Table 1.

General information from the tDCS studies included in the meta-analysis

Author	Country	Sample size N (M/F)	Jadad	Clinical Condition	Groups (Age±SD)	Pain duration (months±SD)	Protocol	tDCS Duration	Anode/Cathode	Intensity	Sham tDCS	Exercise	Safety	Pain outcome
Chang. et al (2017)	Australia	30 (10/20)	4	Knee osteoarthritis	(1) a-tDCS before Exercise(59.8 ± 9.1); (2) s-tDCS before Exercise() 64.1 ± 11.1)	(1) 7.2± 5.3 (2) 9 ± 7.3	8 weeks: tDCS and exercise twice weekly (16 sessions) and completing home exercises twice per week	20 min	M1 contralateral /SO ipsilateral	1mA	Electrodes over the same position and stimulation was turned on for the first 15 seconds and then turned off.	30 min of 5 standardized quadriceps strengthening exercises with ankle cuff weights or resistance bands (3 sets of 10 repetitions with a 30 s break between sets for each exercise) provided by a physiotherapist.	(1) Active tDCS and exercise group: 1 subject with pain and swelling (gout), 1 single episode of headache. (2) Sham tDCS and exercise group: 1 subject with painful sensation under tDCS during the ramped up	VAS (0–100 mm) on walking over the past week
Mendonca et al (2016)	Brazil	45 (1/44)	4	Fibromyalgia	(1) a-tDCS + Aerobic Exercise simultaneously(44.5±14); (2) a-tDCS+Sham Exercise simultaneously(49.9±10.6); (3) sham-tDCS + Aerobic Exercise simultaneously(48±11.8)	(1) 140.6±72.2 (2) 149.3±111.1 (3) 125.6±100.2	4 weeks: first week: tDCS 5 times/week and Aerobic exercise 3 times/week. The next 3 weeks: Aerobic Exercise 3 times/week	20 min	left M1/right SO	2mA	Electrodes over the same position and stimulation only on the initial 30s, then the power was turned off	30 min of aerobic exercise on a treadmill (intensity of 60% - 70% of the maximum HR). Sham Exercise: the HR was maintained within 5% of the resting Heart Rate.	All were mild and did not differ between groups. Related to Aerobic Exercise: mild muscle pain; related to tDCS: headache, neck pain, tingling, skin redness, somnolence, concentration issues.	VNS (0–10 cm) at the moment
Oliveira, L. B. (2015)	Brazil	32 (3/29)	5	Chronic temporomandibular pain -myofascial pain	(1) a-tDCS before Exercise (23.8 ± 7.3); (2) s-tDCS after Exercise(25.5 ± 6.3)	(1) 29.8 ± 17.1 (2) 33.7 ± 22.8	4 week: First week: exercise and tDCS for 5 days. Then, 3 weeks: exercise 2 days per week until completed 10 sessions	20 min	M1 contralateral/ SO ipsilateral	2mA	Electrodes over the same position and stimulation only on the initial 30s, then the power was turned off	15 min of 6 repetitions of each exercise, progressing from lying down to the sitting position. The exercises involved cervical traction and self-stretching of the posterior muscles of the head and neck maintained for 20 s.	One subject suffered burns on the fifth day of stimulus application, due to acne in the supraorbital region. At the end of the exercise sessions, the skin was completely healed with a small scar measuring 2x2 mm	VAS (0–10 cm) at rest
Sakrajai P. et al (2014)	Thailand	31 (22/9)	4	Myofascial Pain Syndrome	(1) a- tDCS + Exercise(49.94 ±8.25); (2) s-tDCS + Exercise(45.93±10.24)	(1) 5.91±2.55 (2) 5.69±1.69	5 consecutive days of tDCS and standard treatment	20 min	M1 contralateral /SO ipsilateral	1 mA	Electrodes over the same position and stimulation only on the initial 30s, then the power was turned off while the power indicator remained on and the control switch was covered by an opaque adhesive	Daily stretching of the group of muscles throughout the available range of motion. Treatment also included ultrasound therapy for 5–10 min followed by the application of hot packs over the affected part 20 min 3 times/week for 2 weeks.	Active tDCS: 2 patients developed a transient erythematous rash with no pruritus or pain under the reference electrode, which resolved within 1 hour.	NRS (0–10 cm) average on the last 24 hours and immediately after the treatment
Riberto et al (2011)	Brazil	23 (0/23)	4	Fibromyalgia	(1)a-tDCS before the Rehabilitation program (58.3 ±12.1); (2) s-tDCS before the Rehabilitation program (52.4 ±11.5)	(1) 9.9 ±11.8 (2) 6.4 ±10.2	4 months: 10 sessions of tDCS (1 each week) and exercise 3 times a week	20 min	M1 contralateral /SO ipsilateral	2mA	Electrodes over the same position and stimulation only on the initial 30s, then the power was turned off	Rehabilitation program for 2 hours: 1 hour [educative interventions or cognitive behavior group therapy focused in pain. Subjects are oriented on posture and ergonomics by physical and occupational therapists and behavioral modulation by psychologists and social workers] and 1 hour [cardiovascular and strengthening training or stretching exercises]	none adverse events reported	(1) SF-36 pain subscale on the last 4 weeks. (2) VAS (0–100 mm) at the moment on each extremity (values not reported).
Straudi et al (2018)	Italy	35 (9/26)	5	Low back pain	(1) a-tDCS before Exercise(54.3±12.4); (2) s-tDCS before Exercise(56±12.9)	(1)9.4±9.2; (2) 7.8±5.3	4 weeks: first week: 5 daily sessions of tDCS and 2 or 3 times per week sessions of exercise. Next 3 weeks: aerobic exercise 2 or 3 times per week (total of 11 exercise sessions)	20 min	M1 contralateral /SO ipsilateral or M1 dominant hemisphere if pain was central / SO contralateral of anode	2 mA	Stimulation only on the initial 30s, then the power was turned off	Group exercise (10 participants) of 1 hour including education(neurophysiology of pain and ergonomic advices), strengthening exercise (low moderate intensity of submaximal contractions on abdominal and back exercises), stretching exercise (elongation position of all structures that support the spine for 15–20 s) and relaxation techniques (correct breathing techniques, reduce stress, muscle tension and anxiety with activities)	29 reported mild side-effects (16 in the active tDCS and 13 in sham tDCS) as skin redness, tingling, headache, sleepiness, trouble to concentrate, dizziness, mood fluctuation.	VAS (0–100 mm, doesn’t specify the time)

tDCS: Transcranial Direct Current Stimulation; SO: Supraorbital; s-tDCS: sham-tDCS; a-tDCS: active tDCS; VAS: visual analog scale; SF-36: 36-Item Short Form Survey; NRS: Numerical Rating Scale.