Biomedical Engineering Reference
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it allows greater control over the loading regimen. (For rodents on treadmills,
ambulation is probably a more accurate term than ''running'', as there is at least
one paw in contact with the ground at speeds commonly used.) The loading
magnitude can be increased by either attaching additional weight to the animals or
increasing the inclination or speed of the treadmill. The rate of loading and number
of loading cycles are controlled by the speed of the treadmill and the duration of
training. There are few data on bone strains engendered in rats by running, but the
available data indicate similar values as in humans. In growing male rats, ulnar
strains of 700-1200 le were recorded by Mosley et al. [
25
] during running on a
level surface. In addition, tibial strains of approximately 700 le were reported by
Rabkin et al. [
26
] during treadmill running, with a modest increase (+13%) in
strain magnitude with a doubling of speed (from 8 to 16 m/min). The influence of
age on strains produced during running is unclear. Indrekvam et al. [
27
] reported
that peak strain on the femoral diaphysis during treadmill running did not differ
significantly between rats aged 1.5, 3 and 12 months. Similarly, Keller and
Spengler [
28
] reported no significant changes in strain magnitude on the femur of
running rats from 1.5 to 7 months age, despite a threefold increase in body weight
during this interval. Thus, available data indicate no change in bone strain
engendered by running during growth and maturation, although we could find no
data on changes from maturity to old age.
Raab et al. used treadmill running to examine the influence of aging on
mechano-responsiveness [
29
] (Table
2
). They evaluated the effect of 10 weeks of
treadmill running on fat-free weight and mechanical properties (as determined by
three-point bending) of femur and humerus of young (2.5 months) and old
(25 months) female rats. Compared to sedentary control, running increased the fat-
free weight of the femur in both young and old rats by a similar amount. Trained
rats of both age groups also had significantly greater ultimate force in the femur
and humerus and greater yield force in the humerus. However the moment of
inertia of the humerus and femur (mid-diaphysis) was unchanged. It was con-
cluded that the bone adaptation in response to treadmill running was similar in
young and old rats, even though the old rats ran at a slower speed (young: 36 m/min;
old: 15 m/min) and thus may have had a lower magnitude strain stimulus.
Leppanen et al. made similar observations on comparing the response of mature
(11 months) and old (22 months) female rats to treadmill running [
30
]. Compared
to the sedentary control, 14 weeks of treadmill running increased the ultimate force
of the femur (mid-diaphysis) of old rats but not mature rats. Changes at the femoral
neck, a common site of osteoporosis related fractures, were also studied. In older
rats running increased the ultimate force (determined by compression test), the
cross-sectional area and bone mineral content (BMC) at the femoral neck. Running
did not influence these parameters in mature rats. The values of these parameters
were similar for trained old rats and sedentary mature rats suggesting that running
was not anabolic but prevented bone loss in older animals. Also exercise had no
influence on the tibial metaphysis in either age group, implying that the bone
adaptation is site specific in this model. In the same study, Leppanen et al. reported
on treadmill running effects in mature (11 months) and old (19 months) male rats.
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