scholarly journals Fueling shivering thermogenesis during passive hypothermic recovery

2007 ◽  
Vol 103 (4) ◽  
pp. 1346-1351 ◽  
Author(s):  
François Haman ◽  
Chris G. Scott ◽  
Glen P. Kenny
Keyword(s):  
Oxidation Rate ◽  
Utilization Rate ◽  
Moderate Hypothermia ◽  
Relative Importance ◽  
Adult Men ◽  
Fuel Metabolism ◽  
Regulatory Processes ◽  
Fuel Selection ◽  
Passive Rewarming ◽  
Shivering Thermogenesis

In humans, the relative importance of oxidative fuels for sustaining shivering during passive hypothermic recovery or rewarming is still unclear. The main goals of this study were 1) to quantify the respective contributions of lipids and carbohydrates (CHO) during passive rewarming and 2) to determine the effects of precooling exercise on the pattern of fuel utilization. With indirect calorimetry methodologies, changes in fuel metabolism were quantified in nonacclimatized adult men shivering to rewarm from moderate hypothermia (core temperature ∼34.5°C) not following (Con) or following a precooling exercise at 75% V̇o2max for 15 min (Pre-CE). As hypothermic individuals shiver to normothermia, results showed that CHO dominate at all shivering intensities above 50% Shivpeak, while lipids were preferred at lower intensities. This change in the relative importance of CHO and lipids to total heat production was dictated entirely by modulating CHO oxidation rate, which decreased by as much as 10-fold from the beginning to the end of rewarming (from 1,611 ± 396 to 141 ± 361 mg/min for Con and 1,555 ± 230 to 207 ± 261 mg/min for Pre-CE). In contrast, lipid oxidation rate remained constant and low (relatively to maximal rates at exercise) throughout rewarming, averaging 183 ± 141 for Con and 207 ± 118 mg lipids/min for Pre-CE. In addition, this pattern of fuel selection remained the same between treatments. We concluded that fuel selection is regulated entirely by changes in CHO oxidation rate. Further research should focus on establishing the exact regulatory processes involved in achieving this large upregulation of CHO utilization rate following hypothermia.

Effects of carbohydrate availability on sustained shivering II. Relating muscle recruitment to fuel selection

2004 ◽  
Vol 96 (1) ◽  
pp. 41-49 ◽  
Author(s):  
François Haman ◽  
Stéphane R. Legault ◽  
Mark Rakobowchuk ◽  
Michel B. Ducharme ◽  
Jean-Michel Weber
Keyword(s):  
Voluntary Contraction ◽  
Whole Body ◽  
Carbohydrate Diet ◽  
Adult Men ◽  
Low Carbohydrate Diet ◽  
Fuel Metabolism ◽  
Relative Contribution ◽  
Fuel Selection ◽  
Low Carbohydrate ◽  
Fuel Mixtures

The purpose of this study was to quantify how shivering activity would be affected by large changes in fuel metabolism (see Haman F, Peronnet F, Kenny GP, Doucet E, Massicotte D, Lavoie C, and Weber J-M, J Appl Physiol 96: 000–000, 2004). Adult men were exposed to 10°C for 2 h after a low-carbohydrate diet and exercise (Lo) and after high-carbohydrate diet without exercise (Hi). Using simultaneous metabolic and electromyographic (EMG) measurements, we quantified the effects of changes in fuel selection on the shivering activity of eight large muscles representing >90% of total shivering muscle mass. Contrary to expectation, drastic changes in fuel metabolism [carbohydrates 28 vs. 65% of total heat production (Ḣprod), lipids 53 vs. 23% Ḣprod, and proteins 19 vs. 12% Ḣprod for Lo and Hi, respectively] are achieved without altering the EMG signature of shivering muscles. Results show that total shivering activity and the specific contribution of each muscle to total shivering activity are not affected by large changes in fuel selection. In addition, we found that changes in burst shivering rate (∼4 bursts/min), relative contribution of burst activity to total shivering (∼10% of total shivering activity), and burst shivering intensity (∼12% of maximal voluntary contraction) are the same between Lo and Hi. Spectral analysis of EMG signals also reveals that mean frequencies of the power spectrum remained the same under all conditions (whole body average of 78 ± 5 Hz for Lo and 83 ± 7 Hz for Hi). During low-intensity shivering, humans are therefore able to sustain the same thermogenic rate by oxidizing widely different fuel mixtures within the same muscle fibers.

scholarly journals Effects of ingesting [13C]glucose early or late into cold exposure on substrate utilization

2010 ◽  
Vol 109 (3) ◽  
pp. 654-662 ◽  
Author(s):  
Denis P. Blondin ◽  
François Péronnet ◽  
François Haman
Keyword(s):  
Cold Exposure ◽  
Resting Metabolic Rate ◽  
Utilization Rate ◽  
Low Intensity ◽  
Exogenous Glucose ◽  
Cold Condition ◽  
Glycogen Utilization ◽  
Endogenous Reserves ◽  
Fuel Source ◽  
Shivering Thermogenesis

One of the factors limiting the oxidation of exogenous glucose during cold exposure may be the delay in establishing a shivering steady state (∼60 min), reducing glucose uptake into skeletal muscle. Therefore, using indirect calorimetry and isotopic methodologies in non-cold-acclimatized men, the main purpose of this study was to determine whether ingesting glucose at a moment coinciding with the maximal shivering intensity could increase the utilization rate of the ingested glucose. 13C-enriched glucose was ingested (800 mg/min) from the onset (G0) or after 60 min (G60) of cold exposure when the thermogenic rate was stabilized to low-intensity shivering (∼2.5 times resting metabolic rate). For the same quantity of glucose ingested, the oxidation rate of exogenous glucose was 35% higher in G60 (159 ± 17 vs. 118 ± 17 mg/min in G0) between minutes 60 and 90. By the end of cold exposure, exogenous glucose oxidation was significantly greater in G0, reaching 231 ± 14 mg/min, ∼15% higher than the only rates previously reported. This considerably reduced the utilization of endogenous reserves over time and compared with the G60 condition. This study also demonstrates a fall in muscle glycogen utilization, when glucose was ingested from the onset of cold exposure (from ∼150 to ∼75 mg/min). Together, these findings indicate the importance of ingesting glucose immediately on exposure to a cold condition, relying on shivering thermogenesis and sustaining that consumption for as long as possible. This substrate not only provides an auxiliary fuel source for shivering thermogenesis, but, more importantly, preserves the limited endogenous glucose reserves.

Increased fetal glucose concentration decreases ovine fetal leucine oxidation independent of insulin

1993 ◽  
Vol 265 (4) ◽  
pp. E617-E623 ◽  
Author(s):  
E. A. Liechty ◽  
D. W. Boyle ◽  
H. Moorehead ◽  
Y. M. Liu ◽  
S. C. Denne
Keyword(s):  
Glucose Concentration ◽  
Oxidation Rate ◽  
Glucose Utilization ◽  
Essential Amino Acids ◽  
Glucose Infusion ◽  
Utilization Rate ◽  
Fed State ◽  
Leucine Oxidation ◽  
Ovine Fetal

Fetal leucine oxidation rate is elevated during fasting of the ewe. Euglycemic hyperinsulinemia causes the leucine oxidation rate to decline. However, it is unclear whether this is a direct effect of insulin or is secondary to increased insulin-mediated glucose utilization. To better delineate the mechanism of decreased oxidation, we suppressed fetal insulin secretion by somatostatin infusion. Glucose was infused at a variable rate to achieve glucose concentrations 125 and 150% of basal. Leucine rate of appearance (Ra) was determined by infusion of [15N, 1-13C]leucine. Fraction of leucine appearance oxidized was determined by [1-14C]leucine infusion and determination of fetal 14CO2 excretion. Each fetus was studied during ad libitum maternal feeding and after a 5-day complete maternal fast. Changes were noted in fetal leucine oxidation, which declined from 8.4 +/- 1.2 to 5.0 +/- 0.8 mumol/min in the fed state during glucose infusion. Basal leucine oxidation was elevated during fasting (11 +/- 1.5 mumol/min, P < 0.05) and declined to 8.0 +/- 1.4 mumol/min during glucose infusion (P = 0.056). Leucine carbon Ra was unchanged by fasting and by glucose infusion; leucine nitrogen Ra declined in the fed state only. Leucine oxidation was inversely correlated with glucose concentration (oxidation = 12-0.26 x glucose concentration, r = 0.42, P = 0.004). Leucine oxidation was not correlated with insulin concentration (r = 0.2). Changes in fetal glucose concentration may alter the pattern of utilization of essential amino acids, independent of changes in insulin and insulin-mediated glucose utilization rate.

Shivering in the cold: from mechanisms of fuel selection to survival

2006 ◽  
Vol 100 (5) ◽  
pp. 1702-1708 ◽  
Author(s):  
François Haman
Keyword(s):  
Future Research ◽  
Selection Mechanism ◽  
Glycogen Depletion ◽  
Human Survival ◽  
Fuel Selection ◽  
New Information ◽  
Fundamental Research ◽  
Specific Muscle ◽  
Fuel Mixtures ◽  
Shivering Thermogenesis

In cold-exposed adult humans, significant or lethal decreases in body temperature are delayed by reducing heat loss via peripheral vasoconstriction and by increasing rates of heat production via shivering thermogenesis. This brief review focuses on the mechanisms of fuel selection responsible for sustaining long-term shivering thermogenesis. It provides evidence to explain large discrepancies in fuel selection measurements among shivering studies, and it proposes links between choices in fuel selection mechanism and human survival in the cold. Over the last decades, a number of studies have quantified the contributions of carbohydrate (CHO) and lipid to total heat generation. However, the exact contributions of these fuels still remain unclear because of large differences in fuel selection measurements even at the same metabolic rate. Recent advances on the mechanisms of fuel selection during shivering provide some plausible explanations for these discrepancies between shivering studies. This new evidence indicates that muscles can sustain shivering over several hours using a variety of fuel mixtures achieved by modifying diet (changing the size of CHO reserves) or by changing muscle fiber recruitment (increasing or decreasing the recruitment of type II fibers). From a practical perspective, how does the choice of fuel selection mechanism affect human survival in the cold? Based on a glycogen-depletion model, estimates of shivering endurance show that, whereas the oxidation of widely different fuel mixtures does not improve survival time, the selective recruitment of fuel-specific muscle fibers provides a substantial advantage for cold survival. By combining fundamental research on fuel metabolism and applied strategies to improve shivering endurance, future research in this area promises to yield important new information on what limits human survival in the cold.

Influence of skeletal muscle glycogen on passive rewarming after hypothermia

1988 ◽  
Vol 65 (2) ◽  
pp. 805-810 ◽  
Author(s):  
P. D. Neufer ◽  
A. J. Young ◽  
M. N. Sawka ◽  
S. R. Muza
Keyword(s):  
Body Fat ◽  
Muscle Glycogen ◽  
Cold Water ◽  
Mild Hypothermia ◽  
Water Immersion ◽  
Cold Water Immersion ◽  
Moderate Hypothermia ◽  
Group A ◽  
Passive Rewarming ◽  
Group B

To examine the influence of muscle glycogen on the thermal responses to passive rewarming subsequent to mild hypothermia, eight subjects completed two cold-water immersions (18 degrees C), followed by 75 min of passive rewarming (24 degrees C air, resting in blanket). The experiments followed several days of different exercise-diet regimens eliciting either low (LMG; 141.0 +/- 10.5 mmol.kg.dry wt-1) or normal (NMG; 526.2 +/- 44.2 mmol.kg.dry wt-1) prewarming muscle glycogen levels. Cold-water immersion was performed for 180 min or to a rectal temperature (Tre) of 35.5 degrees C. In four subjects (group A, body fat = 20 +/- 1%), postimmersion Tre was similar to preimmersion Tre for both trials (36.73 +/- 0.18 vs. 37.26 +/- 0.18 degrees C, respectively). Passive rewarming in group A resulted in an increase in Tre of only 0.13 +/- 0.08 degrees C. Conversely, initial rewarming Tre for the other four subjects (group B, body fat = 12 +/- 1%) averaged 35.50 +/- 0.05 degrees C for both trials. Rewarming increased Tre similarly in group B during both LMG (0.76 +/- 0.25 degrees C) and NMG (0.89 +/- 0.13 degrees C). Afterdrop responses, evident only in those individuals whose body core cooled during immersion (group B), were not different between LMG and NMG. These data support the contention that Tre responses during passive rewarming are related to body insulation. Furthermore these results indicate that low muscle glycogen levels do not impair rewarming time nor alter after-drop responses during passive rewarming after mild-to-moderate hypothermia.

scholarly journals Can Metabolic Thresholds be used as Exercise Intensity Markers in Adult men with Obesity?

2018 ◽  
Author(s):  
Peric Ratko ◽  
Nikolovski Zoran
Keyword(s):  
Oxygen Consumption ◽  
Exercise Intensity ◽  
Oxidation Rate ◽  
Pearson Correlation ◽  
Maximal Oxygen Consumption ◽  
Fat Oxidation ◽  
Coefficient Of Determination ◽  
Pearson Correlation Coefficient ◽  
Adult Men ◽  
Paired T Test

AbstractThe first aim of the study was to identify the exercise intensity eliciting the highest (FATmax) and the lowest (FATmin) fat oxidation rate in men with obesity. The second aim was to evaluate if FATmax and FATmin correlate with aerobic (AeT) and anaerobic (AnT) thresholds, which in turn could be used as exercise intensity markers. Nineteen adult sedentary men participated in the study. Breath-by-breath analysis was performed throughout the test to assess maximal oxygen consumption (VO2max) with stoichiometric equations used to calculate fat oxidation rate. Pearson correlation coefficient (r), coefficient of determination (R2) and paired t-test were used to evaluate differences between VO2 at AeT and at FATmax and VO2 at AnT and at FATmin, respectively. FATmax and AeT occurred at 42.80 ± 2.68 % of VO2max and 43.02 ± 2.73 % of VO2max, while FATmin and AnT occurred at 53.40 ± 3.65 % of VO2max and 53.38 ± 3.65 % of VO2max, respectively. A high correlations were found between VO2 at FATmax and at AeT (r = 0.86, p < 0.01) and VO2 at FATmin and at AnT (r = 0.99, p < 0.01). The existing correlations suggest that metabolic thresholds may be used as exercise intensity markers in men with obesity.

Can metabolic thresholds be used as exercise intensity markers in adult men with obesity – fat burn points used as an exercise marker

2020 ◽  
Vol 16 (2) ◽  
pp. 113-119
Author(s):  
R. Peric ◽  
Z. Nikolovski
Keyword(s):  
Oxygen Consumption ◽  
Exercise Intensity ◽  
Oxidation Rate ◽  
Pearson Correlation ◽  
Maximal Oxygen Consumption ◽  
Fat Oxidation ◽  
Coefficient Of Determination ◽  
Pearson Correlation Coefficient ◽  
Adult Men ◽  
Paired T Test

We aimed to determine the exercise intensity eliciting the highest (FATmax) and the lowest (FATmin) fat oxidation rate in sedentary men with obesity and to examine if these intensities correlate with their individual aerobic (AeT) and anaerobic (AnT) thresholds, respectively. Nineteen obese males performed breath-by-breath analysis to assess maximal oxygen consumption (VO2max) and to calculate their fat oxidation rate. Pearson correlation coefficient (r), coefficient of determination (R2) and paired t-test were used to evaluate VO2 at AeT and at FATmax and VO2 at AnT and at FATmin, respectively. FATmax and AeT occurred at 42.80±2.68% of VO2max and 43.02±2.73% of VO2max, while FATmin and AnT occurred at 53.40±3.65% of VO2max and 53.38±3.65% of VO2max, respectively. A high correlations were found between intensities matching FATmax and AeT (r=0.86, P<0.01) and those at FATmin and at AnT (r=0.99, P<0.01). The existing correlations suggest that metabolic thresholds may be used as exercise intensity markers assuring more tailored exercise approach in men with obesity.

scholarly journals Oxidative fuel selection and shivering thermogenesis during a 12- and 24-h cold-survival simulation

2016 ◽  
Vol 120 (6) ◽  
pp. 640-648 ◽  
Author(s):  
François Haman ◽  
Olivier L. Mantha ◽  
Stephen S. Cheung ◽  
Michel B. DuCharme ◽  
Michael Taber ◽  
...  
Keyword(s):  
Cold Exposure ◽  
Muscle Glycogen ◽  
Whole Body ◽  
Muscle Recruitment ◽  
Glycogen Depletion ◽  
Total Carbohydrate ◽  
Fuel Selection ◽  
Isotopic Methods ◽  
Shivering Thermogenesis

Because the majority of cold exposure studies are constrained to short-term durations of several hours, the long-term metabolic demands of cold exposure, such as during survival situations, remain largely unknown. The present study provides the first estimates of thermogenic rate, oxidative fuel selection, and muscle recruitment during a 24-h cold-survival simulation. Using combined indirect calorimetry and electrophysiological and isotopic methods, changes in muscle glycogen, total carbohydrate, lipid, protein oxidation, muscle recruitment, and whole body thermogenic rate were determined in underfed and noncold-acclimatized men during a simulated accidental exposure to 7.5°C for 12 to 24 h. In noncold-acclimatized healthy men, cold exposure induced a decrease of ∼0.8°C in core temperature and a decrease of ∼6.1°C in mean skin temperature (range, 5.4-6.9°C). Results showed that total heat production increased by approximately 1.3- to 1.5-fold in the cold and remained constant throughout cold exposure. Interestingly, this constant rise in Ḣprod and shivering intensity was accompanied by a large modification in fuel selection that occurred between 6 and 12 h; total carbohydrate oxidation decreased by 2.4-fold, and lipid oxidation doubled progressively from baseline to 24 h. Clearly, such changes in fuel selection dramatically reduces the utilization of limited muscle glycogen reserves, thus extending the predicted time to muscle glycogen depletion to as much as 15 days rather than the previous estimates of approximately 30–40 h. Further research is needed to determine whether this would also be the case under different nutritional and/or colder conditions.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

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