Intensive exercise training suppresses testosterone during bed rest

Beyond the Finish Line: The Impact and Dynamics of Biomarkers in Physical Exercise-A Narrative Review

The research of biomarkers continues to emerge as a developing academic field which is attracting substantial interest. The study of biomarkers proves to be useful in developing and implementing new screening methods for a wide variety of diseases including in the sports area, whether for leisure activities or professional sports. Novel research has brought into question the immune system and the limitations it may impose on sports practicing. As the well-being of athletes is a priority, the state of their immune function offers valuable information regarding their health status and their ability to continue training. The assessment of various biomarkers may contribute to a more accurate risk stratification and subsequent prevention of some invalidating or even fatal pathologies such as the sudden cardiac death. Therefore, we have reviewed several studies that included sports-related pathology or specific morphofunctional alterations for which some immune biomarkers may represent an expression of the underlying mechanism. These include the defensins, immunoglobulin A (IgA), interleukin-6 (IL-6), the tumoral necrosis factor α (TNF-α), and the white blood cells (WBC) count. Similarly, also of significant interest are various endocrine biomarkers, such as cortisol and testosterone, as well as anabolic or catabolic markers, respectively. Literature data highlight that these values are greatly influenced not only by the duration, but also by the intensity of the physical exercise; moderate training sessions actually enhance the immune function of the body, while a significant increase in both duration and intensity of sports activity acts as a deleterious factor. Therefore, in this paper we aim to highlight the importance of biomarkers’ evaluation in connection with sports activities and a subsequent more adequate approach towards personalized training regimens.

Aging-like metabolic and adrenal changes in microgravity: State of the art in preparation for Mars

Endocrine and metabolic changes that typically accompany aging on Earth have been consistently observed in space. Support for the role of gravity in aging has mostly come from ground simulation studies in head down bed rest. However, uncertainties remain and have to be resolved in planning for the ambitious enterprise of sending humans to Mars and back. Stress-related corticosteroid changes and metabolic adaptation to microgravity and their relationship with aging are the object of the present review mostly, albeit of course non exclusively, coming from the personal experience of the authors. The picture coming out of it is that of some, not easily proven, stress-induced cortisol increase accompanied by insulin resistance, both of which represent typical aging-like phenomena mediated by chronic low-grade inflammation. This suggests the need for humans to consider the long journey to safely land, live and work on Mars by taking advantage of integrative medicine solutions including synthetic torpor and/or continuous self-monitoring of eating, sleeping, moving to enable remotely supervised self-treatment.

Efficacy of Testosterone plus NASA Exercise Countermeasures during Head-Down Bed Rest

INTRODUCTION

Prolonged confinement to head-down bed rest (HDBR) results in musculoskeletal losses similar to those observed during long-duration space flight. Exercise countermeasures by themselves have not completely prevented the deleterious losses in muscle mass or function in HDBR or space flight.

PURPOSE

The objective was to investigate the safety and efficacy of intermittent, low-dose testosterone treatment in conjunction with NASA exercise (SPRINT) countermeasures during 70 d of 6° HDBR.

METHODS

Healthy men (35 ± 8 yr) were randomized into one of three groups that remained inactive (CON) or performed exercise 6 d·wk in addition to receiving either placebo (PEX) or testosterone treatment (TEX, 100 mg·wk). Testosterone/placebo injections were administered once a week for 2 wk, followed by 2 wk off and so on, during HDBR.

RESULTS

Total, leg, and trunk lean body mass (LBM) consistently decreased in CON, increased in TEX, and had little or no changes in PEX. Total, leg, and trunk fat mass consistently increased in CON and PEX and decreased in TEX. Leg strength decreased in CON, whereas PEX and TEX were protected against loss in strength. Changes in leg LBM correlated positively with changes in leg muscle strength.

CONCLUSIONS

Addition of a testosterone countermeasure enhanced the preventative actions of exercise against body composition changes during long-term HDBR in healthy eugonadal men. This is the first report to demonstrate that cycled, low-dose testosterone treatment increases LBM under conditions of strict exercise control. These results are clinically relevant to the development of safe and effective therapies against muscle atrophy during long-term bed rest, aging, and disease where loss of muscle mass and strength is a risk. The potential space flight applications of such countermeasure combinations deserve further investigations.

Sport, doping and male fertility

It is universally accepted that lifestyle interventions are the first step towards a good overall, reproductive and sexual health. Cessation of unhealthy habits, such as tobacco, alcohol and drug use, poor nutrition and sedentary behavior, is suggested in order to preserve/improve fertility in humans. However, the possible risks of physical exercise per se or sports on male fertility are less known. Being "fit" does not only improve the sense of well-being, but also has beneficial effects on general health: in fact physical exercise is by all means a low-cost, high-efficacy method for preventing or treating several conditions, ranging from purely physical (diabetes and obesity) to psychological (depression and anxiety), highly influencing male reproduction. If male sexual and reproductive health could be positively affected by a proper physical activity, inadequate bouts of strength - both excessive intensity and duration of exercise training - are more likely to have detrimental effects. In addition, the illicit use of prohibited drugs (i.e. doping) has reached pandemic proportions, and their actions, unfortunately very often underestimated by both amateur and professional athletes, are known to disrupt at different levels and throughout various mechanisms the male hypothalamic-pituitary-gonadal axis, resulting in hypogonadism and infertility.

Recent Progress in Space Physiology and Aging

Astronauts coming back from long-term space missions present with different health problems potentially affecting mission performance, involving all functional systems and organs and closely resembling those found in the elderly. This review points out the most recent advances in the literature in areas of expertise in which specific research groups were particularly creative, and as they relate to aging and to possible benefits on Earth for disabled people. The update of new findings and approaches in space research refers especially to neuro-immuno-endocrine-metabolic interactions, optic nerve edema, motion sickness and muscle-tendon-bone interplay and aims at providing the curious - and even possibly naïve young researchers – with a source of inspiration and of creative ideas for translational research.

Effects of strict prolonged bed rest on cardiorespiratory fitness: systematic review and meta-analysis

The aim of this systematic review and meta-analysis [International Prospective Register of Systematic Reviews (PROSPERO) CRD42017055619] was to assess the effects of strict prolonged bed rest (without countermeasures) on maximal oxygen uptake (V̇o2max) and to explore sources of variation therein. Since 1949, 80 studies with a total of 949 participants (>90% men) have been published with data on strict bed rest and V̇o2max. The studies were conducted mainly in young participants [median age (interquartile range) 24.5 (22.4–34.0) yr]. The duration of bed rest ranged from 1 to 90 days. V̇o2max declined linearly across bed rest duration. No statistical difference in the decline among studies reporting V̇o2max as l/min (−0.3% per day) compared with studies reporting V̇o2max normalized to body weight (ml·kg−1·min−1; −0.43% per day) was observed. Although both total body weight and lean body mass declined in response to bed rest, we did not see any associations with the decline in V̇o2max. However, 15–26% of the variation in the decline in V̇o2max was explained by the pre-bed-rest V̇o2max levels, independent of the duration of bed rest (i.e., higher pre-bed-rest V̇o2max levels were associated with larger declines in V̇o2max). Furthermore, the systematic review revealed a gap in the knowledge about the cardiovascular response to extreme physical inactivity, particularly in older subjects and women of any age group. In addition to its relevance to spaceflight, this lack of data has significant translational implications because younger women sometimes undergo prolonged periods of bed rest associated with the complications of pregnancy and the incidence of hospitalization including prolonged periods of bed rest increases with age.

NEW & NOTEWORTHY Large interindividual responses of maximal oxygen uptake (V̇o2max) to aerobic exercise training exist. However, less is known about the variability in the response of V̇o2max to prolonged bed rest. This systematic review and meta-analysis showed that pre-bed-rest V̇o2max values were inversely associated with the change in V̇o2max independent of the duration of bed rest. Moreover, we identified a large knowledge gap about the causes of decline in V̇o2max, particularly in postmenopausal women, which may have clinical implications.

Changes in stress hormone levels with the application of vibrations before resistance exercises at different intensities

[Purpose] The purpose of the present study was to determine whether vibrations should be applied before resistance exercises by examining changes in stress hormone levels with vibrations applied before different exercise intensities. [Subjects] Eighteen male subjects in their 20s were included, and were randomly divided into one-repetition maximum (1RM) 50% group (50% RMG, n = 6), 1RM 70% group (70%RMG, n = 6), and 1RM 90% group (90% RMG, n = 6). [Methods] Three sets of Smith squats were performed at 1RM 50%, 70%, and 90% according to resistance intensities, and vibrations were applied for 1 min at a fixed frequency of 30 Hz before each set. Epinephrine, norepinephrine, and dopamine stress hormone levels were analyzed. [Results] Epinephrine levels were significantly higher immediately after exercise than at rest in the 50%RMG; however, no significant changes were noted in the 70%RMG and 90%RMG. Norepinephrine levels were significantly higher immediately after exercise than at rest in all three groups. However, no significant changes in dopamine levels were noted in the three groups. [Conclusion] The application of vibrations at a frequency of 30 Hz before 70%RM and 90%RM resistance exercises suppressed increases in the stress hormone epinephrine levels immediately after exercise.

The Paternal Provisioning Hypothesis: effects of workload and testosterone production on men's musculature

OBJECTIVES

Testosterone supports male reproduction through a broad range of behavioral and physiological effects, including the maintenance of sexually dimorphic muscle used in male-male competition. Although it is often assumed that a persistent relationship exists between men's testosterone production and musculature, most studies either fail to find evidence for such a relationship, or document very weak associations. In nonhuman primates, by contrast, correlations between testosterone and muscle mass are higher. Here, we propose the "Paternal Provisioning Hypothesis," which predicts that men's skeletal muscle is less dependent on the effects of androgens than that of other primates, and more sensitive to the physical demands of men's work. This permits human fathers to downregulate testosterone, which has negative impacts on pair-bonding and parenting effort, but without sacrificing the strength and musculature necessary to provision mates and offspring.

METHODS

We tested predictions of the Paternal Provisioning Hypothesis by assessing parental status, salivary testosterone levels, anthropometry, and strength among 122 men (ages 18-78) at the Mogielica Human Ecology Study Site in rural Poland. We chose this population because men practice subsistence agriculture, regularly engaging in physically demanding labor. Grip and chest strength were assessed using a dynamometer, and upper-body musculature was estimated from arm muscle circumference.

RESULTS

In this population, testosterone showed no association with measures of strength or musculature, and was lower in older men and pair-bonded fathers. Marital and parental status and workload, by contrast, were positive predictors of muscle mass and strength measures.

DISCUSSION

These findings offer support for the Paternal Provisioning Hypothesis.

Long-duration space flight and bed rest effects on testosterone and other steroids

CONTEXT

Limited data suggest that testosterone is decreased during space flight, which could contribute to bone and muscle loss.

OBJECTIVE

The main objective was to assess testosterone and hormone status in long- and short-duration space flight and bed rest environments and to determine relationships with other physiological systems, including bone and muscle.

DESIGN

Blood and urine samples were collected before, during, and after long-duration space flight. Samples were also collected before and after 12- to 14-d missions and from participants in 30- to 90-d bed rest studies.

SETTING

Space flight studies were conducted on the International Space Station and before and after Space Shuttle missions. Bed rest studies were conducted in a clinical research center setting. Data from Skylab missions are also presented.

PARTICIPANTS

All of the participants were male, and they included 15 long-duration and nine short-duration mission crew members and 30 bed rest subjects.

MAIN OUTCOME MEASURES

Serum total, free, and bioavailable testosterone were measured along with serum and urinary cortisol, serum dehydroepiandrosterone, dehydroepiandrosterone sulfate, and SHBG.

RESULTS

Total, free, and bioavailable testosterone was not changed during long-duration space flight but were decreased (P < 0.01) on landing day after these flights and after short-duration space flight. There were no changes in other hormones measured. Testosterone concentrations dropped before and soon after bed rest, but bed rest itself had no effect on testosterone.

CONCLUSIONS

There was no evidence for decrements in testosterone during long-duration space flight or bed rest.

The effects of bed-rest and countermeasure exercise on the endocrine system in male adults: evidence for immobilization-induced reduction in sex hormone-binding globulin levels

BACKGROUND AND AIM

There is limited data on the effects of inactivity (prolonged bed-rest) on parameters of endocrine and metabolic function; we therefore aimed to examine changes in these systems during and after prolonged (56- day) bed-rest in male adults.

SUBJECTS AND METHODS

Twenty healthy male subjects underwent 8 weeks of strict bed-rest and 12 months of follow-up as part of the Berlin Bed Rest Study. Subjects were randomized to an inactive group or a group that performed resistive vibration exercise (RVE) during bed-rest. All outcome parameters were measured before, during and after bed-rest. These included body composition (by whole body dual X-ray absorptiometry), SHBG, testosterone (T), estradiol (E2), PRL, cortisol (C), TSH and free T3 (FT3).

RESULTS

Serum SHBG levels decreased in inactive subjects but remained unchanged in the RVE group (p<0.001). Serum T concentrations increased during the first 3 weeks of bed-rest in both groups (p<0.0001), while E2 levels sharply rose with re-mobilization (p<0.0001). Serum PRL decreased in the control group but increased in the RVE group (p=0.021). C levels did not change over time (p≥0.10). TSH increased whilst FT3 decreased during bed-rest (p all ≤0.0013).

CONCLUSIONS

Prolonged bed-rest has significant effects on parameters of endocrine and metabolic function, some of which are related to, or counteracted by physical activity.

Disuse of the musculo-skeletal system in space and on earth

Muscle mass and strength are well known to decline in response to actual and simulated microgravity exposure. However, despite the considerable knowledge gained on the physiological changes induced by spaceflight, the mechanisms of muscle atrophy and the effectiveness of in-flight countermeasures still need to be fully elucidated. The present review examines the effects and mechanisms of actual and simulated microgravity on single fibre and whole muscle structural and functional properties, protein metabolism, tendon mechanical properties, neural drive and reflex excitability. The effects of inflight countermeasures are also discussed in the light of recent advances in resistive loading techniques, in combined physical, pharmacological and nutritional interventions as well as in the development of artificial gravity systems. Emphasis has been given to the pioneering work of Pietro Enrico di Prampero in the development of artificial gravity systems and in the progress of knowledge on the limits of human muscular performance in space.

Effects of carbohydrate supplementation on competitive runners undergoing overload training followed by a session of intermittent exercise

This study evaluated the effects of a micro cycle of overload training (1st-8th day) on metabolic and hormonal responses in male runners with or without carbohydrate supplementation and investigated the cumulative effects of this period on a session of intermittent high-intensity running and maximum-performance-test (9th day). The participants were 24 male runners divided into two groups, receiving 61% of their energy intake as CHO (carbohydrate-group) and 54% in the control-group (CON). The testosterone was higher for the CHO than the CON group after the overload training (694.0 +/- 54.6 vs. CON 610.8 +/- 47.9 pmol/l). On the ninth day participants performed 10 x 800 m at mean 3 km velocity. An all-out 1000 m running was performed before and after the 10 x 800 m. Before, during, and after this protocol, the runners received solution containing CHO or the CON equivalent. The performance on 800 m series did not differ in either group between the first and last series of 800 m, but for the all-out 1000 m test the performance decrement was lower for CHO group (5.3 +/- 1.0 vs. 10.6 +/- 1.3%). The cortisol concentrations were lower in the CHO group in relation to CON group (22.4 +/- 0.9 vs. 27.6 +/- 1.4 pmol/l) and the IGF1/IGFBP3 ratio increased 12.7% in the CHO group. During recovery, blood glucose concentrations remained higher in the CHO group in comparison with the CON group. It was concluded that CHO supplementation possibly attenuated the suppression of the hypothalamic-pituitary-gonadal axis and resulted in less catabolic stress, and thus improved running performance.

Functional coupling between the Na+/Ca2+ exchanger and nonselective cation channels during histamine stimulation in guinea pig tracheal smooth muscle

Airway smooth muscle (ASM) contracts partly due to an increase in cytosolic Ca(2+). In this work, we found that the contraction caused by histamine depends on external Na(+), possibly involving nonselective cationic channels (NSCC) and the Na(+)/Ca(2+) exchanger (NCX). We performed various protocols using isometric force measurement of guinea pig tracheal rings stimulated by histamine. We observed that force reached 53 +/- 1% of control during external Na(+) substitution by N-methyl-D-glucamine(+), whereas substitution by Li(+) led to no significant change (91 +/- 1%). Preincubation with KB-R7943 decreased the maximal force developed (52.3 +/- 5.6%), whereas preincubation with nifedipine did not (89.7 +/- 1.8%). Also, application of the nonspecific NCX blocker KB-R7943 and nifedipine on histamine-precontracted tracheal rings reduced force to 1 +/- 3%, significantly different from nifedipine alone (49 +/- 6%). Moreover, nonspecific NSCC inhibitors SKF-96365 and 2-aminoethyldiphenyl borate reduced force to 1 +/- 1% and 19 +/- 7%, respectively. Intracellular Ca(2+) measurements in isolated ASM cells showed that KB-R7943 and SKF-96365 reduced the peak and sustained response to histamine (0.20 +/- 0.1 and 0.19 +/- 0.09 for KB-R, 0.43 +/- 0.16 and 0.47 +/- 0.18 for SKF, expressed as mean of differences). Moreover, Na(+)-free solution only inhibited the sustained response (0.54 +/- 0.25). These data support an important role for NSCC and NCX during histamine stimulation. We speculate that histamine induces Na(+) influx through NSCC that promotes the Ca(2+) entry mode of NCX and Ca(V)1.2 channel activation, thereby causing contraction.