Pre-exercise carbohydrate meals: application of glycemic index.

PURPOSE: The purpose of this study was to compare postprandial glycemic, insulinemic, and physiologic responses to a pre-exercise meal calculated to have a low glycemic index (LGI) with one calculated to have a moderately high glycemic index (HGI); each meal provided three foods totaling 1.5 g carbohydrate/kg body weight. METHODS: After an overnight fast, 10 trained cyclists consumed one of the test meals or water 30 min before cycling 2 h at 70% of maximum oxygen uptake (VO2max), followed by cycling to exhaustion at 100% of VO2max. RESULTS: Plasma insulin levels were significantly lower (P < 0.05) after LGI than after HGI through 20 min of exercise. Significantly higher (P < 0.05) respiratory exchange ratios were observed after HGI than after LGI until 2 h of exercise. At that time plasma glucose levels were significantly higher and ratings of perceived exertion lower (P < 0.05) after LGI compared with after HGI. Time to exhaustion was 59% longer after LGI (206.5+/-43.5 s) than after HGI (129.5+/-22.8 s). CONCLUSIONS: These results suggest a pre-exercise LGI may positively affect maximal performance following sustained exercise. The LGI maintained higher plasma glucose levels at the end of 2 h of strenuous exercise than the HGI, which may have better supported subsequent maximal effort.

Thermoregulatory effects of caffeine ingestion during submaximal exercise in men.

BACKGROUND: The exclusive effect of caffeine ingestion on exercise thermoregulation is unclear; data indicate that caffeine may have a positive effect, a negative effect, or no effect. METHODS: Rectal (TRE) and mean skin (TSK) temperatures, skin heat conductance (HSK), and sweat rate (MSW) were measured during 30 min of rest and subsequent 70 min of submaximal cycle-ergometer exercise (67% VO2PEAK) in 11 aerobically conditioned men (mean +/- SD 29 +/- 6 yr, 49 +/- 6 mL x min(-1) x kg(-1) VO2PEAK) under two conditions: a caffeine (10 mg x kg(-1) ingestion (CI) session and a noncaffeine ingestion (NCI) control session. RESULTS: There were no significant differences in physiological or thermoregulatory parameters during exercise: X (+/-SE) end exercise levels for the NCI and CI sessions, respectively, were VO2 = 2.50 +/- 0.09 vs. 2.55 +/- 0.09 L x min(-1); heart rate = 145 +/- 7 vs. 145 +/- 5 bpm; HSK = 30 +/- 3 vs. 28 +/- 3 kcal x m(-2) x h(-1) x degrees C(-1); MSW = 393 +/- 35 vs. 378 +/- 36 g x m(-2) x h(-1); and TRE = 38.3 +/- 0.2 vs. 38.4 +/- 0.1 degrees C. Control TSK was lower than that for CI by 0.4 to 0.5 degrees C at rest and during exercise. CONCLUSION: Ingestion of a high level (10 mg x kg(-1) of caffeine has no effect on skin heat conductance, sweating, or the rate of increase and final level of rectal temperature during moderate, submaximal leg exercise.

The physiological effects of step training with and without handweights.

The purpose of this study was to examine the physiological effects of eight weeks of step training with (N = 12) and without (N = 12) handweights. Twenty-four college-aged females volunteered as subjects for the study which involved pre- and post-laboratory testing consisting of the following: an incremental treadmill test for determination of aerobic work indices, which included maximal oxygen uptake rate (VO2max), maximal heart rate, ventilatory threshold oxygen uptake rate (VT-VO2), and ventilatory threshold heart rate (VT-HR); hydrostatic weighing for determination of body composition, which included percent body fat (%BF), fat mass (FM), and lean body mass (LBM); anthropometric measurements for determination of body build characteristics, which included the endomorphic (ENDO) somatotype rating, mesomorphic (MESO) somatotype rating, and ectomorphic somatotype rating; isokinetic strength testing at 60 degrees.sec-1 for determination of flexion and extension strength of the arm at the shoulder joint, forearm at the elbow joint, and leg at the knee joint; and the concentric leg press for determination of overall lower body strength. Two-way analysis of covariance indicated that the main effect of step training resulted in significant (p < 0.05) overall improvements in VO2max (38.29 +/- 1.05 to 41.32 +/- 0.95 ml.kg-1/min-1), VT-VO2 (22.86 +/- 0.86 to 26.03 +/- 0.84 (ml.kg-1/min-1), VT-HR (159.62 +/- 3.01 to 168.29 +/- 3.19 b/min-1), %BF (26.16 +/- 1.05 to 23.95 +/- 1.06%), FM (15.13 +/- 0.96 to 13.82 +/- 0.96 kg), ENDO rating (5.24 +/- 0.18 to 4.93 +/- 0.18 units), MESO rating (3.22 +/- 0.19 to 3.50 +/- 0.19 units), arm flexion strength (30.73 +/- 1.83 to 35.08 +/- 1.73 N/m), forearm flexion strength (26.89 +/- 1.13 to 29.21 +/- 1.14 N/m), and forearm extension strength (28.13 +/- 1.26 to 31.07 +/- 1.38 N/m). Similar improvements were observed in both the handweight and no-handweight groups of subjects.

The effects of age and body weight on anthropometric estimations of minimal wrestling weight in high school wrestlers.

The purpose of this study was to determine the effects of age and body weight on anthropometric estimations of minimal wrestling weight (MWW) in high school wrestlers. Five hundred and twenty-two high school wrestlers (M age +/- SD = 16.45 +/- 1.03 years) volunteered as subjects for this study. The total sample (N = 522) was dichotomized by age (less than 16 years, n = 171; greater than or equal to 16 years, n = 351) and body weight (less than or equal to 62.60 kg, n = 252; greater than 62.60 kg, n = 270). Cross-validation analyses included examination of the constant error (CE), standard error of estimate (SEE), r, and total error (TE). The results indicated that the quadratic skinfold equation of Lohman (EQ1; Table 2) most accurately estimated MWW in each group. Furthermore, it was recommended that MWW be calculated from EQ1 using the conversion constants of Lohman ([(5.03/BD)-4.59] x 100) to estimate relative fat from body density.

Validity of anthropometric estimations of body composition in high school wrestlers.

The purpose of this study was to determine the validity of 23 anthropometric equations for estimating body composition and minimal wrestling weight in high school wrestlers. A total of 409 high school wrestlers (M age +/- SD = 16.42 +/- 1.03 yrs) volunteered for this study. Twenty-three anthropometric measures including eight skinfolds, nine circumferences, and six diameters were obtained from each subject. The mean body density, determined from underwater weighing, was 1.0748 +/- 0.0100 g.cm-3. The crossvalidation analyses indicated that the quadratic skinfold equation of Lohman resulted in the most accurate estimation of body density. The total error, constant error, standard error of estimate, and r for this equation were 0.0077 g.cm-3, -0.0003 g.cm-3, 0.0076 g.cm-3 and .65, respectively. Furthermore, the results of this investigation indicated that the minimal wrestling weight equations of Tcheng and Tipton resulted in total error values (5.54 to 6.06 kg) which were too large to be of practical use for high school wrestlers.

Validity of anthropometric equations for determination of changes in body composition in adult males during training.

Twenty-six males (26.5 +/- 6.0 yr; X +/- SD) were studied before and after a fourteen week endurance training program to determine the validity of anthropometric equations for estimating changes in body composition (BC). Anthropometric measures included skinfolds (SF), circumferences, and diameters. Body density (BD) was determined by underwater weighing corrected for residual lung volume. Training resulted in an increase in BD (1.061 +/- 0.002 to 1.067 +/- 0.002 g/ml; X +/- SEM) and decreases in body weight (73.0 +/- 2.1 to 71.4 +/- 2.0 kg), relative fat (16.6 +/- 0.9 to 14.1 +/- 0.8%), fat weight (12.4 +/- 1.0 to 10.2 +/- 0.8 kg), and seventeen of the anthropometric measures (p less than 0.05). Cross-validation of twenty-four equations revealed validity coefficients (r2) and total error in relative fat (RFE) of r2 = 0.40-0.77 and RFE = 2.60-10.15% before training and r2 = 0.14-0.61 and RFE = 2.62-9.45% after training. Linear and base 10 logarithmic (log10) equations using primarily SF measures tended to have higher r2 and lower RFE than equations based on quadratic and natural logarithmic (loge) models and other anthropometric measures. Paired t-tests revealed that of these equations with higher r2 and lower RFE, only the linear equation by Forsyth & Sinning (BD = 1.10647--0.00162(scapSF)--0.00144(abdSF)--0.00077(triSF++ +) + 0.00071(midaxSF] was a stable predictor of BD during training. These results suggest that many existing equations may not be accurate predictors of changes in BC during training.

Validity and intertester error of anthropometric estimations of body density.

The purposes of this study were to evaluate the intertester error in anthropometry and its effect on estimations of actual body density (ABD), as well as to assess the validity of predicted body density (PBD) from selected anthropometric equation. Sixteen adult males X +/- SD = 21.98 +/- 1.65 years) volunteered to be measured by three experienced and reliable testers at eight circumference, two diameter, and eight skinfold sites as well as by underwater weighing. Eighteen commonly used anthropometric equations which predict body density were selected for evaluation. Repeated measures ANOVA with Tukey post-hoc comparisons were used to determine differences between testers for each anthropometric measure and the PBD values, as well as between the PBD values and ABD. There were significant (p less than 0.01) differences between testers for all anthropometric measures except bi-iliac diameter and hips circumference. However, the magnitude of the differences between testers were considered to be quite small and of no practical concern. There were significant differences among the PBD values and ABD for all equations except the base 10 logarithmic transformations of Durnin and Womersley. Seven of the equations, however, resulted in a constant error of less than or equal to 0.0085 g.ml-1. Overall, there was no single anthropometric equation which satisfied all of the cross-validation criteria suggested by previous investigators, however the linear equation of Forsyth and Sinning which included the scapular and abdominal skinfolds, as well as the bitrochanteric diameter resulted in an extremely small constant error (0.0024 g.ml-1) and an appropriate standard deviation of the PBD values (0.0127 g.ml-1).

Isokinetic strength and body composition of high school wrestlers across age.

The purpose of this study was to determine the changes in body composition as well as absolute and relative isokinetic forearm and leg strength of high school wrestlers across age. One hundred ninety-five wrestlers (means age +/- SD = 16.36 +/- 1.12 yr) volunteered to be measured for strength using a Cybex II dynamometer at 30, 180, and 300 degrees.s-1. In addition, underwater weighing was used to determine body composition characteristics. The subjects were divided into four age groups: group 1 (G1) = 14.17-15.00 yr (N = 20); group 2 (G2) = 15.01-16.00 yr (N = 60); group 3 (G3) = 16.01-17.00 yr (N = 52); and group 4 (G4) = 17.01-18.50 yr (N = 63). One-way ANOVA or ANCOVA with Tukey post hoc comparisons indicated significant (P less than 0.05) changes across age for height, body weight, and fat-free weight, as well as absolute and relative forearm and leg strength. The results of this study indicated that, while a large portion of the improvements in strength across age were associated with increases in lean tissue, there was an additional "age effect" which could not be accounted for by changes in fat-free weight. Although the mechanism responsible for the "age effect" is unclear, it is possible that neural development contributed to the strength increases across age.

Estimation of minimal wrestling weight using measures of body build and body composition.

This study evaluated field methods for establishing minimal body weight in wrestlers based upon estimates of fat-free body weight (FFB): 239 high school wrestlers were measured for height, weight, 13 diameters, 24 circumferences, and 7 skinfolds, as well as for underwater weight to determine body density and resultant FFB. To estimate FFB, anthropometric models were used which were based upon diameters, circumferences, and/or skinfolds. Correlations between actual and predicted FFB were high, ranging from r = 0.89 to 0.92 for the models employing diameters and r = 0.96 for those employing circumferences, which respectively increased to r = 0.96 and r = 0.97 when body weight was included in theses models. The skinfold-based and mixed model estimates of FFB were r = 0.97 and r = 0.91 to 0.97, respectively. The corresponding total error (TE) in these estimates for the diameter-based models ranged from 6.54 to 3.80 kg (inclusion of body weight further reduced TE to 2.77 kg). Among the circumference models, TE ranged from 2.50 to 2.33 kg, with inclusion of body weight accounting for the lower value. Skinfold-based estimates of FFB demonstrated a TE level ranging from 2.48 to 2.33 kg. The lowest TE (2.32 kg) was demonstrated by a mixed model which included skinfolds, diameter, height, and body weight. Cross-validation of these new equations revealed the lowest TE values (less than 2.2 kg) for the skinfold and the mixed model equations, thereby identifying highly valid field techniques for determining the present level of FFB, which can serve as the basis upon which minimal body weight estimates can be made.

Strength and anaerobic responses of elite young female sprint and distance runners.

The purpose of this study was to assess the strength and anaerobic responses of elite young female runners, in order to determine the relationship of these characteristics to age and high proficiency in sprint events. Thirty-one national junior-level sprint and middle distance runners were evaluated for isokinetic peak torque for leg extension at velocities ranging for 30 degrees to 300 degrees X s-1, anaerobic power and capacity based on the Wingate test, and body composition based on underwater weighing. Age-related and event-related differences were noted for both the peak torque and anaerobic response measures. Peak torques were greater for the older (greater than 11.67 yr) runners and greater for the sprinters when measured at the higher testing velocities. Anaerobic power and capacity were also greater for the older runners, but event-related differences only appeared when anaerobic power was adjusted for fat-free weight (adjusted anaerobic power was greater in the older sprinters). These results indicate that both age and fat-free weight influence strength and anaerobic responses in young female runners and that exceptional levels of such characteristics only appear for sprinters within the upper age groups of youth competition.

Basic Conditioning Principles for High School Wrestlers.

In brief: Tired wrestlers bore the crowd and disappoint themselves and their coaches. By contrast, skilled, aggressive wrestlers who are conditioned to attack and defend throughout a six-minute match can generate excitement equal to that of any athletic contest. To maintain the appropriate fitness required to perform at this level, a specific conditioning program is needed. This article describes a conditioning program based on a year-round schedule that helps wrestlers achieve and maintain their highest possible level of performance.