A 3-Year School-Based Exercise Intervention Improves Muscle Strength

A Prospective Controlled Population-Based Study in 223 Children

Fredrik Detter; Jan-Åke Nilsson; Caroline Karlsson; Magnus Dencker; Björn E Rosengren; Magnus K Karlsson

BMC Musculoskelet Disord. 2014;15(353)

Abstract and Introduction

Abstract

Background Intense physical activity (PA) improves muscle strength in children, but it remains uncertain whether moderately intense PA in a population-based cohort of children confers these benefits.

Methods We included children aged 6–9 years in four schools where the intervention school increased the school curriculum of PA from 60 minutes/week to 40 minutes/school day while the control schools continued with 60 minutes/week for three years. We measured muscle strength, as isokinetic Peak Torque (PT) (Nm) of the knee flexors in the right leg at speeds of 60°/second and 180°/second, at baseline and at follow-up, in 47 girls and 76 boys in the intervention group and 46 girls and 54 boys in the control group and then calculated annual changes in muscle strength. Data are provided as means with 95% confidence intervals.

Results Girls in the intervention group had 1.0 Nm (0.13, 1.9) and boys 1.9 Nm (0.9, 2.9) greater annual gain in knee flexor PT at 60°/second, than girls and boys in the control group. Boys in the intervention group also had 1.5 Nm (0.5, 2.5) greater annual gain in knee flexors PT at 180°/second than boys in the control group.

Conclusion A 3-year moderately intense PA intervention program within the school curriculum enhances muscle strength in both girls and boys.

1 2 3 4 5 6

Next Section

Abstract and Introduction
Background
Methods
Results
Discussion
Conclusion
References

Table 1. Lifestyle factors
	Girls			Boys
	Cases (n = 47)	Controls (n = 46)	P- value	Cases (n = 76)	Controls (n = 54)	P- value
Baseline
Age	7.7 (0.6)	7.9 (0.6)	0.07	7.8 (0.6)	7.9 (0.6)	0.23
Lifestyle factors
Excluding dairy products	0	3 (7%)	0.11	1 (1%)	7 (13%)	<0.01
Drinking coffee	3 (6%)	1 (2%)	0.62	3 (4%)	0	0.27
Smoking	0	0	NA	0	0	NA
Alcohol	0	0	NA	0	0	NA
Tried to lose weight	1 (2%)	0	1.0	0	0	NA
Current disease	3 (6%)	3 (7%)	1.0	7 (9%)	3 (6%)	0.52
Ongoing medication	5 (11%)	2 (4%)	0.43	10 (13%)	4 (7%)	0.39
Previous medication	4 (9%)	2 (4%)	0.68	3 (4%)	5 (9%)	0.28
Previous Fracture	5 (11%)	6 (13%)	0.72	6 (8%)	6 (11%)	0.53
Tanner stage 1/2/3/4/5	47/0/0/0/0	46/0/0/0/0	NA	76/0/0/0/0	48/0/0/0/0	NA
Follow-up (after 3 years)
Age	10.7 (0.6)	11.1 (0.7)	0.003	10.8 (0.6)	11.1 (0.6)	0.01
Lifestyle factors
Smoking	0	0	NA	0	0	NA
Alcohol	0	0	NA	0	0	NA
Tanner stage 1/2/3/4/5 (%)	17/18/9/2/0	10/20/14/2/0	0.12	65/9/2/0/0	11/26/14/1/0	<0.001
Menarche	3 (6%)	1 (2%)	0.62	——	——	——

Baseline and follow-up data in the subsample of girls and boys who were measured, presented as numbers and proportion (%) or as means with standard deviations (SD). Statistically significant differences are bolded.

Table 2. Physical activity
	Girls			Boys
	Cases (n = 47)	Controls (n = 46)	P- value	Cases (n = 76)	Controls (n = 54)	P- value
Baseline
Organized physical activity before study start (hours/week)
Total physical activity	1.7 (0.7)	2.4 (1.7)	0.02	2.7 (1.6)	2.3 (1.3)	0.18
Organized physical activity after study start (hours/week)
School curriculum	3.3	1.0	<0.001	3.3	1.0	<0.001
Outside School	0.7 (0.7)	1.4 (1.7)	0.02	1.7 (1.6)	1.3 (1.3)	0.18
Total physical activity	4.0 (0.7)	2.4 (1.7)	<0.001	5.0 (1.6)	2.3 (1.3)	<0.001
Follow-up (after 3 years)
Organized physical activity (hours/week)
School curriculum	3.3	1.0	<0.001	3.3	1.0	<0.001
Outside School	2.3 (2.0)	2.8 (2.5)	0.38	3.3 (3.3)	2.9 (2.4)	0.50
Total physical activity	5.6 (2.0)	3.8 (2.5)	<0.001	6.6 (3.3)	3.9 (2.4)	<0.001

Baseline and follow-up physical activity data in the subsample of girls and boys who were measured. Questionnaire-evaluated duration of organized physical activity was estimated as mean hours per week. Data are presented as mean with standard deviation (SD). Statistically significant group differences are bolded.

Table 3. Muscle strength
Girls
	Baseline		Between-group differences baseline			Annual changes		Between-group differences annual changes
	Cases (n = 47)	Controls (n = 46)	Adjusted difference (95% CI)	P₁-value	P₂-value	Cases (n = 47)	Controls (n = 46)	Adjusted difference (95% CI)	P₃-value	P₄-value
Anthropometry (kg)
Height (cm)	128.0 (5.2)	129.9 (7.9)	-0.5 (-2.8, 1.9)	0.18	0.70	6.2 (5.9, 6.5)	6.0 (5.7, 6.3)	0.3 (-0.1, 0.03)	0.48	0.09
Weight (kg)	27.6 (5.5)	27.8 (5.6)	-0.2 (-2.1, 2.5)	0.90	0.84	4.1 (3.6, 4.5)	3.5 (3.1, 3.9)	0.4 (-0.01, 0.8)	0.04	0.05
BMI (kg/m²)	16.8 (3.0)	16.3 (1.9)	0.4 (-0.7, 1.4)	0.35	0.48	0.6 (0.4, 0.7)	0.4 (0.2, 0.5)	0.2 (0.01, 0.3)	0.02	0.04
Lean body mass (kg)
Total Body	19.8 (2.3)	20.4 (2.8)	-0.2 (-1.2, 0.8)	0.25	0.66	2.4 (2.2, 2.6)	2.3 (2.1, 2.5)	0.1 (-0.03, 0.3)	0.37	0.12
Legs	6.3 (1.0)	6.4 (1.2)	-0.03 (0.4, 0.5)	0.55	0.87	1.0 (0.9, 1.1)	1.0 (0.9, 1.0)	0.04 (-0.03, 0.1)	0.37	0.24
Arms	1.6 (0.3)	1.7 (0.4)	-0.1 (-0.2, 0.1)	0.10	0.20	0.3 (0.2, 0.3)	0.2 (0.2, 0.2)	0.04 (-0.01, 0.1)	0.10	0.01
Fat mass (kg)
Total Body	4.8 (3.1)	5.0 (3.1)	0.2 (-1.5, 1.1)	0.76	0.76	1.6 (1.3, 1.9)	1.0 (0.7, 1.2)	0.5 (0.2, 0.9)	0.003	0.001
Legs	2.1 (1.1)	2.2 (1.2)	0.1 (-0.6, 0.4)	0.70	0.73	0.6 (0.5, 0.7)	0.4 (0.3, 0.5)	0.2 (0.1, 0.3)	0.02	0.002
Arms	0.5 (0.4)	0.5 (0.4)	-0.04 (-0.2, 0.1)	0.68	0.66	0.1 (0.1, 0.2)	0.1 (0.03, 0.1)	0.1 (0.02, 0.1)	<0.001	0.03
Peak torque (Nm)
PT_Ex60	40.9 (9.7)	44.4 (9.8)	-1.6 (-5.2, 1.9)	0.09	0.36	10.5 (9.3, 11.8)	10.8 (9.7, 12.0)	-0.6 (-2.1, 0.8)	0.75	0.40
PT_Fl60	19.6 (5.1)	24.4 (6.2)	-4.1 (-6.4, -1.9)	<0.001	<0.001	6.3 (5.7, 7.0)	5.2 (4.6, 5.9)	1.0 (0.1, 1.9)	0.02	0.03
PT_Ex180	31.9 (7.9)	36.1 (7.4)	-2.8 (-5.7, 0.1)	0.01	0.06	7.4 (6.6, 8.2)	7.1 (6.4, 7.7)	0.3 (-0.6, 1.2)	0.54	0.57
PT_Fl180	16.9 (5.5)	22.1 (4.6)	-4.5 (-6.5, -2.5)	<0.001	<0.001	4.8 (4.2, 5.4)	4.1 (3.4, 4.7)	0.4 (0.5, 1.4)	0.10	0.35
Relative peak torque (Nm/Kg)
PT_Ex60	1.5 (0.3)	1.7 (0.3)	-0.1 (-0.2, 0.03)	0.03	0.13	0.1 (0.1, 0.2)	0.1 (0.1, 0.2)	-3.4 (-6.9, 0.2)	0.26	0.06
PT_Fl60	0.7 (0.2)	0.9 (0.1)	-0.2 (-0.2, -0.1)	<0.001	<0.001	0.1 (0.1, 0.1)	0.1 (0.04, 0.1)	1.5 (-1.3, 4.3)	0.08	0.30
PT_Ex180	1.2 (0.2)	1.3 (0.2)	-0.1 (-0.2. -0.03)	0.001	<0.01	0.1 (0.1, 0.1)	0.1 (0.1, 0.1)	-1.0 (-3.2, 1.3)	0.91	0.41
PT_Fl180	0.6 (0.2)	0.8 (0.1)	-0.1 (-0.2, -0.1)	<0.001	<0.001	0.1 (0.04, 0.1)	0.03 (0.02, 0.1)	-1.0 (-3.4, 1.5)	0.048	0.44
Boys
	Baseline		Between-group differences baseline			Annual changes		Between-group differences annual changes
	Cases (n = 76)	Controls (n = 54)	Adjusted difference (95% CI)	P₁-value	P₂-value	Cases (n = 76)	Controls (n = 54)	Adjusted difference (95% CI)	P₃-value	P₄-value
Anthropometry (kg)
Height (cm)	129.4 (6.6)	130.0 (6.8)	-0.2 (-1.8, 2.2)	0.62	0.83	5.5 (5.3, 5.6)	5.6 (5.4, 5.8)	0.1 (-0.2, 0.4)	0.32	0.53
Weight (kg)	28.4 (5.8)	27.8 (5.6)	1.2 (-0.6, 3.0)	0.54	0.20	3.5 (3.2, 3.8)	3.6 (3.3, 3.9)	-0.004 (-0.5, 0.4)	0.71	0.88
BMI (kg/m²)	16.8 (2.5)	16.3 (2.1)	0.7 (-0.1, 1.5)	0.21	0.11	0.4 (0.3, 0.5)	0.5 (0.4, 0.6)	-0.1 (-0.3, 0.1)	0.30	0.32
Lean body mass (kg)
Total Body	21.8 (3.1)	21.6 (2.9)	0.5 (-0.4, 1.4)	0.72	0.27	2.2 (2.1, 2.3)	2.3 (2.2, 2.4)	-0.1 (-0.2, 0.1)	0.28	0.60
Legs	6.8 (1.3)	6.8 (1.3)	0.2 (-0.2, 0.6)	0.81	0.27	1.0 (0.9, 1.0)	1.1 (1.0, 1.1)	-0.1 (-0.1, -0.02)	0.05	0.16
Arms	1.8 (0.4)	1.8 (0.4)	0.04 (-0.1, 0.2)	0.90	0.47	0.3 (0.2, 0.3)	0.2 (0.2, 0.2)	0.03 (-0.004, 0.1)	0.16	0.08
Fat mass (kg)
Total Body	3.8 (3.0)	3.7 (2.6)	0.3 (-0.7, 1.3)	0.81	0.56	1.1 (0.9, 1.4)	1.1 (0.8, 1.3)	0.1 (-0.2, 0.4)	0.62	0.57
Legs	1.7 (1.1)	1.6 (0.9)	0.1 (-0.2, 0.5)	0.66	0.40	0.5 (0.4, 0.6)	0.4 (0.4, 0.5)	0.01 (-0.1, 0.1)	0.64	0.90
Arms	0.3 (0.3)	0.4 (0.4)	0.1 (-0.2, 0.1)	0.27	0.41	0.1 (0.1, 0.1))	0.1 (0.03, 0.1)	0.03 (-0.01, 0.1)	0.03	0.11
Peak torque (Nm)
PT_Ex60	43.9 (11.0)	44.6 (10.9)	0.6 (-2.5, 3.7)	0.71	0.70	9.8 (8.8, 10.7)	10.8 (9.6, 12.0)	-0.8 (-2.5, 0.9)	0.17	0.36
PT_Fl60	21.8 (6.7)	25.0 (6.7)	-2.4 (-4.5, -0.4)	0.01	0.02	7.1 (6.6, 7.7)	5.9 (5.3, 6.5)	1.9 (0.9, 2.9)	0.005	<0.001
PT_Ex180	35.9 (8.3)	35.8 (7.5)	1.1 (-1.1, 3.3)	0.90	0.34	7.0 (6.5, 7.5)	7.6 (7.0, 8.3)	-0.4 (-1.3, 0.5)	0.15	0.42
PT_Fl180	19.3 (5.5)	23.0 (5.1)	-3.2 (-4.9, -1.6)	<0.001	<0.001	5.6 (5.1, 6.1)	4.3 (3.8, 4.8)	1.5 (0.5, 2.5)	0.001	0.004
Relative peak torque (Nm/Kg)
PT_Ex60	1.6 (0.2)	1.7 (0.3)	-0.1 (-0.2, 0.01)	<0.05	0.10	0.1 (0.1, 0.1)	0.1 (0.1, 0.2)	-0.5 (-4.6, 3.6)	0.82	0.80
PT_Fl60	0.8 (0.2)	0.9 (0.2)	-0.1 (-0.2, -0.1)	<0.001	<0.001	0.1 (0.1, 0.1)	0.1 (0.06, 0.1)	3.2 (0.6, 5.8)	<0.001	0.02
PT_Ex180	1.3 (0.2)	1.3 (0.2)	-0.1 (-0.1, 0.02)	0.07	0.15	0.1 (0.1, 0.1)	0.1 (0.1, 0.01)	0.8 (-3.2, 1.6)	0.62	0.51
PT_Fl180	0.7 (0.2)	0.9 (0.1)	-0.2 (-0.2, -0.1)	<0.001	<0.001	0.1 (0.1, 0.1)	0.03 (0.03, 0.1)	3.1 (0.7, 5.5)	<0.001	0.01

Baseline data and annual changes in the subsample of girls and boys who were measured. Baseline data are presented as unadjusted means with standard deviation (SD). Group comparisons of baseline data were done unadjusted (p₁) and adjusted for age at baseline (p₂). Annual changes are presented as unadjusted means with 95% confidence intervals (95% CI). Mean difference, in annual changes, are presented as adjusted mean (95% CI). Group comparison of annual changes is done unadjusted (p₃) and (p₄) adjusted for age at baseline, baseline parameter, annual change in height and Tanner stage at follow-up. Statistically significant changes are bolded.