Effects of jumping exercise on maximum ground reaction force and bone in 8- to 12-year-old boys and girls: a 9-month randomized controlled trial.
OBJECTIVE
To assess adaptations of the lower leg muscle-bone unit in 8- to 12-year-old children following a randomized controlled jumping exercise intervention for 9 months.


METHODS
Twelve boys and 10 girls (INT) performed a supervised jumping protocol during the first 10 min of their regularly scheduled physical education class twice a week, while 11 boys and 12 girls (CON) completed the regular curriculum. We assessed maximum voluntary ground reaction force during multiple one-legged hopping (F(m1LH)), and tibial bone strength/geometry by peripheral quantitative computed tomography (pQCT) at the 4-, 14-, 38- and 66%-site pre, intermediate, and post intervention.


RESULTS
Whether increases in F(m1LH) (+2.1% points, P= 0.752), nor changes in bone strength/geometry (+1 to +3% points, 0.169<P<0.861), were significantly different for INT relative to CON. The relationship between F(m1LH) and volumetric bone mineral content at the 14%-site (vBMC(14%)) was very strong for both groups, pre and post intervention (0.51≤R(2)≤0.88). However, changes in F(m1LH) and vBMC(14%) were not correlated.


CONCLUSIONS
In children, growth and exercise did not increase maximum muscle force and bone strength in proportion to each other, meaning that the adaptive processes were not tightly coupled or follow different time courses.
Exercise Physiology, Institute of Human Movement Sciences, ETH Zurich, Zurich, Switzerland.
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Anliker
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Dick
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Rawer
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Toigo
D001696:Biomechanical Phenomena / Q000502:physiology; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D002648:Child; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D007866:Leg / Q000033:anatomy & histology / Q000254:growth & development*; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000254:growth & development*; D010809:Physical Fitness / Q000502:physiology*; D011859:Radiography