Search Results

You are looking at 1 - 2 of 2 items for

  • Author: John C. Wirth x
  • Refine by Access: All Content x
Clear All Modify Search
Restricted access

Influence of Caffeine on Metabolic and Cardiovascular Functions during Sustained Light Intensity Cycling and at Rest

Hermann-J. Engels, John C. Wirth, Sueda Celik, and Jodee L. Dorsey

This study assessed the influence of caffeine on metabolic and cardiovascular functions during sustained, light intensity cycling and at rest. Eight healthy, recreationally active adults participated in four randomly assigned, double-blind experimental trials of 60 min upright seated cycle exercise (30% VO2max) or equivalent rest with caffeine (5 mg ⋅ kg−1) or placebo consumed 60 min prior to data collection. Gas exchange was measured by open-circuit spirom-etry indirect calorimetry. Global blood flow was evaluated by thoracic impedance cardiography and arterial blood pressure by auscultation. A repeated measures ANOVA indicated that pretrial caffeine increased oxygen uptake and energy expenditure rate (p < 0.05) but did not change respiratory exchange ratio. Systolic, diastolic, and mean arterial blood pressure were elevated following caffeine intake (p < 0.05). Cardiac output, heart rate, stroke volume, and systemic vascular resistance were not significantly different between caffeine and placebo sessions. For each of the metabolic and hemodynamic variables examined, the effects of caffeine were similar during constant-load, light intensity cycling and at rest. These data illustrate that caffeine's mild thermogenic influence can be mediated without a major shift in substrate oxidation mixture. Caffeine at this dosage level alters cardiovascular dynamics by augmenting arterial blood pressure.

Restricted access

Predictors of Social Physique Anxiety in Elite Female Youth Athletes

Jeffrey J. Martin, Hermann J. Engels, John C. Wirth, and Kari L. Smith

The purpose of this study was to examine predictors of social physique anxiety (SPA). SPA, self-esteem, body-esteem, public body consciousness (PBC) and percent body fat (%BF) were assessed with elite female youth athletes (̲N=68) competing in either figure skating, soccer or gymnastics. Stepwise multiple regression analyses, controlling for BF%, accounted for 59% of the variance in SPA. Self-esteem entered first, after BF%, followed by body-esteem and PBC. The psychological variables accounted for 57% of the variance with self-esteem contributing the most (R square change = 45%). Contrary to previous research, BF% did not significantly contribute to SPA. Additionally, a MANOVA and follow-up ANOVA and Scheffe’s tests revealed significant sport differences among SPA, self-esteem, and body-esteem.