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Abstract ObjectivesTo use a mouse model to investigate the relationships among the components of the systemic robusticity hypothesis (SRH): voluntary exercise on wheels, spontaneous physical activity (SPA) in cages, growth hormones, and skeletal robusticity, especially cranial vault thickness (CVT). Materials and MethodsFifty female mice from lines artificially selected for high running (HR) and 50 from nonselected control (C) lines were housed in cages with (Active) or without wheels (Sedentary). Wheel running and SPA were monitored daily. The experiment began at 24–27 days of age and lasted 12 weeks. Food consumption was measured weekly. Mice were skeletonized and their interparietal, parietal, humerus, and femur were µCT scanned. Mean total thickness of the parietal and interparietal bones was determined, along with thickness of the cortical and diploe layers individually. Geometric cross‐sectional indicators of strength were calculated for the long bones. Blood samples were assayed for IGF‐1 and IGFBP‐3. ResultsPhysical activity differed significantly among groups, based both on linetype (C vs. HR) and activity (A vs. S). However, contrary to our predictions, the ratio of IGF‐1 to IGFBP‐3 was higher in C mice than in HR mice. Neither CVT nor postcranial robusticity was affected by linetype or activity, nor were most measures of CVT and postcranial robusticity significantly associated with one another. DiscussionOur results fail to provide support for the systemic robusticity hypothesis, suggesting it is important to rethink the long‐standing theory that increased CVT inHomo erectusreflects increased physical activity compared other hominin species.
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Exercise‐induced loading increases ilium cortical area in a selectively bred mouse model
Abstract ObjectivesLittle is known about how ilium cortical bone responds to loading. Using a mouse model, this study presents data testing the hypothesis that iliac cross‐sectional properties are altered in response to increased activity. Materials and MethodsThe sample derives from lines of High Runner (HR) mice bred for increased wheel‐running activity. Four treatment groups of female mice were tested: non‐selected control lines housed without (N = 19) and with wheels (N = 20), and HR mice housed without (N = 17) and with wheels (N = 18) for 13 weeks beginning at weaning. Each pelvis was μCT‐scanned, cross‐sectional properties (cortical area—Ct.Ar, total area—Tt.Ar, polar moment of area, and polar section modulus) were determined from the ilium midshaft, and robusticity indices (ratio of the square root ofCt.ArorTt.Arto caudal ilium length) were calculated. Mixed models were implemented with linetype, wheel access, and presence of the mini‐muscle phenotype as fixed effects, replicate line nested within linetype as a random effect, and body mass as a covariate. ResultsResults demonstrate that the mouse ilium morphologically resembles a long bone in cross section. Body mass and the mini‐muscle phenotype were significant predictors of iliac cross‐sectional properties. Wheel access only had a statistically significant effect onCt.Arand its robusticity index, with greater values in mice with wheel access. DiscussionThese results suggest that voluntary exercise increases cortical area, but does not otherwise strengthen the ilium in these mice, corroborating previous studies on the effect of increased wheel‐running activity on femoral and humeral cross‐sectional properties in these mice.
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- Award ID(s):
- 1655362
- PAR ID:
- 10462608
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Physical Anthropology
- Volume:
- 168
- Issue:
- 3
- ISSN:
- 0002-9483
- Page Range / eLocation ID:
- p. 543-551
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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