Craig A. Horswill
Craig A. Horswill
Since the 1930s, scientists have attempted to determine if increasing the body’s ability to buffer metabolic acids will enhance physical performance. The buffer of major interest has been bicarbonate; to a lesser degree, citrate and phosphate salts have been investigated. In theory, the buffers facilitate performance by decreasing the accumulation of hydrogen ions that would otherwise presumably inhibit glycolysis and interfere with energy production or impair cross-bridge formation between myofilaments and thereby reduce force production. Literature findings indicate variable results, but overall it appears that bicarbonate salts taken at dosages of 0.3 g · kg−1 may improve performance during repeated sprints or at the end of a progressively more intense exercise test. Athletes are advised of potential ill effects of bicarbonate ingestion, such as gastrointestinal distress. Prior to applying the agents in a competitive setting, athletes should test the effects of buffers on performance during training sessions and consider the sport governing body’s stand on buffer usage.
Craig A. Horswill
Amateur wrestlers practice weight loss for ergogenic reasons. The effects of rapid weight loss on aerobic performance are adverse and profound, but the effects on anaerobic performance are equivocal Anaerobic performance—strength and power—may be the most relevant type of performance to the wrestler. Maintenance of or even small decrements in anaerobic performance may translate into improvements in performance relative to the weight class, the factor by which wrestlers are matched for competition. During the recovery period between the official weigh-in and competition, wrestlers achieve at least partial nutritional recovery, which appears to benefit performance. Successive bouts of (a) weight loss to make weight and (b) recovery for performance lead to weight cycling. There is speculation that weight cycling may contribute to chronic glycogen depletion, reductions in fat-free weight, a decrease in resting metabolic rate, and an increase in body fat. The latter two would augment the difficulty of losing weight for subsequent weigh-ins. Most research indicates that the suppressed resting metabolic rate with weight loss in wrestlers appears to be transient, but subsequent research is needed for confirmation.
Craig A. Horswill
As a result of exercise-induced sweating, athletes and trained individuals can lose up to 3 L of fluid per hour. Fluid replacement is required to maintain hydration and allow the athlete to continue to perform. Inadequate fluid intake will adversely affect temperature regulation, cardiovascular function, and muscle metabolism. To maximize fluid intake and effectively replace fluid, athletes must employ behavioral strategies. Athletes can also select beverages with characteristics that complement their behavioral efforts. Palatability, rapid absorption, retention of the fluid, and ergogenicity are the major attributes to consider for enhancing hydration during training and physical activity.
Iulian B. Dragusin and Craig A. Horswill
Sports drinks have been implicated in contributing to obesity and chronic diseases by providing surplus calories and excess sugars. Using existing literature we compared energy intake from sports drinks consumed during exercise with the exercise-induced calorie expenditure to determine whether sports drink use might eliminate the energy deficit and jeopardize conditions for improved metabolic fitness. We identified 11 published studies that compared sport drink consumption to placebo during exercise with a primary focused on the effect of sport drinks or total carbohydrate content on enhancing physical performance. Energy expenditure (EE) was calculated using VO2, RER, and exercise duration for the exercise protocol. Energy ingestion (EI) was determined using the carbohydrate dosing regimen administered before and during the exercise protocol. A two-tailed t test was used to test whether the energy balance (EI-EE) was different from zero (alpha level = 0.05). Sport drink consumption during aerobic exercise of sufficient duration (≥ 60 min) did not abolish the energy deficit (p < .001). Mean ± SD were EE, 1600 ± 639 Cal; EI, 394 ± 289 Cal; and EI-EE,-1206+594 Cal; VO2, 3.05 ± 0.55 L/min; RER, 0.91 ± 0.04; exercise duration 110 ± 42 min. Ingesting sports drinks to enhance performance did not abolish the caloric deficit of aerobic exercise. Sports drinks can be used in accordance with research protocols that typically provide 30–60 g of carbohydrate per hour when exercising at adequate durations for moderate to high intensity and still maintain a substantive caloric deficit.
Dennis Passe, Mary Horn, John Stofan, Craig Horswill and Robert Murray
This study investigated the relationship between runners’ perceptions of fluid needs and drinking behavior under conditions of compensable heat stress (ambient temperature = 20.5 ± 0.7 °C, 68.9 °F; relative humidity = 76.6%). Eighteen experienced runners (15 men, 40.5 ± 2.5 y, and 3 women, 42 ± 2.3 y) were given ad libitum access to a sports drink (6% carbohydrate-electrolyte solution) at Miles 2, 4, 6, and 8. After the run (75.5 ± 8.0 min), subjects completed questionnaires that required them to estimate their individual fluid intake and sweat loss. Dehydration averaged 1.9% ± 0.8% of initial body weight (a mean sweat loss of 21.6 ± 5.1 mL·kg−1·h−1). Subjects replaced only 30.5% ± 18.1% of sweat loss and underestimated their sweat loss by 42.5% ± 36.6% (P ≤ 0.001). Subjects’ self-estimations of fluid intake (5.2 ± 3.2 mL·kg−1·h−1) were not significantly different from actual fluid intake (6.1 ± 3.4 mL·kg−1·h−1) and were significantly correlated (r = 0.63, P = 0.005). The data indicate that even under favorable conditions, experienced runners voluntarily dehydrate (P ≤ 0.001), possibly because they are unable to accurately estimate sweat loss and consequently cannot subjectively judge how much fluid to ingest to prevent dehydration. This conclusion suggests that runners should not depend on self-assessment to maintain adequate hydration, underscores the need for runners to enhance their ability to self-assess sweat losses, and suggests that a predetermined regimen of fluid ingestion might be necessary if they wish to maintain more optimal hydration.
Craig A. Horswill, William B. Zipf, C. Lawrence Kien and E. Bowie Kahle
Insulin is an anabolic hormone with stimulatory effects on glucose and amino acid uptake, possibly protein synthesis, and bone growth, and inhibitory effects on protein breakdown. The precise role of insulin in the growth of healthy children is unclear, but two clinical models can be examined to illustrate insulin’s potential role in the growth of children. The cystic fibrosis (CF) patient, who exhibits poor linear growth and low lean body mass, may exhibit inadequate insulin secretion or impaired insulin action. The obese child typically has an excess of peripheral insulin, an associated acceleration of linear growth, and an accretion of lean body mass and adipose tissue. Speculation is offered on the putative role of exercise in affecting insulin action and secretion, which in turn could impact growth in children with CF or obesity.
Lindsay B. Baker, John R. Stofan, Henry C. Lukaski and Craig A. Horswill
Simultaneous whole-body wash-down (WBW) and regional skin surface sweat collections were completed to compare regional patch and WBW sweat calcium (Ca), magnesium (Mg), copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) concentrations. Athletes (4 men, 4 women) cycled in a plastic open-air chamber for 90 min in the heat. Before exercise, the subjects and cycle ergometer (covered in plastic) were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on saturation. After exercise, the subjects and cycle ergometer were washed with 5 L of 15-mM ammonium sulfate solution to collect all sweat minerals and determine the volume of unevaporated sweat. Control trials were performed to measure mineral contamination in regional and WBW methods. Because background contamination in the collection system was high for WBW Mn, Fe, and Zn, method comparisons were not made for these minerals. After correction for minimal background contamination, WBW sweat [Ca], [Mg], and [Cu] were 44.6 ± 20.0, 9.8 ± 4.8, and 0.125 ± 0.069 mg/L, respectively, and 5-site regional (weighted for local sweat rate and body surface area) sweat [Ca], [Mg], and [Cu] were 59.0 ± 15.9, 14.5 ± 4.8, and 0.166 ± 0.031 mg/L, respectively. Five-site regional [Ca], [Mg], and [Cu] overestimated WBW by 32%, 48%, and 33%, respectively. No individual regional patch site or 5-site regional was significantly correlated with WBW sweat [Ca] (r = –.21, p = .65), [Mg] (r = .49, p = .33), or [Cu] (r = .17, p = .74). In conclusion, regional sweat [Ca], [Mg], and [Cu] are not accurate surrogates for or significantly correlated with WBW sweat composition.
Craig A. Horswill, Dennis H. Passe, John R. Stofan, Mary K. Horn and Robert Murray
We compared ad libitum fluid consumption in adolescent (n = 15) and adult athletes (n = 34) exercising in similar environmental conditions (26.5°C, 27.3% relative humidity) and similar modes and intensities of exercise (80-85% of their age-predicted maximum heart rate). Throughout 1 hr of exercise, participants had access to sports bottles containing a sports drink (6% carbohydrate with electrolytes and identical flavoring). Sweat rate (SR) and percent dehydration were calculated from the change in body weight corrected for urine loss and fluid intake (FI). FI was significantly higher for the adults than for the adolescents. SR was also higher for the adults compared with that of the adolescents. Compared with adults, adolescents had significantly lower FI and SR, the combination of which allowed them to meet their fluid needs more closely during exercise. Minimal voluntary dehydration occurred in either group during exercise, possibly because of the nature of the exercise (noncompetitive) or the beverage characteristics (presence of sodium and sweetness) or availability of the beverage.
Craig A. Horswill, Dave G. Curby, William P. Bartoli, John R. Stofan and Robert Murray
We examined whether the type of fluid ingested during wrestling training would affect arm ergometry in adolescent athletes. Wrestlers (n = 11) trained for 2-hr sessions and consumed fluid containing 6% carbohydrate or a placebo of equal volume administered double blind and in randomized fashion. To account for training demands across beverage comparisons, energy expenditure (EE) was estimated by using the rate of appearance of CO2 (RaCO2) after 13C-bicarbonate ingestion. The performance test was completed after training and consisted of 6 min of intermittent, high-intensity arm cranking. The results showed the difference in total arm work (kg • m−2 • min) between carbohydrate (2,130 ± 263) and placebo (1,961 ± 401) conditions approached statistical significance (p = .07). Fluid intake matched 50% of sweat loss, resulting in modest dehydration for both treatments. Carbohydrate ingestion during training may enhance high-intensity intermittent arm work in adolescent wrestlers; however, the additive effects of carbohydrate dose and fluid volume for hydration need to be teased apart in subsequent research on adolescents performing such exercise.