During multiday training exercises, soldiers almost systematically face a moderate-to-large energy deficit, affecting their body mass and composition and potentially their physical and cognitive ...performance. Such energy deficits are explained by their inability to increase their energy intake during these highly demanding periods. With the exception of certain scenarios in which rations are voluntarily undersized to maximize the constraints, the energy content of the rations are often sufficient to maintain a neutral energy balance, suggesting that other limitations are responsible for such voluntary and/or spontaneous underconsumption. In this review, the overall aim was to present an overview of the impact of military training on energy balance, a context that stands out by its summation of specific limitations that interfere with energy intake. We first explore the impact of military training on the various components of energy balance (intake and expenditure) and body mass loss. Then, the role of the dimensioning of the rations (total energy content above or below energy expenditure) on energy deficits are addressed. Finally, the potential limitations inherent to military training (training characteristics, food characteristics, timing and context of eating, and the soldiers’ attitude) are discussed to identify potential strategies to spontaneously increase energy intake and thus limit the energy deficit.
The neuromuscular system is able to quickly adapt to exercise-induced muscle damage (EIMD), such that it is less affected by subsequent damaging exercise, a phenomenon known as the repeated bout ...effect (RBE). The objective was to determine whether the mechanical properties of the quadriceps, as evaluated by shear wave elastography (SWE), were less affected when a second bout of eccentric-biased exercise was performed 2 weeks later. It was hypothesized that the first bout would confer protection against extensive muscle damage through an adaptation of the muscle stiffness before the second bout (i.e., higher muscle stiffness).
Sixteen males performed two identical bouts of downhill walking separated by 2 weeks (45 min at 4.5 km.h
; gradient: 25%; load: 30% of the body mass).
(RF) and
(VL) resting shear elastic modulus (µ) and EIMD symptoms were measured before and up to 7 days following the exercise bouts. Changes in neuromuscular function was evaluated by maximal voluntary contraction torque, voluntary activation level, evoked mechanical response to single and double (10 and 100 Hz doublets) electrical stimulation. An index of protection (IP) was calculated for EIMD symptoms to assess magnitude the RBE.
EIMD symptoms were less affected after the second than the first exercise bout. RF and VL-µ increased (
< 0.001) only after the first exercise. RF µ was elevated up to 2 weeks after the end of the first exercise (
< 0.001) whereas VL µ was only increased up to 24 h. The increase in µ observed 2 weeks after the end of the first exercise was correlated with the IP; i.e., attenuation of alterations in muscle µ, 10 Hz-doublet amplitude and rate of torque development after the second exercise bout (
< 0.05).
We showed that muscle µ assessed by SWE was sensitive to the RBE, with a differential effect between VL and RF. The persistent increase in µ was associated with the attenuation of neuromuscular impairments observed after the second bout, suggesting that the increased muscle stiffness could be a "protective" adaptation making muscles more resistant to the mechanical strain associated to eccentric contractions.
Understanding the regulation of human food intake in response to an acute exercise session is of importance for interventions with athletes and soldiers, as well as overweight individuals. However, ...the influence of hot and cold environments on this crucial function for the regulation of body mass and motor performance has not been summarized. The purpose of this review was to exhaustively search the literature on the effect of ambient temperature during an exercise session on the subsequent subjective feeling of appetite, energy intake (EI) and its regulation. In the absence of stress due to environmental temperature, exercise-induced energy expenditure is not compensated by EI during an ad libitum meal following the session, probably due to decreased acylated ghrelin and increased peptide tyrosine tyrosine (PYY), glucagon-like peptide 1 (GLP-1), and pancreatic polypeptide (PP) levels. No systematic analysis has been yet made for major alterations of relative EI in cold and hot environments. However, observed eating behaviors are altered (proportion of solid/liquid food, carbohydrate/fat) and physiological regulation appears also to be altered. Anorexigenic signals, particularly PYY, appear to further increase in hot environments than in those that are thermoneutral. Ghrelin and leptin may be involved in the observed increase in EI after exercise in the cold, in parallel with increased energy expenditure. The potential influence of ambient thermal environment on eating behaviors after an exercise session should not be neglected.
Properly replacing energy and fluids is a challenge for 24-h ultramarathoners because such unusually high intake may induce adverse effects (gastrointestinal symptoms GIS and exercise-associated ...hyponatremia EAH). We analyzed such intake for 12 twelve elite athletes (6 males and 6 females; age: 46 ± 7 years, height: 170 ± 9 cm, weight: 61.1 ± 9.6 kg, total distance run: 193-272 km) during the 2019 24-h World Championships and compared it to the latest nutritional recommendations described by the International Society of Sports Nutrition in 2019. We hypothesized that these elite athletes would easily comply these recommendations without exhibiting detrimental adverse symptoms.
Ad libitum food and fluid intake was recorded in real-time and energy, macronutrient, sodium, and caffeine intake then calculated using a spreadsheet in which the nutritional composition of each item was previously recorded. GIS, markers of dehydration (body mass modifications, plasma and urine osmolality, and plasma volume; samples obtained 26 h before and just after the race) and EAH (plasma and urine sodium concentrations) were also assessed.
Fluid, energy, and carbohydrate intake of the 11 finishers was 16.4 ± 6.9 L, 35.1 ± 15.7 MJ, and 1.49 ± 0.71 kg, respectively. Individual analyses showed that all but one (for fluid intake) or two (for energy and carbohydrate intake) consumed more than the minimum recommendations. The calculated energy balance remained, however, largely negative (- 29.5 ± 16.1 MJ). Such unusually high intake was not accompanied by detrimental GIS (recorded in 75%, but only transiently 3.0 ± 0.9 h) or EAH (0%). The athletes were not dehydrated, shown by the absence of significant body mass loss (- 0.92 ± 2.13%) and modifications of plasma osmolality and an increase in plasma volume (+ 19.5 ± 15.8%). Performance (distance ran) positively correlated with energy intake (ρ = 0.674, p = 0.023) and negatively (ρ = - 0.776, p = 0.005) with fluid intake.
Overall, almost all of these elite 24-h ultramarathoners surpassed the nutritional recommendations without encountering significant or the usual adverse effects.
Despite its high prevalence in children with sickle cell anemia (SCA), the pathophysiology of silent cerebral infarcts (SCI) remains elusive. The main objective of this study was to explore the ...respective roles of major determinants of brain perfusion in SCA children with no past or current history of intracranial or extracranial vasculopathy. We used a multimodal approach based notably on perfusion imaging arterial spin labeling (ASL) magnetic resonance imaging (MRI) and near infra-red spectroscopy (NIRS), as well as biomarkers reflecting blood rheology and endothelial activation. Out of 59 SCA patients (mean age 11.4±3.9 yrs), eight (13%) had a total of 12 SCI. Children with SCI had a distinctive profile characterized by decreased blood pressure, impaired blood rheology, increased P-selectin levels, and marked anemia. Although ASL perfusion and oximetry values did not differ between groups, comparison of biological and clinical parameters according to the level of perfusion categorized in terciles showed an independent association between high perfusion and increased sP-selectin, decreased red blood cell deformability, low hemoglobin F level, increased blood viscosity and no a-thalassemia deletion. NIRS measurements did not yield additional novel results. Altogether, these findings argue for early MRI detection of SCI in children with no identified vasculopathy and suggest a potential role for ASL as an additional screening tool. Early treatment targeting hemolysis, anemia and endothelial dysfunction should reduce the risk of this under diagnosed and serious complication.
The aim of this study was to investigate the time course of the resting
(VL) muscle shear elastic modulus (μ) measured with ultrasound shear-wave elastography during repetition of isometric maximal ...voluntary contractions (MVCs) of the knee extensors (KE). Fifteen well-trained young males repeated 60 5-s isometric MVCs. Evoked electrical stimulations and the VLμ were measured every ten MVCs at rest. The resting VLμ significantly decreased (-34.7 ± 6.7%;
< 0.001) by the end of the fatigue protocol. There was also a 38.4 ± 12.6 % decrease in MVC after exercise (
< 0.001). The potentiated doublet and single twitch torque amplitudes and properties were significantly modified by the end of exercise (
< 0.001). This study shows the time course of the resting VLμ during the repetition of maximal voluntary fatiguing exercise of the KE muscles. The decrease of the resting VLμ could directly affect the force transmission capabilities accounting for peripheral fatigue.
The aim of this review was to (1) characterize the time-course of markers of exercise-induced muscle damage (EIMD) based on the level of maximal voluntary contraction torque loss at 24-48h ...post-exercise (MVC.sub.loss24-48h ), (2) identify factors (e.g., exercise and population characteristics) affecting the level of MVC.sub.loss24-48h, and (3) evaluate the appropriateness of EIMD markers as indicators of MVC.sub.loss24-48h. Magnitude of change of each EIMD markers was normalized using the standardized mean differences method to compare the results from different studies. Time-course of EIMD markers were characterized according to three levels of MVC.sub.loss24-48h based on a clustering analysis of the 141 studies included. Association between MVC.sub.loss24-48h levels and participant's characteristics or exercise type/modalities were assessed. Meta-regressions were performed to investigate the associations between MVC.sub.loss24-48h and EIMD markers changes at 96h after exercise. Time-course of EIMD markers recovery differs between levels of MVC.sub.loss24-48h . Training status and exercise type/modality were associated with MVC.sub.loss24-48h level (p<0.05). MVC.sub.loss24-48h was correlated to changes in myoglobin concentration (<6h), jump height (24h) and range of motion (48h) (p<0.001). As the exercise could differently affect markers as function of the EIMD severity (i.e., MVC.sub.loss24-48h levels), different markers should be used as function of the timing of measurement. Mb concentration should be used during the first hours after the exercise (<6h), whereas jump height (24h) and range of motion (48h) could be used as surrogate for maximal voluntary contraction later. Moreover, training status and exercise type/modality could influence the magnitude of MVC.sub.loss24-48h.
Benefits obtained after heat acclimation/acclimatization should be completely lost after an estimated period of 6 weeks. However, this estimate is still hypothetical. We evaluate the long-term ...effects of heat acclimatization on the level of heat tolerance. Physiological and subjective markers of heat tolerance were assessed during a heat stress test (HST: 3 × 8-min runs outdoors ~ 40 °C and 20% RH at 50% of their estimated speed at VO
) performed on the 2nd day upon arrival to the desert military base in the United Arab Emirates after a first day of mostly passive exposure to heat. Among the 50 male French soldiers, 25 partook in a 4-month military mission in countries characterized by a hot environment ~ 6 months prior to the study (HA). The other 25 participants were never heat acclimatized (CT). Rectal temperature (p = 0.023), heart rate (p = 0.033), and perceived exertion (p = 0.043) were lower in the HA than CT group at the end of HST. Soldiers who experienced a former 4-month period of natural heat acclimatization very likely had a higher level of heat tolerance during exercise in the heat, even 6 months after returning from the previous desert mission, than that of their non-acclimatized counterparts.
We investigated the
effects of voluntary fatiguing isometric contractions of the knee extensor muscles on the viscoelastic properties of the
(VL). Twelve young males (29.0 ± 4.5 years) performed an ...intermittent voluntary fatigue protocol consisting of 6 sets × 10 repetitions of 5-s voluntary maximal isometric contractions with 5-s passive recovery periods between repetitions. Voluntary and evoked torque were assessed before, immediately after, and 20 min after exercise. The shear modulus (μ) of the VL muscle was estimated at rest and during a ramped isometric contraction using a conventional elastography technique. An index of active muscle stiffness was then calculated (slope from the relationship between shear modulus and absolute torque). Resting muscle viscosity (η) was quantified using a shear-wave spectroscopy sequence to measure the shear-wave dispersion. Voluntary and evoked torque decreased by ∼37% (
< 0.01) immediately after exercise. The resting VL μ was lower at the end of the fatigue protocol (-57.9 ± 5.4%,
< 0.001), whereas the resting VL η increased (179.0 ± 123%,
< 0.01). The active muscle stiffness index also decreased with fatigue (
< 0.05). By 20 min post-fatigue, there were no significant differences from the pre-exercise values for VL η and the active muscle stiffness index, contrary to the resting VL μ. We show that the VL μ is greatly reduced and η greatly enhanced by fatigue, reflecting a more compliant and viscous muscle. The quantification of both shear μ and η moduli
may contribute to a better understanding of the mechanical behavior of muscles during fatigue in sports medicine, as well as in clinical situations.
The objective of this meta-analysis was to assess the effect of acute heat/cold exposure on subsequent energy intake (EI) in adults. We searched the following sources for publications on this topic: ...PubMed, Ovid Medline, Science Direct and SPORTDiscus. The eligibility criteria for study selection were: randomized controlled trials performed in adults (169 men and 30 women; 20–52 years old) comparing EI at one or more meals taken ad libitum, during and/or after exposure to heat/cold and thermoneutral conditions. One of several exercise sessions could be realized before or during thermal exposures. Two of the thirteen studies included examined the effect of heat (one during exercise and one during exercise and at rest), eight investigated the effect of cold (six during exercise and two at rest), and three the effect of both heat and cold (two during exercise and one at rest). The meta-analysis revealed a small increase in EI in cold conditions (g = 0.44; p = 0.019) and a small decrease in hot conditions (g = −0.39, p = 0.022) for exposure during both rest and exercise. Exposures to heat and cold altered EI in opposite ways, with heat decreasing EI and cold increasing it. The effect of exercise remains unclear.
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