María Zakynthinaki

Type of delivery is not affected by light resistance and toning exercise training during pregnancy: a randomized controlled trial

OBJECTIVE We examined the effect of light-intensity resistance exercise training that is performed during the second and third trimester of pregnancy by previously sedentary and healthy women on the type of delivery and on the dilation, expulsion, and childbirth time. STUDY DESIGN We randomly assigned 160 sedentary women to either a training (n=80) or a control (n=80) group. We recorded several maternal and newborn characteristics, the type of delivery (normal, instrumental, or cesarean), and dilation, expulsion, and childbirth time. RESULTS The percentage of women who had normal, instrumental, or cesarean delivery was similar in the training (70.8%, 13.9%, and 15.3%, respectively) and control (71.4%, 12.9%, and 15.7%, respectively) groups. The mean dilation, expulsion, and childbirth time did not differ between groups. CONCLUSION Light-intensity resistance training that is performed over the second and third trimester of pregnancy does not affect the type of delivery.

A Model of Heart Rate Kinetics in Response to Exercise

Abstract We present a mathematical model, in the form of two coupled ordinary differential equations, for the heart rate kinetics in response to exercise. Our heart rate model is an adaptation of the model of oxygen uptake kinetics of Stirling et al. [21]; a physiological justification for this adaptation, as well as the physiological basis of our heart rate model is provided. We also present the optimal fit of the heart rate model to a set of raw un averaged data for multiple constant intensity exercises for an individual at a particular level of fitness.

Counterpoint: The kinetics of oxygen uptake during muscular exercise do not manifest time-delayed phases

The existence of time-delayed phases ([1][1]) is not supported by oxygen uptake kinetics data. Despite many attempts for a number of years, no convincing physiological mechanism for such behavior has been proven to exist. The reason is that these time-delayed phases are a figment of the incorrect

Modeling the basin of attraction as a two-dimensional manifold from experimental data: applications to balance in humans.

We present a method of modeling the basin of attraction as a three-dimensional function describing a two-dimensional manifold on which the dynamics of the system evolves from experimental time series data. Our method is based on the density of the data set and uses numerical optimization and data modeling tools. We also show how to obtain analytic curves that describe both the contours and the boundary of the basin. Our method is applied to the problem of regaining balance after perturbation from quiet vertical stance using data of an elite athlete. Our method goes beyond the statistical description of the experimental data, providing a function that describes the shape of the basin of attraction. To test its robustness, our method has also been applied to two different data sets of a second subject and no significant differences were found between the contours of the calculated basin of attraction for the different data sets. The proposed method has many uses in a wide variety of areas, not just human balance for which there are many applications in medicine, rehabilitation, and sport.

Body sway and performance at competition in male pistol and rifle Olympic shooters

Summary Study aim: We examine the body sway differences between a) pistol and rifle and b) elite and national level senior male Olympic shooters, as well as the possible relation between body sway and performance at competition in Olympic shooting. Material and methods: Two body sway tests (feet together and feet apart) were performed by 28 Spanish male senior Olympic shooters just before competition. Performance was measured as the actual score at competition. Total center of mass (COM) areas and average/maximum COM velocities were calculated from force platform data. ANCOVA tests were implemented with age as a covariable. The non-parametric test U of Mann Whitney was used to study the differences between national and elite shooters. Pearson correlations were used to examine the relation between performance and total COM area. Results: At the feet apart position, rifle and elite shooters were found to have statistically less body sway than pistol and national level shooters respectively (total COM areas: F1,25 = 6.7; p < 0.05, and Z = 2.36; p < 0.01). No statistically significant differences were found regarding the feet together position, regardless the level or discipline (total COM areas: F1,25 = 1.49 ; p > 0.05; 1 – β = 0.22, average COM velocities: F1,25 = 0.58; p > 0.05; 1 – β = 0.11, maximum COM velocities: F1,25 = 0.03; p > 0.05; 1 – β = 0.05). No significant relation was found between body sway and performance at competition (feet together: r = 0.13, feet apart: r = 0.14, p > 0.05). Age and body sway were not found to be significantly correlated (F1,25 = 0.23; p > 0.05; 1 – β = 0.08). Conclusions: Easy to carry out, non-specific body sway tests can be used for the selection of novice shooters.

Simulating heart rate kinetics during incremental and interval training

Summary Study aim: To apply a recently proposed dynamical systems model to simulate, for the first time, the heart rate (HR) response to exercise of time-dependent intensity. Material and methods: The applied model is expressed in the form of two coupled ordinary differential equations, one giving the rate of change of HR and the other providing the time dependency of exercise intensity. According to the model, the HR is assumed to depend on time, velocity, lactate accumulation and the subject’s overall cardiovascular condition. For the purposes of the present work, training sessions were simulated, consisting of exponentially and step-wise increasing intensities, as well as interval training. Results: Training sessions of exponentially and step-wise increasing velocity, as well as an interval training session, have been simulated. Successful simulations of the corresponding HR response were achieved. Conclusions: The present work successfully demonstrates the model’s excellent performance in simulating the HR response to exercises of time-dependent intensity. The applied model has been shown to correctly simulate the heart rate response also during exercises of complicated intensity patterns, such as the interval training session. The study confirms the ability of the implemented mathematical model not only to simulate and predict heart rate kinetics for any given exercise intensities but also to provide important information regarding an individual’s cardiovascular condition. This is of vast importance, not only in the area of fitness and sport, where it can serve as a fundamental tool for the design of efficient training sessions, but also in the areas of cardiovascular health, prediction and rehabilitation.

Anabolic drugs consumption of high school students participating in school championships of physical education

This paper aims to analyse the use of anabolic drugs among Greek students participating in school championships of physical education (PE). In order to do it, a survey was conducted during the 2008 to 2009 academic year in suburban, urban and metropolitan areas in Greece. The sample was 2,535 high school students from the 10 to 12th grade, participating in the school physical education championships. The results showed that 9.6% of boys and 3.7% of girls reported that they had used anabolic drugs sometime in the past whereas 11.2% boys and 4.8% girls reported that they would intend to use them in the future. This confirms that anabolic steroids are an important problem among adolescents, and educational programs should increase their knowledge about these drugs. Information should come not only from the state, but also from coaches, teachers, trainers and parents.

Last Word on Point:Counterpoint: The kinetics of oxygen uptake during muscular exercise do/do not manifest time-delayed phases

TO THE EDITOR: Not one of the proposed physiological mechanisms support the existence of time-delayed instantaneous stepwise increments in oxygen demand that mark the beginning of each time-delayed phase and are the very foundation of the time-delayed three-phase exponential model. The chance of finding physiological mechanisms to support such behavior is nonexistent, due mainly to the instantaneous nature of the increment. Not one of the proposed physiological mechanisms contradicts the model (2, 3), as even without time-delayed phases it produces features that only become apparent after a period of time. As shown in (5), this model can incorporate a far more realistic oxygen demand (i.e., one that changes smoothly with intensity and time to account for inertia and changing underlying physiological processes) than the obviously erroneous instantaneous increments of the three-phase model.

Geometry and transport in a model of two coupled quadratic nonlinear waveguides.

This paper applies geometric methods developed to understand chaos and transport in Hamiltonian systems to the study of power distribution in nonlinear waveguide arrays. The specific case of two linearly coupled chi((2)) waveguides is modeled and analyzed in terms of transport and geometry in the phase space. This gives us a transport problem in the phase space resulting from the coupling of the two Hamiltonian systems for each waveguide. In particular, the effect of the presence of partial and complete barriers in the phase space on the transfer of intensity between the waveguides is studied, given a specific input and range of material properties. We show how these barriers break down as the coupling between the waveguides is increased and what the role of resonances in the phase space has in this. We also show how an increase in the coupling can lead to chaos and global transport and what effect this has on the intensity.