Table 1.

Results of subgroup analysis.

Subgroup	Heterogeneity Test I²(﹪) P-Value		Group	RR (95%CI)	The Number of Study	Sample Size
Exercise methods	37%	0.19	Additional hamstring eccentric training	0.71 (0.59–0.87)	4	4376
	88%	<0.001	FIFA 11+	0.66 (0.48–0.90)	8	6835
	0%	0.82	FIFA11	0.94 (0.85–1.05)	2	2548
	-	-	FIFA11+Kids	0.52 (0.33–0.83)	1	962
Exercise frequency per week	0%	0.38	Once per week	1.00 (0.84–1.18)	2	2357
	0%	0.52	Twice per week	0.60 (0.49–0.72)	5	3329
	89%	<0.01	More than twice a week	0.69 (0.53–0.90)	6	5303
Exercise period	67%	0.03	10–20weeks	0.68 (0.54–0.87)	4	2243
	86%	<0.01	21–30weeks	0.62 (0.38–1.01)	4	3334
	79%	<0.01	More than 31weeks	0.77 (0.60–1.00)	7	9144
Competition level	84%	<0.01	Youth	0.75 (0.56–0.99)	7	9688
	80%	<0.02	Elite	0.73 (0.57–0.93)	6	4762
	0%	0.41	Amateur	0.54 (0.38–0.75)	2	271

“-“ Indicates no data.