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Objective: To evaluate a personalized adaptive training program designed for stress prevention using graduated stress exposure., Background: Astronauts in the high-risk space mission environment are prone to performance-impairing stress responses, making preemptive stress inoculation essential for their training., Methods: This work developed an adaptive virtual reality-based system that adjusts environmental stressors based on real-time stress indicators to optimize training stress levels. Sixty-five healthy subjects underwent task training in one of three groups: skill-only (no stressors), fixed-graduated (prescheduled stressor changes), and adaptive . Psychological (subjective stress, task engagement, distress, worry, anxiety, and workload) and physiological (heart rate, heart rate variability, blood pressure, and electrodermal activity) responses were measured., Results: The adaptive condition showed a significant decrease in heart rate and a decreasing trend in heart rate variability ratio, with no changes in the other training conditions. Distress showed a decreasing trend for the graduated and adaptive conditions. Task engagement showed a significant increase for adaptive and a significant decrease for the graduated condition. All training conditions showed a significant decrease in worry and anxiety and a significant increase in the other heart rate variability metrics., Conclusion: Although all training conditions mitigated some stress, the preponderance of trial effects for the adaptive condition supports that it is more successful at decreasing stress., Application: The integration of real-time personalized stress exposure within a VR-based training program not only prepares individuals for high-stress situations by preemptively mitigating stress but also customizes stressor levels to the crew member's current state, potentially enhancing resilience to future stressors., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Introduction: This study evaluates whether a health club membership is associated with meeting the US physical activity (PA) guidelines and/or favorable cardiovascular health., Methods: Using cross-sectional data of health club members (n = 204) and non-members (n = 201) from April to August 2013, this is the first study to our knowledge to examine a health club membership in relation to objectively measured cardiovascular health indicators including resting blood pressure, resting heart rate, body mass index, waist circumference, and cardiorespiratory fitness based on a non-exercise test algorithm. To determine the total PA and sedentary time, this study used a comprehensive PA questionnaire about both aerobic and resistance activities at the health club, as well as lifestyle activities in other settings, which was developed based on the International Physical Activity Questionnaire (IPAQ)., Results: The odds ratios (95% confidence interval) of meeting either the aerobic, resistance, or both aerobic and resistance PA guidelines for members compared to non-members were 16.5 (9.8-27.6), 10.1 (6.2-16.3), and 13.8 (8.5-22.4), respectively. Significant associations of health club membership with more favorable cardiovascular health outcomes and sedentary behavior were observed for resting heart rate (B: -4.8 b/min, p<0.001), cardiorespiratory fitness (B: 2.1 ml/kg/min, p<0.001), and sedentary time (B: -1.4 hours, p<0.001). Participants with a health club membership of >1 year had more favorable health outcomes, with a smaller waist circumference (men, B: -4.0 cm, p = 0.04; women, B: -3.4 cm, p = 0.06), compared to non-members., Conclusions: Health club membership is associated with significantly increased aerobic and resistance physical activity levels and more favorable cardiovascular health outcomes compared to non-members. However, longitudinal, randomized controlled trials would be clearly warranted as cross-sectional data prohibits causal inferences., Competing Interests: The authors have declared that no competing interests exist.

The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or -100 mmHg, separated by 1 week. Heart rate, stroke volume (impedance cardiography), blood pressure (Finapres), and forearm blood flow were assessed, as was HRV in both time and frequency domains. The trial-to-trial responses to LBNP common to all subjects (LBNP< or =-60 mmHg and at test termination) showed parallel changes, suggesting similar responses between both trials. Good reproducibility estimates were found for the resting HRV data (lowest: R=0.62 for low frequency/high frequency ratio; highest: R=0.94 for standard deviation of normal R-R intervals). During LBNP, reproducibility estimates varied but were generally similar to that seen at rest. At test termination, they were unacceptably low (R<0.41) for the HRV data assessed in the frequency domain and expressed in absolute units. LBNP tolerance was lower in the first trial [LBNP tolerance index: 404 (21) versus 437 (15) mmHg min(-1); P<0.05] but the intraclass correlation coefficient was high (R=0.87). These data suggest that (1) HRV responses to submaximal LBNP up to -60 mmHg are consistent across trials, (2) the considerable variability seen in the HRV parameters at maximal LBNP can be reduced by expressing these data in either the time domain or using normalized units in the frequency domain, and (3) cardiovascular responses to sub- and maximal LBNP are reproducible. Data are presented as mean (SEM) unless otherwise stated.

Background: Endurance-trained males may be more prone to orthostatic hypotension than untrained subjects and this is reflected in differences in their cardiovascular responses to lower body negative pressure (LBNP). It is uncertain if the type of endurance training used affects these responses., Hypothesis: Endurance-trained runners will differ from endurance-trained swimmers in their cardiovascular responses to LBNP., Methods: Male intercollegiate cross country runners (XC, n = 9), sprinters (SP, n = 7) and swimmers (SW, n = 12) underwent exposures to -10, -20 and -40 mm Hg LBNP. Forearm blood flow, heart rate (HR) and blood pressure were measured throughout. Maximal oxygen consumption (VO2max) was determined separately via combined arm-and-leg cycle ergometry., Results: The XC were more fit than the SW and SP (VO2max = 64.5 +/- 3.5 vs. 51.7 +/- 1.9, 49.5 +/- 2.4 ml.kg-1.min-1; x +/- SEM; p < 0.05). Resting mean arterial pressure (MAP, 93 +/- 3 mm Hg) and forearm vascular resistance (FVR; 26.2 +/- 6.0 units) did not differ significantly between groups although HR was 17 +/- 3 b.min-1 higher (p < 0.05) in SW vs. SP and XC. Neither the pulse pressure, MAP, HR, nor FVR responses to the LBNP exposures differed significantly between the 3 groups. Compared to rest, pulse pressure was reduced (p < 0.05) 14% at -40 mm Hg. Similarly, HR was increased (p < 0.05) 10% at -40 mm Hg. FVR increased (p < 0.05) with each increase in LBNP becoming 91% greater at -40 mm Hg vs. rest., Conclusions: These data suggest that the cardiovascular responses to LBNP up to -40 mm Hg do not differ in chronically exercising males training with different modalities.

The purpose of the present study was to determine if common indexes of exercise intensity, assessed with land-based exercise, could be applied to swimming. Consequently, the heart rate (HR) and oxygen uptake (VO2) responses to submaximal and maximal treadmill running (TR) and free swimming (SW) in 11 fitness swimmers were assessed to determine if the responses to TR could be used to predict those of SW. A maximal graded exercise test using a discontinuous protocol was used for TR, while four graded submaximal 200 yd swims and one 400 yd maximal swim was used for SW. Rest periods were similar for each mode. Significantly lower (p < 0.05) peak values were found in SW compared to TR for both HR (174 +/- 3 vs 183 +/- 3 bt x min(-1)) and VO2 (3.58 +/- 0.18 vs 3.97 +/- 0.22 L x min(-1)), SW vs TR; +/- SE, respectively. However, regression analyses of submaximal HR vs VO2 for each subject revealed similar slopes for TR and SW (30.5 +/- 1.7 vs 29.9 +/- 3.5 bt x L(-1), p > 0.05) and similar intercepts (67.3 +/- 2.6 vs 66.5 +/- 11.5 bt x min(-1), p > 0.05). At the VO2 equivalent to 50% treadmill VO2max, the heart rate predicted from SW did not differ significantly from TR (118 +/- 5 vs 124 +/- 1 bt x min(-1), p > 0.05). This was also true at 85% treadmill VO2max (171 +/- 4 vs 166 +/- 3 bt x min(-1), SW vs TR, respectively; p > 0.05). These data suggest that peak heart rate and oxygen uptake appear to be mode specific, but exercising at a given submaximal oxygen uptake will elicit a similar heart rate regardless of the mode. Thus, target heart rate ranges designed for land-based exercise appear to be appropriate for fitness swimmers during swimming.