Query: Relating mechanics and energetics during exercise

title: Relating mechanics and energetics during exercise.

title: Relating mechanics and energetics during exercise.

title: Mechanics and energetics of the stretch shortening cycle: a stimulating discussion
abstract: The target article about stretch shortening cycles was triggered by controversies on this topic among biomechanists and exercise physiologists and by the difficulties in relating knowledge obtained at different levels of organization. The purpose of the article was to stimulate a dialogue between scientists in different fields. We are therefore very pleased that so many distinguished experts from various disciplines responded with constructive, engaging commentaries. Before reacting to specific points addressed by the commentators, we will attempt to clarify a few points that seem to have caused confusion.

title: Comparative vertebrate exercise physiology unifying physiological principles
abstract: Cellular Energetics During Exercise. Solving the Common Problem: Matching ATP Synthesis to ATP Demand During Exercise. Structural Basis of Muscle Performance. The Mechanical Design of the Muscular System. Relating Energetics and Mechanics During Exercise. Circulatory Function During Exercise: Integration of Convection and Diffusion. Respiratory Gas Exchange During Exercise.

title: Respiratory muscles during exercise: mechanics, energetics, and fatigue
abstract: The respiratory muscles encompass a variety of functions and roles, their action during exercise facilitates arterial blood gas and pH regulation. Exercise hyperpnea is the first line of defense to meet increased metabolic demand. In so doing, the muscles of respiration encounter several challenges, which may lead to respiratory muscle fatigue and impaired exercise tolerance. The focus of this brief review is to summarize recent developments in the study of respiratory muscle mechanics, energetics, and fatigue during exercise. Advances in the field are highlighted and directions of potential future research identified.

title: The energetics and mechanics of jet propulsion swimming in European common cuttlefish (Sepia officinalis)
abstract: The locomotive systems of animals play a key role in behaviours such as foraging, predator avoidance and migrations. The range of behaviours and morphologies exhibited by animals have led to a variety of locomotor strategies. This thesis investigates the jet propulsion of cuttlefish (Sepia officinalis) where water is taken into a compressible cavity, this is compressed by surrounding musculature, forcing water out and forming a jet. This process involves the transfer of chemical energy into mechanical energy, before mechanical energy is transferred into the wake, propelling the animal through the water. Here the energy transduction chain is investigated from the biochemical level through the mechanical and ultimately into the wake of the animal, providing the most complete investigation into the energy transduction chain during locomotion to date. Investigations into the structure and function of cuttlefish jet propulsion swimming found cuttlefish produced two distinct jet modes. Jet mode use differed between hatchlings and juveniles. Differential use of jet modes may relate to flow environments inhabited by animals. Different flow environments may impact propulsive efficiency, where hatchlings are more efficient than juveniles. Juvenile propulsive efficiency was ~73 the highest reported value among cephalopods to date. Further investigations into the mechanical properties of mantle musculature found shortening velocities scale weakly with animal age, while cyclic measures revealed frequencies which produce the greatest net mechanical power decreased with age. Mechanical and hydrodynamic data reveal a transfer efficiency of ~26 Biochemical analyses of mantle muscle worked at three cycle frequencies revealed musculature heavily utilised ATP and phosphagen stores, however, no significant differences were seen between cycle frequencies, with the contractile efficiency being ~26 Taken together, these data revealed ~19 of the available biochemical energy was successfully transferred into useful movement, this seems to question the idea of jet propulsion swimming being an inefficient mode of locomotion; this value does not account for recovery processes, suggesting efficiency may be lower.

title: Left ventricular energetics: new insight into the plasticity of regional contributions at rest and during exercise.
abstract: Although the human left ventricle (LV) operates as a functional syncytium and previous studies have reported a single value for LV stroke work at rest, more intricate plasticity of regional LV energetics may be required during enhanced cardiovascular demand. We compared kinetic energy of the LV base and apex, respectively, during ventricular contraction and relaxation at rest and during continuous and discontinuous incremental exercise. At rest, prior to both exercise trials, the accumulated kinetic energy during contraction and relaxation was significantly higher at the LV base compared with the apex (P 0.05) With increasing exercise intensity, kinetic energy during contraction increased significantly more at the LV base (interaction effect: P 0.0001) while kinetic energy during relaxation increased significantly more at the apex during high intensity exercise (interaction effect: P 0.001) Total kinetic energy produced over the entire cardiac cycle was significantly greater at the LV apex during high exercise intensities (P 0.05) We further show that the region specific differences in kinetic energy at rest and during exercise are explained by significantly different wall mechanics, showing heterogenic contributions from radial, circumferential, and angular components at the base and apex, respectively. In conclusion, the present findings provide unique insight into human LV function by demonstrating that within this functional syncytium, significant differences in the regional contributions of kinetic energy to overall LV work exist. Importantly, regional contributions are not fixed but highly plastic and the underpinning LV wall energetics adjust according to the prevailing cardiovascular demand.

title: Working out the energetic cost of breathing during exercise
abstract: In healthy humans, the energetic cost of breathing at rest is low. However, during exercise, theworkof breathing increases as a function of ventilation in an exponential fashion. Age and biological sex are factors known to influence the total work of breathing (Guenette, Querido, Eves, Chua, Sheel, 2009; Smith, Cross, Van Iterson, Johnson, Olson, 2018) a measure that can be partitioned into resistive and viscoelastic components. The work of breathing for a given minute ventilation during exercise is greater in young females compared with young males, which is attributed to sex differences in the resistive component of the work of breathing, arising, it seems, because of anatomically narrower conducting airways in females, even when controlling for lung size. Healthy ageing increases the work of breathing, with recognized alterations to respiratory mechanics that can contribute to increased resistive and/or viscoelastic components of the work of breathing. In this issue of Experimental Physiology, Molgat Seon, Dominelli, Guenette, and Sheel (2019) set to work to determine the effects of ageing and sex on the constituent components of the work of breathing. The authors hypothesized that advancing age would increase the viscoelastic work of breathing, associated with changes to lung and chest wall compliance, and that age and sex would increase the resistive work of breathing, owing to increased airways resistance associatedwith structural differences in the conducting airways influencing turbulent airflow. To determine the effects of age and sex on the work of breathing, the authors modelled the relationship between the work of breathing and ventilation in younger female (21 28 years old) younger male (21 28 years old) older female (60 78 years old) and older male (62 80 years old) participants, revisiting a previous study that generated oesophageal pressure volume loops during incremental cycle ergometer tests to exhaustion (Molgat Seon et al. 2018) The mathematics revealed that ageing increased the resistive and viscoelastic work of breathing, independent of sex. There was

title: Running Economy from a Muscle Energetics Perspective
abstract: The economy of running has traditionally been quantified from the mass specific oxygen uptake; however, because fuel substrate usage varies with exercise intensity, it is more accurate to express running economy in units of metabolic energy. Fundamentally, the understanding of the major factors that influence the energy cost of running (Erun) can be obtained with this approach. Erun is determined by the energy needed for skeletal muscle contraction. Here, we approach the study of Erun from that perspective. The amount of energy needed for skeletal muscle contraction is dependent on the force, duration, shortening, shortening velocity, and length of the muscle. These factors therefore dictate the energy cost of running. It is understood that some determinants of the energy cost of running are not trainable: environmental factors, surface characteristics, and certain anthropometric features. Other factors affecting Erun are altered by training: other anthropometric features, muscle and tendon properties, and running mechanics. Here, the key features that dictate the energy cost during distance running are reviewed in the context of skeletal muscle energetics.

title: Stress increases intracardiac 4D flow cardiovascular magnetic resonance derived energetics and vorticity and relates to VO2max in Fontan patients
abstract: BackgroundWe hypothesize that dobutamine induced stress impacts intracardiac hemodynamic parameters and that this may be linked to decreased exercise capacity in Fontan patients. Therefore, the purpose of this study was to assess the effect of pharmacologic stress on intraventricular kinetic energy (KE) viscous energy loss (EL) and vorticity from four dimensional (4D) Flow cardiovascular magnetic resonance (CMR) imaging in Fontan patients and to study the association between stress response and exercise capacity.MethodsTen Fontan patients underwent whole heart 4D flow CMR before and during 7.5 mg/kg/min dobutamine infusion and cardiopulmonary exercise testing (CPET) on the same day. Average ventricular KE, EL and vorticity were computed over systole, diastole and the total cardiac cycle (vorticity_volavg cycle, KEavg cycle, ELavg cycle) The relation to maximum oxygen uptake (VO2 max) from CPET was tested by Pearson's correlation or Spearman's rank correlation in case of non normality of the data.ResultsDobutamine stress caused a significant 88 52% increase in KE (KEavg cycle: 1.8 0.5 vs 3.3 0.9 mJ, P 0.001) a significant 108 49% increase in EL (ELavg cycle: 0.9 0.4 vs 1.9 0.9 mW, P 0.001) and a significant 27 19% increase in vorticity (vorticity_volavg cycle: 3441 899 vs 4394 1322 mL/s, P 0.002) All rest stress differences were negatively correlated to VO2 max (KEavg cycle: r 0.83, P 0.003; ELavg cycle: r 0.80, P 0.006; vorticity_volavg cycle: r 0.64, P 0.047).Conclusions4D flow CMR derived intraventricular kinetic energy, viscous energy loss and vorticity in Fontan patients increase during pharmacologic stress and show a negative correlation with exercise capacity measured by VO2 max.