The purposes of this study were (a) to describe the relation of 1-mile run/walk time (MRWT) to skinfold thickness measures in a national probability sample of students 8 to 18 years of age (NCYFS I and II, n = 11,123) and (b) to evaluate the impact of adjusting MRWT scores for the effect of skinfold thickness on the classification of scores using percentile ranks and criterion referenced standards (CRS). MRWT was significantly related to the sum of subscapular and triceps skinfolds in all age-gender groups. In 12-year-olds, MRWT scores adjusted for sum of skinfolds by regression analysis resulted in individual percentile ranks that differed by more than 10 from percentile ranks of unadjusted scores in 29% of girls and 39% of boys, and altered classifications on the Fitnessgram and AAHPERD mile run/walk time CRS in 11-14% of boys and girls. It is concluded that the relation between MRWT and skinfold thickness is strong enough, and the impact of adjusting MRWT scores for skinfold thickness sufficient, to justify using adjusted scores for classification of cardiorespiratory capacity as part of the assessment of health related physical fitness in youth. Additional research is needed to cross-validate the equations developed in this study.
Adjustment of 1-Mile Run/Walk Test Scores for Skinfold Thickness in Youth
Kirk J. Cureton, Ted A. Baumgartner, and Beth G. McManis
Ergogenic Effects of Low Doses of Caffeine on Cycling Performance
Nathan T. Jenkins, Jennifer L. Trilk, Arpit Singhal, Patrick J. O’Connor, and Kirk J. Cureton
The purpose of this experiment was to learn whether low doses of caffeine have ergogenic, perceptual, and metabolic effects during cycling. To determine the effects of 1, 2, and 3 mg/kg caffeine on cycling performance, differentiated ratings of perceived exertion (D-RPE), quadriceps pain intensity, and metabolic responses to cycling exercise, 13 cyclists exercised on a stationary ergometer for 15 min at 80% VO2peak, then, after 4 min of active recovery, completed a 15-min performance ride 60 min after ingesting caffeine or placebo. Work done (kJ/kg) during the performance ride was used as a measure of performance. D-RPE, pain ratings, and expired-gas data were obtained every 3 min, and blood lactate concentrations were obtained at 15 and 30 min. Compared with placebo, caffeine doses of 2 and 3 mg/kg increased performance by 4% (95% CI: 1.0–6.8%, p = .02) and 3% (95% CI: –0.4% to 6.8%, p = .077), respectively. These effects were ergogenic, on average, but varied considerably in magnitude among individual cyclists. There were no effects of caffeine on D-RPE or pain throughout the cycling task. Selected metabolic variables were affected by caffeine, consistent with its known actions. The authors conclude that caffeine preparations of 2 and 3 mg/kg enhanced performance, but future work should aim to explain the considerable interindividual variability of the drug’s ergogenic properties.
Grape Consumption’s Effects on Fitness, Muscle Injury, Mood, and Perceived Health
Patrick J. O’Connor, Amanda L. Caravalho, Eric C. Freese, and Kirk J. Cureton
Compounds found in the skins of grapes, including catechins, quercetin, and resveratrol, have been added to the diet of rodents and improved run time to exhaustion, fitness, and skeletal-muscle mitochondrial function. It is unknown if such effects occur in humans. The purpose of this experiment was to investigate whether 6 wk of daily grape consumption influenced maximal oxygen uptake (VO2max), work capacity, mood, perceived health status, inflammation, pain, and arm-function responses to a mild eccentric-exercise-induced arm-muscle injury. Forty recreationally active young adults were randomly assigned to consume a grape or placebo drink for 45 consecutive days. Before and after 42 d of supplementation, assessments were made of treadmill-running VO2max, work capacity (treadmill performance time), mood (Profile of Mood States), and perceived health status (SF-36 Health Survey). The day after posttreatment treadmill tests were completed, 18 high-intensity eccentric actions of the nondominant elbow flexors were performed. Arm-muscle inflammation, pain, and function (isometric strength and range of motion) were measured before and on 2 consecutive days after the eccentric exercise. Mixed-model ANOVA showed no significant effect of grape consumption on any of the outcomes. Six weeks of supplemental grape consumption by recreationally active young adults has no effect on VO2max, work capacity, mood, perceived health status, inflammation, pain, or physical-function responses to a mild injury induced by eccentric exercise.
Effects of Varying Levels of Hypohydration on Ratings of Perceived Exertion
Donald R. Dengel, Peter G. Weyand, Donna M. Black, and Kirk J. Cureton
To investigate the effects of varying levels of hypohydration on ratings of perceived exertion (RPE) during moderate and heavy submaximal exercise, and at the lactate threshold (LT) and ventilatory threshold (VT), 9 male subjects cycled under states of euhydration (EU), moderate hypohydration (MH), and severe hypohydration (SH). The desired level of hypohydration was achieved over a 36-hr period by having subjects cycle at 50% VO2max in a 38°C environment on two occasions while controlling fluid intake and diet. During submaximal exercise, oxygen uptake, ventilation, heart rate, blood lactate, and RPE were not significantly different among treatments. Hypohydration did not significantly alter LT or VT, or perceptual responses at LT or VT. It is concluded that hypohydration of up to 5.6% caused by fluid manipulation and exercise in the heat over a 36-hr period does not alter RPE or the lactate or ventilatory threshold, nor RPE at the lactate and ventilatory thresholds measured during moderate and heavy submaximal cycling in a neutral (22°C) environment.
Effect of Six Weeks of Sprint Interval Training on Mood and Perceived Health in Women at Risk for Metabolic Syndrome
Eric C. Freese, Rachelle M. Acitelli, Nicholas H. Gist, Kirk J. Cureton, Ellen M. Evans, and Patrick J. O’Connor
The purpose of this investigation was to determine whether 6 weeks of sprint interval training (SIT) is associated with changes in mood and perceived health in women at risk for developing metabolic syndrome (MetS). Physically inactive women (30–65 years) were randomized to 6 weeks of nutrition meetings and SIT (n = 23; 3 bouts/week of 4–8 30-s cycle sprints with 4-min recovery) or a nonexercise control condition (CON; n = 24). Before and after the 6-week intervention, perceived health status and mood were assessed. Clinically relevant increases in role-physical scores (ES = 0.64) and vitality (ES = 0.52) were found after 6 weeks of SIT compared with a nonexercise control group. For middle-aged women at risk for MetS, it is concluded that high-intensity, low-volume SIT (1) increases feelings of vitality and perceptions of having fewer physical limitations and (2) does not induce mood disturbances as occurs with high-volume, high-intensity training.
Caffeinated Sports Drink: Ergogenic Effects and Possible Mechanisms
Kirk J. Cureton, Gordon L. Warren, Mindy L. Millard-Stafford, Jonathan E. Wingo, Jennifer Trilk, and Maxime Buyckx
This double-blind experiment examined the effects of a caffeinated sports drink during prolonged cycling in a warm environment. Sixteen highly trained cyclists completed 3 trials: placebo, carbohydrate-electrolyte sports drink (CES), and caffeinated sports drink (CES+CAF). Subjects cycled for 135 min, alternating between 60% and 75% VO2max every 15 min for the first 120 min, followed by a 15-min performance ride. Maximal voluntary (MVC) and electrically evoked contractile properties of the knee extensors were measured before and after cycling. Work completed during the performance ride was 15–23% greater for CES+CAF than for the other beverages. Ratings of perceived exertion were lower with CES+CAF than with placebo and CES. After cycling, the MVC strength loss was two-thirds less for CES+CAF than for the other beverages (5% vs. 15%). Data from the interpolated-twitch technique indicated that attenuated strength loss with CES+CAF was explained by reduced intrinsic muscle fatigue.
Hydration during Exercise in Warm, Humid Conditions: Effect of a Caffeinated Sports Drink
Mindy L. Millard-Stafford, Kirk J. Cureton, Jonathan E. Wingo, Jennifer Trilk, Gordon L. Warren, and Maxime Buyckx
Caffeine is regarded as a diuretic despite evidence that hydration is not impaired with habitual ingestion. The purpose of this study was to determine whether a caffeinated sports drink impairs fluid delivery and hydration during exercise in warm, humid conditions (28.5 °C, 60% relative humidity). Sixteen cyclists completed 3 trials: placebo (P), carbohydrate-electrolyte (CE), and caffeinated (195 mg/L) sports drink (CAF+CE). Subjects cycled for 120 min at 60–75%VO2max followed by 15 min of maximal-effort cycling. Heart rate and rectal temperature were similar until the final 15 min, when these responses and exercise intensity were higher with CAF+CE than with CE and P. Sweat rate, urine output, plasma-volume losses, serum electrolytes, and blood deuterium-oxide accumulation were not different. Serum osmolality was higher with CAF+CE vs. P but not CE. The authors conclude that CAF+CE appears as rapidly in blood as CE and maintains hydration and sustains cardiovascular and thermoregulatory function as well as CE during exercise in a warm, humid environment.