PubMed Health⌕ Search

Biomedical subjects

A C Hackney

Publications and source records attributed to A C Hackney.

At least 19 recordsLinked to original sources
PubMed2006

Physiological day-to-day variability of select hormones at rest in exercise-trained men.

The purpose was to determine the day-to-day variability of total testosterone (tT), total T4 (tT4), total 3,5,3'-T3 (tT3), and cortisol (C) levels in exercise-trained men [no.=63, 24+/-4 yr (X+/-SD)]. Resting blood samples were collected at the same time of day (morning) over 3 consecutive days, 24 h apart, under controlled conditions. Subjects were instructed to minimize mental stress and physical activity and to maintain a consistent diet, and sleep patterns during the period of blood collections. Radioimmunoassay procedures were used to measure all hormones. Repeated measures analysis of variances were used to test for differences within each hormone across days, and intra-class correlations (ICC) and typical error were used to assess reliability of hormone concentrations across days. Results revealed resting hormonal values were within accepted clinical ranges. No significant mean differences (p>0.05) from day-to-day were found in any of the hormones. Furthermore, each hormone displayed highly significant (p<0.01) ICC values; tT 0.891, tT4 0.861, tT3 0.705, C 0.886, and consistent daily typical errors. These findings suggest resting tT, tT4, tT3, and C concentrations are not highly variable and appear reliable from day-to-day in exercise-trained men. If researchers measure any of these hormones at rest, before and after (ie, 24-48 h later) an experimental exercise treatment, they can presume that any changes seen at the 24-48 h point (that exceed the typical error appropriately) are due to their treatment and not an artifact of day-to-day variability.

Adult↗
PubMed2005

Testosterone and human performance: influence of the color red.

This study examined the testosterone responses of men to an exercise bout simulating a competitive sporting effort in order to determine if the wearing of red-colored apparel influenced the hormonal response. Male subjects (n = 10) were placed into sets of matched-pairs and performed VO(2max) cycle ergometry exercise test to exhaustion to simulate the competitive effort. Each member of a pairing was randomly assigned to one of two treatment groups-the wearing of red-colored clothing, or the wearing of black-colored clothing. Blood samples were collected before exercise (REST), an immediate postexercise sample was collected at exhaustion (EXH), and a final sample was taken at 15 min into recovery (REC) from exercise. Blood was biochemically analyzed for total testosterone. In response to the exercise, performance characteristics (i.e., VO(2max) and maximal workload) of treatment groups did not differ significantly. A significant increase (P < 0.01) in the testosterone was observed in both treatment groups postexercise at EXH and at REC as compared to REST. However, no differences were observed between treatment groups in the before or postexercise hormonal concentrations. These findings suggest that the wearing of red-colored apparel had no affects on the testosterone responses to an exercise bout simulating a competition.

Analysis of Variance↗
PubMed2005

Testosterone and endurance exercise: development of the "exercise-hypogonadal male condition".

During the last 30 years a large number of research studies have been conducted examining reproductive endocrine dysfunction in exercising women. The number of similar studies examining men is still relatively small. Nevertheless, an increasing amount of research studies in men indicate endurance exercise training has significant effects upon the major male reproductive hormone, testosterone, and the hypothalamic-pituitary-testicular axis that regulates reproductive hormones. This review article addresses one reproductive endocrine dysfunction found in exercising men, what has been deemed the "exercise-hypogonadal male condition". Specifically, men with this condition exhibit basal (resting-state) free and total testosterone levels that are significantly and persistently reduced. The exact physiological mechanism inducing the reduction of testosterone is currently unclear, but is postulated to be a dysfunction (or perhaps a readjustment) within the hypothalamic-pituitary-testicular regulatory axis. The time course for the development of the "exercise-hypogonadal condition" or the threshold of exercise training necessary to induce the condition remains unresolved. The potential exists for these reduced testosterone levels within the exercise-hypogonadal male to disrupt and be detrimental to some anabolic or androgenic testosterone-dependent physiological processes. Unfortunately, extremely few research studies have addressed whether such processes are affected, and thus findings are inconclusive. Conversely, the alterations in testosterone levels brought about by endurance exercise training have the potential for cardiovascular protective effects and thus could be beneficial to the health of these men. Current evidence suggests this condition is limited to men who have been persistently involved in chronic endurance exercise training for extended periods of time (i.e., years). Many questions, however, regarding the male reproductive endocrine adaptive process to exercise and exercise training remain unanswered, necessitating the need for further research on this topic.

Cumulative Trauma Disorders↗
PubMed2004

Relationship between stress hormones and testosterone with prolonged endurance exercise.

Previous pharmacological and pathological studies have reported negative relationships between circulating testosterone and certain stress hormones (i.e., cortisol and prolactin) in humans. These relationships have subsequently been used in hypotheses explaining the subclinical resting testosterone levels often found in some endurance-trained males, but as of yet no one has specifically examined these relationships as they relate to exercise. Thus, we examined the relationship between total and free testosterone levels and cortisol, and between total and free testosterone and prolactin following prolonged endurance exercise in trained males. Twenty-two endurance-trained males volunteered to run at 100% of their ventilatory threshold (VT) on a treadmill until volitional fatigue. Blood samples were taken at pre-exercise baseline (B0); volitional fatigue (F0); 30 min (F30), 60 min (F60), and 90 min (F90) into recovery; and at 24 h post-baseline (P24 h). At F0 [mean running time = 84.8 (3.8) min], exercise induced significant changes (P<0.05) from B0 in total testosterone, cortisol and prolactin. All three of these hormones were still significantly elevated at F30; but at F60 only cortisol and prolactin were greater than their respective B0 values. Free testosterone displayed no significant changes from B0 at F0, F30, or the F60 time point. At F90, neither cortisol nor prolactin was significantly different from their B0 values, but total and free testosterone were reduced significantly from B0. Cortisol, total testosterone and free testosterone at P24 h were significantly lower than their respective B0 levels. Negative relationships existed between peak cortisol response (at time F30) versus total testosterone (at F90, r=-0.53, P<0.05; and at P24 h, r=-0.60, P<0.01). There were no significant relationships between prolactin and total or free testosterone. In conclusion, the present findings give credence to the hypothesis suggesting a linkage between the low resting testosterone found in endurance-trained runners and stress hormones, with respect to cortisol.

Adult↗
PubMed2003

Basal testicular testosterone production in endurance-trained men is suppressed.

Research indicates that endurance-trained men have lower basal testosterone concentrations than age-matched sedentary control men. The physiological cause for this finding is uncertain. Therefore, we examined the peripheral component in the hypothalamic-pituitary-testicular (H-P-T) axis in endurance-trained men to determine if their basal testicular production of testosterone was compromised. The study design was retrospective, with a case-control approach. Age-matched, trained (n=5, TRN) and sedentary control men (n=6, SED) were infused with gonadotrophin-releasing hormone (GnRH) to induce testicular testosterone production via subsequent luteinizing hormone elevations. Testosterone production rate was statistically analyzed with adjustments for confounding factors and compared between groups. The basal testosterone concentrations differed significantly between the TRN and SED groups [pooled mean values; 13.9 (3.0) nmol x l(-1) vs 23.4 (3.2) nmol x l(-1), P<0.05]. The testosterone production rate was significantly lower (approximately 20-30%; P<0.05) in the TRN men as compared with the SED men following GnRH infusion. It was concluded that the exogenous stimulated testicular production rate of endurance-trained men is suppressed. This finding may account, in part, for the lower circulating basal testosterone concentrations found in these men. The present evidence supports the hypothesis that endurance exercise training induces a degree of peripheral adaptation (i.e., testicle) in the H-P-T axis. Whether this adaptation in the axis is a permanent or transient phenomenon in these men remains to be determined.

Adaptation, Physiological↗
PubMed2003

Day to day variability in the transferrin receptor/ferritin index in female athletes.

OBJECTIVE: To determine the within subject (day to day) variability for variables reflecting iron status (concentrations of ferritin and soluble transferrin receptor (sTfR), and the sTfR/logFerr index) in female athletes during a training camp, and in female control subjects. RESULTS: The error for ferritin concentration was nearly twice as high in athletes as in controls, that for sTfR concentration was identical in the two groups, and that for the sTfR/logFerr index was about 50% higher in athletes than in controls. CONCLUSIONS: The within subject, day to day error for the sTfR/logFerr index computed from data recorded for untrained subjects cannot serve as a reference value for training athletes. When the sTfR/logFerr index is used to monitor iron stores in athletes, an error value of 0.20 should be used, because determination of the index after a few days of rest may not be feasible.

Adult↗
PubMed2003

Relationship between caloric intake, body composition, and physical activity to leptin, thyroid hormones, and cortisol in adolescents.

This study examined the interrelationships between (1) the hormones leptin, TSH, free T3, and cortisol, and (2) caloric intake, body composition, and physical activity to these select hormones in adolescent boys and girls (n = 125, age = 13.4 +/- 0.9 years). The data indicate that adolescent boys and girls have some common hormonal interrelationships. However, certain hormonal relationships are not in agreement with reports for adults, suggesting that researchers should not assume that all endocrine findings in adults are automatically applicable to adolescents.

Adolescent↗
PubMed2002

Resting thyroid and leptin hormone changes in women following intense, prolonged exercise training.

This study examined whether free (f) triidothyronine (T3), f thyroxine (T4), thyroid stimulating hormone (TSH), and leptin concentrations at rest changed in response to 20 weeks of exercise-training. Two groups of women were recruited for participation in the study, collegiate athletes ( n=17) and sedentary controls (n=4). Exercise training consisted of daily athletic activity such as rowing, running, and weight lifting. Subjects were initially grouped into rowers and controls. However, earlier suggested criteria were further used to categorize hormone changes (percentages) in the subjects into (+) responders (increases), (-) responders (decreases), or non-responders (no changes). The fT3 results of the rowers revealed two distinct categories of responses, (-) responder (all decreases; n=10) and non-responder (no change; n=7) rowers. In the responders fT3 concentration decreased (P<0.05) from baseline (BL) during an intense training period [(mean SEM) at 5 weeks by -28.2 (6.2)% and at 10 weeks by -24.9 (7.9)%], then returned towards BL levels (20 weeks compared to BL, P>0.05). Similar changes (P<0.05), at comparable times, were noted for leptin and TSH concentrations in the (-) responder rowers. The non-responder rowers and control subjects displayed no significant (P>0.05) hormone changes over the 20 weeks. The hormone changes observed in the (-) responder rowers were not significantly (P>0.05) correlated with changes in body composition or hydration status during the study. The mechanism for the hormone changes in the (-) responder rowers is unclear. We speculate the decrease in concentrations of TSH and fT3 could be attributable to a lower hypothalamic-pituitary signaling action, and this is related to the decreased leptin concentrations, and could represent a possible means of energy conservation in these exercising women.

Adult↗
PubMed2002

Training intensity influences leptin and thyroid hormones in highly trained rowers.

Leptin (L) is associated with body-weight-regulating and adipostatic functions. Its receptors also may be found centrally. Thyroid hormones regulate metabolic processes mainly by binding at peripheral receptors. Aim of this study was to show if there is a link between those central and peripheral regulation systems and to investigate the influence of different training intensities on L and the hypothalamic-thyroid-axis (HTA) in highly trained rowers. Six rowers (18.9 +/- 2.6 y; BMI 22.8 +/- 2.1 kg/m (2)) undertook high intensity resistance training (RT) for three weeks followed by three weeks of endurance training (ET). After each training cycle the subjects had one week for recovery (R1, R2). Blood samples were taken before and at the end of RT, R1, ET and R2. L, thyroid stimulating hormone (TSH), free T3 (fT3) and free T4 (fT4) were measured. After RT, a significant reduction in L, TSH and fT3 was found (p < 0.05). fT4 was unchanged. L remained decreased until the end of R1. After ET, a significant increase of TSH was found. L correlated to basal TSH levels (r = 0.49, p = 0.006) during R. BMI and body fat were unchanged throughout the study and were not correlated with hormonal levels. We speculate a high energy flux during intensified training (RT) caused the decrease of L and the HTA, independent of BMI or body fat. Thus, we conclude a depression of L and HTA is associated with training intensity.

Adolescent↗
PubMed2001

Influence of prolonged continuous exercise on hormone responses to subsequent exercise in humans.

This study examined the possibility that fatigue may modify the hormone responses to exercise. A group of 12 endurance trained athletes ran for 2 h (blood lactate concentrations of approximately 2 mmol x l(-1)) in order to induce fatigue. The subjects exercised for 10 min at 70% maximal oxygen uptake before (1st test) and after (2nd test) the 2 h run to assess hormone responsiveness. A 1 min anaerobic power test was performed to assess muscle power. Cortisol, growth hormone, testosterone and insulin concentrations were determined before and after the 1st and 2nd tests. The 1st test resulted in increases in concentrations (P < 0.05) of cortisol and growth hormone, a decrease in insulin concentration (P<0.01) and no change in testosterone concentration. The 2 h run caused decreases of insulin, increases of growth hormone concentration and variable responses in the concentrations of cortisol and testosterone. The 2nd test decreased insulin concentration further (P < 0.05), but responses of the concentrations of testosterone, growth hormone and cortisol were variable. In 6 subjects (group A) cortisol displayed an increase [mean (SD)] from baseline concentrations [+ 304.0 (60.0) nmol x l(-1)], while in the other 6 subjects (group B) a decrease or no change was seen [+ 3.1 (5.3) nmol x l(-1), between groups, P<0.05]. Growth hormone concentration was substantially higher in group A [+ 14.7 (4.8) ng x ml(-1)] than group B [+ 6.0 (2.9) ng x ml(-1)] following the 2nd test. In group A anaerobic muscle power was higher, while in group B it was lower, after the 2 h run than before the 2 h run (P < 0.05). The findings suggest that fatigue from prolonged endurance activity may introduce a resetting in the pituitary-adrenocortical component of the endocrine system, expressed either by intensified or by suppressed endocrine functions.

Adult↗
PubMed2001

Endurance exercise training and reproductive endocrine dysfunction in men: alterations in the hypothalamic-pituitary-testicular axis.

Research indicates that endurance exercise training has significant effects upon the reproductive endocrine system of humans. Until recently, this effect was thought to be limited primarily to women. However, a growing body of evidence demonstrates that the male reproductive endocrine system is also effected. Specifically, the circulating hormonal levels of testosterone are found to be at low concentrations; and, the hypothalamic-pituitary-testicular axis that regulates testosterone production is altered in endurance trained men. The physiological mechanism inducing the lower testosterone is currently unclear; but in many respects, these men display hypogonadotropic hypogonadism characteristics. Currently, the time course of the changes in the reproductive endocrine system is unresolved and in need of much furthers scientific investigation. The evidence available, however, suggests that a slowly developing process requiring years of exercise training results in these changes. Potentially, the lowered testosterone levels of the endurance-trained male could disrupt some of their anabolic or androgenic dependent processes. To date, there are only a limited number of findings suggesting that a consistent disruption of testosterone dependent processes occur due to endurance exercise training (e.g., oligo-spermatogenesis). Conversely, the alterations in testosterone concentration brought about by endurance training could have cardiovascular protective effects and thus be beneficial to the health of these men.

Exercise↗
PubMed2000

Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise.

Very little is known about the cardiovascular responses of exercising individuals when exposed to carbon monoxide (CO). Sixteen healthy nonsmoking men aged 18-29 years participated in the study. Using a combination of exposures to CO by breathing from a bag or in an environmental chamber, subjects performed a randomized sequence of brief (5 min) multi-level treadmill and hand-crank exercises on different days at less than 2% carboxyhemoglobin (COHb) and after attaining target levels of 5%, 10%, 15%, and 20% COHb. To assess cardiac function changes we employed noninvasive impedance cardiography (ICG) and three-lead electrocardiograms (ECG). The ICG was used to estimate cardiac output, stroke volume, heart rate, cardiac contractility, and time-to-peak ejection time. The ECG was used to assess myocardial irritability and ischemia, and changes in cardiac rhythm. The results showed that the cardiovascular system compensated for the reduced O2-carrying capacity of the blood by augmenting heart rate, cardiac contractility, and cardiac output for both upper-body and lower-body exercise. While this mechanism served well in submaximal exercise, the enhanced cardiovascular response to exercise was not without physiological costs because it began to fail at moderate levels of CO exposure and exercise. We concluded that young, apparently healthy men can perform submaximal upper and lower-body exercise without overt impairment of cardiovascular function after CO exposures attaining 20% COHb.

Adolescent↗
PubMed2000

Diclofenac sodium (Voltaren) reduced exercise-induced injury in human skeletal muscle.

PURPOSE: To examine the effects of prolonged systemic administration of diclofenac sodium (Voltaren), a nonsteroidal anti-inflammatory drug, on objective indices of exercise-induced muscle damage in humans. METHODS: Fifty-four volunteers (mean age, 26.4 yr; range, 18-35) participated in this randomized double-blind, placebo-controlled trial. To achieve steady-state tissue levels, either placebo or diclofenac was orally administered two times a day for 27 consecutive days. A strenuous 20-min stepping exercise program, about which the subjects were unfamiliar, was conducted on day 15. Creatine kinase (CK) activities were measured immediately before the exercise session and on days 16, 18, and 27. Vastus lateralis muscle samples were obtained immediately before exercise and on day 27 for subsequent histological characterization of muscle inflammation. RESULTS: The preexercise muscle samples revealed no difference in muscle damage between the two groups. However, the postexercise muscle samples showed that the diclofenac-treated group demonstrated less muscle tissue damage than placebo-treated subjects (P = 0.002). The administration of diclofenac also resulted in a significant lowering of post-/pre-exercise CK ratios on days 18 (P = 0.03) and 27 (P = 0.02) compared with the placebo group, an indirect finding that supports the possibility of diclofenac reducing exercise-induced muscle damage. CONCLUSION: These findings demonstrate preadministration of diclofenac (in accordance with tissue half-life pharmacokinetics) significantly reduces quantitative indices of exercise-induced skeletal muscle damage in human muscle.

Administration, Oral↗
PubMed2000

The Effect of sex steroid hormones on substrate oxidation during prolonged submaximal exercise in women.

In animals, female sex steroid hormones (SS, estrogens-progesterone) influence the energy substrate that is metabolized. Human research on this issue is controversial. This study examined whether changes in circulating SS hormone levels affected the carbohydrate-lipid metabolism during submaximal prolonged (60 min) exercise. Young, physically active females were studied. Four were classified as anovulatory-oligomenorrheic and four were classified as ovulatory-eumenorrheic. Subject responses were pooled to form one group (n = 8) and then their responses under low (L) and high (H) pharmaceutically manipulated SS hormone conditions were examined. During exercise, the mean oxygen consumption levels were 1.70 +/- 0.10/ x min(-1) for L-SS and 1.75 +/- 0.11/ x min(-1) for H-SS (p = 0.07), respectively. The respiratory exchange ratio (RER) responses were significantly different during exercise between the conditions: 0.93 +/- 0.04 for L-SS and 0.90 +/- 0.04 for H-SS (p < 0.05), respectively. RER responses were utilized to calculate substrate oxidation. Significantly less carbohydrate oxidation was found in the H-SS condition as compared to the L-SS condition (p < 0.05). Lipid oxidation was also significantly different, but for this measure, the levels of oxidation were greater in the H-SS than in the L-SS condition (p < 0.05). Finally, total energy expenditure for the 60 min of exercise was not significantly different between the hormonal conditions. Results suggest that sex steroid hormones have an impact upon substrate oxidation in women during exercise. Specifically, high circulating concentrations of the SS hormones result in an enhanced reliance upon the oxidation of lipid as an energy substrate and consequently induce a reduction in carbohydrate oxidation. The mechanism inducing this "metabolism shift" appears due to sex steroid hormones directly and indirectly increasing lipid mobilization and lipolysis.

Adult↗
PubMed1999

Twenty-four-hour cortisol response to multiple daily exercise sessions of moderate and high intensity.

The aim of this study was to characterize and describe the cortisol responses in athletes over a 24-h period on different days involving multiple exercise sessions of varied intensity. Seventeen endurance athletes volunteered to undergo three experimental treatment conditions: (a) a control day involving no exercise; (b) an exercise day with two sessions of high-intensity exercise; and (c) an exercise day with two sessions of moderate-intensity exercise. Significant changes (P < 0.01) were found owing to the influence of both types of exercise during the daytime (high-intensity exercise producing a greater cortisol response than moderate intensity). At night after the moderate-intensity exercise (at selected times), cortisol response was significantly less than during the control condition at corresponding times (P < 0.05). After high-intensity exercise (at selected times), cortisol levels were significantly less (P < 0.05) than in the control condition at corresponding times. Additionally, certain night-time responses after the high-intensity exercise were significantly less than the moderate-intensity exercise responses at similar time points. The results indicate that daytime multiple exercise sessions produce suppressed cortisol levels at night, and the magnitude of this effect is dependent upon the intensity at which the daytime exercise is performed. The physiological mechanism inducing this effect upon cortisol levels at night is unclear from the present data.

Adolescent↗
PubMed1999

Blood leukocyte and glutamine fluctuations after eccentric exercise.

Skeletal muscle, as a producer of glutamine, is important for lymphocytes, monocytes and macrophages. Exercise-induced muscle damage could burden the immune system by concurrently eliciting a local inflammatory response and decreasing glutamine availability. The aim of this study was to determine whether blood leukocyte and glutamine concentrations were affected in individuals with high serum creatine kinase (CK) activity (indirect indication of muscle damage) compared to those with no change in CK. Twelve females performed maximal eccentric resistance exercise using one arm and one leg. Blood leukocyte subsets and glutamine were measured at 24 and 0 h pre-exercise, and post-exercise at intervals up to 9 d post-exercise. Eleven subjects were placed in High (n = 6) and Low CK (n = 5) groups. Lymphocytes, (total, natural killer, and T), monocytes, and granulocytes did not change significantly in either group, at any time. Whole blood glutamine concentration decreased (p < 0.05) from 437 microM pre-exercise to 332 microM 3 d post-exercise in both groups. The decrease in glutamine suggests that the metabolism of the muscle may be affected by this exercise, however, the occurrence of this decrease in both groups suggests that this change was not a response to muscle damage.

Adult↗
PubMed1998

Effects of endurance exercise on free testosterone concentration and the binding affinity of sex hormone binding globulin (SHBG).

Our purpose was to examine the changes in free testosterone concentration following moderately prolonged endurance exercise to determine whether such changes were due to alterations in the binding affinity of sex hormone binding globulin (SHBG). Ten trained men completed control (45 min rest) and exercise (45 min @ 70% VO2max) experimental sessions. Blood samples were collected before (pre-) and immediately after (post-) each of the sessions and analyzed for total testosterone, free testosterone, LH, FSH, cortisol, estradiol, SHBG, epinephrine and norepinephrine. The association constant (Ka) of SHBG for testosterone was assessed to evaluate binding affinity. No significant difference was seen between the pre-control and the pre-exercise session values for any of the measures. However, within the exercise session significant (p<0.01) increases in post samples were evident for total testosterone (+32.0%), free-testosterone (+39.6%), cortisol (+38.0%), norepinephrine (+365.2%) and epinephrine (+225.8%). All other hormonal changes and the responses for Ka were non-significant. The results of the correlation analysis indicated that only norepinephrine was significantly (p<0.05) related to the changes observed in free testosterone (r = +0.92). We conclude that the free testosterone increase with moderately, prolonged endurance exercise was not associated with the change in the binding affinity of SHBG. Furthermore, the data suggest that the exercise induced increase in testosterone involves increased production which may be mediated by sympathetic stimulation of the testicles.

Adult↗