-
Applied Physiology, Nutrition, and... Apr 2020The transient increase in torque of an electrically evoked twitch following a voluntary contraction is called postactivation potentiation (PAP). Phosphorylation of... (Review)
Review
The transient increase in torque of an electrically evoked twitch following a voluntary contraction is called postactivation potentiation (PAP). Phosphorylation of myosin regulatory light chains is the most accepted mechanism explaining the enhanced electrically evoked twitch torque. While many authors attribute voluntary postactivation performance enhancement (PAPE) to the positive effects of PAP, few actually confirmed that contraction was indeed potentiated using electrical stimulation (twitch response) at the time that PAPE was measured. Thus, this review aims to investigate if increases in voluntary performance after a conditioning contraction (CC) are related to the PAP phenomenon. For this, studies that confirmed the presence of PAP through an evoked response after a voluntary CC and concurrently evaluated PAPE were reviewed. Some studies reported increases in PAPE when PAP reaches extremely high values. However, PAPE has also been reported when PAP was not present, and unchanged/diminished performance has been identified when PAP was present. This range of observations demonstrates that mechanisms of PAPE are different from mechanisms of PAP. These mechanisms of PAPE still need to be understood and those studying PAPE should not assume that regulatory light chain phosphorylation is the mechanism for such enhanced voluntary performance. The occurrence of PAP does not necessarily mean that the voluntary performance will be improved. Improvement in voluntary performance is sometimes observed when the PAP level reaches extremely high values. Other mechanisms may be more relevant than that for PAP in the manifestation of acute increases in performance following a conditioning contraction.
Topics: Athletic Performance; Electric Stimulation; Exercise; Humans; Muscle Contraction; Muscle, Skeletal
PubMed: 31557447
DOI: 10.1139/apnm-2019-0406 -
Acta Physiologica (Oxford, England) Aug 2019
Topics: Animals; Humans; Muscle Contraction; Muscle, Skeletal
PubMed: 30040172
DOI: 10.1111/apha.13165 -
The effects of imaginary voluntary muscle contraction and relaxation on cerebellar brain inhibition.Neuroscience Research Aug 2018The purpose of this study was to investigate cerebellar brain inhibition (CBI) of the contralateral primary motor cortex (M1) during imaginary muscle contraction...
The purpose of this study was to investigate cerebellar brain inhibition (CBI) of the contralateral primary motor cortex (M1) during imaginary muscle contraction (Contract-I) and relaxation (Relax-I) using transcranial magnetic stimulation (TMS). Twenty-nine healthy adults completed two experiments. Motor evoked potentials (MEPs) in the right first dorsal interosseous (FDI) muscle were induced by TMS over the left M1 and measured with or without TMS over the right cerebellum during Contract-I (first experiment) and Relax-I (second experiment) of the right FDI, and these were compared to the findings in a no-imagery (No-I) condition. MEPs during Contract-I were significantly higher than those during No-I, and MEPs during Relax-I were significantly lower than those during No-I. In contrast, CBI was significantly higher during Contract-I than during No-I, while there was no significant difference in CBI between Relax-I and No-I. These findings indicate that the cerebellum exerts facilitatory control over M1 excitability during imaginary muscle contraction but not during imaginary muscle relaxation.
Topics: Adult; Cerebellum; Electromyography; Evoked Potentials, Motor; Female; Humans; Imagination; Male; Muscle Contraction; Muscle Relaxation; Neural Inhibition; Transcranial Magnetic Stimulation; Young Adult
PubMed: 29154805
DOI: 10.1016/j.neures.2017.11.004 -
Journal of Neurophysiology Oct 2022It is important to understand the effects of rapid changes in weight on neuromuscular functions of combat athletes. The purpose of this case study was to investigate...
It is important to understand the effects of rapid changes in weight on neuromuscular functions of combat athletes. The purpose of this case study was to investigate time-course changes in muscle strength, muscle size, and neural input during rapid weight loss in a professional boxer. One professional male boxer (26 yr) participated in two matches during measurements: welterweight (66.6 kg; weight loss: WL) and super welterweight (69.85 kg; control: CON). His muscle contraction properties and body composition were measured from 6 wk (baseline) before the matches to 1 wk after them. Maximal voluntary isometric knee extension torque, muscle cross-sectional area (mCSA) of the vastus lateralis using ultrasound, and high-density surface electromyography of the vastus lateralis during submaximal ramp-up contraction were measured. Individual motor units were identified, and modified discharge rates were calculated from a regression line between the recruitment threshold and discharge rates at 60%-70% of maximum torque according to the baseline value. His body weights for WL and CON decreased from 70.80 and 71.42 kg at the baseline to 68.75 and 71.36 kg immediately before the matches, respectively. Muscle strength changed little for either match. For WL, skeletal muscle mass and mCSA decreased, but there was no decrease for CON. The modified motor unit discharge rate for WL increased immediately before the match compared with other periods but did not change for CON. After rapid weight loss, neural input increased to compensate for lost muscle mass, and muscle strength was maintained. This case study found that neural input to muscle, which was evaluated by high-density surface electrocardiography, increased to compensate for the decline of body weight and muscle mass and to maintain muscle strength during rapid weight loss, while neuromuscular characteristics were not markedly changed during no significant weight loss.
Topics: Electromyography; Humans; Isometric Contraction; Male; Muscle Contraction; Muscle Strength; Muscle, Skeletal; Quadriceps Muscle; Weight Loss
PubMed: 36129200
DOI: 10.1152/jn.00307.2022 -
Journal of Electromyography and... Apr 2022The spatial distributions of muscle innervation zone (IZ) and muscle fiber conduction velocity (CV) were examined in nine healthy young male participants. High-density...
The spatial distributions of muscle innervation zone (IZ) and muscle fiber conduction velocity (CV) were examined in nine healthy young male participants. High-density surface electromyography (EMG) was collected from the biceps brachii muscle when subjects performed isometric elbow flexions at 20% to 80% of the maximal voluntary contraction (MVC). A total of 9498 samples of IZs were identified and CVs were calculated using the Radon transform. The center and width of IZ sample distribution were compared within four different force levels and six medial to lateral electrode column positions using repeated measures ANOVA and multiple comparison tests. Significant shifts of IZ center were observed in the medial columns (Columns 5, 6, and 7) compared with the lateral columns (Columns 3 and 4) (p < 0.05). Similarly, significant differences in the IZ width were found in Column 7 and 8 compared to Column 3 (p < 0.05). In contrast, muscle CV was unaffected by column position. Instead, muscle CV was faster at 40% and 80% MVC compared to 20% MVC (p < 0.05). The findings of this study add further insights into the physiological properties of the biceps brachii muscle.
Topics: Arm; Electromyography; Humans; Isometric Contraction; Male; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal
PubMed: 35176686
DOI: 10.1016/j.jelekin.2022.102637 -
The Journal of Physiological Sciences :... Jan 2017Knowledge accumulated in the field of energetics of muscle contraction has been reviewed in this article. Active muscle converts chemical energy into heat and work.... (Review)
Review
Knowledge accumulated in the field of energetics of muscle contraction has been reviewed in this article. Active muscle converts chemical energy into heat and work. Therefore, measurements of heat production and mechanical work provide the framework for understanding the process of energy conversion in contraction. In the 1970s, precise comparison between energy output and the associated chemical reactions was performed. It has been found that the two do not match in several situations, resulting in an energy balance discrepancy. More recently, efforts in resolving these discrepancies in the energy balance have been made involving chemical analysis, phosphorus nuclear magnetic resonance spectroscopy, and microcalorimetry. Through reviewing the evidence from these studies, the energy balance discrepancy developed early during isometric contraction has become well understood on a quantitative basis. In this situation energy balance is established when we take into account the binding of Ca to sarcoplasmic proteins such as troponin and parvalbumin, and also the shift of cross-bridge states. On the other hand, the energy balance discrepancy observed during rapid shortening still remains to be clarified. The problem may be related to the essential mechanism of cross-bridge action.
Topics: Actomyosin; Animals; Calorimetry; Energy Metabolism; Humans; Muscle Contraction; Muscle, Skeletal
PubMed: 27412384
DOI: 10.1007/s12576-016-0470-3 -
Proceedings of the National Academy of... Jan 2020Fluid fills intracellular, extracellular, and capillary spaces within muscle. During normal physiological activity, intramuscular fluid pressures develop as muscle...
Fluid fills intracellular, extracellular, and capillary spaces within muscle. During normal physiological activity, intramuscular fluid pressures develop as muscle exerts a portion of its developed force internally. These pressures, typically ranging between 10 and 250 mmHg, are rarely considered in mechanical models of muscle but have the potential to affect performance by influencing force and work produced during contraction. Here, we test a model of muscle structure in which intramuscular pressure directly influences contractile force. Using a pneumatic cuff, we pressurize muscle midcontraction at 260 mmHg and report the effect on isometric force. Pressurization reduced isometric force at short muscle lengths (e.g., -11.87% of P at 0.9 L), increased force at long lengths (e.g., +3.08% of P at 1.25 L), but had no effect at intermediate muscle lengths ∼1.1-1.15 L This variable response to pressurization was qualitatively mimicked by simple physical models of muscle morphology that displayed negative, positive, or neutral responses to pressurization depending on the orientation of reinforcing fibers representing extracellular matrix collagen. These findings show that pressurization can have immediate, significant effects on muscle contractile force and suggest that forces transmitted to the extracellular matrix via pressurized fluid may be important, but largely unacknowledged, determinants of muscle performance in vivo.
Topics: Animals; Biomechanical Phenomena; Body Fluids; Collagen; Extracellular Matrix; Hamstring Muscles; Hydrostatic Pressure; Isometric Contraction; Models, Biological; Muscle Contraction; Muscle, Skeletal; Rana catesbeiana
PubMed: 31879350
DOI: 10.1073/pnas.1914433117 -
Mathematical Biosciences Sep 2019Smooth muscle contraction regulates the size of the blood vessel lumen which directly affects the mechanical response of the vessel. Folding in arteries has been...
Smooth muscle contraction regulates the size of the blood vessel lumen which directly affects the mechanical response of the vessel. Folding in arteries has been observed in arteries during excessive contraction, known as a coronary artery spasm. The interplay of muscle contraction, geometry, and material responses and their effects on stability can be understood through mathematical models. Here, we consider a three-layer cross-sectional model of a coronary artery with anisotropic properties and intimal thickening, and perform a linear stability analysis to investigate the circumferential folding patterns that emerge due to muscle contraction. Our model shows that a critical level of contractile activity yields a uniform strain distribution across the arterial wall. When the muscle is contracted above this critical level, the tissue behaves isotropically and it is more prone to circumferential instability. This theoretical framework could serve as a valuable tool to understand the relationship between arterial lumen morphology and wall contraction in health and disease.
Topics: Biomechanical Phenomena; Coronary Vessels; Humans; Models, Biological; Muscle Contraction; Muscle, Smooth, Vascular; Tunica Intima
PubMed: 31276682
DOI: 10.1016/j.mbs.2019.108223 -
Mechanisms of Ageing and Development Apr 2022Nervous system maladaptation is linked to the loss of maximal strength and motor control with aging. Motor unit discharge rates are a critical determinant of force... (Meta-Analysis)
Meta-Analysis Review
Nervous system maladaptation is linked to the loss of maximal strength and motor control with aging. Motor unit discharge rates are a critical determinant of force production; thus, lower discharge rates could be a mechanism underpinning maximal strength and motor control losses during aging. This meta-analysis summarized the findings of studies comparing motor unit discharge rates between young and older adults, and examined the effects of the selected muscle and contraction intensity on the magnitude of discharge rate difference between these two groups. Estimates from 29 studies, across a range of muscles and contraction intensities, were combined in a multilevel meta-analysis, to investigate whether discharge rates differed between young and older adults. Motor unit discharge rates were higher in younger than older adults, with a pooled standardized mean difference (SMD) of 0.66 (95%CI= 0.29-1.04). Contraction intensity had a significant effect on the pooled SMD, with a 1% increase in intensity associated with a 0.009 (95%CI= 0.003-0.015) change in the pooled SMD. These findings suggest that reductions in motor unit discharge rates, especially at higher contraction intensities, may be an important mechanism underpinning age-related losses in maximal force production.
Topics: Aged; Aging; Humans; Isometric Contraction; Motor Neurons; Muscle Contraction; Muscle, Skeletal; Patient Discharge
PubMed: 35218849
DOI: 10.1016/j.mad.2022.111647 -
Exercise and Sport Sciences Reviews Jan 2023The rate at which an individual can develop force during rapid voluntary contractions can be influenced by both the neural drive to a muscle and its intrinsic...
The rate at which an individual can develop force during rapid voluntary contractions can be influenced by both the neural drive to a muscle and its intrinsic musculotendinous properties. We hypothesize that the maximal rate of force development across human individuals is mainly attributable to the rate of motor unit recruitment.
Topics: Humans; Muscle Contraction; Motor Neurons; Muscle, Skeletal; Recruitment, Neurophysiological; Electromyography; Isometric Contraction
PubMed: 36123735
DOI: 10.1249/JES.0000000000000306