Edmund O. Acevedo

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.

Increased training intensity effects on plasma lactate, ventilatory threshold, and endurance

The purpose of this study was to determine the effects of increased training intensity (ITI) on VO2max, plasma lactate accumulation, ventilatory threshold (VT), and performance in trained distance runners. Seven trained male distance runners increased their training intensity three d.wk-1 at 90-95% HRmax for eight wk. ITI did not alter VO2max (65.3 +/- 2.3 vs 65.8 +/- 2.4 ml.kg-1.min-1) but improved 10 km race time (means = 63 s decrease) and increased run time to exhaustion on the treadmill at the same speed and grade (means = 3.88 min). Significant decreases in plasma lactate concentration at 85 and 90% of VO2max were observed after ITI. No differences were found in plasma lactate at 65, 70, 75 or 80% of VO2max or VT following ITI. Significant correlations were obtained between 10 km race times and changes in plasma lactate at 85 and 90% of VO2max (r = 0.69 and 0.73, respectively). Lactate accumulation at both 2.5 and 4.0 mM were at a significantly greater percent of VO2max after ITI. Additionally, the changes in plasma lactate were dissociated from alterations in VT after ITI. These data indicate that previously trained runners can increase training intensity to improve endurance performance by lowering lactate at the intensity at which they trained despite no changes in VO2max and VT.

Adiponectin responses to continuous and progressively intense intermittent exercise.

PURPOSE Adiponectin is a recently discovered adipocyte protein that is lower in patients with coronary artery disease and in Type II diabetics who have insulin resistance. Regular exercise is known to be a preventative factor in the development of atherosclerosis and Type II diabetes. Acute exercise increases insulin sensitivity; however, it also increases beta-adrenergic and glucocorticoid activities that may suppress adiponectin expression. Two experiments were conducted to determine whether acute exercise affects adiponectin concentrations. METHODS In the first experiment, six healthy male subjects completed 30 min of heavy continuous running exercise at 79% of VO (2max). In the second experiment, well-trained runners completed strenuous intermittent exercise consisting of treadmill running at 60, 75, 90, and 100% VO (2max). A resting control trial for the second experiment was also conducted. RESULTS Glucose and insulin were not altered significantly in the first experiment, but both increased significantly (P < 0.05) in the second experiment. A significant increase (P < 0.05) in adiponectin in the first experiment was no longer significant after correction for plasma volumes shifts. In the second experiment, there were significant (P < 0.05) changes in adiponectin concentrations over time but not a significant difference between adiponectin responses in exercise and control trials. CONCLUSIONS The data suggest that 30 min of heavy continuous running or more strenuous intermittent running does not stimulate an increase in production and release of adiponectin, and small increases in adiponectin concentrations resulting from the exercise may be attributed to normal plasma volume shifts.

Cardiovascular reactivity, stress, and physical activity.

Psychological stress has been proposed as a major contributor to the progression of cardiovascular disease (CVD). Acute mental stress can activate the sympathetic-adrenal-medullary (SAM) axis, eliciting the release of catecholamines (NE and EPI) resulting in the elevation of heart rate (HR) and blood pressure (BP). Combined stress (psychological and physical) can exacerbate these cardiovascular responses, which may partially contribute to the elevated risk of CVD and increased proportionate mortality risks experienced by some occupations (e.g., firefighting and law enforcement). Studies have supported the benefits of physical activity on physiological and psychological health, including the cardiovascular response to acute stress. Aerobically trained individuals exhibit lower sympathetic nervous system (e.g., HR) reactivity and enhanced cardiovascular efficiency (e.g., lower vascular reactivity and decreased recovery time) in response to physical and/or psychological stress. In addition, resistance training has been demonstrated to attenuate cardiovascular responses and improve mental health. This review will examine stress-induced cardiovascular reactivity and plausible explanations for how exercise training and physical fitness (aerobic and resistance exercise) can attenuate cardiovascular responses to stress. This enhanced functionality may facilitate a reduction in the incidence of stroke and myocardial infarction. Finally, this review will also address the interaction of obesity and physical activity on cardiovascular reactivity and CVD.

Inspiratory muscle training fails to improve endurance capacity in athletes

PURPOSE The purpose of this study was to examine the effects of specific inspiratory muscle training (IMT) on respiratory muscle strength and endurance and whole-body endurance exercise capacity in competitive endurance athletes. METHODS Seven collegiate distance runners (5 male/2 female; VO2max = 59.9 +/- 11.7 mL.kg-1.min-1) were recruited to participate in this study. Initial testing included maximal oxygen consumption (VO2max), sustained maximal inspiratory mouth pressure (MIP), breathing endurance time (BET) at 60% MIP, and endurance run time (ERT) at 85% VO2max. Heart rate (HR), minute ventilation (VE), oxygen consumption (VO2), and ratings of perceived dyspnea (RPD) were recorded at 5-min intervals and during the last minute of the endurance run. Blood lactate concentration (BLC) was also obtained immediately before and at 2 min after the endurance run. All testing was repeated after 4 wk of IMT (50-65% MIP, approximately 25 min x d(-1), 4-5 sessions/week, 4 wk). RESULTS After 4 wk of IMT, MIP and BET were significantly increased compared with pretraining values (P < 0.05). No significant differences between pre and post values were observed in VO2max or ERT at 85% VO2max after IMT. No significant differences between pre and post values were detected in HR, VE, VO2, or RPD during the endurance run as measured at steady state and end of the test after IMT. BLC was not significantly different before or at 2 min after the endurance run between pre and post IMT. CONCLUSION These results suggest that IMT significantly improves respiratory muscle strength and endurance. However, these improvements in respiratory muscle function are not transferable to VO2max or endurance exercise capacity as assessed at 85% VO2max in competitive athletes.

Corticosterone response in the chick separation–stress paradigm

Corticosterone response to separation stress and its sensitivity to the anxiolytic, chlordiazepoxide (CDP), were examined in 7-day-old domestic fowl (Gallus gallus). Saline or CDP (8.0 mg/kg) was injected intramuscularly 30 min before tests. Chicks were placed in isolation either with or without mirrors for a 15-min observation period, in which distress vocalizations were recorded. After testing, chicks were euthanized and blood was collected for the corticosterone assay. Chicks tested in the No-Mirror condition displayed an increase in vocalizations that was attenuated by CDP. Similarly, corticosterone levels were highest in chicks tested in the No-Mirror condition; however, CDP only modestly attenuated corticosterone levels. The present findings demonstrate that corticosterone levels parallel the behavioral marker of distress vocalizations in this paradigm, but this biological marker may be less sensitive than the behavioral marker to benzodiazepine anxiolytic manipulations.

Cardiorespiratory responses of firefighters to a computerized fire strategies and tactics drill during physical activity.

Firefighters are subjected to a combination of physical and mental challenges in the course of their occupational responsibilities. However, due to the ecological factors involved with firefighting, it makes it extremely difficult to examine physiological and psychological changes that occur as a result of these combined challenges. The purpose of this study was to examine the efficacy of a computer-based Fire Strategies and Tactics Drill (FSTD) in eliciting psychological and physiological measures of stress in professional firefighters. In one session, participants exercised at 60% VO(2max) for 37 min (exercise alone condition, EAC), and in the other session the firefighter exercised for an equal amount of time and responded to the FSTD (dual challenge condition; DCC) while exercising. Cardiorespiratory (heart rate [HR], respiration rate [RR], minute ventilation [V(E)], oxygen consumption [VO(2)], ventilatory efficiency [V(E)/VO(2)], and respiratory exchange ratio [RER]) and psychometric measures (State Anxiety Inventory [SAI] and Ratings of Perceived Exertion [RPE]) were obtained throughout the experimental protocols. The NASA Task Load Index was used to assess perceived physical and mental load during each condition. The results demonstrated that the participants perceived overall workload to be higher in the DCC. Repeated measures ANOVAs revealed no differences between the EAC and DCC for VO(2) or RER, but the DCC did elicit significantly greater elevations in HR, RR, V(E), and V(E)/VO(2) compared to the EAC. These results suggest that the FSTD utilized in this study provides an effective method for examining the physiological and psychological responses of firefighters in a research laboratory environment.

Psychological stress during exercise: immunoendocrine and oxidative responses

The purpose of this study was to examine the changes in catecholamines (epinephrine [EPI] and norepinephrine [NE]), interleukin-2 (IL-2) and a biomarker of oxidative stress (8-isoprostane) in healthy individuals who were exposed to a dual challenge (physical and psychological stress). Furthermore, this study also examined the possible relationships between catecholamines (NE and EPI) and 8-isoprostane and between IL-2 and 8-isoprostane following a combined physical and psychological challenge. Seven healthy male subjects completed two experimental conditions. The exercise-alone condition (EAC) consisted of cycling at 60% VO2max for 37 min, while the dual-stress condition (DSC) included 20 min of a mental challenge while cycling. DSC showed greater EPI and 8-isoprostane levels (significant condition by time interaction). NE and IL-2 revealed significant change across time in both conditions. In addition, following dual stress, EPI area-under-the-curve (AUC) demonstrated a positive correlation with NE AUC and IL-2 AUC. NE AUC was positively correlated with IL-2 AUC and peak 8-isoprostane, and peak IL-2 was positively correlated with peak 8-isoprostane in response to a dual stress. The potential explanation for elevated oxidative stress during dual stress may be through the effects of the release of catecholamines and IL-2. These findings may further provide the potential explanation that dual stress alters physiological homeostasis in many occupations including firefighting, military operations and law enforcement. A greater understanding of these responses to stress can assist in finding strategies (e.g. exercise training) to overcome the inherent psychobiological challenges associated with physically and mentally demanding professions.

Obesity-Related Oxidative Stress: the Impact of Physical Activity and Diet Manipulation

Obesity-related oxidative stress, the imbalance between pro-oxidants and antioxidants (e.g., nitric oxide), has been linked to metabolic and cardiovascular disease, including endothelial dysfunction and atherosclerosis. Reactive oxygen species (ROS) are essential for physiological functions including gene expression, cellular growth, infection defense, and modulating endothelial function. However, elevated ROS and/or diminished antioxidant capacity leading to oxidative stress can lead to dysfunction. Physical activity also results in an acute state of oxidative stress. However, it is likely that chronic physical activity provides a stimulus for favorable oxidative adaptations and enhanced physiological performance and physical health, although distinct responses between aerobic and anaerobic activities warrant further investigation. Studies support the benefits of dietary modification as well as exercise interventions in alleviating oxidative stress susceptibility. Since obese individuals tend to demonstrate elevated markers of oxidative stress, the implications for this population are significant. Therefore, in this review our aim is to discuss (i) the role of oxidative stress and inflammation as associated with obesity-related diseases, (ii) the potential concerns and benefits of exercise-mediated oxidative stress, and (iii) the advantageous role of dietary modification, including acute or chronic caloric restriction and vitamin D supplementation.

Stress hormones and vascular function in firefighters during concurrent challenges

The purpose of this study was to examine the effects of concurrent physical and mental challenge on stress hormones and indicators of vascular function in firefighters. Twelve professional firefighters exercised at 60% VO(2max) while participating in a computerized Fire Strategies and Tactics Drill (FSTD-fire strategies condition [FSC]), and again at the same intensity without the mental challenge (EAC). No differences in the amount of work performed between conditions existed, although the FSC resulted in greater perceptions of overall workload. Epinephrine and norepinephrine demonstrated significant interaction effects with elevated levels during the FSC. Cortisol responses were significantly elevated across time and for the FSC. Positive correlations were found between cortisol and interleukin-6, endothelin-1, and thromboxane-B(2), and a negative correlation between interleukin-6 and thromboxane-B(2). These results suggest that concurrent challenges results in exacerbated responses of stress hormones and suggests mechanisms that could contribute to the prevalence of cardiovascular events among firefighters.