title: Bone strength is maintained after 8 months of inactivity in hibernating golden-mantled ground squirrels, Spermophilus lateralis.
abstract: Prolonged inactivity leads to disuse atrophy, a loss of muscle and bone mass. Hibernating mammals are inactive for 6-9 months per year but must return to full activity immediately after completing hibernation. This necessity for immediate recovery presents an intriguing conundrum, as many mammals require two to three times the period of inactivity to recover full bone strength. Therefore, if hibernators experience typical levels of bone disuse atrophy during hibernation, there would be inadequate time available to recover during the summer active season. We examined whether there were mechanical consequences as a result of the extended inactivity of hibernation. We dissected femur and tibia bones from squirrels in various stages of the annual hibernation cycle and measured the amount of force required to fracture these bones. Three groups were investigated; summer active animals were captured during the summer and immediately killed, animals in the 1 month detraining group were captured in the summer and killed following a 1-month period of restricted mobility, hibernating animals were killed after 8 months of inactivity. A three-point bend test was employed to measure the force required to break the bones. Apparent flexural strength and apparent flexural modulus (material stiffness) were calculated for femurs. There were no differences between groups for femur fracture force, tibia fracture force, or femur flexural strength. Femur flexural modulus was significantly less for the 1 month detraining group than for the hibernation and summer active groups. Thus, hibernators seem resistant to the deleterious effects of prolonged inactivity during the winter. However, they may be susceptible to immobilization-induced bone loss during the summer.
authors.affiliation: School of Life Sciences, University of Nevada at Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154, USA.
authors.forename: Jenifer C
authors.initials: JC
authors.lastname: Utz
authors.forename: Stacy
authors.initials: S
authors.lastname: Nelson
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: O'Toole
authors.forename: Frank
authors.initials: F
authors.lastname: van Breukelen
mesh_terms: D000818:Animals; D001284:Atrophy; D015519:Bone Density; D004548:Elasticity; D005269:Femur / Q000033:anatomy & histology / Q000473:pathology / Q000502:physiology*; D006605:Hibernation; D012589:Sciuridae / Q000033:anatomy & histology / Q000502:physiology*; D013977:Tibia / Q000033:anatomy & histology / Q000473:pathology / Q000502:physiology*
references.citation: J Anat. 2007 Feb;210(2):160-9
references.pmid: 17261138
references.citation: J Appl Physiol (1985). 1999 Jul;87(1):189-95
references.pmid: 10409574
references.citation: J Bone Miner Res. 1990 Aug;5(8):843-50
references.pmid: 2239368
references.citation: J Exp Biol. 2003 Dec;206(Pt 23):4233-9
references.pmid: 14581593
references.citation: Am J Physiol Regul Integr Comp Physiol. 2008 Feb;294(2):R639-50
references.pmid: 18032471
references.citation: Anat Rec. 1972 Jan;172(1):97-108
references.pmid: 5007373
references.citation: Cryobiology. 1976 Feb;13(1):84-94
references.pmid: 1261296
references.citation: Sports Med. 2002;32(7):459-76
references.pmid: 12015807
references.citation: J Biomech. 2006;39(8):1480-8
references.pmid: 15975583
references.citation: Bone. 2008 Feb;42(2):396-404
references.pmid: 18037367
references.citation: Physiol Rev. 2003 Oct;83(4):1153-81
references.pmid: 14506303
references.citation: J Exp Biol. 2006 May;209(Pt 9):1630-8
references.pmid: 16621944
references.citation: Physiol Behav. 1995 Oct;58(4):653-7
references.pmid: 8559773
references.citation: J Exp Biol. 2004 Jan;207(Pt 3):475-82
references.pmid: 14691095
references.citation: Anat Rec. 1985 Dec;213(4):481-95
references.pmid: 4083529
references.citation: Q Rev Biol. 1990 Jun;65(2):145-74
references.pmid: 2201054
references.citation: J Morphol. 1981 Jan;167(1):43-51
references.pmid: 7241597
references.citation: Bone. 1986;7(6):431-9
references.pmid: 3801236
references.citation: J Exp Biol. 1999 Sep;202(Pt 18):2495-503
references.pmid: 10460736
references.citation: Cornell Vet. 1977 Apr;67(2):265-71
references.pmid: 870287
references.citation: Science. 1989 Jun 30;244(4912):1593-5
references.pmid: 2740905
references.citation: Proc Biol Sci. 1996 Mar 22;263(1368):287-94
references.pmid: 8920251
references.citation: J Biomech. 2005 Nov;38(11):2143-50
references.pmid: 16115638
references.citation: J Biomech. 2004 Oct;37(10):1513-20
references.pmid: 15336926
references.citation: J Exp Zool. 1979 Dec;210(3):537-41
references.pmid: 541606
references.citation: Histol Histopathol. 1986 Apr;1(2):155-60
references.pmid: 2980111
references.citation: J Dent Res. 1977 Dec;56(12):1552-7
references.pmid: 277478
references.citation: J Biomech. 2001 Dec;34(12):1631-6
references.pmid: 11716865
references.citation: Clin Orthop Relat Res. 2003 Mar;(408):295-301
references.pmid: 12616074