Somatomedin-C, Physical Fitness, and Bone Density*

Kelly, Paul; Eisman, John A.; Stuart, Margaret C.; Pocock, Nicholas; Sambrook, Philip N.; Gwinn, Tom

doi:10.1210/jcem-70-3-718

Cited by 136 publications

(63 citation statements)

References 20 publications

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“…values between our study groups contradict previous findings (12,14) that suggested that the age-associated decline in IGF-I concentration is indicative of reduced physical activity rather than an effect of aging per se. However, whereas Kelly et al (14) indirectly derived VO 2 max. from submaximal exercise tests, a strategy that is unreliable in the elderly (31), aerobic capacity was directly measured in our study participants.…”

Section: European Journal Of Endocrinology (1998) 138contrasting

confidence: 87%

“…A number of authors have suggested that aerobic exercise might restore or maintain the integrity of IGF-I status in later life (12)(13)(14), but these conclusions were inferred from weak statistical correlation (12), predicted rather than directly measured maximal aerobic capacity (VO 2 max.) (14) and on the basis of small increases in IGF-I without comparison against a control group (13).…”

Section: Introductionmentioning

confidence: 99%

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Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

Cooper

Taaffe

Guido

et al. 1998

European Journal of Endocrinology

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To investigate putative abrogating effects of habitual endurance exercise on age-related changes in endocrine function and body composition, we compared insulin-like growth factor-I (IGF-I), sex hormonal status and body composition in 15 Masters runners and 15 minimally exercising men (MEM) aged 60-70 years. A higher maximal oxygen uptake (VO 2 max.) in the runners (41.4 Ϯ 1.6 compared with 27.3 Ϯ 1.4 ml/kg/min, P ¼ 0.0001; mean Ϯ S.E.M.) reflected our group allocations. Analysis of body composition and bone mineral density (BMD) by dual energy X-ray absorptiometry showed no group differences in lean tissue mass or in regional or whole body BMD, but MEM were heavier, reflecting greater adiposity. Of nine muscle groups tested, only quadriceps strength differed significantly, being greater in runners (60.3 Ϯ 2.8 compared with 51.1 Ϯ 2.3 kg, P ¼ 0.02). Total IGF-I (129 Ϯ 10 compared with 124 Ϯ 11 ng/ml, P ¼ 0.72) and IGF-binding protein-3 (2854 Ϯ 94 compared with 2623 Ϯ 128 ng/ml, P ¼ 0.16), were similarly depressed compared with young adult norms in both groups. There was no relationship between total or bioavailable IGF-I and any body composition, BMD or muscle strength variable. In the runners, concentrations of total testosterone (19.1 Ϯ 0.8 compared with 15.0 Ϯ 0.9 nmol/l, P ¼ 0.002) and sex hormone binding globulin (SHBG) (124.4 Ϯ 21.6 compared with 67.7 Ϯ 11.6 nmol/l, P ¼ 0.03) were significantly greater, but the free androgen index was significantly lower (20.7 Ϯ 2.7 compared with 31.4 Ϯ 4.1, P ¼ 0.04). Directly measured free testosterone, however, was similar between the runners and MEM (47.9 Ϯ 1.8 compared with 47.1 Ϯ 2.0 nmol/l, P ¼ 0.80). Therefore the group differences in total testosterone and free androgen index were due to their different SHBG concentrations. Although estrone concentration was higher in MEM (85.1 Ϯ 5.2 compared with 108 Ϯ 6.7 pmol/l, P ¼ 0.03), estradiol concentration was similar between groups (73.0 Ϯ 6.3 compared with 81.8 Ϯ 8.0 pmol/l, P ¼ 0.18), indicating that estrogens were not responsible for the increased SHBG in runners. These results indicate that even high levels of regular endurance exercise do not prevent the decline in the somatotropic axis that occurs with aging. Furthermore, the somatic effects of exercise in older men (reduced adiposity and increased regional muscle strength) occurred independently of somatotropic or androgen status. Although habitual exercise does not influence free testosterone concentrations in older men, it appears to enhance the age-associated increase in SHBG synthesis.

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Section: European Journal Of Endocrinology (1998) 138contrasting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

Cooper

Taaffe

Guido

et al. 1998

European Journal of Endocrinology

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“…The concentration of IGF-I had been known to be influenced by age [1][2][3][4][5][6]. However, there was no reference value for serum IGF-I in adults based on the extraction method, except in a recent Swedish report [7].…”

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confidence: 99%

Serum Insulin-Like Growth Factor-I (IGF-I) in Normal Japanese Adults.

et al. 1995

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Abstract.To evaluate surgical and medical treatment of GH-producing pituitary tumors and GH supplement to GH-deficient patients, we determined the reference values for serum IGF-I in Japanese adults. The serum IGF-I concentration in 454 apparently healthy subjects (246 men aged 21-70 years and 208 women aged 21-72 years) was measured with a commercial RIA kit after acid-ethanol extraction. The concentration of serum IGF-I decreased with age in both sexes. The IGF-I in females was significantly higher than that in males in the group aged 21-30 years and lower in the group aged 61-72 years. We conclude that an age-or sex-related standard is necessary for comparing IGF-I values in patients.

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“…A pivotal mechanism for the improved function is the unique, naturally occurring anabolic effects of exercise ( I ) , such as skeletal and cardiac muscle hypertrophy (2), increased capillarization and mitochondria (3), and increased bone density (4). Because exercise stimulates GH secretion (5) and because GH (either directly or in combination with IGF-I) is a potent growth factor for skeletal iind heart muscle (6-9), it is not surprising that many investigations in both human beings (10, I I) and other species (12)(13)(14) indicate that GH plays an important role in the adaptation to exercise.…”

mentioning

confidence: 99%

Effect of Growth Hormone Suppression on Exercise Training and Growth Responses in Young Rats

et al. 1994

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ABSTRACT. Exercise training improves maximal oxygen uptake and endurance times in adult human beings and other animals. The mechanism of this improvement results in part from anabolic effects of exercise and may be mediated by growth hormone (GH). Little is known about the role of GH in the adaptation to exercise in younger, stilldeveloping organisms. To examine this role, we began a 4-wk treadmill exercise training protocol in 14-d-old female rats. GH was suppressed by passive immunization with anti-GH releasing hormone antisera. There were four experimental groups: I) GH-control (normal GH secretory capacity), untrained (n = 21); 2) GH-suppressed, untrained (n = 13); 3) GH-control, trained (n = 14); and 4) GHsuppressed; trained (n = 11). At the end of the training period, maximal oxygen uptake and treadmill endurance running time were measured. Serum GH and IGF-I were assessed using RIA, and whole hind limb musculature succinate dehydrogenase (an indicator of mitochondria1 function) was measured with standard fluorometric technique. Body weight gain was markedly reduced in GHsuppressed rats (mean, 54% of GH-controls in untrained rats and 55% in trained; p < 0.05). No apparent effect of training on linear growth was observed. As expected, serum IGF-I was markedly reduced by GH suppression, but no exercise-induced increase occurred in IGF-I as a result of training in either the GH-control or GH-suppressed rats. In GH-control rats, maximal oxygen uptake and succinate dehydrogenase were 69% and 25% greater, respectively, in trained compared with untrained rats (p < 0.05). Despite GH inhibition, similar increases were found in the trained GH-suppressed rats (68% greater than controls for maximal oxygen uptake and 34% for succinate dehydrogenase, In mature human beings and animals of many species, increased physical activity leads, to improved functional capabilities often measured as increased Vozmax or exercise endurance time. A pivotal mechanism for the improved function is the unique, naturally occurring anabolic effects of exercise ( I ) , such as skeletal and cardiac muscle hypertrophy (2), increased capillarization and mitochondria (3), and increased bone density (4). Because exercise stimulates GH secretion (5) and because GH (either directly or in combination with IGF-I) is a potent growth factor for skeletal iind heart muscle (6-9), it is not surprising that many investigations in both human beings (10, I I) and other species (12)(13)(14) indicate that GH plays an important role in the adaptation to exercise. Despite this finding, the role of GH in exerciseinduced growth is not understood, and evidence exists that exogenous GH administration does not enhance the effect of exercise training on muscle growth or strength in young, welltrained adult males ( 15-17).Far less is known about responses to repeated bouts of physical activity in the younger, developing organism where overall body growth is rapid and secretory patterns of growth factors (such as GH) are in a state of flux (18). The purpose of this ...

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Somatomedin-C, Physical Fitness, and Bone Density*

Cited by 136 publications

References 20 publications

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

Serum Insulin-Like Growth Factor-I (IGF-I) in Normal Japanese Adults.

Effect of Growth Hormone Suppression on Exercise Training and Growth Responses in Young Rats

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