Biomedical subjects

C A Horswill

Publications and source records attributed to C A Horswill.

At least 19 recordsLinked to original sources

PubMed1999

Splanchnic uptake of leucine in healthy children and in children with cystic fibrosis.

Interpretation of tracer studies of amino acid kinetics in the fed state is dependent on knowledge of splanchnic uptake of diet-derived amino acids. We studied five healthy control children and five children with cystic fibrosis (CF). After an overnight fast, the children ingested, hourly, a formula diet for 11 h. 5,5,5-[2H3]Leucine was added to the feedings during the last 6 h, and an i.v. infusion of 1-[13C]leucine was administered during the last 2 h of the formula feeding. The mean rate of splanchnic uptake of leucine was similar in the CF and control group, 23.8 +/- 24.0 and 21.5 +/- 21.2 mumol.kg-1.h-1, respectively. Fractional splanchnic uptake of leucine was not significantly different in the patients with CF (0.16 +/- 0.112 mean +/- SD) compared with the control children (0.244 +/- 0.256(-1)). The rate of whole body protein breakdown was not significantly different between the groups (CF versus control) with (159 +/- 18 versus 135 +/- 28 mumol.kg-1.h-1) or without (135 +/- 14 versus 114 +/- 20 mumol.kg-1.h-1) correction for splanchnic leucine uptake. However, for the 10 cases combined, protein breakdown corrected for splanchnic leucine uptake (147 +/- 26 mumol.kg-1.h-1) was 18% greater than uncorrected protein breakdown (124 +/- 20 mumol.kg-1.h-1) (p = 0.009). The data suggest that companion studies of splanchnic uptake might enhance the interpretation of leucine kinetics in the fed state.

Carbon Isotopes↗

PubMed1998

Effective fluid replacement.

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.

Behavior↗

PubMed1997

Measuring energy costs of leisure activity in adolescents using a CO2 breath test.

To determine whether a 13C-bicarbonate, isotope dilution technique could be used to estimate relative changes in energy expenditure of leisure activities of short duration, we studied eight adolescents who performed the following activities: watching television (120 min); playing a stringed instrument (60 min plus 60 min of sitting); and walking plus rest during two approximately isocaloric sessions (slow walk at 40% of peak VO2 for 43 min plus 77 min of sitting; fast walk at 73% of peak VO2 for 22 min plus 98 min of sitting). The rate of appearance of CO2 (RaCO2) was determined from the ratio of the oral dose of 13C-bicarbonate and the isotopic enrichment of breath CO2. The net rates of excretion of CO2 (VCO2) and oxygen consumption were measured. VCO2 and RaCO2, were correlated (r = 0.93; P < 0.05). To adjust for the systematic difference in CO2 production between methods, determinations were expressed as a fraction of that during television viewing. For RaCO2, the ratios for instrument playing, walking at 40% peak VCO2, and walking at 73% peak VO2 were respectively 133 +/- 20%, 186 +/- 38%, and 206 +/- 34%; for VCO2, the respective ratios were 129 +/- 19, 210 +/- 50, and 232 +/- 39 (P > 0.05 for methods and interaction, two-way ANOVA). RaCO2 may be a useful method for detecting relative differences in energy expenditure associated with leisure activities of brief duration.

Adolescent↗

PubMed1996

Association between mild, routine exercise and improved insulin dynamics and glucose control in obese adolescents.

The association between mild routine exercise and glucose homeostasis, insulin dynamics, and risk factors for coronary artery disease was investigated in obese adolescent males. Subjects (n = 7; mean +/- SD age 13.3 +/- 1.4 yr) were tested before and after 15 wk of supervised mild intensity exercise. Serum glucose (GLU), insulin (IN), and C-peptide (CP) were measured in response to a mixed meal before and after the 15 wk period. Weight, body composition, peak oxygen uptake (peak VO2), resting blood pressure (BP), and blood lipid levels were also assessed pre- and post-training. After training, percent fat and body weight were not decreased compared to the initial values. Relative changes (p < or = 0.02) in mean values for GLU and peptides after training were: fasting GLU, -15%; total GLU response, -15%; peak IN response, -51%; total IN response, -46%; peak CP response, +55%; and total CP response, +53%. Following training, the subjects did not have an increased peak VO2, but showed consistent reductions in systolic BP and LDL-cholesterol (p < 0.05). Increases in hepatic insulin clearance (decreased insulin levels but increased CP levels) might be training adaptations unique to low intensity exercise or to obese youth. Decreased insulin levels with concurrent decreases in resting blood pressure and the LDL-cholesterol levels suggest that mild exercise training may reduce health risk factors without weight loss in the obese adolescent male.

Adolescent↗

PubMed1996

Effects of feeding on protein turnover in healthy children and in children with cystic fibrosis.

We hypothesized that there is less suppression of whole-body protein breakdown with feeding in patients with cystic fibrosis (CF) who exhibit decreased insulin secretion after a single meal. Using [1-13C]leucine, we measured rates of nonoxidative leucine disappearance (whole-body protein synthesis) and protein breakdown in nine CF patients (6-11 y of age) and five healthy control subjects (8-10 y of age) during feeding and fasting. In the CF patients, synthesis and breakdown (x +/- SD) were 172 +/- 61 and 157 +/- 67 mumol.kg-1.h-1 during feeding and 140 +/- 24 and 178 +/- 26 mumol.kg-1.h-1 during fasting. The respective control values were 129 +/- 27 and 114 +/- 20 mumol.kg-1.h-1 during feeding and 136 +/- 13 and 173 +/- 18 mumol.kg-1.h-1 during fasting. Leucine balance was nearly identical in the two groups. By analysis of variance, there was a significant effect of feeding on protein breakdown but no difference between the groups. However, when each group was analyzed separately, feeding resulted in a 34% decrease in breakdown in the control subjects (P = 0.001) and a 23% increase in synthesis in the CF group (P = 0.058). Plasma insulin concentrations did not differ in the two groups. Thus, feeding may affect protein turnover differently in children with CF than in control children independently of plasma insulin concentration.

Case-Control Studies↗

PubMed1996

American College of Sports Medicine position stand. Weight loss in wrestlers.

Despite a growing body of evidence admonishing the behavior, weight cutting (rapid weight reduction) remains prevalent among wrestlers. Weight cutting has significant adverse consequences that may affect competitive performance, physical health, and normal growth and development. To enhance the education experience and reduce the health risks for the participants, the ACSM recommends measures to educate coaches and wrestlers toward sound nutrition and weight control behaviors, to curtail "weight cutting," and to enact rules that limit weight loss.

Humans↗

PubMed1995

Effects of bicarbonate, citrate, and phosphate loading on performance.

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.

Administration, Oral↗

PubMed1995

Elevated hepatic glucose production in children with cystic fibrosis.

We hypothesized that elevated hepatic glucose output (HGO) may occur in children with cystic fibrosis (CF) as an early sign of declining insulin secretion and that tolbutamide therapy would correct the defect. We studied eight glucose-tolerant CF patients (mean +/- SD, 9.1 +/- 1.9 y) and five healthy controls (9.0 +/- 1.6 y). Fasting glucose, insulin, and insulin-connecting peptide concentrations were not different in the CF and control subjects; however, meal stimulation tests in the CF patients suggested that insulin secretion was defective in the fed state. HGO (mg.kg-1 body weight.min-1) was 26% higher in the CF patients (4.2 +/- 0.7 versus 3.1 +/- 0.6 in HC) (p = 0.016). When normalized for fat-free mass (mg.kg fat-free mass-1.min-1), HGO was 27% higher in CF (4.9 +/- 0.8 versus 3.8 +/- 0.5) (p = 0.015). However, when expressed as a function of resting energy expenditure (mg.kcal-1), HGO was not significantly different in CF (121 +/- 22) versus healthy controls (116 +/- 30). In seven of the CF group, HGO was re-assessed after a 2-h glucose infusion at a rate of 0.90 +/- 0.02 mg.kg-1.min-1. HGO was suppressed (p < 0.05) by an amount equal to 103 +/- 18% of the glucose infusion rate. Finally, in five CF patients, HGO was re-measured after 2 wk of oral therapy with tolbutamide (750 mg/d). Tolbutamide did not affect HGO (fasting or during the glucose infusion). In conclusion, fasting HGO was elevated in the CF patients in proportion to energy expenditure.

C-Peptide↗

PubMed1995

Energy expenditure in adolescents during low intensity, leisure activities.

We sought to determine how a stationary activity such as playing a stringed instrument may affect energy expenditure (EE) in adolescents. Using automated indirect calorimetry, we measured EE in eight adolescents (1 male, 7 females, 14.2 +/- 2.1 yr) while they each performed the following activities: watching television (TV) (60 min), playing a stringed instrument (60 min), and walking at 40% of peak oxygen uptake (43 min). Measurements were made during three, 6- to 7-min steady state periods of each activity. EE (mean +/- SD) was lower during TV (1.0 +/- 0.2 kcal.min-1) and instrument playing (1.4 +/- 0.2 kcal.min-1) than during walking (3.4 +/- 0.4 kcal.min-1) (P < 0.05). EE during instrument playing was 41% greater than during television viewing (P < 0.05). We conclude that relatively sedentary activities such as playing a stringed instrument can elevate EE. Conceivably, other stationary, leisure activities performed by adolescents may increase EE and have substantial, cumulative effects on long-term energy balance and fat accretion.

Adolescent↗

PubMed1994

Influence of rapid weight gain after the weigh-in on success in collegiate wrestlers.

UNLABELLED: We investigated whether acute weight gain between the weigh-in and competition was associated with success in a collegiate wrestling tournament. Wrestlers at the NCAA championships were weighed at the official weigh-in and again just before the first round of the tournament (20 h later). Weight gain and the weight discrepancy between first-round opponents were calculated (N = 607 excluding heavyweights). Indices of success included season record (% wins in total matches), tournament seeding, the sum of the advancement and placement points scored during the tournament (team points), and final placement in the tournament. ANOVA showed no differences in weight variation between placewinners and non-placewinners, or across placewinners only. Correlation coefficients among weight variables and indices of success were also low (P > 0.05). Multiple logistic regression, used to determine whether weight gain or weight discrepancy between opponents contributed to success in the first round of the tournament, revealed that neither variables was predictive of first-round outcome even after attempting to account for differences in ability (e.g., forcing team points into the regression first). CONCLUSION: neither acute weight gain after the weight-in or the weight discrepancy between opponents in the first round influenced success in a collegiate wrestling tournament.

Analysis of Variance↗

PubMed1994

Acute weight gain in collegiate wrestlers following a tournament weigh-in.

UNLABELLED: The purpose of this study was to determine the magnitude of weight gained in collegiate wrestlers between the weigh-in and beginning of tournament competition. Body weight of the qualifiers for the NCAA Division I, II, and III wrestling finals (N = 668) was recorded at the official weigh-in and again approximately 20 h later, before the first round of competition in the tournament. The results showed that on average (+/- SD), wrestlers gained 4.9 +/- 2.4% (3.3 +/- 1.5 kg) of body weight before competing. An inverse relationship was found such that wrestlers in the lightest weight classes gained the most weight (kg) compared with heavier wrestlers (r = -0.45, P < 0.05). Despite the large mean weight gain, the mean discrepancy between first round opponents was 2.1 +/- 3.0 kg and even less when heavyweight wrestlers were excluded from the analyses (1.5 +/- 1.2 kg, N = 607). A significant correlation between weight gain and weight discrepancy of opponents was found (r = 0.65, P < 0.05). CONCLUSION: collegiate wrestlers, excluding heavyweights, gained significant amounts of weight (3.7 kg average) during the 20-h period prior to tournament competition. The magnitude of weight gain was positively correlated to the degree of weight discrepancy (size advantage) over the opponent; however, because weight gain of some magnitude after the weigh-in was common in most participants, the average discrepancy between opponents was only about 1.5 kg.

Adult↗

PubMed1993

Weight loss and weight cycling in amateur wrestlers: implications for performance and resting metabolic rate.

Amateur wrestlers practice weight loss for ergogenic reasons. The effects of rapid weight loss on aerobic performance are adverse and profound, but the effects of 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.

Basal Metabolism↗

PubMed1992

Anaerobic and aerobic power in arms and legs of elite senior wrestlers.

UNLABELLED: The purpose of this study was to characterize anaerobic power and aerobic power (power at peak oxygen uptake, or peak VO2) of elite senior (post-collegiate) wrestlers. Subjects (n = 14) from the U.S. national senior freestyle and Greco Roman wrestling teams were evaluated at separate tests using cycle ergometry for peak VO2 of the arms, peak VO2 of the legs, arm anaerobic peak power, and leg anaerobic peak power. Power output at peak VO2 was recorded for each test and compared to the anaerobic power of the appropriate body segment. The results (mean +/- SD) showed that wrestlers produced 2.3 +/- 0.4 W.kg body weight-1 at arm peak VO2 (43.7 +/- 4.6 ml.kg body weight-1. min-1), 4.2 +/- 0.5 W.kg body weight-1 at leg peak VO2 (50.9 +/- 5.1 ml.kg body weight-1.min-1), arm PP of 7.7 +/- 1.0 W.kg body weight-1, and leg PP of 10.5 +/- 1.7 W.kg body weight-1. Comparing power output during anaerobic and aerobic tests, the subjects performed at 3.4 +/- 0.6 times their peak oxygen uptake during arm anaerobic ergometry, whereas leg anaerobic peak power was 2.7 +/- 0.4 times the power at peak oxygen uptake for the legs (p < 0.05 for difference between ratios). CONCLUSION: relative to aerobic power, elite senior wrestlers may produce power anaerobically in the upper body at significantly higher levels than in the lower body.

Adult↗

PubMed1992

Applied physiology of amateur wrestling.

The general physiological profile of the successful wrestler is of one having high anaerobic power (mean range of 6.1 to 7.5 W/kg for arms; mean range of 11.5 to 19.9 W/kg for legs); high anaerobic capacity (range for arms 4.8 to 5.2 W/kg; range for legs 7.4 to 8.2 W/kg); high muscular endurance; average to above average aerobic power (range 52 to 63 ml/kg/min); average pulmonary function (range 1.90 to 2.02 L/kg/min for VEmax); normal flexibility; a high degree of leanness (range 3.7 to 13.0% fat) excluding heavyweights; and a somatotype that emphasises mesomorphy. Training methods include wrestling, and nonwrestling activities for increasing strength and power (i.e. resistance training), and to improve cardiovascular fitness (i.e. endurance training). Unfortunately, data on the isolated effects of wrestling on fitness and the type of training programme most effective for success in wrestling are scarce. The practice of weight loss is commonly used by wrestlers to enhance performance. Rapid weight loss has profound adverse effects on the wrestler's physiology but little effect on strength or anaerobic power performance as measured in the laboratory. In contrast, muscular endurance appears to be impaired by the rapid weight loss. Current research on weight loss and performance in wrestlers has taken 2 directions: (a) towards nutritional treatments to prevent suboptimal muscular endurance, and (b) towards the development of programmes to estimate minimal weight based on body composition techniques and thereby prevent weight reductions.

Body Temperature Regulation↗

PubMed1991

Test development for the study of physical performance in wrestlers following weight loss.

This study was conducted to develop a testing protocol which would determine the extent of upper-body power output decrements in subjects following weight loss. Five athletes who had trained via upper-body exercise performed a 6-minute variable intensity arm crank test on an isokinetic ergometer before and after a 3-day, 4.5% body weight loss. Blood samples were drawn from a forearm vein pre- and 1, 3, and 5 min post-arm cranking for assessment of lactate, pH, hemoglobin, and hematocrit. The work performed pre-weight loss was significantly (paired t-test, p less than 0.05) greater than that performed post-weight loss. Repeated measures ANOVA yielded no significant differences in blood variables; however, pre-weight loss lactate values were higher and hemoglobin, hematocrit, and pH values were lower than post-weight loss values. It was concluded that a 4.5% body weight reduction resulted in performance decrements during this arm crank test. Survey information obtained from collegiate wrestlers (n = 14) subsequently tested under this protocol indicates the physical demands of this test approximate the physical demands of actual wrestling competition. It would therefore be appropriate to use this protocol during future testing of wrestlers in weight loss studies.

Adult↗

PubMed1991

Effects of tolbutamide on growth and body composition of nondiabetic children with cystic fibrosis.

Previously, we reported that nondiabetic children with cystic fibrosis show a blunted insulin response to a meal stimulus. In the study presented here, using tolbutamide, we determined the effects of augmented insulin secretion/action on height and lean body mass of children with cystic fibrosis. Twelve subjects (mean +/- SEM age, 11.0 +/- 0.5 y) were studied for three 4-mo periods: 1) pretreatment, 2) treatment, consisting of 750 mg/d of tolbutamide, and 3) posttreatment. Before the pretreatment period, insulin response to a meal stimulus was evaluated in relation to three doses of tolbutamide: 0, 250, and 500 mg. Growth was monitored during each period, and incremental changes in lean body mass were calculated from height data. To validate the change in lean body mass based on height measurements, we determined lean body mass in seven subjects during the treatment period by using a criterion method (H218O). Growth velocity (cm/4 mo) significantly increased (p less than 0.05) during the treatment (2.58 +/- 0.31) compared with the pretreatment period (0.88 +/- 0.20). The increase in lean body mass calculated from height was greater during the treatment (1.61 +/- 0.29 kg/4 mo) than during the pretreatment period (0.44 +/- 0.18 kg/4 mo) (p less than 0.05). There was also a significant increase (p less than 0.05) in lean body mass during the treatment as measured with H218O (1.91 +/- 0.65 kg/4 mo). Acute administration of either 250 or 500 mg of tolbutamide reduced (p less than 0.05) the area under the glucose concentration curve in response to a meal compared with the control condition of no tolbutamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1991

Elevated blood pressure in obese children: influence of gender, age, weight and serum insulin levels.

Prepubescent and early pubescent obese children (n = 114, mean percent IBW = 165, mean age 7.3 years) were studied to determine the relationship of weight (WT), percent of ideal body weight (percent IBW), gender, and insulin (I) to systolic (SBP) and diastolic (DBP) blood pressure. Subjects were assessed for weight, height, percent IBW, systolic and diastolic blood pressure, and Tanner stage; subjects with Tanner stage greater than 3 were excluded. Multiple regression revealed that body weight accounted for the greatest variance in SBP (adj. R2 = 0.34, P less than 0.05), followed by the age. For DBP, weight also accounted for the greatest variance (adj. R2 = 0.16, P less than 0.05) followed by gender. A subgroup (n = 50) was evaluated for oral glucose tolerance. Subjects ingested 1.75 g glucose (GLU)/kg weight and had blood samples drawn at 0, 30, 60, 90, 120 and 180 min. Pearson correlations showed SBP correlated significantly to I at 0 (r = 0.44) and the total integrated area for insulin (r = 0.45); however, adjusting SBP for age by using z-score transformations negated all correlations between SBP and insulin. GLU at 0 and the total integrated area were not significantly correlated to SBP or DBP in absolute or age-adjusted terms. These data on prepubescent, nondiabetic, obese children suggest an association between insulin and elevations in SBP, but not DBP, that is largely due to a mutual association between age and weight. Also, insulin resistance as reflected in GLU response was not related to SBP or DBP.

Age Factors↗

PubMed1990

Changes in the protein nutritional status of adolescent wrestlers.

The protein nutritional status of adolescent wrestlers was studied to determine whether changes occur during a season of competition and weight loss. Subjects (N = 18) were measured prior to the start of the season (PRE), twice in the midseason, and once during late season (LATE) for weight, percent body fat, and height. At each of these times, a venous blood sample was obtained from the subjects, who were fasted, and analyzed for concentrations of albumin, prealbumin, retinol binding protein (RBP), blood urea nitrogen (BUN), hemoglobin, hematocrit, and 23 amino acids. Diet records were kept by subjects to assess daily energy, protein, fat, and carbohydrate intake. Data were analyzed by repeated measures ANOVA. Results showed that wrestlers decreased weight by an average of 6.6 +/- 0.9% and that percent body fat, fat-free weight, plasma levels of prealbumin and RBP, the ratio of total essential amino acids to total amino acids, and dietary energy nutrient intakes were significantly lower at LATE compared to PRE. RBP decreased during midseason and averaged (+/- SE) 3.21 +/- 0.15 mg.100 ml-1 at LATE; prealbumin was significantly lower at LATE with a mean value of 19.8 +/- 1.0 mg.100 ml-1. Total energy intake decreased from PRE values by 35%, to approximately 27 kcal.kg-1.d-1 during the season. In conclusion, in these high school wrestlers who lost approximately 6.6% of weight, there were adverse effects on some of the indices of protein nutritional status.

Adolescent↗