The authors state that they have no conflicts of interest.
Exercise When Young Provides Lifelong Benefits to Bone Structure and Strength†
Article first published online: 13 NOV 2006
Copyright © 2007 ASBMR
Journal of Bone and Mineral Research
Volume 22, Issue 2, pages 251–259, February 2007
How to Cite
Warden, S. J., Fuchs, R. K., Castillo, A. B., Nelson, I. R. and Turner, C. H. (2007), Exercise When Young Provides Lifelong Benefits to Bone Structure and Strength. J Bone Miner Res, 22: 251–259. doi: 10.1359/jbmr.061107
- Issue published online: 4 DEC 2009
- Article first published online: 13 NOV 2006
- Manuscript Accepted: 7 NOV 2006
- Manuscript Revised: 23 OCT 2006
- Manuscript Received: 15 SEP 2006
- growth and development;
- mechanical loading;
Short-term exercise in growing rodents provided lifelong benefits to bone structure, strength, and fatigue resistance. Consequently, exercise when young may reduce the risk for fractures later in life, and the old exercise adage of “use it or lose it” may not be entirely applicable to the skeleton.
Introduction: The growing skeleton is most responsive to exercise, but low-trauma fractures predominantly occur in adults. This disparity has raised the question of whether exercised-induced skeletal changes during growth persist into adulthood where they may have antifracture benefits. This study investigated whether brief exercise during growth results in lifelong changes in bone quantity, structure, quality, and mechanical properties.
Materials and Methods: Right forearms of 5-week-old Sprague-Dawley rats were exercised 3 days/week for 7 weeks using the forearm axial compression loading model. Left forearms were internal controls and not exercised. Bone quantity (mineral content and areal density) and structure (cortical area and minimum second moment of area [IMIN]) were assessed before and after exercise and during detraining (restriction to home cage activity). Ulnas were removed after 92 weeks of detraining (at 2 years of age) and assessed for bone quality (mineralization) and mechanical properties (ultimate force and fatigue life).
Results: Exercise induced consistent bone quantity and structural adaptation. The largest effect was on IMIN, which was 25.4% (95% CI, 15.6–35.3%) greater in exercised ulnas compared with nonexercised ulnas. Bone quantity differences did not persist with detraining, whereas all of the absolute difference in bone structure between exercised and nonexercised ulnas was maintained. After detraining, exercised ulnas had 23.7% (95% CI, 13.0–34.3%) greater ultimate force, indicating enhanced bone strength. However, exercised ulnas also had lower postyield displacement (−26.4%; 95% CI, −43.6% to −9.1%), indicating increased brittleness. This resulted from greater mineralization (0.56%; 95% CI, 0.12–1.00%), but did not influence fatigue life, which was 10-fold greater in exercised ulnas.
Conclusions: These data indicate that exercise when young can have lifelong benefits on bone structure and strength, and potentially, fracture risk. They suggest that the old exercise adage of “use it or lose it” may not be entirely applicable to the skeleton and that individuals undergoing skeletal growth should be encouraged to perform impact exercise.