Isokinetic eccentric exercise can induce skeletal muscle injury within the physiologic excursion of muscle-tendon unit: a rabbit model.
OBJECTIVE
Intensive eccentric exercise can cause muscle damage. We simulated an animal model of isokinetic eccentric exercise by repetitively stretching stimulated triceps surae muscle-tendon units to determine if such exercise affects the mechanical properties of the unit within its physiologic excursion.


METHODS
Biomechanical parameters of the muscle-tendon unit were monitored during isokinetic eccentric loading in 12 rabbits. In each animal, one limb (control group) was stretched until failure. The other limb (study group) was first subjected to isokinetic and eccentric cyclic loading at the rate of 10.0 cm/min to 112% (group I) or 120% (group II) of its initial length for 1 hour and then stretched to failure. Load-deformation curves and biomechanical parameters were compared between the study and control groups.


RESULTS
When the muscle-tendon unit received eccentric cyclic loading to 112%, changes in all biomechanical parameters - except for the slope of the load-deformation curve - were not significant. In contrast, most parameters, including the slope of the load-deformation curve, peak load, deformation at peak load, total energy absorption, and energy absorption before peak load, significantly decreased after isokinetic eccentric cyclic loading to 120%.


CONCLUSIONS
We found a threshold for eccentrically induced injury of the rabbit triceps surae muscle at between 12% and 20% strain, which is within the physiologic excursion of the muscle-tendon units. Our study provided evidence that eccentric exercise may induce changes in the biomechanical properties of skeletal muscles, even within the physiologic range of the excursion of the muscle-tendon unit.
Tsuang
Yang-Hwei
YH
Department of Orthopedic Surgery, Taipei City Hospital, Taipei, Taiwan. DAJ23@tpech.gov.tw
Lam
Shui-Ling
SL
Wu
Lien-Chen
LC
Chiang
Chang-Jung
CJ
Chen
Li-Ting
LT
Chen
Pei-Yu
PY
Sun
Jui-Sheng
JS
Wang
Chien-Che
CC
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