Inter-limb coordination and energy cost in swimming.

OBJECTIVES: This study investigated the relationship between inter-arm coordination and the energy cost of locomotion in front crawl and breaststroke and explored swimmers' flexibility in adapting their motor organization away from their preferred movement pattern. DESIGN: Nine front-crawlers performed three 300-m in front crawl and 8 breaststrokers performed three 200-m in breaststroke at constant submaximal intensity and with 5-min rests. Each trial was performed randomly in a different coordination pattern: freely chosen, 'maximal glide' and 'minimal glide'. Two underwater cameras videotaped frontal and side views to analyze speed, stroke rate, stroke length and inter-limb coordination. METHODS: In front crawl, inter-arm coordination was quantified by the index of coordination (IdC) and the leg beat kicks were counted. In breaststroke, four time gaps quantified the arm to leg coordination (i.e., time between leg and arm propulsions; time between beginning, 90° flexion and end of arm and leg recoveries). The energy cost of locomotion was calculated from gas exchanges and blood lactate concentration. RESULTS: In both front crawl and breaststroke, the freely chosen coordination corresponded to glide pattern and showed the lowest energy cost (12.8 and 17.1Jkg(-1)m(-1), respectively). Both front-crawlers and breaststrokers were able to reach 'maximal glide' condition (respectively, +35% and +28%) but not 'minimal glide' condition for front crawl. CONCLUSIONS: The freely chosen pattern appeared more economic because more trained. When coordination was constrained, the swimmers had higher coordination flexibility in breaststroke than in front crawl, suggesting that breaststroke coordination was easier to regulate by changing glide time.

Antagonistic functions of LMNA isoforms in energy expenditure and lifespan.

Alternative RNA processing of LMNA pre-mRNA produces three main protein isoforms, that is, lamin A, progerin, and lamin C. De novo mutations that favor the expression of progerin over lamin A lead to Hutchinson-Gilford progeria syndrome (HGPS), providing support for the involvement of LMNA processing in pathological aging. Lamin C expression is mutually exclusive with the splicing of lamin A and progerin isoforms and occurs by alternative polyadenylation. Here, we investigate the function of lamin C in aging and metabolism using mice that express only this isoform. Intriguingly, these mice live longer, have decreased energy metabolism, increased weight gain, and reduced respiration. In contrast, progerin-expressing mice show increased energy metabolism and are lipodystrophic. Increased mitochondrial biogenesis is found in adipose tissue from HGPS-like mice, whereas lamin C-only mice have fewer mitochondria. Consistently, transcriptome analyses of adipose tissues from HGPS and lamin C-only mice reveal inversely correlated expression of key regulators of energy expenditure, including Pgc1a and Sfrp5. Our results demonstrate that LMNA encodes functionally distinct isoforms that have opposing effects on energy metabolism and lifespan in mammals.

Moderate hypercapnia exerts beneficial effects on splanchnic energy metabolism during endotoxemia.

PURPOSE: Low tidal volume ventilation and permissive hypercapnia are required in patients with sepsis complicated by ARDS. The effects of hypercapnia on tissue oxidative metabolism in this setting are unknown. We therefore determined the effects of moderate hypercapnia on markers of systemic and splanchnic oxidative metabolism in an animal model of endotoxemia. METHODS: Anesthetized rats maintained at a PaCO(2) of 30, 40 or 60 mmHg were challenged with endotoxin. A control group (PaCO(2) 40 mmHg) received isotonic saline. Hemodynamic variables, arterial lactate, pyruvate, and ketone bodies were measured at baseline and after 4 h. Tissue adenosine triphosphate (ATP) and lactate were measured in the small intestine and the liver after 4 h. RESULTS: Endotoxin resulted in low cardiac output, increased lactate/pyruvate ratio and decreased ketone body ratio. These changes were not influenced by hypercapnia, but were more severe with hypocapnia. In the liver, ATP decreased and lactate increased independently from PaCO(2) after endotoxin. In contrast, the drop of ATP and the rise in lactate triggered by endotoxin in the intestine were prevented by hypercapnia. CONCLUSIONS: During endotoxemia in rats, moderate hypercapnia prevents the deterioration of tissue energetics in the intestine.

Optimisation of energy provision with supplemental parenteral nutrition in critically ill patients: a randomised controlled clinical trial.

BACKGROUND: Enteral nutrition (EN) is recommended for patients in the intensive-care unit (ICU), but it does not consistently achieve nutritional goals. We assessed whether delivery of 100% of the energy target from days 4 to 8 in the ICU with EN plus supplemental parenteral nutrition (SPN) could optimise clinical outcome. METHODS: This randomised controlled trial was undertaken in two centres in Switzerland. We enrolled patients on day 3 of admission to the ICU who had received less than 60% of their energy target from EN, were expected to stay for longer than 5 days, and to survive for longer than 7 days. We calculated energy targets with indirect calorimetry on day 3, or if not possible, set targets as 25 and 30 kcal per kg of ideal bodyweight a day for women and men, respectively. Patients were randomly assigned (1:1) by a computer-generated randomisation sequence to receive EN or SPN. The primary outcome was occurrence of nosocomial infection after cessation of intervention (day 8), measured until end of follow-up (day 28), analysed by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00802503. FINDINGS: We randomly assigned 153 patients to SPN and 152 to EN. 30 patients discontinued before the study end. Mean energy delivery between day 4 and 8 was 28 kcal/kg per day (SD 5) for the SPN group (103% [SD 18%] of energy target), compared with 20 kcal/kg per day (7) for the EN group (77% [27%]). Between days 9 and 28, 41 (27%) of 153 patients in the SPN group had a nosocomial infection compared with 58 (38%) of 152 patients in the EN group (hazard ratio 0·65, 95% CI 0·43-0·97; p=0·0338), and the SPN group had a lower mean number of nosocomial infections per patient (-0·42 [-0·79 to -0·05]; p=0·0248). INTERPRETATION: Individually optimised energy supplementation with SPN starting 4 days after ICU admission could reduce nosocomial infections and should be considered as a strategy to improve clinical outcome in patients in the ICU for whom EN is insufficient. FUNDING: Foundation Nutrition 2000Plus, ICU Quality Funds, Baxter, and Fresenius Kabi.

Coordination pattern adaptability: energy cost of degenerate behaviors.

This study investigated behavioral adaptability, which could be defined as a blend between stability and flexibility of the limbs movement and their inter-limb coordination, when individuals received informational constraints. Seven expert breaststroke swimmers performed three 200-m in breaststroke at constant submaximal intensity. Each trial was performed randomly in a different coordination pattern: 'freely-chosen', 'maximal glide' and 'minimal glide'. Two underwater and four aerial cameras enabled 3D movement analysis in order to assess elbow and knee angles, elbow-knee pair coordination, intra-cyclic velocity variations of the center of mass, stroke rate and stroke length and inter-limb coordination. The energy cost of locomotion was calculated from gas exchanges and blood lactate concentration. The results showed significantly higher glide, intra-cyclic velocity variations and energy cost under 'maximal glide' compared to 'freely-chosen' instructional conditions, as well as higher reorganization of limb movement and inter-limb coordination (p<0.05). In the 'minimal glide' condition, the swimmers did not show significantly shorter glide and lower energy cost, but they exhibited significantly lower deceleration of the center of mass, as well as modified limb movement and inter-limb coordination (p<0.05). These results highlight that a variety of structural adaptations can functionally satisfy the task-goal.

Altered high-energy phosphate metabolism predicts contractile dysfunction and subsequent ventricular remodeling in pressure-overload hypertrophy mice.

To study the role of early energetic abnormalities in the subsequent development of heart failure, we performed serial in vivo combined magnetic resonance imaging (MRI) and (31)P magnetic resonance spectroscopy (MRS) studies in mice that underwent pressure-overload following transverse aorta constriction (TAC). After 3 wk of TAC, a significant increase in left ventricular (LV) mass (74 +/- 4 vs. 140 +/- 26 mg, control vs. TAC, respectively; P < 0.000005), size [end-diastolic volume (EDV): 48 +/- 3 vs. 61 +/- 8 microl; P < 0.005], and contractile dysfunction [ejection fraction (EF): 62 +/- 4 vs. 38 +/- 10%; P < 0.000005] was observed, as well as depressed cardiac energetics (PCr/ATP: 2.0 +/- 0.1 vs. 1.3 +/- 0.4, P < 0.0005) measured by combined MRI/MRS. After an additional 3 wk, LV mass (140 +/- 26 vs. 167 +/- 36 mg; P < 0.01) and cavity size (EDV: 61 +/- 8 vs. 76 +/- 8 microl; P < 0.001) increased further, but there was no additional decline in PCr/ATP or EF. Cardiac PCr/ATP correlated inversely with end-systolic volume and directly with EF at 6 wk but not at 3 wk, suggesting a role of sustained energetic abnormalities in evolving chamber dysfunction and remodeling. Indeed, reduced cardiac PCr/ATP observed at 3 wk strongly correlated with changes in EDV that developed over the ensuing 3 wk. These data suggest that abnormal energetics due to pressure overload predict subsequent LV remodeling and dysfunction.

Brain energy metabolism measured by (13) C magnetic resonance spectroscopy in vivo upon infusion of [3-(13) C]lactate.

The brain uses lactate produced by glycolysis as an energy source. How lactate originated from the blood stream is used to fuel brain metabolism is not clear. The current study measures brain metabolic fluxes and estimates the amount of pyruvate that becomes labeled in glial and neuronal compartments upon infusion of [3-(13) C]lactate. For that, labeling incorporation into carbons of glutamate and glutamine was measured by (13) C magnetic resonance spectroscopy at 14.1 T and analyzed with a two-compartment model of brain metabolism to estimate rates of mitochondrial oxidation, glial pyruvate carboxylation, and the glutamate-glutamine cycle as well as pyruvate fractional enrichments. Extracerebral lactate at supraphysiological levels contributes at least two-fold more to replenish the neuronal than the glial pyruvate pools. The rates of mitochondrial oxidation in neurons and glia, pyruvate carboxylase, and glutamate-glutamine cycles were similar to those estimated by administration of (13) C-enriched glucose, the main fuel of brain energy metabolism. These results are in agreement with primary utilization of exogenous lactate in neurons rather than astrocytes. © 2014 Wiley Periodicals, Inc.

A Cellular Perspective on Brain Energy Metabolism and Functional Imaging.

The energy demands of the brain are high: they account for at least 20% of the body's energy consumption. Evolutionary studies indicate that the emergence of higher cognitive functions in humans is associated with an increased glucose utilization and expression of energy metabolism genes. Functional brain imaging techniques such as fMRI and PET, which are widely used in human neuroscience studies, detect signals that monitor energy delivery and use in register with neuronal activity. Recent technological advances in metabolic studies with cellular resolution have afforded decisive insights into the understanding of the cellular and molecular bases of the coupling between neuronal activity and energy metabolism and point at a key role of neuron-astrocyte metabolic interactions. This article reviews some of the most salient features emerging from recent studies and aims at providing an integration of brain energy metabolism across resolution scales.