Mouse Buddies Pitching In

Published June 17, 2009 Hansma et. al.: Testing Mouse Femora
U.C. Santa Barbara

Hypothesis: short term running has ...benefit on the mechanical properties of the femur.

A previous model system shows elastic modulus, hardness, and IDI (indentation distance as shown by the bone diagnostic instrument) as the best "discriminators" of differences in mechanical properties (between one bone and another).

The Bone Diagnostic Instrument, imaged below at work, was developed in the Hansma Physics Lab to determine the mechanical properties of bone and as a predictor of fracture risk.

The instrument indents into the bone with various forces directed by the researcher. The "indentation distance" is measured. Lesser distance at a given force indicates stronger bone. Note varying distances in the image below.
Indentation distance with this instrument provides a way to measure the bone's ability to resist additional deformation. With this instrument Hansma makes strength calculations for live bone, whereas Planck was limited to models.

And so, Hansma exercises 5 young mice on a treadmill for 30 min./day for but 21 days. 5 sedentary youngsters provide a control group. "The mice were the same sex and strain (male)". 10 older mice exercised for 4 months since this is an osteoporosis study. The results between old and young mice were roughly the same in terms of differences in bone strength between exercised and sedentary.

A maximum applied loading force was calibrated on the instrument. 9 lesser loads were also applied for comparison.

Results: "A relatively brief 21-day period of running induced significant changes in IDI in the femora of young mice...This shows that short term exercise in young developing bone may reduce the risk of fracture...exercise in developing bone may lead to fracture resistance."

And so, there you have it. Actual research on live bone indicating that exercise produces a positive effect on bone mineralization.

Some questions about this research which is done primarily to promote practical applications for Bone Indentation Instrument in terms of osteoporosis, i.e. these physicists have less interest in bone mineralization and more interest in selling their instrument.

Note above that Hansma indicates he's looking at three (of many) bone strenght qualities:

elastic modulus
strength
IDI (indentation distance from his instrument that has been previously correlated to
bone strength qualities.

Now, Hansma indicates: "Neither the elastic modulus nor the hardness showed significant difference with exercise (compared to sedentary)."

Thus, though there's differences in indentation distance between exercised and sedentary, there's zero difference in elastic modulus and hardness.

Note, e.g. that hardness is just one of numerous bone qualities, and if you already have maximum hardness in a sedentary person, exercise would fail to improve. I think that's what they are meaning, though it is unclear as Hansma avoids stating how he reached the conclusion. Nevertheless, I think this merely speaks to my dinosaur reference, that the basic nature of bone does not change because you are exercising it, except in some limited respects that are referred to on this blog.

Ramifications of Hansma, next post.
The article at: http://hansmalab.physics.ucsb.edu/pdf/BoneDiagnostic3.pdf

Training:
Tues. 2/2: Pasture Romp and 5 min tack walk.
Wed. 2/3: Pasture Romp and 5 min. tack walk.
Thurs. 2/4: Quality pasture romp in ideal conditions were they raced each other in short spurts, followed by an intermittent mile of riderless work in the running paddock finally available after almost 60 days. 20-30 yards of speed here and there. 10 min of trot-walk under tack.