Of all the physiological perturbations that can cause early fatigue during exercise, dehydration is arguably the most important, if only because the consequences of dehydration are potentially life threatening. The rise in body temperature that normally accompanies exercise stimulates an increase in blood flow to the skin and the onset of sweating. Normal hydration is protective of these thermoregulatory responses, whereas even a slight amount of dehydration results in measurable declines in cardiovascular and thermoregulatory function. Mild to severe dehydration commonly occurs among athletes, even when fluid is readily available. This voluntary dehydration compromises physiological function, impairs exercise performance, and increases the risk of heat illness. Recent research illustrates that maintaining normal hydration (or close to it) during exercise maintains cardiovascular and thermoregulatory responses and improves exercise performance. Consequently, it is in the athlete’s best interest to adopt fluid-replacement practices that promote fluid intake in proportion to sweat loss.
Robert J. Rotella and Mi Mi Murray
Homophobia has been an issue of concern in the world of sport for decades. It has had a negative impact on the world of athletes, coaches, and sport psychology consultants. Both heterosexuals and homosexuals are affected. Homophobia has kept some from striving for excellence while interfering with and hindering some who pursued success in sport. Specialists in sport psychology who claim to care about the development of human potential in sport must be concerned about the impact of homophobia. An honest look at attitudes, beliefs, and values is a necessary step forward if change is to occur. A move in the direction of healthy acceptance of differing sexual preferences is suggested, along with an effective philosophy for doing so. A wish list for the future is included.
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.
Dennis H. Passe, Mary Horn, John Stofan and Robert Murray
Palatability and voluntary intake of 4 beverages commonly available to athletes were compared in a laboratory exercise protocol designed to mimic aerobic training or competitive conditions in which limited time is available for drinking. Diluted orange juice (DOJ), homemade 6% carbohydrate-electrolyte sports beverage (HCE), commercially available 6% carbohydrate-electrolyte sports beverage (CCE), and water (W) were tested. Fifty adult triathletes and runners (34 males, 16 females) exercised for 75 min at 80–85% of age-predicted heart rate, during which time they were given brief access (60 s) to one of the beverages after 30 min and 60 min of exercise. Results indicated that for overall palatability, CCE > W, HCE, DOJ; W > DOJ, and for amount of beverage consumed, CCE > W, HCE, DOJ; HCE > W, DOJ. The palatability of these beverages varied substantially, as did their voluntary intakes during exercise.
Xiaocai Shi, William Bartoli, Mary Horn and Robert Murray
Eight healthy subjects, aged 39.0 ± 2.4 years, consumed four 6% carbohydrate-electrolyte solutions containing either one (glucose or fructose) or two transportable carbohydrates in single (glucose + fructose) or bound (sucrose) forms. Solution osmolalities ranged from 250 to 434 mOsm/kg H2O. The test solutions were ingested at rest in the amount of 6 ml/kg of body weight at a temperature of 12 °C. Gastric emptying rate was measured by repeated aspirations via a nasogastric tube using the modified George double-sampling technique. The intragastric temperature was determined by a temperature probe attached to the nasogastric tube. There were no significant differences in gastric emptying rates and gastric volumes among the solutions. Intragastric temperature dropped from 36.5 °C to 23.3±3 °C immediately after beverage ingestion but recovered to above 30 °C within 5 min. These data suggest that the gastric emptying rate of the specified beverages is not affected by the number and type of carbohydrates or by solution osmolalities within the tested range. Within 5 min after ingestion, cold beverages are warmed to above 30 °C in the stomach. This infers that the effect of cold solution temperature on gastric emptying rate is likely to be small and transitory.
Robert Murray, William Bartoli, John Stofan, Mary Horn and Dennis Eddy
The purpose of this study was to determine the effects of repeated ingestion of drinks containing varying concentrations of carbohydrate on gastric emptying rate during steady-state exercise. On five separate occasions, 14 subjects cycled for 90 min at an average power output of 151 ± 2 W. At 15-min intervals, subjects ingested 227 ± 3 ml of either water, 4% carbohydrate (CHO), 6% CHO, or 8% CHO. Gastric volume was determined prior to each drink and at 90 min using the modified double-sampling technique. Gross gastric volumes were significantly greater and mean gastric emptying rates and the percentage of ingested beverage emptied from the stomach were significantly less for 8% CHO. These data indicate that repeated ingestion of an 8% CHO beverage during exercise significantly reduces gastric emptying rate, whereas lower concentrations of carbohydrate do not. In addition, beverage osmolality is not as important as beverage energy content in influencing gastric emptying rate at these carbohydrate concentrations.
Hugh H.K. Fullagar, Robert McCunn and Andrew Murray
While there are various avenues for performance improvement in college American football (AF), there is no comprehensive evaluation of the collective array of resources around performance, physical conditioning, and injury and training/game characteristics to guide future research and inform practitioners. Accordingly, the aim of the present review was to provide a current examination of these areas in college AF. Recent studies show that there is a wide range of body compositions and strength characteristics between players, which appear to be influenced by playing position, level of play, training history/programming, and time of season. Collectively, game demands may require a combination of upper- and lower-body strength and power production, rapid acceleration (positive and negative), change of direction, high running speed, high-intensity and repetitive collisions, and muscle-strength endurance. These may be affected by the timing of and between-plays and/or coaching style. AF players appear to possess limited nutrition and hydration practices, which may be disadvantageous to performance. AF injuries appear due to a multitude of factors—strength, movement quality, and previous injury—while there is also potential for extrinsic factors such as playing surface type, travel, time of season, playing position, and training load. Future proof-of-concept studies are required to determine the quantification of game demands with regard to game style, type of opposition, and key performance indicators. Moreover, more research is required to understand the efficacy of recovery and nutrition interventions. Finally, the assessment of the relationship between external/internal-load constructs and injury risk is warranted.
Charles J. Dillman, Tricia A. Murray and Robert A. Hintermeister
Confusion of the terms open and closed kinetic chain and scarcity of research comparing kinetic chain exercises that have similar mechanics and loading prompted this case study. Exercises were classified by the boundary condition of the distal segment and presence of an external load. Classifications included a fixed boundary condition with an external load (FEL), a movable boundary with an external load (MEL), and a movable boundary with no external load (MNL). It was hypothesized that if the direction and mass of loading in MEL and FEL exercises were similar, the electromyographic activity of the primary muscle groups involved would be comparable. Muscular activity was monitored from six shoulder muscles during one MNL, four MEL, and five FEL exercises. The results indicated that MEL and FEL exercises having similar biomechanics produced comparable muscular activity. Evaluation and selection of exercises for patients should be based upon mechanics and loading that achieve appropriate muscle activity.
Nathan D. Dicks, Nicholas A. Jamnick, Steven R. Murray and Robert W. Pettitt
To investigate a new power-to-body-mass (BM) ratio 3-min all-out cycling test (3MT%BM) for determining critical power (CP) and finite work capacity above CP (W ′).
The gas-exchange threshold (GET), maximal oxygen uptake (VO2max), and power output evoking VO2max (W peak) and GET (W GET) for cycle ergometry were determined in 12 participants. CP and W′ were determined using the original “linear factor” 3MT (3MTrpm^2) and compared with CP and W′ derived from a procedure, the 3MT%BM, using the subject’s body mass and self-reported physical activity rating (PA-R), with values derived from linear regression of the work–time model and power–inverse-time model (1/time) data from 3 separate exhaustive squarewave bouts.
The VO2max, VO2GET, W peak, and W GET values estimated from PA-R and a non-exercise-regression equation did not differ (P > .05) from actual measurements. Estimates of CP derived from the 3MT%BM (235 ± 56 W), 3MTrpm^2 (234 ± 62 W), work–time (231 ± 57 W), and 1/time models (230 ± 57 W) did not differ (F = 0.46, P = .72). Similarly, estimates of W′ between all methods did not differ (F = 3.58, P = .07). There were strong comparisons of the 3MT%BM to 1/time and work–time models with the average correlation, standard error of the measurement, and CV% for critical power being .96, 8.74 W, and 4.64%, respectively.
The 3MT%BM is a valid, single-visit protocol for determining CP and W′.
John G. Seifert, Greg L. Paul, Dennis E. Eddy and Robert Murray
The effects of preexercise hyperinsulinemia on exercising plasma glucose, plasma insulin, and metabolic responses were assessed during 50 min cycling at 62%