Have been tested that exercise at an early age by promoting games and sports from kindergarten, gives effects on bone mineral density are more stable and higher than in subjects who were not stimulated early.
The normal daily physical activity, not subject to specific programs is insufficient stimulus to improve bone mass. Definitely overload exercises allow significant improvements in both sexes and any age on BMD
Excessive physical activity and often highly competitive sport beyond the tolerances of bone stimulation causing negative effects on both physiology and structure of bone.
The effects of exercise on bone tissue are possible only when a food base is established. The effects of recommended intakes of calcium are enhanced by the addition of exercise. This effect is most evident in aged subjects and in women in perimenopausal period.
INTRODUCTION
Osteoporosis is a systemic disease characterized by low bone mass and architecture poor, both increase bone fragility leaving it susceptible to fracture.
One in three postmenopausal women in particular have advanced osteopenia francs osteporosis values. Interestingly, this decline in BMD was significantly correlated with levels of sarcopenia, ie loss of muscle tissue, which characterizes the sedentary elderly. This correlation is less significant in men and women of the same age but who remain physically active. Per year in Europe is recorded about 650,000 hip fractures, which cause a 20% mortality and 50% partial or complete disability.
Other variables or factors that may affect bone metabolism, bone would be the use of psychoactive drugs, loss of muscle strength. In rlacion to fractures, loss of stability and balance, and lost some senses like hearing and sight, predispose to falls and fractures.
In this article we will discuss the relationship between exercise and bone and try to give some idea about the intensity of exercise for optimizing exercise and diet for bone health. (1)
WHAT IS THE MECHANISM MEDIATOR BETWEEN THE EFFECTS OF EXERCISE AND BONE?
One of the most important factors related to structural characteristics. The functional demand imposed on the bone is a major determinant in the structural characteristics of this. The intensity of the applied stress on the bone segment affects its geometry, its microarchitecture and composition of the matrix (2). Definitely the intensity of the burden for the recently described effects is important and not the duration of effort, a minimum strain (a strain is equal to one unit of strength by amending the arquitctura moments bone) is required to produce an effect on bone. It has developed a theory which translate mecanoestatos impact force signals that allow an imbalance between osteoblast activity (which builds bone) and osteoclasts (bone absorbing). It is not clear if that signal increases or decreases osteoblastic activity osteoclastic or both. The strain imposed on the active bone osteocyte initiating an increase in the production of prostacyclin and the osteoblast produces prostacyclin and prostaglandin E2, minutes later it has been shown that the osteocyte is an increase of glucose 6 phosphate dehydrogenase and 24 hours later an increase in mRNA for growth factors (3).
AT WHAT AGE THE EXERCISE HAS AN EFFECT ON THE BONE?
First we have to take into account that the growth of bone mass is acquired until the third decade and remains more or less constant until 50 and then begins to decline, there are few studies that have highlighted that the intake of calcium with physical activity completed in the first 30 years of life allows these individuals end up at that age with a higher bone mass, cross-sectional studies have also shown that subjects until 50 years of age who participate in exercise programs have an average between 8 and 12% higher BMD than their peers without exercise, after 50 years this difference is only 6%. In subjects over 50 years has been observed in 1% increments in BMD (4).
26 children under 11 years were subjected to a gymnastics training 3 hours per day and three hours watching television. A second group of the same age was only 1 hour a day of intense exercise and 4 hours of television. We obtained a much higher correlation between BMD and number of hours of exercise in the most active group of both arms and spine. The Amsterdam study on the health and growth habit of life correlated with lumbar BMD at 30 years of age.
WHAT IS THE TYPE OF EXERCISE MORE EFFECTIVE?
Paraplegic subjects unable to walk have a 40% decrease in BMD within the pelvis and 25% in the lower limbs after a year of detention. Patients undergoing spaceflight or the absence of gravity have a 0.5% loss of bone calcium per month. It is unclear if this negative balance of bone is the result mainly due to increased absorption or a decrease in training. It has been shown that passive mechanical stress on bone of a paraplegic may decrease bone loss (5).
On the other hand, several studies have shown that athletes have between 25 and 30% more BMD than a commonplace subject with normal activity, including overhead activities including walking have a greater impact on bone than those who are swimming or cycling. Postmenopausal adult women subjected to work overload after 9 months the lumbar spine increased by 1.6% while the control women have decreased by 3.6% from baseline. In children under stress and impact activities have increased both in femoral neck BMD as radio, trochanter and lumbar spine (6).
In a longitudinal study in which 22 young cyclists were subjected to 10 hours per week of exercise bike for 2 years, BMD was lower than control subjects.
All this helps to understand that only the high-resistance exercise and short-term impact stimulates BMD and that this effect is local and not systemic thing that becomes clear when we see that the cortical area of the humerus of the active arm of a tennis player holds up to 20% more bone than the contralateral arm
Only women who walked over 10 miles per week were so slight but significant higher BMD than those who walked only 1.5 km per week. Moreover postmenopausal women after 6 months of a program that included jumps, there was an increase of 4% in BMD. Finally do 10 minutes of work load is more productive than 30 minutes without charge for bone mass, this has been clearly demonstrated also in animals.
DOES THE EFFECT OF EXERCISE IS PERMANENT?
Unfortunately not. According to the theory of bone mass mecanoestatos always needs to be adapting to the stress of mechanical load. Several major groups of adult women have been trained for 2 years increased lumbar bone mass by 6% within 1 year of rest, or normal life without regular exercise, these women were up to 1% less than the control subjects ( 7).
However, in follow-up studies in children before age 30 have an increased bone mass has been observed to have a protective effect over a lifetime.
The answer to this type of exercise that undoubtedly has an interindividual variability and possibly this in relation to genetic polymorphism, for example it was found that subjects with different amounts of Vit.D receptors have different response to the same type of stimulus.
EXERCISE IS THE EXCESS IS DANGEROUS?
There is no evidence that this type of exercise causes adverse effects or abnormal level of growth in children, however this type of exercise stimulates growth hormone synthesis achieving a more complete expression of his genes on height. But young athletes in competitive sports under the presence of oligomenorrhea and amenorrhea correlates with bone loss and bone fracture stress (8).
Approximately 50% of highly competent women have had some experience oligo-or amenorrheic compared with only 5% of the population in general.
The belief that the effect of resistance exercise produce a negative effect on the joints in old age has never been evidenced when the workload was appropriate for the level of functional ability of the musculature of each.
In osteopenic women with low BMD or inappropriate, exercises such as crunches or flexion and extension exercises column due to the effects of compression on the vertebral bodies can cause fractures.
IS THERE ANY INTERACTION BETWEEN EXERCISE AND DIET?
Studies in monozygotic twins has been established that environmental factors like diet and exercise, account for 20% of the varians of each. Several factors associated with diet, have an influence on bone mass and physiology, calcium, phosphorus, fluorine, zinc, copper, magnesium, manganese, sodium, potassium, Vit. K, and other bioactive substances such as phytoestrogens. Probably all this amount of nutrients in an adequate intake are necessary for the exercise has a positive effect on bone mass, however there are compelling studies that indicate that both the size composition and bone density in communities with low intakes calcium are similar to communities with high calcium intake (9).
In a longitudinal study in postmenopausal women, in women treated with exercise only had a decrease in BMD of the forearm, the other group treated with exercise and calcium showed the same phenomenon, while the group treated with exercise and estrogen present in increased BMD. This forces us to consider hormone replacement therapy as an additional factor for success in the exercise plan designed to preserve or increase bone mass in postmenopausal women.
Other studies have clearly demonstrated that the increase in BMD was positively correlated with calcium intake was only when accompanied with an exercise program (10).
Finally it is interesting that the intestinal absorption of calcium is reduced when bone mechanical demands are low. In children when calcium demands are met exercise is the most important determining factor in bone mass.
Special mention needs zinc and its influence on estrogen receptors and Vit.D, on the metabolism of nucleic acids on collagen and mucopolysaccharide metabolism on the activity of collagenase, on carbonic anhydrase on alkaline phosphatase and prostaglandins, all factors involved in the mechanisms of bone metabolism. Groups of animals treated with the same exercise programs and diet, femoral neck BMD was higher in those with a zinc supplement in the diet.
credit to: García Pan, D., Saavedra C.
Tags: Bone Health, bone mass, bone mineral density, exercise, nutrition, physical activity
