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PubMed2004

Tooth whitening effects of an experimental power whitening toothbrush relative to an 8.7% hydrogen peroxide paint-on gel control.

PURPOSE: To assess the whitening efficacy of a new whitening power toothbrush, designed specifically for the removal of extrinsic stains, relative to an 8.7% hydrogen peroxide paint-on gel control. METHODS: This study was a randomized, single center, two-treatment, parallel design, 4-week, controlled study (n = 27) conducted to measure the whitening ability of an experimental power toothbrush relative to a peroxide paint-on gel control used in conjunction with a manual toothbrush. Subjects were randomized to the experimental battery-powered toothbrush group (twice a day brushing with Crest Cavity Protection dentifrice for 2 minutes each time) or the peroxide paint-on gel control group who applied Colgate Simply White Night per manufacturer's instructions once a day prior to bedtime for the first 14 days of the study as well as brushed twice a day with Crest Cavity Protection dentifrice for 2 minutes using the ADA manual reference toothbrush over the 4-week study period. Study evaluations included objective digital image analysis (L* a* b*) and oral soft tissue examinations at baseline, Week 2 and Week 4. In addition, a pilot, single center, 1-week study (n = 9) was conducted to measure the absolute whitening ability of the experimental power toothbrush as measured by digital imaging analysis in a high stain population, induced by 1 week of rinsing with tea. Study evaluations included digital image analysis (L*a*b*) and oral soft tissue examinations at baseline and Week 1 following brushing with the experimental power toothbrush. RESULTS: In the comparative study, the average baseline L*, b*, and W* values were well-balanced across treatment groups. At the Week 2 visit, adjusted (via ANCOVA) mean deltaL*, delta(a)*, delta(b)* and deltaW* values of 0.08, -0.41, -0.08, and -0.28, respectively, were observed in the peroxide paint-on control group, relative to adjusted mean deltaL*, delta(a)*, delta(b)* and deltaW* values of 0.16, -0.19, -0.38, and -0.33, respectively, in the experimental power toothbrush group. No statistically significant differences were observed between the two treatment groups for any of the endpoints. However, delta(b)* and deltaW* values for the experimental power toothbrush group were statistically significantly improved relative to baseline. At the Week 4 visit, adjusted (via ANCOVA) mean deltaL*, delta(a)*, delta(b)* and deltaW* values of -0.15, -0.24, -0.14, and -0.04, respectively, were observed in the peroxide paint-on control group, relative to adjusted mean deltaL*, delta(a)*, delta(b)* and deltaW* values of 0.02, -0.12, -0.22, and -0.15, respectively, in the experimental power toothbrush group. No statistically significant differences were observed between the two treatments groups for any color endpoints of deltaL*, delta(a)*, delta(b)*, or deltaW*. In the induced stain study, the average baseline L*, a*, b*, and W* values were 71.21, 8.28, 19.01, and 35.52, respectively. At the Week 1 visit, the mean deltaL*, delta(a)*, delta(b)*, and deltaW* values were 0.55, -0.27, 0.00, and -0.51 respectively. The deltaL* and deltaW* were statistically significantly improved (P < 0.05) relative to baseline.

Adult↗

PubMed2005

Do nurses exercise power in rehabilitation wards?

AIM: Nowadays, there is a change in nursing policy. The nurse-centred model is shifting to the patient-centred model. Decision-making is therefore transferred to the customer (Power to the Patient). Data from literature mainly deals with acute care and long-term care facilities. The aim of the study was to evaluate whether: i) a nurse-centred model is still effective in rehabilitation wards; ii) patients' dignity is nevertheless considered; iii) nurses experience role satisfaction in a rehabilitation setting. METHODS: A cross-sectional design was applied. Forty-eight nurses of our rehabilitation centre were invited to compile -in an anonymous way- a questionnaire developed by Finnish researchers from both acute care and geriatric units. More questions dealt with personal data. RESULTS: The sum of variables describing the nurses' exercise of power showed that power was most commonly exercised in obligatory daily activities. Power was less in activities necessitated by obligatory daily activities and in voluntary activities. Nurses' power was due to the necessity of organising the individual rehabilitation programs, which are tailored for each patient and require the observance of time-schedules. Nevertheless, patients had a say in many choices and their dignity was maintained. The nurses also answered that work in rehabilitation wards was more stressful than in both medical or surgical acute care. A third of them felt themselves not involved in the rehabilitation of the patients. CONCLUSIONS: The exercise of power is not a negative phenomenon in situations requiring safety, control, quick decisions, coping with time-contingencies, as it daily happens in rehabilitation wards. However, subject's dignity is compatible with that exercise of power. Rehabilitation staff should be aware of the nurse role, which can be only partially perceived. Better communication between nurses and other components of the rehabilitative staff would improve self-esteem and hasten motivation. Apparently, when the association between the ''experience'' variable and the sum variable was considered, it was found that the group of low clinical experience believed that power was exercised more often.

Adolescent↗

PubMed1993

[Effects of typhoon-caused power failure on medical care facilities].

In the evening of September 27, Typhoon 19 passed Yamaguchi prefecture. The wind velocity exceeded anything that the local meteorological observatory has ever recorded so far in this area. When the typhoon was off shore near Yamaguchi prefecture, the gale brought down many electric-light poles around Hofu city with power failure in Hofu city continuing for more than a week. At the same time the total number of emergency patients in Hofu area was the most in the prefecture. Because the power failure continued for many days, there was more indirect damage attributable to this power failure than the damage related directly to the typhoon. The capacity of the emergency electric power generator equipment installed in the Central prefectural hospital in Hofu city is the largest in Yamaguchi prefecture. Even while electric power failed completely in the Hofu city area, treatment of most of the emergency patients at this hospital was possible. There is no hospital that has as large an electric generator as the Central hospital has. Had this typhoon hit in another area, the ensuring confusion which might have occurred at hospitals in that area would have put many patients in danger with the power failure in many hospitals. Power consumption needs in hospitals have increased over that expected on the time the hospital was built. Therefore, the electric power generators installed in hospitals are of the times very small and unable to cope with massive electrical outage.

Disasters↗

PubMed1981

Insensible water loss in the critically III neonate. Combined effect of radiant-warmer power and phototherapy.

To quantitate radiant power and insensible water loss under phototherapy, 12 neonates were studied under radiant warmers for one hour each with and without phototherapy. Warmer power was measured by wattmeter and thermopile. Power density received from phototherapy was 4.4 mW/sq cm. Addition of phototherapy to the servocontrolled warmer caused a disease in power density received from the warmer (17.1 to 12.9 mW/sq cm). However, the total radiant-power density received with phototherapy and the warmer combined (17.3 mW/sg cm) did not differ from net power density received without phototherapy (17.1 mW/sq cm). Insensible water loss, measured with a metabolic balance, increased from 2.54 to 3.73 mL/kg/hr, with addition of phototherapy. Since the total radiant-power density did not change, mechanisms other than increased radiant-power delivery must exist to explain the increased insensible water loss observed with phototherapy.

Female↗

PubMed2000

Statistical power comparisons among alternative morphometric methods.

This paper compares the statistical power of various tests that have been proposed to test for equality of shape in two populations. Power surfaces are computed with emphasis on the simplest case of three points in the plane (i.e., landmarks at the vertices of a triangle). Goodall's ([1991] J Roy Stat Soc Serb 53:285-339) F-test was found to have the highest power followed by T(2)-tests using Kendall tangent space coordinates. Power for T(2)-tests using Bookstein shape coordinates was good if the baseline was not the shortest side of the triangle. The Rao and Suryawanshi ([1996] Proc Natl Acad Sci 93:12132-12136 and Rao and Suryawanshi [1998] Proc Natl Acad Sci 95:4121-4125) shape variables had much lower power when triangles were not close to being equilateral. Power surfaces for the EDMA-I T statistic revealed very low power for many shape comparisons including those between very different shapes. Power surface for the EDMA-II Z statistic were also complicated and depended strongly on the choice of baseline used for size scaling. The type I error rate was also often not correct for this method. Results for more than three landmarks are also presented. The implications of the results for practical applications of morphometrics are discussed.

Anthropology, Physical↗

PubMed2003

Power calculations for survival analyses via Monte Carlo estimation.

BACKGROUND: Power calculations can be a useful step in the design of epidemiologic studies. For occupational and environmental cohort studies, however, the calculation of statistical power has been difficult because researchers are often interested in situations where exposure assignment is time-dependent, and in research questions that pertain to cumulative exposure-mortality trends evaluated with statistical methods for survival analysis. These conditions are not easily accommodated by available software or published formulas for power calculation. METHODS: Monte Carlo methods can be used to estimate statistical power for survival analyses. Simple computer programs are presented to illustrate this approach. RESULTS: We show that, for the simple case of a randomized clinical trial involving a dichotomous exposure, the results of power calculations derived via this Monte Carlo approach conform to values derived using a previously published formula. We then illustrate how the Monte Carlo approach may be extended to obtain estimates of statistical power for analyses of cumulative exposure-mortality trends under conditions more typical of occupational cohort studies. CONCLUSIONS: The Monte Carlo approach provides a way to perform power calculations for a wide range of study conditions. The approach illustrated in this study should simplify the task of calculating power for survival analyses, particularly in epidemiologic research on occupational cohorts.

Epidemiologic Research Design↗

PubMed2001

Millimeter wave power density in aqueous biological samples.

Power density distribution inside a water sample placed between two parallel lossy dielectric plates (Polystyrene) was calculated using Fresnel equations for the frequency range of 42.25-53.57 GHz. Due to the multiple internal reflections from the sample boundaries, the distribution of the power density within the thin sample is more uniform than that within a semi-infinite medium. The power density in a sample depends on the thicknesses of the sample and the adjacent dielectric plates. For the given frequency range the sample thickness optimal for power density uniformity varies between 0.28 and 0.33 mm. The front plate has a significant effect on the magnitude of the power density within the sample but little effect on the power density distribution. The thicker the rear plate, the greater is the non uniformity of the power density distribution within the sample. Based on the calculated data, we determined the dimension of an exposure chamber providing the optimal power density distribution uniformity for mm-wave irradiation.

Air↗

PubMed1999

Power loss for multiallelic transmission/disequilibrium test when errors introduced: GAW11 simulated data.

Many researchers are considering the use of transmission/disequilibrium tests (TDT) for trios of genotypes (father, mother, child) as a method for localizing genes associated with complex diseases. We evaluate the effect of random errors (allele changes) in trios on the power to detect linkage. For a marker in the simulated data set, one allele is associated with the fictitious disease in a certain subpopulation. For the data as given (no errors), our power to detect linkage using the multiallelic TDT (TDTmhet) is 68% (critical p-value set at 0.0001). We introduce errors into trios at various rates (1%, 5%, or 10%), remove only trios displaying mendelian inconsistencies, and recalculate power to detect linkage. Our principal finding is that there is power loss to detect linkage with the TDTmhet when errors are introduced. We observe power losses of 8%, 16%, and 48% for error rates of 1%, 5%, and 10%, respectively. To determine the source of the power loss, we perform Monte Carlo simulations. At the 1% and 5% rates, we conclude that power loss is due primarily to loss in sample size. At the 10% rate, we observe substantial power loss due to error introduction in addition to sample size reduction. We also determine, given a particular error rate, the probability that we detect errors if we use only mendelian consistency as a check. We find that the mean detection rates for the data sets with 1%, 5%, or 10% error rates are 58%, 60%, and 62%, respectively. As a result, the apparent error rate appears to be almost half the true error rate. Based on these results, we recommend that researchers maintain error rates below 5% when using the TDTmhet for linkage, use additional methods beyond mendelian consistency checks when searching for errors in their data, and modify sample size calculations when accounting for errors in their genotype data.

Alleles↗

PubMed2004

Contrast-enhanced power Doppler sonography of ductal pancreatic adenocarcinomas: correlation with digital subtraction angiography findings.

PURPOSE: The purpose of this prospective study was to utilize contrast-enhanced power Doppler sonography to evaluate the enhancement characteristics of ductal pancreatic adenocarcinomas and correlate them with the tumor vascularity observed on digital subtraction angiography (DSA). METHODS: Twenty consecutive patients with ductal pancreatic adenocarcinoma underwent power Doppler sonography and DSA. Tumor vascularity was assessed using unenhanced and contrast-enhanced power Doppler sonography. The contrast agent Levovist was administered intravenously by bolus injection of a dose of 2.5 g at a concentration of 350 mg/mL; saline was administered immediately thereafter. The patients were asked to hold their breath for 30 seconds (for the period 15-45 seconds after saline injection) while the early phase of enhancement was studied; the delayed phase of enhancement was observed between 60 and 120 seconds after saline administration, while patients breathed gently. RESULTS: None of the 20 pancreatic carcinomas showed any color signals on power Doppler sonography before administration of the contrast medium. Seventeen (85%) of the 20 pancreatic carcinomas also showed no enhancement in the early and delayed phases of contrast-enhanced power Doppler sonography. However, in the early phase of contrast-enhanced power Doppler sonography; 1 lesion showed pronounced enhancement and 2 showed mild enhancement. On DSA, the 17 carcinomas showing no enhancement on power Doppler sonography were found to be hypovascular, whereas the remaining 3 carcinomas with contrast enhancement on power Doppler sonography were found to be hypervascular. CONCLUSIONS: The enhancement characteristics of the ductal pancreatic adenocarcinomas correlated well with the tumor vascularity observed on DSA. However, further study is needed to determine the accuracy of contrast-enhanced sonography in the diagnosis of pancreatic masses.

Adult↗

PubMed2003

Power and sample size calculations for generalized regression models with covariate measurement error.

Covariate measurement error is often a feature of scientific data used for regression modelling. The consequences of such errors include a loss of power of tests of significance for the regression parameters corresponding to the true covariates. Power and sample size calculations that ignore covariate measurement error tend to overestimate power and underestimate the actual sample size required to achieve a desired power. In this paper we derive a novel measurement error corrected power function for generalized linear models using a generalized score test based on quasi-likelihood methods. Our power function is flexible in that it is adaptable to designs with a discrete or continuous scalar covariate (exposure) that can be measured with or without error, allows for additional confounding variables and applies to a broad class of generalized regression and measurement error models. A program is described that provides sample size or power for a continuous exposure with a normal measurement error model and a single normal confounder variable in logistic regression. We demonstrate the improved properties of our power calculations with simulations and numerical studies. An example is given from an ongoing study of cancer and exposure to arsenic as measured by toenail concentrations and tap water samples.

Arsenic↗

PubMed2007

Does three-dimensional power Doppler ultrasound help in discrimination between benign and malignant ovarian masses?

OBJECTIVES: To determine if tumor vascularity as assessed by three-dimensional (3D) power Doppler ultrasound can be used to discriminate between benign and malignant ovarian tumors, if adding 3D power Doppler ultrasound to gray-scale imaging improves differentiation between benignity and malignancy, and if 3D power Doppler ultrasound adds more to gray-scale ultrasound than does two-dimensional (2D) power Doppler ultrasound. METHODS: One hundred and six women scheduled for surgery because of an ovarian mass were examined with transvaginal gray-scale ultrasound and 2D and 3D power Doppler ultrasound. The color content of the tumor scan was rated subjectively by the ultrasound examiner on a visual analog scale. Vascularization index (VI), flow index (FI) and vascularization flow index (VFI) were calculated in the whole tumor and in a 5-cm(3) sample taken from the most vascularized area of the tumor. Logistic regression analysis was used to build models to predict malignancy. RESULTS: There were 79 benign tumors, six borderline tumors and 21 invasive malignancies. A logistic regression model including only gray-scale ultrasound variables (the size of the largest solid component, wall irregularity, and lesion size) was built to predict malignancy. It had an area under the receiver-operating characteristics (ROC) curve of 0.98, sensitivity of 100%, false positive rate of 10%, and positive likelihood ratio (LR) of 10 when using the mathematically best cut-off value for risk of malignancy (0.12). The diagnostic performance of the 3D flow index with the best diagnostic performance, i.e. VI in a 5-cm(3) sample, was superior to that of the color content of the tumor scan (area under ROC curve 0.92 vs. 0.80, sensitivity 93% vs. 78%, false positive rate 16% vs. 27% using the mathematically best cut-off value). Adding the color content of the tumor scan or FI in a 5-cm(3) sample to the logistic regression model including the three gray-scale variables described above improved diagnostic performance only marginally, an additional two tumors being correctly classified. CONCLUSIONS: Even though 2D and 3D power Doppler ultrasound can be used to discriminate between benign and malignant ovarian tumors, their use adds little to a correct diagnosis of malignancy in an ordinary population of ovarian tumors. Objective quantitation of the color content of the tumor scan using 3D power Doppler ultrasound does not seem to add more to gray-scale imaging than does subjective quantitation by the ultrasound examiner using 2D power Doppler ultrasound.

Diagnosis, Differential↗

PubMed1990

The correlation of cardiac power output to exercise capacity in chronic heart failure.

Cardiac haemodynamics are deranged in chronic heart failure but fail to predict the exercise capacity of the patient. Cardiac power output is a descriptor of cardiac function derived from preload, blood pressure and cardiac output. Forty-one patients with moderately severe and severe chronic heart failure were exercised on a cycle ergometer to determine the relationship between traditional haemodynamics and cardiac power output and exercise capacity. Resting cardiac power output was no more predictive of exercise capacity than resting stroke-work index or resting cardiac index (r = 0.53, 0.61 and 0.51 respectively). Maximum cardiac power output and the ability to increase cardiac power output, however, were correlated with exercise capacity (r = 0.79 and 0.80). It is concluded that resting cardiac power output does not predict subsequent exercise capacity but that maximum cardiac power output and the ability to increase cardiac power output on stimulation are good descriptors of functional cardiac reserve.

Adult↗

PubMed1996

Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition.

To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W.kg-1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power. expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.

Adult↗

PubMed1995

The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit.

The regression of oxygen uptake (VO2) on power output and the O2 demand predicted for suprapeak oxygen uptake (VO2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean VO2peak = 67.9 (SD 4.2) ml.kg-1.min-1] and nine active, yet untrained men [UT, mean VO2peak = 54.1 (SD 6.5) ml.kg-1.min-1]. The VO2-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%-85% VO2peak. Minute ventilation (VE), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([la-]b) and rectal temperature (Tre) were measured at rest and during CON4. The slope of the VO2-power regression was greater (P < or = 0.05) in C [12.4 (SD 0.7) ml.min-1.W-1] compared to UT [11.7 (SD 0.4) ml.min-1.W-1]; as a result, the O2 demand (at 432 W) was also higher (P < or = 0.05) in C [5.97 (SD 0.23) l.min-1] than UT [5.70 (SD 0.15) l.min-1]. Exercise R and [la-]b were lower (P < or = 0.05) in C in comparison to UT at all power outputs, whereas VE and HR were relatively lower (P < or = 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in VO2-power slopes between the groups and up to 46% of the difference in VO2 at a given intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

The power of the classical twin study to resolve variation in threshold traits.

We explore the power of the twin study to resolve sources of familial resemblance when the data are measured at the binary or ordinal level. Four components of variance were examined: additive genetic, nonadditive genetic, and common and specific environment. Curves are presented to compare the power of the continuous case with those of threshold models corresponding to different prevalences in the population: 1, 5, 10, 25, and 50%. Approximately three times the sample size is needed for equivalent power to the continuous case when the threshold is at the optimal 50%, and this ratio increases to about 10 times when 10% are above threshold. Some power may be recovered by subdividing those above threshold to form three or more ordered classes, but power is determined largely by the lowest threshold. Non-random ascertainment of twins (i) through affected twins and examining their cotwins or (ii) through ascertainment of all pairs in which at least one twin is affected increases power. In most cases, strategy i is more efficient than strategy ii. Though powerful for the rarer disorders, these methods suffer the disadvantage that they rely on prior knowledge of the population prevalence. Furthermore, sampling from hospital cases may introduce biases, reducing their value. A useful approach may be to assess the population with a screening instrument; the power calculations indicate that sampling all concordant and half of the discordant pairs would be efficient, as along as the cost of screening is not too high.

Bias↗

PubMed2001

Effect of continuous versus dichotomous outcome variables on study power when sample sizes of orthopaedic randomized trials are small.

It is often not feasible to conduct large trials in orthopaedic surgery. Therefore, surgeons must identify strategies to optimize the statistical power of their smaller studies. The aim of this study was to compare study power in randomized trials with continuous versus dichotomous outcome variables. We performed a systematic review of the literature to identify randomized trials in orthopaedic trauma. Of these, we examined only those trials with small sample sizes (50 patients or less). The outcomes in each eligible study were categorized as continuous or dichotomous. Standard power calculations were performed for each study, and comparisons were made between continuous and dichotomous outcome variables. We identified 196 randomized trials in orthopaedic trauma. Of these, 76 trials had a sample size of 50 patients or fewer (29 trials with continuous outcomes, 47 trials with dichotomous outcomes). Studies that reported continuous outcomes had a significantly higher mean power than those that reported dichotomous variables (power 49% vs 38%, p=0.042). Twice as many trials with continuous outcome variables reached acceptable levels of study power (i.e. >80% power) when compared with trials with dichotomous variables (37% vs 18.6%, p=0.04). When orthopaedic surgeons anticipate small sample sizes for their study, they can optimize their study's statistical power by choosing a continuous outcome variable.

Cluster Analysis↗

PubMed2003

Measuring power during the sit-to-stand transfer.

Power has been demonstrated to be an early and potent marker of frailty. The measurements currently available are tied to locality. Usually, measurements include single joint movements or movements of only the legs and the resistance is not adjusted for body weight. In this study, a portable method to measure power in the sit-to-stand transfer was developed and tested. Mean power was calculated from the vertical ground reaction force of body weight, the difference between height in a sitting and in an upright position and the time taken to stand up. The results of this power measurement were compared with an isokinetic force measurement, the "Nottingham power rig", and measurement of physical performance in a five-repetition chair rise (five-chair rise). A convenience sample of 33 healthy elderly subjects [mean (SD) age: 67.8 (6.7) years; 17 men, 16 women] was included. Measurement of power during the sit-to-stand transfer showed good correlation to isokinetic force measurement (r=0.68) and to the "Nottingham power rig" (r=0.6). Correlation to five-chair rise was poor (r=-0.08). In conclusion, the study shows that the method presented is able to measure power during performance of a daily task. The poor correlation between the introduced measurement and the five-chair rise suggests that it might be able to detect decline in muscle function earlier by the introduced measurement than by measurement of the functional status. As it is inexpensive and portable, its use in clinical practice and research contexts, including home-bound individuals, is feasible.

Aged↗

PubMed1999

Human power output during repeated sprint cycle exercise: the influence of thermal stress.

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5) degrees C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5) degrees C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment. These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat.

Acid-Base Equilibrium↗