Prediction of maximal aerobic power from the 20-m multi-stage shuttle run test.

The purpose of this study was to test the accuracy of the 20-m multi-stage shuttle run (SR) test to predict VO2max in young adults. VO2max was measured during a graded treadmill test in 60 men and 62 women (mean age 25.3 and 25.1 years, respectively). Each subject was familiarized with the SR procedure and the completed the SR test to predict VO2max on a separate day. The mean terminal SR stage was 9.5 for men and 7.8 for women. The regression equations of Léger et al. (1988) and Léger and Gadoury (1989) systematically underpredicted VO2max for both males and females (p < 0.05). New regression equations were developed from present data to predict VO2max for males: Y = 2.75X + 28.8 (r2 = 0.77, SEE = 4.07 ml.kg-1.min-1); and for females: Y = 2.85X + 25.1 (r2 = 0.66, SEE = 3.64 ml.kg-1.min-1), where X equals the last half-stage of the SR completed. We suggest that these gender-distinct equations provide more accurate predictions of VO2max from the SR.     

A new incremental test for VO2max accurate measurement by increasing VO2max plateau duration, allowing the investigation of its limiting factors

The purpose of this study was to (1) validate a new exercise protocol for accurate measurement of VO(2max) by obtention of a VO(2max) plateau for all subjects fit and unfit (2) test the hypothesis that VO(2max) plateau duration is not correlated with VO(2max) and (3) verify that limiting factors of VO(2max) plateau duration are different from those of VO(2max) amplitude. Therefore, 14 subjects performed two incremental cycling tests: (1) a classical incremental test (CIT) to determine VO(2max), the power at VO(2max) (PVO(2max)) and at the lactate threshold (PLT) (2) a new incremental test (NIT) in which the power was decreased just after the subject reached VO(2max). During both protocols, heart rate, stroke volume, cardiac output, the arterio-venous difference and the oxygen blood saturation were recorded. The results showed that, with the NIT, subject could maintain a long VO(2max) plateau (6 ± 3 min), even those who could not reach VO(2max) plateau at the end of CIT (n = 5). The VO(2max) plateau duration was not correlated with VO(2max) amplitude which was correlated with the power at SV(max) (r = 0.888, p < 0.001). The VO(2max) plateau duration was correlated with the power decrease (W/s) during the VO(2max) plateau (r = -0.72, p = 0.003) but not with cardiac-related factors nor with PVO(2max). In conclusion, these experiments showed that it was possible to get a long VO(2max) plateau at the end of NIT whatever the individual VO(2max) amplitude was. The limiting factor of VO(2max) duration was the power output.     

Generalized self-efficacy and performance on the 20-metre shuttle run in children.

It has been argued that motivation significantly affects the measurement of aerobic capacity when using field tests with children. In this study, the impact of generalized self-efficacy on performance (Stage Completed) in the Léger shuttle run is examined in a cohort of children (N = 2,245, 9.38 +/- 0.52 years old) in Grade 4 from 75 elementary schools. Children completed the Children's Self-perceptions of Adequacy in and Predilection for Physical Activity scale (CSAPPA) to establish levels of generalized self-efficacy toward physical activity, were measured for height and weight, and then completed the Léger Shuttle run to predict aerobic capacity. Regression analysis was used to study the impact of self-efficacy on test performance. After adjusting for age, gender, and BMI, two of the three CSAPPA factor subscales, higher perceived adequacy regarding physical activity (beta = 0.196, P < 0.001) and greater predilection to select physical over sedentary activities (beta = 0.123, P < 0.001), were independently associated with better test performance as indicated by stage completed. Together, self-efficacy accounted for 9% of the total variation in Léger shuttle run performance. A significant interaction between BMI and perceived adequacy was found (beta = -0.106, P < 0.005). Children with both high BMI scores and below average perceived adequacy had the poorest performance results. Generalized self-efficacy, as measured by the CSAPPA, is significantly related to Léger shuttle run performance. Moreover, self-efficacy influences the relationship between other known factors affecting test performance (BMI), suggesting that self-perception of ability/competence has a complex effect on test performance. These results illustrate the importance of considering psychological factors when interpreting physiologic assessments in children.     

Ramp-incremented and RPE-clamped test protocols elicit similar VO2max values in trained cyclists

Purpose

The present study compared the efficacy of ramp incremented and ratings of perceived exertion (RPE)-clamped test protocols for eliciting maximal oxygen uptake (VO_2max).

Methods

Sixteen trained cyclists (age 34 ± 7 years) performed a ramp-incremented protocol and an RPE-clamped protocol 1 week apart in a randomized, counterbalanced order. The RPE-clamped protocol consisted of five, 2-min stages where subjects self-selected work rate and pedal cadence to maintain the prescribed RPE. After completing both test protocols subjects were asked which they preferred.

Results

The mean ± SD test time of 568 ± 72 s in the ramp protocol was not significantly different to the 600 ± 0 s in the RPE-clamped protocol (mean difference = 32 s; p = 0.09), or was the VO_2max of 3.86 ± 0.73 L min^?1 in the ramp protocol significantly different to the 3.87 ± 0.72 L min^?1 in the RPE-clamped protocol (mean difference = 0.002 L min^?1; p = 0.97). Furthermore, no significant differences were observed for peak power output (p = 0.21), maximal minute ventilation (p = 0.97), maximal respiratory exchange ratio (p = 0.09), maximal heart rate (p = 0.51), and post-test blood lactate concentration (p = 0.58). The VO_2max attained in the preferred protocol was significantly higher than the non-preferred protocol (mean difference = 0.14 L min^?1; p = 0.03).

Conclusion

The RPE-clamped test protocol was as effective as the ramp-incremented protocol for eliciting VO_2max and could be considered as a valid alternative protocol, particularly where a fixed test duration is desirable.     

A comparison of various methods for the determination of VO2max

Summary Previous studies have shown that true maximal oxygen uptake (VO₂max) obtained by means of cycle ergometer and step test are lower than the VO₂max measured during uphill treadmill running. The predicted VO₂max measured by ergometer was even lower. Four different methods for the determination of VO₂max within the same group of examinees were compared: True VO₂max by treadmill, ergometer, step test, and predicted VO₂max (Astrand-Rhyming). This study was performed on 15 healthy non-professional sportsmen. They underwent progressive test protocols on alternating days and the results were as follows — VO₂max expressed in ml O₂ kg BW/min (mean±SD): treadmill running 63.8±4.7; ergometer cycling 60.2±5.6; step test 59.6±5.2 and predicted VO₂max 59.9±6.9.The VO₂max as determined by uphill treadmill running was significantly higher than with the other methods. No significant difference was found between true VO₂max determined by the ergometer and step test. However, step test and properly executed Astrand-Rhyming test again proved to be reliable and deviate from the treadmill test by only 6%. Maximal heart rate was sgnificantly higher in the treadmill and step tests than in the direct ergometer test.     

Effect of paddling cadence on time to exhaustion and VO2 kinetics at the intensity associated with VO2max in elite white-water kayakers.

The influence of paddling cadence on the time to exhaustion (t.lim) and VO2 kinetics at the intensity associated with VO2max (IVO2max) was examined in seven highly-trained white water kayakers. All subjects were engaged in national or international competitions. Subjects took part in three constant-load tests at IVO2max, each test performed at a different paddling cadence (50, 60 or 70 cycles min(-1). The VO2 kinetics recorded during these constant-load tests at IVO2max were fitted with a mono-exponential equation. A significant increase in t.lim (P <.05) was observed as the paddling cadence increased from 50 to 70 cycles min(-1). No effect was found either on values of VO2peak, post-exercise blood lactate concentration, or on the time at which VO2peak was attained (TAVO2peak). Our results suggest that experienced kayakers may choose a high paddling cadence during physiological assessments at IVO2max. Further experiments are needed in order to identify the physiological significance of t.lim at IVO2max.     

Use of constants from Mark-Houwink-Sakurada equation for estimating the characteristic ratio of a polymer chain

A new procedure for the estimation of the characteristic ratio of flexible chain polymers is proposed. It is based on a combination of the parameters of the Mark-Houwink-Sakurada equation with a theoretical relationship of Kurata and Stockmayer. It is checked against data obtained under “theta” conditions. Good results are provided with systems where the Mark-Houwink-Sakurada exponent is lower than 0,65.     

Artificial neural networks for source localization in the human brain

Summary Source localization in the brain remains an ill-posed problem unless further constraints about the type of sources and the head model are imposed. Human head is modeled in various ways depending critically on the computing power available and/or the required level of accuracy. Sophisticated and truly representative models may yield more accurate results in general, but at the cost of prohibitively long computer times and huge memory requirements. In conventional source localization techniques, solution source parameters are taken as those which minimize an index of performance, defined relative to the model-generated and clinically measured voltages. We propose the use of a neural network in the place of commonly employed minimization algorithms such as the Simplex Method and the Marquardt algorithm, which are iterative and time consuming. With the aid of the error-backpropagation technique, a neural network is trained to compute source parameters, starting from a voltage set measured on the scalp. Here we describe the methods of training the neural network and investigate its localization accuracy. Based on the results of extensive studies, we conclude that neural networks are highly feasible as source localizers. A trained neural network's independence of localization speed from the head model, and the rapid localization ability, makes it possible to employ the most complex head model with the ease of the simplest model. No initial parameters need to be guessed in order to start the calculation, implying a possible automation of the entire localization process. One may train the network on experimental data, if available, thereby possibly doing away with head models.     

Comparing several equations that predict peak VO2 using the 20-m multistage-shuttle run-test in 8-10-year-old children

This study compared the validity of reported equations as predictors of peak VO₂ in 8–10-year-old children. Participants (90 boys and girls aged 8–10 years) performed the multistage-shuttle-run-test (MSRT) and peak VO₂ was measured in field using a portable gas analyser. The equations that estimated peak VO₂ from the MSRT performance were chosen according to the age range of this study. As follows, the FITNESSGRAM reports and the equations of Leger et al. (Can J Appl Sport Sci 5: 77–84, 1988), Barnett et al. (Pediatr Exerc Sci 5:42–50, 1993), Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004) and Fernhall et al. (Am J Ment Retard 102:602–612, 1998) were used to estimate the peak VO₂ and compared with the directly measured value. The equation of Leger et al. (Can J Appl Sport Sci 5: 77–84, 1988) provided a mean difference (d) of 4.7 ml kg⁻¹ min⁻¹ and a 1.0 slope. The equation of Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004)(a) using maximal speed (MS) showed a higher d (5.4) than the remaining using total laps d (4.2). The equation of Barnett et al. (Pediatr Exerc Sci 5:42–50, 1993)(a) that includes triceps skinfold and MS showed the highest d (6.1) but the smallest range (24.1) and slope (0.6). Data from the FITNESSGRAM had the smallest d (1.8 ml kg⁻¹ min⁻¹), but also had the highest range between limits of agreement (28.6 ml kg⁻¹ min⁻¹) and a 1.2 slope. The lowest slope (0.4) and range (22.2 ml kg⁻¹ min⁻¹) were observed using the equation of Fernhall et al. (Am J Ment Retard 102:602–612, 1998). Log transformation of the data revealed that the equations of Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004)(a) (1.1*/÷1.25) and Fernhall et al. (Am J Ment Retard 102:602–612, 1998) (1.17*/÷1.25) showed the closest agreement among all, but they still yield unsatisfactory accuracy.     

Bmp2 is required for cephalic neural tube closure in the mouse

BMPs have been shown to play a role in neural tube development particularly as dorsalizing factors. To explore the possibility that BMP2 could play a role in the developing neural tube (NT) beyond the lethality of Bmp2 null embryos, we created Bmp2 chimeras from Bmp2 null ES cells and WT blastocysts. Analysis of Bmp2 chimeras reveals NT defects at day 9.5 (E9.5). We found that exclusion of Bmp2 null ES cells from the dorsal NT did not always prevent defects. For further comparison, we used a Bmp2 mutant line in a mixed background. Phenotypes observed were similar to chimeras including open NT defects, postneurulation defects, and abnormal neural ectoderm in heterozygous and homozygous null embryos demonstrating a pattern of dose‐dependent signaling. Our data exposes BMP2 as a unique player in the developing NT for dorsal patterning and identity, and normal cephalic neural tube closure in a dose‐dependent manner. Developmental Dynamics 238:110–122, 2009. Published 2008 Wiley‐Liss, Inc.     

A method for estimating contact time of red blood cells through lung capillary from O2 and CO2 concentrations in rebreathing air in man

The gas exchange ratio (R) obtained from O2 and CO2 concentrations measured in rebreathing air usually shows a linear relation to the PCO2. By referring to this relation and the R which equals the Haldane effect coefficient and zero, the true- and oxygenated-venous PCO2 are obtained in addition to the alveolar PCO2. When these PCO2 are evaluated, the R-PCO2 line can also be computed theoretically from a numerical solution on the overall O2 and CO2 diffusions in the red blood cell. By comparing both the experimental and theoretical R-PCO2 lines with each other, we derived a contact time equation. Since the linear approximation of the R-PCO2 relation gave rise to an error in the contact time (tc), first a factor to correct the linearity of the R-PCO2 line was derived. Next, using these parameter values, tc was quantitatively determined from experimental data obtained during rebreathing in 5 normal subjects and it was compared with that estimated from the pulmonary diffusing capacity for CO in the same rebreathing experiment. When the extracellular HCO3- dehydration rate was taken to be 0.1 s in time constant, the tc, being ca. 0.7 and 0.4 s at rest and during exercise, respectively, showed good agreement with those obtained from the diffusing capacity for CO.     

Application of a stool antigen test to evaluate the incidence of Helicobacter pylori infection in children and adolescents from Tehran, Iran

Helicobacter pylori infection is acquired mainly in childhood, especially in developing countries, where a low-cost, rapid diagnostic technique which is reliable for all age groups may be useful for the management of H. pylori infection. For this purpose, we used an HpSA test (Equipar) to detect H. pylori infection in children and adolescents from Tehran, Iran. Thirty-five children who were positive or negative for H. pylori infection by endoscopy-based tests were used as positive and negative controls for the HpSA test. Stools were collected from 430 randomly selected children and adolescents (4 to 18 years old) from southwest, near the center, and northwest of Tehran. A questionnaire that included presence of recurrent abdominal pain (RAP), family history of infection and/or peptic ulcer disease (PUD), and income of parents was completed. A good agreement was found between the results of endoscopy-based tests and those of the HpSA test; the sensitivity and specificity of the Equipar-HpSA test were 100% and 83.4%, respectively. Among 430 children and adolescents, 47% were positive by the HpSA test, of whom 82% had RAP. No difference in incidence was observed between the two sexes; the various categories of age showed an increasing incidence, ranging from 24% (ages 4 to 6) to 58% (ages 16 to 18). The rate of infection in children and adolescents from the southwest was significantly higher (70%) than the rate in those from the northwest (32%), and a family history of H. pylori infection or PUD was observed in 59% of the HpSA positive subjects. The HpSA test is a useful test to detect H. pylori infection in children and adolescents from developing countries.