PubMed Health⌕ Search

Biomedical subjects

W S Myles

Publications and source records attributed to W S Myles.

At least 19 recordsLinked to original sources
PubMed1995

Sleep deprivation: effects on work capacity, self-paced walking, contractile properties and perceived exertion.

The primary purpose of this study was to examine the effect of a 48-hour period of sleep deprivation on the performance of selected physical work tasks [30-45% of maximum oxygen consumption (VO2max)]. In addition, this study assessed the effect of continual performance of physical work during sleep deprivation on standardized physiological and psychological test scores. Nineteen male subjects performed six different physical tasks, designed to involve all major muscle groups, during a 48-hour period of sleep deprivation. Fourteen subjects served as sleep-deprivation controls. Performance on all physical work tasks decreased significantly. Neither sleep deprivation (SD) or sleep deprivation in conjunction with continuous physical work (SDW) had any effect on muscle contractile properties, anaerobic power measures or resting blood glucose and lactate concentrations. Only SD subjects demonstrated a decline in cardiorespiratory function. Self-selected walking pace decreased and perceived exertion increased significantly in the SDW group. Positive and negative mood scores were adversely affected in both groups, the total change being greatest in SD subjects. The results indicate that performance of physical work tasks requiring 30-45% VO2max declines significantly over a 48-hour period of sleep deprivation. However, maximal physiological function is not unduly compromised by either the work tasks in conjunction with sleep deprivation or by sleep deprivation alone.

Adult↗
PubMed1988

Physical performance and physiological responses following 60 hours of sleep deprivation.

The effect of 60 h of sleep deprivation (SD) upon physical performance and physiological responses to exercise was examined in 11 male subjects. The experiment consisted of two conditions separated by at least 10 d. In the experimental condition (E) subjects remained awake for 60 h and in the control condition (C) the same subjects had 7 h of sleep per night. In both conditions subjects reported to the laboratory on the evening prior to d 1 and slept for 7 h. Physical performance testing was carried out on d 1 and again on d 3 after either two nights of sleep or two nights of SD. Results obtained on d 3 are expressed relative to d 1, the control day. Maximal isometric and isokinetic muscular strength and endurance of selected upper and lower body muscle groups, performance of the Wingate Anaerobic Power Test, simple reaction time, the blood lactate response to cycle exercise at 70% VO2max, and most of the cardiovascular and respiratory responses to treadmill running at 70% and 80% VO2max, were not significantly altered as a result of SD. These results suggest that sleep loss of up to 60 h will not impair the capability for physical work, a finding of considerable importance in sustained military operations which frequently involve the combination of both physical and mental tasks.

Adult↗
PubMed1988

Electro-mechanical response times and muscle strength after sleep deprivation.

This study examined the effect of 60 h of sleep deprivation (SD) on electromechanical response times (EMRT), maximal voluntary isometric contraction (MVC), rate of force development (RFD), and times required to reach various percentages of MVC, during a maximal voluntary isometric contraction of both the forearm flexors and leg extensors. Eleven male subjects were either sleep deprived for 60 h (E) or performed similar daily activities and slept 7 h per night (C). Performance variables were evaluated at the same time intervals during both conditions. No significant differences were observed between the E and C conditions for EMRT (pre-motor time, electro-mechanical delay, total reaction time) or muscular performance (MVC, RFD). The results suggest that subjects who have undergone 60 h of SD can react as fast, and with as much force, as those who have had 7 h of sleep per night.

Adult↗
PubMed1986

A comparison of response and production protocols for assessing perceived exertion.

Two cycle ergometer protocols for assessing perceived exertion were compared before and after a fatiguing run. In the response (R) protocol, the subject rated the perceived exertion (RPE) of a series of power outputs assigned by the investigator. In the production (P) protocol, the investigator selected the RPE values and the subject adjusted his power output using a hand-held control. The relationship between RPE and power output (the regression coefficient and the slope and intercept of the regression line) was the same for both protocols. Fatigue due to the run caused a small increase in RPE (average 1.5 units) at a given exercise intensity and a commensurate decrease in power output (average 19 W) for a given RPE. The P protocol is safer than the R protocol because it makes no assumptions with regard to the physical condition of the subject. It is superior to the R protocol because it is an interval scale. These advantages suggest that the P protocol should be used instead of, or at least in addition to, the more traditional R protocol.

Adult↗
PubMed1985

Sleep deprivation, physical fatigue, and the perception of exercise intensity.

This paper presents the results of three experiments to determine the effect of sleep deprivation and physical fatigue on ratings of perceived exertion (RPE) for exercise of short (30 s) and long (15-50 min) duration. In the first, 12 male subjects walked on a treadmill, 50 min every 3 h, at 28% of their VO2max for 60 h without sleep. The RPE, recorded at the mid-point of each exercise bout, increased progressively with sleep loss. In the second experiment, when 12 female subjects performed ten 30-s bicycle exercise bouts before and after 54 h without sleep, there was no significant increase in RPE. In the third experiment, which examined the effect of physical fatigue on RPE, seven males performed two sets of ten 30-s bouts of cycle exercise before and after treadmill exercise at 70% of their VO2max to voluntary exhaustion. In one set, RPE was recorded; in the other, power output was measured. During the treadmill running, increases in RPE were observed and attributed to fatigue. This same fatigue caused only small changes in RPE and power output for the cycle exercise. The combined data suggest that where the exercise is of several minutes' duration, RPE is increased by sleep deprivation and by physical fatigue. Where the exercise period is as short as 30 s, sleep deprivation has no effect and physical fatigue causes only a small change in the perception of exercise intensity.

Adult↗
PubMed1983

The relationship between aerobic fitness and certain cardiovascular risk factors.

Aerobic fitness and the incidence of risk factors related to cardiovascular disease (CVD) were compared for 2501 Canadian servicemen 18-50 years of age. Aerobic power (VO2max) was predicted from heart rate measured during submaximal bicycle exercise. The risk factors--serum cholesterol, serum triglycerides, blood pressure and body fat (sum of three skinfolds)--were measured; the incidence of cigarette smoking was obtained from a questionnaire. The total population tested was divided into three age groups which were subdivided into four fitness categories. An inverse relationship was demonstrated between fitness category and the mean values for all measured risk factors. Although this relationship was most evident in the older subjects, it is significant that it was also present in men under 30 years of age. A similar inverse relationship was demonstrated for all age groups between fitness category and the percent of subjects considered to have an elevated cholesterol, triglyceride, blood pressure, or skinfold thickness. The incidence of cigarette smoking was inversely related to fitness category only in those 30 years of age and over. Although this type of cross-sectional study does not establish cause and effect, there is evidence to suggest that participation in a program to improve physical fitness may lead the individual to modify other components of his lifestyle.

Adolescent↗
PubMed1982

A cycle ergometer test of maximal aerobic power.

An indirect test of maximal aerobic power (IMAP) was evaluated in 31 healthy male subjects by comparing it with a direct treadmill measurement of maximal aerobic power (VO2 max), with the prediction of VO2 max from heart rate during submaximal exercise on a cycle ergometer using Astrand's nomogram, with the British Army's Basic Fitness Test (BFT, a 2.4 km run performed in boots and trousers), and with a test of maximum anaerobic power. For the IMAP test, subjects pedalled on a cycle ergometer at 75 revs X min-1. The workload was 37.5 watts for the first minute, and was increased by 37.5 watts every minute until the subject could not continue. Time to exhaustion was recorded. Predicted VO2 max and times for BFT and IMAP correlated significantly (p less than 0.001) with the direct VO2 max: r = 0.70, r = 0.67 and r = 0.79 respectively. The correlation between direct VO2 max and the maximum anaerobic power test was significant (p less than 0.05) but lower, r = 0.44. Although lactate levels after direct VO2 max determination were significantly higher than those after the IMAP test, maximum heart rates were not significantly different. Submaximal VO2 values measured during the IMAP test yielded a regression equation relating VO2 and pedalling time. When individual values for direct and predicted VO2 max and times for BFT and IMAP were compared with equivalent standards, the percentages of subjects able to exceed the standard were 100, 65, 87, and 87 respectively. These data demonstrate that the IMAP test provides a valid estimate of VO2 max and indicate that it may be a practical test for establishing that an individual meets a minimum standard.

Adult↗
PubMed1979

The physiological cost of carrying light and heavy loads.

Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.

Adult↗
PubMed1979

The energy cost of an 80 km run.

Data was collected from two men who attempted an 80 km run. Measurements of aerobic power (VO2 max) and determinations of heart rate (HR) and submaximal oxygen consumption (VO2) during treadmill running were carried out one week before the run. Throughout the 80 km run, HR was recorded by telemetry and used together with the laboratory data to estimate VO2 as a percentage of VO2 max. One subject completed the 80 km distance at 58% of VO2 max, the other subject, operating at 74% of VO2 max, was obliged to retired after 55 km. The data in this and other studies indicate that the high energy costs reported for the marathon (70-85% of VO2 max) cannot be sustained over the 80 km distance but that about 60% of VO2 max can be continued for seven hours and longer.

Adult↗
PubMed1979

A survey of aerobic fitness levels in a Canadian military population.

Aerobic fitness was assessed for 3171 men aged 17-55 years and for 610 women aged 17-29 years serving in almost every segment of the Canadian Forces (CF). Maximal oxygen uptake (Vo2 max) was predicted from heart rate measured during submaximal exercise. The survey showed that recruit training markedly improved Vo2 max for both men and women but that, after graduates were assigned to their trades and classifications and fitness training was no longer compulsory, fitness returned to pre-training levels. The relationship between daily activity and aerobic fitness was further demonstrated by comparing land, air, and sea elements in the CF. The active life of the young infantry soldiers is reflected in their relatively high Vo2 max. The available evidence indicates that, unless their duties involve compulsory fitness training (recruits) or hard physical work (infantry soldiers), the military in Canada have aerobic fitness levels which are not markedly higher than their civilian counterparts.

Adolescent↗
PubMed1979

Self-pacing during sustained, repetitive exercise.

During Exercise Fastball, 25 young French infantry soldiers walked 204 km in 6 d. A different load weight was assigned to each subject to ensure that they all worked at the same percentage of their aerobic power (Vo2max). The actual energy expended during the march was monitored by recording heart rates by ECG telemetry. The results confirmed that adjusting the load weight is a practical means of ensuring the same relative workload for subjects with different Vo2max. Furthermore, fit young soldiers will self-pace at 30-40% of Vo2max and will continue to do so for at least 6 d. The factor limiting performance for many of these subjects was the condition of their feet as a result of walking on the hard road surface.

Energy Metabolism↗
PubMed1976

Survial of fasted rats exposed to altitude.

Rats fasted for 48-96h before exposure were shown to have a longer survival time at groups 33,500 ft (1 ft = 0.305 m) simulated altitude than nonfasted controls. Although both become hypothermic at 33500 ft, colonic temperatures of the fasted rats were not sufficiently lower than those of nonfasted animals to explain the difference in survival time. The injection of glucose and insulin before exposure almost completely eliminated the protection afforded by fasting, whereas glucose alone had no effect on survival. It is therefore suggested that an alteration in carbohydrate metabolism, possibly in combination with other starvation-induced changes, allowed fasted rats to survive at 33500 ft until declining body temperature reduced metabolic rate to a level compatible with oxygen supply.

Altitude Sickness↗