Boguslaw Wilk

Self-efficacy and perceived exertion of girls during exercise

BackgroundAn important national goal in Healthy People 2010 is to reduce the high prevalence of sedentary lifestyles and resultant overweight and obesity among girls. ObjectivesThe purpose of the present study was threefold: (a) to determine if pre-exercise self-efficacy predicted girls’ perceptions of exertion during exercise, (b) to determine if these perceptions, in turn, influenced postexercise self-efficacy, and (c) to assess if exercise self-efficacy increased following completion of an exercise task. MethodsA sample of 103 girls, 8 to 17 years of age, pedaled 20 minutes on a cycle ergometer at 60% of their predetermined peak VO2 in a climatic chamber (90°F, 50% relative humidity). Ratings of perceived exertion were obtained every 4 minutes. Exercise self-efficacy was assessed before and after the exercise session. ResultsControlling for peak VO2 and percent body fat, pre-exercise efficacy exerted an independent effect on perception of exertion during exercise with girls high on pre-exercise self-efficacy reporting lower perceived exertion during exercise, than girls low on self-efficacy. Both pre-exercise efficacy and perceived exertion explained postexercise efficacy. Exercise self-efficacy increased significantly from pre- to postexercise. ConclusionsPre-exercise efficacy is an important factor influencing girls’ perceptions of exertion during exercise and their postexercise efficacy. Increased exercise self-efficacy of girls following successful completion of an exercise challenge suggests possible strategies to increase physical activity.

PREVENTING DEHYDRATION IN CHILDREN WITH CYSTIC FIBROSIS WHO EXERCISE IN THE HEAT

PURPOSE In healthy children who exercise in the heat, the addition of flavor, carbohydrate, and 18 mmol x L(-1) NaCl to water induced a major increase in voluntary drink intake compared with the intake of unflavored water. This increase was sufficient to prevent voluntary dehydration. We hypothesized that, to achieve a similar effect in children with cystic fibrosis (CF), whose NaCl losses in sweat are markedly excessive, the drink should include an NaCl concentration higher than 18 mmol x L(-1). METHODS Eleven subjects with CF (6 girls, 5 boys, ages 10.9-19.5 yr) attended three 3-h sessions of intermittent exercise of moderate intensity (four 20-min bouts), at 35 degrees C, 50% relative humidity. Either water (W), flavored water (FW), or a 30 mmol x L(-1) NaCl plus 6% carbohydrate solution (Na30) was offered ad libitum, in a counterbalanced sequence. Six subjects performed an additional session in which they drank a 50 mmol x L(-1) NaCl-6% CHO solution (Na50). RESULTS There was no significant drink effect on body fluid balance, core temperature, heart rate, or serum electrolytes with W, FW, or Na30. Serum osmolality decreased throughout the sessions from 290.6 +/- 1.1 (mean +/- SEM) to 281.3 +/- 1.2 mmol x kg(-1) (P < 0.0005), serum sodium from 143.1 +/- 0.5 to 141.1 +/- 0.7 mmol x L(-1) (P = 0.01) and serum chloride from 109.1 +/- 0.5 to 107.5 +/- 0.5 mmol X L(-1) (P < 0.001). In contrast, the 50 mmol x L(-1) NaCl drink induced a near significant (P = 0.08) higher fluid intake, and it significantly ameliorated the rate of progressive dehydration. CONCLUSIONS The marked loss of NaCl in the sweat of CF patients may induce an hypo-osmolar state in the serum, even when the drink contains 30 mmol x L(-1) NaCl. This may diminish the thirst drive triggered by hypothalamic osmoreceptors and may lead to voluntary dehydration. A flavored drink with an even higher salt content (50 mmol X L(-1)), however, enhances drinking and attenuates the voluntary dehydration.

The effect of pain-free treadmill training on fibrinogen, haematocrit, and lipid profile in patients with claudication

Objective: To assess the effect of pain-free treadmill training on changes of plasma fibrinogen, haematocrit, lipid profile, and walking ability in patients with claudication. Design: Randomized control trial. Methods: Sixty-eight patients with peripheral obstructive arterial disease and intermittent claudication (Fontaine stage II) were randomly assigned into the treadmill training (repetitive intervals to onset of claudication pain, three times a week) or a control group (no change in physical activity) over 3 months. Both groups performed treadmill test to assess pain-free walking time (PFWT) and maximal walking time (MWT) and had blood analyses [for haematocrit, fibrinogen, triglycerides, and cholesterol: total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL)] done at baseline and after 6 and 12 weeks of the study. Results: Total and LDL cholesterol levels in the training group decreased (p < 0.05) by 14.8% and 20,5%, respectively. Significant (p < 0.05) HDL cholesterol increased (14.6%) and triglycerides decreased (19%) in the training group but changes of all these lipids were insignificant in the control group over the 3 months. Haematocrit and fibrinogen changes were insignificant in both groups. PFWT was prolonged by 109% and MWT increased by 54% in the training group (p < 0.01), but not in the control group. Conclusion: The improvement in walking time over 3 months of pain-free treadmill training parallels with progressive normalization of lipid profiles in patients with claudication.

Exercise Capacity in Pediatric Patients with Inflammatory Bowel Disease

OBJECTIVE To examine exercise capacity in youth with Crohns disease (CD) and ulcerative colitis (UC). STUDY DESIGN Eleven males and eight females with CD and six males and four females with UC participated. Patients performed standard exercise tests to assess peak power (PP) and mean power (MP) and peak aerobic mechanical power (W(peak)) and peak oxygen uptake (VO(2peak)). Fitness variables were compared with reference data and also correlated with relevant clinical outcomes. RESULTS Pediatric patients with inflammatory bowel disease had lower PP (∼90% of predicted), MP (∼88% of predicted), W(peak) (∼91% of predicted), and VO(2peak) (∼75% of predicted) compared with reference values. When patients with CD or UC were compared separately to reference values, W(peak) was significantly lower only in the CD group. No statistically significant correlations were found between any exercise variables and disease duration (r = 0.01 to 0.14, P = .47 to .95) or disease activity (r = -0.19 to -0.31, P = .11 to .38), measured by pediatric CD activity index or pediatric ulcerative colitis activity index. After controlling for chronological age, recent hemoglobin levels were significantly correlated with PP (r = 0.45, P = .049), MP (r = 0.63, P = .003), VO(2peak) (r = 0.62, P = .004), and W(peak) (r = 0.70, P = .001). CONCLUSIONS Pediatric patients with inflammatory bowel disease exhibit impaired aerobic and anaerobic exercise capacity compared with reference values.

Fluid Balance and Dehydration in the Young Athlete Assessment Considerations and Effects on Health and Performance

Many young athletes train and compete under conditions that put their body fluid balance at risk, and hypohydration is usually the major concern. Another less frequent condition is hyperhydration that—if accompanied by other risk factors—may cause hyponatremia. Water and electrolyte losses during physical activities occur primarily from sweat. Such losses have been identified mostly in active (but nonathletic) young populations under laboratory settings. Studies have been trying to estimate fluid losses in the athletic population under field conditions, taking into account the sport modality and environmental conditions. Besides these external conditions, young athletes adopt different drinking attitudes, which may depend on knowledge, education, and the opportunities to drink during the break periods as well as fluid availability. Focusing on the young athlete, this review will discuss water and sodium losses from sweat, the effects of hypohydration on performance, and fluid intake attitudes within and during practices and competitions. Some considerations related to the methods of identifying hydration status and guidelines are also given, with the understanding that they should be individually adapted for the athlete and activity. The young athlete, parents, coaches, and athletic/health professionals should be aware of such information to prevent fluid imbalances and the consequent hazardous effects on performance and health.

Effect of milk consumption on rehydration in youth following exercise in the heat

Low-fat milk is thought to be an effective postexercise rehydration beverage in adults; however, little is known about milks rehydration ability in children after exercising in the heat. This study tested the hypothesis that because of its electrolyte and protein content, skim milk (SM) would be more effective than both water (W) and a carbohydrate/electrolyte solution (CES) in replacing body fluid losses in children following exercise in the heat. Thirty-eight (19 females) heat-acclimated pre- to early pubertal (PEP, aged 7-11 years) and mid- to late-pubertal (MLP, aged 14-17 years) children performed 3 sessions in 34.5 °C, 47.3% relative humidity, consisting of 2 × 20-min cycling bouts at 60% peak oxygen uptake followed by consumption of either W, CES, or SM. Each beverage was consumed immediately after exercise in a volume equal to 100% of their body mass loss during exercise. Urine samples were collected before, during, and after exercise, as well as the 2-h period following beverage consumption. On average, children dehydrated 1.3% ± 0.4%. Children ingested 0.40 ± 0.11 L (PEP) and 0.74 ± 0.20 L (MLP) of fluid. The fraction of the ingested beverage retained at 2 h of recovery was greater with SM (74% ± 18%) than W (47% ± 26%) and CES (59% ± 20%, p < 0.001 for both), and greater in CES than W (p < 0.001). All participants were in a hypohydrated state after 2 h of recovery, following the pattern SM < CES < W. In both PEP and MLP children, SM is more effective than W and CES at replacing fluid losses that occur during exercise in the heat.

Effects of postexercise milk consumption on whole body protein balance in youth

In adults, adding protein to a postexercise beverage increases muscle protein turnover and replenishes amino acid stores. Recent focus has shifted toward the use of bovine-based milk and milk products as potential postexercise beverages; however, little is known about how this research translates to the pediatric population. Twenty-eight (15 girls) pre- to early pubertal (PEP, 7-11 yr) and mid- to late-pubertal (MLP, 14-17 yr) children consumed an oral dose of [(15)N]glycine prior to performing 2 × 20-min cycling bouts at 60% V̇O(2 peak) in a warm environment (34.5°C, 47.3% relative humidity). Following exercise, participants consumed either water (W), a carbohydrate-electrolyte solution (CES), or skim milk (SM) in a randomized, cross-over fashion in a volume equal to 100% of their body mass loss during exercise. Whole body nitrogen turnover (Q), protein synthesis (S), protein breakdown (B), and whole body protein balance (WBPB) were measured over 16 h. Protein intake from SM was 0.40 ± 0.10 g/kg. Over 16 h, Q and S were significantly greater (P < 0.01) with SM than W and CES. B demonstrated a trend for a main effect for beverage (P = 0.063). WBPB was more negative (P < 0.01) with W and CES than with SM. In the SM trial, WBPB was positive in PEP, although it remained negative in MLP. Boys exhibited significantly more negative WBPB than girls (P < 0.05). Postexercise milk consumption enhances WBPB compared with W and CES; however, additional protein intake may be required to sustain a net anabolic environment over 16 h.

Responses of children with cerebral palsy to arm-crank exercise in the heat.

PURPOSE In response to passive heating, adults with hemispheric brain infarction demonstrate lower skin temperatures (Tsk) and higher sweating rates (SR) on the affected side. It is unknown whether children with similar conditions demonstrate a similar response and whether this response is advantageous to defending body temperature during exercise in the heat. The purpose of this study was to determine whether children with spastic cerebral palsy (CP) demonstrate less thermal strain than healthy peers during short (10 min each) bouts of arm cranking, a mode of exercise where metabolic rate can be matched between the two groups. METHODS Eleven young people (8.3-18.3 yr) with spastic CP and 11 individually matched (body size, age, and maturity) healthy controls (CON) performed 3 x 10-min arm-cranking bouts (40 rpm) in 35 degrees C, 50% RH. Body mass, metabolic and heart rate (HR) responses, and body temperatures were periodically measured. Individuals within each CP-CON pair worked at the same intensity (0.55 +/- 0.18 W.kg-1 body mass). Data were analyzed using a repeated measures ANOVA (alpha = 0.05). RESULTS Subjects with CP showed no difference from CON in metabolic and HR responses, or SR (as inferred from body mass changes corrected for fluid intake and output). There were also no differences between the groups in the rectal temperature change from room temperature (21-23 degrees C). The increase in Tsk from room temperature, however, was slightly (0.6 degrees C) but significantly lower (P < 0.0001; 95% CI = 0.5-0.7 degrees C) in the subjects with CP compared with CON. CONCLUSION Subjects with CP demonstrate thermal strain responses similar to CON during upper-body exercise at relatively low intensities for short duration in a warm climate.

Water, Hydration and Sports Drink

Hypohydration has more consistently been proven to impair aerobic and high intensity endurance activities than muscular strength and cognitive activities. During exercise, as hypohydration reaches levels >3%, core temperature rise may be accentuated and pose health risks. This is of special concern in children and adolescents as well as older individuals who may be more susceptible to heat-related diseases, especially when exercise is performed in warm conditions. A fluid replacement plan is then necessary if hypohydration is expected due to intense sweating. Under some circumstances, ingestion of beverages, known as sports drinks, containing a proper mixture of electrolytes and carbohydrate have shown some benefits compared with plain water. Inclusion of other ingredients (caffeine, vitamins, taurine) has not been proven efficacious and may indeed cause adverse effects. Given the widespread consumption of these beverages, practical recommendations regarding their use, timing, and optimal composition are needed.

Anaerobic muscle performance of children after long-term recovery from Guillain-Barré syndrome.

The aim of this study was to evaluate anaerobic muscle performance in children after long‐term recovery from Guillain‐Barré syndrome (GBS). Participants were recruited from all children and adolescents with GBS admitted to The Hospital for Sick Children, University of Toronto, Canada, between 1988 and 1995. We assessed 17 children (nine males, eight females; mean age at GBS diagnosis 7 years 11 months, SD 4 years 2 months; mean age at testing 14 years 1 month) more than two years after acute GBS. Participants completed the Wingate anaerobic test to evaluate mean and peak muscle power. For mean arm muscle power (mean 47.5% [SD 17.4%] of normal), only two participants were in the normal range. For mean leg muscle power (mean 83% [SD 28.3%] of normal), 15 participants were in the normal range. For arm peak power (mean 92.6% [SD 20.7%] of normal), 12 participants were in the normal range. For leg peak power (mean 116.3% of normal, SD 15.8%), all participants were in the normal range. Detailed manual muscle testing with the modified Medical Research Council scale was done on 34 muscle groups. Data were pooled to give a mean arm and leg muscle strength score (9.7, SD 0.30 and 9.4, SD 0.50 respectively). Pearsons correlations of muscle endurance with arm and leg strength were not significant. Children with GBS have excellent long‐term recovery of peak muscle power. Muscle endurance, measured by mean muscle power, was normal in the legs but markedly low in the arms. Pediatric rehabilitation programs after GBS should specifically target endurance of arm muscles.