Low Fit Subjects Research Articles

Impact of data averaging strategies on V̇O2max assessment: Mathematical modeling and reliability.

No consensus exists on how to average data to optimize O2max assessment. Although the O2max value is reduced with larger averaging blocks, no mathematical procedure is available to account for the effect of the length of the averaging block on O2max. AIMS: To determine the effect that the number of breaths or seconds included in the averaging block has on the O2max value and its reproducibility and to develop correction equations to standardize O2max values obtained with different averaging strategies. Eighty-four subjects performed duplicate incremental tests to exhaustion (IE) in the cycle ergometer and/or treadmill using two metabolic carts (Vyntus and Vmax N29). Rolling breath averages and fixed time averages were calculated from breath-by-breath data from 6 to 60 breaths or seconds. O2max decayed from 6 to 60 breath averages by 10% in low fit ( O2max <40mLkg-1 min-1 ) and 6.7% in trained subjects. The O2max averaged from a similar number of breaths or seconds was highly concordant (CCC>0.97). There was a linear-log relationship between the number of breaths or seconds in the averaging block and O2max (R2 >0.99, P<0.001), and specific equations were developed to standardize O2max values to a fixed number of breaths or seconds. Reproducibility was higher in trained than low-fit subjects and not influenced by the averaging strategy, exercise mode, maximal respiratory rate, or IE protocol. The O2max decreases following a linear-log function with the number of breaths or seconds included in the averaging block and can be corrected with specific equations as those developed here.

Reduced arterial stiffness in very fit boys and girls.

Low cardiorespiratory fitness is associated with higher cardiovascular risk, whereas high levels of cardiorespiratory fitness protect the cardiovascular system. Carotid intima-media thickness and arterial distensibility are well-established parameters to identify subclinical cardiovascular disease. Therefore, this study investigated the influence of cardiorespiratory fitness and muscular strength on carotid intima-media thickness and arterial distensibility in 697 children and adolescents (376 girls), aged 7-17 years. Cardiorespiratory fitness and strength were measured with the test battery FITNESSGRAM; carotid intima-media thickness, arterial compliance, elastic modulus, stiffness index β, and pulse wave velocity β were assessed by B- and M-mode ultrasound at the common carotid artery. In bivariate correlation, cardiorespiratory fitness was significantly associated with all cardiovascular parameters and was an independent predictor in multivariate regression analysis. No significant associations were obtained for muscular strength. In a one-way variance analysis, very fit boys and girls (58 boys and 74 girls>80th percentile for cardiorespiratory fitness) had significantly decreased stiffness parameters (expressed in standard deviation scores) compared with low fit subjects (71 boys and 77 girls<20th percentile for cardiorespiratory fitness): elastic modulus -0.16±1.02 versus 0.19±1.17, p=0.009; stiffness index β -0.15±1.08 versus 0.16±1.1, p=0.03; and pulse wave velocity β -0.19±1.02 versus 0.19±1.14, p=0.005. Cardiorespiratory fitness was associated with healthier arteries in children and adolescents. Comparison of very fit with unfit subjects revealed better distensibility parameters in very fit boys and girls.

Aerobic Fitness Affects the Exercise Performance Responses to Nitrate Supplementation.

Dietary nitrate supplementation has been shown to reduce O2 cost of submaximal exercise, improve exercise tolerance, and enhance performance in moderately trained individuals. In contrast, data have been provided that elite athletes do not benefit from nitrate supplementation. The aim of this study was to evaluate the effects of short-term nitrate supplementation on endurance performance in subjects with different levels of aerobic fitness. Twenty-one subjects (mean age, 22.7 ± 1.8 yr) with different aerobic fitness level (V˙O2peak value ranging from 28.2 to 81.7 mL·kg·min) participated in a crossover double-blind placebo-controlled study. Subjects were tested after 6 d of supplementation with either 0.5 l per day of nitrate (5.5 mmol)-containing water (NITR) or nitrate-free water (PLA). Participants performed an incremental running test until exhaustion and four repetitions of 6-min submaximal (approximately 80% of gas exchange threshold) constant load exercise on a motorized treadmill. Moreover, subjects performed a 3-km running time trial on the field. After NITR, a negative correlation between reduction of O2 cost of submaximal exercise and individual aerobic fitness level was observed (r = 0.80; P < 0.0001). A significant inverse correlation was also found between aerobic fitness level and improvement in performance for 3-km time trial after NITR (r = 0.76; P < 0.0001). Additionally, subjects responded differently to dietary nitrate supplementation according to aerobic fitness level with higher-fit subjects showing a lower increase in plasma [NO3] (r = 0.86; P < 0.0001) and [NO2] (r = 0.75; P < 0.0001). The results of the present study suggest that the individual aerobic fitness level affects the ergogenic benefits induced by dietary nitrate supplementation. The optimal nitrate loading regimen required to elevate plasma [NO2] and to enhance performance in elite athletes is different from that of low-fit subjects and requires further studies.

Higher cardiorespiratory fitness attenuates the risk of atherosclerosis associated with ADRB3 Trp64Arg polymorphism

β3-Adrenergic receptor (ADRB3) Trp64Arg polymorphism is associated with atherogenic risk factors that include weight gain, insulin resistance, and diabetes. Habitual exercise brings higher cardiorespiratory fitness and results in the amelioration of atherosclerotic risk factors. However, the effects of cardiorespiratory fitness level and ADRB3 Trp64Arg polymorphism on the risk of cardiovascular disease remain unclear. A cross-sectional investigation of 877 Japanese men and women (18-75 years old) was performed to clarify the effects of cardiorespiratory fitness on the relationship between ADRB3 Trp64Arg polymorphism and risk of cardiovascular disease. Common carotid intima-media thickness (ccIMT) and blood lipid profiles were assessed as surrogate markers of atherosclerosis. We measured peak oxygen uptake (V̇O(2peak)) during incremental cycle ergometer exercise testing. Subjects were divided into groups with high (High-Fit) and low (Low-Fit) levels of cardiorespiratory fitness based on the median value of V̇O(2peak) for sex and decade. Levels of body fat, triglycerides, and plasma glucose were lower and high-density lipoprotein cholesterol levels and V̇O(2peak) were higher in High-Fit subjects than Low-Fit subjects. ADRB3 Trp64Arg polymorphism did not significantly affect ccIMT or blood lipid profiles. In Low-Fit subjects, ccIMT was higher in individuals with the Arg/Arg genotype compared to the Trp/Trp and Trp/Arg genotypes (each P < 0.0001); however, ADRB3 polymorphism had no effect in High-Fit subjects. Higher levels of cardiorespiratory fitness may attenuate the risk of atherosclerosis associated with ADRB3 Trp64Arg polymorphism.

Cardiorespiratory fitness affects polymorphism in ADRB3 Trp64Arg‐caused increase in common carotid intima‐media thickness

PURPOSEIn the present study, a cross‐sectional investigation of 769 Japanese men and women (18–75 years old) was performed to clarify the effects of cardiorespiratory fitness on the relationship between risk of cardiovascular disease and beta3‐adrenergic receptor (ADRB3) Trp64Arg gene polymorphism.METHODSCommon carotid intima‐media thickness (ccIMT) was assessed as a risk of atherosclerosis. We measured peak oxygen uptake (VO2peak) during incremental cycle ergometer exercise test, and then the subjects were divided into high‐(High‐Fit) and low‐cardiorespiratory fitness (Low‐Fit) groups based on the median value of VO2peak in each sex and decade.RESULTSBody fat, triglyceride and plasma glucose levels were lower and HDL cholesterol levels and VO2peak were higher in High‐Fit subjects compared with in Low‐Fit subjects, but there were no significant effect of ADRB3 polymorphism. There was no significant effect of ADRB3 Trp64Arg polymorphism on ccIMT. In Low‐Fit subjects, ccIMT increased in ArgArg genotype individuals compared with TrpTrp and TrpArg genotype of ADRB3, however, had no effect on ADRB3 polymorphisms in High‐Fit subjects.CONCLUSIONThese results suggest that the higher cardiorespiratory fitness may attenuate a risk of atherosclerosis associated with ADRB3 Trp64Arg polymorphism.This work was supported by a Grant‐in‐Aid for Scientific Research of Japan (#20300231, #20700563).

Lack of carotid stiffening associated with MTHFR 677TT genotype in cardiorespiratory fit adults

The TT genotype of C677T polymorphism in 5,10-methylenetetrahydrofolate reductase (MTHFR) induces elevation of homocysteine level and leads to atherosclerosis and arterial stiffening. Furthermore, cardiorespiratory fitness level is also associated with arterial stiffness. In the present study, a cross-sectional investigation of 763 Japanese men and women (18-70 yr old) was performed to clarify the effects of cardiorespiratory fitness on the relationship between arterial stiffness and MTHFR C677T gene polymorphism. Arterial stiffness was assessed by carotid beta-stiffness with ultrasonography and tonometry. The study subjects were divided into high-cardiorespiratory fitness (High-Fit) and low-cardiorespiratory fitness (Low-Fit) groups based on the median value of peak oxygen uptake in each sex and decade. The plasma homocysteine level was higher in the TT genotype of MTHFR C677T polymorphism compared with CC and CT genotype individuals. MTHFR C677T polymorphism showed no effect on carotid beta-stiffness, but there was a significant interaction effect between fitness and MTHFR C677T polymorphism on carotid beta-stiffness (P = 0.0017). In the Low-Fit subjects, carotid beta-stiffness was significantly higher in individuals with the TT genotype than the CC and CT genotypes. However, there were no such differences in High-Fit subjects. In addition, beta-stiffness and plasma homocysteine levels were positively correlated in Low-Fit subjects with the TT genotype (r = 0.71, P < 0.0001), but no such correlations were observed in High-Fit subjects. In CC and CT genotype individuals, there were also no such correlations in either fitness level. These results suggest that the higher cardiorespiratory fitness may attenuate central artery stiffening associated with MTHFR C677T polymorphism.

More automation and less cognitive control of imagined walking movements in high- versus low-fit older adults.

Using motor imagery, we investigated brain activation in simple and complex walking tasks (walking forward and backward on a treadmill) and analyzed if the motor status of older adults influenced these activation patterns. Fifty-one older adults (64–79 years of age) were trained in motor execution and imagery and then performed the imagination task and two control tasks (standing, counting backward) in a horizontal position within a 3T MRI scanner (first-person perspective, eyes closed). Walking backward as compared to walking forward required larger activations in the primary motor cortex, supplementary motor area, parietal cortex, thalamus, putamen, and caudatum, but less activation in the cerebellum and brainstem. Motor high-fit individuals showed more activations and larger BOLD signals in motor-related areas compared to low-fit participants but demonstrated lower activity in the dorsolateral prefrontal cortex. Moreover, parietal activation in high-fit participants remained stable throughout the movement period whereas low-fit participants revealed an early drop in activity in this area accompanied by increasing activity in frontal brain regions. Overall, walking forward seemed to be more automated (more activation in cerebellum and brainstem), whereas walking backward required more resources, e.g., for visual-spatial processing and sensorimotor control. Low-fit subjects in particular seemed to require more cognitive resources for planning and controlling. High-fit subjects, on the contrary, revealed more movement automation and a higher “attention span.” Our results support the hypothesis that high fitness corresponds with more automation and less cognitive control of complex motor tasks, which might help to free up cognitive resources.

Effect of Fitness Level on Physiological, Perceptual, and Affective responses during Treadmill Walking at a Self-Selected Pace

PURPOSE: The purpose of this study was to compare the physiological, perceptual, and affective responses during treadmill walking at a self-selected pace in individuals of high and low fitness levels. METHODS: Thirty-eight apparently healthy women were assigned to two groups according to their aerobic fitness (High Fit (HF), N = 20, age: 32.1 ± 8.0 yr, body mass: 61.8 ± 8.7 kg, VO2max: 38.3 ± 3.8 ml.kg-1.min-1, and Low Fit (LF), N = 19, age: 31.6 ± 7.1 yr, body mass: 66.0 ± 12.0 kg, VO2max: 29.8 ± 2.0 ml.kg-1.min-1). Each participant performed an incremental treadmill test to determine VO2max and a 20-min treadmill walking bout at a self-selected pace. During the 20-min of treadmill walking at a self-selected pace, the physiological (oxygen uptake, VO2) responses were recorded continuously. Furthermore, the perceptual (Borg-RPE for the overall body, 6-20) and affective (Feeling Scale, Hardy & Rejeski, 1989) responses were determined every 5 min throughout the test. Differences in physiological, perceptual and affective responses between HF and LF were identified by using an independent t test. RESULTS: LF subjects self-selected a slower walking speed compared to HF subjects (1.54 ± 0.17 m.sec-1 and 1.68 ± 0.2 m.sec-1, respectively, P < .05). Furthermore, the VO2 was higher for the HF (21.6 ± 4.4 ml.kg-1.min-1, P < .05) than LF (18.2 ± 2.2 ml.kg-1.min-1) individuals during the 20 min treadmill walk, corresponding to a similar %VO2max (56.1 ± 11.4 and 61.7 ± 10.0 %, respectively). HF and LF subjects also showed similar perceptual (11.5 ± 1.5 vs. 12.2 ± 1.0, respectively) and affective responses (3.6 ± 1.1 vs. 3.1 ± 1.2, respectively) during the 20-min bout of treadmill walking at a self-selected pace. CONCLUSIONS: The results of the present study demonstrate that physiological, but not perceptual and affective responses of healthy women, are influenced by aerobic fitness during treadmill walking at a self-selected pace.

Effect of Endothelin 1 Genotype on Blood Pressure Is Dependent on Physical Activity or Fitness Levels

Contributions of the DNA sequence variation at the endothelin 1 locus to the risk of hypertension and to endurance training-induced changes in blood pressure were investigated in the Aerobics Center Longitudinal Study and the Health, Risk Factors, Exercise Training and Genetics Family Study cohorts. We identified 586 normotensive control subjects and 607 incident hypertensive case subjects from the Aerobics Center Longitudinal Study cohort (all whites) who were normotensive and healthy at their first clinic visit. The case subjects were diagnosed with hypertension during an average follow-up of 9.5 years, whereas the control subjects remained normotensive. The allele and genotype frequencies of 5 endothelin 1 haplotype tagging single nucleotide polymorphisms did not differ significantly between the case and control subjects. However, we observed a significant (P=0.0025) interaction between the endothelin 1 rs5370 (G/T; Lys198Asn) genotype and cardiorespiratory fitness level on the risk of hypertension: among low-fit subjects, the rs5370 minor allele (T; 198Asn) was associated with higher risk of hypertension (odds ratio: 1.95; 95% CI: 1.36 to 2.81; P=0.0003), whereas the risk did not differ among genotypes in high-fit subjects. In the white Health, Risk Factors, Exercise Training and Genetics subjects (N=480), the rs5370 T allele was associated with blunted systolic blood pressure (P=0.0046) and pulse pressure (P=0.0016) responses to a 20-week endurance training program. The Lys198Asn variant of the endothelin 1 locus is associated with blood pressure phenotypes in whites. However, the expression of the genotype effect is modulated by physical activity or cardiorespiratory fitness level. Our study provides an illustrative example of how physical activity and fitness level modifies the associations between a candidate gene and outcome phenotype.

Effect of Fitness Level on Thermoregulatory Variables in Healthy Males After Cold Exposure

INTRODUCTION: Previous research has elucidated that training status or fitness level may influence the thermoregulatory response during acute cold exposure (ACE). However, it is uncertain whether fitness level has a similar response during re-warming (ACE-REC). PURPOSE: To determine the effect of fitness level on the thermoregulatory response during a two hour recovery period from exposure to 10oC cold air. METHODS: Ten males (25.6 ± 1.6 y) underwent pre-experimental testing to determine VO2max and body composition. Subjects were then randomly divided into low-fit (LF: VO2 = 36.6 ± 0.9 ml.kg-1.min-1; %BF = 22.9 ± 0.8 %) and high fit (HF: VO2 = 52.0 ± 1.2 ml.kg-1.min-1; %BF = 15.5 ± 1.2) groups. Each subject underwent 2 trials which consisted of 120 min of exposure to 10oC air and 120 min of recovery in 25oC air. Maximal oxygen consumption (VO2), mean skin temperature (Tsk), and core temperature (Tre) were measured continuously. RESULTS: Percent body fat was significantly different between the HF and LF subjects (p=0.007). ANOVA did not reveal a main effect for fitness for Tre (p=0.856) and Tsk (p= 0.223). However, VO2 was significantly different (p= 0. 013) between high-fit and low-fit subjects during ACE-REC. CONCLUSION: Based on these data, fitness level demonstrated a differential response with regard to VO2 during the recovery period following ACE. Since high-fit individuals tend to have a reduced resistor to heat exchange, i.e. percent body fat, they were able to maintain Tre via an increase in metabolic heat production.

Fitness: The Ultimate Marker for Risk Stratification and Health Outcomes?

Fitness: The Ultimate Marker for Risk Stratification and Health Outcomes?

Cardiorespiratory Responses of Hi Fit and Low Fit Subjects to Mental Challenge during Exercise

The influence of psychological states on physiological responses during exercise is of considerable importance to individuals for which the efficiency of energy production is critical to occupational performance. Numerous studies have shown that aerobic fitness is associated with enhanced cardiovascular efficiency at rest and that responses to mental stress demonstrate evidence of increased sensitivity (relative increase in HR response) and enhanced efficiency (a decrease in absolute HR). However, the effect of aerobic fitness and its impact on cardiorespiratory (CR) responses to psychological stress during exercise has not been investigated. Therefore, the purpose of this study was three-fold; (1) to examine during exercise, anxiety, effort sense, and CR responses to a mental challenge, (2) to examine anxiety and heart rate (HR) responses from rest to exercise with mental challenge between below average fitness (Low Fit) and well-above average fitness (Hi Fit) individuals (exercising at similar relative intensities), and (3) to examine anxiety, effort sense, and CR responses of Low Fit and Hi Fit individuals to a mental challenge during exercise at a similar relative intensity. Twelve Low Fit and eleven Hi Fit subjects participated in two, 32-minute cycle ergometer rides at 65 % of VO2max. In the mental challenge condition (MCC), subjects rode while participating in mentally challenging tasks (Stroop Color-Word task and mental arithmetic) from min 6 to min 14 of the protocol. In the no mental challenge condition (NMCC), subjects exercised at the same intensity and duration without a stressor. Subjects were counter-balanced between fitness levels and condition. HR, VE, VE/VO2, RR, VO2, RER, effort sense (RPE), and state anxiety (SAI) were assessed at 5, 14, 24, and 30 min. SAI was also assessed at - 5 min before exercise and after 15 min of recovery. In addition, the NASA task load index (NTLX) was used to assess perceived overall workload. SAI increased significantly at 14 min in the MCC. NTLX scores indicated that the MCC was perceived as a greater overall workload. Furthermore, HR, VE, VE/VO2, and RR were significantly elevated during the mental challenge condition at 14 min. The Hi Fit subjects tended to respond to the dual stress of exercise and mental challenge with a relative increase in HR, while absolute HR was similar in both groups. An examination of fitness group differences revealed that SAI and NTLX were similar for Low Fit and Hi Fit subjects when exercising in the MCC, although, Hi Fit subjects demonstrated lower HR responses from 6 min to 14 min. VE, VE/VO2, and RR were similar for Low Fit and Hi Fit subjects. These results suggest that psychological stress during physical activity can exacerbate cardiorespiratory responses and suggests that factors that impact CR adjustment to mental challenge from resting baseline may differ from the factors that impact CR adjustment to mental challenge during exercise. Finally, fitness level attenuates HR and may attenuate additional cardiorespiratory responses while participating in a dual stress condition, of exercise and mental challenge.

THE INFLUENCE OF FITNESS AND FATNESS ON EXERCISE INTENSITY SELECTION WHILE WALKING ON A TREADMILL

PURPOSE: To determine the impact of aerobic fitness and fatness on physiological, mechanical, and perceptual responses during self-selected treadmill (TM) walking in 60 healthy college-aged women. METHODS: Subjects were classified as high (≥ 23.7%) or low body fat (≤ 20.6%) based on bioelectrical impedance analysis. A graded treadmill test (GXT) was used to assess maximal oxygen uptake (VO2max). Subjects with a VO2max ≤ 33.8 ml· kg−1· min−1 were considered low-fit while subjects with a VO2max ≥ 36.7 ml· kg−1· min−1 were considered high-fit. Fifteen women were then placed into one of four categories based on fitness and fatness. Within 2–3 days of the GXT, subjects walked on a TM at a self-selected speed for 15-min at 2.5% grade. Dependant variables were oxygen uptake (VO2), heart rate (HR), ratings of perceived exertion for the overall body (RPE-O), and total energy expenditure (TEE). RESULTS: The two-factor ANOVA indicated no significant interactions between fitness and fatness for any of the dependant variables. Percent of VO2max (% VO2max), percent of maximal HR (% HRmax), RPE-O, treadmill speed (TMS), and TEE did not differ between individuals of varying levels of fatness. Low fit subjects walked at a TMS that resulted in a higher (p = 0.03) % HRmax (69.16 vs. 63.47) and a higher (p < 0.0005) % VO2max (52.4 vs 39.56) than the high fit subjects. CONCLUSION: These findings suggest that fitness, and not fatness, influence self-selected exercise intensity during TM walking in college-aged women. Further analysis revealed that TMS selected by high and low fit women resulted in similar VO2 (mean = 16.46 ml· kg−1· min−1) and HR (mean = 126 bpm). Activity undertaken at this level is considered to be moderate intensity and is sufficient for most people to achieve health benefits. Further research should employ subjects with a wider range of fitness and fatness.

AEROBIC FITNESS INFLUENCES ARTERIAL BLOOD PRESSURE IN ABDOMINAL OBESITY

Central (or abdominal) body fat distribution has been shown to be related to cardiovascular disease (CVD) risk to a greater extent than overall body fat. Cardiorespiratory fitness is known to be protective against the development of CVD. We tested the hypothesis that, among individuals with waist circumference in the high risk category (≥ 40 inches in males, ≥ 32 inches in females), systolic, diastolic, mean arterial, and pulse pressure would be lower in those with higher levels of cardiorespiratory fitness. Waist circumference and cardiorespiratory fitness were assessed at East Carolina University from 1982 to the present. High-fit subjects were defined as those in the upper 30% of each gender, based on maximal treadmill exercise test, and low-fit subjects as those in the lower 30%. There are currently 4017 persons in the data set with average age 40 years (17–79 years), 79% male and 21% female. Our final analysis included 368 males and 135 females. Subjects who smoked or who were taking blood pressure medications were eliminated from the analysis and age was statistically controlled. Systolic (high-fit: 122 mmHg (95% CI = 117, 127) vs. low-fit: 129 mmHg (95% CI = 128, 131), diastolic (high-fit: 77 mmHg (95% CI = 74, 81) vs. low-fit: 86 mmHg (95% CI = 85, 87)) and mean arterial (high-fit: 92 mmHg (95% CI = 89, 96) vs. low-fit: 100 mmHg (95% CI = 99, 101)) blood pressure were significantly lower in males with high vs. low cardiorespiratory fitness despite similar levels of waist circumference. In addition, females with similar waist circumference showed significant differences between fitness groups for diastolic (high-fit: 74 mmHg (95% CI = 71, 78) vs. low-fit: 80 mmHg (95% CI = 78, 82)) and mean arterial blood pressure (high-fit: 89 mmHg (95% CI = 85, 93) vs. low-fit: 95 mmHg (95% CI = 93, 97)). Pulse pressure was not significantly different between fitness groups in either males or females. These results suggest cardiorespiratory fitness exerts a favorable influence on arterial blood pressure even in persons with high-risk body fat distribution phenotypes.

Association between aerobic fitness and visuospatial performance in healthy older adults.

This study examined whether chronic physical exercise activity is associated with better neurocognitive performance in older adults. One hundred five men participated in 1 of 3 age groups (18-28, 35-45, and 60-73). For each age group, subjects were classified as high or low in fitness on the basis of self-reported activity levels and the results of a submaximal bicycle ergometer test. A comprehensive battery of neuropsychological tests was administered to each subject, and older subjects scored significantly lower than the younger groups on most tests. Significant differences between high- and low-fit subjects were found only on tasks with heavy visuospatial demands, and these differences were most notable in the older adult group. These findings suggest that participation in aerobic exercise activity selectively preserves some cognitive functions that normally decline with age. The benefits of activity appear to be most evident on tasks that require visuospatial processing.

Physical fitness and cardiovascular regulation: mechanisms of orthostatic intolerance

We studied three groups of eight men each--high, mid, and low fit (peak O2 consumption 60.0 +/- 0.8, 48.9 +/- 1.0, and 35.7 +/- 0.9 ml.min-1.kg-1)--to determine the mechanism of orthostatic intolerance in endurance athletes. Tolerance was defined by progressive lower body negative pressure (LBNP) to presyncope. Maximal calf vascular conductance (Gmax) was measured. The carotid baroreflex was characterized using both stepwise R-wave-triggered and sustained (2 min) changes in neck chamber pressure. High-fit subjects tended to have lower LBNP tolerance than mid- and low-fit subjects but similar baroreflex responses. Subjects with poor LBNP tolerance had larger stroke volumes (SV) (120 +/- 6 vs. 103 +/- 3 ml) and greater decline in SV with LBNP to -40 mmHg (40 +/- 2 vs. 26 +/- 4%). Stepwise multiple linear regression analysis revealed that Gmax and steady-state gain of the carotid baroreflex contributed significantly toward explaining interindividual variations in LBNP tolerance. Thus endurance athletes may have decreased LBNP tolerance, but apparently not as a simple linear function of aerobic fitness. Orthostatic tolerance depends on complex interactions among functional characteristics that appear both related (Gmax and SV) and unrelated (baroreflex function) to fitness or exercise training.

Ratings of perceived exertion in individuals with varying fitness levels during walking and running.

It was the purpose of this investigation to: 1) compare the ratings of perceived exertion (RPEs) in high and low fit individuals when walking and running at comparable exercise intensities and 2) to determine if ventilation (VE) provides a central signal for RPEs. Nine high fit and nine low fit male subjects completed two exercise bouts on a treadmill, one uphill walking and the other level running. Workloads for each bout were set at 90% of each subject's ventilatory threshold (VT) as determined from a graded exercise test. Oxygen consumption (Vo2), heart rate (HR), and VE were all similar between the walk and run trials for the low fit subjects (P greater than 0.05). HR were found to be significantly greater during the walk trial vs. the run trial (P less than 0.05) for the high fit subjects, whereas, VE was significantly greater during the run trial. Oxygen consumption was similar for the high fit subjects during both trials (P greater than 0.05). During the walk and run trials, central (12.1 +/- 1.6 vs. 11.4 +/- 1.5), local (14.0 +/- 1.3 vs. 13.9 +/- 1.1) and overall (12.8 +/- 1.2 vs. 12.4 +/- 1.4) RPEs were not found to be significantly different for the low fit group (P greater than 0.05). In contrast, during the walk vs. the run trial there was a significant increase in central (10.7 +/- 2.0 vs. 9.2 +/- 1.9), local (11.5 +/- 2.0 vs. 9.8 +/- 1.8) and overall (11.2 +/- 2.4 vs. 9.6 +/- 2.3) RPEs for the high fit group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic fitness and response to psychological stress

This experiment was conducted to determine whether aerobic fitness was related to subjects' cardiovascular and subjective responses to psychological stress. Sixteen High Fit and 16 Low Fit female subjects had their levels of cardiovascular and subjective arousal assessed during a baseline period and during a stressful cognitive test. Cardiovascular arousal was also assessed after a brief recovery period. Initial analyses indicated that, when compared to Low Fit subjects, High Fit subjects performed better on a 12-min walk/run test of aerobic fitness and had lower baseline levels of cardiovascular arousal (systolic blood pressure and heart rate). More importantly, when confronted with the stressful cognitive test the High Fit subjects evinced reliably smaller cardiovascular responses (systolic and diastolic blood pressure, heart rate) and reported reliably smaller increases in cognitive and somatic arousal than the Low Fit subjects. There were no differences in cardiovascular arousal after the recovery period.

Influence of a brief aerobic training program on heart rate and subjective response to a psychologic stressor.

An experiment was conducted to determine whether a brief program of aerobic exercise would reduce the heart rate and subjective responses of high- and low-fit subjects to a psychologic stressor. Thirty-four high-fit and 34 low-fit subjects were exposed to a moderate stressor (recall of digits backwards test) while their heart rates and subjective responses were monitored. Approximately half of the high- and low-fit subjects then participated in a 13-week aerobic exercise training program, whereas the other subjects did not. After the 13-week period, the subjects were again exposed to the stressor. Results indicated that a) in the pretest the low-fit subjects showed a greater heart rate response to the stressor than the high-fit subjects, b) the training program was effective for increasing subjects' levels of aerobic fitness, and c) the training program was effective for reducing the heart rate response to the stressor of low-fit subjects. These findings provide support for the relationship between fitness and the response to psychologic stressors and they suggest that aerobic training may be an effective way of helping low-fit persons deal with psychologic stressors.

Efficiency of coping with a real-life stressor: a multimodal comparison of aerobic fitness.

ABSTRACTThe mediating effects of aerobic fitness on the psychological and physiological responses to a real‐life psychological stressor (rappelling) were examined. Subjective anxiety, heart rate, nor epinephrine, epinephrine, and cortisol were monitored in IS male novice rappellers at various intervals before and following the rappel task. Results showed that high fit compared to low fit subjects maintained overall lower heart rate levels. Aerobic power was associated with faster recovery from subjective anxiety and a more efficient recovery for relative plasma epinephrine measures. Norepinephrine, heart rate, and cortisol did not parallel this recovery pattern. These results provide some support for the research which indicates that high levels of aerobic power are associated with greater coping efficiency.