TABLE 2.

Search strategy: number of hits on keywords and combined keywords in PubMed, Web of Science, and Cochrane Library.

Keywords	PubMed	Web of science	Cochrane library
	No. of hits (20/08/2020)	No. of hits (20/08/2020)	No. of hits (20/08/2020)
(1) Near infrared spectroscopy OR NIRS OR magnetic resonance imaging OR MRI or near infrared spectroscopy [MeSH] OR magnetic resonance imaging [MeSH]	608,218	487,775	33,168
(2) Physical performance OR exercise performance OR endurance performance OR time trial OR time to exhaustion OR physical endurance OR athletic performance OR physical endurance [MeSH] OR athletic performance [MeSH] OR motor activity [MeSH]	336,117	137,120	31,398
(3) Oxygenation OR BOLD response OR hemodynamic response OR cerebrovascular circulation OR cerebrovascular circulation [MeSH]	124,655	77,973	51,012
(4) prefrontal cortex OR frontal lobe OR frontal lobe [MeSH]	107,239	118,480	7524
Combined key words
(1) AND (2)	6566	549	1664
(1) AND (2) AND (3)	4650	389	352
(1) AND (2) AND (3) AND (4)*	921	202	335
(1) AND (2) AND (4)	1408	48	350

Combined keywords with a “*” were included in the study.