The purpose of this study was to determine if changes in heart rate variability during incremental exercise could be used to estimate lactate threshold and ventilatory threshold in healthy adults. Twenty-four adults performed graded maximal cycle ergometry to volitional fatigue. Blood lactate, heart rate, RR interval, and respiratory gas exchange were monitored. Heart rate variability was analyzed using time domain indices (standard deviation and mean successive difference). A marked RR interval deflection point was found in the region of lactate threshold and ventilatory threshold, and was identified as the heart rate variability threshold. Mean differences between heart rate variability threshold, ventilatory threshold, and lactate threshold ranged from 0.06 +/- 0.3 to 0.12 +/- 0.2 L.min (-1). Correlations between the different measures ranged from 0.82 - 0.89. A small but significant difference was found between ventilatory threshold and lactate threshold (p < 0.05). There was not a significant difference between heart rate variability threshold and lactate threshold (p > 0.05), nor between heart rate variability threshold and ventilatory threshold (p > 0.05). The data suggest the heart rate variability threshold coincides with lactate threshold and ventilatory threshold during graded exercise and can be used for the detection of lactate threshold in healthy adults.

These findings suggest that a season of training in American football results in a significant decrease in both s-IgA and the secretion rate of s-IgA as well as an increase in the incidence of URTI. Among the various methods commonly employed to express s- IgA levels, the secretion rate of s-IgA may be the most useful clinical biomarker to predict the incidence of URTI.

This study examined the effectiveness of a unique extracurricular after-school initiative designed to promote healthy diets and exercise in urban African Americans. The Students and Parents Actively Involved in Being Fit after-school program was offered for 12 weeks to students and their parents/guardians at an urban middle school. Specific aims of the intervention were to increase participants' vegetable and fruit intake by using established 5 A Day for Better Health educational resource materials/activities and to affect their health-related fitness through dance, games, and fitness activities. Fifty-six children and 25 parents/guardians completed a standard battery of evaluations before and after the program. Pre-post pairwise t test revealed that both children and their parents/guardians showed an increase in fruit consumption and a reduction in diastolic blood pressure (P <.05). Moreover, children showed improvements in systolic blood pressure and fruit juice, salad, and nonfried potato consumption while parents/guardians showed a decrease in body fat, body mass index, and endurance walk/run time (P <.05). Overall, findings indicate that children tended to gain more diet-related benefits while parents/guardians tended to derive more fitness-related benefits. After-school programs like the Students and Parents Actively Involved in Being Fit initiative can potentially contribute to improved health levels in urban African Americans.

Caffeine intake is associated with an increase in heart rate (HR) variability. This study sought to examine the effects of caffeine on HR variability measures before and during progressive exercise in 11 healthy volunteers in a double-blind randomized and counterbalanced placebo-controlled paradigm. As expected, there were significant increases in HR and decreases in HR variability after exercise during both placebo and caffeine conditions; however, pre-exercise caffeine condition was associated with a significant increase of HR variability, especially in the high-frequency range (0.15-0.5 Hz), and also approximate entropy (APEN), which is usually attributed to cardiac vagal function. But during progressive exercise, caffeine intake resulted in a greater decrease of HF power as well as HR APEN. Caffeine also was associated with significantly higher LF power during exercise compared to the placebo condition. These results suggest that caffeine may have different effects on HR variability at rest, compared to exercise. These findings may have implications for patients with cardiac illness and anxiety, depression, and psychotic disorders who use beverages containing excessive caffeine.

The Transtheoreticai Model of behavior change was applied to a sample of 669 preadolescents (M age = 8.2) to determine whether stages of exercise could be observed. Associations between stage of exercise classification and demographic, fitness, and cognitive variables were examined. Stage of exercise classifications, on the basis of the Children’s Stage of Exercise Algorithm, were as follows: maintenance (50.8%), action (36.5%), preparation (3.1%), contemplation (4.9%), and precontemplation (4.6%). Stage of exercise was significantly related to gender, age, and grade level. Controlling for these differences, the relationship between exercise beliefs and stage of exercise was significant.