Dietary preparation before rest and exercise testing

Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis

The effects of nutrition on exercise metabolism and performance remain an important topic among sports scientists, clinical, and athletic populations. Recently, fasted exercise has garnered interest as a beneficial stimulus which induces superior metabolic adaptations to fed exercise in key peripheral tissues. Conversely, pre-exercise feeding augments exercise performance compared with fasting conditions. Given these seemingly divergent effects on performance and metabolism, an appraisal of the literature is warranted. This review determined the effects of fasting vs pre-exercise feeding on continuous aerobic and anaerobic or intermittent exercise performance, and post-exercise metabolic adaptations. A search was performed using the MEDLINE and PubMed search engines. The literature search identified 46 studies meeting the relevant inclusion criteria. The Delphi list was used to assess study quality. A meta-analysis and meta-regression were performed where appropriate. Findings indicated that pre-exercise feeding enhanced prolonged (P = .012), but not shorter duration aerobic exercise performance (P = .687). Fasted exercise increased post-exercise circulating FFAs (P = .023) compared to fed exercise. It is evidenced that pre-exercise feeding blunted signaling in skeletal muscle and adipose tissue implicated in regulating components of metabolism, including mitochondrial adaptation and substrate utilization. This review's findings support the hypothesis that the fasted and fed conditions can divergently influence exercise metabolism and performance. Pre-exercise feeding bolsters prolonged aerobic performance, while seminal evidence highlights potential beneficial metabolic adaptations that fasted exercise may induce in peripheral tissues. However, further research is required to fully elucidate the acute and chronic physiological adaptations to fasted vs fed exercise.

Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis

This study aimed to verify the effect of aerobic exercise performed in the fasted v. fed states on fat and carbohydrate metabolism in adults. Searches were conducted in March 2015, and updated in July 2016, using PubMed®, Scopus and Cochrane databases (terms: ‘fasting’, ‘exercise’, ‘aerobic exercise’, ‘substrate’, ‘energy metabolism’, ‘fat’, ‘glucose’, ‘insulin’ and ‘adult’) and references from selected studies. Trials that compared the metabolic effects of aerobic exercise (duration ≤120 min) performed in the fasted v. fed states in adults were accepted. The outcomes evaluated were fat oxidation during exercise and the plasma concentrations of insulin, glucose and NEFA before and immediately after exercise; two independent reviewers extracted the data (A. F. V. and L. C.). The results were presented as weighted mean differences between treatments, with 95 % CI. Of 10 405 articles identified, twenty-seven studies – with a total of 273 participants – were included. There was a significant increase in fat oxidation during exercise performed in the fasted, compared with fed, state (−3·08 g; 95 % CI −5·38, −0·79; I2 39·1 %). The weighted mean difference of NEFA concentrations was not significantly different between states (0·00 mmol/l; 95 % CI −0·07, 0·08; I2 72·7 %). However, the weighted mean differences of glucose (0·78 mmol/l; 95 % CI 0·43, 1·14; I2 90·8 %) and insulin concentrations (104·5 pmol/l; 95 % CI 70·8, 138·2; I2 94·5 %) were significantly higher for exercise performed in the fed state. We conclude that aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.

Modeling and relationship of respiratory exchange ratio to athletic performance

Previous research has related the results of tests of maximum aerobic capacity to performance for endurance athletes. These results are often only able to predict the running velocity of races such as the marathon. This investigation sought to determine the absolute V[Combining Dot Above]O2 at various respiratory exchange ratio (RER) values (0.85, 0.90, 0.95, 1.0, 1.05, and 1.10) by using a third-order polynomial regression to model the physiological responses for V[Combining Dot Above]O2 and RER obtained from an assessment of maximum aerobic capacity. The V[Combining Dot Above]O2 determined was subsequently correlated to race performance. The participants in the study were selected from a population of National Collegiate Athletic Association Division 1 crosscountry runners (male n = 7, female n = 7, age 20.5 ± 0.9 years; height 170.3 ± 8.2 cm; weight 59.7 ± 8.7 kg; V[Combining Dot Above]O2max 57.0 ± 7.8 ml O2·kg·min). Third-order regression analysis resulted in strong curve fitting between the variables (r = 0.949 ± 0.03). Partial correlations (controlled for weight) were used to assess the relationship between oxygen consumption at the desired points of RER and race performance. The partial correlations revealed that the absolute oxygen consumptions at all RER points of interest were significantly correlated to race performance (r > 0.740, p < 0.01). There was a significant difference in the strength of the correlations for the points RER 0.95 (t = 2.68957, p = 0.01), 1.0 (t = 2.18516, p = 0.03), and 1.05 (t = 1.85668, p = 0.04) and the correlations found for RER 0.85. After converting the oxygen consumption at the RER points to estimated horizontal running speeds, only the estimate at RER 1.05 was not statistically different from the actual speed achieved in the culminating XC race. It can be suggested based upon these results that coaches of collegiate crosscountry runners who engage in metabolic testing of athletes examine the estimated running pace at RER 1.05 to gain an insight into a runner's potential.

Body metabolic rate and electromyographic activities of antigravitational muscles in supine and standing postures

We measured metabolic (oxygen uptake, carbon dioxide production, respiratory ratio), cardio-circulatory (heart rate, systolic and diastolic arterial blood pressure, rate-pressure product, an index of myocardial oxygen consumption calculated by multiplying heart rate by systolic pressure) and electromyographic (integrated electromyographic activities of two antigravitational muscles of the lower limb, soleus and gastrocnemius) variables on 12 young healthy subjects in supine and standing positions at rest. We found statistically significant increments of oxygen uptake, carbon dioxide production, heart rate and integrated electromyographic activities in standing versus supine position. Rate-pressure product increased but not significantly, and no other significant changes were detected. We conclude that postural changes influence metabolic rate, antigravitational muscle reflex activities, and heart rate. A significant positive correlation was found between oxygen uptake and carbon dioxide production and integrated electromyographic activities of antigravitational muscles, while the same was not found for cardio-circulatory variables. These results suggest that the increased metabolic rate in standing position is, at least in part, due to antigravitational muscle tone.

Effect of exercise and medium-chain fatty acids on postprandial lipemia

The purpose of this study was to evaluate the effect of medium-chain triglycerides (MCT) with and without exercise on postprandial lipemia (PPL). Subjects were 25 young men and women. Each subject performed three trials: 1) control (fat meal only, 1.5 g fat/kg) 2) MCT (substitution of MCT oil, 30% of fat calories), and 3) MCT + Ex (exercise 12 h before the MCT meal). Before each trial, the subject underwent consistent dietary preparation. Blood was collected on 2 separate days for baseline measurements of postheparin lipases and, in each trial, at 0 h (premeal), at 2, 4, 6, and 8 h after the fat meal for triglycerides and cholesterol ester transfer protein (CETP), and at 8 h for postheparin lipoprotein lipase (LPL) and hepatic lipase activities (HL). ANOVA indicated that the partial substitution of MCT oil to the fat meal did not affect the PPL response. However, the PPL was significantly lower after the MCT + Ex trial vs. the other trials. LPL activity was significantly elevated after all trials compared with baseline, whereas HL was lower in the MCT + Ex trial only. CETP mass was significantly lower at 4 and 8 h than 0 h during all trials but relatively higher in the MCT + Ex trial vs. the nonexercise trials. These results suggest that MCT does not affect the TG response to a fat meal. LPL and CETP are affected by a fat meal with or without exercise, but HL is affected only when exercise is included.

Effects of exercise and n-3 fatty acids on postprandial lipemia

Because n-3 fatty acid ingestion and aerobic exercise each has been associated with diminished postprandial lipemia (PPL), the purpose of this study was to evaluate the effect of a combination of these two factors on PPL. Sedentary men underwent a standard dietary preparation, including a 12-h fast before each trial. Six subjects performed a control trial (fat meal, 100 g fat) and an n-3 fatty acid trial (fat meal after 3 wk of n-3 fatty acid supplementation at 4 g/day). In a parallel experiment, six different subjects underwent a control trial and n-3 fatty acid supplementation + 60 min of exercise before ingestion of the fat meal. Supplementation with n-3 fatty acid significantly decreased baseline triglyceride (TG) concentrations but did not significantly affect PPL. The combination of n-3 fatty acid and exercise had no effect on the postprandial TG response. The present study suggests that n-3 fatty acid supplementation lowers resting TG concentrations but inhibits the beneficial effect of aerobic exercise on the postprandial TG response.