Table 2.
Study protocols for muscular strength exercises.
| References | Intervention protocol (a-tDCS) | Control | Strength exercise characteristic | Main outcomes | |||||
|---|---|---|---|---|---|---|---|---|---|
| Montage of electrodes | Electrode size (cm2) | Current intensity (mA) | Duration (min) | Muscle investigated | Type of contraction | Muscle strength test | |||
| Lattari et al., 2016 | Left DLPFC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Elbow flexors | Dynamic | Volume-load (kg) | a-tDCS > sham (p < 0.05) |
| Lattari et al., 2017 | Central MC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Ankle, hip, and knee extensors | Dynamic | Muscle power (W) | ≠ between the conditions |
| Lattari et al., 2018b | Left DLPFC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Ankle, hip, and knee extensors | Dynamic | Volume-load (kg) | a-tDCS > sham (p < 0.05) |
| Hazime et al., 2017 | MC dominant limb (stimulus) and ipsilateral OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Internal and external rotator | Isometric | MIVC (N/kg) | MIVC (internal and external rotator): a-tDCS > sham (p < 0.05) |
| Vargas et al., 2018 | Left and right MC (stimulus) and ipsilateral OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Knee extensors | Isometric | MIVC (N/kg) in dominant and non-dominant limb | Dominant a-tDCS > sham (p < 0.05) Non-dominant ≠ between the conditions |
| Sales et al., 2016 | Left TC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Knee extensors | Dynamic | Isokinetic testing (angular velocity of 180°·s−1 and 60°·s−1):Total work (J) and peak torque (N.m) | Total work: a-tDCS > sham (p < 0.05) Peak torque: ≠ between the conditions |
| Cogiamanian et al., 2007 | Right MC (stimulus) and right shoulder (reference) | 35 (stimulus and reference) | 1.5 | 10 | No intervention | Left elbow flexors | Isometric | MIVC (N) and TTE with 35% of the MIVC (s) | MIVC: ≠ between the conditions TTE: a-tDCS > control (p < 0.05) |
| Frazer et al., 2017 | Left MC (stimulus) and right OFC (reference) | 25 | 2 | 20 | 30 (s) (sham) | Left biceps brachii | Dynamic | 1RM | ↑ Strength of the untrained limb |
| Hendy and Kidgell, 2014 | Left MC (stimulus) and Left OFC (reference) | 25 | 2 | 20 | 30 (s) (sham) | Wrist extensor muscles | Dynamic | 1RM | ↑ Strength of untrained wrist extensor muscles |
| Williams et al., 2013 | Right MC (stimulus) and left OFC | 35 | 1.5 | 20 | 30 (s) (sham) | Left elbow flexors | Isometric | MVC and TTF at 20% MVC | TTE: ↑ Endurance time |
| Angius et al., 2016 | Two montages of the electrodes: First: Left MC (stimulus) and right OFC (reference); Second: Left MC (stimulus) and left shoulder (reference) | 12 (stimulus and reference) | 2 | 10 | 30 (s) (sham) | Right knee extensors | Isometric | MIVC (N.m) TTE with 20% of the MIVC (s) | MIVC: NR TTE: Second position-a-tDCS > sham (p < 0.05); First position ≠ between the conditions |
| Kan et al., 2013 | Right MC (stimulus) and right shoulder (reference) | 24 (stimulus and reference) | 2 | 10 | 30 (s) (sham) | Left elbow flexors | Isometric | MIVC (N.m) and TTE with 30% of the MIVC (s) | MIVC: ≠ between the conditions TTE: ≠ between the conditions |
| Abdelmoula et al., 2016 | Left MC (stimulus) and right shoulder (reference) | 35 | 1.5 | 10 | 90 (s) (sham) | Left elbow flexors | Isometric | MIVC (N) and TTE at 35% MVC | TTE: ↑ Endurance time |
| Tanaka et al., 2009 | Right MC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 10 | 30 (s) (sham) | Adduction between the left great toe and the digitus secundus (leg pinch force) adduction Between the Index finger and the Thumb pad of the Left hand (hand pinch force) | Isometric | PF (N) | PF (Leg): a-tDCS > sham (p < 0.01) |
| Montenegro et al., 2015 | Left MC (stimulus) and right OFC (reference) | 35 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Knee extensors and flexors | Dynamic | Isokinetic testing (angularvelocity of 60°·s−1:Total work (J) and peak torque (N.m) | Total work: ≠ between the conditions Peak torque: ≠ between the conditions |
| Flood et al., 2017 | Positioning of the electrodes (4 × 1) MC contralateral to the non-dominant side (stimulus, C3 or C4) and four cathodal electrodes placed at a distance of 5 cm around the anode (reference); radius ≈ 1.1 cm | − | 2 | 20 | At the start and at the end (2 mA in ramping) | Elbow flexors | Isometric | MIVC (N.m) and TTE at 30% MVC | No improvement |
| Ciccone et al., 2018 | Two montages of electrodes: First- Left TC (stimulus) and right OFC (reference); Second- Right TC (stimulus) and left OFC (reference) | 25 (stimulus and reference) | 2 | 20 | 30 (s) (sham) | Knee extensors | Dynamic | Isokinetic testing (angular velocity of 180°·s−1): Average work (Nm.s) | ≠ between the conditions |
| Radel et al., 2017 | Two montages of electrodes (4x1): First: Right MC (stimulus) and four cathodal electrodes placed at a distance of 4 cm around the anode (reference); Second: Right DLPFC (stimulus) and four cathodal electrodes placed at a distance of 4 cm around the anode (reference); radius ≈1.1 cm | - | 2 | ≤ 20 | 30 (s) (sham) | Elbow flexors | Isometric | TTE at 35% MVC | No improvement |
↑ (increased); maximal dynamic strength (1RM); maximal voluntary contraction (MVC); peak power output (PPO); a-tDCS- anodal transcranial direct current stimulation; CG, control group; cm2, square centimeter; mA, milliamps; min, minutes; s, seconds; MC, motor cortex; DLPFC, dorsolateral prefrontal cortex; OBF, orbitofrontal cortex; ≈, approximately; MIVC, Maximal Isometric Voluntary Contraction; PF, Pinch Force; N, Newtons; N.m, Newtons per meter; N/kg, Newtons per kilogram (normalized by the body mass of each participant); Kg, Kilogram; J, Joules; %, percentage; Nm.s, Newtons meter per second; TTF, Time to failure; TTE, time to exhaustion; NR, not reported.