Anthony C. Hackney

Exercise and circulating Cortisol levels: The intensity threshold effect

This study examined the influence of exercise intensity upon the cortisol response of the hypothalamic-pituitaryadrenal (HPA) axis. Specifically, we examined exercise at intensities of 40, 60, and 80% maximal oxygen uptake (VO2max) in an attempt to determine the intensity necessary to provoke an increase in circulating cortisol. Twelve active moderately trained men performed 30 min of exercise at intensities of 40, 60, and 80% of their VO2max, as well as a 30-min resting-control session involving no exercise on separate days. Confounding factors such as time of day — circadian rhythms, prior diet — activity patterns, psychological stress, and levels of exercise training were controlled. Cortisol and ACTH were assessed in blood collected immediately before (pre-) and after (post-) each experimental session. Statistical analysis involved repeated measures analysis of variance and Tukey posthoc testing. The percent change in cortisol from pre- to post-sampling at each session was: resting-control, 40, 60, and 80% sessions (mean±SD) =−6.6±3.5%, +5.7±11.0%, +39.9±11.8%, and +83.1±18.5%, respectively. The 60% and 80% intensity magnitude of change was significantly greater than in the other sessions, as well as from one to another. The ACTH responses mirrored those of cortisol, but only the 80% exercise provoked a significant (p<0.05) increase pre- to post-exercise. The calculated changes in plasma volume for the resting-control, 40%, 60%, and 80% sessions were: +2.2±3.0%, −9.9±5.0%, −15.6±3.5%, and −17.2±3.3%, respectively. Collectively, the cortisol findings support the view that moderate to high intensity exercise provokes increases in circulating cortisol levels. These increases seem due to a combination of hemoconcentration and HPA axis stimulus (ACTH). In contrast, low intensity exercise (40%) does not result in significant increases in cortisol levels, but, once corrections for plasma volume reduction occurred and circadian factors were examined, low intensity exercise actually resulted in a reduction in circulating cortisol levels.

Reproductive hormonal profiles of endurance-trained and untrained males

This study compares the resting reproductive hormonal profiles of untrained (N = 11) and endurance-trained (N = 11) males. Testosterone, free testosterone, estradiol, luteinizing hormone (LH), prolactin, and cortisol were measured by radioimmunoassay in resting blood samples (8 h fast) collected every 60 min for 4 h. The endurance-trained group had been active for (mean +/- SE) 12.4 +/- 6.7 yr, 6.6 +/- 0.2 d.wk-1, 68.5 +/- 4.4 min.d-1, while the untrained group was sedentary. Neither group had histories of hypothalamic-pituitary-testicular disorders. The overall 4 h mean testosterone and free testosterone levels were significantly (P less than 0.05) lower in the trained group (4.99 +/- 0.46 vs 7.25 +/- 0.67 ng.ml-1, and 17.2 +/- 1.4 vs 23.6 +/- 0.6 pg.ml-1, for the trained and untrained groups, respectively). The LH of the endurance-trained group was higher (15.3 +/- 1.9 vs 11.7 +/- 1.2 mIU.ml-1, P = 0.06); however, LH pulse frequency and amplitude did not differ between groups. An enhanced estradiol feedback to the hypothalamus-pituitary could not account for the elevated LH, as estradiol levels were similar in the groups. Prolactin and cortisol levels were normal and did not differ between groups. The results suggested normal hypothalamic-pituitary function existed in the trained subjects, and prolactin and cortisol were not causative factors in the lowered resting testosterone and free testosterone levels. The findings indicate that chronic endurance training lowers testosterone and free testosterone in males possibly by impairing testicular function.

Interactions of Metabolic Hormones, Adipose Tissue and Exercise

AbstractPhysiological and psychological systems work together to determine energy intake and output, and thus maintain adipose tissue. In addition, adipose tissue secretes leptin and cytokines, which induces satiety and has been linked to catecholamines, cortisol, insulin, human growth hormone, thyroid hormones, gonadotropin and lipolysis. Thus, adipose tissue is acted upon by a number of physiological stimuli, including hormones, and simultaneously, is an active component in the regulation of its own lipid content. All of the hormones mentioned above are associated with each other and respond to exercise and exercise training. Thus, exercise is one of the major links between the hormonal modulators of energy intake and output. It appears that the sympathetic nervous system and the catecholamines are key components facilitating the lipolytic activity during exercise. These two neuroendocrine factors directly affect adipose metabolism and metabolic hormones that influence adipose metabolism. Acute low- and moderate-intensity exercise causes hormonal changes that facilitate lipolytic activity. Exercise training reduces these hormonal responses, but the sensitivity to these hormones increases so that lipolysis may be facilitated. Large amounts of adipose tissue blunt the metabolic hormonal responses to exercise, but the sensitivity of these hormones is increased; thus maintaining normal lipolytic activity. Although the physiological role of the endocrine system during exercise and training is significant, other training effects may have as great, or greater influence on lipolytic activity in adipose tissue.

The male reproductive system and endurance exercise.

During the last decade extensive research on the role of exercise upon the human reproductive system has been conducted. Primarily these investigations have focused on female subjects, but an increasing number of studies have examined male related issues. Evidence now suggests that men who participate in chronic endurance training display mild degrees of reproductive system abnormalities. The major abnormalities noted thus far are reduced resting levels of testosterone, altered pituitary release of luteinizing hormone and prolactin, and altered sperm characteristics. The purpose of this article is to briefly review the research literature on this topic and address select aspects of the impact of exercise upon the male reproductive system. The principal topics addressed in this article are acute and chronic exercise effects, consequences of hormonal changes associated with endurance training, and potential mechanisms for the reproductive system changes detected.

Stress and the neuroendocrine system: the role of exercise as a stressor and modifier of stress

In this article, the physiological impact of one form of stress – physical exercise – on the neuroendocrine system will be discussed. The specific intent of the review is to present an overview of stress endocrinology, the conceptual models associated with this area of study, and a discourse on the dual role of exercise as both a stressor and a modifier of stress within the neuroendocrine system. These points are addressed with respect to the current research literature dealing with exercise endocrinology in an adult population.

Effects of endurance exercise on the reproductive system of men: The “exercise-hypogonadal male condition”

An increasing number of investigative research studies point to participation in endurance exercise training as having significant detrimental effects upon reproductive hormonal profiles in men. Specifically, men chronically exposed to this type of exercise training exhibit persistently reduced basal (resting-state) free and total testosterone concentrations without concurrent LH elevations. Men displaying these symptoms have been deemed to exhibit the “exercise-hypogonadal male condition”. The exact physiological mechanism inducing the reduction of testosterone in these men is currently unclear, but is postulated to be a dysfunction (or perhaps a readjustment) within the hypothalamic-pituitary-testicular regulatory axis. The potential exists for the reduced testosterone concentrations within exercise-hypogonadal men to be disruptive and detrimental to some anabolic-androgenic testosterone-dependent physiological processes. Findings on this point are limited, but do suggest spermatogenesis problems may exist in some cases. Alternatively, reductions in circulating testosterone concentrations could have cardiovascular protective effects and thus be beneficial to the health of these men. Present evidence suggests the exercise-hypogonadal condition is limited to men who have been persistently involved in chronic endurance exercise training for an extended period time (i.e., years), and it is not a highly prevalent occurrence (although, a thorough epidemiological investigation on the topic is lacking in the literature). Many questions regarding the male reproductive endocrine adaptive process to exercise training still remain unanswered, necessitating the need for much further investigation on the topic, especially with respect to the exercise-hypogonadal condition.

The effects of an individualized exercise intervention on body composition in breast cancer patients undergoing treatment

CONTEXT AND OBJECTIVE Changes in metabolism have been reported in the majority of patients undergoing cancer treatment, and these are usually characterized by progressive change in body composition. The effects of aerobic exercise programs to combat the cancer and cancer treatment-related side effects, which include the negative changes in body composition, have been extensively reported in the literature. However, few resistance exercise intervention studies have hypothesized that breast cancer patients might benefit from this type of exercise. The purpose of this study was to determine whether exercise protocols that emphasize resistance training would change body composition and strength in breast cancer patients undergoing treatment. DESIGN AND SETTING Randomized controlled trial, at the Campus Recreation Center and Rocky Mountain Cancer Rehabilitation Institute of the University of Northern Colorado, and the North Colorado Medical Center. METHODS Twenty inactive breast cancer patients were randomly assigned to a 21-week exercise group (n = 10) or a control group (n = 10). The exercise group trained at low to moderate intensity for 60 minutes on two days/week. The primary outcome measurements included body composition (skinfold method) and muscle strength (one repetition maximum). RESULTS Significant differences in lean body mass, body fat and strength (p = 0.004, p = 0.004, p = 0.025, respectively) were observed between the groups at the end of the study. CONCLUSION The results suggest that exercise emphasizing resistance training promotes positive changes in body composition and strength in breast cancer patients undergoing treatment.

The association between insulin resistance and cytokines in adolescents: the role of weight status and exercise

Increased adiposity is associated with insulin resistance (IR) and an inflammatory response in adults. We tested the hypotheses that cytokines associated with adiposity are also correlated with IR in early adolescents and that these relationships are moderated by weight status, levels of vigorous physical activity (VPA), or maximal aerobic power (pVO2max). Body mass, stature, and a fasting blood sample were obtained from 120 midpubertal adolescents (60 girls and 60 boys). Habitual VPA was obtained by a survey. Predicted VO2max was determined using a cycle ergometer test. Weight status was based on body mass index (BMI) percentiles (normal weight=BMI<75th percentile, overweight=BMI>95th percentile). Glucose, insulin, adiponectin, resistin, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 were measured; and IR index was based on the Homeostatic Model Assessment. Adiponectin, resistin, and TNF-alpha were associated with IR in all adolescents (R2=0.329, P<.001; R2=0.152, P=.001; and R2=0.141, P=.002; respectively); but interleukin-6 was not (R2=0.148, P=.114). The degree of association between adiponectin and IR was stronger in overweight than in normal-weight adolescents (P<.050). When regression models included weight status, neither TNF-alpha nor resistin was significantly related to IR (P>.050). Exercise did not moderate the association between these cytokines and IR. However, higher levels of VPA and/or pVO2max were associated with higher adiponectin, lower resistin, and lower TNF-alpha in at least one of the sexes. Our results indicate that the pathophysiology of obesity is already established in early adolescents. Increased adiposity, resulting in reduced adiponectin and increased resistin and TNF-alpha, may link these cytokines with IR in adolescents.

Twenty-five years of research on the effects of exercise training in breast cancer survivors: A systematic review of the literature

AIM To investigate the role of exercise training the past 25 years on major physiological-psychological outcomes studied thus far in this patient population. METHODS PubMed, MedlinePlus, the Cochrane Library, Web of Science, SportDiscus, Embase, Scorpus, and Google Scholar were searched from September to November 2013 to identify exercise training studies that used objective measurements of fitness and/or patient reported outcomes assessed pre and post-exercise training with statistical analyses performed in at least one of the following outcome measurements: Cardiorespiratory function, body composition, muscular strength, fatigue, depression, and overall quality of life. Five reviewers independently identified the studies that met the criteria for the review and discrepancies were resolved by consensus among all authors. RESULTS Fifty-one studies were included in this review with 5 from the period between 1989-1999, 11 from 2000-2006, and 35 from 2007-2013. The evolution of study designs changed from aerobic only exercise training interventions (1989-1999), to a combination of aerobic and resistance training (2000-2006), to studies including an arm of resistance training or examining the effects of resistance training as the main mode of exercise (2007-2013). Overall, the benefits of exercise showed improvements in cardiorespiratory function, body composition, strength, and patient reported outcomes including fatigue, depression, and quality of life. CONCLUSION Exercise training appears to be safe for most breast cancer patients and improvements in physiological, psychological, and functional parameters can be attained with regular participation in moderate intensity exercise.

Research Methodology: Endocrinologic Measurements in Exercise Science and Sports Medicine

OBJECTIVE To provide background information on methodologic factors that influence and add variance to endocrine outcome measurements. Our intent is to aid and improve the quality of exercise science and sports medicine research endeavors of investigators inexperienced in endocrinology. BACKGROUND Numerous methodologic factors influence human endocrine (hormonal) measurements and, consequently, can dramatically compromise the accuracy and validity of exercise and sports medicine research. These factors can be categorized into those that are biologic and those that are procedural-analytic in nature. RECOMMENDATIONS Researchers should design their studies to monitor, control, and adjust for the biologic and procedural-analytic factors discussed within this paper. By doing so, they will find less variance in their hormonal outcomes and thereby will increase the validity of their physiologic data. These actions can assist the researcher in the interpretation and understanding of endocrine data and, in turn, make their research more scientifically sound.