Etudes cardio

Effets de l’acétaminophène sur la performance?

14/02/2018 | Etudes cardio

 

Acute acetaminophen ingestion improves performance and muscle activation during maximal intermittent knee extensor exercise
Paul T. Morgan                   European Journal of Applied Physiology March 2018, Volume 118, Issue 3, pp 595–605

Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it may improve endurance exercise performance. This study investigated some of the physiological mechanisms by which acute acetaminophen ingestion might blunt muscle fatigue development.

Methods
Thirteen active males completed 60 × 3 s maximum voluntary contractions (MVC) of the knee extensors with each contraction separated by a 2 s passive recovery period. This protocol was completed 60 min after ingesting 1 g of maltodextrin (placebo) or 1 g of acetaminophen on two separate visits. Peripheral nerve stimulation was administered every 6th contraction for assessment of neuromuscular fatigue development, with the critical torque (CT), which reflects the maximal sustainable rate of oxidative metabolism, taken as the mean torque over the last 12 contractions. Surface electromyography was recorded continuously as a measure of muscle activation.

Results
Mean torque (61 ± 11 vs. 58 ± 14% pre-exercise MVC) and CT (44 ± 13 vs. 40 ± 15% pre-exercise MVC) were greater in the acetaminophen trial compared to placebo (both P 

< 0.05). Voluntary activation and potentiated twitch declined at a similar rate in both conditions (P > 0.05). However, the decline in electromyography amplitude was attenuated in the acetaminophen trial, with electromyography amplitude being greater compared to placebo from 210 s onwards (P 

< 0.05).

Conclusion
These findings indicate that

acute acetaminophen ingestion might be ergogenic by increasing CT and preserving muscle activation during high-intensity exercise.

Effets d’un supplément de corps cétoniques sur l’endurance?

24/01/2018 | Etudes cardio et Etudes Compléments alimentaires

 

Effect of acute ingestion of β-hydroxybutyrate salts on the response to graded exercise in trained cyclists
Mark Evans             European Journal of Sport Science Pages 1-11 | Published online: 16 Jan 2018

Acute ingestion of ketone salts induces nutritional ketosis by elevating β-hydroxybutyrate (βHB), but few studies have examined the metabolic effects of ingestion prior to exercise. Nineteen trained cyclists (12 male, 7 female) undertook graded exercise (8 min each at ∼30%, 40%, 50%, 60%, 70%, and 80% VO2peak) on a cycle ergometer on two occasions separated by either 7 or 14 days. Trials included ingestion of boluses of either (i) plain water (3.8 mL kg body mass−1) (CON) or (ii) βHB salts (0.38 g kg body mass−1) in plain water (3.8 mL kg body mass−1) (KET), at both 60 min and 15 min prior to exercise. During KET, plasma [βHB] increased to 0.33 ± 0.16 mM prior to exercise and 0.44 ± 0.15 mM at the end of exercise (both p < .05). Plasma glucose was 0.44 ± 0.27 mM lower (p < .01) 30 min after ingestion of KET and remained ∼0.2 mM lower throughout exercise compared to CON (p < .001). Respiratory exchange ratio (RER) was higher during KET compared to CON (p < .001) and 0.03–0.04 higher from 30%VO2peak to 60%VO2peak (all p < .05). No differences in plasma lactate, rate of perceived exertion, or gross or delta efficiency were observed between trials. Gastrointestinal symptoms were reported in 13 out of 19 participants during KET. Acute ingestion of βHB salts induces nutritional ketosis and alters the metabolic response to exercise in trained cyclists.

Elevated RER during KET may be indicative of increased ketone body oxidation during exercise, but at the plasma βHB concentrations achieved, ingestion of βHB salts does not affect lactate appearance, perceived exertion, or muscular efficiency.

Rôle de la Ghréline, post-exercice

23/01/2018 | Etudes cardio et Etudes sur les hormones

 

Ghrelin mediates exercise endurance and the feeding response post-exercise
Bharath K. Mani         Mol Met. 2018.01.006

Highlights
•High intensity exercise transiently increases plasma ghrelin.
•Without ghrelin action on its receptors (growth hormone secretagogue receptors), exercise markedly reduces food intake.
•An intact ghrelin system enhances exercise endurance.


Objective
Exercise training has several well-established health benefits, including many related to body weight, appetite control, and blood glucose homeostasis. However, the molecular mechanisms and, in particular, the hormonal systems that mediate and integrate these beneficial effects are poorly understood. In the current study, we aimed to investigate the role of the hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR; ghrelin receptor), in mediating the effects of exercise on food intake and blood glucose following exercise as well as in regulating exercise endurance capacity.

Methods
We used two mouse models of treadmill running to characterize the changes in plasma ghrelin with exercise. We also assessed the role of the ghrelin system to influence food intake and blood glucose after exercise, exercise endurance, and parameters potentially linked to responses to exercise. Mice lacking GHSRs (GHSR-null mice) and wild-type littermates were studied.

Results
An acute bout of exercise transiently elevated plasma acyl-ghrelin. Without the action of this increased ghrelin on GHSRs (as in GHSR-null mice), high intensity interval exercise markedly reduced food intake compared to control mice. The effect of exercise to acutely raise blood glucose remained unmodified in GHSR-null mice. Exercise-induced increases in plasma ghrelin positively correlated with endurance capacity, and time to exhaustion was reduced in GHSR-null mice as compared to wild-type littermates. In an effort to mechanistically explain their reduced exercise endurance, exercised GHSR-null mice exhibited an abrogated sympathoadrenal response, lower overall insulin-like growth factor-1 levels, and altered glycogen utilization.

Conclusions
Exercise transiently increases plasma ghrelin. GHSR-null mice exhibit decreased food intake following high intensity interval exercise and decreased endurance when submitted to an exercise endurance protocol. These data suggest that an intact ghrelin system limits the capacity of exercise to restrict food intake following exercise, although it enhances exercise endurance.

Cryothérapie Corps Entier Vs eau froide pour la récupération?

10/01/2018 | Etudes cardio et Echauffement et blessures

 

Recovery following a marathon: a comparison of cold water immersion, whole body cryotherapy and a placebo control
Laura J. Wilson     European Journal of Applied Physiology January 2018, Volume 118, Issue 1, pp 153–163 | Cite as

Purpose
Cryotherapy is an increasingly popular recovery strategy used in an attempt to attenuate the negative impact of strenuous physical activity on subsequent exercise. Therefore, this study aimed to assess the effects of whole body cryotherapy (WBC) and cold water immersion (CWI) on markers of recovery following a marathon.

Methods
Thirty-one endurance trained males completed a marathon. Participants were randomly assigned to a CWI, WBC or placebo group. Perceptions of muscle soreness, training stress and markers of muscle function were recorded before the marathon and at 24 and 48 h post exercise. Blood samples were taken at baseline, post intervention and 24 and 48 h post intervention to assess inflammation and muscle damage.

Results
WBC had a harmful effect on muscle function compared to CWI post marathon. WBC positively influenced perceptions of training stress compared to CWI. With the exception of C-reactive protein (CRP) at 24 and 48 h, neither cryotherapy intervention positively influenced blood borne markers of inflammation or structural damage compared to placebo.

Conclusion
The findings show WBC has a negative impact on muscle function, perceptions of soreness and a number of blood parameters compared to CWI, contradicting the suggestion that WBC may be a superior recovery strategy. Further, cryotherapy is no more effective than a placebo intervention at improving functional recovery or perceptions of training stress following a marathon. These findings lend further evidence to suggest that treatment belief and the placebo effect may be largely responsible for the beneficial effects of cryotherapy on recovery following a marathon.

Les vêtements de sudation font-ils brûler plus de calories?

23/12/2017 | Etudes cardio et Etudes Perte de poids

 

Acute Metabolic Responses of Exercise with a Sauna Suit
Lexie B. Loring     Medicine & Science in Sports & Exercise. 49(5S):926, May 2017.


PURPOSE: The purpose of this study was to examine acute metabolic responses of exercise with a sauna suit (SS) under different exercise intensity and duration conditions.

METHODS: Twelve physically active men (age = 27.1±7.5 yrs, height = 175.4±6.3 cm, weight = 75.6±7.9 kg, maximal oxygen uptake – VO2max = 38.6±7.8 mL×kg-1×min-1) completed four experimental trials on a cycle ergometer: 1) 30min moderate-intensity (MI) exercise (55-60% heart rate reserve–HRR) with SS, 2) 20min vigorous-intensity (VI) exercise (75-80% HRR) with SS, 3) 30min MI exercise (55-60% HRR) without a sauna suit (CON), and 4) 20min VI exercise (75-80% HRR) CON. Trials were separated by 24-96 hours and performed in randomized order. Exercise energy expenditure (EE), one hour excess post-exercise oxygen consumption (EPOC), and one hour post-exercise weight loss (PEWL) were measured for each trial.

RESULTS: There were significant differences (p

<0.05) in exercise EE, one hour EPOC and one hour PEWL between SS and CON under both MI and VI conditions. MI results:

exercise EE was greater with SS vs. CON (282.6±34.7 kcal vs. 247.8±40.2 kcal), one hour EPOC was greater with SS vs. CON (69.9±4.3 kcal vs. 45.2±3.0 kcal), and the SS condition resulted in greater change in one hour PEWL (0.52±0.14 kg vs. 0.37±0.15 kg). VI results: exercise EE was greater with SS vs. CON (204.7±24.2 kcal vs. 184.6±21.3 kcal), one hour EPOC was greater with SS vs. CON (87.7±7.0 kcal vs. 72.1±3.4 kcal), and the SS condition resulted in greater change in one hour PEWL (0.63±0.15 kg vs. 0.39±0.12 kg).

CONCLUSION: Our findings support the feasibility of exercise training with a sauna suit–and the amplified exercise EE and EPOC–to contribute to long-term energy balance and thus improve cardiovascular health.

Une supplémentation en corps cétoniques booste la récupération énergétique

17/08/2017 | Etudes cardio et Etudes Compléments alimentaires et Etudes Perte de poids

 

A Ketone Ester Drink Increases Postexercise Muscle Glycogen Synthesis in Humans
HOLDSWORTH, DAVID A         Medicine & Science in Sports & Exercise: September 2017 - Volume 49 - Issue 9 - p 1789–1795

Introduction: Physical endurance can be limited by muscle glycogen stores, in that glycogen depletion markedly reduces external work. During carbohydrate restriction, the liver synthesizes the ketone bodies, D-β-hydroxybutyrate, and acetoacetate from fatty acids. In animals and in the presence of glucose, D-β-hydroxybutyrate promotes insulin secretion and increases glycogen synthesis. Here we determined whether a dietary ketone ester, combined with plentiful glucose, can increase postexercise glycogen synthesis in human skeletal muscle.

Methods: After an interval-based glycogen depletion exercise protocol, 12 well-trained male athletes completed a randomized, three-arm, blinded crossover recovery study that consisted of consumption of either a taste-matched, zero-calorie control or a ketone monoester drink, followed by a 10-mM glucose clamp or saline infusion for 2 h. The three postexercise conditions were control drink then saline infusion, control drink then hyperglycemic clamp, or ketone ester drink then hyperglycemic clamp. Skeletal muscle glycogen content was determined in muscle biopsies of vastus lateralis taken before and after the 2-h clamps.

Results: The ketone ester drink increased blood D-β-hydroxybutyrate concentrations to a maximum of 5.3 versus 0.7 mM for the control drink (P < 0.0001). During the 2-h glucose clamps, insulin levels were twofold higher (31 vs 16 mU·L−1, P < 0.01) and glucose uptake 32% faster (1.66 vs 1.26 g·kg−1, P < 0.001). The ketone drink increased by 61 g, the total glucose infused for 2 h, from 197 to 258 g, and muscle glycogen was 50% higher (246 vs 164 mmol glycosyl units per kilogram dry weight, P < 0.05) than after the control drink.

Conclusion: In the presence of constant high glucose concentrations, a ketone ester drink increased endogenous insulin levels, glucose uptake, and muscle glycogen synthesis.

Rôle de l’entraînement sur la densité mitochondriale

09/06/2017 | Etudes cardio et Etudes Perte de poids

 

Exercise training increases skeletal muscle mitochondrial volume density by enlargement of existing mitochondria and not de novo biogenesis
Anne-Kristine Meinild Lundby       Acta physiol 2017

Aims

1) determine whether exercise induced increases in muscle mitochondrial volume density (MitoVD) is related to enlargement of existing mitochondria or de novo biogenesis, 2) establish if measures of mitochondrial-specific enzymatic activities are valid biomarkers for exercise induced increases in MitoVD.
Method

Skeletal muscle samples were collected from twenty-one healthy males prior to and following 6 weeks of endurance training. Transmission electron microscopy was used for estimation of mitochondrial densities and profiles. Biochemical assays, western blotting and high resolution respirometry were applied to detect changes in specific mitochondrial functions.
Result

MitoVD increased with 55 ± 9% (P

< 0.001), whereas the number of mitochondrial profiles per area of skeletal muscle remained unchanged following training

. Citrate synthase activity (CS) increased (44 ± 12%, P < 0.001) however, there were no functional changes in oxidative phosphorylation capacity (OXPHOS, CI+IIP) or cytochrome c oxidase (COX) activity. Correlations were found between MitoVD and CS (P=0.01; r=0.58), OXPHOS, CI+CIIP (P=0.01; R=0.58) and COX (P=0.02; R=0.52) before training, after training a correlation was found between MitoVD and CS activity only (P=0.04; R=0.49). Intrinsic respiratory capacities decreased (P < 0.05) with training when respiration was normalized to MitoVD. This was not the case when normalized to CS activity although the percentage change was comparable.
Conclusions

MitoVD was increased by inducing mitochondrial enlargement rather than de novo biogenesis. CS activity may be appropriate to track training induced changes in MitoVD.

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