Effect of a Meal on Cardiopulmonary and Metabolic Changes During Exercise

Abstract

Four subjects exercised at two levels of power output, approximating to 30% and 60% of their maximum O2 uptake, on three occasions: after a 24-h fast, after a 12-h fast, and 1 h after a 3000 Cal mixed meal. Measurements during exercise did not show any consistent effect on O2 uptake or heart rate. CO2 output, the respiratory exchange ratio, and ventilation were increased following the meal. Changes in blood lactate and the lactate/pyruvate ratio were variable and small. The increase in blood glycerol with exercise was least following the meal, indicating a lower level of fat mobilization; blood free fatty acids were lower. Blood glucose fell (from high resting levels) in three subjects following the meal, suggesting an increased usage of blood-borne glucose. The physiological effects of a meal on exercise performance in healthy subjects appear to be due mainly to inhibition of free fatty acid mobilization. This leads to an increased usage of carbohydrate energy sources, higher respiratory exchange ratio, and CO2 output, in turn leading to higher ventilation. No cardiovascular effects were detected.

The Reproducibility of the Respiratory Responses to Maximum Exercise

“…We at tribute the changes in VCO2 to lunch time carbohydrate loading despite having in structed the volunteers to eat only light meals and were associated with signifi cantly increased Ve for the group as a whole (p<0.05). Jones and Haddon [9] have shown significant increases in VCO2, R and Ve 1 h after a 3,000-calorie meal. Our results indicate that the effect of a carbohydrate meal on VCO2 and R per sists for much longer than 1 h since the av erage time between lunch and the exercise period for our subjects was over 2 h. Since an average of 8 h elapsed between the morning and afternoon studies, it is un likely that there would be any carryover of the effects of the first study on the second of the same day.…”

Absence of long-term modulation of ventilation by dead-space loading during moderate exercise in humans

“…In addition, our demonstration of a progressively falling RER during exercise over the course of the conditioning and post-conditioning trials is strongly suggestive of a shift in the metabolic substrate towards fat, with a predictable decrease in _ QCO 2 (and increase in muscle O 2 consumption) -our subjects being post-absorptive at the start of the study. The reduced _ QCO 2 , when transformed to _ V CO 2 , would require an equivalent reduction in _ V E (Jones and Haddon 1973). Neither our study design (nor that of previous investigations) allowed us to rule out such possibilities.…”

“…Also, as such associative conditioning studies are lengthy (lasting several hours), the substrate mixture undergoing oxidation might shift progressively towards fat utilisation, with a reduced metabolic CO 2 production (QCO 2 ) and _ V CO 2 . This, in turn, would be expected to induce a similarly progressive reduction in _ V E (Jones and Haddon 1973;Ward et al 1983). However, with the exception of Martin and Mitchell's study on conscious goats (1993) and a brief report from Turner et al (1996) in humans, no V D -based LTM studies have taken _ V CO 2 into account when interpreting post-conditioning _ V E responses.…”

The Assessment of 24-Hour Energy Expenditure in Elderly Women by Minute-by-Minute Heart Rate Monitoring

“…1 the mean HR over the 3 days would have been only 3 beats/ min lower, calculated TEEnRind would have been 9.9 MJ/day instead of 11.7MJ/day, which is substantially lower. HR is influenced not only by the level of physical activity but also by other factors such as coffee consumption, mental stress, illness and posture during activi ties, all of which will increase HR [ 15,[24][25][26][27], Especially when subjects have an activity pat tern which is low to moderate, these effects will have a relatively high impact on the energy expenditure estimated from HR and will al ways result in an overestimation of TEE.…”