Critical power as an endurance index

The relationship between exhaustion time (t(lim)) and the work performed at the end of constant-power exercises can be described by a linear relationship (Wlim = a + b t(lim)) for work involving the whole body (eg cycling) or part of the body (eg knee extensions). The slope b in the equation is termed the critical power and has been proposed as an index of the capacity to perform work over a long period of time. The first objective of the present study was to compare the values of slopes b calculated from whole-body work of short duration, ie maximal and supra-maximal cycling exercises (slope b1), with the values calculated from the same work, the durations of which were between 3.5 and 35 min (slope b3), as in the protocols used by Scherrer and Monod (1960) for body-part work. Slope b1 was significantly higher than slope b3 in 10 subjects who performed 5 cycling exhausting exercises (60, 73, 86, 100 and 120% of maximal aerobic power (MAP) in watts). Exhaustion times corresponding to power outputs equivalent to b1 and b3 were equal to 29.0 +/- 19.1 min and 48.6 +/- 9.8 min respectively. Moreover, the exhaustion times at 60 and 73%,MAP were significantly correlated with slope b3 (expressed in %MAP) but not with slope b1. Consequently, slope b3 should be considered as the critical power instead of slope b1 as in some studies in the literature (Moritani et al, 1981). The second objective was to study the physiological significance of the critical power (slope b3) of whole-body work (cycling). The workload that corresponded to a lactate steady state was not significantly different from b3 (68.8 +/- 6.0 vs 68.7 +/- 6.3% MAP). Nevertheless, slope b3 represents a workload corresponding to a slight but significant drift of heart rate or oxygen uptake. These results probably explain why b3 is a power which can be maintained for a long time but not beyond about l h in an average subject.     

Ratings of perceived exertion (RPE) during cycling exercises at constant power output

The purpose of the present investigation was to study the overall rating of perceived exertion (RPEov) according to the 6-20 scale proposed by Borg (1970) and muscular RPE (RPEmu) in exercises at constant load. The relationship between RPE and heart rate for three different loads was studied during exhausting exercises in 10 participants. Whether the drift of RPE during a 20 min exercise at constant load could be an index of the endurance time during long-lasting exercises at constant load was also investigated. At 1-week intervals, the participants performed cycling exercises up to exhaustion at 60, 73, and 86% maximal aerobic power (MAP) measured during an incremental test. Heart rate, RPEov, RPEmu and exhaustion time (tlim) were measured. The upward shift of the HRmax-RPE regressions was significant between 86, 73 and 60% MAP (p < 0.001) for RPEov and RPEmu. This result suggests that the equation HR = 10 x RPE proposed by Borg (1973) for incremental exercise is not valid for long-lasting exercise at constant load until exhaustion because the heart rate corresponding to a given RPE depends on load and time. Mean RPE increased linearly with time up to exhaustion. Unexpectedly, the relationships between RPEmu or RPEov and percentage of exhaustion time were similar for exercises at 60 and 73% MAP although the exhaustion times were very different (79.40 +/- 30.64 min versus 36.19 +/- 15.99 min, respectively) (p < 0.001). Consequently, it is likely that RPE was a subjective estimation of the hardness of exercise rather than the intensity of exercise. The RPE pattern at the beginning of long-lasting exercises at constant load (60 and 73% MAP) cannot be considered as a sensitive predictor of the point of self-imposed exhaustion for individuals. Indeed, the errors in the estimation of exhaustion time from extrapolation of RPE at the beginning of exercise were very large. Moreover, at 60% MAP, a steady-state in RPE was observed during 20 min in five subjects whose tlim were not longer than tlim of the other subjects. In addition, the data of the present study indicate that RPEmu could be more useful than RPEov in cycling.     

Increasing automobile seat belt use: An intervention emphasizing risk susceptibility.

A seat-belt (SB) promotion program was implemented that was based on the finding by the 1st author (1984) that many people fail to take their SB use into account when thinking about their risk of being injured in an automobile accident. The goal of the program was to increase SB use by making the link between SB use and personal risk more salient. The program was instituted at the headquarters of a large corporation. Five weeks of baseline observations were followed by 1-wk active intervention program composed of stickers for car dashboards, permanent signs in the parking deck, and temporary signs in the cafeteria. Six weeks of posttreatment observations showed that the number of people using SBs increased 31% at one entrance and 7% at the other, with both increases statistically significant. SB use at a control site was stable during this period. Six months following the intervention, the number of people using SBs had climbed 61% above baseline at one entrance and 33% above the baseline at the other. Interviews before and after the program did not reveal the anticipated increase in spontaneous references to SB use as a risk factor for auto injury. Possible reasons for the success of the intervention and for the differential impact at 2 parking deck entrances are discussed. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vibration reduction of resonant structures using charge controlled piezoelectric actuators

A new charge controller design for piezoelectric transducers attached to highly resonant flexible beams is presented that significantly dampens the structure and naturally reduces the negative effects of hysteresis. Experimental results demonstrating the effectiveness of this technique are included.     

Contribution to the study of the band structure of amorphous selenium

From a study of the conductivity and photoconductivity of amorphous Se layers we are able to propose a model for the electronic states in the band gap.     

Do balanced scales assess bipolar constructs? The case of the STAI scales.

Balanced scales, that is, scales based on items whose content is either negatively or positively polarized, are often used in the hope of measuring a bipolar construct. Research has shown that usually balanced scales do not yield 1-dimensional measurements. This threatens their construct validity. The authors show how to test bipolarity while accounting for method effects. This is demonstrated on a data set of state and trait anxiety measured with the State-Trait Anxiety Inventory (STAI; C. D. Spielberger, R. L. Gorsuch, R. Lushene, P. R. Vagg, & G. A. Jacobs, 1983) scales. Taking a test–retest perspective, assuming temporally stable method effects, the authors tested the bipolarity of the temporal change through suitable constraints specified in a structural equation model adapted from S. Vautier, R. Steyer, and A. Boomsma (2008). The model fit the data closely, χ2(13, N = 888) = 20.75, p = .07. Thus, the state and trait scales seem to measure bipolar constructs plus temporally stable method effects. Parameter estimates suggest reliable change scores for the state anxiety scale (ρ? = .90) and specific method effects for the state and trait scales of the STAI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

VEGF‐Functionalized Polyelectrolyte Multilayers as Proangiogenic Prosthetic Coatings

Stimulation of transprosthetic vascularization represents an interesting strategy in implantology to allow rapid tissue integration and finally to avoid prosthetic rejection. To achieve this goal, we modified the surface of porous titanium implants with polyelectrolyte multilayer (PEM) films functionalized with vascular endothelial growth factor (VEGF). Among the two PEM systems investigated, poly(L‐lysine)/poly(L‐glutamic acid) (PLL/PGA) and poly(allylamine hydrochloride)/poly(sodium 4‐styrenesulfonate) (PAH/PSS), the (PAH/PSS)₄ architecture was selected to functionalize porous titanium, both for its high efficiency to adsorb VEGF and for its biocompatibility toward endothelial cells. In an original way, we unambiguously demonstrated that VEGF adsorbed on (PAH/PSS)₄ maintains its bioactivity in vitro and stimulates endothelial cells proliferation. This effect was correlated with specific activation of intracellular signaling pathways induced by successive phosphorylation of the endothelial VEGF receptor VEGFR2 and mitogen‐activated protein kinases (MAPK) ERK1/2. By clearly demonstrating the proangiogenic activity of the VEGF‐PEM coating in vitro, the present study constitutes a first step toward in vivo application.     

Platooning Control for Sailboats Using a Tack Strategy

International Journal of Control, Automation and Systems - This paper addresses the problem of platooning control for a fleet of sailboats. A quadrilateral path is proposed to avoid going into the...     

An evolutionist approach to information bipolarity: Representations and affects in human cognition

This paper investigates the psychological plausibility of the bipolarity concept, i.e., that positive and negative kinds of information are treated differently. Sections 2 and 3 review relevant investigations of the representational and affective systems in the experimental psychology literature. Section 4 provides new data supporting the idea that even when considering how affective changes occur, a certain level of independence exists between the positive and negative sides of affect. Together the studies reported here strongly support the psychological plausibility of bipolarity: Positive and negative kinds of information are not processed in the same way whichever domain is considered, preferences (affect) or beliefs (mental categories). © 2008 Wiley Periodicals Inc.