Exercise when young provides lifelong benefits to bone structure and strength

Stuart J. Warden, Robyn K. Fuchs, Alesha Castillo, Ian R. Nelson, Charles H. Turner

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)251-259
Number of pages9
JournalJournal of Bone and Mineral Research
Volume22
Issue number2
DOIs
StatePublished - Feb 2007

Fingerprint

Ulna
Bone and Bones
Forearm
Skeleton
Fatigue
Growth
Physiologic Calcification
Weight-Bearing
Bone Density
Sprague Dawley Rats
Rodentia
Wounds and Injuries

Keywords

  • Biomechanics
  • Detraining
  • Growth and development
  • Mechanical loading
  • Osteoporosis

ASJC Scopus subject areas

  • Surgery

Cite this

Exercise when young provides lifelong benefits to bone structure and strength. / Warden, Stuart J.; Fuchs, Robyn K.; Castillo, Alesha; Nelson, Ian R.; Turner, Charles H.

In: Journal of Bone and Mineral Research, Vol. 22, No. 2, 02.2007, p. 251-259.

Research output: Contribution to journalArticle

Warden, Stuart J. ; Fuchs, Robyn K. ; Castillo, Alesha ; Nelson, Ian R. ; Turner, Charles H. / Exercise when young provides lifelong benefits to bone structure and strength. In: Journal of Bone and Mineral Research. 2007 ; Vol. 22, No. 2. pp. 251-259.
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N2 - 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.

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