Young and old subjects matched for aerobic capacity have similar noradrenergic responses to exercise

Circadian Effects on Performance and Effort in Collegiate Swimmers

Although individual athletic performance generally tends to peak in the evening, individuals who exhibit a strong diurnal preference perform better closer to their circadian peak. Time-of-day performance effects are influenced by circadian phenotype (diurnal preference and chronotype-sleep-wake patterns), homeostatic energy reserves and, potentially, genotype, yet little is known about how these factors influence physiological effort. Here, we investigate the effects of time of day, diurnal preference, chronotype, and PER3 (a circadian clock gene) genotype on both effort and performance in a population of Division I collegiate swimmers (n = 27). Participants competed in 200m time trials at 7:00 and 19:00 and were sampled pre- and post-trial for salivary α-amylase levels (as a measure of physiological effort), allowing for per-individual measures of performance and physiological effort. Hair samples were collected for genotype analysis (a variable-number tandem-repeat (VNTR) and a single nucleotide polymorphism (SNP) in PER3). Our results indicate significant and parallel time-of-day by circadian phenotype effects on swim performance and effort; evening-type swimmers swam on average 6% slower with 50% greater α-amylase levels in the morning than they did in the evening, and morning types required 5-7 times more effort in the evening trial to achieve the same performance result as the morning trial. In addition, our results suggest that these performance effects may be influenced by gene (circadian clock gene PER3 variants) by environment (time of day) interactions. Participants homozygous for the PER3^4,4 length variant (rs57875989) or who possess a single G-allele at PER3 SNP rs228697 swam 3-6% slower in the morning. Overall, these results suggest that intra-individual variation in athletic performance and effort with time of day is associated with circadian phenotype and PER3 genotype.

Differential effects of aging and exercise on intra-abdominal adipose arteriolar function and blood flow regulation

Adipose tissue (AT), which typically comprises an increased percentage of body mass with advancing age, receives a large proportion of resting cardiac output. During exercise, an old age-associated inability to increase vascular resistance within the intra-abdominal AT may compromise the ability of the cardiovascular system to redistribute blood flow to the active musculature, contributing to the decline in exercise capacity observed in this population. We tested the hypotheses that 1) there would be an elevated perfusion of AT during exercise with old age that was associated with diminished vasoconstrictor responses of adipose-resistance arteries, and 2) chronic exercise training would mitigate the age-associated alterations in AT blood flow and vascular function. Young (6 mo; n = 40) and old (24 mo; n = 28) male Fischer 344 rats were divided into young sedentary (YSed), old sedentary (OSed), young exercise trained (YET), or old exercise trained (OET) groups, where training consisted of 10-12 wk of treadmill exercise. In vivo blood flow at rest and during exercise and in vitro α-adrenergic and myogenic vasoconstrictor responses in resistance arteries from AT were measured in all groups. In response to exercise, there was a directionally opposite change in AT blood flow in the OSed group (≈ 150% increase) and YSed (≈ 55% decrease) vs. resting values. Both α-adrenergic and myogenic vasoconstriction were diminished in OSed vs. YSed AT-resistance arteries. Exercise training resulted in a similar AT hyperemic response between age groups during exercise (YET, 9.9 ± 0.5 ml · min(-1) · 100(-1) g; OET, 8.1 ± 0.9 ml · min(-1) · 100(-1) g) and was associated with enhanced myogenic and α-adrenergic vasoconstriction of AT-resistance arteries from the OET group relative to OSed. These results indicate that there is an inability to increase vascular resistance in AT during exercise with old age, due, in part, to a diminished vasoconstriction of AT arteries. Furthermore, the results indicate that exercise training can augment vasoconstriction of AT arteries and mitigate age-related alterations in the regulation of AT blood flow during exercise.

Undulation training for development of hierarchical fitness and improved firefighter job performance

Firefighters routinely encounter physical demands that contribute to countless musculoskeletal injuries. Seemingly, a progressive prescription for fitness would offer superior protection against intrinsic job risks. The purpose of this study was to investigate the influence of two resistance training interventions on fitness adaptations among firefighters, and to assess the degree of transfer to job-specific tasks. Firefighter trainees were recruited for participation in this experimental study. Two distinct, periodized training models-undulation training (UT; n = 7) and standard training control (STCo; n = 7)-were used to determine the differential affects for muscular fitness and transference to firefighter performance batteries. Specific tests were administered to evaluate 1) upper- and lower-body muscular strength, 2) lower-body power output, 3) sprint speed and jumping ability, 4) anthropometry, and 5) firefighter Grinder performance (i.e., firefighter-specific job tests). The 9-week UT experimental treatment prescription was characterized by daily "nonlinear" fluctuations in training to preferentially elicit specific and distinct muscular fitness components, whereas the STCo treatment conformed to a traditional model, in which each fitness component was systematically targeted during a specified mesocycle. For both treatments, nearly all fitness and performance measures significantly increased from baseline (p < 0.05), with a trend in favor of UT. Further, the UT group experienced significantly greater improvements (p < 0.05) in Grinder performance over the STCo group. Calculation of effect sizes identified meaningful differences in the magnitude of changes in outcomes (effect size > 0.50) in favor of UT for measures of thigh circumference, vertical jump, 1RM squat, Grinder performance, and peak power output. These findings suggest a potentially greater stimulus for multidimensional muscular fitness development with UT, over a periodized STCo. This study effectively establishes that UT may offer a greater transference to performance for firefighter-specific job tasks.

Performance requirements of physically strenuous occupations: validating minimum standards for muscular strength and endurance

Employment rights legislative mandates passed in the USA over the last three decades emphasize the importance of validating performance standards for physically strenuous occupations. This study validated minimally acceptable standards for the muscular strength and endurance necessary to perform fire suppression activities. Incumbent firefighters (n=153) selected for key demographic characteristics completed a simulated set of firefighting tasks (Fire Suppression Evolution) and then a Predictor Test Battery of physical abilities tests. Regression analysis revealed that three predictor test items (hose drag/high rise pack carry; arm lift; arm endurance) combined to significantly predict performance time of the Fire Suppression Evolution (p < or =0.01). Firefighters (n=41) rating videotaped performance times of the Fire Suppression Evolution determined that more than one-half a standard deviation slower than the mean time established by the incumbents reflected unacceptable performance. Approximately 80% of incumbent firefighters passed the minimally acceptable performance standard. Use of the 3-predictor test battery would correctly identify 89% of successful performers and 72% of unsuccessful performers. This study demonstrates that validation of minimal physical performance standards will identify a cohort of individuals with a high probability of not being able to perform critical fire suppression activities. This finding has important implications for examining the relationship between physical performance standards and medical and economic outcomes.

Selective reductions of cardiac autonomic responses to light bicycle exercise with aging in healthy humans

We examined on 56 (age 38+/-2 [range: 16-60] years) healthy subjects the effects of aging on cardiovascular autonomic responses to progressive supine bicycle exercise of light intensity. Autoregressive spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided measures of the exercise-induced changes in baroreflex gain (by index alpha) and in sympathetic and vagal modulation of the SA node (by the normalized low [LF] and high frequency [HF] component of RR interval variability, respectively), as well as of changes in sympathetic vasomotor control (LF(SAP)). For each hemodynamic and autonomic variable, the gain of the response was expressed both as individual step increments, and as the slope of the linear regression of the sequential data points from rest and during the three steps of exercise. Age resulted significantly correlated to changes in spectral derived markers of SA modulation (LF(RR), HF(RR) and index alpha). Conversely, no significant relationships were found with changes in RR interval, in SAP and indices of vascular regulation (LF(SAP)). In addition, exercise-induced changes in indices of SA node regulation were more evident in the youngest tertile (age 25+/-1 years), compared to the oldest tertile (age 52+/-1 years). In conclusion, we have observed that aging progressively and selectively reduces the cardiac autonomic excitatory response to light exercise, while hemodynamic and vascular responsiveness are maintained.

Age, fitness, and regional blood flow during exercise in the heat

During dynamic exercise in warm environments, the requisite increase in skin blood flow (SkBF) is supported by an increase in cardiac output (Qc) and decreases in splanchnic (SBF) and renal blood flows (RBF). To examine interactions between age and fitness in determining this integrated response, 24 men, i.e., 6 younger fit (YF), 6 younger sedentary (YS), 6 older fit (OF), and 6 older sedentary (OS) rested for 50 min, then exercised at 35 and 60% maximal O2 consumption (VO2max) at 36 degrees C ambient temperature. YF had a significantly higher Qc and SkBF than any other group during exercise, but fitness level had no significant effect on any measured variable in the older men. At 60% VO2max, younger subjects had significantly greater decreases in SBF and RBF than the older men, regardless of fitness level. Total flow redirected from these two vascular beds (deltaSBF + deltaRBF) followed YF >> YS > OF > OS. A rigorous 4-wk endurance training program increased exercise SkBF in OS, but deltaSBF and deltaRBF were unchanged. Under these conditions, older men distribute Qc differently to regional circulations, i.e., smaller increases in SkBF and smaller decreases in SBF and RBF. In younger subjects, the higher SkBF associated with a higher fitness level is a function of both a higher Qc and a greater redistribution of flow from splanchnic and renal circulations, but the attenuated splanchnic and renal vasoconstriction in older men does not appear to change with enhanced aerobic fitness.

Plasma noradrenaline and ageing: effects of smoking habits

We tested the hypothesis that long-term smoking is responsible for increased plasma noradrenaline (NA) in elderly healthy subjects. Thirty-nine subjects were studied both at rest and during exercise: 10 young non-smokers (median age 24 years, range 21-33), 10 young smokers (30.5 years, 27-36), 10 elderly non-smokers (64 years, 52-75) and nine elderly smokers (62 years, 56-68). The young and elderly subjects had smoked for an average of 15 years and 46.8 years respectively. Plasma NA was significantly elevated in elderly long-term smokers compared with elderly non-smokers, young non-smokers and young smokers in both supine and sitting positions (supine: 1.06 +/- 0.24 vs. 0.71 +/- 0.22, 0.53 +/- 0.12, and 0.70 +/- 0.29 nmol L-1 respectively; sitting: 3.01 +/- 0.83 vs. 2.07 +/- 0.77, 1.89 +/- 0.52 and 2.25 +/- 0.47 nmol L-1 respectively). Plasma adrenaline did not differ among the groups. At submaximal exercise (60 W), plasma NA was significantly elevated in the elderly smokers compared with the other groups, owing to the elevated basal values. Increments in plasma NA at 60, 100 and 140 W were correlated with the relative exertion and not influenced by smoking. Plasma NA increased more in young subjects than in the elderly during maximal work load (21.7 +/- 8.0 vs. 13.4 +/- 5.4 nmol L-1) and correlated with the peak O2 uptake. Total blood volume was not different among the four groups and correlated inversely with basal plasma NA. It is concluded that long-term smoking may contribute to increased basal plasma NA concentrations and probably also increased sympathetic nerve activity in elderly healthy subjects, whereas smoking has little if any effect on plasma NA responses induced by exercise. Interindividual variability in basal plasma NA concentrations may in part be explained by differences in blood volume.

Salivary alpha-amylase as a measure of endogenous adrenergic activity

This investigation was designed to evaluate the production rates and concentrations of salivary alpha-amylase as a measure of adrenergic activity under several conditions of stress in human subjects. Saliva and blood samples were simultaneously collected from men at four 15 min intervals both before and after regimens for exercise, a written examination, or a rest period. The regressions of salivary alpha-amylase on plasma norepinephrine (NE) concentrations were significant for both exercise (P < 0.001) and examination (P < 0.01) protocols. Aerobic exercise induced a 3-fold mean increase in alpha-amylase; both NE and epinephrine (EP) increased approximately 5-fold over control levels. Levels of alpha-amylase and NE returned to control levels within 30-45 min after exercise, but EP remained elevated by approximately 2-fold during the remaining hour of observation. During the written examination, alpha-amylase and NE, but not EP, concentrations increased in parallel. In further studies the effects of exercise and exposure to heat and cold on the relationship of salivary alpha-amylase to heart rate and body temperature were investigated. Greater intensities of exercise were associated with greater increases in alpha-amylase concentrations. During heat exposure in a sauna (66 degrees C for 40 min) amylase, heart rate and body temperature all increased progressively. However, during exposure to cold (4 degrees C for 40 min) amylase increased rapidly, though heart rate and body temperature remained unchanged. Salivary cortisol concentrations were unchanged during exposure to heat or cold. We conclude that salivary alpha-amylase concentrations are predictive of plasma catecholamine levels, particularly NE, under a variety of stressful conditions, and may be a more direct and simple end point of catecholamine activity than are changes in heart rate.

Basal and exercise-induced changes in plasma catecholamines: relationship to age, smoking habits and sampling times

Contrary to earlier investigations, we have previously shown that the initial increase in venous plasma noradrenaline (NA) during exercise did not differ in young and elderly non-smoking subjects exercising at the same relative workload (75%), and that the greatest increase at maximal workload was observed in the young subjects. In order to determine whether the observed discrepancy could be explained by long-term smoking, plasma NA and adrenaline (A) were evaluated in eight elderly male smokers (mean age 67 years). The results were compared with data reported previously [Jensen et al. (1994) Exercise-induced changes in plasma catecholames and neuropeptide Y: relation to age and sampling times. J Appl Physiol, 76, 1269-1273] in seven young (mean age 27 years) and seven elderly (mean age 61 years) non-smoking male subjects. As shown earlier, basal plasma NA was significantly increased in elderly smokers compared to young and elderly non-smokers. During exercise at 75% of maximal work capacity, no difference was observed between elderly smokers and non-smokers. No difference in plasma A was found between elderly smokers and non-smokers either at rest or during exercise. These findings indicate that the exercise-induced increase in plasma NA did not differ in elderly smokers and non-smokers despite increased resting levels in the former group, and that the increase in the elderly subjects was not augmented compared to that in young subjects.

Cardiovascular, plasma norepinephrine, and thermal adjustments to prolonged exercise in young and older healthy humans

We tested the hypothesis that the whole body energy expenditure, plasma norepinephrine, cardiovascular, and internal body temperature adjustments to prolonged submaximal exercise (i.e., 'cardiovascular drift') performed at the same per cent of peak oxygen uptake (per cent VO2peak) under thermoneutral ambient conditions would be smaller in older compared to young non-physically trained men. Healthy young (25 +/- 1 years; VO2max = 49.3 +/- 1.6 ml kg-1 min-1; n = 6) and older (66 +/- 2 years; VO2max = 31.5 +/- 2.3 ml kg-1 min-1; n = 6) untrained men with similar levels of chronic physical activity were studied during pre-exercise standing rest and serially during 45 min of constant load treadmill walking at approximately 65% VO2peak (Ta = approximately 23 degrees C; approximately 40 RH). There were no group differences at rest. From rest to 5 min of exercise, the increases in heart rate were less (P < 0.05), the changes in arterial blood pressure and per cent delta blood volume were not different, and the rise in plasma norepinephrine concentration was greater (P < 0.05) in the older men vs. young controls. Consistent with our hypothesis, the increases in rectal temperature and plasma norepinephrine concentrations from 5 to 45 min of exercise were smaller in the older men (1.06-0.18 vs. 1.46 +/- 0.16 degrees C and 110 +/- 132 vs. 443 +/- 189%, respectively, P < 0.05). In contrast, the progressive increases in VO2, heart rate, and perceived effort, as well as the time-dependent reductions in systolic, mean and diastolic arterial blood pressure and per cent delta blood volume, were not different in the two groups. Thus, the whole body energy expenditure and selected cardiovascular adjustments to prolonged submaximal treadmill exercise performed at the same per cent VO2peak under comfortable ambient conditions are not different in healthy, physical activity-matched young and older men, despite a smaller elevation in internal body temperature in the latter.

Effect of age on renal blood flow during exercise

The present study examined the effect of age on the control of renal blood flow (RBF; PAH clearance) and renal vascular conductance (RVC = RBF/mean arterial pressure) during and after a bout of dynamic exercise in a warm environment. Six healthy fit older men (O; 67 +/- 1 years) and 6 young men (Y; 24 +/- 2 years) were matched for body size, adiposity, and maximal oxygen uptake (VO2max). Subjects exercised at approximately 50% of VO2max for 90 minutes in an environment of 30 degrees C, 60% humidity on each of 4 consecutive days, with data collected on days 1 and 4. There was no effect of repeated days of exercise on RBF or RVC, despite a 4% expansion of blood volume in Y (< 1% in O). On each day, resting RBF was significantly lower in O (e.g., Y = 1127 +/- 67, O = 852 +/- 114 mL/min on day 1; p < 0.05). During exercise, Y decreased RBF to a significantly (p < 0.05) greater extent [-508 (-45%) and -365 (-36%) mL/min on days 1 and 4, respectively] than the O [-98 (-12%) and -83 (-12%) mL/min]. RVC followed a similar pattern, decreasing by 52% and 37% during exercise for Y vs only 15% and 13% for O. The relationships between delta RBF and HR and delta RBF and plasma norepinephrine concentration were independent of age, implying similar sympathetic control during exercise. During recovery, RBF and RVC increased as expected in Y, but continued to decrease in O, falling significantly below exercise values (p < 0.05). Compared to young men, fit healthy older men redistribute less blood flow away from the kidneys during dynamic exercise in the heat, an effect which appears to result from the existence of a smaller resting RBF rather than differential sympathetic control. On the other hand, chronological age seems to be associated with altered control of RBF and RVC during recovery from exercise.