Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
from September 2014
©Journal of Sports Science and Medicine (2013) 12, 1 - 9

Research article
Short-Term Free-Fall Landing Causes Reduced Bone Size and Bending Energy in Femora of Growing Rats
Hsin-Shih Lin1,2, Tsang-Hai Huang2, , Ho-Seng Wang1, Shih-Wei Mao3, Yuh-Shiou Tai4, Hung-Ta Chiu2, Kuang-You B. Cheng2, Rong-Sen Yang5
Author Information
1 Department of Physical Education, National Taiwan Normal University,
2 Institute of Physical Education, Health and Leisure Studies, National Cheng Kung University, Tainan, Taiwan
3 Department of Mechanical Engineering, R.O.C. Military Academy, Kaohsiung, Taiwan
4 Department of Civil Engineering, R.O.C. Military Academy, Kaohsiung, Taiwan
5 Department of Orthopaedics, National Taiwan University & Hospital, Taipei, Taiwan

Tsang-Hai Huang
‚úČ Associate Professor, Institute of Physical Education, Health and Leisure Studies, National Cheng-Kung University, No. 1, University Rd. 701, Tainan, Taiwan
Publish Date
Received: 16-04-2012
Accepted: 28-08-2012
Published (online): 01-03-2013
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The purpose of this study was to determine the effects of a mechanical loading course (short-term free-fall landing) on femoral geometry and biomechanical properties in growing rats. Thirty-two female Wistar rats (7-week-old) were randomly assigned to three groups: L30 (n = 11), L10 (n = 11) and CON (n = 10) groups. Animals in the L10 and L30 groups were subjected to a 5-day free-fall landing program in which animals were dropped from a height of 40cm 10 and 30 times per day, respectively. Landing ground reaction force (GRF) was measured on the 1st and 5th days of landing training. All animals were subjected to two fluorescent labeling injections on the days before and after the 5-day landing training. Three days after the last labeling injection, animals were sacrificed under deep anesthesia. Methods of dynamic histomorphometry, tissue geometry and tissue biomechanical measurements were used to investigate the response in femora. A significant decrease in peak GRF in the hind-limb was shown from day 1 to day 5. No significant difference was shown among groups in dynamic histomorphometry. Biomechanical property analyses showed significantly lower maximal energy and post-yield energy in the L10 and L30 groups as compared to the CON group (p < 0.05). Moreover, geometric measurements revealed that cross-sectional cortical areas and thicknesses were significantly lower in landing groups than in the CON group. Short-term (5-day) free-fall landing training resulted in minor compromised long bone tissue, as shown by reduced bending energy and cortical bone area but not in other mechanical properties or tissue measurements (e.g. weights and length) of growing female rats. Further studies would be valuable to investigate whether this compromised bone material represents the existence of a latency period in the adaptation of bone material to external mechanical loading.

Key words: Bone, mechanical load, biomechanical properties, post-yield energy, animal model

           Key Points
  • Short-term free-fall landing causes compromised bone material as shown by reduced post-yield energy in long bones of rodents.
  • The results of the current study suggest the existence of unsettled bone material after a short-term mechanical loading regime.
  • The connection of the present animal study to the stress fractures occurring in young athletes needs to be clarified.
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