Biomedical Engineering Reference
In-Depth Information
It's well known that patients with pathological acidosis suffer negative bone turn-over,
which causes a net bone mineral loss.
26
Endurance exercise may induce acidosis, which
negatively affects bone metabolism. However, transient acidosis caused by exercise is
buffered by HCO
3
and disappears within hours after exercise.
27
In addition, it has been
suggested that acid buffer capacity is enhanced after a period of exercise training.
28
At the
cellular level, a single bout of intense exercise induces transient increases in serum and urine
calcium levels without showing cellular osteoclastical activities.
29,30
With respect to the impact from abnormalities of hormone regulation, oligomenorrhea and
amenorrhea related to bone loss are often reported in female runners undergoing intensive
training. However, recent investigations suggest that endurance running does not directly
cause menstrual disorders and the subsequent bone loss.
31-33
Menstrual disorders in
endurance runners are more likely due to either energy or nutrition deficiencies. Therefore,
dietary adjustment is usually more effective than hormone replacement therapy for
restoring menstrual cycles and bone metabolism.
34
In males, ERT is known to lower
testosterone, but lower testosterone does not necessarily correlate with lower BMD.
35
In
addition, runners with different training mileage (from 5 to 75 mile/week) do not
significantly differ in serum testosterone levels.
15
Regarding studies of bone metabolism status, healthy distance runners at rest usually
exhibit normal bone metabolism, and some studies even show a positive bone metabolism
status, as revealed by serum bone markers.
3, 4
Brahm
et al.,
in a study of bone metabolism in
runners using various serum markers, found that runners had lower bone formation as well
as lower bone resorption activities.
3
Moreover, triathletes reveal no difference in bone
metabolism during the intense competitive season as compared to their non-training
period.
4
2.2 Limitation of human studies
To summarize the above, distance runners do not seem to acquire much benefit from their
training when densitometric measurements are used to determine the bone health.
However, as shown by serum bone marker assays, distance runners did not reveal an
inadequate bone metabolism status. Actually, over the past decades, an increasing number
of reports suggest that BMD does not accurately predict bone health or bone strength.
Patients with fractures also show normal BMD values.
36
The BMD and BMC measures
apparently correlate strongly with body mass and body size.
11, 37-39
Today, “bone quality” is used as a new term to represent bone health, which is composed of
various parameters, including tissue architecture, turnover, microfracture and
mineralization, of a healthy bone.
40
Further, the organization of the bone matrix may also
play an important role in bone strength.
41
Unfortunately, many of the bone quality
measurements are too invasive to be feasible in human subjects. Thus, animal studies have
been frequently used for further clarifying related issues.
3. Comprehensive results of animal studies: BMD and BMC
In biomedical science, animal experiments are performed to establish models that mimic
human physiological phenomena. Either estimation methods or experimental designs,
which may not be feasible in humans, can then be performed to further investigate possible
mechanisms. Rodent models of treadmill activity are commonly used to investigate the
effects and mechanisms of exercise on bone metabolism. This section reviews the findings of
