR during FES stress tests, while HRpeak was unchanged in three others.

Two studies using FES ambulation training, both with the commercial Parastep® system, found that training promoted favourable adaptations to the vascular system (i.e. larger arteries and greater flow responses) or improvements to VO2peak following the training program. A single prospective cohort study by Carty et al. (Carty et al. 2012) assessed the efficacy of 8 weeks of NMES resistance training and found that participants improved VO2peak in an incremental wheelchair test following their training. They also found increased peak HR across their full cohort. Only two other studies using NMES have reported cardiorespiratory data: Stoner (Stoner et al. 2007) and Sabatier (Sabatier et al. 2006) have assessed arterial structure and function but did not observe any changes to femoral artery diameter or resting function. Stoner (2007) did note improved blood flow responses post-occlusion, but these were not significant in Sabatier’s (Sabatier et al. 2006) participants.

Conclusions

There is Level 2 evidence (Carty et al. 2012) that 8 weeks of 1-hour NMES training, 5 times per week can improve aerobic capacity (ie. peak oxygen uptake), and allow individuals to achieve higher peak exercising HR.

There is level 4 evidence (Berry et al. 2008; Faghri et al. 1992; Gerrits et al. 2001; Hjeltnes et al. 1997; Hooker et al. 1992; Hooker et al. 1995; Hopman et al. 2002; Janssen & Pringle 2008; Mutton et al. 1997; Pollack et al. 1989) that 6-52 weeks training with 2-3 sessios per week of FES training promotes improvements to aerobic capacity (ie. peak oxygen uptake) and exercise performance

There is Level 4 evidence (Janssen & Pringle 2008; Pollack et al. 1989) that 6-28 weeks, 2-3 sessions per week FES training can result in increased ventilatory capacity without no changes in lung volumes, per se. 

There is Level 4 evidence (Hopman et al. 2002; Zbogar et al. 2008) that 6-12 weeks, 3 sessions per week of FES training can lead to positive cardiovascular adaptations, including favourable alterations to arterial structure and function.

There is Level 4 evidence (Brurok et al. 2011; Gibbons et al. 2016; Gurney et al. 1998; Jeon et al. 2010; Krauss et al. 1993; Mutton et al. 1997; Qiu et al. 2016; Solinsky et al. 2020; Taylor et al. 2014; Wheeler et al. 2002) that 6-36 weeks FES-hybrid training (FES-LES+ACE and FES-rowing), results in improved aerobic capacity (ie. peak oxygen uptake) and exercise performance.

There is Level 4 evidence (Brurok et al. 2011; Mutton et al. 1997; Pollack et al. 1989; Qiu et al. 2016; Taylor et al. 2014) that 8-36 weeks of FES-hybrid training can improve peak ventilation during exercise.

There is Level 4 evidence (Brurok et al. 2011; Gibbons et al. 2016) that FES-hybrid training (FES-LES+ACE and FES-rowing) can promote positive cardiovascular adaptations, including increased heart size and improved pumping and filling function. This training may also increase peak exercising HR.

There is Level 4 evidence (Stoner et al. 2007)that 18 weeks of NMES training, 2 times per week, may promote cardiovascular adaptations, including positive alterations to arterial structure and function.

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