Henry C. Lukaski

Effect of heat acclimation on sweat minerals.

PURPOSEnThis study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations.nnnMETHODSnEight male subjects walked on a treadmill at 3.5 mph, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5 degrees C on 10 consecutive days in an environmental chamber set at 45 degrees C, 20% relative humidity. Arm sweat samples were collected during the first 30 min of exercise-heat stress on days 1 and 10 using a polyethylene arm glove.nnnRESULTSnFinal core temperature and HR values were significantly lower (P < 0.05) on day 10 versus day 1. Whole-body sweating rates increased by approximately 6% (P = 0.12). Sweat sodium concentration on day 10 (36.22 +/- 7.22 mM) was significantly lower than day 1 (54.49 +/- 16.18 mM) (P < 0.05). Sweat mineral concentrations of calcium (approximately 29%), copper (approximately 50%), and magnesium (approximately 43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P < 0.05). A trend for lower sweat iron (approximately 75%; P = 0.07) and zinc (approximately 23%; P = 0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration x whole-body sweat rate) were reduced for calcium (approximately 27%), copper (approximately 46%), and magnesium (approximately 42%) (P < 0.05), but not iron (75%) or zinc (approximately 16%) (P > 0.05), from day 1 to day 10.nnnCONCLUSIONnExercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium, and may reduce sweat iron and zinc concentrations.

A comparison of methods of assessment of body composition including neutron activation analysis of total body nitrogen.

Fourteen healthy men underwent determinations of total body nitrogen (TBN) by prompt gamma neutron activation analysis and total body potassium (TBK) by whole body counting to estimate the muscle and nonmuscle components of the fat-free body mass (FFBM) and their protein contents. Comparison of FFBM estimated from TBN and TBK (60.6 +/- 6.9 kg, mean +/- SD), densitometry (62.3 +/- 7.1 kg), TBK alone (62.2 +/- 8.0 kg) and TBW (63.9 +/- 7.8 kg) showed no differences among the techniques. Similarly, there were neither differences in fat mass nor percent body fat among the methods. Analysis of the chemical composition of FFBM of this group showed TBK/FFBM = 62.6 +/- 2.3 mEq/kg, TBW/FFBM = 74.6 +/- 0.2%, TBN/FFBM = 32.74 +/- 1.09 g/kg, protein/FFBM = 20.5+/- 0.7%. The calculated mineral content of the FFBM was 6.4%. These values are strikingly similar to the values calculated by direct chemical analysis. It was concluded that the combined TBN-TBK method is a valid technique for estimating body composition in man.

Surface contamination artificially elevates initial sweat mineral concentrations

Several sweat mineral element concentrations decline with serial sampling. Possible causes include reduced dermal mineral concentrations or flushing of surface contamination. The purpose of this study was to simultaneously sample mineral concentrations in transdermal fluid (TDF), sweat, and serum during extended exercise-heat stress to determine if these compartments show the same serial changes during repeat sampling. Sixteen heat-acclimated individuals walked on a treadmill (1.56 m/s, 3.0% grade) in a 35°C, 20% relative humidity (RH), 1 m/s wind environment 50 min each hour for 3 h. Mineral concentrations of Ca, Cu, Fe, K, Mg, Na, and Zn were measured each hour from serum, sweat from upper back (sweat pouch) and arm (bag), and TDF from the upper back. Sites were meticulously cleaned to minimize surface contamination. Mineral concentrations were determined by spectrometry. TDF remained stable over time, with exception of a modest increase in TDF [Fe] (15%) and decrease in TDF [Zn] (-18%). Likewise, serum and pouch sweat samples were stable over time. In contrast, the initial arm bag sweat mineral concentrations were greater than those in the sweat pouch, and [Ca], [Cu], [Mg], and [Zn] declined 26-76% from initial to the subsequent samples, becoming similar to sweat pouch. Nominal TDF mineral shifts do not affect sweat mineral concentrations. Arm bag sweat mineral concentrations are initially elevated due to skin surface contaminants that are not removed despite meticulous cleaning (e.g., under fingernails, on arm hair), then decrease with extended sweating and approach those measured from the scapular region.

Further Outcomes and Tentative Predictor Variables from an Evolving Comprehensive Program for the Behavioral Control of Smoking.

This paper reports further outcome data from an evolving comprehensive program for the behavioral control of smoking. At a six-month follow up evaluation, 50 per cent of the participants were fully abstinant from all forms of tobacco. Clinical and physiological correlates of success are noted and discussed.

A practical and reliable method for determination of urinary 3-methylhistidine

A practical and reliable semiautomated method for analysis of urinary 3-methylhistidine (3-MH) was designed combining the isolation of 3-MH by ion-exchange chromatography with the color reaction given by ninhydrin-orthopthalaldehyde (ninhydrin-OPT) reagent after alkalinization. 2 ml of urine were passed through disposable columns packed with an ion-exchange resin (Dowex 50-X8, 200-400 mesh) and the acidic and neutral amino acids were eluted with 10 ml of 0.2 M pyridine solution. Then, the 3-MH was quantitatively eluted and separated from histidine with a volume of 9 ml of a 1.5 M pyridine solution. Standard Autoanalyzer equipment was used for the automation of spectrophotometry. The method permits the analysis of 40 samples in duplicate per day. The 3-MH color reaction was linear for concentrations from 0.015 to 0.24 mu mol/ml. The mean recoveries of 3-MH from standards and urine were 98.6 +/- 1.3 and 99.0 +/- 1.3%, respectively. Duplicate determinations of urine samples showed a variation coefficient of 1.8%. An excellent agreement was obtained between urine samples analyzed by the present method and by an amino acid analyzer. The need for the elimination of the interfering amino acids was clearly demonstrated.