Joe F. Smith

Effects of Carbohydrate-Electrolyte Content of Beverages on Voluntary Hydration in a Simulated Industrial Environment

This study examined the effects of ingesting beverages of varying electrolyte-carbohydrate (ECHO) composition on hydration, sensory response, physiological function, and work performance during 4 hours of simulated industrial work for subjects wearing impermeable protective clothing (PC). Male subjects (N=18) completed four separate work sessions. Each session consisted of 30 min of treadmill walking with intermittent arm curls at 300 kcal per hour (moderate work rate), followed by 30 min of rest, for a total of 4 hours at 33 degrees C wet-bulb globe temperature. Excessive physiological strain prevented only four subjects from completing the 4-hour protocol. A different beverage was provided for consumption ad libitum for each work trial in a repeated measures, double-blind design. The beverages included lime colored water (W), lemon-lime placebo (P), lemon-lime ECHO with 18 mEq/L NaCl (ECHO18), and lemon-lime ECHO with 36 mEq/L NaCl (ECHO36). There was no difference in sweat production among the four trials (p = 0.61). Mean (standard deviation [SD]) fluid consumption was significantly greater for the ECHO36 [771 (+/-264) mL per hour] as compared with the W [630.6 (+/-234) mL per hour] and the P [655.2 (+/-228) mL per hour] (p<0.05), but not significantly greater than the ECHO18 [740.4 (+/-198) mL per hour]. Also, consumption of the ECHO18 was significantly greater than the W. Mean (SD) weight change, expressed as a percentage of total body weight (pre minus post), was -0.55(+/-0.8) for W, -0.31(+/-1.0) for P, -0.01(+/-1.1) for ECHO18, and +0.11(+/-1.1) for ECHO36 (p = 0.06). Subjects drank less and tended to experience greater weight loss in trials in which W or P were provided compared with trials in which either ECHO was provided. Thus, ECHO beverages, when provided ad libitum to workers wearing PC in a hot environment, produced better hydration than water.

Body composition prediction in university football players.

This study was intended to determine if previously-developed body composition prediction equations were valid for use with a Division I university football team. A sample of 68 Division I football players with a mean age of 19.7 yr, was assessed for body density (BD) by underwater weighing (UWW), residual volume by helium dilution, and 26 selected anthropometric measures. A predicted BD was obtained by using two sets of equations developed from college football players and from three generalized equations. The differences between predicted and observed body densities were analyzed. Seven of the nine models examined failed to accurately predict the BD for this population of university football players. One sport-specific equation of White, Mayhew, and Piper for individuals in the backfield and a generalized model of Jackson and Pollock (JP) containing two circumferences performed well when considering the mean of differences and the magnitude of total error relative to the published standard error. However, both of these models overestimate body density for players with low BD and underestimate BD when actual BD is high. Using the JP model for a player whose actual BD is near the sample mean of 1.070, the estimated mean is very close at 1.069. However, for players with actual BD of 1.050, the estimated mean is 1.054, and if actual BD is 1.085, the JP estimated mean is 1.078. The bias is linear between these points.

Excess post-exercise oxygen consumption in untrained men following exercise of equal energy expenditure: comparisons of upper and lower body exercise

Aim:  This study assessed excess post‐exercise oxygen consumption (EPOC) following continuous 200‐ kcal bouts of upper body exercise (UBE) and lower body exercise (LBE).

Empirical prediction of physiological response to prolonged work in encapsulating protective clothing.

Work in moderate or hotter environments while wearing encapsulating protective clothing (PC) results in heat storage and substantial diminution of work productivity, as well as being a potential health risk. An ability to predict the responses of workers using PC would be very useful. Predictions were made of work times at 21 degrees C of 15 subjects performing prolonged hard work (450 W gross) while wearing PC, based upon prior measures of short-duration bench stepping in PC and heart rate responses. A simple model was derived that shows good potential for predicting work time in moderate temperatures in PC; Total Time = 7.2 (bench step duration) - 34 (bench comfort) + 4 (height); R2 = 0.83, C.V. = 13. Unexpectedly, models that incorporated recovery heart rate as a variable were not as effective. With further refinement, the prediction approach tested in this study would be immediately useful for managing military and civilian personnel working in PC. Additionally, it could be utilized at minimal cost during routine training.

Stability of a practical measure of recovery from resistance training.

McLester et al. (2003) proposed a practical protocol to determine optimal recovery times between resistance training workouts. For this protocol to be useful, it must be stable. The purpose of this study was to investigate the stability of that protocol. College-aged resistance trained men (n = 10) performed 3 sets to volitional failure using a 10-repetition maximum load for 6 exercises. Recovery was evaluated on 4 occasions by the number of repetitions performed for each individual exercise after recovery periods of 48, 72, 96, and 120 hours in counterbalanced order. To evaluate stability, this procedure was performed twice. The number of repetitions after each recovery interval were compared with initial baseline performances. A priori, adequate stability was defined as 70% of the participants achieving similar recovery duration on both trials. Pooled repetitions over all 6 exercises indicated that 80% of participants returned to baseline strength levels after the same recovery duration for both trials. However, when individual muscle group repetition performance was evaluated, stability varied from 20 to 70%. Variability in rest, nutrition, prior activity, and other factors probably induced instability in individual strength measures, but not sufficiently to influence the aggregate results. Some muscle groups may have greater sensitivity to variations in ecological factors such as these. We believe that the tested protocol may be useful in establishing recovery times for multimuscle group workouts, but not stable enough to be useful in establishing recovery times for individual muscle groups.

A Review of Fluid Replacement for Workers in Hot Jobs

Prolonged work in hot environments leads to progressive water and electrolyte loss from the body. The rate of sweating varies among individuals and depends on the environmental conditions, but in protective clothing and very hot environments rates can reach 2.25 L/hour. Because hypohydration will impair work performance and increases the risk of heat injury, consumption of fluids is necessary to prevent dehydration and enhance performance. Much of the research on rehydration has been conducted in athletic settings. The purpose of this review is to interpret the existing research literature on hydration in a way that is useful to industrial hygienists and safety experts. The authors hope to provide industrial hygienists and safety professionals with scientific bases for making recommendations regarding beverage availability and hydration practices. Although water is a very common beverage, some previous research has reported that drinks containing low to moderate levels of electrolytes and carbohydrates may provide some significant advantages in industrial situations. In general these studies seem to support the use of electrolyte-carbohydrate beverages as a supplement to water or as a replacement for water.

Validation of body composition models for high school wrestlers

This study investigates the utility of two equations for predicting minimum wrestling weight and three equations for predicting body density for the population of high school wrestlers. A sample of 54 wrestlers was assessed for body density by underwater weighing, residual volume by helium dilution, and selected anthropometric measures. The differences between observed and predicted responses were analyzed for the five models. Four statistical tests were used to validate the equations, including tests for the mean of differences, proportion of positive differences, equality of standard errors from regression, and equivalence of regression coefficients between original and second sample data. The Michael and Katch equation and two Forsyth and Sinning equations (FS1 and FS21) for body density did not predict as well as expected. The Michael and Katch equation tends to overpredict body density while FS1 underpredicts. The FS2 equation, consisting of a constant adjustment to FS1, predicts well near the mean but not at the ends of the sample range. The two Tcheng and Tipton equations produce estimates which slightly but consistently overpredict minimum wrestling weight, the long form equation by 2.5 pounds and the short form by 3.8 pounds. As a result the proportion of positive differences is less than would be expected. But based on the tests for the standard errors and regression coefficients, the evidence does not uniformly reject these two equations.

Rebounding exercise: Are the training effects sufficient for cardiorespiratory fitness?

Additional research is needed in order to document the effects of rebound training. Efforts should focus on the factors that are necessary for standardising the intensity of exercise such as step height and frequency. In addition, attention may be given to alternative methods of increasing exercise intensity while rebounding. One such method may be to increase the total muscle mass involved by adding the pumping of handheld weights to the rebounding exercise. Data from our laboratory (Bishop et al. 1986) has demonstrated that the addition of pumping 1-, 2- and 3-pound (0.45, 0.91 and 1.36 kg) handheld weights, at 2- and 3-foot (30 and 45 cm) heights, to rebounding exercise will increase the oxygen requirement from 26 to 60%. Assessing these effects in a training study would necessitate testing for adaptation in the upper extremities. This type of training highlights the need for activity specific tests. More specifically, additional research is needed to: 1. Determine the energy cost of activities other than jogging/bouncing that may be possible on a mini-trampoline, such as those described by White (1984). 2. Determine the training response of subjects in studies in which the controllable factors affecting intensity are standardised. 3. Examine the effects of longer periods of rebound training. Because rebounding exercise is novel to most subjects, it would appear that the length of training should allow subjects to maintain a reasonable frequency, intensity, and duration of exercise above that needed for familiarization with the new activity. 4. Determine if the prolonged use of other training aids (limb weights) with rebounding is feasible and effective in long term training.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological factors limiting work tolerance in chemical protective clothing

Abstract Work tolerance in protective clothing (PC) is greatly limited compared to normal clothing. The purpose of this study was to determine if this limitation is attributable to any readily identifiable aspect of physiology. Male volunteers (N = 15) completed an average of 263 min of endurance exercise at a metabolic cost of 40–44% of maximal oxygen uptake (VO2 max) which consisted of repeated bouts of 15 min treadmill walking followed by 5 min of arm curls. Subjects continued to walk-arm curls to exhaustion. For safety reasons, they were also stopped if their rectal temperature (Tre) exceeded 39°C. The termination of work by either of these criteria ended a work “cycle”. On completion of a cycle, subjects rested 48 min then resumed exercise. The exercise day ended when the subject refused to continue or experiment time equaled 8 h. All 15 subjects completed two work cycles and 8 completed three cycles. Work ended on 28 work cycles due to fatigue and on 10 cycles due to Tre. Heart rate (HR), rating of perceived exertion, maximal voluntary ventilation, thermal comfort, oxygen uptake (VO2), blood lactic acid levels, and 3 measures of breathing comfort were measured throughout testing. Significant changes across time were seen only in HR and the subjects perceptions of the stressors but, HR increases were insufficient to explain the termination of work. Work tolerance in this situation apparently cannot be extended by resolving any simple physiological limitations.