The interplay between propelling efficiency, hydrodynamic position and energy cost of front crawl in 8 to 19-year-old swimmers.

The aim of this study was to investigate the interplay between the arm stroke efficiency (an index of propelling efficiency, eta (P)) and the static and dynamic position in water (indexes of hydrodynamic resistance, W (d)) in determining the energy cost of front crawl (C) during a swimmer's growth. These three parameters are indeed related by the following equation: C=W(d)/(eta(P).eta(o)) where eta (o) is the overall efficiency of swimming. The experiments were carried out on 72 swimmers (38 M and 34 F; 8-19 years) who were asked to swim at 1 m s(-1). The static position in water was assessed by measuring the underwater torque (T'); the dynamic position in water by measuring the projected frontal area (A (eff)). The ratio between the average values of the eldest to youngest class of age was 3.84 and 2.27 for T', 2.13 and 1.68 for A (eff), and 1.13 and 1.24 for eta (P) (in M and F, respectively). The increase in T' and in A (eff) was larger than the increase in efficiency suggesting that, in this age range, C should increase, the more so in M than F. Indeed, C increased by 1.58 in male and 1.17 in female swimmers. Based on the values of C and eta (P) (and assuming a constant value of eta (o)) it is possible to estimate that, in this age range, W (d) increases by about 1.97 in male and 1.32 in female swimmers, an increase which is proportional to the observed increase in A (eff).

Determination of methyl bromide in foods by headspace capillary gas chromatography with electron capture detection.

Methyl bromide (MB, bromomethane) is determined in a variety of foods by headspace capillary gas chromatography with electron capture detection. The comminuted food sample as an aqueous sodium sulfate slurry is equilibrated with stirring for 1 h at room temperature before a 1 mL headspace aliquot is removed and injected using a modified on-column syringe needle. Methyl bromide is cryogenically focussed at -60 degrees C and then eluted by temperature programming. The procedure requires blending of soft samples, e.g. raisins, prunes, or oranges, and ultrasonic homogenization of hard samples, e.g. wheat, cocoa beans, corn, or nuts, with portions of water and ice so the final temperature of the food-water slurry is less than 1 degree C. A 20 g aliquot (4 g food) is then added to a cold headspace vial containing 4 g sodium sulfate. Losses of MB during a 3.5 min ultrasonic homogenization of wheat were 11% at 0.95 ppb and 4.4% at 4.8 ppb. For flour, cocoa, and finely divided spices, which do not require blending, 4 g is added to the cold headspace vial containing 16 mL cold water and 4 g sodium sulfate. Studies show that comminution of wheat or peanuts must be carried out to release MB trapped within the food so the headspace equilibrium can be attained in 1 h as well as to obtain homogeneous samples and representative sampling. No interferences were noted with the above foods or with many grain-based baking mixes analyzed.(ABSTRACT TRUNCATED AT 250 WORDS)