Thesis (Ph. D.)--University of Chicago, Committee on Human Nutrition and Nutritional Biology, March 2001. / Includes bibliographical references. Also available on the Internet.

To determine the influence of running on certain blood-born parameters that are involved in bone metabolism, serum levels of calcium, alkaline phosphatase (ALP, a marker of bone formation), growth hormone (hGH), and parathyroid hormone (PTH), were analyzed in 10 male subjects following a 40 min. run at 70% VO2max. Each trial was preceeded by 1 day of inactivity, a 8-12 hr. fast, and drawing of a baseline blood sample by venipuncture. All other blood samples were taken via an indwelling catheter which was inserted in an antecubital vein immediately following the completion of the exercise bout. When the catheter was in place, an "immediate post" sample was drawn. Subsequent samples were taken at 1, 2, 3, 4, 5, 10, 15, 20, 30, 45, and 60 min. after the immediate post sample. Analysis of serum calcium concentrations demonstrated that levels were significantly elevated by 12% following exercise, going from a fasted level of 9.7 ± .53 mg/dl to post-exercise levels of 11.8 ± .73 mg/dl. Serum calcium remained elevated during the first 4 min. following exercise. By 5 min. post-exercise, calcium levels dropped to levels that were significantly lower than the post-exercise sample. However, serum alkaline phosphatase did not change significantly following exercise, as the values remained within normal range throughout the experimental period. Concentrations tended to decrease over time but were not significantly lower than the preor post-exercise levels by the end of the sampling period. Serum concentrations of hGH were more than doubled following a single bout of exercise, going from 4.0 ± 0.98 ng/ml before exercise to 8.8 ± 1.6 ng/ml immediately post-exercise. Following this initial rise, hGH progressively declined and returned to baseline values by 30 min. post-exercise. The concentrations of PTH did not change significantly following exercise. The postexercise sample tended to be higher than baseline values but were not significantly different. The results presented here indicate that an exercise bout 40 min. at 70% V02max results in an elevation of serum calcium and hGH, but does not alter PTH secretion or ALP activity. The data presented in this study indicate that the temporary rise in calcium following exercise is unrelated to PTH. It is hypothesized that the increase in calcium that we observed is attributable to lactate accumulation that would result from an exercise bout of this nature. The buildup of lactic acid and drop in pH causes a dissolution of the crystaline calcium hydroxyapatite compartment of the skeleton, thus causing an increase in ionized calcium. It is not known whether a single bout of exercise can influence hormonal secretion to a sufficient degree to affect bone density, but the hormonal changes demonstrated here could be involved in long-term effects of training. / School of Physical Education

Age-related bone loss is a serious public health problem affecting 15 to 20 million people in the United States (1). In the last decade, several studies have investigated the effects of repeated bouts of exercise on bone density. Although this increase in bone density is mediated via hormones and/or cellular metabolites few studies have linked the increase in bone density with changes in these hormones or metabolites. Therefore, the purpose of this study was to determine the effect of a single bout of weight bearing exercise on the growth factors that alter bone metabolism. Seven healthy female subjects (age 23 ± 5 yrs.) agreed to participate in this study. A V02 max test was administered to each subject to determine their overall fitness level. A treadmill speed corresponding to 70% of their V02 max was then developed and the subjects ran for 40 minm on the treadmill at that speed. Blood samples were drawn pre and 1, 2, 3, 4, 5, 10, 15, 20, 30, 45, and 60 min post-exercise and assayed for serum growth hormone, calcium, parathyroid hormone, and alkaline phosphatase. No significant change was found in parathyroid hormone, calcium, or alkaline phosphatase serum levels. Growth hormone was found to be significantly decreased 30, 45, and 60 min. post-exercise as compared to pre-exercise levels (7.089, 5.399, 4.728, and 11.28 ng/mL, respectively). While this indicates that exercise may cause a depression in growth hormone levels during recovery, the elevated pre-exercise levels of three of the seven subjects masked the exercise stimulated release of growth hormone. Growth hormone stimulates bone absorption via insulin-like growth factors and the GH data suggests that these hormones may have been released well after our last measurement time point. In conchusion, 40 minutes of running exercise at 70% of V02 max does not produce a change in any of the hormones or metabolic factors directly associated with calcium turnover in the bone, suggesting that acute exercise has no immediate effect on bone metabolism. However, the exercise protocol did stimulate GH release which influences bone growth indirectly by its ability to regulate IGF release. Therefore, even though no acute effects were evident, a single bout of exercise may alter the long term control of bone metabolism. / School of Physical Education