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Biomedical subjects

G Atkinson

Publications and source records attributed to G Atkinson.

At least 19 recordsLinked to original sources
PubMed2005

Can cycling performance in an early morning, laboratory-based cycle time-trial be improved by morning exercise the day before?

The normal circadian rhythm in exercise performance may be altered by the habitual timing of training. We have investigated if morning time trial performance is affected by the time at which moderate exercise is performed on the previous day. Eight male cyclists undertook two separate exercise sessions of sub-maximal cycle ergometry (60% V.O2peak for 30 min) at 07:00 h and 12:00 h the day before a 16.1-km time trial at 07:00 h. Heart rate, power output, ratings of perceived exertion, and rectal temperature were measured at rest and every 5 min in the pre-time trial exercises, and every 1.61 km during the time trial. Blood samples were taken at rest and immediately after the time trial for the measurement of lactate concentration. The time trial performed the day after the 07:00 h sub-maximal exercise was completed in 1672+/-135 s, compared to 1706+/-159 s for the time trial performed the day after the noon pre-time trial exercise (p=0.027). The time trial after exercise the previous morning was associated with higher work-rates (p=0.031), a higher net lactate accumulation after the time trial (p=0.018), and a trend for higher heart rates (p=0.093) compared to the time trial after exercise the previous noon. These findings suggest that cycling performance in an early morning time trial is improved if an athlete participates in early-morning rather than noontime moderate exercise the day before. This finding cannot be attributed to the physiological responses to the exercise on the pre-time trial day or to environmental factors. It is suggested that it might partly reflect an advantage gained by performing exercise in the day(s) immediately beforehand at the same time as the competition.

Adult↗
PubMed2005

Performance characteristics of gas analysis systems: what we know and what we need to know.

It is important that sources of variation in gas analysis measurements are identified and described in an accurate and informative manner. In this paper, we discussed the potential sources of error, which should be considered in any measurement study on gas analysis systems. We then covered how errors in various terms associated with gas laws propagate to outcome measurements of gas exchange to help quantify the relative importance of sources of error. Finally, we performed a literature survey to explore the statistical methods researchers have employed to arrive at conclusions on the performance characteristics of gas analysis methods. We found examples of excellent practice in the literature, but there were also gaps in the knowledge of error in gas analysis systems. Consequently, we supplied guidelines for future method comparison studies. These guidelines included (i) a sample size of at least 40 participants and the citation of confidence intervals, (ii) a description of the relationships between systematic and random errors and the size of measured value, (iii) the parallel examination of test-retest error within a method comparison study, and (iv) an a priori-made judgement on how much systematic and random error between methods is acceptable for practical applications. We stressed that this judgement should be based on expert-agreed position statements about acceptable error, which unfortunately have yet to be formulated for gas analysis systems.

Breath Tests↗
PubMed2005

Circadian rhythms in sports performance--an update.

We discuss current knowledge on the description, impact, and underlying causes of circadian rhythmicity in sports performance. We argue that there is a wealth of information from both applied and experimental work, which, when considered together, suggests that sports performance is affected by time of day in normal entrained conditions and that the variation has at least some input from endogenous mechanisms. Nevertheless, precise information on the relative importance of endogenous and exogenous factors is lacking. No single study can answer both the applied and basic research questions that are relevant to this topic, but an appropriate mixture of real-world research on rhythm disturbances and tightly controlled experiments involving forced desynchronization protocols is needed. Important issues, which should be considered by any chronobiologist interested in sports and exercise, include how representative the study sample and the selected performance tests are, test-retest reliability, as well as overall design of the experiment.

Behavior↗
PubMed2004

Effects of music on work-rate distribution during a cycling time trial.

Previous research work on the ergogenic effects of music has mainly involved constant power tests to exhaustion as dependent variables. Time trials are more externally valid than constant power tests, may be more reliable and allow the distribution of self-selected work-rate to be explored. We examined whether music improved starting, finishing and/or overall power during a 10-km cycling time trial, and whether heart rate and subjective responses to this time trial were altered by music. Sixteen participants performed two 10-km time trials on a Cybex cycle ergometer with, and without, the presence of a form of dance music known as "trance" (tempo = 142 beats x min (-1), volume at ear = 87 dB). Participants also completed the Brunel music rating inventory (BMRI) after each time trial in the music condition. The mean +/- SD time to complete the time trial was 1030 +/- 79 s in the music condition compared to 1052 +/- 77 s without music (95 % CI of difference = 10 to 34 s, p = 0.001). Nevertheless, ratings of perceived exertion were consistently (0.8 units) higher throughout the time trial with music (p < 0.0005). The interaction between distance and condition was significant for cycling speed measured during the time trial (p = 0.007). The largest music-induced increases in cycling speed and heart rate were observed in the first 3 km of the time trial. After completion of the BMRI, participants rated the "tempo" and "rhythm" of the music as more motivating than the "harmony" and "melody" aspects. These results suggest that music improves cycling speed mostly in the first few minutes of a 10-km time trial. In contrast to the findings of previous research, which suggested that music lowers perceived exertion at a constant work-rate, the participants in our time trials selected higher work-rates with music, whilst at the same time perceived these work-rates as being harder than without music.

Adult↗
PubMed2004

Dietetic guidelines: diet in secondary prevention of cardiovascular disease (first update, June 2003).

AIM: To update dietetic guidelines summarizing the systematic review evidence on dietary advice to prevent further events in people with existing cardiovascular disease (CVD) (secondary prevention). METHODS: The Cochrane Library, MEDLINE and EMBASE were comprehensively searched to November 2002 for systematic reviews on aspects of diet and heart health. Reviews were included if they searched systematically for randomised controlled trials relating to diet and secondary prevention of CVD. Two members of the UK Heart Health and Thoracic Dietitians Group critically appraised each review. The quality and results of each review were discussed and summarized in a meeting of the whole group. RESULTS: Providing evidence-based dietary information (including increasing omega-3 fat intake) to all people who have had a myocardial infarction will save more lives than concentrating dietary advice on just those in need of weight loss or lipid lowering. The practice of prioritizing dietetic time in secondary prevention to those with raised lipids is out of date since the advent of statin therapy. However, effective dietary advice for those with angina, stroke, peripheral vascular disease or heart failure is less clear. CONCLUSION: There is good systematic review evidence that dietary advice to those with coronary heart disease can reduce mortality and morbidity as well as modify some risk factors. Dietary advice that does this most effectively should be prioritized.

Cardiovascular Diseases↗
PubMed2003

The effects of massage on intra muscular temperature in the vastus lateralis in humans.

The aim of the current investigation was to evaluate the effect of different durations of massage, and ultrasound treatment, on the temperature of the vastus lateralis muscle in males. Deep effleurage massage of the vastus lateralis was performed on seven healthy males (mean +/- SD; age; 28 +/- 4 years, height 1.84 +/- 0.05 m, body mass 85.7 +/- 12 kg) for 5, 10 and 15 min periods. A 5-min period of ultrasound at 45 KHz was also completed by all subjects. Intra muscular temperature (at 1.5, 2.5 and 3.5 cm) and thigh skin temperature were assessed pre and post treatment. Heart rate was monitored continuously throughout all conditions. Pre treatment intra muscular temperature increased as depth of measurement increased (p = 0.00002). Changes in muscle temperature at 1.5 and 2.5 cm were significantly greater following massage than ultrasound (p < 0.002). No significant differences between massage treatments and ultrasound were noted when intra muscular temperature was measured at 3.5 cm (p > 0.05). Massage also significantly increased both heart rate and thigh skin temperature compared to ultrasound (p < 0.005). Increases in intra muscular temperature, heart rate and thigh skin temperature were the same irrespective of massage duration. These data suggest that massage and ultrasound have only limited effects on deep muscle temperature. As a result such approaches may not be suitable as a preparation strategy for exercise.

Adult↗
PubMed2002

The effect of even, positive and negative pacing on metabolic, kinematic and temporal variables during breaststroke swimming.

The aim of this investigation was to determine the effect of even, negative and positive pacing on metabolic, kinematic and temporal variables during breaststroke swimming. Nine male swimmers [mean (SD): age 21 (3) years, height 178 (5) cm, body mass 77.2 (6.7) kg, 200 m-time 158.6 (13.6) s] completed a 200-m breaststroke time trial and then 72 h later three paced (even, positive, negative) 175-m breaststroke swims in random order, 48 h apart. The swimmers paced accurately in all trials. The evenly paced trial produced lower post-exercise peak blood lactate and rating of perceived exertion values compared to the positively paced trial ( P<0.05). Peak oxygen uptake was not significantly different between trials ( P>0.05). Heart rate immediately following exercise was lower in the negatively paced trial ( P<0.05) than the other paced trials. Stroke rates were lower during the first half of the evenly and negatively paced trials compared to the positively paced trial ( P<0.01), but no differences were observed between the second half of the trials. Across all trials the stroke count increased as the trials progressed ( P<0.01). Turning times were observed to be shorter during the first half of the positively paced trial compared to the other paced trials ( P<0.01). Even paced swimming appears to be less physically stressful than positively paced swimming during high intensity exercise, as indicated by a lower post-exercise blood lactate concentration, perceived exertion and variability within turning times.

Adult↗
PubMed2002

Exercise does not necessarily influence the phase of the circadian rhythm in temperature in healthy humans.

Seventeen healthy adults exercised for 30 min (70% VO2max), at different times of the day and night throughout a 24 h period. The effect on the phase of core temperature rhythm was assessed by comparing the rhythms on the day immediately before and immediately after the day of exercise with the participants living normally on these 2 days. Assessments were made upon data that had been corrected for the thermogenic effects of sleep and activity. When exercise was performed in the period between 4 h before and 1 h after the temperature minimum, there was a phase delay of 1.03 +/- 0.78 h (mean +/- s; n = 6); when performed between 3 and 8 h after the temperature minimum, there was a phase advance of 1.07 +/- 1.23 h (n = 9). Both means were significantly different from zero (Student's one-sample t-tests: P < 0.05). Performed at other times, exercise had no significant effect on the phase of the temperature rhythm. The phase changes were not significantly different from those previously observed by us in sedentary individuals exposed to domestic lighting. We conclude that the amount of physical activity has very little effect on the body clock.

Activities of Daily Living↗
PubMed2002

A comparison of the suitabilities of rectal, gut, and insulated axilla temperatures for measurement of the circadian rhythm of core temperature in field studies.

Eight healthy males were studied for a total of 13 subject-days to assess if gut (from an ingested pill) and axilla (from a thermally insulated skin probe) temperatures would act as a substitute for rectal temperature in field studies of the circadian rhythm of core temperature. Subjects slept and went about their activities, indoors and outdoors, normally. Regular recordings (at 6 min intervals) were made of temperatures from the three sites. In addition, activity was measured (by a sensor on the nondominant wrist) so that the raw temperature data could be "purified," that is, corrected for the direct effects of sleep and activity. Inspection of the raw data indicated that there was a close parallelism between rectal and gut temperatures, but that the parallelism between rectal and insulated axilla temperatures was less reliable. This parallelism was supported by initial calculations of the correlations between rectal and gut temperatures (high and positive) and between rectal and insulated axilla (lower, though still positive) temperatures. Calculation of the limits of agreement between the parameters of the cosine curves fitted to the raw data confirmed that the rectal and gut temperatures were far closer with regard to acrophase and amplitude than were rectal and insulated axilla temperatures (-0.31 +/- 0.89 vs. +0.75 +/- 6.03 h and +0.002 +/- 0.116 vs. +0.083 +/- 0.625 degrees C, respectively). After purification of the temperature data, the limits of agreement for the cosine parameters acrophase and amplitude still indicated that there was a closer agreement between rectal and gut temperatures than between rectal and insulated axilla temperatures (-0.30 +/- 1.12 vs. +0.58 +/- 6.69 h, and +0.007 +/- 0.116 vs. +0.104 +/- 0.620 degrees C, respectively). Part of the explanation of this difference was the unreliable relationships between temperature changes in insulated axilla temperature and bursts of activity and going to bed. It is concluded that, whereas gut temperature is a viable alternativ to rectal temperature (from the viewpoints of both user acceptability and the reliability of data obtained), insulated axilla temperature, though acceptable to subjects, is unreliable from an experimental viewpoint.

Adult↗
PubMed2002

Identifying some determinants of "jet lag" and its symptoms: a study of athletes and other travellers.

BACKGROUND: Travelling across multiple time zones disrupts normal circadian rhythms and induces "jet lag". Possible effects of this on training and performance in athletes were concerns before the Sydney Olympic Games. OBJECTIVE: To identify some determinants of jet lag and its symptoms. METHODS: A mixture of athletes, their coaches, and academics attending a conference (n = 85) was studied during their flights from the United Kingdom to Australia (two flights with a one hour stopover in Singapore), and for the first six days in Australia. Subjects differed in age, sex, chronotype, flexibility of sleeping habits, feelings of languor, fitness, time of arrival in Australia, and whether or not they had previous experience of travel to Australia. These variables and whether the body clock adjusted to new local time by phase advance or delay were tested as predictors for jet lag and some of its symptoms by stepwise multiple regression analyses. RESULTS: The amount of sleep in the first flight was significantly greater in those who had left the United Kingdom in the evening than the morning (medians of 5.5 hours and 1.5 hours respectively; p = 0.0002, Mann-Whitney), whereas there was no significant difference on the second flight (2.5 hours v 2.8 hours; p = 0.72). Only the severity of jet lag and assessments of sleep and fatigue were commonly predicted significantly (p<0.05) by regression analysis, and then by only some of the variables. Thus increasing age and a later time of arrival in Australia were associated with less jet lag and fatigue, and previous experience of travel to Australia was associated with an earlier time of getting to sleep. Subjects who had adjusted by phase advance suffered worse jet lag during the 5th and 6th days in Australia. CONCLUSIONS: These results indicate the importance of an appropriate choice of itinerary and lifestyle for reducing the negative effects of jet lag in athletes and others who wish to perform optimally in the new time zone.

Adult↗
PubMed2001

Independent contributions of GR-1+ leukocytes and Fas/FasL interactions to induce apoptosis following interleukin-12 gene therapy in a metastatic model of prostate cancer.

In a mouse model of prostate cancer, adenovirus-mediated interleukin-12 (Ad.mIL-12) gene therapy resulted in significant growth inhibition of both the injected primary tumor and synchronous metastases. Within 2 days of vector injection, two distinct patterns of apoptosis were detected within the primary tumor, the inhibition of which with a caspase inhibitor substantially negated growth suppression. The dominant pattern displayed localized sheets of apoptotic cells in close association with necrosis containing polymorphic neutrophils (PMNs). Depletion of PMNs resulted in the loss of this pattern of apoptosis and reduced growth suppression. A second major wave of growth suppression within the primary tumor was mediated by an immune response. Natural killer (NK) cell activity was detected within tumor-infiltrating lymphocytes (TIL) by the eighth day post-vector injection, the depletion of which resulted in a significant loss of survival enhancement. A more modest role for T cells was identified, which in the absence of documented cytotoxic T lymphocyte (CTL) activity may be related to a significant reduction in interferon-gamma (IFN-gamma) levels found in mice depleted of T cells, thereby reducing the secondary influences of IFN-gamma. However, depletion of NK cells or T cells had no discernible negative effect on IL-12-mediated anti-metastatic activity. Attention focused on the role of IFN-gamma, observed following Ad.mIL-12 therapy, to mediate the diffuse pattern of apoptosis seen in the primary and metastatic lesions. In vitro studies noted the ability of IFN-gamma to up-regulate tumor cell expression of Fas and FasL to mediate apoptosis, whereas in vivo blockage of Fas/FasL interactions with soluble Fas resulted in a modest reduction in primary tumor growth suppression but complete abrogation within metastatic lesions.

Adenoviridae↗
PubMed2001

Effect of low-dose temazepam on physiological variables and performance tests following a westerly flight across five time zones.

Rapid travel across multiple time zones disturbs circadian rhythms and induces "jet lag". The aims of this study were 1) to monitor a selection of subjective, physiological and performance variables in elite athletes and sedentary subjects following a westerly flight across five time zones, and 2) to examine whether the promotion of sleep by means of a low-dose benzodiazepine drug influences these responses to transmeridian travel. Subjects comprised eight members of the British men's gymnastics squad, aged 18-30 years, and nine members of the British Olympic Association's support staff, aged 24- 55 years (4 females, 5 males). Subjects were pair-matched for age, sex and athleticism (apart from one person) and assigned to either the treatment (n = 9) or placebo (n = 8) group. All subjects travelled from U.K., arriving at Tallahassee, Florida, at approximately 22:00 hours local time. A test battery was administered to the subjects at 07:00, 12:00, 17:00 and 21:00 hours on the first full day of arrival (this was designated day one) and then on alternate days (day 3, day 5 and day 7). Immediately before retiring to bed on days 1, 2 and 3, subjects were administered, in a double-blind fashion, either 10mg of temazepam or a placebo. Measures in the test battery included sleep quality, sleep length, subjective jet lag (one-to-ten simple analogue scale), tympanic temperature, one-, two-, four- and eight-choice reaction time, grip strength (left and right), leg strength and back strength. Over the 24 h of each test day, subjects also recorded the volume of each urine voided. Data were analysed with a repeated measures general linear model. Alpha was set at 0.01 to control for type I errors with multiple dependent variables. Mean subjective jet lag reduced from 4.6 units to baseline, and mean sleep quality improved by 2.0 units from day 1 to day 5 (P<0.001), after which no further alterations were noted. Subjective jet lag, left and right grip strength and choice reaction time all showed post-flight day x time of day interactions (P < 0.01). On day 1, these variables deteriorated as the day progressed to the worst recorded values. On days 3, 5 and 7, diurnal variations with the conventional high in the early evening and morning-to-evening differences of about 10% were evident. There was a trend for the reduction in subjective jet lag over the post-flight days to be more rapid following ingestion of a low dose of temazepam (P= 0.037). We cannot rule out the possibility that this could be a type I error, since none of the treatment by day interactions reached the alpha level of significance (set at 0.01). The morning-to-evening variations of body temperature and grip strength were greater in the young athletes than in the older sedentary support staff (P < 0.01). Sleep quality was greater in the athletic subjects after the first full day in Tallahassee. These results suggest that the nightly administration of a low dose (10 mg) of temazepam has little influence on the recovery of subjective, physiological and performance measures following a westward flight across five time zones. In both the treatment and control groups, subjective jet lag and performance were worst in the evening of the first full day after arrival, and the young athletes slept better than the older support staff that same night. This illustrates the importance of monitoring jet lag symptoms and performance variables at different times of day following a flight to a new time zone.

Adult↗
PubMed2001

Are there hangover-effects on physical performance when melatonin is ingested by athletes before nocturnal sleep?

Athletes ingest melatonin in an attempt to improve sleep quality or alleviate symptoms of jet lag after transmeridian travel. It is not known whether there are residual effects of this hormone on physical performance in fit subjects. After a sample size estimation involving a meaningful effect on performance of 5%, five milligrams of melatonin or placebo were ingested by twelve physically-active subjects before sleep in a double-blind experiment. The following morning, subjective sleep quality (latency and maintenance) were measured together with intra-aural temperature, grip strength of the left and right hands, and time to complete a 4 km time trial on a cycle ergometer. The subjects also rated perceived exertion during the latter test. The null hypothesis of no effect of melatonin on either subjective sleep quality or physical performance measured the morning after administration could not be rejected on the basis of our observations (P > 0.30). The mean differences between treatments were less than 1% for the strength tests and time trial performance. The confidence intervals for these differences for left and right grip strength and the cycling test were - 2.1 to 2.8 kg, - 3.1 to 2.7 kg and -3.0 to 4.5 s, respectively. In conclusion, it is unlikely that 5 mg of melatonin would have any meaningful effects on physical performance in the morning after fit subjects ingest the hormone. There was also little evidence that it improves sleep quality in this population. Further research is needed concerning the effects of daytime and nighttime admistration of melatonin on performance, in both situations of normal and disturbed sleep.

Adult↗
PubMed2001

Selected issues in the design and analysis of sport performance research.

The aim of this review is to discuss some issues in the design and statistical analysis of sport performance research, rather than to supply an authoritative 'cookbook' of methods. In general, we try to communicate some possible solutions to the conundrum of how to maintain both internal and external validity, as well as optimize statistical power, in applied sport performance research. We start by arguing that some sport performance research has been overly concerned with physiological predictors of performance, at the expense of not providing a valid and reliable description of the exact nature of the task in question. We show how the influence of certain factors on competitive performances can be described using linear or logistic regression. We discuss the choice of analysis for factorial repeated-measures designs, which is complicated by the assumption of 'sphericity' in a univariate general linear model, and the relatively low statistical power of the multivariate approach when used with small samples. We consider a little-used and simpler technique known as 'analysis of summary statistics'. In multi-group pre- and post-test designs, a useful technique can be to pair-match individuals on their performance scores in a counterbalanced fashion before the intervention or control has been introduced. Finally, we outline how confidence intervals can help in making statements about the probability of the population difference in performance exceeding the value designated as being worthwhile or not.

Humans↗
PubMed2001

How to show that unicorn milk is a chronobiotic: the regression-to-the-mean statistical artifact.

Few chronobiologists may be aware of the regression-to-the-mean (RTM) statistical artifact, even though it may have far-reaching influences on chronobiological data. With the aid of simulated measurements of the circadian rhythm phase of body temperature and a completely bogus stimulus (unicorn milk), we explain what RTM is and provide examples relevant to chronobiology. We show how RTM may lead to erroneous conclusions regarding individual differences in phase responses to rhythm disturbances and how it may appear as though unicorn milk has phase-shifting effects and can successfully treat some circadian rhythm disorders. Guidelines are provided to ensure RTM effects are minimized in chronobiological investigations.

Biometry↗
PubMed2000

Famciclovir in chronic hepatitis B: results of a dose-finding study.

BACKGROUND/AIMS: Famciclovir, an orally available nucleoside analogue with potent in vitro activity against HBV, is being investigated for treatment of chronic hepatitis B. METHODS: A dose-finding study was conducted in patients with hepatitis B e antigen present in serum. Patients received famciclovir 125 mg, 250 mg, 500 mg three times daily (tid) or placebo for 16 weeks, followed by 8 months post-treatment observation, and 16 weeks open-label treatment. More than 90% of patients had previously received alpha-interferon or had baseline characteristics indicating a high likelihood of poor response to alpha-interferon. RESULTS: Famciclovir induced rapid, dose-dependent suppression of viral replication and reduction in alanine aminotransferase (ALT), with greatest efficacy in the 500-mg tid treatment group. HBV DNA reduction was maintained throughout the treatment period. ALT also steadily declined during the treatment period. Approximately 40% of patients with pretreatment ALT>upper limit of normal (ULN) receiving famciclovir 500 mg tid, experienced sustained normalization of ALT at the end of the 8-month follow-up. Anti-HBe seroconversion occurred more frequently in patients receiving famciclovir 500 mg tid compared with placebo (p=0.04). Famciclovir was generally well tolerated; the incidence of adverse events was comparable to placebo. Exacerbation of liver disease or serious ALT flares were not observed. CONCLUSION: Famciclovir 500 mg three times daily may offer an alternative to alpha-interferon for treatment for chronic hepatitis B. Anti-HBe seroconversion in the famciclovir 500-mg tid group suggests that 16 weeks treatment has the potential for HBV clearance. Further studies with a longer treatment duration are warranted.

2-Aminopurine↗