Effect of brief exercise on circulating insulin-like growth factor I

Exercise to spot the differences: a framework for the effect of exercise on hippocampal pattern separation in humans

Exercise has a beneficial effect on mental health and cognitive functioning, but the exact underlying mechanisms remain largely unknown. In this review, we focus on the effect of exercise on hippocampal pattern separation, which is a key component of episodic memory. Research has associated exercise with improvements in pattern separation. We propose an integrated framework mechanistically explaining this relationship. The framework is divided into three pathways, describing the pro-neuroplastic, anti-inflammatory and hormonal effects of exercise. The pathways are heavily intertwined and may result in functional and structural changes in the hippocampus. These changes can ultimately affect pattern separation through direct and indirect connections. The proposed framework might guide future research on the effect of exercise on pattern separation in the hippocampus.

Plasma microRNA-320a as a Potential Biomarker of Physiological Changes during Training in Professional Volleyball Players

A deeper insight into the mechanisms responsible for athlete performance that may serve as specific and detailed training indicators is still desired, because conventionally used biomarkers provide limited information about the adaptive processes that occur during exercise. The objective of our study was to assess insulin-like growth factor 1 receptors (IGF1R) gene expression and evaluate plasma concentration of selected microRNAs (miRNAs) during a 10-week training period (sampling times: week 1, 4, 7, and 10) in a group of 12 professional female volleyball players. Circulating miRNAs (miR-223, miR-320a, and miR-486) with established concentration in plasma and documented association with the IGF1 signaling pathway, which is involved in muscle development and recovery, were tested. The levels of analyzed miRNAs, tested by one-way ANOVA, were significantly different between four training periods during a 10-week training cycle (miR-223 p < 0.0001, miR-320a p = 0.00021, miR-486 p = 0.0037, respectively). The levels of IGF1R also appeared to be different (p = 0.00092), and their expression showed a trend to increase between the first and third periods. In the fourth period, the expression decreased, although it was higher compared with the baseline. Correlations between concentration levels of miR-223 and miR-320a (rs = 0.54, p < 0.001), as well as between miR-320a and miR-486 (rs = 0.73, p < 0.001) were also found. In the fourth period, a negative correlation between miR-223 plasma level and leucocyte IGF1R expression was found (rs = -0.63, p = 0.028). Multiple linear regression analysis showed that miR-320a (p = 0.024) and creatine kinase (p = 0.028) had the greatest impact on the expression levels of the IGF1R gene. Future studies are required to define whether these miRNAs, especially miR-320a, as well as IGF1R expression could be useful biomarkers of physiological changes during exercise and to discover their detailed biological roles in mode-specific exercise training adaptations of professional athletes.

Comparison of the effects of open vs. closed skill exercise on the acute and chronic BDNF, IGF-1 and IL-6 response in older healthy adults

BACKGROUND

Accumulating evidence shows that physical exercise has a positive effect on the release of neurotrophic factors and myokines. However, evidence regarding the optimal type of physical exercise for these release is still lacking. The aim of this study was to assess the acute and chronic effects of open-skill exercise (OSE) compared to closed-skill exercise (CSE) on serum and plasma levels of brain derived neurotrophic factor (BDNFS, BDNFP), and serum levels of insulin like growth factor 1 (IGF-1), and interleukin 6 (IL-6) in healthy older adults.

METHODS

To investigate acute effects, thirty-eight participants were randomly assigned to either an intervention (badminton (aOSE) and bicycling (aCSE), n  = 24, 65.83 ± 5.98 years) or control group (reading (CG), n  = 14, 67.07 ± 2.37 years). Blood samples were taken immediately before and 5 min after each condition. During each condition, heart rate was monitored. The mean heart rate of aOSE and aCSE were equivalent (65 ± 5% of heart rate reserve). In a subsequent 12-week training-intervention, twenty-two participants were randomly assigned to either a sport-games (cOSE, n  = 6, 64.50 ± 6.32) or a strength-endurance training (cCSE, n  = 9, 64.89 ± 3.51) group to assess for chronic effects. Training intensity for both groups was adjusted to a subjective perceived exertion using the CR-10 scale (value 7). Blood samples were taken within one day after the training-intervention.

RESULTS

BDNFS, BDNFP, IGF-1, and IL-6 levels increased after a single exercise session of 30 min. After 12 weeks of training BDNFS and IL-6 levels were elevated, whereas IGF-1 levels were reduced in both groups. However, only in the cOSE group these changes were significant. We could not find any significant differences between the exercise types.

CONCLUSION

Our results indicate that both exercise types are efficient to acutely increase BDNFS, BDNFP, IGF-1 and IL-6 serum levels in healthy older adults. Additionally, our results tend to support that OSE is more effective for improving basal BDNFS levels after 12 weeks of training.

A Single Bout of High-intensity Interval Exercise Increases Corticospinal Excitability, Brain-derived Neurotrophic Factor, and Uncarboxylated Osteolcalcin in Sedentary, Healthy Males

Exercise induces neuroplasticity in descending motor pathways facilitating motor learning, and as such it could be utilized as an intervention in neurorehabilitation, for example when re-learning motor skills after stroke. To date, however, the neurophysiological and molecular mechanisms underlying exercise-induced neuroplasticity remain largely unknown impeding the potential utilization of exercise protocols as 'motor learning boosters' in clinical and non-clinical settings. Here, we assessed corticospinal excitability, intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) using transcranial magnetic stimulation (TMS) and serum biochemical markers including brain-derived neurotrophic factor (BDNF), total and precursor cathepsin B (tCTSB, proCTSB), uncarboxylated and carboxylated osteocalcin (unOCN, cOCN) and irisin using ELISA. Measurements were carried out in sedentary, healthy males before and after a single session of high-intensity interval exercise (HIIE) or in individuals who rested and did not perform exercise (No Exercise). We found that HIIE increased corticospinal excitability, BDNF and unOCN, and decreased cOCN. We also determined that greater increases in BDNF were associated with increases in unOCN and irisin and decreases in cOCN only in participants who underwent HIIE, suggesting that unOCN and irisin may contribute to exercise-induced BDNF increases. Conversely, no changes other than a decrease in serum unOCN/tOCN were found in No Exercise participants. The present findings show that a single session of HIIE is sufficient to modulate corticospinal excitability and to increase BDNF and unOCN in sedentary, healthy males.

Targeting Diet and Exercise for Neuroprotection and Neurorecovery in Glaucoma

Glaucoma is a leading cause of blindness worldwide. In glaucoma, a progressive dysfunction and death of retinal ganglion cells occurs, eliminating transfer of visual information to the brain. Currently, the only available therapies target the lowering of intraocular pressure, but many patients continue to lose vision. Emerging pre-clinical and clinical evidence suggests that metabolic deficiencies and defects may play an important role in glaucoma pathophysiology. While pre-clinical studies in animal models have begun to mechanistically uncover these metabolic changes, some existing clinical evidence already points to potential benefits in maintaining metabolic fitness. Modifying diet and exercise can be implemented by patients as an adjunct to intraocular pressure lowering, which may be of therapeutic benefit to retinal ganglion cells in glaucoma.

Understanding the Neurophysiological and Molecular Mechanisms of Exercise-Induced Neuroplasticity in Cortical and Descending Motor Pathways: Where Do We Stand?

Exercise is a promising, cost-effective intervention to augment successful aging and neurorehabilitation. Decline of gray and white matter accompanies physiological aging and contributes to motor deficits in older adults. Exercise is believed to reduce atrophy within the motor system and induce neuroplasticity which, in turn, helps preserve motor function during aging and promote re-learning of motor skills, for example after stroke. To fully exploit the benefits of exercise, it is crucial to gain a greater understanding of the neurophysiological and molecular mechanisms underlying exercise-induced brain changes that prime neuroplasticity and thus contribute to postponing, slowing, and ameliorating age- and disease-related impairments in motor function. This knowledge will allow us to develop more effective, personalized exercise protocols that meet individual needs, thereby increasing the utility of exercise strategies in clinical and non-clinical settings. Here, we review findings from studies that investigated neurophysiological and molecular changes associated with acute or long-term exercise in healthy, young adults and in healthy, postmenopausal women.

Acute exercise following skill practice promotes motor memory consolidation in Parkinson's disease

Acute cardiovascular exercise has shown to promote neuroplastic processes supporting the consolidation of newly acquired motor skills in healthy adults. First results suggest that this concept may be transferred to populations with motor and cognitive dysfunctions. In this context, Parkinson's disease (PD) is highly relevant since patients demonstrate deficits in motor learning. Hence, in the present study we sought to explore the effect of a single post-practice exercise bout on motor memory consolidation in PD. For this purpose, 17 patients with PD (Hoehn and Yahr: 1 - 2.5, age: 60.1 ± 7.9 y) practiced a whole-body skill followed by either (i) a moderate-intense bout of cycling, or (ii) seated rest for a total of 30 min. The motor skill required the participants to balance on a tiltable platform (stabilometer) for 30 s. During skill practice, participants performed 15 trials followed by a retention test 1 day and 7 days later. We calculated time in balance (platform within ± 5° from horizontal) for each trial and within- and between-group differences in memory consolidation (i.e. offline learning = skill change from last acquisition block to retention tests) were analyzed. Groups revealed similar improvements during skill practice (F_4,60 = 0.316, p = 0.866), but showed differences in offline learning, which were only evident after 7 days (F_1,14 = 5.602, p = 0.033). Our results suggest that a single post-practice exercise bout is effective in enhancing long-term motor memory consolidation in a population with motor learning impairments. This may point at unique promoting effects of exercise on dopamine neurotransmission involved in memory formation. Future studies should investigate the potential role of exercise-induced effects on the dopaminergic system.

Impact of exercise on older adults' mood is moderated by sleep and mediated by altered brain connectivity

Older adults comprise the fastest growing global demographic and are at increased risk of poor mental health outcomes. Although aerobic exercise and sleep are critical to the preservation of emotional well-being, few studies have examined their combined mood-enhancing effects, or the potential neural mechanisms underlying these effects. Here, we used a randomized crossover design to test the impact of acute exercise on mood and the intrinsic functional connectivity (iFC) of the cingulo-opercular network in physically healthy older adults. Wrist actigraphy provided objective indices of sleep. Results revealed that 30 min of moderate-intensity aerobic exercise acutely enhanced positive affect (PA) and reduced iFC between the cingulo-opercular network and the hippocampus. Both effects were magnified among older adults with greater sleep disturbance. Exercise-induced changes in hippocampal iFC mediated relations between sleep disturbance and exercise-induced increases in PA. These findings provide evidence that aerobic exercise enhances mood, that it does so by altering connectivity between the anterior insula-a key hub in the cingulo-opercular network-and the hippocampus and that lower sleep quality is a stronger predictor of these effects among older adults. These observations underscore the benefits of moderate-intensity exercise-a safe and scalable behavioral intervention-and provide new clues about the neural circuitry underlying the interactive effects of sleep and exercise on mood.

Role of Regular Physical Activity in Neuroprotection against Acute Ischemia

One of the major obstacles that prevents an effective therapeutic intervention against ischemic stroke is the lack of neuroprotective agents able to reduce neuronal damage; this results in frequent evolution towards a long-term disability with limited alternatives available to aid in recovery. Nevertheless, various treatment options have shown clinical efficacy. Neurotrophins such as brain-derived neurotrophic factor (BDNF), widely produced throughout the brain, but also in distant tissues such as the muscle, have demonstrated regenerative properties with the potential to restore damaged neural tissue. Neurotrophins play a significant role in both protection and recovery of function following neurological diseases such as ischemic stroke or traumatic brain injury. Unfortunately, the efficacy of exogenous administration of these neurotrophins is limited by rapid degradation with subsequent poor half-life and a lack of blood-brain-barrier permeability. Regular exercise seems to be a therapeutic approach able to induce the activation of several pathways related to the neurotrophins release. Exercise, furthermore, reduces the infarct volume in the ischemic brain and ameliorates motor function in animal models increasing astrocyte proliferation, inducing angiogenesis and reducing neuronal apoptosis and oxidative stress. One of the most critical issues is to identify the relationship between neurotrophins and myokines, newly discovered skeletal muscle-derived factors released during and after exercise able to exert several biological functions. Various myokines (e.g., Insulin-Like Growth Factor 1, Irisin) have recently shown their ability to protects against neuronal injury in cerebral ischemia models, suggesting that these substances may influence the degree of neuronal damage in part via inhibiting inflammatory signaling pathways. The aim of this narrative review is to examine the main experimental data available to date on the neuroprotective and anti-ischemic role of regular exercise, analyzing also the possible role played by neurotrophins and myokines.

Exercise-induced immune system response: Anti-inflammatory status on peripheral and central organs

A wide array of molecular pathways has been investigated during the past decade in order to understand the mechanisms by which the practice of physical exercise promotes neuroprotection and reduces the risk of developing communicable and non-communicable chronic diseases. While a single session of physical exercise may represent a challenge for cell homeostasis, repeated physical exercise sessions will improve immunosurveillance and immunocompetence. Additionally, immune cells from the central nervous system will acquire an anti-inflammatory phenotype, protecting central functions from age-induced cognitive decline. This review highlights the exercise-induced anti-inflammatory effect on the prevention or treatment of common chronic clinical and experimental settings. It also suggests the use of pterins in biological fluids as sensitive biomarkers to follow the anti-inflammatory effect of physical exercise.

Interplay between hormones and exercise on hippocampal plasticity across the lifespan

The hippocampus is a brain structure known to play a central role in cognitive function (namely learning and memory) as well as mood regulation and affective behaviors due in part to its ability to undergo structural and functional changes in response to intrinsic and extrinsic stimuli. While structural changes are achieved through modulation of hippocampal neurogenesis as well as alterations in dendritic morphology and spine remodeling, functional (i.e., synaptic) changes can be noted through the strengthening (i.e., long-term potentiation) or weakening (i.e., long-term depression) of the synapses. While age, hormone homeostasis, and levels of physical activity are some of the factors known to module these forms of hippocampal plasticity, the exact mechanisms through which these factors interact with each other at a given moment in time are not completely understood. It is well known that hormonal levels vary throughout the lifespan of an individual and it is also known that physical exercise can impact hormonal homeostasis. Thus, it is reasonable to speculate that hormone modulation might be one of the various mechanisms through which physical exercise differently impacts hippocampal plasticity throughout distinct periods of an individual's life. The present review summarizes the potential relationship between physical exercise and different types of hormones (namely sex, metabolic, and stress hormones) and how this relationship may mediate the effects of physical activity during three distinct life periods, adolescence, adulthood, and senescence. Overall, the vast majority of studies support a beneficial role of exercise in maintaining hippocampal hormonal levels and consequently, hippocampal plasticity, cognition, and mood regulation.

Effects of acute cardiovascular exercise on motor memory encoding and consolidation: A systematic review with meta-analysis

Emerging evidence indicates that acute bouts of cardiovascular exercise promote motor memory formation. In this preregistered meta-analysis (CRD42018106288) we synthesize data from 22 studies published until February 2020, including a total of 862 participants. We calculated standardized mean differences (SMDs) with 95 % confidence intervals (CIs) to assess exercise effects on motor memory encoding and consolidation, respectively. The pooled data indicate that exercise mainly benefits the consolidation of memories, with exercise prior to motor practice improving early non-sleep consolidation (SMD, 0.58; 95 % CI, 0.30-0.86; p < 0.001), and post-practice exercise facilitating sleep-dependent consolidation (SMD, 0.62; 95 % CI, 0.34-0.90; p < 0.001). Strongest effects exist for high exercise intensities, and motor task nature appears to be another relevant modulator. We demonstrate that acute cardiovascular exercise particularly promotes the consolidation of acquired motor memories, and exercise timing, and intensity as well as motor task nature seem to critically modulate this relationship. These findings are discussed within currently proposed models of motor memory formation and considering molecular and systemic mechanisms of neural plasticity.

Discordance Between Stimulated and Spontaneous Growth Hormone Levels in Short Children Is Dependent on Cut-Off Level and Partly Explained by Refractoriness

BACKGROUND

A growth hormone (GH) stimulation test is the recommended method for evaluating GH levels in children with possible GH deficiency (GHD). However, serial measurements of nocturnal spontaneous GH secretion are also performed. Divergent results from these tests have been reported, but with variable frequencies.

OBJECTIVES

To investigate whether performing one or two GH tests is associated with the probability to diagnose a child with GHD; the frequency of divergent results in the arginine-insulin tolerance test (AITT) and the nocturnal spontaneous test using different cut-off levels, and whether refractoriness may explain some of the discordance.

METHODS

In a population-based setting, the medical records of all short children evaluated for possible GHD during January 1993-February 2017 were reviewed. Twenty-one patients had been evaluated with one GH test only and 102 children had been evaluated with a spontaneous nocturnal GH test followed immediately by a complete AITT. Divergent results were defined as having a pathological response on only one of the tests when using 3, 5, 7, and 10 µg/L as cut-offs for peak GH on both tests, 1.1 and 3.3 µg/L for mean nocturnal values and receiver operating characteristic curves-derived cut-offs for nocturnal values.

RESULTS

Children evaluated with one test only were more often diagnosed with GHD compared with children evaluated with both tests (48 vs. 19%, p = 0.019). Divergent results were found in 6-42% of the patients, with higher frequencies seen when higher cut-offs were applied. A higher proportion of patients with stimulated peak values ≤ 7 and ≤ 5 µg/L had a spontaneous peak within 2 h before the start of the AITT compared with patients with higher stimulated peak values (68 vs. 45%, p = 0.026, and 77 vs. 48%, p = 0.033, respectively).

CONCLUSIONS

Divergent results between AITT and nocturnal spontaneous secretion are common in short children, dependent on the cut-offs applied and partly due to refractoriness. Performing both tests decreases the risk of over diagnosing GHD in short children.

The effect of 30-m repeated sprint exercise on muscle damage indicators, serum insulin-like growth factor-Iand cortisol

Study aim: The purpose of this study was to examine the effects of arepeated sprint exercise protocol on muscle damage indicators, serum IGF-Iand cortisol levels.

Material and methods: Nine trained male subjects (age 23.3 ± 3.6 years) completed arepeated sprint protocol consisting of two sets of 10 × 30-m maximal sprints with 30 s of active recovery between sprints and 5 min of passive recovery between sets. The isometric strength and flexibility were measured before, immediately after and 24 hours after exercise. 30-m maximal sprint time was measured before and 24 hours after exercise. Blood samples were taken before, immediately after and 24 hours after exercise.

Results: Isometric strength and flexibility were significantly decreased after exercise and 24 hours after exercise (p < 0.05). 30-m sprint time was significantly increased 24 hours after exercise (p < 0.05). Asignificant increase in serum lactate dehydrogenase, IGF-Iand cortisol were found after exercise (p < 0.05). Serum creatine kinase increased significantly immediately after and 24 hours after exercise compared to pre-exercise values (p < 0.05).

Conclusion: Our data show that due to increased serum IGF-Ilevel, repeated sprint exercise may have anabolic effects as well as traumatic effects on the muscles.

The Neuroprotective Effects of Exercise: Maintaining a Healthy Brain Throughout Aging

Physical activity plays an essential role in maintaining a healthy body, yet it also provides unique benefits for the vascular and cellular systems that sustain a healthy brain. While the benefit of exercise has been observed in humans of all ages, the availability of preclinical models has permitted systematic investigations into the mechanisms by which exercise supports and protects the brain. Over the past twenty-five years, rodent models have shown that increased physical activity elevates neurotrophic factors in the hippocampal and cortical areas, facilitating neurotransmission throughout the brain. Increased physical activity (such as by the voluntary use of a running wheel or regular, timed sessions on a treadmill) also promotes proliferation, maturation and survival of cells in the dentate gyrus, contributing to the process of adult hippocampal neurogenesis. In this way, rodent studies have tremendous value as they demonstrate that an 'active lifestyle' has the capacity to ameliorate a number of age-related changes in the brain, including the decline in adult neurogenesis. Moreover, these studies have shown that greater physical activity may protect the brain health into advanced age through a number of complimentary mechanisms: in addition to upregulating factors in pro-survival neurotrophic pathways and enhancing synaptic plasticity, increased physical activity promotes brain health by supporting the cerebrovasculature, sustaining the integrity of the blood-brain barrier, increasing glymphatic clearance and proteolytic degradation of amyloid beta species, and regulating microglia activation. Collectively, preclinical studies demonstrate that exercise initiates diverse and powerful neuroprotective pathways that may converge to promote continued brain health into old age. This review will draw on both seminal and current literature that highlights mechanisms by which exercise supports the functioning of the brain, and aids in its protection.

Exercise-Induced Neuroplasticity: A Mechanistic Model and Prospects for Promoting Plasticity

Aerobic exercise improves cognitive and motor function by inducing neural changes detected using molecular, cellular, and systems level neuroscience techniques. This review unifies the knowledge gained across various neuroscience techniques to provide a comprehensive profile of the neural mechanisms that mediate exercise-induced neuroplasticity. Using a model of exercise-induced neuroplasticity, this review emphasizes the sequence of neural events that accompany exercise, and ultimately promote changes in human performance. This is achieved by differentiating between neuroplasticity induced by acute versus chronic aerobic exercise. Furthermore, this review emphasizes experimental considerations that influence the opportunity to observe exercise-induced neuroplasticity in humans. These include modifiable factors associated with the exercise intervention and nonmodifiable factors such as biological sex, ovarian hormones, genetic variations, and fitness level. To maximize the beneficial effects of exercise in health, disease, and following injury, future research should continue to explore the mechanisms that mediate exercise-induced neuroplasticity. This review identifies some fundamental gaps in knowledge that may serve to guide future research in this area.

Sex-related differences in fuel utilization and hormonal response to exercise: implications for individuals with type 1 diabetes

Sex-related differences in metabolic and neuroendocrine response to exercise in individuals without diabetes have been well established. Men and women differ in fuel selection during exercise, in which women rely to a greater extent on fat oxidation, whereas males rely mostly on carbohydrate oxidation for energy production. The difference in fuel selection appears to be mediated by sex-related differences in hormonal (including catecholamines, growth hormone, and estrogen) response to different types and intensities of exercise. In general, men exhibit an amplified counter-regulatory response to exercise, with elevated levels of catecholamines compared with women. However, women exhibit greater sensitivity to the lipolytic action of the catecholamines and deplete less of their glycogen stores than men during exercise, which suggests that women may experience a greater defense in blood glucose control after exercise than men. Conversely, little is known about sex-related differences in response to exercise in individuals with type 1 diabetes (T1D). A single study investigating sex-related differences in response to moderate aerobic exercise in individuals with T1D found sex-related differences in catecholamine response and fuel selection, but changes in blood glucose were not measured. To our knowledge, there are no studies investigating sex-related differences in blood glucose responses to different types and intensities of exercise in individuals with T1D. This review summarizes sex-related differences in exercise responses that could potentially impact blood glucose levels during exercise in individuals with T1D and highlights the need for further research.

Neurotrophic and Neuroregenerative Effects of GH/IGF1

Introduction. Human neurodegenerative diseases increase progressively with age and present a high social and economic burden. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are both growth factors exerting trophic effects on neuronal regeneration in the central nervous system (CNS) and peripheral nervous system (PNS). GH and IGF-1 stimulate protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells, and favor neuronal survival, inhibiting apoptosis. This study aims to evaluate the effect of GH and IGF-1 on neurons, and their possible therapeutic clinical applications on neuron regeneration in human subjects. Methods. In the literature, we searched the clinical trials and followed up studies in humans, which have evaluated the effect of GH/IGF-1 on CNS and PNS. The following keywords have been used: “GH/IGF-1” associated with “neuroregeneration”, “amyotrophic lateral sclerosis”, “Alzheimer disease”, “Parkinson’s disease”, “brain”, and “neuron”. Results. Of the retrieved articles, we found nine articles about the effect of GH in healthy patients who suffered from traumatic brain injury (TBI), and six studies (four using IGF-1 and two GH therapy) in patients with amyotrophic lateral sclerosis (ALS). The administration of GH in patients after TBI showed a significantly positive recovery of brain and mental function. Treatment with GH and IGF-1 therapy in ALS produced contradictory results. Conclusions. Although strong findings have shown the positive effects of GH/IGF-1 administration on neuroregeneration in animal models, a very limited number of clinical studies have been conducted in humans. GH/IGF-1 therapy had different effects in patients with TBI, evidencing a high recovery of neurons and clinical outcome, while in ALS patients, the results are contradictory. More complex clinical protocols are necessary to evaluate the effect of GH/IGF-1 efficacy in neurodegenerative diseases. It seems evident that GH and IGF-1 therapy favors the optimal recovery of neurons when a consistent residual activity is still present. Furthermore, the effect of GH/IGF-1 could be mediated by, or be overlapped with that of other hormones, such as estradiol and testosterone.

Skeletal Muscle as an Endocrine Organ: The Role of Myokines in Exercise Adaptations

Exercise stimulates the release of proteins with autocrine, paracrine, or endocrine functions produced in skeletal muscle, termed myokines. Based on the current state of knowledge, the major physiological function of myokines is to protect the functionality and to enhance the exercise capacity of skeletal muscle. Myokines control adaptive processes in skeletal muscle by acting as paracrine regulators of fuel oxidation, hypertrophy, angiogenesis, inflammatory processes, and regulation of the extracellular matrix. Endocrine functions attributed to myokines are involved in body weight regulation, low-grade inflammation, insulin sensitivity, suppression of tumor growth, and improvement of cognitive function. Muscle-derived regulatory RNAs and metabolites, as well as the design of modified myokines, are promising novel directions for treatment of chronic diseases.

Combined sprint and resistance training abrogates age differences in somatotropic hormones

The aim of this investigation was to compare serum growth hormone (GH), insulin-like growth factor-1 (IGF-1) and insulin-like growth factor-binding protein-3 (IGFBP-3) in response to a combined sprint and resistance training (CSRT) program in young and middle-aged men.Thirty-eight healthy, moderately trained men participated in this study. Young and middle-aged men were randomly assigned to, a young training group (YT = 10, 21.4±1.2yrs) ora young control group (YC = 9, 21.6±1.8 yrs), a middle-aged training group (MAT = 10, 40.4±2.1 yrs) or a middle-aged control group (MAC = 9, 40.5±1.8 yrs). Participants performed the Wingate Anaerobic Test (WAnT) before and after a 13-week CSRT program (three sessions per week). Blood samples were collected at rest, after warm-up, immediately post-WAnT, and 10 min post-WAnT. CSRT induced increases in GH at rest and in response to the WAnT in YT and MAT (P<0.05). CSRT-induced increases were observed for IGF-1 and IGFBP-3 at rest in MAT only (P<0.05). Pre-training, GH, IGF-1 and IGFBP-3 were significantly higher at rest and in response to the WAnT in young participants as compared to their middle-aged counterparts (P<0.05). Post-training, YT and MAT had comparable basal GH (P>0.05). In response to the WAnT, amelioration of the age-effect was observed between YT and MAT for IGF-1 and IGF-1/IGFBP-3 ratio following CSRT (P>0.05). These data suggest that CSRT increases the activity of the GH/IGF-1 axis at rest and in response to the WAnT in young and middle-aged men. In addition, CSRT reduces the normal age-related decline of somatotropic hormones in middle-age men.

Relation between serum myokines and phase II cardiac rehabilitation

Patients with coronary heart disease or acute myocardial infarction after cardiac catheterization with stenting referred for phase II cardiac rehabilitation (CR) were grouped according to their preference. Cardio-pulmonary exercise testing (CPET) was used to determine oxygen uptake ((Equation is included in full-text article.)) at peak exercise and anaerobic threshold (AT). The control patients received counseling only while the experiment group received 36 sessions of CR in 3 to 6 months. Exercise physiology parameters and serum myokines (myostatin, insulin-like growth factor-1 (IGF-1), and interleukin-6 (IL-6) were measured pre- and postrehabilitation.There were 29 patients in the experiment group and 10 in the control group, with no significant differences in baseline parameters. The experiment group had prominent progress in aerobic capacity and body composition after CR, but their serum myokine concentrations did not change significantly. Serum myostatin is positively correlated to peak (Equation is included in full-text article.)pre- and post-training, and pretraining AT (Equation is included in full-text article.), after adjusting for age, sex, and body composition. Serum IGF-1 is positively correlated with grip strength before training.Serum myostatin level is positively correlated to aerobic capacity, and IGF-1 level is positively correlated to grip strength in cardiac patients receiving CR.

The Effects of Acute Exercise on Mood, Cognition, Neurophysiology, and Neurochemical Pathways: A Review

A significant body of work has investigated the effects of acute exercise, defined as a single bout of physical activity, on mood and cognitive functions in humans. Several excellent recent reviews have summarized these findings; however, the neurobiological basis of these results has received less attention. In this review, we will first briefly summarize the cognitive and behavioral changes that occur with acute exercise in humans. We will then review the results from both human and animal model studies documenting the wide range of neurophysiological and neurochemical alterations that occur after a single bout of exercise. Finally, we will discuss the strengths, weaknesses, and missing elements in the current literature, as well as offer an acute exercise standardization protocol and provide possible goals for future research.

Acute effects of physical exercise on the serum insulin-like growth factor system in women with fibromyalgia

BACKGROUND

Increased Serum insulin-like growth factor-1 (S-IGF-1) has been noted after physical activity in healthy subjects, while the acute release of S-IGF-1 in relation to exercise has not previously been studied in women with fibromyalgia (FM). S-IGF-1 and its binding protein (S-IGFBP-3) are mediated by growth hormone and have anabolic effects on the skeletal muscle. Aim of the study was to investigate acute release of IGF-1 after aerobic exercise in women with FM.

METHODS

The acute effect of physical exercise on S-IGF-1 and S-IGFBP-3 were studied in 22 women with FM and in 27 healthy controls during moderate and high-intensity cycling (i.e. ratings 12-13 and 15-17, on Borg's perceived exertion scale (RPE), respectively). Self-reported pain and fatigue were recorded. Differences within and between the two groups were analyzed.

RESULTS

After 15 min of bicycling, S-IGF-1 and S-IGFBP-3 increased both within the group with FM and in the healthy controls (p < 0.01). The increases in S-IGF-1 did not significantly differ between the women with FM and the healthy control group (mean increase 11 ± 10 vs. 11 ± 15 ng/ml and 13 ± 10 vs. 19 ± 22 ng/ml) when bicycling at moderate or high intensity, respectively. Self-reported pain and fatigue during exercise, irrespective of intensity, were higher in women with FM compared with healthy controls (p < 0.001).

CONCLUSIONS

Fifteen minutes bicycling at moderate intensity was sufficient to acutely mobilise S-IGF-1 in women with FM similarly to healthy controls in spite of higher score of fatigue and pain in women with FM. Hence, patients with FM were able to activate their skeletal muscle metabolism during a short, moderate bout of exercise and were not resistant to training effects. The result is important for encouraging clinical rehabilitation of patients with FM who commonly exercise at a moderate, rather than at a high-intensity level.

TRIAL REGISTRATION

ClinicalTrials.govNCT01592916 , May 4, 2012.

Rigorous Running Increases Growth Hormone and Insulin-Like Growth Factor-I Without Altering Ghrelin

It has been suggested that ghrelin may play a role in growth hormone (GH) responses to exercise. The present study was designed to determine whether ghrelin, GH, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGFBP-3) were altered by a progressively intense running protocol. Six well-trained male volunteers completed a progressively intense intermittent exercise trial on a treadmill that included four exercise intensities: 60%, 75%, 90%, and 100% of Vo2max. Blood samples were collected before exercise, after each exercise intensity, and at 15 and 30 mins following the exercise protocol. Subjects also completed a separate control trial at the same time of day that excluded exercise. GH changed significantly over time, and GH area under the curve (AUC) was significantly higher in the exercise trial than the control trial. Area under the curve IGF-I levels for the exercise trial were significantly higher than the control trial. There was no difference in the ghrelin and IGFBP-3 responses to the exercise and control trials. Pearson correlation coefficients revealed significant relationships between ghrelin and both IGF-I and IGFBP-3; however, no relationship between ghrelin and GH was found. In conclusion, intense running produces increases in total IGF-I concentrations, which differs from findings in previous studies using less rigorous running protocols and less frequent blood sampling regimens. Moreover, running exercise that produces substantial increases in GH does not affect peripheral ghrelin levels; however, significant relationships between ghrelin and both IGF-I and IGFBP-3 exist during intense intermittent running and recovery, which warrants further investigation.

Association of serum myokines and aerobic exercise training in patients with spinal cord injury: an observational study

Background

Patients with spinal cord injury (SCI) have a higher prevalence of cardiovascular diseases compared to the healthy population. Aerobic exercise training is one of the recommended treatments. However, literature regarding the effect of aerobic training on patients with SCI is scarce. This study evaluated changes in parameters of exercise physiology and serum myokines immediately after exercise and after a training program among patients with SCI.

Methods

Male patients with SCI and age- and sex-matched healthy individuals were recruited. Cardio-pulmonary exercise testing (CPET) was used to determine oxygen uptake at peak exercise and anaerobic threshold in both groups. The patients with SCI attended aerobic exercise training for 36 sessions within 12–16 weeks. Basic data, hemodynamic and exercise physiology parameters, and serum myokine (myostatin, IGF-1, and follistatin) concentrations were measured pre- and post-exercise in both groups, and were repeated in patients with SCI post-training.

Results

Eleven patients with SCI underwent CPET and 5 completed the training. The 11 patients and 16 healthy adults had no differences in baseline serum myokine concentrations before CPET. Immediately after the CPET, the reference group had an 18 ± 19 % increase in serum IGF-1, while the patients had no observable myokine changes. After aerobic exercise training, the 5 patients had a 48 ± 18 % increase in serum myostatin compared to the pre-training level, although the body weight and exercise physiology parameters remained unchanged.

Conclusions

Acute exercise to exhaustion in CPET results in an immediate increase in serum IGF-1 in healthy individuals while aerobic exercise training results in increased serum myostatin in patients with SCI.

Estimated Prestroke Peak VO2 Is Related to Circulating IGF-1 Levels During Acute Stroke

Background Insulin-like growth factor-1 (IGF-1) is neuroprotective after stroke and is regulated by insulin-like binding protein-3 (IGFBP-3). In healthy individuals, exercise and improved aerobic fitness (peak oxygen uptake; peak VO₂) increases IGF-1 in circulation. Understanding the relationship between estimated prestroke aerobic fitness and IGF-1 and IGFBP-3 after stroke may provide insight into the benefits of exercise and aerobic fitness on stroke recovery. Objective The purpose of this study was to determine the relationship of IGF-1 and IGFBP-3 to estimated prestroke peak VO₂ in individuals with acute stroke. We hypothesized that (1) estimated prestroke peak VO₂ would be related to IGF-1 and IGFBP-3 and (2) individuals with higher than median IGF-1 levels will have higher estimated prestroke peak VO₂ compared to those with lower than median levels. Methods Fifteen individuals with acute stroke had blood sampled within 72 hours of hospital admission. Prestroke peak VO₂ was estimated using a nonexercise prediction equation. IGF-1 and IGFBP-3 levels were quantified using enzyme-linked immunoassay. Results Estimated prestroke peak VO₂ was significantly related to circulating IGF-1 levels (r = .60; P = .02) but not IGFBP-3. Individuals with higher than median IGF-1 (117.9 ng/mL) had significantly better estimated aerobic fitness (32.4 ± 6.9 mL kg^-1 min^-1) than those with lower than median IGF-1 (20.7 ± 7.8 mL kg^-1 min^-1; P = .03). Conclusions Improving aerobic fitness prior to stroke may be beneficial by increasing baseline IGF-1 levels. These results set the groundwork for future clinical trials to determine whether high IGF-1 and aerobic fitness are beneficial to stroke recovery by providing neuroprotection and improving function.

Molecular and Cellular Mechanisms of Muscle Aging and Sarcopenia and Effects of Electrical Stimulation in Seniors

The prolongation of skeletal muscle strength in aging and neuromuscular disease has been the objective of numerous studies employing a variety of approaches. It is generally accepted that cumulative failure to repair damage related to an overall decrease in anabolic processes is a primary cause of functional impairment in muscle. The functional performance of skeletal muscle tissues declines during post- natal life and it is compromised in different diseases, due to an alteration in muscle fiber composition and an overall decrease in muscle integrity as fibrotic invasions replace functional contractile tissue. Characteristics of skeletal muscle aging and diseases include a conspicuous reduction in myofiber plasticity (due to the progressive loss of muscle mass and in particular of the most powerful fast fibers), alteration in muscle-specific transcriptional mechanisms, and muscle atrophy. An early decrease in protein synthetic rates is followed by a later increase in protein degradation, to affect biochemical, physiological, and morphological parameters of muscle fibers during the aging process. Alterations in regenerative pathways also compromise the functionality of muscle tissues. In this review we will give an overview of the work on molecular and cellular mechanisms of aging and sarcopenia and the effects of electrical stimulation in seniors..

Linking brains and brawn: exercise and the evolution of human neurobiology

The hunting and gathering lifestyle adopted by human ancestors around 2 Ma required a large increase in aerobic activity. High levels of physical activity altered the shape of the human body, enabling access to new food resources (e.g. animal protein) in a changing environment. Recent experimental work provides strong evidence that both acute bouts of exercise and long-term exercise training increase the size of brain components and improve cognitive performance in humans and other taxa. However, to date, researchers have not explored the possibility that the increases in aerobic capacity and physical activity that occurred during human evolution directly influenced the human brain. Here, we hypothesize that proximate mechanisms linking physical activity and neurobiology in living species may help to explain changes in brain size and cognitive function during human evolution. We review evidence that selection acting on endurance increased baseline neurotrophin and growth factor signalling (compounds responsible for both brain growth and for metabolic regulation during exercise) in some mammals, which in turn led to increased overall brain growth and development. This hypothesis suggests that a significant portion of human neurobiology evolved due to selection acting on features unrelated to cognitive performance.

GH responses to two consecutive bouts of respiratory muscle endurance training in healthy adults

Repetition of voluntary exercise bouts and of different pharmacological GH-releasing stimuli at 2-h intervals is associated with a complete abolishment of GH responsiveness. By contrast, a different pattern is observed after repeated neuromuscular electrostimulation, which is characterized by preservation of GH responsiveness. Aim of the study was to evaluate GH responses to repeated bouts of respiratory muscle endurance training (RMET) by mean of a specific commercially available device (Spiro Tiger®). Eight healthy men underwent an incremental progressive RMET protocol of 11 daily sessions. Blood samplings for GH, cortisol and lactate (LA) determinations were collected during the 12th session, which was composed of two consecutive bouts of RMET (of identical intensity and duration: 1 min at a respiration rate of 28 acts/min, 5 min at 32 acts/min, 5 min at 34 acts/min, 4 min at 36 acts/min) at a 2 h interval. Baseline GH levels (mean: 0.9±0.4 ng/ml) significantly (p<0.01) increased after the first bout of RMET (peak: 15.7±4.0 ng/ml). The administration of the second bout of RMET resulted in a significantly lower (p<0.05) GH increase (peak: 3.9±0.8 ng/ml) in comparison with the first one. Baseline LA levels (mean: 1.2±0.1 mmol/l) significantly increased (p<0.001) after the first bout of RMET (peak: 2.3±0.2 mmol/l). The administration of the second RMET bout resulted in a comparable LA increase (from a basal value of 1.2±0.1 mmol/l up to a peak of 2.0±0.1 mmol/l, p<0.001). The first bout of RMET caused a significant increase of cortisol levels (p<0.01), starting from a basal mean value of 142.9±9.4 ng/ml up to a peak of 188.8±10.3 ng/ml. By contrast, the second bout of RMET did not induce any significant change of cortisol levels (basal: 149.1±9.0 ng/ml, peak: 168.5±5.1 ng/ml). In conclusion, a single bout of RMET is capable of stimulating GH and cortisol secretions and LA production. When a second bout is repeated after 2 h, there is a blunting of GH and cortisol responses with a preservation of LA release. Further studies are needed to schedule long-term RMET protocols capable of persistently stimulating GH-IGF-I release and to maximally enhance the ergogenic and metabolic benefits of this intervention either in normal subjects (e.g. athletes) or patients with an impairment of motor capabilities requested to perform normal daily activities (i.e. severely obese and elderly people).

IGF-I measurement across blood, interstitial fluid, and muscle biocompartments following explosive, high-power exercise

Insulin-like growth factor-I (IGF-I) resides across different biocompartments [blood, interstitial fluid (ISF), and muscle]. Whether circulating IGF-I responses to exercise reflect local events remains uncertain. We measured the IGF-I response to plyometric exercise across blood, ISF, and muscle biopsy from the vastus lateralis. Twenty volunteers (8 men, 12 women, 22 ± 1 yr) performed 10 sets of 10 plyometric jump repetitions at a 40% 1-repetition maximum. Blood, ISF, and muscle samples were taken pre- and postexercise. Circulating IGF-I increased postexercise: total IGF-I (preexercise = 546 ± 42, midexercise = 585 ± 43, postexercise = 597 ± 45, +30 = 557 ± 42, +60 = 536 ± 40, +120 = 567 ± 42 ng/ml; midexercise, postexercise, and +120 greater than preexercise, P < 0.05); Free IGF-I (preexercise = 0.83 ± 0.09, midexercise = 0.78 ± 0.10, postexercise = 0.79 ± 0.11, +30 = 0.93 ± 0.10, +60 = 0.88 ± 0.10, + 120 = 0.91 ± 0.11 ng/ml; +30 greater than all other preceding time points, P < 0.05). No exercise-induced changes were observed for ISF IGF-I (preexercise = 2.35 ± 0.29, postexercise = 2.46 ± 0.35 ng/ml). No changes were observed for skeletal muscle IGF-I protein, although IGF-I mRNA content increased ∼40% postexercise. The increase in circulating total and free IGF-I was not correlated with increases in ISF IGF-I or muscle IGF-I protein content. Our data indicate that exercise-induced increases in circulating IGF-I are not reflective of local IGF-I signaling.

Aerobic exercise improves hippocampal function and increases BDNF in the serum of young adult males

Physical activity has been reported to improve cognitive function in humans and rodents, possibly via a brain-derived neurotrophic factor (BDNF)-regulated mechanism. In this study of human subjects, we have assessed the effects of acute and chronic exercise on performance of a face-name matching task, which recruits the hippocampus and associated structures of the medial temporal lobe, and the Stroop word-colour task, which does not, and have assessed circulating concentrations of BDNF and IGF-1 in parallel. The results show that a short period of high-intensity cycling results in enhancements in performance of the face-name matching, but not the Stroop, task. These changes in cognitive function were paralleled by increased concentration of BDNF, but not IGF-1, in the serum of exercising subjects. 3 weeks of cycling training had no effect on cardiovascular fitness, as assessed by VO2 scores, cognitive function, or serum BDNF concentration. Increases in fitness, cognitive function and serum BDNF response to acute exercise were observed following 5 weeks of aerobic training. These data indicate that both acute and chronic exercise improve medial temporal lobe function concomitant with increased concentrations of BDNF in the serum, suggesting a possible functional role for this neurotrophic factor in exercise-induced cognitive enhancement in humans.

Relationship between exercise capacity and brain size in mammals

BACKGROUND

A great deal of experimental research supports strong associations between exercise, cognition, neurogenesis and neuroprotection in mammals. Much of this work has focused on neurogenesis in individual subjects in a limited number of species. However, no study to date has examined the relationship between exercise and neurobiology across a wide range of mammalian taxa. It is possible that exercise and neurobiology are related across evolutionary time. To test this hypothesis, this study examines the association between exercise and brain size across a wide range of mammals.

METHODOLOGY/PRINCIPAL FINDINGS

Controlling for associations with body size, we examined the correlation between brain size and a proxy for exercise frequency and capacity, maximum metabolic rate (MMR; ml O(2) min(-1)). We collected brain sizes and MMRs from the literature and calculated residuals from the least-squares regression line describing the relationship between body mass and each variable of interest. We then analyzed the correlation between residual brain size and residual MMR both before and after controlling for phylogeny using phylogenetic independent contrasts. We found a significant positive correlation between maximum metabolic rate and brain size across a wide range of taxa.

CONCLUSIONS

These results suggest a novel hypothesis that links brain size to the evolution of locomotor behaviors in a wide variety of mammalian species. In the end, we suggest that some portion of brain size in nonhuman mammals may have evolved in conjunction with increases in exercise capacity rather than solely in response to selection related to cognitive abilities.

A novel, noninvasive transdermal fluid sampling methodology: IGF-I measurement following exercise

This study tested the hypothesis that transdermal fluid (TDF) provides a more sensitive and accurate measure of exercise-induced increases in insulin-like growth factor-I (IGF-I) than serum, and that these increases are detectable proximal, but not distal, to the exercising muscle. A novel, noninvasive methodology was used to collect TDF, followed by sampling of total IGF-I (tIGF-I) and free IGF-I (fIGF-I) in TDF and serum following an acute bout of exercise. Experiment 1: eight men (23 ± 3 yrs, 79 ± 7 kg) underwent two conditions (resting and 60 min of cycling exercise at 60% V̇o2peak) in which serum and forearm TDF were collected for comparison. There were no significant changes in tIGF-I or fIGF-I in TDF obtained from the forearm or from serum following exercise ( P > 0.05); however, the proportion of fIGF-I to tIGF-I in TDF was approximately fourfold greater than that of serum ( P ≤ 0.05). These data suggest that changes in TDF IGF-I are not evident when TDF is sampled distal from the working tissue. To determine whether exercise-induced increases in local IGF-I could be detected when TDF was sampled directly over the active muscle group, we performed a second experiment. Experiment 2: fourteen subjects (22 ± 4 yr, 68 ± 11 kg) underwent an acute plyometric exercise condition consisting of 10 sets of 10 plyometric jumps with 2-min rest between sets. We observed a significant increase in TDF tIGF-I following exercise ( P ≤ 0.05) but no change in serum tIGF-I ( P > 0.05). Overall, these data suggest that TDF may provide a noninvasive means of monitoring acute exercise-induced changes in local IGF-I when sampled in proximity to exercising muscles. Moreover, our finding that the proportion of free to tIGF-I was greater in TDF than in serum suggests that changes in local IGF-I may be captured more readily using this system.

GH responses to two consecutive bouts of whole body vibration, maximal voluntary contractions or vibration alternated with maximal voluntary contractions administered at 2-h intervals in healthy adults

BACKGROUND

Pharmacological or exercise stimuli repeated at a short interval (but not electrical muscle stimulation) are associated with a blunting of GH responsiveness.

AIM

To compare GH responses to repeated bout of three different GH-releasing stimuli.

METHODS

The effects of two consecutive bouts (with a 2-h interval) of whole body vibrations (WBV), maximal voluntary contractions alone (MVC), or alternated with WBV (MVC-WBV) on blood GH and lactate (LA) were assessed in nine young males.

RESULTS

Baseline levels of both GH and LA increased significantly after the first bout of all the tested stimuli, and were significantly lower after WBV than after MVC or MVC alternated with WBV, no difference being detected between these last. The administration of a second bout resulted in significantly lower GH increases than those elicited in the first bout in the three different tests; significantly lower LA responses were recorded after the second bout of MVC and MVC-WBV when compared with those obtained after the first bout, while no significant differences were observed after the two WBV bouts for LA. All responses after the second bout of MVC and MVC-WBV were significantly higher than those observed after WBV alone. GH concentrations were significantly correlated with LA after all stimuli, although LA concentrations after the second bout were associated with markedly lower GH levels.

CONCLUSIONS

A significant blunting of GH responsiveness ensues after a second bout of different GH-releasing stimuli, independent from the amount of GH released after the first bout. This is a pattern also observed for other pharmacological stimuli and exercise modalities, and suggests a common mechanism underlying different GH-releasing stimuli.

Effect of high- and low-intensity exercise and metabolic acidosis on levels of GH, IGF-I, IGFBP-3 and cortisol

OBJECTIVE

The purpose of the present study was to examine the acute hormonal response of a short term high-intensity training (HIT) versus a high volume endurance training (HVT) and to determine the contribution of the metabolic acidosis as a stimulus for possibly different reactions of circulating hGH, IGF-1, IGFBP-3 and cortisol.

DESIGN

Eleven subjects participated in three experimental trials separated by one week. Two times subjects performed four 30s maximal effort exercise bouts on a cycle ergometer separated by 5 min rest each. Before the exercise subjects either received (single-blinded) bicarbonate (HIT (B)) or a placebo (HIT (P)). The third exercise trail consisted of a constant load exercise for 1h at 50% VO₂max (HVT). Venous blood samples were taken under resting conditions, 10 min, 60 min and 240 min after each exercise condition to determine hGH, IGF-1, IGFBP-3 and cortisol serum concentrations. Capillary blood samples were taken to determine lactate concentrations and blood gas parameters.

RESULTS

Power output, mean lactate concentrations and mean pH values were significantly higher during HIT (B) compared to HIT (P). Serum cortisol and hGH concentrations were significantly increased 10 min post exercise in both HIT interventions. IGFBP-3 was only significantly increased after HIT (P), whereas IGF-1 was not affected by any of the interventions. HVT showed no significant effects on cortisol, hGH, IGF-1 and IGFBP-3 levels. Additionally it was shown that the diminished acidosis during HIT (B) attenuates the cortisol and hGH response.

CONCLUSIONS

The present study suggests that HIT/acidosis is a stimulus for exercise-induced cortisol/hGH secretion, but not for IGF-1 and IGFBP-3 under these experimental conditions. These findings might be relevant for arrangements of interval training, due to the fact that active or passive recovery during rest periods influence the acid base status and may therefore influence the hormonal response.

Effect of low-intensity aerobic exercise on insulin-like growth factor-I and insulin-like growth factor-binding proteins in healthy men

Increased concentrations of circulating insulin-like growth factor-I (IGF-I) or IGF-I relative to IGF-binding proteins (IGFBPs) are associated with increased risk of developing several forms of cancer. Conversely, exercise is linked with reduced risk. This study aims to investigate the effect of a low-intensity exercise program on circulating levels of IGF-I, IGFBP-1, and IGFBP-3, in previously sedentary males. Fourteen healthy men participated in cycle ergometer training at lactate threshold intensity for 60 min/day, 5 days/week for 6 weeks. After aerobic training, insulin sensitivity improved by 20%, while fasting insulin levels decreased by 13%. Simultaneously, low-intensity aerobic training decreased the circulating levels of IGF-I by 9%, while IGFBP-1 levels increased by 16%. An interesting finding was that higher pretraining level of IGF-I was associated with greater decline in IGF-I with training. Insulin-sensitizing low-intensity aerobic exercise is thus considered to be an effective method for downregulating IGF-I and upregulating IGFBP-1 levels.

Brief, high intensity exercise alters serum ghrelin and growth hormone concentrations but not IGF-I, IGF-II or IGF-I bioactivity

Exercise stimulates growth hormone (GH) release, but there are conflicting reports regarding the acute effects of exercise on circulating ghrelin and insulin-like growth factor (IGF) concentrations. This investigation examined (1) the effect of a single sprint on circulating GH, ghrelin and IGF concentrations as well as a marker of IGF-I bioactivity, and (2) whether the number of muscle actions performed during a sprint influences these responses. Seven healthy men completed 3 trials in a random order. In two exercise trials they performed a single 30-s sprint on a cycle ergometer against a resistance equivalent to either 7% (FAST) or 9% (SLOW) of their body mass. In the other they rested in the laboratory (CON). Blood samples were taken pre-, immediately post-, 10 and 30 min post-exercise, and at equivalent times in the CON trial. Total ghrelin concentrations declined after the sprint and were significantly lower after 30 min of recovery than they were pre-exercise (pre-exercise vs. 30 min; FAST, 0.62 (0.19) vs. 0.49 (0.16) microg/L, P<0.001; SLOW, 0.59 (0.15) vs. 0.47 (0.13) microg/L, P<0.001). GH concentrations increased in both exercise trials and were greater in the FAST than the SLOW trial. Serum concentrations of total IGF-I, free IGF-I, total IGF-II, and IGF-I bioactivity did not change after sprinting. In conclusion, sprint exercise suppresses total ghrelin concentrations and stimulates GH release but does not alter IGF concentrations or bioactivity.

Immunological and growth mediator response to cross-country training in adolescent females

BACKGROUND

Exercise affects growth and development through a complex interaction between the endocrine, immune, and nervous systems. To date very little is known about how these systems respond to exercise in children or adolescents. Moreover, there are few studies that have examined growth factors, pro-inflammatory cytokines, and peripheral blood mononuclear cell responses to 'real-life' or field exercise solely in girls.

AIM

To determine the acute exercise-induced alterations in the growth hormone (GH)-insulinlike growth factor-I (IGF-I) axis, inflammatory cytokines, and certain aspects of immune function (white blood cell [WBC] subpopulations and their associated adhesion molecules) in a group of adolescent girls following a typical cross country practice.

METHODS

Eight, healthy, postpubertal, high school females, 15-18 years old, performed a single, typical, one hour cross-country practice session. Blood was sampled before and after the session.

RESULTS

Following exercise, lactate increased by 364 +/- 67% (p < 0.001). Significant increases were noted in circulating IL-6 (p < 0.023), TNF-alpha (p < 0.027), IL-1beta (p < 0.047) and IL-1ra (p < 0.002), as well as a substantial increase in GH (p < 0.007). The exercise led to significant increases in all WBC subpopulations and platelets. The most significant changes were observed for natural killer cells (p < 0.0005). The exercise significantly influenced adhesion molecules (such as CD62L, CD54).

CONCLUSIONS

These data demonstrate that an intense exercise bout in adolescent females leads to profound increases in inflammatory cytokines, with substantial changes in WBC and adhesion molecules. The role of these frequent, almost-daily perturbations on growth, development and immunity has yet to be determined.

The physiology of growth hormone and sport

The growth hormone (GH)/ insulin-like growth factor-I (IGF-I) axis exerts short-and long-term metabolic effects that are potentially important during exercise. Exercise is a potent stimulus to GH release and there is some evidence that the acute increase in GH is important in regulating substrate metabolism post-exercise. Regular exercise also increases 24-hour GH secretion rates, which potentially contributes to the physiologic changes induced by training. The effects of GH replacement in GH-deficient adults provide a useful model with which to study the effects of the more long-term effects of the GH/ IGF-I axis. There is convincing evidence that GH replacement increases exercise capacity. Measures of exercise performance including maximal oxygen uptake (VO2max) and ventilatory threshold (VeT) are impaired in GH deficiency and improved by GH replacement, probably through some combination of increased oxygen delivery to exercising muscle, increased fatty acid availability with glycogen sparing, increased muscle strength, improved body composition and improved thermoregulation. Administration of supraphysiologic doses of GH to athletes increases fatty acid availability and reduces oxidative protein loss particularly during exercise, and increases lean body mass. It is not known whether these effects translate to improved athletic performance, although recombinant human GH is known to be widely abused in sport. The model of acromegaly provides evidence that long-term GH excess does not result in improved performance but it is possible that a "window" exists in which the protein anabolic effects of supraphysiologic GH might be advantageous.

Effects of continuous versus intermittent exercise, obesity, and gender on growth hormone secretion

CONTEXT

Obesity attenuates spontaneous GH secretion and the GH response to exercise. Obese individuals often have low fitness levels, limiting their ability to complete a typical 30-min bout of continuous exercise. An alternative regimen in obese subjects may be shorter bouts of exercise interspersed throughout the day.

OBJECTIVE

The objective of the study was to examine whether intermittent and continuous exercise interventions evoke similar patterns of 24-h GH secretion and whether responses are attenuated in obese subjects or affected by gender.

DESIGN

This was a repeated-measures design in which each subject served as their own control.

SETTING

This study was conducted at the University of Virginia General Clinical Research Center.

SUBJECTS

Subjects were healthy nonobese (n = 15) and obese (n = 14) young adults.

INTERVENTIONS

Subjects were studied over 24 h at the General Clinical Research Center on three occasions: control, one 30-min bout of exercise, and three 10-min bouts of exercise.

MAIN OUTCOME MEASURES

Twenty-four hour GH secretion was measured.

RESULTS

Compared with unstimulated 24-h GH secretion, both intermittent and continuous exercise, at constant exercise intensity, resulted in severalfold elevation of 24-h integrated serum GH concentrations in young adults. Basal and pulsatile modes of GH secretion were attenuated both at rest and during exercise in obese subjects.

CONCLUSIONS

The present data suggest that continuous and intermittent exercise training should be comparably effective in increasing 24-h GH secretion.

The growth hormone/insulin-like growth factor-I axis in exercise and sport

The syndrome of adult GH deficiency and the effects of GH replacement therapy provide a useful model with which to study the effects of the GH/IGF-I axis on exercise physiology. Measures of exercise performance including maximal oxygen uptake and ventilatory threshold are impaired in adult GH deficiency and improved by GH replacement, probably through some combination of increased oxygen delivery to exercising muscle, increased fatty acid availability with glycogen sparing, increased muscle strength, improved body composition, and improved thermoregulation. In normal subjects, in addition to the long-term effects of GH/IGF-I status, there is evidence that the acute GH response to exercise is important in regulating substrate metabolism after exercise. Administration of supraphysiological doses of GH to athletes increases fatty acid availability and reduces oxidative protein loss, particularly during exercise, and increases lean body mass. Despite a lack of evidence that these metabolic effects translate to improved performance, GH abuse by athletes is widespread. Tests to detect GH abuse have been developed based on measurement in serum of 1) indirect markers of GH action, and 2) the relative proportions of the two major naturally occurring isoforms (20 and 22kDa) of GH. There is evidence that exercise performance and strength are improved by administration of GH and testosterone in combination to elderly subjects. The potential benefits of GH in these situations must be weighed against potential adverse effects.

Abuse of growth hormone among young athletes

The underground abuse of growth hormone (GH) among young athletes presents a challenge to medical professionals. Health care professionals providing knowledgeable guidance regarding healthy ways to improve performance and appearance, as well as accurate information regarding substances' perceived benefits, risks, and unknown qualities, is invaluable to the young athlete. Further research focused on the profile and motivation of young people who use GH is essential to understanding and intervening better with those who use these substances.

Effect of exercise, training, circadian rhythm, age, and sex on insulin-like growth factor-1 in the horse1

Insulin-like growth factor-1 could be a useful marker in the horse for diagnostic, selection, or forensic purposes, provided its physiological regulation is well understood. The objective of this study was to investigate factors, such as acute exercise, fitness training, time of day, sex, and age, that may influence serum IGF-1 in normal, healthy horses. Throughout a 9-wk training program, 6 geldings maintained a mean (+/- SEM) IGF-1 concentration of 302 +/- 29 ng/mL. Moderate or high intensity exercise had no effect on IGF-1 concentrations, when pre- and postexercise values were compared. Over a 24-h period, there was some variation in IGF-1 concentrations but no clear diurnal rhythm. Concentrations of IGF-1 were measured in a large population of thoroughbred horses (1,880) on 3 continents. The population deviated slightly from a normal distribution (P < 0.001) because of large IGF-1 concentrations in 10 horses. The global mean IGF-1 concentration was 310 +/- 2.2 ng/mL, with a greater mean value (P < 0.001) in gonad-intact males (336 +/- 5.6 ng/mL) than in females (303 +/- 3.2 ng/mL) or geldings (302 +/- 3.2 ng/mL). However, the greatest IGF-1 concentrations observed for all stallions, mares, and geldings were 627, 676, and 709 ng/mL, respectively. In mares and geldings, IGF-1 concentrations showed a gradual decrease with advancing age (P < 0.001), but the effect was much less marked in stallions. This study confirms that IGF-1 concentrations are stable, compared with GH concentrations, in the horse and that a meaningful measure of IGF-1 status can be obtained from a daily serum sample.

The ghrelin response to exercise before and after growth hormone administration

CONTEXT

We have previously shown that exercise-induced GH release is not mediated by ghrelin, but it remains to be studied whether the increase in GH may suppress postexercise ghrelin levels.

OBJECTIVE

The objective of this study was to characterize systemic ghrelin levels after exercise with and without concomitant GH administration.

DESIGN, PARTICIPANTS, AND INTERVENTION

Group A: Twenty-nine elite athletes (age, 18-37 yr) were studied after a maximal exercise test. Group B: In a double blind, placebo-controlled, parallel study, 32 healthy subjects (age, 18-33 yr) were randomized to placebo, GH 0.1 IU/kg per day, or GH 0.2 IU/kg per day for 4 wk. These subjects performed a multistage fitness test to assess maximum oxygen uptake at baseline and after 4 wk. We measured total circulating ghrelin levels before and immediately after exercise and at 15, 30, 60, 90, and 120 min after exercise.

RESULTS

Group A: Serum ghrelin levels after exercise decreased significantly (P < 0.01). Group B: Exercise at baseline was associated with a significant lowering of ghrelin levels after exercise (P < 0.0001). In addition, 4 wk of high-dose GH were followed by a further approximately 20% reduction in basal and after exercise serum ghrelin (micrograms per liter): 0.78 (range 0.52-1.17) vs. 0.63 (range 0.50-0.91), P < 0.05.

CONCLUSIONS

1) Ghrelin levels decrease significantly after exercise in elite athletes and healthy subjects. 2) High-dose GH suppresses ghrelin levels. 3) These data support the hypothesis that GH feedback inhibits ghrelin secretion.