Bioenergetics of exercising humans

Exercise induces tissue-specific adaptations to enhance cardiometabolic health

The risk associated with multiple cancers, cardiovascular disease, diabetes, and all-cause mortality is decreased in individuals who meet the current recommendations for physical activity. Therefore, regular exercise remains a cornerstone in the prevention and treatment of non-communicable diseases. An acute bout of exercise results in the coordinated interaction between multiple tissues to meet the increased energy demand of exercise. Over time, the associated metabolic stress of each individual exercise bout provides the basis for long-term adaptations across tissues, including the cardiovascular system, skeletal muscle, adipose tissue, liver, pancreas, gut, and brain. Therefore, regular exercise is associated with a plethora of benefits throughout the whole body, including improved cardiorespiratory fitness, physical function, and glycemic control. Overall, we summarize the exercise-induced adaptations that occur within multiple tissues and how they converge to ultimately improve cardiometabolic health.

Assessing exogenous carbohydrate intake needed to optimize human endurance performance across sex: insights from modeling runners pursuing a sub-2-h marathon

Carbohydrate (CHO) availability sustains high metabolic demands during prolonged exercise. The adequacy of current CHO intake recommendations, 30-90 g·h-1 dependent on CHO mixture and tolerability, to support elite marathon performance is unclear. We sought to scrutinize the current upper limit recommendation for exogenous CHO intake to support modeled sub-2-h marathon (S2M) attempts across elite male and female runners. Male and female runners (n = 120 each) were modeled from published literature with reference characteristics necessary to complete a S2M (e.g., body mass and running economy). Completion of a S2M was considered across a range of respiratory exchange rates, with maximal starting skeletal muscle and liver glycogen content predicted for elite male and female runners. Modeled exogenous CHO bioavailability needed for male and female runners were 93 ± 26 and 108 ± 22 g·h-1, respectively (P < 0.0001, d = 0.61). Without exogenous CHO, males were modeled to deplete glycogen in 84 ± 7 min, females in 71 ± 5 min (P < 0.0001, d = 2.21) despite higher estimated CHO oxidation rates in males (5.1 ± 0.5 g·h-1) than females (4.4 ± 0.5 g·h-1; P < 0.0001, d = 1.47). Exogenous CHO intakes ≤ 90 g·h-1 are insufficient for 65% of modeled runners attempting a S2M. Current recommendations to support marathon performance appear inadequate for elite marathon runners but may be more suitable for male runners in pursuit of a S2M (56 of 120) than female runners (28 of 120).NEW & NOTEWORTHY This study scrutinizes the upper limit of exogenous carbohydrate (CHO) recommendations for elite male and female marathoners by modeling sex-specific needs across an extreme metabolic challenge lasting ∼2 h, a sub-2-h marathon. Contemporary nutritional guidelines to optimize marathon performance appear inadequate for most elite marathon runners but appear more appropriate for males over their female counterparts. Future research examining possible benefits of exogenous CHO intakes > 90 g·h-1 should prioritize female athlete study inclusion.

The relevance of body composition assessment for the rating of perceived exertion in trained and untrained women and men

Introduction: Mechanic power output (MPO) and oxygen consumption (VO2) reflect endurance capacity and are often stated relative to body mass (BM) but less often per skeletal muscle mass (SMM). Rating of perceived exertion (RPE) has previously shown conflicting results between sexes at submaximal intensities. Individual body composition, however, largely differs due to sex and training status. It was the aim of this study to evaluate RPE of untrained and trained individuals of both sexes considering body composition and to estimate whether RPE could be improved as a tool to determine endurance capacity. Methods: The study included 34 untrained adults (age 26.18 ± 6.34 years, 18 women) and 29 endurance trained (age 27.86 ± 5.19, 14 women) who were measured for body composition (InBody 770, InBody Europe B.V., Germany) and tested on a treadmill (Pulsar, H/P/Cosmos, Germany) for aerobic capacity (Metalyzer 3B, Cortex Biophysik GmbH, Germany) in an all-out exercise test applying the Bruce-protocol. VO2, MPO, heart rate (HR), and RPE were obtained at each exercise stage. VO2 and MPO were calculated per BM and SMM. RPE values were correlated with absolute VO2 and MPO, as well as relative to BM, and SMM. HR values and the parameters' standardized values served for comparison to standard procedures. Results: VO2 and MPO were higher in men compared to women and in trained compared to untrained participants. No differences between groups and sexes exist when VO2 and MPO were calculated per BM. When calculated per SMM, VO2 and MPO indicate opposite results already at low intensity stages of exercise test. RPE values had highest correlation with MPO per SMM (R2 = 0.8345) compared to absolute MPO (R2 = 0.7609), or MPO per BM (R2 = 0.8176). Agreement between RPE and MPO per SMM was greater than between RPE and HR (p = 0.008). Conclusion: Although RPE represents a subjective value at first glance, it was shown that RPE constitutes a valuable tool to estimate endurance capacity, which can be further enhanced if individual body composition is considered. Furthermore, MPO and VO2 should be considered relative to SMM. These findings might help to avoid over-exertion, especially among untrained people, by adjusting the training intensity for each subject according to the individual strain evaluated in an exercise test based on individual body composition.

A century of exercise physiology: key concepts in muscle energetics

In the mid-nineteenth century, the concept of muscle behaving like a stretched spring was developed. This elastic model of contraction predicted that the energy available to perform work was established at the start of a contraction. Despite several studies showing evidence inconsistent with the elastic model, it persisted into the twentieth century. In 1923, W. O. Fenn published a paper in which he presented evidence that appeared to clearly refute the elastic model. Fenn showed that when a muscle performs work it produces more heat than when contracting isometrically. He proposed that energy for performing work was only made available in a muscle as and when that work was performed. However, his ideas were not adopted and it was only after 15 years of technical developments that in 1938 A. V. Hill performed experiments that conclusively disproved the elastic model and supported Fenn's conclusions. Hill showed that the rate of heat production increased as a muscle made the transition from isometric to working contraction. Understanding the basis of the phenomenon observed by Fenn and Hill required another 40 years in which the processes that generate force and work in muscle and the associated scheme of biochemical reactions were established. Demonstration of the biochemical equivalent of Hill's observations-changes in rate of ATP splitting when performing work-in 1999 was possible through further technical advances. The concept that the energy, from ATP splitting, required to perform work is dynamically modulated in accord with the loads a muscle encounters when contracting is key to understanding muscle energetics.

Effects of Physical Exercise Program in Adults with Intellectual and Developmental Disabilities-A Study Protocol

We developed a physical exercise (PE) program for people with Intellectual and Developmental Disabilities (IDD), aiming to determine the effects on physical fitness, health, cognitive ability, and quality of life (QoL). Using experimental methodology, this intervention study recruited 21 adults (18 to 65 years old), institutionalized and with no other associated pathology, who will be allocated to one of the different groups: (i) gym/indoor intervention group (using weight machines), (ii) outdoor intervention group (using low-cost materials), or (iii) control group (without specific intervention, who continue with their normal daily activities). Both intervention groups will engage in 45 min of training per session, twice a week, for 24 weeks. Assessments will be conducted at baseline (initial assessment), 3 months (mid-term assessment), and 6 months (final assessment). Variables assessed include anthropometrics, body composition, functional capacity, muscle strength, general health, cognitive ability, and QoL. The results of this study will assist in the development of more effective strategies, recommendations, and interventions to ensure better and greater adherence to PE by institutionalized individuals with IDD, namely, recommendations for assessment, prescription, and implementation of PE for this population. Additionally, we intend to make available two PE programs, if they are adapted and promote positive effects.

Efficacy of Exercise on Muscle Function and Physical Performance in Older Adults with Sarcopenia: An Updated Systematic Review and Meta-Analysis

This study aimed to analyze the efficacy of exercise interventions on muscle strength, muscle mass, and physical performance in older adults with sarcopenia. Randomized controlled studies assessing exercise effects on sarcopenia were searched in Web of Science, PubMed, Cochrane Library, ProQuest, EBSCOhost, Scopus, EMBASE, and VIP and CNKI up to 31 March 2022. Data were expressed as weighted/standardized mean difference (MD/SMD) with 95% confidence intervals (CI). I² index was employed for heterogeneity. The initial search identified 5379 studies, and 23 studies involving 1252 participants met the inclusion criteria for further analysis. Results revealed that exercise interventions can significantly improve grip strength (MD = 2.38, 95%CI = 1.33–3.43), knee extension strength (SMD = 0.50, 95%CI = 0.36–0.64), muscle mass of lower extremities (MD = 0.28, 95%CI = 0.01–0.56), walking speed (SMD = 0.88, 95%CI = 0.49–1.27), and functional mobility (MD = −1.77, 95%CI = −2.11–−1.42) among older adults with sarcopenia. No significant exercise effects were found on fat-free muscle mass, appendicular muscle mass, skeletal muscle mass, and muscle mass of the upper extremities. The results of subgroup analysis indicated that both resistance training and multicomponent exercise could significantly increase the muscle strength, while aerobic exercise did not. The findings suggest that exercise intervention can effectively improve muscle function and physical performance in older adults with sarcopenia, but has limited effects on the muscle mass of the upper extremities. In addition, it is highly recommended to apply group-based and supervised resistance training and multicomponent exercise in the prevention and treatment of sarcopenia among the older population.

Comparison of the Effect of Endurance, Strength, and Endurance-Strength Training on Inflammatory Markers and Adipokines Levels in Overweight and Obese Adults: Systematic Review and Meta-Analysis of Randomised Trials

The aim of this meta-analysis was to compare the effects of endurance, strength, and combined training on inflammatory markers and adipokine concentrations in overweight and obese adults. We performed a literature search of the Cochrane Library, PubMed, Scopus, and Web of Science databases and identified 24 randomised control trials published prior to June 2021. Our findings indicate that endurance training was significantly more beneficial than strength training in reducing C-reactive protein (CRP) (standard mean difference (SMD): −1.317, 95% confidence intervals (CI): −2.565, −0.070, p = 0.0385), interleukin 6 (IL-6) (SMD: −0.363, 95% CI: −0.648, −0.078, p = 0.0126), and visfatin (SMD: −0.618, 95% CI: −1.015, −0.222, p = 0.0023) concentrations. Moreover, combined training was more beneficial than strength training alone in lowering tumour necrosis factor-alpha (TNF-α) levels (SMD: 0.890, 95% CI: −0.301, 1.478, p = 0.0030). There were no differences between the effects of different types of training programmes on adiponectin and leptin concentrations. In conclusion, compared with strength training, endurance training is more effective in lowering CRP, IL-6, and visfatin concentrations, while combined training is more beneficial in reducing TNF-α levels in overweight and obese adults. Further studies are needed to determine which type of training has a better effect on adiponectin and leptin concentrations in this population.

A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise

After a short historical account, and a discussion of Hill and Meyerhof’s theory of the energetics of muscular exercise, we analyse steady-state rest and exercise as the condition wherein coupling of respiration to metabolism is most perfect. The quantitative relationships show that the homeostatic equilibrium, centred around arterial pH of 7.4 and arterial carbon dioxide partial pressure of 40 mmHg, is attained when the ratio of alveolar ventilation to carbon dioxide flow (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}}_{A}/{\dot{V}}_{R}{CO}_{2}$$\end{document}V˙A/V˙RCO2) is − 21.6. Several combinations, exploited during exercise, of pertinent respiratory variables are compatible with this equilibrium, allowing adjustment of oxygen flow to oxygen demand without its alteration. During exercise transients, the balance is broken, but the coupling of respiration to metabolism is preserved when, as during moderate exercise, the respiratory system responds faster than the metabolic pathways. At higher exercise intensities, early blood lactate accumulation suggests that the coupling of respiration to metabolism is transiently broken, to be re-established when, at steady state, blood lactate stabilizes at higher levels than resting. In the severe exercise domain, coupling cannot be re-established, so that anaerobic lactic metabolism also contributes to sustain energy demand, lactate concentration goes up and arterial pH falls continuously. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}}_{A}/{\dot{V}}_{R}{CO}_{2}$$\end{document}V˙A/V˙RCO2 decreases below − 21.6, because of ensuing hyperventilation, while lactate keeps being accumulated, so that exercise is rapidly interrupted. The most extreme rupture of the homeostatic equilibrium occurs during breath-holding, because oxygen flow from ambient air to mitochondria is interrupted. No coupling at all is possible between respiration and metabolism in this case.

Comparing muscle VO2 from near-infrared spectroscopy desaturation rate to pulmonary VO2 during cycling below, at and above the maximal lactate steady state

Muscle oxygen uptake (V̇O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O_2m. However, its correspondence with pulmonary oxygen uptake (V̇O_2p) during exercise remains unknown.

PURPOSE

to investigate the V̇O_2m and V̇O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

METHODS

Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2-3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4-6) constant-PO exercise bouts to task failure at (i) 15% below MLSS (MLSS_-15%); (ii) MLSS; (iii) 15% above MLSS (MLSS_+15%). V̇O_2m was estimated at baseline, at min 5, 10, 20, 30, and at task failure. V̇O_2p was continuously recorded during the constant-PO bouts.

RESULTS

V̇O_2pand V̇O_2m significantly increased from min 5 to min 30 in MLSS condition (all p < 0.05) and from min 5 to min 10 in MLSS_+15% condition (all p < 0.05). V̇O_2pand V̇O_2m were correlated (r² adj range of 0.70-0.98, all p < 0.001) amongst exercise intensities in both females and males. Additionally, both variables were also correlated when expressed as percent (r² adj range of 0.52-0.77, all p < 0.001).

CONCLUSION

V̇O_2p and V̇O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇O_2p andV̇O_2m were correlated regardless the exercise intensity and sex of the participants.

Trade-Offs (and Constraints) in Organismal Biology

AbstractTrade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Trade-offs can be defined, categorized, and studied in at least six, not mutually exclusive, ways. (1) Allocation constraints are caused by a limited resource (e.g., energy, time, space, essential nutrients), such that increasing allocation to one component necessarily requires a decrease in another (if only two components are involved, this is referred to as the Y-model, e.g., energy devoted to size versus number of offspring). (2) Functional conflicts occur when features that enhance performance of one task decrease performance of another (e.g., relative lengths of in-levers and out-levers, force-velocity trade-offs related to muscle fiber type composition). (3) Shared biochemical pathways, often involving integrator molecules (e.g., hormones, neurotransmitters, transcription factors), can simultaneously affect multiple traits, with some effects being beneficial for one or more components of Darwinian fitness (e.g., survival, age at first reproduction, fecundity) and others detrimental. (4) Antagonistic pleiotropy describes genetic variants that increase one component of fitness (or a lower-level trait) while simultaneously decreasing another. (5) Ecological circumstances (or selective regime) may impose trade-offs, such as when foraging behavior increases energy availability yet also decreases survival. (6) Sexual selection may lead to the elaboration of (usually male) secondary sexual characters that improve mating success but handicap survival and/or impose energetic costs that reduce other fitness components. Empirical studies of trade-offs often search for negative correlations between two traits that are the expected outcomes of the trade-offs, but this will generally be inadequate if more than two traits are involved and especially for complex physiological networks of interacting traits. Moreover, trade-offs often occur only in populations that are experiencing harsh environmental conditions or energetic challenges at the extremes of phenotypic distributions, such as among individuals or species that have exceptional athletic abilities. Trade-offs may be (partially) circumvented through various compensatory mechanisms, depending on the timescale involved, ranging from acute to evolutionary. Going forward, a pluralistic view of trade-offs and constraints, combined with integrative analyses that cross levels of biological organization and traditional boundaries among disciplines, will enhance the study of evolutionary organismal biology.

Relating cardiorespiratory responses to work rate during incremental ramp exercise on treadmill in children and adolescents: sex and age differences

Purpose

Evaluation of cardiopulmonary exercise testing (CPET) slopes such as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d\mathrm{H}\mathrm{R}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}dHR/dWRtot (cardiac/skeletal muscle function) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${d \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}dV˙O2/dWRtot (O₂ delivery/utilization), using treadmill protocols is limited because the difficulties in measuring the total work rate (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}WRtot). To overcome this limitation, we proposed a new method in quantifying \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}WRtot to determine CPET slopes.

Methods

CPET’s were performed by healthy patients, (n = 674, 9–18 year) 300 female (F) and 374 male (M), using an incremental ramp protocol on a treadmill. For this protocol, a quantitative relationship based on biomechanical principles of human locomotion, was used to quantify the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}WRtot of the subject. CPET slopes were determined by linear regression of the data recorded until the gas exchange threshold occurred.

Results

The method to estimate \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}WRtot was substantiated by verifying that: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}dV˙O2/dWRtot for treadmill exercise corresponded to an efficiency of muscular work similar to that of cycle ergometer; \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}dV˙O2/dWRtot (mL min⁻¹ W⁻¹) was invariant with age and greater in M than F older than 12 years old (13–14 years: 9.6 ± 1.5(F) vs. 10.5 ± 1.8(M); 15–16 years: 9.7 ± 1.7(F) vs. 10.6 ± 2.2(M); 17–18 years: 9.6 ± 1.7(F) vs. 11.0 ± 2.3(M), p < 0.05); similar to cycle ergometer exercise, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$dHR/d{WR}_{tot}$$\end{document}dHR/dWRtot was inversely related to body weight (BW) (r = 0.71) or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2,{\text{~peak}}}}$$\end{document}V˙O2,peak (r = 0.66) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}dV˙O2/dWRtot was not related to BW (r = − 0.01), but had a weak relationship with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2,{\text{~peak}}}}$$\end{document}V˙O2,peak (r = 0.28).

Conclusion

The proposed approach can be used to estimate \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$\end{document}WRtot and quantify CPET slopes derived from incremental ramp protocols at submaximal exercise intensities using the treadmill, like the cycle ergometer, to infer cardiovascular and metabolic function in both healthy and diseased states.

Contextualizing the biological relevance of standardized high-resolution respirometry to assess mitochondrial function in permeabilized human skeletal muscle

Aim

This study sought to provide a statistically robust reference for measures of mitochondrial function from standardized high‐resolution respirometry with permeabilized human skeletal muscle (ex vivo), compare analogous values obtained via indirect calorimetry, arterial‐venous O₂ differences and ³¹P magnetic resonance spectroscopy (in vivo) and attempt to resolve differences across complementary methodologies as necessary.

Methods

Data derived from 831 study participants across research published throughout March 2009 to November 2019 were amassed to examine the biological relevance of ex vivo assessments under standard conditions, ie physiological temperatures of 37°C and respiratory chamber oxygen concentrations of ~250 to 500 μmol/L.

Results

Standard ex vivo‐derived measures are lower (Z ≥ 3.01, P ≤ .0258) en masse than corresponding in vivo‐derived values. Correcting respiratory values to account for mitochondrial temperatures 10°C higher than skeletal muscle temperatures at maximal exercise (~50°C): (i) transforms data to resemble (Z ≤ 0.8, P > .9999) analogous yet context‐specific in vivo measures, eg data collected during maximal 1‐leg knee extension exercise; and (ii) supports the position that maximal skeletal muscle respiratory rates exceed (Z ≥ 13.2, P < .0001) those achieved during maximal whole‐body exercise, e.g. maximal cycling efforts.

Conclusion

This study outlines and demonstrates necessary considerations when actualizing the biological relevance of human skeletal muscle respiratory control, metabolic flexibility and bioenergetics from standard ex vivo‐derived assessments using permeabilized human muscle. These findings detail how cross‐procedural comparisons of human skeletal muscle mitochondrial function may be collectively scrutinized in their relationship to human health and lifespan.

5 km front crawl in pool and open water swimming: breath-by-breath energy expenditure and kinematic analysis

PURPOSE

Breath-by-breath energy expenditure during open water swimming has not yet been explored in an ecological environment. This study aimed to investigate and compare energetics and kinematics of 5 km swimming, in both swimming pool and open water conditions.

METHODS

Through four independent studies, oxygen uptake ([Formula: see text]₂) kinetics, heart rate (HR), blood lactate concentration ([La^-]) and glucose level (BGL), metabolic power ([Formula: see text]), energy cost (C) and kinematics were assessed during 5 km front crawl trials in a swimming pool and open water conditions. A total of 38 competitive open water swimmers aged 16-27 years volunteered for this four part investigation: Study A (pool, ten females, 11 males), Study B (pool, four females, six males), Study C (pool case study, one female) and Study D (open water, three females, four males).

RESULTS

In the swimming pool, swimmers started with an above average swimming speed (v), losing efficiency along the 5 km, despite apparent homeostasis for [La^-], BGL, [Formula: see text]₂, [Formula: see text] and C. In open water, swimmers started the 5 km with a below average v, increasing the stroke rate (SR) in the last 1000 m. In open water, [Formula: see text]₂ kinetics parameters, HR, [La^-], BGL, respiratory exchange ratio and C were affected by the v and SR fluctuations along the 5 km.

CONCLUSIONS

Small fluctuations were observed for energetic variables in both conditions, but changes in C were lower in swimming pool than in open water. Coaches should adjust the training plan accordingly to the specificity of open water swimming.

Adaptations to Endurance and Strength Training

The capacity for human exercise performance can be enhanced with prolonged exercise training, whether it is endurance- or strength-based. The ability to adapt through exercise training allows individuals to perform at the height of their sporting event and/or maintain peak physical condition throughout the life span. Our continued drive to understand how to prescribe exercise to maximize health and/or performance outcomes means that our knowledge of the adaptations that occur as a result of exercise continues to evolve. This review will focus on current and new insights into endurance and strength-training adaptations and will highlight important questions that remain as far as how we adapt to training.

The Science and Translation of Lactate Shuttle Theory

Once thought to be a waste product of anaerobic metabolism, lactate is now known to form continuously under aerobic conditions. Shuttling between producer and consumer cells fulfills at least three purposes for lactate: (1) a major energy source, (2) the major gluconeogenic precursor, and (3) a signaling molecule. "Lactate shuttle" (LS) concepts describe the roles of lactate in delivery of oxidative and gluconeogenic substrates as well as in cell signaling. In medicine, it has long been recognized that the elevation of blood lactate correlates with illness or injury severity. However, with lactate shuttle theory in mind, some clinicians are now appreciating lactatemia as a "strain" and not a "stress" biomarker. In fact, clinical studies are utilizing lactate to treat pro-inflammatory conditions and to deliver optimal fuel for working muscles in sports medicine. The above, as well as historic and recent studies of lactate metabolism and shuttling, are discussed in the following review.

Lactate metabolism: historical context, prior misinterpretations, and current understanding

Lactate (La^-) has long been at the center of controversy in research, clinical, and athletic settings. Since its discovery in 1780, La^- has often been erroneously viewed as simply a hypoxic waste product with multiple deleterious effects. Not until the 1980s, with the introduction of the cell-to-cell lactate shuttle did a paradigm shift in our understanding of the role of La^- in metabolism begin. The evidence for La^- as a major player in the coordination of whole-body metabolism has since grown rapidly. La^- is a readily combusted fuel that is shuttled throughout the body, and it is a potent signal for angiogenesis irrespective of oxygen tension. Despite this, many fundamental discoveries about La^- are still working their way into mainstream research, clinical care, and practice. The purpose of this review is to synthesize current understanding of La^- metabolism via an appraisal of its robust experimental history, particularly in exercise physiology. That La^- production increases during dysoxia is beyond debate, but this condition is the exception rather than the rule. Fluctuations in blood [La^-] in health and disease are not typically due to low oxygen tension, a principle first demonstrated with exercise and now understood to varying degrees across disciplines. From its role in coordinating whole-body metabolism as a fuel to its role as a signaling molecule in tumors, the study of La^- metabolism continues to expand and holds potential for multiple clinical applications. This review highlights La^-'s central role in metabolism and amplifies our understanding of past research.

The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution

We examined the effects of inserting 3-s recovery periods during high-intensity cycling exercise at 25-s and 10-s intervals on pulmonary oxygen uptake (V̇o_2p), muscle deoxygenation [deoxyhemoglobin (HHb)], their associated kinetics (τ), and energy system contributions. Eleven men (24 ± 3 yr) completed two trials of three cycling protocols: an 8-min continuous protocol (CONT) and two 8-min intermittent exercise protocols with work-to-rest periods of 25 s to 3 s (25INT) and 10 s to 3 s (10INT). Each protocol began with a step-transition from a 20-W baseline to a power output (PO) of 60% between lactate threshold and maximal V̇o_2p (Δ60). This PO was maintained for 8 min in CONT, whereas 3-s periods of 20-W cycling were inserted every 10 s and 25 s after the transition to Δ60 in 10INT and 25INT, respectively. Breath-by-breath gas exchange measured by mass spectrometry and turbine and vastus lateralis [HHb] measured by near-infrared spectroscopy were recorded throughout. Arterialized-capillary lactate concentration ([Lac^-]) was obtained before and 2 min postexercise. The τV̇o_2p was lowest (P < 0.05) for 10INT (24 ± 4 s) and 25INT (23 ± 5 s) compared with CONT (28 ± 4 s), whereas HHb kinetics did not differ (P > 0.05) between conditions. Postexercise [Lac^-] was lowest (P < 0.05) for 10INT (7.0 ± 1.7 mM), was higher for 25INT (10.3 ± 1.9 mM), and was greatest in CONT (14.3 ± 3.1 mM). Inserting 3-s recovery periods during heavy-intensity exercise speeded V̇o_2p kinetics and reduced overall V̇o_2p, suggesting an increased reliance on PCr-derived phosphorylation during the work period of INT compared with an identical PO performed continuously.NEW & NOTEWORTHY We report novel observations on the effects of differing heavy-intensity work durations between 3-s recovery periods on pulmonary oxygen uptake (V̇o_2p) kinetics, muscle deoxygenation, and energy system contributions. Relative to continuous exercise, V̇o_2p kinetics are faster in intermittent exercise, and increased frequency of 3-s recovery periods improves microvascular O₂ delivery and reduces V̇o_2p and arterialized-capillary lactate concentration. The metabolic burden of identical intensity work is altered when performed intermittently vs. continuously.

Energy demand and supply in human skeletal muscle

The energy required for muscle contraction is provided by the breakdown of ATP but the amount of ATP in muscles cells is sufficient to power only a short duration of contraction. Buffering of ATP by phosphocreatine, a reaction catalysed by creatine kinase, extends the duration of activity possible but sustained activity depends on continual regeneration of PCr. This is achieved using ATP generated by oxidative processes and, during intense activity, by anaerobic glycolysis. The rate of ATP breakdown ranges from 70 to 140 mM min^-1 during isometric contractions of various intensity to as much as 400 mM min^-1 during intense, dynamic activity. The maximum rate of oxidative energy supply in untrained people is ~50 mM min^-1 which, if the contraction duty cycle is 0.5 as is often the case in cyclic activity, is sufficient to match an ATP breakdown rate during contraction of 100 mM min^-1. During brief, intense activity the rate of ATP turnover can exceed the rates of PCr regeneration by combined oxidative and glycolytic energy supply, resulting in a net decrease in PCr concentration. Glycolysis has the capacity to produce between 30 and 50 mM of ATP so that, for example, anaerobic glycolysis could provide ATP at an average of 100 mM min^-1 over 30 s of exhausting activity. The creatine kinase reaction plays an important role not only in buffering ATP but also in communicating energy demand from sites of ATP breakdown to the mitochondria. In that role, creatine kinases acts to slow and attenuate the response of mitochondria to changes in energy demand.

A new method to calculate external mechanical work using force-platform data in ecological situations in humans: Application to Parkinson's disease

BACKGROUND AND AIM

To accurately quantify the cost of physical activity and to evaluate the different components of energy expenditure in humans, it is necessary to evaluate external mechanical work (WEXT). Large platform systems surpass other currently used techniques. Here, we describe a calculation method for force-platforms to calculate long-term WEXT.

METHODS

Each force-platform (2.46×1.60m and 3.80×2.48m) rests on 4 piezoelectric sensors. During long periods of recording, a drift in the speed of displacement of the center of mass (necessary to calculate WEXT) is generated. To suppress this drift, wavelet decomposition is used to low-pass filter the source signal. By using wavelet decomposition coefficients, the source signal can be recovered. To check the validity of WEXT calculations after signal processing, an oscillating pendulum system was first used; then, 10 healthy subjects performed a standardized exercise (squatting exercise). A medical application is also reported in eight Parkinsonian patients during the timed "get-up and go" test and compared with the same test in ten healthy subjects.

RESULTS

Values of WEXT with the oscillating pendulum showed that the system was accurate and reliable. During the squatting exercise, the average measured WEXT was 0.4% lower than theoretical work. WEXT and mechanical work efficiency during the "get-up and go" test in Parkinson's disease patients in comparison with that of healthy subjects were very coherent.

CONCLUSIONS

This method has numerous applications for studying physical activity and mechanical work efficiency in physiological and pathological conditions.

Physiological and pathophysiological reactive oxygen species as probed by EPR spectroscopy: the underutilized research window on muscle ageing

Reactive oxygen and nitrogen species (ROS and RNS) play crucial roles in triggering, mediating and regulating physiological and pathophysiological signal transduction pathways within the cell. Within the cell, ROS efflux is firmly controlled both spatially and temporally, making the study of ROS dynamics a challenging task. Different approaches have been developed for ROS assessment; however, many of these assays are not capable of direct identification or determination of subcellular localization of different ROS. Here we highlight electron paramagnetic resonance (EPR) spectroscopy as a powerful technique that is uniquely capable of addressing questions on ROS dynamics in different biological specimens and cellular compartments. Due to their critical importance in muscle functions and dysfunction, we discuss in some detail spin trapping of various ROS and focus on EPR detection of nitric oxide before highlighting how EPR can be utilized to probe biophysical characteristics of the environment surrounding a given stable radical. Despite the demonstrated ability of EPR spectroscopy to provide unique information on the identity, quantity, dynamics and environment of radical species, its applications in the field of muscle physiology, fatiguing and ageing are disproportionately infrequent. While reviewing the limited examples of successful EPR applications in muscle biology we conclude that the field would greatly benefit from more studies exploring ROS sources and kinetics by spin trapping, protein dynamics by site-directed spin labelling, and membrane dynamics and global redox changes by spin probing EPR approaches.

Higher rate of fat oxidation during rowing compared with cycling ergometer exercise across a range of exercise intensities

The relative contribution of carbohydrate and fat oxidation to energy expenditure during exercise is dependent on variables including exercise intensity, mode, and recruited muscle mass. This study investigated patterns of substrate utilization during two non-weightbearing exercise modalities, namely cycling and rowing. Thirteen young, moderately trained males performed a continuous incremental (3-min stages) exercise test to exhaustion on separate occasions on an electronically braked cycle (CYC) ergometer and an air-braked rowing (ROW) ergometer, respectively. On two further occasions, participants performed a 20-min steady-state exercise bout at ∼50%VO2peak on the respective modalities. Despite similar oxygen consumption, rates of fat oxidation (FATox ) were ∼45% higher during ROW compared with CYC (P < 0.05) across a range of power output increments. The crossover point for substrate utilization occurred at a higher relative exercise intensity for ROW than CYC (57.8 ± 2.1 vs 42.1 ± 3.6%VO2peak , P < 0.05). During steady-state submaximal exercise, the higher FATox during ROW compared with CYC was maintained (P < 0.05), but absolute FATox were 42% (CYC) and 28% (ROW) lower than during incremental exercise. FATox is higher during ROW compared with CYC exercise across a range of exercise intensities matched for energy expenditure, and is likely as a consequence of larger muscle mass recruited during ROW.

Integrative biology of exercise

Exercise represents a major challenge to whole-body homeostasis provoking widespread perturbations in numerous cells, tissues, and organs that are caused by or are a response to the increased metabolic activity of contracting skeletal muscles. To meet this challenge, multiple integrated and often redundant responses operate to blunt the homeostatic threats generated by exercise-induced increases in muscle energy and oxygen demand. The application of molecular techniques to exercise biology has provided greater understanding of the multiplicity and complexity of cellular networks involved in exercise responses, and recent discoveries offer perspectives on the mechanisms by which muscle "communicates" with other organs and mediates the beneficial effects of exercise on health and performance.