Hello Undog,
Made mostly of calcium and protein, bone is a living tissue, that
constantly undergoes replacement. Bone is broken down, reabsorbed by
the body, and rebuilt in a constant renewal process. Without exercise,
bones absorb less calcium, and become weaker. I have posted numerous
excerpts that explain this, contained in the answer.
?Bone constantly undergoes a process of remodeling. Vertical bone
growth ends at approximately age 18, but bone continues to increase in
mass for 10-15 years longer, until about the age of 35, when peak bone
mass is reached. After peak bone mass is achieved, age-related bone
loss begins to occur, slowly at first, but faster after menopause.
About 1% average bone loss per year occurs from age 35 on resulting in
20% already lost by age 55.
From childhood through adolescence, skeletal mineral demands for bone
formation are at their highest. A high protein, high sugar, fat and
salt diet; and physical inactivity during these bone-forming years can
reduce bone density and lay the foundation for osteoporosis in later
years. When peak bone mass is reached at age 35, the larger the bone
mass, the less risk of developing osteoporosis.?
http://www.ucheepines.org/osteoporosis.htm
?At the cellular level, bone consists of specialized bone cells
(osteoblasts, osteocytes and osteoclasts), minerals, proteins,
hormones, water and other molecules such as sugars. Osteocytes are
bone cells and are found within the bone?s structure. Osteoblasts are
bone-forming cells, which line the surface of a bone?s structure.
Osteoclasts are cells that resorb bone trough a degradation process.
The remodeling process, which is balanced between resorption and
formation, can be affected by a number of factors. For example,
smoking has been shown to slow the process of bone formation, while
exercise such as walking or running which applies mechanical force to
the body on impact, has been shown to stimulate the process of bone
formation.?
http://www.therics.com/documentation/Bone_Physiology.pdf
?Bone constantly grows through a regular process of breaking down
(resorption) and renewing itself (formation) until peak bone mass
(maximum bone density and strength) is reached during a person's
mid-20s. Typically, from that point on, bone loss outpaces formation.
If left untreated, osteoporosis can occur. Osteoporosis is more likely
to develop if optimal bone mass is not reached during the bone
building years from childhood to the mid-20s.
This study developed a model for good bone health that was applied
both to women already on HRT and women not on HRT. For many years,
experts believed that the best way for postmenopausal women to
increase or maintain bone density was to go on HRT. While the effect
of HRT on bone health is well established, recent independent studies
revealed a growing list of side effects from this treatment,
challenging some of the major benefits of HRT and leading many women
to re-evaluate whether this therapy is right for them. The researchers
in this study, funded by the National Institute of Arthritis and
Musculoskeletal and Skin Diseases of the National Institutes of Health
(NIH), found that weight-bearing and resistance exercises plus
adequate calcium intake from food and calcium citrate were effective
in improving bone density in women not on HRT as well as in women on
HRT.?
http://www.supplementquality.com/efficacy/calcium_exercise.htm
?In long-term studies, researchers have found that regular
participation in weight-bearing exercise, leads to a significant
increase in bone mineral content. In many instances, osteoporosis can
be improved. The more active we are, the thicker our bones grow.
There is a connection between muscle strength and bone density. When
we move our muscles, the pull of muscles on bones and the jolting of
exercise, encourages the bones to absorb more calcium.
Exercise, to be effective in maintaining bone density and overall
fitness, needs to be undertaken at all stages of life; from childhood
on through advancing age. People who are just beginning to show signs
of osteoporosis can prevent its progression by adding an exercise
program to their daily schedule. This is as important as beginning a
new eating program. Healing is slow and gradual, and takes place over
the course of many months and possibly years. Once osteoporosis has
developed to the point of a high fracture rate, extreme care must be
taken when initiating exercise, because even small body stresses can
cause fractures.
Another concern is exercising too much. Excessive exercise, such as
the kind of training needed to participate in marathon running or
professional dancing, can cause painful heels, shin splints,
headaches, blood in the urine, irregular or stopped menstruation. It
can also cause bones to become thin and weak. This type of
osteoporosis has been found in women as young as 25 years.?
http://www.ucheepines.org/osteoporosis.htm
?In a remarkable feedback loop directed by hormones secreted by the
pituitary gland, calcium is released into the bloodstream and
recruited to create and regenerate bone tissue as needed. Cells called
osteoclasts break down and reabsorb old bone tissue, causing calcium
salts to be released into the bloodstream, thus building up the
blood's calcium supply. When the blood's calcium supply is too high,
cells called osteoblasts deposit calcium on the protein framework of
the bone, creating bone tissue and at the same time reducing the
blood's level of calcium. This process explains why, when there is not
enough calcium in the bloodstream, the body will take what it needs
from our bones.?
http://health.yahoo.com/centers/bone_health/207
?Exercise has known benefits to the skeleton, increasing the amount of
mineral present and the size of exercised bones. These changes
increase bone strength and, thus, reduce the potential of a bone to
break or fracture. Evidence from studies in humans suggest that bone
is most responsive to exercise prior to puberty, and that the response
decreases in the post-pubertal years. Thus, a 'window-of-opportunity'
exists when bone is most responsive to exercise.?
http://www.shrs.iupui.edu/pt/alt.php?load=content/musculoskeletal.php
? ?Activation: Preosteoclasts are stimulated and differentiated under
the influence of cytokine and growth factors to mature into active
osteoclasts.
? Resorption: Osteoclasts digest mineral matrix, old bone.
? Reversal: End of resorption
? Formation: Osteoblasts are responsible for bone matrix synthesis
(collagen). Two other non-collagenous proteins are also formed:
ostocalcin and osteonectin.
?Osteoblasts are responsible for bone matrix synthesis. They secrete a
collagen rich ground substance essential for later mineralization of
hydroxyapatite and other crystals. The collagen actually strands to
form osteoids: spiral fibers of bone matrix. Osteoblasts cause calcium
salts and phosphorus to precipitate from the blood, these minerals
bond with the newly formed osteoid to mineralize the bone tissue.
Alkaline phosphatase is contained in osteoblasts and secreted during
osteoblastic activity. The osteoblasts also have estrogen receptors.
Estrogens can actually increase the number of osteoblasts, increasing
therefore collagen production.?
http://www.medes.fr/Eristo/Osteoporosis/BoneRemodeling.html
?Weight-bearing activities improve bone health for many reasons.
First, weight-bearing exercise appears to stimulate bone formation.
Second, it strengthens muscles that in turn pull or tug on bones. This
action keeps bones strong. And third, physical activity improves your
strength, balance, and coordination--all of which help reduce your
risk of falls and bone injuries.?
?What can I do to help prevent osteoporosis?
Nutrition (especially calcium intake), lifestyle (including exercise),
and hormones (estrogen) are three factors that affect bone health.
Exercise and dietary habits throughout your life influence your risk
of developing this disease.
Will exercise alone protect my bones?
Weight-bearing exercise alone is not enough to protect you from
osteoporosis. Even if you do weight-bearing exercise regularly,
failing to eat enough calcium-rich foods will weaken your bones.
Scientists agree that good nutrition can reduce the likelihood of
osteoporosis by as much as one-half. Many Americans today don't
consume enough calcium. Fortunately, it's never too late to improve
your bone health by consuming enough calcium-rich foods.?
http://www.primusweb.com/fitnesspartner/library/activity/bonehlth.htm
?Bone turnover tends to occur most rapidly at skeletal sites rich in
trabecular bone, such as the spine and proximal femur of the hip.
Remodeling helps to provide elasticity and strength to bone and
produces a steady source of calcium for essential body functions. It
is a cyclic process that takes place in specific skeletal sites, with
each remodeling cycle lasting about four months. Since bone resorption
occurs rather quickly, most of the cycle is devoted to bone formation,
which includes the synthesis of collagen and other substances as well
as mineralization of the matrix.
Even subtle changes in bone remodeling over time can result in
significant losses of bone tissue. Osteoporosis is characterized by an
increase in bone resorption at those sites in the skeleton where
fracture is most likely to occur: namely the hip, spine and wrist.
Additionally, there can be a decline in the amount of bone that is
replaced after resorption takes place. Increased bone resorption and
impaired bone formation are both likely to occur in individuals with
osteoporosis.?
http://www.osteo.org/newfile.asp?doc=n403&doctitle=Biochemical+Markers+of+Bone+Turnover&doctype=HTML+Newsletter
?Bones are generally richly supplied with blood, via periosteal
vessels, vessels that enter close to the articular surfaces and
nutrient arteries passing obliquely through the cortex before dividing
into longitudinally directed branches. Loss of the arterial supply to
parts of a bone results in death of bone tissue, usually called
avascular necrosis or osteonecrosis.?
http://www.fleshandbones.com/readingroom/pdf/113.pdf
?Men can experience a marked loss of bone as they age, and this
decline in bone mass is an important contributor to the development of
osteoporosis. There are several reasons for this loss of bone.
Declining testosterone levels may cause bone loss that is similar to
the bone loss that occurs in women at the time of menopause. In
addition, estrogen may play a critical role in bone health in men.
Changes in estrogen levels with age may be as important, if not more
important, as those changes in testosterone. Moreover, the amount of
time devoted to exercising generally declines with age, and dietary
calcium intake, as well as the ability to absorb calcium, tends to
fall. Finally, there may be age-related changes in the basic metabolic
activity in bone that contribute to bone loss. The risk of fracture
posed by age-related bone loss is increased considerably by a tendency
for the elderly to fall more often.?
?Preventing bone loss and fractures is of primary importance. Where
possible, risk factors such as smoking and excessive alcohol intake
should be avoided; a balanced diet replete in calcium and vitamin D
should be a priority; and proper exercise, particularly weight-bearing
exercises, should be a regular part of weekly activities. Finally, the
prevention of falls is very important and common household hazards
(such as slippery floors and unlit stairways) and medications or drugs
that dull the senses and produce drowsiness should be avoided.?
http://www.nof.org/men/strategies_men.htm
Here are some great animations showing bone remodeling
http://courses.washington.edu/bonephys/opmovies.html
?For the exercise to be effective in maintaining bone strength, it
must follow the "overload" principle. In other words, the exercise
must apply a force to the bone that will "stress" it and thus
stimulate it to "adapt" to the exercise. Bones respond to
weight-bearing exercise by strengthening themselves.
There are many types of exercise that can fit the bill of
"weight-bearing". Jogging, high intensity resistance training, stair
climbing/descending, and activities that involve jumping (volleyball,
tennis, basketball, soccer, jump-roping, plyometrics, etc.) are
effective modes.?
http://www.myfooddiary.com/resources/ask_the_expert/exercise_bone_density.asp
?Bone is responsive to physical strain. Changes in the forces applied
to bone produce effects in bone. For example, weightlessness and
immobilisation induce
marked degrees of bone loss. On the other hand, athletes tend to have
greater bone mineral density, although this effect is often site
specific. For example,
tennis players have increased bone density in their dominant but not
non-dominant arm and weight lifters have greater femoral bone density
than other athletes. This is consistent with a local effect of
exercise
on bone.?
Bone remodeling is a term meaning bone turnover.
?Bone remodeling is heavily influenced by nutritional and hormonal
factors. Calcium and vitamin D are nutrients required for normal bone
growth. Parathyroid hormone regulates the mineral composition of bone,
with higher levels causing resorption of calcium and bone.
Glucocorticoid hormones cause osteoclast activity to increase, causing
bone resorption. Calcitonin, estrogen and testosterone increase
osteoblast activity, causing bone growth.
The loss of estrogen following menopause causes a phase of rapid bone
loss. Similarly, testosterone levels in men diminish with advancing
age and are related to male osteoporosis.
Physical activity causes bone remodeling. People who remain physically
active throughout life have a lower risk of osteoporosis. Conversely,
people who are bedridden are at a significantly increased risk.
Physical activity has its greatest impact during adolescence,
affecting peak bone mass most. In adults, physical activity helps
maintain bone mass, and can increase it by 1 or 2%. However, excessive
exercise can lead to constant damages to the bones which can cause
exhaustion of the structures as described above. There are numerous
examples of marathon runners who developed severe osteoporosis later
in life.?
http://www.answers.com/topic/osteoporosis
?? male soccer players have higher bone turnover compared with age-
and gender-matched controls. Changes in physical activity level were
associated with changes in bone formation and resorption as evaluated
by bone markers within weeks, and after 2 weeks rest, ICTP was higher
in the athletes than the controls. We conclude that the higher
age-related diminution in BMD, previously reported in former soccer
players compared with age- and gender-matched controls, may be the
result of increased bone resorption, evaluated by ICTP, compared with
the controls.?
http://www.springerlink.com/(3jgcmumixbee2dyayrkqyq45)/app/home/contribution.asp?referrer=parent&backto=issue,7,19;journal,31,122;linkingpublicationresults,1:100120,1
?? athletes have increased bone turnover with a particular stimulation
of bone resorption.?
http://www.extenza-eps.com/WDG/doi/abs/10.1515/CCLM.2004.258
?? if the exercise is maintained, the bone tissue can suffer from
ischemia caused by reduced blood flow into the medullary canal and
hence to the inner two-thirds of the cortex. Site specificity is
caused by the lack, in certain regions of the cortex, of compensating
matrix-consolidation-driven fluid flow which brings nutrients from the
periosteal surface to portions of the cortex. Upon cessation of the
exercise, re-flow of fresh blood into the vasculature leads to
reperfusion injury, causing an extended no-flow or reduced flow to
that portion of the bone most strongly denied perfusion during the
exercise. This leads to a cell-stress-initiated remodeling which
ultimately weakens the bone, predisposing it to fracture.?
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10616033&dopt=Citation
?Bone becomes strong when muscles attached to it become strong.?
?In a meta-analysis, Wolff found that exercise-training programs
prevented or reversed an average of 1% bone loss per year across
randomized control studies. Since bone loss is about 1% a year before
menopause and returns to about 1% a year at approximately 5 years
after menopause, strength training at least can halt bone loss. The
effect was nearly twice as large when women chose to be in the
exercise vs. the control group, so the assumption is that women who
were more enthusiastic about their training worked more intensely and
had better results. Wolff concluded that ?strength training programs
(that failed to show changes in BMD) might not all have imposed the
required unusual strain distributions, high strains, and high strain
rates.?
http://www.elainemansfield.com/exercise%20bone%20density.htm
?Physical activity is considered an important factor in attaining bone
mass. However, the mechanisms by which exercise affects bone
metabolism are not completely understood. The present study was
performed to investigate the effects of aerobic and anaerobic exercise
on bone turnover.? ?While aerobic training led to changes compatible
with reduced bone resorption activity, anaerobic training seems to
result in an overall accelerated bone turnover. Therefore, the impact
of physical activity on bone turnover may depend on the kind of
exercise performed.?
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9844096&dopt=Abstract
?The renewal of bone is responsible for bone strength throughout our
life. Old bone is removed (resorption) and new bone is created
(formation). During childhood and the beginning of adulthood, bone
becomes larger, heavier and denser, bone formation is then more
important than bone resorption.?
http://www.medes.fr/Eristo/Osteoporosis/BoneRemodeling.html
?What kind of training is the best for increasing your bone strength?
Activities that stimulate muscle growth and strength gains also
stimulate the growth of bone and associated connective tissue.
Trainers generally refer to this type of training as "weight bearing"?
http://www.bodytrends.com/articles/benefits/strengthbones.htm
Other resources:
================
http://www.breastcancer.org/bone_causes.html
http://faculty.washington.edu/kepeter/118/notes/bone_intro.htm
http://darkwing.uoregon.edu/~ericdc/physiology.html
Soft bones due to osteomalacia
http://courses.washington.edu/bonephys/hypercalU/opmal2.html
Inside bones
http://www.medes.fr/Eristo/Osteoporosis/BonePhysiology.html
I hope this has answered your question. If not, please request an
Answer Clarification, before rating. I will be glad to assist you
further on this question.
Sincerely, Crabcakes
Search Terms
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Osteoporosis + inactivity
exercise affects bone turnover
Cause + bone loss
exercise + bone remodeling
Bone strength + weight bearing |
