Table 3. Overview of included studies: Optimization of exercise training.
| Study | D&B Quality Rating | Population Age, TSI: years (Mean± SD) | Methods | Duration | Functional implications |
|---|---|---|---|---|---|
| Shields and Dudley-Javoroski, 2006 [22] | 48% | Participants: 7(C5-T10) SCI, Age: 29.14±8.40, Muscle(s): Flexor muscles, TSI: Within 6 wks. | Contraction: Isometric. Objective: To determine the long-time effect of FES long time training effect on PT, fatigue index, TTi and contractile speed. Study design: Within subject control design. Supramaximal stimulation of 10-pulse train (15 Hz; duration: 667 ms) every 2 s was used. Participants completed 4 bouts of exercise during each session (A bout of exercise consisted of 125 trains). Implication on the distal tibia trabecular BMD was observed. Stimulation pattern: PW: 667 ms, Frequency: 15 Hz, Amplitude: 0–200 mA | 2 to 3 years. Laboratory based test and 2 to 4 times monthly,4 stimulation bouts per day on 5 days each week with 5 min of rest between each bout. | At 2 years, the untrained limbs showed a decrease (P = 0.05) in peak torque while the trained limb generated higher torque, ability to sustain work (TTi) and fatigue resistance. The BMD was, on average, 40 mg/cm3 higher in the trained limb than in the untrained limb (P = 0.05). |
| Shields et al., 2006 [54] | 61% | Participants: 15 (5 chronic and 10 acute (C5-T10) SCI, Age:38±13.1,Muscle(s): Soleus, TSI:8.79±1.85 years for Chronic SCI and within 6 weeks for Acute SCI | Contraction: Isometric. Objective: To quantify post-fatigue potentiation in the acutely and chronically paralyzed soleus and determine the effect of long-term electrical stimulation training on the potentiation characteristics of recently paralyzed muscle. Study design: While the participants remained in their wheelchairs, the ankle was stabilized in a system designed to measure the isometric plantar flexion torque of one leg. A stimulator was programmed to deliver a 10-pulse train (15 Hz; train duration 667 ms) every 2 s. The training protocol specified that 10,000 electrically stimulated contractions be completed each month (4 bouts of 125 contractions per day x 5 days x 4 week = 10,000 contractions). A bout of exercise consisted of 125 trains. Compliance was calculated as the percentage of the recommended number of contractions a participant completed in each month. Stimulation: PW: 667 ms, Frequency: 15 Hz, Amplitude: 0–200 mA | Participants in the training group attended laboratory-based stimulation sessions 1 to 4 times monthly identical with the home based training. Each participant completed 4 bout of exercise during each session with a 5 min rest between each bout. The protocol took 35 min to complete. | After 2 years of training, the bout 4 fatigue indices for the trained and untrained limbs were (82±1.08 and 62±4.3) % respectively (P = 0.05).Minimization of fatigue and post-fatigue potentiation during high-intensity FES activity for long duration (~35 min) was indicated. |
| Butler et al., 2004 [56] | 52% | Participants: 8(C4-C6) SCI Age: 33±3Muscle(s): Thenar, TSI:9.9±7.6 | Contraction: Isometric. Objective: To compare the fatigability of the paralyzed human thenar muscles with and without a simultaneous voluntary contractions of the contralateral elbow flexor muscles. Study design: Each participant performed two experiments in random order, separated by at least one day. In both experiments, the fatigability of the thenar muscles was assessed. Experiment 1: involved an increase of thenar muscle perfusion pressure by increasing the systemic blood pressure when thenar muscle was fatigued. Experiment 2: involved no intervention during thenar muscle fatigue. Stimulation: PW: 667 ms, Frequency: 15 Hz, Amplitude: 0–200 mA | During pre-fatigue and fatigue protocol, a bag of weight (2.5-14Kg) were suspended (with the wrist while the elbow was flexed at ~ 90 deg.) while electrical stimuli were delivered and blood pressure was being monitored. The weight used was equivalent to 50% of the maximal one-repeat value. | Changes in mean arterial pressure (MAP) with exercise (median nerve stimulation with and without voluntary contractions) moderately correlated with changes in thenar muscle fatigue (r2 = 0.61; n = 7). For every 10% increase in MAP, fatigue was reduced by ~ 3%. |
| Gerrits et al., 2000 [44] | 43% | Participants: 8 (C5-T8) SCI Age: 40.4±11Muscle(s): Hamstring, Gluteal, and Quadriceps. TSI: 9.9±10 | Contraction: Non-isometric. Objective: To assess if contractile speed and fatigability of paralyzed quadriceps muscles in persons with SCI can be altered by FES-LCE training. Study design: Contractile speed and fatigue characteristics of electrically stimulated isometric contractions were compared before and after 6 weeks of FES-LCE. When the pedalling rate dropped below 45 rpm, the resistance is reduced and when the pedalling rate dropped below 35 rpm, the stimulation was stopped. Stimulation pattern: PW: 450 μs, Frequency: 30 Hz, Amplitude: 140 mA to achieve target pedalling rate of 50rpm. | Participants trained for 30min, three times per week for 6 weeks. | Work output was significantly increased (4±5 kJ to 14±13 kJ; P = 0.019). At the end of 2min of stimulation, force declined to 32+10% of the pre-fatigue value and to 42+10% after training. |
| Gerrits et al., 2002 [55] | 43% | Participants: 6 (C5-T12) SCI and 14 AB, Age: SCI: 41.8± 9.8AB: 27± 2Muscle(s): Quadriceps TSI: 14.9± 8.1 | Contraction: Isometric. Objective: To compare the effects of training with two patterns of FES (repetitive high-frequency stimulation (HFS) and more continuous low-frequency stimulation (LFS)) on the strength, contractile properties, and fatigability of paralyzed muscle. Study design: Both left and right quadriceps muscles of each participant were stimulated, one limb with the LFS protocol while the other was with the HFS protocol. LFS protocol, consisted of 35 min of repeated quadriceps activation with 10 Hz stimulation trains of 20 s duration, followed by a 50 s rest (duty cycle 28%). HFS protocol, consisted of 50 min of repeated stimulation, with 50 Hz trains of 2 s duration and followed by a 50 s rest (duty cycle 4%). Fatigability was assessed by activating the quadriceps muscle repetitively for 2 min at 30 Hz stimulation of 1 s duration every 2 s. Stimulation pattern: PW: 250 μs, Frequency: HFS- 50 Hz, LFS- 10 Hz, Amplitude: 130 ± 6 mA. | A daily bilateral isometric quadriceps contractions of legs for a period of 12 weeks. | Fatigue resistance increased significantly (P<0.05) from 2 weeks of LFS training (by 43%) but not (P>0.05) after HFS training even at 12th week of training. |
| Fornusek and Davis, 2004 [58] | 48% | Participants: 9 (T4-T9) SCI Age: 37.8±10.4Muscle(s): Hamstring, Gluteal, and Quadriceps. TSI: 3.12±0.91 | Contraction: Non-isometric. Objective: To investigate the effect of pedal cadence upon torque production, PO and muscle fatigue rates during FES-evoked cycling. Study design: Trial 1: (n = 8) examined a low vs high pedal rate (20 and 50 rpm) upon isolated muscle fatigue over 5 min. Trial 2: (n = 9) investigated the effect of cadence (15 vs 50 rpm) upon performance during 35 min of FES-evoked cycling. Torque and PO were calculated by iFES-LCE while the quadriceps (300–30deg), hamstrings (60–160deg) and gluteal (6–73deg) muscle groups of both legs were stimulated to produce FES cycling. Stimulation pattern: PW: 250 μs, Frequency: 35 Hz, Amplitude: Trial 1–80 mA, Trial 2- (70–140 mA) | Each cadence was randomised and tested on a different day (Trial 1: 5 min, Trial 2: 35 min) with a maximum of 7 days between tests. | PT from the left quadriceps decayed significantly (P<0.05) faster at the higher pedal cadence. Cycling for over 35min showed that peak and average torques were significantly greater at the lower cadence. From 15min onwards, PO was significantly higher at 50rpm FES-cycling, compared with 15rpm (16.61± 1.14 kJ vs 13.21±1.16 kJ, P< 0.05). |
| Hartkopp et al., 2003 [57] | 57% | Participants: 12 (C5-C6) SCI Age: 7(29–55) for high resistance (Hr) group 5(4–27) for low resistance (Lr) group, Muscle(s): Wrist extensor, TSI: Hr: 5-38Lr: 4–27 | Contraction: Isometric. Objective: To investigate the fatigue resistance capability of two different training protocols. Study design: The Hr group received 30 Hz stimulation with a duty circle of 5 s ‘on’ and 20 s ‘off’ against maximum load. The Lr group received 15 Hz stimulation with a duty circle increasing every third week. Total work output was similar in both protocols. The untrained arm was used as control. Stimulation pattern: PW: 250 μs, Frequency: 30 Hz, Amplitude: 140 mA to achieve target pedalling rate of 50 rpm. | The wrist extensor muscles were stimulated for 30 min/day, 5 days/week, for 12 weeks, using either a Hr or a Lr protocol. | PT at 15 Hz in the Hr group tended to improve by 19% (P<0.1), while Lr group did not improve. Fatigue resistance improved by 42% and 41% (P<0.05) in response to conditioning in the Hr group and Lr group, respectively. |
| Peckham et al.,1976 [53] | 45% | Participants: 12 (C3-C7) SCI Age: 23.17±9.9Muscle(s): Finger flexor, TSI: 1.98±5.05 | Contraction: Isometric. Objective: To investigate whether the strength and endurance of electrically induced contractions in persons with SCI could be increased following FES exercise. Study design: The intramuscular nerves stimulation was modified to activate a relatively constant muscle fibre activation. The stimulation was surged on for a period of 2.5 s and off for the same duration. Exercise effectiveness was assessed by the contractile properties; the maximum tetanic force, the fatigue, and sometimes twitch characteristics. Stimulation: PW: 100 μs, Frequency: 10 Hz for 10 participants and 15 Hz for 2 participants. Amplitude: 20 mA maximum. | Stimulus evoked chronic exercise duration was up to 4 to 6 hours per day for 15±7 weeks in the hospital and at home. | A good trend (r = 0.808) for force development was reported. The correlation of exercise with fatigue changes was good (r = 0.827).The increase of force fatigue resistance was evident with maximum force after 25 weeks. |
| Sabatier et al., 2006 [60] | 52% | Participants: 5(C5-C10) SCI Age: 36±5, Muscle(s): quadriceps, TSI: > 5 | Contraction: Isometric. Objective: To determine whether FES resistance training would (i) reduce muscle fatigability, (ii) reverse reduced arterial diameter, (iii) increase resting blood flow, and (iv) increase reactive and exercise hyperemia. Study design: Stimulus parameters were set to administer an equivalent of work to rest cycle of 5s on and 5s off. For the first 2 weeks, only the weight of the leg was used for the resistant traning while for another 16 weeks the load resistance increased by 0.9–1.8 kg/week. Muscle fatigue was calculated as a percent decline in torque production from the first 5 contractions to the last 5 contractions. Stimulation pattern: PW: 450 μs biphasic pulse and 50 μs phase delay, Frequency: 30 Hz, Amplitude: Current that was sufficient to elicited 30 Nm of torque | FES resistance training of knee extensions was performed twice a week for 18 weeks and measurements were made before training and after 8, 12, and 18 weeks of training. | A significant increase in weight lifted, as well as a 60% reduction in muscle fatigue (P = 0.001) was reported. The femoral arterial diameter range (P = 0.70), resting, reactive hyperemic, and exercise blood flow remained constant with training. |
| Gorgey et al., 2015 [59] | 45% | Participants: 1T6 SCI, Age: 33, Muscle(s): Quadriceps, TSI: NM | Contraction: Non-isometric. Objective: To determine the effect of FES resistant training (RT) conducted once weekly on improving fatigue resistance regional and whole body composition. Study design: Quadriceps fatigue index was obtained from the number of repetitions (reps) achieved out of 30 reps. Total and regional body composition tests were conducted before the first session and one week after the last training session using whole-body dual-energy x-ray absorptiometry. Stimulation pattern: PW: 450 μs, Frequency: 30 Hz Amplitude: Range of 0- 200mA for each training set. | FES RT of the paralyzed quadriceps was conducted once weekly for 12 weeks using ankle weights. | The fatigue resistance of the right knee extensors increased from 56% at week 8 to 100% at week 11; while the left leg only achieved 80% in week 12.Once weekly of FES RT led to increased lean mass, strength, and fatigue resistance of trained knee extensors. |
Abbreviations: SCI- Persons with spinal cord injury; PW- Pulse width; BMD: Bone mineral density; TSI: Time since injury; PT-Peak torque; TTi: Torque-time integral; iFES-LCE: Isokinetic functional electrical stimulation-Leg cycle ergometer, PO: Power output.