Table 4.

Subgroup and single training factor analyses

Subgroup	Studies (n)	Participants (n)	Estimated effect size Mean (95%, CI)	Within group p	Between group p	Within group I2 (%)	Effect descriptor
Sex
Male	14	314	– 0.95 (– 1.36 to – 0.53)	< 0.01	0.31	64	Large
Female	3	59	– 0.60 (– 1.13 to – 0.07)	0.03		0	Moderate
Age groups
Children (≤ 13 years)	3	65	– 1.28 (– 2.02 to – 0.53)	< 0.01	0.13	45	Large
Adolescents (> 13 to ≤ 18 years)	3	73	– 1.21 (– 1.71 to – 0.71)	< 0.01		0	Large
Young adults (19–28 years)	13	282	– 0.63 (– 1.04 to – 0.22)	< 0.01		61	Moderate
Training experience
Elite	4	88	– 0.69 (– 1.21 to – 0.17)	< 0.01	0.61	28	Moderate
Recreational/active/regional level	15	336	– 0.86 (– 1.26 to – 0.47)	< 0.01		64	Large
Training frequency
2 sessions/week	10	229	– 1.07 (– 1.52 to – 0.62)	< 0.01	0.09	58	Large
3 session/week	9	195	– 0.54 (– 0.97 to – 0.12)	≤ 0.01		50	Moderate
Training duration
≤8 weeks	13	301	– 0.81 (– 1.23 to – 0.38)	< 0.01	0.91	66	Large
>8 weeks	6	123	– 0.85 (– 1.34 to – 0.35)	< 0.01		41	Large
Training type
Machine-based training	7	141	– 0.80 (– 1.31 to – 0.29)	< 0.01	0.87	50	Large
Free weights	7	179	– 0.99 (– 1.57 to 0.40)	< 0.01		69	Large
Combined machine-based and free weights training	4	78	– 0.77 (– 1.51 to – 0.03)	< 0.05		58	Moderate
Session duration
≤ 30 min	3	83	– 1.00 (– 1.72 to – 0.28)	< 0.01	0.99	57	Large
≥ 45 min	10	226	– 1.03 (– 1.53 to – 0.47)	< 0.01		69	Large
Total number of training sessions
≤ 16	9	215	– 0.83 (– 1.32 to – 0.33)	< 0.01	0.97	64	Large
> 16	10	209	– 0.81 (– 1.27 to – 0.36)	< 0.01		58	Large
Training intensity
≥ 30 to < 69% 1RM	5	110	– 0.76 (– 1.51 to – 0.01)	< 0.01	0.87	70	Moderate
≥ 70% 1RM	9	192	– 0.77 (– 1.24 to – 0.29)	< 0.01		57	Moderate

CI confidence interval, n number, RM repetition maximum