1
|
Barclay CJ, Curtin NA. Advances in understanding the energetics of muscle contraction. J Biomech 2023; 156:111669. [PMID: 37302165 DOI: 10.1016/j.jbiomech.2023.111669] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Accepted: 05/30/2023] [Indexed: 06/13/2023]
Abstract
Muscle energetics encompasses the relationships between mechanical performance and the biochemical and thermal changes that occur during muscular activity. The biochemical reactions that underpin contraction are described and the way in which these are manifest in experimental recordings, as initial and recovery heat, is illustrated. Energy use during contraction can be partitioned into that related to cross-bridge force generation and that associated with activation by Ca2+. Activation processes account for 25-45% of ATP turnover in an isometric contraction, varying amongst muscles. Muscle energy use during contraction depends on the nature of the contraction. When shortening muscles produce less force than when contracting isometrically but use energy at a greater rate. These characteristics reflect more rapid cross-bridge cycling when shortening. When lengthening, muscles produce more force than in an isometric contraction but use energy at a lower rate. In that case, cross-bridges cycle but via a pathway in which ATP splitting is not completed. Shortening muscles convert part of the free energy available from ATP hydrolysis into work with the remainder appearing as heat. In the most efficient muscle studied, that of a tortoise, cross-bridges convert a maximum of 47% of the available energy into work. In most other muscles, only 20-30% of the free energy from ATP hydrolysis is converted into work.
Collapse
Affiliation(s)
- C J Barclay
- School of Biomedical Sciences, University of Queensland, St Lucia, Queensland, Australia.
| | - N A Curtin
- Cardio-Respiratory Interface, NHLI, Imperial College London, London SW7 2AZ, UK
| |
Collapse
|
2
|
Curtin NA, Barclay CJ. The energetics of muscle contractions resembling in vivo performance. J Biomech 2023; 156:111665. [PMID: 37327644 DOI: 10.1016/j.jbiomech.2023.111665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 05/22/2023] [Indexed: 06/18/2023]
Abstract
Muscle energetics has expanded into the study of contractions that resemble in vivo muscle activity. A summary is provided of experiments of this type and what they have added to our understanding of muscle function and effects of compliant tendons, as well as the new questions raised about the efficiency of energy transduction in muscle.
Collapse
Affiliation(s)
- N A Curtin
- Cardio-Respiratory Interface, NHLI, Imperial College London, London SW7 2AZ UK.
| | - C J Barclay
- School of Biomedical Sciences, University of Queensland, St Lucia, Queensland, Australia
| |
Collapse
|
3
|
Fitzgerald LF, Bartlett MF, Nagarajan R, Francisco EJ, Sup FC, Kent JA. Effects of old age and contraction mode on knee extensor muscle ATP flux and metabolic economy in vivo. J Physiol 2021; 599:3063-3080. [PMID: 33876434 DOI: 10.1113/jp281117] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 04/14/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS We used 31-phosphorus magnetic resonance spectroscopy to quantify in vivo skeletal muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) during three 24 s maximal-effort contraction protocols: (1) sustained isometric (MVIC), (2) intermittent isokinetic (MVDCIsoK ), and (3) intermittent isotonic (MVDCIsoT ) in the knee extensor muscles of young and older adults. ME was not different between groups during the MVIC but was lower in older than young adults during both dynamic contraction protocols. These results are consistent with an increased energy cost of locomotion, but not postural support, with age. The effects of old age on ME were not due to age-related changes in muscle oxidative capacity or ATP flux. Specific power was lower in older than young adults, despite similar total ATP synthesis between groups. Together, this suggests a dissociation between cross-bridge activity and ATP utilization with age. ABSTRACT Muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) is similar in young and older adults during some isometric contractions, but less is known about potential age-related differences in ME during dynamic contractions. We hypothesized that age-related differences in ME would exist only during dynamic contractions, due to the increased energetic demand of dynamic versus isometric contractions. Ten young (Y; 27.5 ± 3.9 years, 6 men) and 10 older (O; 71 ± 5 years, 5 men) healthy adults performed three 24 s bouts of maximal contractions: (1) sustained isometric (MVIC), (2) isokinetic (120°·s-1 , MVDCIsoK ; 0.5 Hz), and (3) isotonic (load = 20% MVIC, MVDCIsoT ; 0.5 Hz). Phosphorus magnetic resonance spectroscopy of the vastus lateralis muscle was used to calculate ATP flux (mM ATP·s-1 ) through the creatine kinase reaction, glycolysis and oxidative phosphorylation. Quadriceps contractile volume (cm3 ) was measured by MRI. ME was calculated using the torque-time integral (MVIC) or power-time integral (MVDCIsoK and MVDCIsoT ), total ATP synthesis and contractile volume. As hypothesized, ME was not different between Y and O during the MVIC (0.12 ± 0.03 vs. 0.12 ± 0.02 Nm. s. cm-3 . mM ATP-1 , mean ± SD, respectively; P = 0.847). However, during both MVDCIsoK and MVDCIsoT , ME was lower in O than Y adults (MVDCIsoK : 0.011 ± 0.003 vs. 0.007 ± 0.002 J. cm-3 . mM ATP-1 ; P < 0.001; MVDCIsoT : 0.011 ± 0.002 vs. 0.008 ± 0.002; P = 0.037, respectively), despite similar muscle oxidative capacity, oxidative and total ATP flux in both groups. The lower specific power in older than young adults, despite similar total ATP synthesis between groups, suggests there is a dissociation between cross-bridge activity and ATP utilization with age.
Collapse
Affiliation(s)
- Liam F Fitzgerald
- Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Miles F Bartlett
- Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Rajakumar Nagarajan
- Human Magnetic Resonance Center, Institute for Applied Life Sciences, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Ericber Jimenez Francisco
- Mechatronics and Robotics Laboratory, Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Frank C Sup
- Mechatronics and Robotics Laboratory, Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Jane A Kent
- Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| |
Collapse
|
4
|
Haeufle DFB, Siegel J, Hochstein S, Gussew A, Schmitt S, Siebert T, Rzanny R, Reichenbach JR, Stutzig N. Energy Expenditure of Dynamic Submaximal Human Plantarflexion Movements: Model Prediction and Validation by in-vivo Magnetic Resonance Spectroscopy. Front Bioeng Biotechnol 2020; 8:622. [PMID: 32671034 PMCID: PMC7332772 DOI: 10.3389/fbioe.2020.00622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 05/21/2020] [Indexed: 11/30/2022] Open
Abstract
To understand the organization and efficiency of biological movement, it is important to evaluate the energy requirements on the level of individual muscles. To this end, predicting energy expenditure with musculoskeletal models in forward-dynamic computer simulations is currently the most promising approach. However, it is challenging to validate muscle models in-vivo in humans, because access to the energy expenditure of single muscles is difficult. Previous approaches focused on whole body energy expenditure, e.g., oxygen consumption (VO2), or on thermal measurements of individual muscles by tracking blood flow and heat release (through measurements of the skin temperature). This study proposes to validate models of muscular energy expenditure by using functional phosphorus magnetic resonance spectroscopy (31P-MRS). 31P-MRS allows to measure phosphocreatine (PCr) concentration which changes in relation to energy expenditure. In the first 25 s of an exercise, PCr breakdown rate reflects ATP hydrolysis, and is therefore a direct measure of muscular enthalpy rate. This method was applied to the gastrocnemius medialis muscle of one healthy subject during repetitive dynamic plantarflexion movements at submaximal contraction, i.e., 20% of the maximum plantarflexion force using a MR compatible ergometer. Furthermore, muscle activity was measured by surface electromyography (EMG). A model (provided as open source) that combines previous models for muscle contraction dynamics and energy expenditure was used to reproduce the experiment in simulation. All parameters (e.g., muscle length and volume, pennation angle) in the model were determined from magnetic resonance imaging or literature (e.g., fiber composition), leaving no free parameters to fit the experimental data. Model prediction and experimental data on the energy supply rates are in good agreement with the validation phase (<25 s) of the dynamic movements. After 25 s, the experimental data differs from the model prediction as the change in PCr does not reflect all metabolic contributions to the energy expenditure anymore and therefore underestimates the energy consumption. This shows that this new approach allows to validate models of muscular energy expenditure in dynamic movements in vivo.
Collapse
Affiliation(s)
- Daniel F B Haeufle
- Multi-level Modeling in Motor Control and Rehabilitation Robotics, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
| | - Johannes Siegel
- Multi-level Modeling in Motor Control and Rehabilitation Robotics, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.,Department of Motion and Exercise Science, Institute of Sport and Movement Science, University of Stuttgart, Stuttgart, Germany
| | - Stefan Hochstein
- Motion Science, Institute of Sport Science, Martin-Luther-University Halle, Halle, Germany
| | - Alexander Gussew
- Department of Radiology, University Hospital Halle (Saale), Halle, Germany
| | - Syn Schmitt
- Computational Biophysics and Biorobotics, Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany.,Stuttgart Center of Simulation Science, University of Stuttgart, Stuttgart, Germany
| | - Tobias Siebert
- Department of Motion and Exercise Science, Institute of Sport and Movement Science, University of Stuttgart, Stuttgart, Germany
| | - Reinhard Rzanny
- Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University, Jena, Germany
| | - Jürgen R Reichenbach
- Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University, Jena, Germany
| | - Norman Stutzig
- Department of Motion and Exercise Science, Institute of Sport and Movement Science, University of Stuttgart, Stuttgart, Germany
| |
Collapse
|
5
|
Lemaire KK, Jaspers RT, Kistemaker DA, van Soest AJK, van der Laarse WJ. Metabolic Cost of Activation and Mechanical Efficiency of Mouse Soleus Muscle Fiber Bundles During Repetitive Concentric and Eccentric Contractions. Front Physiol 2019; 10:760. [PMID: 31293438 PMCID: PMC6599155 DOI: 10.3389/fphys.2019.00760] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 05/31/2019] [Indexed: 11/23/2022] Open
Abstract
Currently available data on the energetics of isolated muscle preparations are based on bouts of less than 10 muscle contractions, whereas metabolic energy consumption is mostly relevant during steady state tasks such as locomotion. In this study we quantified the energetics of small fiber bundles of mouse soleus muscle during prolonged (2 min) series of contractions. Bundles (N = 9) were subjected to sinusoidal length changes, while measuring force and oxygen consumption. Stimulation (five pulses at 100 Hz) occurred either during shortening or during lengthening. Movement frequency (2–3 Hz) and amplitude (0.25–0.50 mm; corresponding to ± 4–8% muscle fiber strain) were close to that reported for mouse soleus muscle during locomotion. The experiments were performed at 32°C. The contributions of cross-bridge cycling and muscle activation to total metabolic energy expenditure were separated using blebbistatin. The mechanical work per contraction cycle decreased sharply during the first 10 cycles, emphasizing the importance of prolonged series of contractions. The mean ± SD fraction of metabolic energy required for activation was 0.37 ± 0.07 and 0.56 ± 0.17 for concentric and eccentric contractions, respectively (both 0.25 mm, 2 Hz). The mechanical efficiency during concentric contractions increased with contraction velocity from 0.12 ± 0.03 (0.25 mm 2 Hz) to 0.15 ± 0.03 (0.25 mm, 3 Hz) and 0.16 ± 0.02 (0.50 mm, 2 Hz) and was -0.22 ± 0.08 during eccentric contractions (0.25 mm, 2 Hz). The percentage of type I fibers correlated positively with mechanical efficiency during concentric contractions, but did not correlate with the fraction of metabolic energy required for activation.
Collapse
Affiliation(s)
- Koen K Lemaire
- Amsterdam Movement Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Richard T Jaspers
- Laboratory for Myology, Amsterdam Movement Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Dinant A Kistemaker
- Amsterdam Movement Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - A J Knoek van Soest
- Amsterdam Movement Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Willem J van der Laarse
- Department of Physiology, Amsterdam Cardiovascular Sciences, Amsterdam University Medical Center, Amsterdam, Netherlands
| |
Collapse
|
6
|
Bunda J, Gittings W, Vandenboom R. Myosin phosphorylation improves contractile economy of mouse fast skeletal muscle during staircase potentiation. ACTA ACUST UNITED AC 2018; 221:jeb.167718. [PMID: 29361581 DOI: 10.1242/jeb.167718] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 12/31/2017] [Indexed: 01/12/2023]
Abstract
Phosphorylation of the myosin regulatory light chain (RLC) by skeletal myosin light chain kinase (skMLCK) potentiates rodent fast twitch muscle but is an ATP-requiring process. Our objective was to investigate the effect of skMLCK-catalyzed RLC phosphorylation on the energetic cost of contraction and the contractile economy (ratio of mechanical output to metabolic input) of mouse fast twitch muscle in vitro (25°C). To this end, extensor digitorum longus (EDL) muscles from wild-type (WT) and from skMLCK-devoid (skMLCK-/-) mice were subjected to repetitive low-frequency stimulation (10 Hz for 15 s) to produce staircase potentiation of isometric twitch force, after which muscles were quick frozen for determination of high-energy phosphate consumption (HEPC). During stimulation, WT muscles displayed significant potentiation of isometric twitch force while skMLCK-/- muscles did not (i.e. 23% versus 5% change, respectively). Consistent with this, RLC phosphorylation was increased ∼3.5-fold from the unstimulated control value in WT but not in skMLCK-/- muscles. Despite these differences, the HEPC of WT muscles was not greater than that of skMLCK-/- muscles. As a result of the increased contractile output relative to HEPC, the calculated contractile economy of WT muscles was greater than that of skMLCK-/- muscles. Thus, our results suggest that skMLCK-catalyzed phosphorylation of the myosin RLC increases the contractile economy of WT mouse EDL muscle compared with skMLCK-/- muscles without RLC phosphorylation.
Collapse
Affiliation(s)
- Jordan Bunda
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
| | - William Gittings
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
| | - Rene Vandenboom
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
| |
Collapse
|
7
|
Jaafar H, Lajili H. Separate and combined effects of time of day and verbal instruction on knee extensor neuromuscular adjustments. Appl Physiol Nutr Metab 2018; 43:54-62. [DOI: 10.1139/apnm-2017-0343] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We examined the effects of time of day and verbal instruction, separately and combined, on knee extensor neuromuscular adjustments, with special reference to rapid muscle force production capacity. Ten healthy male participants performed 4 experimental trials in counterbalanced order: morning “hard-and-fast” instruction, evening hard-and-fast instruction, morning “fast” instruction, and evening fast instruction. During each experimental trial, neuromuscular performance was assessed from the completion of 6 maximal isometric voluntary contractions (rest = 2 min) of the knee extensors with concomitant quadriceps surface electromyography recordings. For each contraction, we determined maximal voluntary force (Fmax), maximal rate of force development (RFDmax) and associated maximal electromechanical delay (EMDmax), and maximal rate of muscle activation (RMAmax). Globally, oral temperature (+2.2%), Fmax (+4.9%) and accompanying median frequency (+6.6%)/mean power frequency (+6.0%) as well as RFDmax (+13.5%) and RMAmax (+15.5%) were significantly higher in the evening than morning (p < 0.05). Conversely, evening in reference to morning values were lower for EMDmax (–4.3%, p < 0.05). Compared with a hard-and-fast instruction, RFDmax (+30.6%) and corresponding root mean square activity (+18.6%) were globally higher using a fast instruction (p < 0.05), irrespectively of the time of day. There was no significant interaction effect of time of day and verbal instruction on any parameter, except for EMDmax (p = 0.028). Despite diurnal variation in maximal or explosive force production of knee extensors and associated neuromuscular parameters, these adjustments occurred essentially independently of the verbal instruction provided.
Collapse
Affiliation(s)
- Hamdi Jaafar
- Institut du savoir Montfort – Recherche, Ottawa, 713 Chemin Montréal, Ottawa, ON K1K 0T2, Canada
- Faculty of Medicine, Biochemistry, Microbiology and Immunology Department, University of Ottawa, Ottawa, Ontario, Canada
| | - Hanene Lajili
- Centre de Rééducation et de Réadaptation Fonctionnelle La Châtaigneraie, Menucourt, France
| |
Collapse
|
8
|
Barclay CJ. The basis of differences in thermodynamic efficiency among skeletal muscles. Clin Exp Pharmacol Physiol 2017; 44:1279-1286. [PMID: 28892557 DOI: 10.1111/1440-1681.12850] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 08/27/2017] [Accepted: 08/31/2017] [Indexed: 12/01/2022]
Abstract
Muscles convert chemical free energy into mechanical work. The energy conversion occurs in 2 steps. First, free energy obtained from oxidation of metabolic substrates (ΔGS ) is transferred to ATP and, second, free energy from ATP hydrolysis (ΔGATP ) is converted into work by myosin cross-bridges. The fraction of ΔGS transferred to ATP is called mitochondrial efficiency (ηM ) and the fraction of ΔGATP converted into work is called cross-bridge efficiency (ηCB ). Overall cross-bridge efficiency varies among muscles from ~20% and 35% and the analysis presented in the current studies shows that this variation is largely due to differences in ηCB whereas ηM is similar (~80%) in all the muscles assessed. There is an inverse, linear relationship between maximum normalised power output and ηCB ; that is, more efficient muscles tend to be less powerful than less efficient muscles. It is proposed that differences in cross-bridge efficiency reflect the extent to which cross-bridges traverse the force-length relationship for attached cross-bridges. In this framework, cross-bridges from tortoise muscle (ηCB = 45%) produce close to the maximum possible work a cross-bridge can perform in a single attachment cycle.
Collapse
|
9
|
Pham T, Tran K, Mellor KM, Hickey A, Power A, Ward ML, Taberner A, Han JC, Loiselle D. Does the intercept of the heat-stress relation provide an accurate estimate of cardiac activation heat? J Physiol 2017; 595:4725-4733. [PMID: 28455843 DOI: 10.1113/jp274174] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 04/20/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The heat of activation of cardiac muscle reflects the metabolic cost of restoring ionic homeostasis following a contraction. The accuracy of its measurement depends critically on the abolition of crossbridge cycling. We abolished crossbridge activity in isolated rat ventricular trabeculae by use of blebbistatin, an agent that selectively inhibits myosin II ATPase. We found cardiac activation heat to be muscle length independent and to account for 15-20% of total heat production at body temperature. We conclude that it can be accurately estimated at minimal muscle length. ABSTRACT Activation heat arises from two sources during the contraction of striated muscle. It reflects the metabolic expenditure associated with Ca2+ pumping by the sarcoplasmic reticular Ca2+ -ATPase and Ca2+ translocation by the Na+ /Ca2+ exchanger coupled to the Na+ ,K+ -ATPase. In cardiac preparations, investigators are constrained in estimating its magnitude by reducing muscle length to the point where macroscopic twitch force vanishes. But this experimental protocol has been criticised since, at zero force, the observed heat may be contaminated by residual crossbridge cycling activity. To eliminate this concern, the putative thermal contribution from crossbridge cycling activity must be abolished, at least at minimal muscle length. We achieved this using blebbistatin, a selective inhibitor of myosin II ATPase. Using a microcalorimeter, we measured the force production and heat output, as functions of muscle length, of isolated rat trabeculae from both ventricles contracting isometrically at 5 Hz and at 37°C. In the presence of blebbistatin (15 μmol l-1 ), active force was zero but heat output remained constant, at all muscle lengths. Activation heat measured in the presence of blebbistatin was not different from that estimated from the intercept of the heat-stress relation in its absence. We thus reached two conclusions. First, activation heat is independent of muscle length. Second, residual crossbridge heat is negligible at zero active force; hence, the intercept of the cardiac heat-force relation provides an estimate of activation heat uncontaminated by crossbridge cycling. Both results resolve long-standing disputes in the literature.
Collapse
Affiliation(s)
- Toan Pham
- Department of Physiology, University of Auckland, Auckland, New Zealand.,Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Kenneth Tran
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | | | - Anthony Hickey
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Amelia Power
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Marie-Louise Ward
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Andrew Taberner
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.,Department of Engineering Science, University of Auckland, Auckland, New Zealand
| | - June-Chiew Han
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Denis Loiselle
- Department of Physiology, University of Auckland, Auckland, New Zealand.,Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| |
Collapse
|
10
|
Barclay CJ. Energy demand and supply in human skeletal muscle. J Muscle Res Cell Motil 2017; 38:143-155. [PMID: 28286928 DOI: 10.1007/s10974-017-9467-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Accepted: 02/14/2017] [Indexed: 12/18/2022]
Abstract
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.
Collapse
Affiliation(s)
- C J Barclay
- School of Allied Health Sciences, Griffith University, Gold Coast, QLD, 4222, Australia.
| |
Collapse
|
11
|
Abstract
Muscles convert energy from ATP into useful work, which can be used to move limbs and to transport ions across membranes. The energy not converted into work appears as heat. At the start of contraction heat is also produced when Ca(2+) binds to troponin-C and to parvalbumin. Muscles use ATP throughout an isometric contraction at a rate that depends on duration of stimulation, muscle type, temperature and muscle length. Between 30% and 40% of the ATP used during isometric contraction fuels the pumping Ca(2+) and Na(+) out of the myoplasm. When shortening, muscles produce less force than in an isometric contraction but use ATP at a higher rate and when lengthening force output is higher than the isometric force but rate of ATP splitting is lower. Efficiency quantifies the fraction of the energy provided by ATP that is converted into external work. Each ATP molecule provides 100 zJ of energy that can potentially be converted into work. The mechanics of the myosin cross-bridge are such that at most 50 zJ of work can be done in one ATP consuming cycle; that is, the maximum efficiency of a cross-bridge is ∼50%. Cross-bridges in tortoise muscle approach this limit, producing over 90% of the possible work per cycle. Other muscles are less efficient but contract more rapidly and produce more power.
Collapse
Affiliation(s)
- C J Barclay
- School of Allied Health Sciences/Griffith Health Institute, Griffith University, Gold Coast, Queensland, Australia
| |
Collapse
|
12
|
Loiselle DS, Johnston CM, Han JC, Nielsen PMF, Taberner AJ. Muscle heat: a window into the thermodynamics of a molecular machine. Am J Physiol Heart Circ Physiol 2015; 310:H311-25. [PMID: 26589327 DOI: 10.1152/ajpheart.00569.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 11/10/2015] [Indexed: 11/22/2022]
Abstract
The contraction of muscle is characterized by the development of force and movement (mechanics) together with the generation of heat (metabolism). Heat represents that component of the enthalpy of ATP hydrolysis that is not captured by the microscopic machinery of the cell for the performance of work. It arises from two conceptually and temporally distinct sources: initial metabolism and recovery metabolism. Initial metabolism comprises the hydrolysis of ATP and its rapid regeneration by hydrolysis of phosphocreatine (PCr) in the processes underlying excitation-contraction coupling and subsequent cross-bridge cycling and sliding of the contractile filaments. Recovery metabolism describes those process, both aerobic (mitochondrial) and anaerobic (cytoplasmic), that produce ATP, thereby allowing the regeneration of PCr from its hydrolysis products. An equivalent partitioning of muscle heat production is often invoked by muscle physiologists. In this formulation, total enthalpy expenditure is separated into external mechanical work (W) and heat (Q). Heat is again partitioned into three conceptually distinct components: basal, activation, and force dependent. In the following mini-review, we trace the development of these ideas in parallel with the development of measurement techniques for separating the various thermal components.
Collapse
Affiliation(s)
- Denis Scott Loiselle
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand; Department of Physiology, The University of Auckland, Auckland, New Zealand
| | | | - June-Chiew Han
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Poul Michael Fønss Nielsen
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand; Department of Engineering Science, The University of Auckland, Auckland, New Zealand; and
| | - Andrew James Taberner
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand; Department of Engineering Science, The University of Auckland, Auckland, New Zealand; and
| |
Collapse
|