Troy D. Chinevere

Minimum rest period for strength recovery during a common isokinetic testing protocol.

PURPOSE The intent of this investigation was to determine the minimal time for a between sets rest period during a common isokinetic knee extension strength-testing protocol. Based on a review of the literature, a set was considered a group of four maximal coupled contractions at a specific velocity. METHODS Eleven normal, healthy college-age men underwent unilateral knee extension testing to determine their individual isokinetic peak torque at 60, 120, 180, 240, and 300 degrees.s-1. Velocities were administered in ascending order. Between sets, rest periods of 15, 60, 180, and 300 s were assigned to subjects in a counterbalanced fashion. RESULTS There were no differences in peak torque at the beginning velocity of 60 degrees.s-1 among any of the rest periods. At 120 degrees.s-1, peak torque production during the 15-s rest period trial was similar to 60 s but lower than 180 and 300 s. Peak torques at 180, 240, and 300 degrees.s-1 produced during the 15-s rest period test were significantly lower than measured torques at the same velocities during the 60, 180, and 300-s rest period tests (P < 0.05). There were no differences in peak torque production between the 60, 180, and 300-s rest period tests. CONCLUSION These data demonstrate that during a common isokinetic strength testing protocol a between set rest period of at least 60 s is sufficient for recovery before the next test set.

Effect of heat acclimation on sweat minerals.

PURPOSE This study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations. METHODS Eight 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. RESULTS Final 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. CONCLUSION Exercise-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.

Serum S-100β Response to Exercise-Heat Strain before and after Acclimation

UNLABELLED Exercise alone or in combination with environmental heat stress can elevate blood S-100beta protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100beta is questionable. It is possible that the process of heat acclimation might afford additional insight. PURPOSE Determine the S-100beta response to moderate-intensity exercise with heat strain before and after heat acclimation. METHODS Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 min of treadmill walking (1.56 m x s(-1), 4% grade) in the heat (45 degrees C, 20% relative humidity). Changes in HR, rectal temperature (T(re)), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for T(re) greater than 38.5 degrees C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and were analyzed for serum osmolality and S-100beta concentration. RESULTS All subjects displayed physiological adaptations to heat acclimation including a significant (P < 0.05) reduction in final HR (161 to 145 bpm) and T(re) (39.0 to 38.4 degrees C), as well as a modest (approximately 10%) increase in SR (1.10 to 1.20 L x h(-1); P = 0.09). No differences were observed in pre- to postexercise serum S-100beta concentrations on day 1 or 10, and no differences were observed in S-100beta values between days 1 and 10. No significant correlations were found between S-100beta values and any variable of interest. CONCLUSIONS S-100beta concentrations do not necessarily increase in response to exercise-heat strain, and no effect of heat acclimation on S-100beta could be observed despite other quantifiable physiological adaptations.

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.

Trace Mineral Losses in Sweat

Copper, iron and zinc are nutritionally essential trace minerals that confer vital biological roles including the maintenance of cell structure and integrity, regulation of metabolism, immune function, oxygen transport, and muscle and central nervous system function. Dietary Reference Intakes (DRIs) for these minerals are useful for the general population, but these guidelines may be inadequate for some populations (e.g., soldiers, athletes) who experience copious sweating due to high physical activity levels and/or frequent exposure to extreme environmental conditions. The trace mineral content of sweat may predispose these populations to subclinical/clinical nutritional deficiencies. Studies on sweat trace mineral losses report highly variable results. Much of the variability may be methodological. Non-standardization of collection techniques, collection sites (local versus whole body), and numerous other variables cloud definitive conclusions on sweat trace mineral losses. The objectives of this manuscript are to 1) review the literature on sweat copper, iron, and zinc losses, 2) present the potential sources of variability, 3) interpret findings in relation to nutritional needs, and 4) identify directions for future research.