A School-Based Exercise Intervention Program Increases Muscle Strength in Prepubertal Boys

Table 1

Baseline data, annual unadjusted absolute changes, and adjusted difference in anthropometry, body composition, muscle strength, and vertical jump height in the intervention and control group.

	Baseline			Annual Changes
	Intervention (𝑛=68)	Controls (𝑛=46)	𝑃-value	Intervention (𝑛=68)	Controls (𝑛=46)	Adjusted difference (95% CI)	𝑃-value
Age (years)	7.8±0.5	7.9±0.6	.23	—	—	—
Anthropometry
Stature (cm)	129.4±6.3	129.5±6.7	.48	5.6 (5.4, 5.9)	5.7 (5.5, 5.9)	−0.07 (−0.41, 0.27)	.70
Body mass (kg)	27.8±4.7	26.8±4.6	.08	3.0 (2.7, 3.3)	3.1 (2.8, 3.4)	−0.06 (−0.49, 0.37)	.79
BMI (kg/m^2)	16.5±1.8	15.9±1.7	.05	0.3 (0.2, 0.5)	0.3 (0.2, 0.5)	−0.03 (−0.24, 0.19)	.81
Total body fat (%)	13.2±6.8	12.6±5.4	.52	2.1 (1.5, 2.7)	1.3 (0.8, 1.7)	0.96 (0.15, 1.76)	.02
Lean body mass (kg)
Total body	21.70±2.74	21.50±2.90	.24	2.28 (2.13, 2.43)	2.13 (2.00, 2.25)	0.15 (−0.06, 0.35)	.17
Legs	6.78±1.15	6.68±1.23	.16	1.00 (0.93, 1.06)	0.96 (0.90, 1.02)	0.03 (−0.06, 0.13)	.46
Arms	1.80±0.35	1.81±0.38	.65	0.30 (0.26, 0.34)	0.19 (0.17, 0.22)	0.11 (0.06, 0.16)	< .001
Fat mass (kg)
Total body	3.56±2.59	3.31±2.01	.44	1.14 (0.88, 1.39)	0.81 (0.59, 1.03)	0.37 (0.01, 0.72)	.04
Legs	1.61±0.96	1.46±0.75	.26	0.43 (0.33, 0.53)	0.36 (0.27, 0.45)	0.08 (−0.06, 0.23)	.26
Arms	0.30±0.31	0.34±0.31	.61	0.14 (0.09, 0.18)	0.02 (−0.02, 0.04)	0.12 (0.07, 0.18)	< .001
Peak Torque—unadjusted (Nm)
PTEx60	43.0±9.9	43.4±10.7	.56	10.2 (8.3, 12.1)	9.8 (8.3, 11.2)	0.74 (−1.79, 3.27)	.56
PTFl60	21.4±6.4	24.4±6.7	.04	8.6 (7.4, 9.9)	7.0 (6.0, 8.1)	1.66 (−0.15, 3.48)	.07
PTEx180	35.1±7.7	35.4±7.7	.47	8.7 (7.5, 9.9)	7.0 (6.2, 7.9)	1.77 (0.20, 3.35)	.03
PTFl180	19.0±4.9	22.6±5.2	< .001	9.7 (8.3, 11.1)	5.0 (4.3, 5.8)	4.87 (2.94, 6.80)	< .001
Peak Torque—body mass-adjusted (Nm/kg)
PTEx60	1.54±0.22	1.61±0.27	.26	0.17 (0.11, 0.23)	0.14 (0.10, 0.18)	0.04 (−0.04, 0.12)	.37
PTFl60	0.77±0.18	0.91±0.20	<.001	0.21 (0.17, 0.25)	0.13 (0.09, 0.16)	0.04 (−0.01, 0.10)	.14
PTEx180	1.26±0.17	1.32±0.19	.25	0.16 (0.12, 0.19)	0.09 (0.07, 0.11)	0.07 (0.02, 0.12)	.003
PTFl180	0.69±0.15	0.84±0.11	<.001	0.25 (0.20, 0.29)	0.07 (0.05, 0.10)	0.14 (0.08, 0.21)	<.001
Physical performance
Vertical jump height (cm)	24.2±4.7	24.8±4.3	.90	2.1 (1.0, 3.2)	1.3 (0.7, 1.9)	0.56 (−0.86, 1.97)	.44

The baseline values are presented as unadjusted means±SD and the annual changes as unadjusted means with 95% confidence interval (95% CI). All baseline comparisons are adjusted for age at baseline. The differences between the annual changes in the intervention and the control group are presented adjusted for differences in age at baseline and, if there was a significant group difference at baseline, the baseline values for that specific measurement (accounts for PT_EX60, PT_EX180, PT_Fl60 and PT_Fl180).