Response of tibialis anterior tendon to a chronic exposure of stretch-shortening cycles: age effects.
BACKGROUND
The purpose of the current study was to investigate the effects of aging on tendon response to repetitive exposures of stretch-shortening cycles (SSC's).


METHODS
The left hind limb from young (3 mo, N = 4) and old (30 mo, N = 9) male Fisher 344 x Brown Norway rats were exposed to 80 maximal SSCs (60 deg/s, 50 deg range of motion) 3 x/week for 4.5 weeks in vivo. After the last exposure, tendons from the tibialis anterior muscle were isolated, stored at -80 degrees C, and then tested using a micro-mechanical testing machine. Deformation of each tendon was evaluated using both relative grip-to-grip displacements and reference marks via a video system.


RESULTS
At failure, the young control tendons had higher strain magnitude than the young exposed (p < 0.01) and the old control tendons (p < .0001). Total load at inflection was affected by age only (p < 0.01). Old exposed and control tendons exhibited significantly higher loads at the inflection point than their young counterparts (p < 0.05 for both comparisons). At failure, the old exposed tendons carried higher loads than the young exposed tendons (p < 0.05). Stiffness was affected by age only at failure where the old tendons exhibited higher stiffness in both exposed and control tendons than their young counterparts (p < 0.05 and p < 0.01, respectively).


CONCLUSIONS
The chronic protocol enhanced the elastic stiffness of young tendon and the loads in both the young and old tendons. The old exposed tendons were found to exhibit higher load capacity than their younger counterparts, which differed from our initial hypothesis.
Ensey
James S
JS
National Institute for Occupational Safety and Health (NIOSH), Health Effects Laboratory Division, Morgantown, West Virginia 26505, USA. jensey@cdc.gov
Hollander
Melinda S
MS
Wu
John Z
JZ
Kashon
Michael L
ML
Baker
Brent B
BB
Cutlip
Robert G
RG
D000375:Aging / Q000502:physiology*; D000818:Animals; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D013314:Stress, Mechanical; D013710:Tendons / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*