The growing prevalence and popularity of interval training necessitate additional guidelines in regard to maximal levels of time and intensity. Purpose: To correlate salivary hormones and time in varying heart-rate (HR) zones. The hypothesis was that chronic exercise durations >9% of total exercise time in the >90% maximum HR zone would lead to decreased variation in salivary cortisol concentration after exercise in a 2-bout high-intensity protocol compared with less or more time in this zone. Methods: A total of 35 healthy adults who regularly exercised for an average of 8 hours per week recorded their HR during every training session for 3 weeks. Later, they completed an experimental day composed of two 30-minute high-intensity interval sessions separated by 4 hours of nonactive recovery. The authors collected saliva samples before, immediately following, and 30 minutes after each exercise session to assess changes in cortisol concentrations. Results: There was a correlation between weekly time training at an intensity >90% maximum HR and the variables associated with overtraining. Salivary cortisol concentration fluctuated less in the participants who exercised in this extreme zone for >40 minutes per week (P < .001). Conclusion: Based on the current study data, for individuals who regularly exercise, 4% to 9% total training time above 90% maximum HR is the ideal duration to maximize fitness and minimize symptoms related to overreaching.
Jinger S. Gottschall, Joshua J. Davis, Bryce Hastings and Heather J. Porter
Brittany G. Travers, Heather L. Kirkorian, Matthew J. Jiang, Koeun Choi, Karl S. Rosengren, Porter Pavalko and Paul Jobin
Folding paper is a seemingly simple act that requires planning, bimanual coordination, and manual strength and control to produce specific forces. Although paper folding has been used as an assessment tool and as a way to promote spatial skills, this study represents the first attempt to document when paper folding emerges across early childhood. Seventy-seven children (ages 18 months to 7 years) and an adult reference group (24 college-aged adults) completed three pre-specified folds on a single piece of paper. Dependent variables included whether children attempted each fold and, if so, the accuracy of each fold. Grip strength, pinch strength, and developmental level were examined as potential correlates of paper folding. The results demonstrated that paper folding emerges as early as 27 months of age but becomes more accurate with age. At least 50% of children between 4 and 5.5 years of age completed folds. Additionally, children with more age-appropriate problem-solving skills attempted more folds, independent of age. These findings provide a descriptive framework for the ages at which paper folding emerges and suggest that paper-folding interventions could be implemented at even earlier ages than what previously has been examined.