Synergy of L-arginine and growth hormone (GH)-releasing peptide (GHRP-2) stimulation of GH in men and women: Modulation by exercise

We investigated the ability of exercise, a multipathway, potent, physiological stimulus for GH release, to alter the synergistic interaction of l-arginine (A) and GH-related peptide (GHRP)-2 (G) observed at rest and the ability of gender to further modulate this putative interaction. Subjects (9 men and 9 early follicular phase women) completed 30 min of constant load aerobic exercise in combination with intravenous infusions of saline (S), A (30 g over 30 min), G (1 µg/kg bolus), or both (AG) in separate study sessions in randomly assigned order. Measures of GH release were logarithmically transformed for statistical analysis. Similar to rest, exercise maintained the rank order (AG > G > A > S) of effective stimulation of GH release for the key response measures in men or women, a gender disparity in the time to reach the maximal serum GH concentration, the calculated endogenous GH half-life, and the observed effect of preinfusion (basal) serum GH concentrations on determining secretagogue responsiveness. Exercise potentiated the individual stimulatory actions of A and G, while blunting the relative magnitude of the synergistic (supra-additive) interaction observed at rest. We infer from the present data that 1) exercise is likely to induce release of both GHRH and somatostatin, 2)l-arginine may facilitate the effect of exercise by limiting somatostatin release, 3) GHRP-2 could further enhance the stimulatory impact of exercise by opposing central actions of somatostatin and/or heightening endogenous GHRH release, and4) gender strongly controls the relative but not absolute magnitude of A/G synergy both at rest and after exercise

High Intensity Interval Training in Healthy Males Does not Improve Markers of Insulin Sensitivity

Purpose: Determine if three weeks of HIT (high-intensity interval training) improves fasting insulin sensitivity in healthy males. Methods: Participants were recreationally active ( = 10 hours per week) men between 18 and 35 years of age (Ht: 180 ± 1.44 cm; Wt: 85 ± 2.95 kg; BMI: 26.1 ± 0.59 kg/m2; body fat: 19.7 ± 1.76%). HIT training occurred 3 days weekly for 3 weeks, at intensities equivalent to 7.5% of body mass. Training volume increased weekly as follows: three sprints per session (week 1), four sprints per session (week 2), and five sprints per session (week 3). Fasting blood samples were collected at baseline and after each week and tested for glucose and insulin. A repeated measures ANOVA was used to measure changes in both fasting glucose and insulin concentrations as well as HOMA(IR) (homeostatic model assessment) and QUICKI (quantitative insulin sensitivity check index). Results: Values were in the normal range throughout the study and there were no significant improvements in glucose (P = 0.346), insulin (P = 0.680), HOMA (P = 0.567), or QUICKI (P = 0.186), as a result of HIT. Conclusion: While HIT may be useful in maintaining insulin sensitivity in healthy males, 3-weeks of HIT did not further improve insulin sensitivity in this group

Body composition by DEXA in older adults: accuracy and influence of scan mode

Dual energy x-ray absorptiometry (DEXA) measures bone mineral content(BMC), bone mineral density (BMD), fat-free mass (FFM), and provides estimates of percent body fat. Changes in scan mode geometry (pencil beam vs array) may impact these measures and body composition estimates using multi-compartment models. Forty-one adults, ages 59-79 yr, were scanned in each mode and also underwent hydrostatic weighing and measurement of total body water (tritiated water dilution). The effect of scan mode on measurement of DEXA BMC, BMD, FFM, and percent body fat (DEXA%Fat) was examined. The effect of scan mode on percentage body fat determined by a 4-compartment body composition model (4 Comp%Fat) and comparison of DEXA%Fat and 4 Comp%Fat were also examined. BMC and DEXA%Fat were greater (1.3% and 3.9%, respectively, P < 0.01), and BMD and FFM were lower (1.1% and 1.9%, respectively, P< 0.01) with the array scan mode. The 4 Comp%Fat was significantly greater(0.2%) when the array scan mode measurements of total body bone mineral were used; however, these differences were physiologically inconsequential. Comparison between DEXA%Fat and 4 Comp%Fat measures revealed a total error of± 5.0% in the older adults examined. These results indicate significant scan mode differences in total body BMC, BMD, FFM, and DEXA%Fat measurements and demonstrate the importance of using a single DEXA scan mode for clinical investigation, particularly with longitudinal studies. For all investigations with DEXA, the scan mode should be reported. Furthermore, the error associated with using DEXA alone to estimate percent fat in an older population suggests that this technique is unacceptable in a research setting

Effects of gender on exercise-induced growth hormone release

We examined gender differences in growth hormone (GH) secretion during rest and exercise. Eighteen subjects (9 women and 9 men) were tested on two occasions each [resting condition (R) and exercise condition (Ex)]. Blood was sampled at 10-min intervals from 0600 to 1200 and was assayed for GH by chemiluminescence. At R, women had a 3.69-fold greater mean calculated mass of GH secreted per burst compared with men (5.4 ± 1.0 vs. 1.7 ± 0.4 µg/l, respectively) and higher basal (interpulse) GH secretion rates, which resulted in greater GH production rates and serum GH area under the curve (AUC; 1,107 ± 194 vs. 595 ± 146 µg · l-1 · min, women vs. men; P = 0.04). Compared with R, Ex resulted in greater mean mass of GH secreted per burst, greater mean GH secretory burst amplitude, and greater GH AUC (1,196 ± 211 vs. 506 ± 90 µg · l-1 · min, Ex vs. R, respectivley; P < 0.001). During Ex, women attained maximal serum GH concentrations significantly earlier than men (24 vs. 32 min after initiation of Ex, respectively; P = 0.004). Despite this temporal disparity, both genders had similar maximal serum GH concentrations. The change in AUC (adjusted for unequal baselines) was similar for men and women (593 ± 201 vs. 811 ± 268 µg · l-1 · min), but there were significant gender-by-condition interactive effects on GH secretory burst mass, pulsatile GH production rate, and maximal serum GH concentration. We conclude that, although women exhibit greater absolute GH secretion rates than men both at rest and during exercise, exercise evokes a similar incremental GH response in men and women. Thus the magnitude of the incremental secretory GH response is not gender dependent

The effect of exercise type on immunofunctional and traditional growth hormone.

The purpose of this study was to compare the growth hormone (GH) response, including the immunfunctional (IF) GH response, between an acute bout of aerobic and resistance exercise in the same subjects. Ten cross-trained males (24.3 ± 1.2 years) performed both 30 min of continuous cycling at 70% of VO2max, and intermittent free weight squatting at 70% of 1-RM, in a randomly assigned crossover design, separated by at least 1 week. Blood samples were collected at 10-min intervals for 2 h (30 min rest, 30 min exercise, 60 min recovery) and analyzed for total human and IF GH. After adjusting for the amount of work performed per minute of exercise, integrated GH AUC was significantly greater during the resistance session than the aerobic session as measured by both the total and IF GH assays (P = 0.008 and P = 0.014, respectively). Peak GH concentrations were significantly greater during the resistance session than the aerobic session (P = 0.05). A similar overall GH pattern was observed in response to both types of exercise, with peak values occurring at the end of exercise, regardless of the GH assay used. These data demonstrate that in young, cross-trained males, intermittent resistance exercise elicits a greater response of GH, including IF GH, compared to a continuous aerobic session, when controlling for the work performed per minute, intersubject variability, relative exercise intensity and session duration

Phosphorylation of the JAK2- STAT5 pathway in response to acute aerobic exercise in young, healthy males.

Growth hormone (GH) is a powerful stimulator of the Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) pathway. Acute exercise is a known stimulus for GH secretion. Purpose: The purpose of this study was to determine the phosphorylation of the JAK2-STAT5 pathway in human skeletal muscle in response to acute aerobic exercise. Methods: Eleven young (22.5 ± 0.6, mean ± SE), healthy, aerobically trained males performed 30 min of cycling at 70% V·O2max. Blood samples were collected at 10- to 15-min intervals and analyzed for human GH, immunofunctional (IF) GH, GH binding protein, and insulin-like growth factor I (IGF-I). Muscle biopsies were taken from the vastus lateralis before exercise, immediately after exercise, as well as, 30 and 60 min postexercise. Muscle samples were analyzed for changes in JAK2 and STAT5 tyrosine phosphorylation, as well as changes in JAK2 and STAT5 protein content. Results: Multivariate ANOVA with post hoc comparisons demonstrated that GH and IF GH were significantly elevated immediately after exercise compared with preexercise (P < 0.001). Exercise significantly increased the phosphorylation of JAK2 immediately after exercise (P = 0.004). A trend toward increasing levels of STAT5 phosphorylation was observed immediately after exercise (P = 0.08) and was significantly elevated 30 min after exercise (P = 0.002), compared with preexercise levels. Muscle JAK2 and STAT5 protein content did not change. Conclusion: The results demonstrate that the JAK2-STAT5 pathway is activated in response to acute aerobic exercise in human skeletal muscle and suggests that the exercise-induced release of GH may play a role in the activation of this pathway

The relationship between exercise-induced and non-stimulated 24-hour growth hormone release

The purpose of this study was to quantify the relationship between the acute exercise-induced growth hormone (GH) response, gender, fitness, age, and body composition with non-exercise stimulated (NES) 24-hr integrated GH concentration (IGHC). Twenty-nine subjects (16 males, 13 females) completed a 24-hr control session without exercise (NES) on one occasion and a 30-min exercise session on a separate occasion. The GH release was analyzed from 10-min intervals using trapezoidal integration during both sessions. Multiple regression analysis in males revealed that significant variability in NES 24-hr IGHC could be adequately explained by subject age and BMI together (P<0.05), but could not be explained by exercise-induced peak GH or 30-min of exercise-induced IGHC on an unrelated day (P=0.750). However, significant variability in NES 24-hr IGHC in females could be uniquely associated with subject age (P<0.05) as well as peak GH and 30-min of exercise-induced IGHC (P<0.05). The findings indicate that in the females only the constant load exercise-induced growth hormone response can adequately predict total 24-hr growth hormone output on a separate day without an exercise stimulus. The data further exemplify gender disparities in exercise-induced growth hormone release and the importance of exercise for females in regards to enhancing total 24-hr growth hormone concentrations

The effects of a duathalon simulation on ventilatory threshold and running economy

Multisport events continue to grow in popularity among recreational, amateur, and professional athletes around the world. This study aimed to determine the compounding effects of the initial run and cycling legs of an International Triathlon Union (ITU) Duathlon simulation on maximal oxygen uptake (VO2max), ventilatory threshold (VT) and running economy (RE) within a thermoneutral, laboratory controlled setting. Seven highly trained multisport athletes completed three trials; Trial-1 consisted of a speed only VO2max treadmill protocol (SOVO2max) to determine VO2max, VT, and RE during a single-bout run; Trial-2 consisted of a 10 km run at 98% of VT followed by an incremental VO2max test on the cycle ergometer; Trial-3 consisted of a 10 km run and 30 km cycling bout at 98% of VT followed by a speed only treadmill test to determine the compounding effects of the initial legs of a duathlon on VO2max, VT, and RE. A repeated measures ANOVA was performed to determine differences between variables across trials. No difference in VO2max, VT (%VO2max), maximal HR, or maximal RPE was observed across trials. Oxygen consumption at VT was significantly lower during Trial-3 compared to Trial-1 (p = 0.01). This decrease was coupled with a significant reduction in running speed at VT (p = 0.015). A significant interaction between trial and running speed indicate that RE was significantly altered during Trial-3 compared to Trial-1 (p < 0.001). The first two legs of a laboratory based duathlon simulation negatively impact VT and RE. Our findings may provide a useful method to evaluate multisport athletes since a single-bout incremental treadmill test fails to reveal important alterations in physiological thresholds

Understanding the role of sleep quality and sleep duration in commercial driving safety

Introduction: Long-haul truck drivers in the United States suffer disproportionately high injury rates. Sleep is a critical factor in these outcomes, contributing to fatigue and degrading multiple aspects of safety-relevant performance. Both sleep duration and sleep quality are often compromised among truck drivers; however, much of the efforts to combat fatigue focus on sleep duration rather than sleep quality. Thus, the current study has two objectives: (1) to determine the degree to which sleep impacts safety-relevant performance among long-haul truck drivers; and (2) to evaluate workday and non-workday sleep quality and duration as predictors of drivers’ safety-relevant performance.Materials and methods: A non-experimental, descriptive, cross-sectional design was employed to collect survey and biometric data from 260 long-haul truck drivers. The Trucker Sleep Disorders Survey was developed to assess sleep duration and quality, the impact of sleep on job performance and accident risk, and other relevant work organization characteristics. Descriptive statistics assessed work organization variables, sleep duration and quality, and frequency of engaging in safety-relevant performance while sleepy. Linear regression analyses were conducted to evaluate relationships between sleep duration, sleep quality, and work organization variables with safety composite variables.Results: Drivers reported long work hours, with over 70% of drivers working more than 11 h daily. Drivers also reported a large number of miles driven per week, with an average of 2,812.61 miles per week, and frequent violations of hours-of-service rules, with 43.8% of drivers “sometimes to always” violating the “14-h rule.” Sleep duration was longer, and sleep quality was better, on non-workdays compared on workdays. Drivers frequently operated motor vehicles while sleepy, and sleepiness impacted several aspects of safety-relevant performance. Sleep quality was better associated with driving while sleepy and with job performance and concentration than sleep duration. Sleep duration was better associated with accidents and accident risk than sleep quality.Discussion: Sleep quality appears to be better associated with safety-relevant performance among long-haul truck drivers than sleep duration. Comprehensive and multilevel efforts are needed to meaningfully address sleep quality among drivers

Effects of acute aerobic and anaerobic exercise on blood markers of oxidative stress

The purpose of this study was to compare oxidative modification of blood proteins, lipids, DNA, and glutathione in the 24 hours following aerobic and anaerobic exercise using similar muscle groups. Ten cross-trained men (24.3 ± 3.8 years, [mean ± SEM]) performed in random order 30 minutes of continuous cycling at 70% of V?O2max and intermittent dumbbell squatting at 70% of 1 repetition maximum (1RM), separated by 1–2 weeks, in a crossover design. Blood samples taken before, and immediately, 1, 6, and 24 hours postexercise were analyzed for plasma protein carbonyls (PC), plasma malondialdehyde (MDA), and whole-blood total (TGSH), oxidized (GSSG), and reduced (GSH) glutathione. Blood samples taken before and 24 hours postexercise were analyzed for serum 8-hydroxy-2'-deoxyguanosine (8-OHdG). PC values were greater at 6 and 24 hours postexercise compared with pre-exercise for squatting, with greater PC values at 24 hours postexercise for squatting compared with cycling (0.634 ± 0.053 vs. 0.359 ± 0.018 nM·mg protein-1). There was no significant interaction or main effects for MDA or 8-OHdG. GSSG experienced a short- lived increase and GSH a transient decrease immediately following both exercise modes. These data suggest that 30 minutes of aerobic and anaerobic exercise performed by young, cross- trained men (a) can increase certain biomarkers of oxidative stress in blood, (b) differentially affect oxidative stress biomarkers, and (c) result in a different magnitude of oxidation based on the macromolecule studied. Practical applications: While protein and glutathione oxidation was increased following acute exercise as performed in this study, future research may investigate methods of reducing macromolecule oxidation, possibly through the use of antioxidant therapy