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.
Hermann-J. Engels, John C. Wirth, Sueda Celik and Jodee L. Dorsey
Stephen H. Wong, Clyde Williams and Neville Adams
This randomized, double-blind study examined the effects of rehydration per se and rehydration plus carbohydrate (CHO) ingestion during recovery (REC) on subsequent endurance running capacity. Nine men ran at 70% V̇O2max on a level treadmill for 90 min (Tl) on two occasions, followed by a 4 hour REC and a further exhaustive run at the same speed (T2). During the first 3 hours of REC, subjects drank either a 6.9% CHO-electrolyte solution (CE) or a CHO- and electrolyte-free sweetened placebo (PL) every 30 min. Volumes prescribed were 200% of the fluid lost after Tl. but the actual volume of fluid ingested during the REC ranged from 113–200% and 88.5–200% of the body mass lost for the CE and PL trials (NS). However, positive fluid balance was found in both trials after REC. During T2. run time was 24.3 ± 4.4 min longer in the CE trial (69.3 ± 5.5 vs. 45.0 ± 4.2 min; p < .05). Higher blood glucose concentrations were observed throughout REC in the CE trial. These results suggest that ingesting a CHO-electrolyte solution is more effective in restoring endurance capacity compared to the same large volume of placebo, even though complete rehydration was achieved in both trials.
Paolo C. Colombani, Eva Kovacs, Petra Frey-Rindova, Walter Frey, Wolfgang Langhans, Myrtha Arnold and Caspar Wenk
A field study was performed to investigate the acute influence of a milk protein hydrolysate supplemented drink (CHO+PRO) on metabolism during and after a marathon run compared to the same drink without protein (CHO). Carbohydrate metabolites and hormones were not influenced by CHO+PRO. Levels of plasma free fatty acids were significantly lower and levels of urea and most amino acids were significantly higher with CHO+PRO. Sweat urea and ammonia nitrogen excretion during the run as well as urinary 3-methylhistidine excretion during the entire exercise day was similar with both treatments. Urinary total nitrogen was significantly increased and urinary pH decreased with CHO+PRO. It was concluded that the supplemented protein was absorbed and probably at least partially oxidized during the run and that no obvious negative metabolic effects occurred. CHO+PRO did not acutely affect myofibrillar protein breakdown as assessed by the 3-methylhistidine method: however, total body protein breakdown was not measured.
Mahmoud S. El-Sayed, Angelheart J.M. Rattu, Xia Lin and Thomas Reilly
We examined the effects of active warm-down (AWD) and carbohydrate ingestion on plasma levels of free fatty acids (FFAs) and glucose changes into recovery following prolonged submaximal exercise. Subjects in Group 1 cycled at 70% of maximal oxygen uptake (
James L. Seale, Robert S. VanZant and Joan M. Conway
Fifteen adult male volunteers were assigned to sedentary, moderately strength-trained, and moderately endurance-trained groups (5 per group) to determine the effect of exercise training on energy expenditure (EE). Subjects were matched for age, weight, and height. Group appointments were based on activity questionnaires and American College of Sports Medicine standards. Subjects consumed a mixed diet of 40% fat, 20% protein, and 40% carbohydrate at weight maintenance intake for 3 weeks while continuing their exercise training programs. There was no significant difference between groups for 24-hr EE measured in the controlled environment of a room-sized calorimeter. Free-living EE measured with
Michael I. Goran
The doubly labeled water technique represents an unobtrusive and noninvasive means to measure total daily energy expenditure in free-living human subjects who are unaware that energy expenditure is being measured. When combined with measurement of resting energy expenditure, the doubly labeled water technique can also be used to estimate energy expenditure related to physical activity. The relatively recent availability of the doubly labeled water technique in humans has led to several advances in the fundamental understanding of whole body energy metabolism in several important areas. The purpose of this paper is to review the areas in which the doubly labeled water technique has specifically advanced our understanding of whole-body energy metabolism in young children.
Kimberly M. White, Roseann M. Lyle, Michael G. Flynn, Dorothy Teegarden and Shawn S. Donkin
The purpose of this study was to test the effect of acute dairy calcium intake on exercise energy metabolism and endurance performance. Trained female runners completed two trials. Each trial consisted of a 90-min glycogen depletion run followed by a self-paced 10K time trial, conducted one hour after consumption of a high dairy (500 mg Ca+2) or low dairy (80 mg Ca+2) meal. During the 90-min run, blood samples and respiratory gases were collected. No treatment main effects of acute dairy intake were found for respiratory exchange ratio (RER), calculated fat oxidation, lactate, glycerol, or 10K time. Following this protocol, acute dairy calcium intake did not alter fat utilization or endurance performance in trained female runners.
Douglas R. Seals, Kevin D. Monahan, Christopher Bell, Hirofumi Tanaka and Pamela P. Jones
Tonic vagal modulation of cardiac period (R-R interval) decreases with advancing age, but is greater in middle-aged and older adults who habitually perform aerobic exercise compared with their sedentary peers. Cardiovagal baroreflex sensitivity also declines markedly with age in sedentary adults but only 50% as much in regularly exercising adults. In previously sedentary middle-aged and older adults, a 3-month program of moderate aerobic exercise increases cardiovagal baroreflex sensitivity by 25%. Tonic (basal) sympathetic nervous system (SNS) activity increases with advancing age in both sedentary and habitually exercising adults. Despite this, SNS b-adrenergic support of energy metabolism (resting metabolic rate-RMR) declines with age in sedentary individuals. However, SNS b-adrenergic support of RMR is maintained with age inenduranceexercise-trainedadultsandthereforeismuchgreaterinmiddle-aged and older individuals who exercise regularly compared with their sedentary peers. Thus, regular aerobic (endurance) exercise modulates selective age associated impairments in autonomic nervous system-physiological function.
Richard B. Kreider
The physiological effects of endurance exercise have been a primary area of research in exercise science for many years. This research has led not only to a greater understanding of human physiology but also the limits of human performance. This is especially true regarding the effects of endurance exercise on energy metabolism and nutrition. However, as science has attempted to understand the physiological and nutritional demands of endurance exercise lasting 1 to 3 hours, an increasing number of athletes have begun participating in ultraendurance events lasting 4 to 24 hours. Consequently some research groups are now investigating the physiological responses to ultraendurance training and performance. This paper reviews the literature on ultraendurance performance and discusses nutritional factors that may affect bioenergetic, thermoregulatory, endocrinological, and hematological responses to ultraendurance performance.
Kathleen Woolf and Melinda M. Manore
The B-vitamins (thiamin, ribofavin, vitamin B-6) are necessary in the energy-producing pathways of the body, while folate and vitamin B-12 are required for the synthesis of new cells, such as the red blood cells, and for the repair of damaged cells. Active individuals with poor or marginal nutritional status for a B-vitamin may have decreased ability to perform exercise at high intensities. This review focuses on the B-vitamins and their role in energy metabolism and cell regeneration. For each vitamin, function related to physical activity, requirement, and status measures are given. Research examining dietary intakes and nutritional status in active individuals is also presented. Current research suggests that exercise may increase the requirements for ribofavin and vitamin B-6, while data for folate and vitamin B-12 are limited. Athletes who have poor diets, especially those restricting energy intakes or eliminating food groups from the diet, should consider supplementing with a multivitamin/mineral supplement.