A comparative study on different methods for the determination of energy expenditure.

In order to determine energy expenditure, the Douglas Bag technique (DB) and Kofranyi-Michaelis respirometers (KM) have been widely used under field conditions for several decades. Some years ago the Oxylog (OX) method was developed, measuring simultaneously the difference of partial oxygen pressure in inspired and expired air (PO2 diff.) by two polarographic oxygen sensors. In order to compare these three methods laboratory experiments (3 test subjects, 5 different bicycle ergometer work loads, 180 measurements per apparatus) were performed. Oxygen uptake (VO2) varied between about 0.9 to 3.0 l/min. The VO2 data obtained by the DB method, which were used as a reference, and those obtained by the KM method agreed fairly well. The recorded data of OX underestimated VO2 up to 21%, with the deviation increasing with work intensity. A sufficient accuracy of recorded VO2 was observed only up to moderate work intensity. OX data calculated from ventilation volume of inspired air per minute (VI) and PO2 diff., measured by OX, were always about 19% higher than those recorded by OX. This means that the calculated VO2 values of the OX corresponded fairly well with DB values at heavy work loads. The reason for the differences between recorded and calculated OX data is still unknown. Further research is urgently needed.

Maximal aerobic power affected by maturation and body growth during childhood and adolescence.

This paper examines the development of maximal aerobic power as a function of maturation by a longitudinal study with annual examinations of representative samples of 56 boys and 56 girls in Norway and Western Germany. The age at which occurred peak height velocity (PHV) (i.e. the age at which the greatest height velocity was observed) was used as a reference of biological age and maturation. Before the PHV the mean maximal aerobic power was the same in two cohorts of children both in absolute values as well as in values relative to total and lean body mass. At and after PHV the boys were similar in their absolute values, but the German girls decreased their exercise fitness and became inferior to the Norwegian girls during later adolescence. When related to age of PHV the maximal aerobic power increased during the prepubertal years, mainly as an effect of growth in body size with little or no additional effect of other factors and approached a ceiling level at the end of adolescence. The boys exhibited clearly superior exercise fitness during all years of childhood and adolescence, this being in contrast to the widely accepted concept that no sex difference exists in exercise fitness before puberty. The maximum level for VO2-max, reached at the end of adolescence, averaged 3.2 1/min with a coefficient of variation of about 12% for the boys, and 2.5 1/min for the Norwegian girls and a similar coefficient of variation. As these ceiling values of maximal oxygen uptake agree with published averages for normal young adults representative for the normal population in these two countries, it is suggested that they represent optimal values brought about mainly by normal growth in body size with no or little additional effects of other factors.

[Experiences with a cardiorecorder system for continuous 24-hour registration of heart rate]. / Erfahrungen mit einem transportablem Gerät zur kontinuierlichen registrierung der Herzfrequenz für Zeiten bis zu 24 Stunden

Studies regarding to the continuous registration of the heart frequency by a transportable instrument, which can store the data of the heart frequency per minute up to 24h, are presented. It is a tape recorder the speed of which is geared down. Thus a normal tape cassette C 60 is sufficient for a registration of the heart frequency during 2 X 24h. The R-wave of the ECG is registered on the first channel of the tape as a biological signal. Moreover every minute an impulse of a clock is recorded on the second channel of the tape. With help of a second instrument the play back procedure for the 24-h-recording can be performed in about 15 min. The signals of both channels of the tape are transformed in digital rectangle impulses by an installed impulse-converter. The serial impulses are counted per minute with help of the time-mark by an interface in a counter. These data are at disposal in BCD-code. They can be passed on the following peripherals: digital printer, computer, pen-recorder and so on. A parallel standardized recording of the physical activity observed by the subject or by an experimenter allows a statistical evaluation and comparison of the physical activity with the corresponding heart frequency data. Some examples of the aread of occupational health, epidemiology and exercise physiology are discussed.