Exercise tolerance and thermoregulatory responses during cycling in boys and men.

PURPOSE: Physiological responses to exercise in the heat differ between prepubertal children and young adults. Whether these maturity-related variations imply lower exercise tolerance, inferior thermoregulation, and greater risk for heat injury in the child is uncertain. This study directly compared thermoregulatory and cardiovascular responses as well as endurance performance between prepubertal boys and adult males during steady-load cycling in moderately hot and cool ambient conditions with moderate humidity. METHODS: Eight prepubertal boys (age 11.7 +/- 0.4 yr) and eight adult men (age 31.8 +/- 2.0 yr) performed steady-load cycling to exhaustion at an intensity equivalent to approximately 65% peak V O2 in both hot (approximately 31 degrees C) and cool (approximately 19 degrees C) environments, with fluid intake ad libitum. RESULTS: Exercise duration in the heat was shorter for both groups (hot: men 30.46 +/- 8.84 min, boys 29.30 +/- 6.19 min; cold: men 42.88 +/- 11.79 min, boys 41.38 +/- 6.30 min), with no significant difference between men and boys (P > 0.05). Increases in rectal temperature, heart rate, and cardiac index were similar between groups and conditions. Stroke index, mean arterial pressure, and arterial venous oxygen difference were stable and similar in both conditions, without group differences. No significant dehydration was observed in men or boys. CONCLUSIONS: This study failed to reveal differences in exercise tolerance, thermoregulatory adaptation, or cardiovascular response to exercise in the heat between euhydrated prepubertal boys and adult men.

Alcohol use associated with cervical spinal cord injury.

OBJECTIVES: To determine whether alcohol use at time of spinal cord injury (SCI) is more common with cervical injury than with lower levels of spinal injury. METHODS: Veterans and nonveterans with SCI were assessed at a Veteran's Affairs Medical Center from 1994 through 2002 and completed a health questionnaire that included information on alcohol use at time of traumatic injury. RESULTS: Of 362 men, 45% had neurologically complete or incomplete cervical injuries. Participants with cervical injury were more likely to have used alcohol when injured (62/162, 38%) compared with participants without cervical injury (45/200, 23%). Adjusting for age at injury and accident type, participants with cervical SCI had an increased relative odds of having used alcohol at injury compared with participants without cervical SCI (2.06, 95% confidence interval = 1.24-3.43). CONCLUSION: Alcohol use at time of SCI is a risk factor for cervical injury. This finding is of public health concern and should be included in alcohol educational programs.

Prepregnancy weight, gestational weight gain, and risk of growth affected neonates.

BACKGROUND: In 2009, the Institute of Medicine published revised gestational weight gain (GWG) guidelines with changes notable for altered body mass index (BMI) categorization as per World Health Organization criteria and a stated range of recommended gain (11-20 pounds) for obese women. The goal of this study was to evaluate associations between maternal BMI-specific GWG adherence in the context of these new guidelines and risk of small for gestational age (SGA) and large for gestational age (LGA) neonates. METHODS: Subjects were a retrospective cohort of 11,203 live birth singletons delivered at 22-44 weeks at a Massachusetts tertiary care center between April 2006 and March 2010. Primary exposure was GWG adherence (inadequate, appropriate, or excessive) based on BMI-specific recommendations. SGA and LGA were defined as <10th and ≥90th percentiles of U.S. population growth curves, respectively. The association between GWG adherence and SGA and LGA was examined in polytomous logistic regression models that estimated adjusted odds ratios (AOR) stratified by prepregnancy weight status, controlling for potential confounders. RESULTS: Before pregnancy, 3.8% of women were underweight, 50.9% were normal weight, 24.6% were overweight, and 20.6% were obese. Seventeen percent had inadequate GWG, and 57.2% had excessive GWG. Neonates were 9.6% SGA and 8.7% LGA. Inadequate GWG was associated with increased odds of SGA (AOR 2.51, 95% confidence interval [CI] 1.31-4.78 for underweight and AOR 1.78, 95% CI 1.42-2.24 for normal weight women) and decreased odds of LGA (AOR 0.5, 95% CI 0.47-0.73 for normal weight and AOR 0.56, 95% CI 0.34-0.90 for obese women). Excessive GWG was associated with decreased odds of SGA (AOR 0.59, 95% CI 0.47-0.73 for normal weight and AOR 0.64, 95% CI 0.47-0.89 for overweight women) and increased odds of LGA (AOR 1.76, 95% CI 1.38-2.24 for normal weight, AOR 2.99, 95% CI 1.92-4.65 for overweight, and AOR 1.55, 95% CI 1.10-2.19 for obese women). CONCLUSIONS: Efforts to optimize GWG are essential to reducing the proportion of SGA and LGA neonates, regardless of prepregnancy BMI.

Impact of updated Institute of Medicine guidelines on prepregnancy body mass index categorization, gestational weight gain recommendations, and needed counseling.

BACKGROUND: Our objective was to quantify how the 2009 revisions of the 1990 Institute of Medicine (IOM) gestational weight gain (GWG) guidelines change women's body mass index (BMI) categorization and BMI-specific GWG adherence categories. The goal was to identify how provider counseling practices need to change on a population level. METHODS: A retrospective review of automated labor and delivery records from a tertiary care hospital in Central Massachusetts was performed. The study cohort included women who delivered singleton, live birth gestations from from April 1, 2006, to September 30, 2009. Records missing weight, height, GWG, gestational age (GA), and/or GA <22 or >43 weeks were excluded. BMI groups and GWG adherence were categorized according to IOM 1990 and 2009 recommendations. Adherence analyses included full-term gestations only. RESULTS: The cohort consisted of 11,688 women, mean age 28.9 (±6.1) years and mean parity 1.0 (±1.1). By 1990 recommendations, 10.1%, 52.5%, 14.1%, and 23.3% gravidas were low weight, normal weight, high weight, and obese; and 19.8%, 33.3%, and 46.9% were undergainers, appropriate gainers, and overgainers, respectively. By 2009 recommendations, 3.9%, 51.3%, 24.5%, and 20.3% gravidas were underweight, normal weight, overweight, and obese, and 16.7%, 30.8%, and 52.6% were undergainers, appropriate gainers, and overgainers, respectively. Differences in categorization by guideline year was significant for BMI category (p<0.0001) and GWG adherence (p<0.0001). Compared to 1990 guidelines, 16.7% of women were classified differently using 2009 guidelines, with fewer classified as underweight, normal weight, or obese and more as overweight; 17.1% of 1990 appropriate gainers would be classified as overgainers, given new guidelines. CONCLUSIONS: Changes in IOM GWG recommendations alter gravidas' BMI categories and, thus, the recommended GWG. As the amount advised is associated with actual gain, accuracy is paramount. GWG is a modifiable parameter associated with immediate and long-term maternal/neonatal health outcomes, and counseling can have a significant public health impact and should involve BMI determination, followed by BMI-specific GWG recommendations in accordance with current guidelines.

Cardiovascular drift in euhydrated prepubertal boys.

"Classic" cardiovascular drift is characterized by findings of decreasing stroke volume and mean arterial pressure, rising heart rate, and stable cardiac output during sustained constant-load exercise. Recent studies in adults indicate that when dehydration is prevented by fluid intake, this pattern is altered, with no change in stroke volume and progressive rise in cardiac output. This study was designed to examine this influence of hydration in prepubertal subjects and assess the relationship between cardiovascular drift and aerobic drift (changes in VO2). Eight boys (Tanner stage 1, mean age 11.7 +/- 0.4 y) cycled at an average of 62.9% +/- 3.9% VO2 peak to exhaustion (41.38 +/- 6.30 min) in a thermoneutral environment. Rectal temperature rose from 37.6 +/- 0.1 degrees C at rest to 38.1 +/- 0.2 degrees C at end exercise. Between 5 min and end exercise, average heart rate rose by 13.2% and cardiac output rose by 14.9%, systemic vascular resistance fell by 10.5%, and stroke volume remained stable. Increases in cardiac output paralleled those of VO2, with no change in arterial venous oxygen difference. These findings are consistent with the conclusion that cardiovascular drift is a reflection of aerobic drift, a relationship obscured by the superimposed physiological effects of dehydration during sustained constant load. This study also suggests that such patterns are no different in prepubertal boys and young adult men.