The present research examined the effects of initial substrate concentration and pH on the yield and productivity of hydrogen production by acidogenic fermentation. Assays were carried out at three different initial pH levels (5.5, 6.5 and 7.5) and three initial substrate concentrations (3, 5 and 10 g COD/L). Glucose was used as carbon source and the experiments were conducted at 37°C in batch tests, after a thermal pretreatment to eliminate methanogenic microorganisms. Conversions of glucose into hydrogen were between 16.75 and 27.25% of theoretical maximum, and high values of hydrogen productivity were obtained. An optimum value for the yield of glucose between initial pH of 6.3 and 3.7 g COD/L and productivity of the 5.95 H2/gVSS h and initial pH of 6.7 and 10 g COD/L were obtained from the response surface.

BACKGROUND: Regular physical exercise is not a widespread habit among the population. Early childhood in a crucial stage for acquiring this habit. The objective of this study was that of ascertaining the behavior of school-age children with regard to the degree of physical activity they do and to examine the factors involved. METHODS: An observational study was conducted by means of a survey based on a questionnaire which 6th and 8th grade students in a Basic Health Care District of Cordoba (N-585) filled out on their own. Questions were asked regarding the frequency of exercise, preferences and prospects for practicing sports, the children’s physical shape and school physical education classes, in addition to other behavior comprising their lifestyles. A dual-variable (p<0.05) and a multiple-variable analysis was conducted employing logistic regression. RESULTS: A total of 548 students filled out the survey (response rate=97.8%). 79.3% (IC95% 75.7-82.6) were involved in extracurricular physical activities, 21.0% (IC95% 17.1-24.7%) being involved in intense physical exercise. 50.5% (IC95% 46.3-54.8) did not think that they were in good physical shape. The age, sex, type of residence, the involvement in sports on the part of their parents or a close friend and what they considered their degree of healthiness to be comprised the variables quite strongly linked to doing exercise (p<0.001). CONCLUSIONS: The prevalence of physical exercise is high, although it progressively decreased with age, especially for girls. A major number of students considered themselves to be in unsatisfactory physical condition.

FUNDAMENTO: El ejercicio físico regular es una práctica poco extendida entre la población. La infancia es una etapa crucial para adquirir este hábito. El objetivo del estudio fue conocer la conducta de los escolares respecto al grado de actividad física que desarrollan y examinar los factores que se relacionan. MÉTODOS: Se llevó a cabo un estudio observacional mediante encuesta basada en un cuestionario autoadministrado a los escolares de 6º y 8º de Enseñanza General Básica de una Zona Básica de Salud de Córdoba (N=585). Se interrogó sobre la frecuencia de ejercicio, preferencias y expectativas para la práctica deportiva, estado de forma física y clases de educación física del colegio, además de otras conductas constitutivas de los estilos de vida. Se llevó a cabo un análisis bivariado (p<0,05) y multivariado con aplicación de regresión logística. RESULTADOS: Contestaron la encuesta un total de 548 alumnos (tasa de respuesta=97,8%). El 79,3% (IC 95%: 75,7-82,6) realizaban actividades físicas extraescolares, y el 21,0% (IC 95%: 17,7-24,7) ejercicio físico intenso. El 50,5% (IC 95%: 46,3-54,8) no consideran bueno su estado de forma física. La edad, el sexo, el tipo de residencia, la práctica deportiva en los padres o el amigo y estado de salud percibido constituyen las variables más fuertemente asociadas a la realización de ejercicio (p<0,001). CONCLUSIONES: Aunque la prevalencia de ejercicio físico es elevada, va declinando con la edad, sobre todo en las niñas. Un importante número de escolares consideran insatisfactorio su estado de forma física.

BACKGROUND: Regular physical exercise is not a widespread habit among the population. Early childhood in a crucial stage for acquiring this habit. The objective of this study was that of ascertaining the behavior of school-age children with regard to the degree of physical activity they do and to examine the factors involved. METHODS: An observational study was conducted by means of a survey based on a questionnaire which 6th and 8th grade students in a Basic Health Care District of Cordoba (N-585) filled out on their own. Questions were asked regarding the frequency of exercise, preferences and prospects for practicing sports, the children’s physical shape and school physical education classes, in addition to other behavior comprising their lifestyles. A dual-variable (p<0.05) and a multiple-variable analysis was conducted employing logistic regression. RESULTS: A total of 548 students filled out the survey (response rate=97.8%). 79.3% (IC95% 75.7-82.6) were involved in extracurricular physical activities, 21.0% (IC95% 17.1-24.7%) being involved in intense physical exercise. 50.5% (IC95% 46.3-54.8) did not think that they were in good physical shape. The age, sex, type of residence, the involvement in sports on the part of their parents or a close friend and what they considered their degree of healthiness to be comprised the variables quite strongly linked to doing exercise (p<0.001). CONCLUSIONS: The prevalence of physical exercise is high, although it progressively decreased with age, especially for girls. A major number of students considered themselves to be in unsatisfactory physical condition.

FUNDAMENTO: El ejercicio físico regular es una práctica poco extendida entre la población. La infancia es una etapa crucial para adquirir este hábito. El objetivo del estudio fue conocer la conducta de los escolares respecto al grado de actividad física que desarrollan y examinar los factores que se relacionan. MÉTODOS: Se llevó a cabo un estudio observacional mediante encuesta basada en un cuestionario autoadministrado a los escolares de 6º y 8º de Enseñanza General Básica de una Zona Básica de Salud de Córdoba (N=585). Se interrogó sobre la frecuencia de ejercicio, preferencias y expectativas para la práctica deportiva, estado de forma física y clases de educación física del colegio, además de otras conductas constitutivas de los estilos de vida. Se llevó a cabo un análisis bivariado (p<0,05) y multivariado con aplicación de regresión logística. RESULTADOS: Contestaron la encuesta un total de 548 alumnos (tasa de respuesta=97,8%). El 79,3% (IC 95%: 75,7-82,6) realizaban actividades físicas extraescolares, y el 21,0% (IC 95%: 17,7-24,7) ejercicio físico intenso. El 50,5% (IC 95%: 46,3-54,8) no consideran bueno su estado de forma física. La edad, el sexo, el tipo de residencia, la práctica deportiva en los padres o el amigo y estado de salud percibido constituyen las variables más fuertemente asociadas a la realización de ejercicio (p<0,001). CONCLUSIONES: Aunque la prevalencia de ejercicio físico es elevada, va declinando con la edad, sobre todo en las niñas. Un importante número de escolares consideran insatisfactorio su estado de forma física.