Exercise effect on growth

EFFECT OF EXERCISE ON CALCIUM HOMEOSTASIS

AND GROWTH FACTORS

Relationship Between Calcium Homeostasis and Exercise

With regard to the effects of exercise on serum calcium and parathyroid hormone (PTH) concentrations, the data are somewhat equivocal, and said effects may depend on the intensity and duration of the exercise regimen and the training status of the individual. Increases in ionized calcium during exercise appear to be related directly to exercise-induced acidosis and therefore, exercise intensity.  However, the increase in serum ionized calcium concentrations during and following prolonged endurance exercise does not result in a decrease in serum PTH concentrations, possibly because of the increase in catecholamines. Short-duration, high-intensity exercise increases ionized calcium with a concomitant decrease in serum PTH concentrations.  Training status appears to affect the exercise-associated response of PTH.  Salvesen and co-workers found that following 50 min of running, well-trained men experienced an increase in serum PTH concentration whereas fire-fighters, who were less trained, did not.  Both groups of men experienced an increase in serum calcium.  However, other studies report that resting PTH concentrations are actually lower in trained vs untrained individuals. It can be concluded from these studies, as well as others, that endurance exercise must last at least 30 min in order to elicit an increase in circulating PTH concentrations. 

Studies involving the effect of resistance training on serum PTH concentrations are conflicting. Rong and co-workers reported an increase in serum PTH concentrations immediately following a period of strength training, whereas others report a decrease. Bell and co-workers studied a relatively small number of male weight-lifters compared with age-matched controls, and although they did not find statistically different PTH concentrations, they did speculate that subtle differences in PTH concentrations may have been of sufficient magnitude to produce the increases in serum 1,25 dihydroxyvitamin D (1,25-(OH)2 D) and urinary cyclic AMP concentrations that were observed. These differences in PTH response to exercise could be due to differences in the intensity and duration of the training periods, as well as acute vs long-term exercise effects on PTH.

Physio Guideline

 

 Relationship Between Growth Factors and Exercise

Growth hormone (GH) and insulin-like growth factor (IGF)-1 have major influences on bone growth and mineralization and are reviewed in detail elsewhere. Briefly, GH and IGF-1 have direct and indirect effects on osteoblasts and osteoclasts. Bone formation and resorption increase when GH is given to GH-deficient individuals, indicating an increase in bone modeling and/or remodeling. GH and IGF-1 increase bone size and BMC, but not BMD. Whereas the GH–IGF axis is likely responsible for the large increases in bone length and bone circumference during early puberty, increased concentrations of estrogen may decrease endosteal resorption and lead to increased cortical thickness in mid to late puberty. Estrogen also plays an important role in the closure of the growth plates.

Duration and intensity of exercise have significant impacts on GH and IGF-1 secretion. Acute endurance exercise results in a significant increase in serum GH concentrations, whereas acute resistance exercise results in a significant decrease in serum IGF-1 and IGF-binding protein (IGFBP)-3 concentrations. Furthermore, skeletal muscle IGF-1 expression is downregulated at the mRNA level during the initial recovery phase following resistance exercise , but increases to levels higher than pre-exercise values at 24 and 48 h after the exercise bout. Treadmill running appears to produce similar results. It is not known what happens to IGF-1 mRNA in bone cells after acute bouts of exercise.

Exercise training, both resistance and endurance, results in significant increases in serum IGF-1 concentrations, which have been observed in both young and older individuals.

 

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