Metabolic Cost Of Exercise Research Articles

Reduced Nonexercise Activity Attenuates Negative Energy Balance in Mice Engaged in Voluntary Exercise.

Exercise alone is often ineffective for treating obesity despite the associated increase in metabolic requirements. Decreased nonexercise physical activity has been implicated in this resistance to weight loss, but the mechanisms responsible are unclear. We quantified the metabolic cost of nonexercise activity, or "off-wheel" activity (OWA), and voluntary wheel running (VWR) and examined whether changes in OWA during VWR altered energy balance in chow-fed C57BL/6J mice (n = 12). Energy expenditure (EE), energy intake, and behavior (VWR and OWA) were continuously monitored for 4 days with locked running wheels followed by 9 days with unlocked running wheels. Unlocking the running wheels increased EE as a function of VWR distance. The metabolic cost of exercise (kcal/m traveled) decreased with increasing VWR speed. Unlocking the wheel led to a negative energy balance but also decreased OWA, which was predicted to mitigate the expected change in energy balance by ∼45%. A novel behavioral circuit involved repeated bouts of VWR, and roaming was discovered and represented novel predictors of VWR behavior. The integrated analysis described here reveals that the weight loss effects of voluntary exercise can be countered by a reduction in nonexercise activity.

Effect of whole-body microtitanium-treated garments on metabolic cost of exercise following strenuous hill running

To determine the effect size of wearing sports garments treated with microscopic titanium particles (AQUA TITAN) during recovery from strenuous running on the restoration of running economy during subsequent exercise. A double-blind crossover was used to determine the effect of AQUA TITAN on running metabolic cost in 10 healthy men. Participants performed 40 min of treadmill running comprising 2×(10 min at 5% and 10 min at -10% grade), followed by random allocation to skin-tight nylon-polyurethane AQUA TITAN treated or non-treated placebo garments covering the torso, limbs, and feet. Garments were worn continuously throughout the next 48-h, during which time participants rested (day 2) then completed a graded treadmill run to determine metabolic outcome (day 3). Body-weight normalised running metabolic cost was evaluated by indirect calorimetry and the effect size referenced against the smallest meaningful change in economy (0.9%) for improvement in distance running performance. The fatigue effect while wearing control garments on metabolic cost at 48-h was small (2.2% 95%CL ±1.2%). In contrast, AQUA TITAN garments most certainly reduced running metabolic cost (-3.1% ±0.9%) vs. control. Additionally, AQUA TITAN increased the respiratory exchange ratio (0.011 ±0.005) and lowered minute ventilation at intensities below the ventilatory threshold (-4.0% ±0.9%). AQUA TITAN garments worn during recovery from strenuous exercise improved subsequent running economy to a magnitude likely to restore endurance performance. Future research should verify the magnitude of garment effects on performance outcomes, and on identifying the acute or passive neural, musculotendinous or metabolic mechanisms responsible.

Cardiovascular and metabolic responses at rest and to exercise during 48 hours of head-out immersion: a case report

Head-out immersion in water (HIW) leads to several cardiovascular adjustments. Cardiac output increases by increasing stroke volume with no substantial changes in heart rate (HR) at rest. Therefore, total peripheral resistance to blood flow declines, leading to elevated O2 delivery. During exercise, cardiac output increases for a given workload while the HR response differs in relation to exercise intensity: it does not change during moderate exercise, but decreases during intense exercise. Oxygen uptake does not change either at rest or during exercise. In this case report, we report data on the cardiovascular and metabolic responses in a 29-year-old man at rest and during constant-load exercise during 48 h of HIW. The subject performed constant-load exercise on cycloergometer at 50% VO2max in the laboratory and during 48 h of HIW. Pulmonary gas exchange, VO2 kinetics, HR and rate of perceived exertion were determined. At rest, HR was similar but \(\dot VO_2 \) increased during HIW relative to the laboratory. During exercise, the metabolic cost of exercise was similar and HR was the same during HIW and in the laboratory. \(\dot VO_2 \) kinetics were faster during HIW. The cardiovascular and metabolic responses at rest and during moderate exercise to a few hours of HIW are not different from those during 48 h of HIW.

The Onset And Magnitude Of Cardiovascular Drift Depend On Exercise Intensity In Recreational Runners

Cardiovascular drift (CVD) is a gradual increase in heart rate (HR) during prolonged steady-state exercise. Despite considerable research on the etiology of this complex phenomenon, little is known as to the effects of CVD on energy consumption. PURPOSE: To examine the potential effects of CVD on aerobic and anaerobic metabolism. METHOD: Recreational runners (n=10, age 40.3±8.3 years, height 176±7 cm, weight 71.29±10.76 kg, VO2max 57.29±5.96 ml·kg-1·min-1) volunteered for this study and signed informed consent forms. Each participant performed 5 running tests 2-4 days apart: a maximal oxygen consumption (VO2max) test (2-min stages to exhaustion), a Maximal Lactate Steady State test (MLSS), and 3 prolonged submaximal bouts (45 min duration each) at intensities corresponding to 95%, 100%, and 105% of the MLSS velocity (1% grade). HR and VO2 were recorded continuously throughout all tests; blood lactate was measured at the end of each stage during the first 2 tests, and every 10 minutes for the 3 prolonged bouts. All protocols were approved by the IRB. RESULTS: Only 3 runners were able to complete the 105% MLSS bout. Onset of CVD was different for every participant, often with no HR plateau in the 105% MLSS bout. Small differences in exercise intensity (0.22 m·sec-1) yielded statistically significant (p < 0.05) differences across the three intensities in the amplitude of CVD (increases of 7 BPM, 14 BPM, and 18 BPM for the 95%, 100%, and 105% respectively), VO2 (1.42 ml·kg-1·min-1, 1.8 ml·kg-1·min-1, and 1.39 ml·kg-1·min-1 respectively), and blood lactate (0.25 mmol·L-1, 0.88 mmol·L-1, and 1.08 mmol·L-1 respectively) between steady state and minute 40. CONCLUSION: We successfully measured the small changes associated with the metabolic cost of exercise during CVD. Our data conclusively indicate that the onset of CVD is affected by the intensity of exercise and the amplitude of CVD is greater as exercise intensity increases. Supported by the Mary Stuart Rogers Foundation and an NSF grant (DUE 0511219).

The onset and magnitude of cardiovascular drift depend on exercise intensity in recreational runners.

PURPOSETo examine the potential effects of cardiovascular drift (CVD) on aerobic and anaerobic metabolism.METHODRecreational runners (n=10, age 40.3±8.3years, height 176±7cm, weight 71.29±10.76kg, VO2max 57.29±5.96ml▸kg−1▸min−1) participated and each performed 5 running tests 2‐4 days apart: a VO2max test (2‐min stages to exhaustion), a Maximal Lactate Steady State test (MLSS), and 3 prolonged (45 min) submaximal bouts at intensities corresponding to 95%, 100%, and 105% of the MLSS velocity (1% grade). HR and VO2 were recorded continuously; blood lactate was measured after each stage during the first 2 tests, and every 10 minutes for the 3 prolonged bouts.RESULTSOnset of CVD was different for every participant, often with no HR plateau in the 105% MLSS bout. Small differences in exercise intensity (0.22 m▸sec−1) yielded significant differences (p &lt; 0.05) across the 3 intensities in the amplitude of CVD (increases of 7 BPM, 14 BPM, and 18 BPM for the 95%, 100%, and 105%), VO2 (1.42 ml▸kg−1▸min−1, 1.8 ml▸kg−1▸min−1, and 1.39 ml▸kg−1▸min−1), and blood lactate (0.25 mmol▸L−1, 0.88 mmol▸L−1, and 1.08 mmol▸L−1) between steady state and minute 40.CONCLUSIONWe successfully measured changes associated with the metabolic cost of exercise during CVD. The onset of CVD is affected by the intensity of exercise and the amplitude of CVD is greater as exercise intensity increases.Supported by the Mary Stuart Rogers Foundation and an NSF grant (DUE 0511219).

Gastrointestinal Blood Flow and Postprandial Metabolism in Swimming Sea BassDicentrarchus labrax

In trout and salmon, the metabolic costs of exercise and feeding are additive, which would suggest that gastrointestinal blood flow during exercise is maintained to preserve digestive and absorptive processes related to the specific dynamic action (SDA) of food. However, in most published studies, gastrointestinal blood flow drops during swimming, hypoxia, and general stress. To test whether gastrointestinal blood flow is spared during exercise after feeding, sea bass were instrumented with flow probes to measure cardiac output and celiacomesenteric blood flow while swimming in a respirometer before and after feeding. Swimming at 2 body lengths per second (bl s(-1)) increased metabolic rate considerably more than did feeding (208% vs. 32% increase, respectively, relative to resting), and a similar pattern was observed for cardiac output. In unfed fish, resting gastrointestinal blood flow was 13.8+/-0.5 mL min(-1) kg(-1). After feeding, resting gastrointestinal blood flow increased by 82% but then decreased progressively with increasing swimming speeds. At 2 bl s(-1), gastrointestinal blood flow in fed fish was not significantly different compared with that in unfed swimming fish, and, therefore, the data do not support the gastrointestinal sparing hypothesis. The magnitude of the SDA was maintained despite the decrease in gastrointestinal blood flow and the consequent reduction in oxygen supply to the gut. An estimate of maximal oxygen flow to the gastrointestinal tract after feeding yielded 2.6 mmol O(2) h(-1) kg(-1), but this amount is not able to cover the oxygen demand of 3.16 mmol O(2) h(-1) kg(-1). Therefore, the SDA must reflect metabolic processes in tissues other than those directly perfused by the celiacomesenteric artery.

Evidence that tryptophan reduces mechanical efficiency and running performance in rats

It has been reported that exercise increases brain tryptophan (TRP), which is related to exhaustive fatigue. To study this further, the effect of increased TRP availability on the central nervous system (CNS) with regard to mechanical efficiency, oxygen consumption (VO 2) and run-time to exhaustion was studied in normal untrained rats. Each rat was anesthetized with thiopental (30 mg/kg ip b. wt.) and fitted with a chronic guiding cannula attached to the right lateral cerebral ventricle 1 week prior to the experiments. Immediately before exercise, the rats were randomly injected through these cannulae with 2.0 μl of 0.15 M NaCl ( n=6) or 20.3 μM l-TRP solution ( n=6). Exercise consisted of running on a treadmill at 18 m min −1 and 5% inclination until exhaustion. TRP-treated rats presented a decrease in their mechanical efficiency (21.25±0.84%, TRP group vs. 24.31±0.98%, saline-treated group; P≤.05), and increased VO 2 at exhaustion (40.3±1.6 ml kg −1 min −1, TRP group vs. 36.0±0.8 ml kg −1 min −1, saline group; P≤.05), indicating that the metabolic cost of exercise was higher in the former group. In addition, a highly significant reduction was also observed in run-time to exhaustion of TRP animals compared to those of the saline-treated group (15.2±1.52 min, TRP group vs. 50.6±5.4 min, saline group; P≤.0001). It can be deduced from the data that intracerebroventricular TRP injection in rats increases O 2 consumption and reduces mechanical efficiency during exercise, diminishing running performance.

The ventilatory stress of exercise in obesity.

The effect of obesity as a factor limiting exercise tolerance is described and can be attributed to three mechanisms: (a) the increased metabolic and therefore ventilatory requirement to perform a given work task; (b) the increased metabolic cost of breathing because of interfering chest wall and abdominal obesity and high breathing frequency; and (c) pulmonary insufficiency in response to the high breathing work and lung atelectasis. The role of support and posture minimizing the effect of obesity should be considered when attempting to improve the work tolerance of obese patients. One cannot predict accurately the O2 cost of exercise in the obese patient from the ergometer load because of uncertainties of distribution of the adipose tissue, the uncertain effects on breathing work, and often reduced motor efficiency or skill. The metabolic cost of exercise in the obese patient, therefore, needs to be directly measured; only then can one establish the degree of normality of the physiologic responses to exercise, e.g., heart rate, blood pressure, cardiac output, and minute ventilation.

Effects of small changes of blood volume on oxygen delivery and tissue oxygenation.

Circulatory effects of small (approximately 10%) changes in blood volume were examined in resting and exercising dogs: controls; group A (-200 ml blood); group B (+200 ml blood); group C (+200 ml 6% dextran). In exercise, cardiac output (Q) increased more in Group A than controls (510.4 ml . kg-1 . min-1 compared to 429.6 ml . kg-1 . min-1; P less than 0.05); oxygen delivery (cardiac output x arterial O2 content) and mixed venous oxygen tension (PVO2) were unchanged from exercising controls. Hypervolemia (group B) did not change Q or O2 delivery compared to controls, but caused a greater reduction in exercise PVO2 (29.3 mmHg compared to 33.1 mmHg in controls; P less than 0.01). Resting PVO2 as raised in group C (50.0 mmHg compared to 46.3 mmHg; P less than 0.05) and exercise PVO2 was reduced less (35.5 mmHg compared to 33.1 mmHg in controls; P less than 0.05). O2 delivery in exercise was higher than in controls (123.4 ml . kg-1 . min-1 compared to 94.3 ml . kg-1 . min-1; P less than 0.001). During exercise, O2 consumption was raised from base line to 34.9 ml . kg-1 . min-1 in controls and raised further to 41.4 ml . kg-1 . min-1 in group A, 44.4 ml . kg-1 . min-1 in group B, and 41.2 ml . kg-1 . min-1 in group C (P less than 0.01). Changes of blood volume that lie within physiological limits thus significantly modify the circulatory response to changed O2 requirements, and also change the metabolic cost of exercise.

Metabolic cost of exercise and physical performance in children with some observations on external loading.

The metabolic cost (VO2) of running was studied on a motor-driven treadmill in nine athletic boys, five athletic girls, and nine active boys aged 11--13 years and the results compared with their performance times during racing out of doors. On 15 of the children, additional observations of the effects of external loading on aerobic power output were made. The results showed that VO2 was proportional to body weight in children but when expressed in ml . kg-1 . min-1, VO2 for a given speed of running was significantly higher in children than expected from previously collected data on adults. There were no significant differences between aerobic cost of running of the athletic boys, girls, or the active boys. The increased VO2 ml . kg-1 . min-1 in children appeared to be independent of stride length and frequency but external loading equivalent to 5% of body weight reduced VO2 (ml . kg-1 . min-1), particularly at the higher speeds. It was suggested in young active and athletic children due to their relatively light body weights and highly developed aerobic power outputs, that the required frequency of leg movement was not optimally matched to the force necessary to produce the most economic conversion of aerobic energy into mechanical work. Thus, in competitive events their performance times were related to their maximal aerobic power output (r = -0.75) but their times were always inferior to those which one might have expected from previous aerobic power weight data collected on adult male and female athletes.