Cognitive performance, hyperoxia, and heart rate following oxygen administration in healthy young adults

It was recently established that supplemental oxygen administration significantly enhances memory formation in healthy young adults. In the present study, a double-blind, placebo-controled design was employed to assess the cognitive and physiological effects of subjects' inspiration of oxygen or air (control) prior to undergoing simple memory and reaction-time tasks. Arterial blood oxygen saturation and heart rate were monitored during each of six phases of the experiment, corresponding to baseline, gas inhalation, word presentation, reaction time, distractor and word recall, respectively. The results confirm that oxygen administration significantly enhances cognitive performance above that seen in the air inhalation condition. Subjects who received oxygen recalled more words and had faster reaction times. Moreover, compared to participants who inhaled air, they exhibited significant hyperoxia during gas administration, word presentation, and the reaction-time task, but not at other phases of the experiment. Compared to baseline, heart rate was significantly elevated during the word presentation, reaction-time, and distractor tasks in both the air and oxygen groups. In the oxygen group, significant correlations were found between changes in oxygen saturation and cognitive performance. In the air group, greater changes in heart rate were associated with more improved cognitive performance. These results are discussed in the context of cognitive demand and metabolic supply. It is suggested that under periods of cognitive demand a number of physiological responses are brought into play that serve to increase the delivery of metabolic substrates to active neural tissue. These mechanisms can be supplemented by increased availability of circulating blood oxygen, resulting in an augmentation of cognitive performance. Heart rate reactivity and the capacity for increased blood oxygen appear to be important physiological individual differences mediating these phenomena.     

Use of perceived effort ratings to control exercise intensity in young healthy adults

Summary The purpose of this study was to evaluate the use of the rating of perceived exertion (RPE) as a means of regulating the intensity of exercise during running. The subjects were healthy, relatively fit young adults (16 men and 12 women). Estimates of effort were recorded using the Borg 6–20 Scale whilst the maximal oxygen uptake of the subjects was measured as they ran on an electrically driven treadmill. In a further session, the same subjects were requested to run on the treadmill at constant exercise intensity based on their interpretation of levels 9, 13 and 17 of the Borg Scale. They regulated their running speed and the treadmill gradient but had no knowledge of performance from the equipment display panel. A linear regression analysis was carried out to examine the relationship between heart rate, perceived exertion and relative metabolic demand. This revealed that the rating of perceived exertion was at least as good a predictor of exercise intensity as heart rate in both the graded exercise test and effort production test. The results support the view that RPE may be used to predict relative metabolic demand, especially at higher workloads and could be a useful medium for controlling intensity of effort during vigorous exercise in such subjects.     

Effects of low and moderate intensity treadmill walking on postprandial lipaemia in healthy young adults

We have previously shown that the lipaemic response to a fatty meal was reduced when prolonged (2 h) low intensity exercise was taken some hours before eating. The purpose of this study was to test the hypothesis that the effect is quantitatively greater after exercise of moderate intensity than after exercise at low intensity. Six men and six women, mean age 26.9 (SEM 1.5) years, took part in three trials, each conducted over 2 days; on the afternoon of day 1 of each of two exercise trials the subjects walked on a treadmill for 90 min at either 31 (SEM 1) % or 61 (SEM 1) % of maximal oxygen uptake, i.e. low and moderate intensity, respectively; on the control trial the subjects refrained from exercise on day 1. On the morning of day 2 of each trial they ingested a test meal (1.28 g fat, 1.44 g carbohydrate, 76 kJ energy · kg^–1 body mass); blood samples were obtained in the fasted state and for 6 h after the meal. Fasting serum triacylglycerol concentration and the area under the postprandial triacylglycerol-time curve were lower than in the control trial (P < 0.05) after moderate intensity walking but not after low intensity walking. The results suggest that the mitigation of the lipaemic response to a meal high in fat and carbohydrate is related to the intensity and/or the energy expenditure of the preceding exercise.     

Day-to-day variation in oxygen consumption and energy expenditure during submaximal treadmill walking in female adolescents.

The day-to-day variation in oxygen consumption (VO2) and energy expenditure (EE) during horizontal treadmill walking was measured using indirect calorimetry in 20 female adolescents (mean age 17.3 years). Two different walking speeds were used: 5 km h-1 and an individually convenient speed of 3.0 km h-1 (mean). The two sets of measurements were performed on 2 consecutive days, and great care was taken to minimize possible disturbing factors. The mean VO2 was 919 ml min-1 at 5 km h-1 and 622 ml min-1 at the individual speed, and the mean values of EE were 4.5 kcal min-1 and 3.1 kcal min-1 respectively. The individual day-to-day variation in VO2 (at 5 km h-1) was between -11.7% and +12.6% of the mean VO2. The coefficient of variation (CV) was 6.4% when values were calculated in ml min-1 kg-1. The energy expenditure varied somewhat less between the 2 days (CV = 5.7%). The corresponding value for EE when walking at the individual speed was 7.2%, and the mean day-to-day variation in VO2 was 7.5% (CV). The rate of perceived exertion according to Borg's scale was lower on day 2 (11.9) compared with day 1 (13.0) when walking at 5 km h-1. There was no difference in heart rate between the 2 days. It is concluded that EE varies somewhat less than VO2 on successive days, probably because of an interchangeable relationship between breathing gases, depending on which substrate is used for combustion. When using VO2 and EE for evaluation of physical capacity, the day-to-day variation in the measurements must be taken into consideration.     

Variability analysis of lower extremity joint kinematics during walking in healthy young adults

The first objective of this study was to determine the kinematic variability of the lower extremity joints using methods from the mathematical chaos theory in a normal walking environment in conjunction with a large population of healthy young adults. The second objective was to test the hypothesis that variability characteristics are different between joints and to further investigate differences between male and female and right and left subgroups. A total of forty young healthy subjects (20 males: 24.1 ± 3.1 years; 20 females: 22.5 ± 3.2 years) volunteered, and their joint motions were captured while walking on a treadmill for 90 s in order to estimate Lyapunov Exponent (LE) values. Means and standard deviations of the LEs ranged from 0.035 ± 0.016 (right ankle) to 0.073 ± 0.023 (left knee) for the male subjects and from 0.028 ± 0.014 (left ankle) to 0.065 ± 0.028 (right hip) for the female subjects. Between the males and females, differences in LEs were observed to be statistically significant only for the left knee. There were no statistically significant differences between the right and left sides of the joints. However, differences between joints were statistically significant except between the hip and knee. These results are the first such comparison of the variability in the lower extremity without the confounding effect of walking speed on the variability of joint motions, and can serve as a normative database.     

Comparison of the metabolic energy cost of overground and treadmill walking in older adults

We assessed whether the metabolic energy cost of walking was higher when measured overground or on a treadmill in a population of healthy older adults. We also assessed the association between the two testing modes. Participants (n = 20, 14 men and 6 women aged between 65 and 83 years of age) were randomly divided into two groups. Half of them went through the overground–treadmill sequence while the other half did the opposite order. A familiarization visit was held for each participant prior to the actual testing. For both modes of testing, five walking speeds were experimented (0.67, 0.89, 1.11, 1.33 and 1.67 m s⁻¹). Oxygen uptake was monitored for all walking speeds. We found a significant difference between treadmill and track metabolic energy cost of walking, whatever the walking speed. The results show that walking on the treadmill requires more metabolic energy than walking overground for all experimental speeds (P < 0.05). The association between both measures was low to moderate (0.17 < ICC < 0.65), and the standard error of measurement represented 6.9–15.7% of the average value. These data indicate that metabolic energy cost of walking results from a treadmill test does not necessarily apply in daily overground activities. Interventions aiming at reducing the metabolic energy cost of walking should be assessed with the same mode as it was proposed during the intervention. If the treadmill mode is necessary for any purposes, functional overground walking tests should be implemented to obtain a more complete and specific evaluation.     

Mechanical power during maximal treadmill walking and running in young and elderly men

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly (P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.     

Interactions between heart rate, psychomotor performance and perceived effort during physical work as influenced by beta-adrenergic blockade.

Effects of a single intravenous dose of propranolol (0,25 mg/kg body weight) were examined in 15 healthy male subjects who performed three reaction-time tasks of different complexity, while pedalling at five work loads on a cycle ergometer. Comparisons between measurements after propranolol and after injection of a placebo solution showed a pronounced reduction of heart rate and an increase in catecholamine excretion following propranolol. Comparisons of psychomotor performance showed no significan difference between the propranolol and placebo conditions. Nor did self-estimates of perceived physical and task-induced efforts reveal any significant effects of propranolol. The results support the notion that heart rate is not a prominent cue for perceived effort.     

Gastrocnemius muscle-tendon behaviour during walking in young and older adults

Aim: Age‐related differences in muscle architectural and tendon mechanical properties have been observed in vivo under static conditions and during single joint contractions. The aim of this study was to determine if there are age‐related differences in gastrocnemius fascicle–tendon interactions during a fundamental locomotor task – walking. Methods: Eight young adults (YA; 27 ± 4 years) and eight older adults (OA; 77 ± 4 years) walked on a treadmill at 1.11 m s⁻¹ whilst length changes in the gastrocnemius lateralis muscle tendon complex (MTC), fascicles and tendinous tissue (TT) were determined from joint angles, ultrasonography and a geometric MTC model (combining MTC and fascicle measurements) respectively. Results: There was no age‐related difference in lengthening of the MTC during stance. However, the fascicle and TT contribution to MTC lengthening was altered; TT lengthening was larger in OA than in YA (P = 0.05) and fascicle lengthening was less in OA than YA (P < 0.05). There were no differences between groups in MTC, fascicle or TT shortening amplitude during push‐off. Conclusion: The observations are consistent with previous reports of increased compliance of TT in older adults.     

Metabolic cost, mechanical work, and efficiency during walking in young and older men

Aim: To investigate mechanical work, efficiency, and antagonist muscle co‐activation with a view to better understand the cause of the elevated metabolic cost of walking (C_W) in older adults. Methods: Metabolic, mechanical and electromyographic measurements were made as healthy young (YOU; n = 12, age = 27 ± 3 years) and older (OLD; n = 20, age = 74 ± 3 years) men of equivalent body mass and leg length walked on a treadmill at four speeds (ranging from 0.83 to 1.67 m s^?1). Results: Net (above resting) C_W, determined by indirect calorimetry was 31% higher (average across speeds) in OLD (P < 0.05). The integrity of the passive pendulum like interchange of mechanical energies of the centre of mass (COM_B), an energy‐saving mechanism, was maintained in OLD. Furthermore, total mechanical work, determined from fluctuations in mechanical energy of COM_B and of body segments relative to COM_B, was not significantly elevated in OLD. This resulted in a lower efficiency in OLD (?17%, P < 0.05). Co‐activation, temporally quantified from electromyography recordings, was 31% higher in OLD for antagonist muscles of the thigh (P < 0.05). Thigh co‐activation was moderately correlated with C_W at three speeds (r = 0.38–0.52, P < 0.05). Conclusion: Healthy septuagenarians with no gait impairment have an elevated C_W which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co‐activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated C_W.     

The influence of the intensity of treadmill walking upon changes in lipid and lipoprotein variables in healthy adults

The purpose of the present study was to compare the acute and delayed effects of low- and moderate-intensity exercise on serum lipoprotein concentrations. Twelve healthy volunteers (five men, seven women), aged 28 (2) years [mean (SEM)], maximal oxygen uptake (O_2max) 48 (3) ml · kg^–1 · min^–1 walked on a treadmill for 90 min, on two separate occasions, in a balanced design. On one occasion walking was at a grade which elicited 32.1 (0.8)% of O_2max, i.e. low intensity, while on the other it elicited 60.1 (1.6)% of O_2max, i.e. moderate intensity (MI). Serum concentrations of total cholesterol (TC), triacylglycerol (TAG), high density lipoprotein cholesterol (HDL-C) and the subfraction HDL₂-C free fatty acids (FFA) and free glycerol were measured in venous blood samples drawn before exercise (after a 12-h fast), during walking and after 1 h and 24 h of recovery. Serum TAG concentrations decreased as a result of the exercise bout over the period of observation (P < 0.05), but this decrease was not different between the two intensities. Changes in serum TC concentrations over time differed between trials (P < 0.05). Serum free glycerol and FFA concentrations increased during exercise bouts, these increases being (P < 0.05) greater with MI. The decrease in serum TAG concentrations during and after a single episode of either prolonged low or moderate intensity exercise may be associated with an increased clearance and/or a decreased secretion of TAG-rich lipoproteins.     

Changes in electroencephalogram and heart rate during treadmill exercise in the rat

To explore whether exercise is related to electroencephalogram (EEG) and heart rate changes, continuous EEG power spectral analysis was performed on rats during treadmill exercise. Compared with before exercise, treadmill exercise resulted promptly in a higher mean power frequency and theta (6-10 Hz) power of the EEG, but lower delta (0.5-4 Hz) power of the EEG together with a lower R-R interval of electrocardiogram. Such changes quickly reversed when the treadmill exercise was stopped. We conclude that the cerebral cortex activates along with the autonomic system during running. Our methodology offers an efficient way to study the interaction of cerebral and brain stem functions with exercise in the rat.     

Snoring in normal young adults: prevalence in sleep stages and associated changes in oxygen saturation, heart rate, and breathing pattern

Six men and three women, asymptomatic light snorers ranging in age from 25-34 years, were studied during sleep to determine the prevalence of snoring in the different sleep stages, the associated changes in oxygen saturation (SaO2), heart rate (HR), and breathing frequency (f), and the associated breathing arrhythmias. Snoring was defined as a 1-minute epoch with more than 80% of the breaths associated with snores. Most of the snoring epochs as well as the apneas and hypopneas occurred during stage 2, mainly because it is the most prolonged sleep stage. The prevalence of snoring, however, normalized for differences in length of sleep stages, was highest in stages 3 and 4 but low in REM, whereas the converse was true for apneas and hypopneas. Snoring caused no change in the mean SaO2, mean HR, or f, as compared with nonsnoring periods in the same sleep stage. Continuous snoring in normal subjects can occur without significant O2 desaturation or breathing arrhythmia. Continuous snoring and breathing arrhythmia tended to occur together in a given subject but were unrelated in time, suggesting a different pathogenesis.     

Effect of carrying a weighted backpack on lung mechanics during treadmill walking in healthy men

Weighted backpacks are used extensively in recreational and occupational settings, yet their effects on lung mechanics during acute exercise is poorly understood. The purpose of this study was to determine the effects of different backpack weights on lung mechanics and breathing patterns during treadmill walking. Subjects (n = 7, age = 28 ± 6 years), completed two 2.5-min exercise stages for each backpack condition [no backpack (NP), an un-weighted backpack (NW) or a backpack weighing 15, 25 or 35 kg]. A maximal expiratory flow volume curve was generated for each backpack condition and an oesophageal balloon catheter was used to estimate pleural pressure. The 15, 25 and 35 kg backpacks caused a 3, 5 and 8% (P < 0.05) reduction in forced vital capacity compared with the NP condition, respectively. For the same exercise stage, the power of breathing (POB) requirement was higher in the 35 kg backpack compared to NP (32 ± 4.3 vs. 88 ± 9.0 J min(-1), P < 0.05; respectively). Independent of changes in minute ventilation, end-expiratory lung volume decreased as backpack weight increased. As backpack weight increased, there was a concomitant decline in calculated maximal ventilation, a rise in minute ventilation, and a resultant greater utilization of maximal available ventilation. In conclusion, wearing a weighted backpack during an acute bout of exercise altered operational lung volumes; however, adaptive changes in breathing mechanics may have minimized changes in the required POB such that at an iso-ventilation, wearing a backpack weighing up to 35 kg does not increase the POB requirement.     

Oxygen transport and oxygen consumption in shock

A review of data from patients in shock, or with very low cardiac output, shows that oxygen consumption is maintained above 90 ml . min-1 . m-2, even at the lowest values of arterial oxygen transport. CAIN [3] has found a limiting value of oxygen delivery in anesthetized, hypoxic dogs of about 10 ml . kg-1 . min-1, below which oxygen consumption falls dramatically. No comparable value has been established for man in shock.     

Constraining eye movement when redirecting walking trajectories alters turning control in healthy young adults

Humans use a specific steering synergy, where the eyes and head lead rotation to the new direction, when executing a turn or change in direction. Increasing evidence suggests that eye movement is critical for turning control and that when the eyes are constrained, or participants have difficulties making eye movements, steering control is disrupted. The purpose of the current study was to extend previous research regarding eye movements and steering control to a functional walking and turning task. This study investigated eye, head, trunk, and pelvis kinematics of healthy young adults during a 90° redirection of walking trajectory under two visual conditions: Free Gaze (the eyes were allowed to move naturally in the environment), and Fixed Gaze (participants were required to fixate the eyes on a target in front). Results revealed significant differences in eye, head, and trunk coordination between Free Gaze and Fixed Gaze conditions (p < 0.001). During Free Gaze, the eyes led reorientation followed by the head and trunk. Intersegment timings between the eyes, head, and trunk were significantly different (p < 0.05). In contrast, during Fixed Gaze, the segments moved together with no significant differences between segment onset times. In addition, the sequence of segment rotation during Fixed Gaze suggested a bottom-up postural perturbation control strategy in place of top-down steering control seen in Free Gaze. The results of this study support the hypothesis that eye movement is critical for the release of the steering synergy for turning control.