Reductions in motoneuron excitability during sustained isometric contractions are dependent on stimulus and contraction intensity

Cervicomedullary stimulation provides a means of assessing motoneuron excitability. Previous studies demonstrated that during low-intensity sustained contractions, small cervicomedullary evoked potentials (CMEPs) conditioned using transcranial magnetic stimulation (TMS-CMEPs) are reduced, whilst large TMS-CMEPs are less affected. Since small TMS-CMEPs recruit motoneurons most active during low-intensity contractions while large TMS-CMEPs recruit a high proportion of motoneurons inactive during the task, these results suggest that reductions in motoneuron excitability could be dependent on repetitive activation. To further test this hypothesis, this study assessed changes in small and large TMS-CMEPs across low- and high-intensity contractions. Twelve participants performed a sustained isometric contraction of the elbow flexor for 4.5 min at the electromyography (EMG) level associated with 20% maximal voluntary contraction force (MVC; low-intensity) and 70% MVC (high-intensity). Small and large TMS-CMEPs with amplitudes of ~15 and ~50% Mmax at baseline, respectively, were delivered every minute throughout the tasks. Recovery measures were taken at 1, 2.5 and 4-min post-exercise. During the low-intensity trial, small TMS-CMEPs were reduced at 2-4 min (p≤0.049) by up to −10% Mmax, while large TMS-CMEPs remained unchanged (p≥0.16). During the high-intensity trial, small and large TMS-CMEPs were reduced at all time-points (p<0.01) by up to −14% and −33% Mmax, respectively, and remained below baseline during all recovery measures (p≤0.02). TMS-CMEPs were unchanged relative to baseline during recovery following the low-intensity trial (p≥0.24). These results provide novel insight into motoneuron excitability during and following sustained contractions at different intensities, and suggest that contraction-induced reductions in motoneuron excitability depend on repetitive activation.

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OXYGEN UPTAKE AND RESISTANCE EXERCISE METHODS: THE USE OF BLOOD FLOW RESTRICTION

Revista Brasileira de Medicina do Esporte ◽

10.1590/1517-869220182405180336 ◽

2018 ◽

Vol 24 (5) ◽

pp. 343-346

Author(s):

Adenilson Targino de Araújo Júnior ◽

Maria do Socorro Cirilo-Sousa ◽

Gabriel Rodrigues Neto ◽

Rodrigo Poderoso ◽

Geraldo Veloso Neto ◽

...

Keyword(s):

Blood Flow ◽

Oxygen Consumption ◽

High Intensity ◽

Blood Flow Restriction ◽

Level Of Evidence ◽

Post Exercise ◽

High Intensity Training ◽

Flow Restriction ◽

Low Intensity ◽

Intensity Training

ABSTRACT Introduction: The literature has shown that a gap is identified regarding the acute effects of blood flow restriction training on aerobic variables. Objective: to analyze oxygen consumption (VO2) during and after two resistance training sessions: traditional high intensity and low intensity with blood flow restriction. Methods: After one-repetition maximum tests, eight male participants (25.7±3 years) completed the two experimental protocols, separated by 72 hours, in a randomized order: a) high intensity training at 80% of 1RM (HIRE) and b) low intensity training at 20% of 1RM combined with blood flow restriction (LIRE + BFR). Three sets of four exercises (bench press, squat, barbell bent-over row and deadlift) were performed. Oxygen consumption and excess post-exercise oxygen consumption were measured. Results: the data showed statistically significant differences between the traditional high intensity training and low intensity training with blood flow restriction, with higher values for traditional training sessions, except for the last five minutes of the excess post-exercise oxygen consumption. Oxygen consumption measured during training was higher (p = 0.001) for the HIRE (20.32 ± 1.46 mL·kg-1·min-1) compared to the LIRE + BFR (15.65 ± 1.14 mL·kg-1·min-1). Conclusion: Oxygen uptakes rates during and after the exercise sessions were higher for the high intensity training methodology. However, when taking into account the volume of training provided by both methods, these differences were attenuated. Level of Evidence III - Non-consecutive studies, or studies without consistently applied reference stand.

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NMR and analytic biochemical evaluation of CrP and nucleotides in the human calf during muscle contraction

Journal of Applied Physiology ◽

10.1152/jappl.1993.74.4.2034 ◽

1993 ◽

Vol 74 (4) ◽

pp. 2034-2039 ◽

Cited By ~ 54

Author(s):

J. Bangsbo ◽

L. Johansen ◽

B. Quistorff ◽

B. Saltin

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Maximal Voluntary Contraction ◽

Work Load ◽

Voluntary Contraction ◽

Isometric Contractions ◽

Contraction Force ◽

Biochemical Evaluation ◽

Male Subjects ◽

Human Calf

This study compared biochemical and 31P-nuclear magnetic resonance (NMR) determinations of energy metabolites during isometric contractions of the human calf muscle at various exercise intensities. Seven male subjects performed one-legged isometric contractions at a work load of 28, 64, and 90% of maximal voluntary contraction force (28-, 64-, and 90%-CON, respectively) for 3 min, 40 s, and 40 s, respectively, in a magnet and in an exact model of the magnet with an arrangement for rapid muscle biopsy sampling from the gastrocnemius. The decrease in phosphocreatine (CrP) determined by NMR was 20, 33, and 71% for 28%-, 64%-, and 90%-CON, respectively. These decreases were the same as those determined biochemically (25, 34, and 61%, respectively). Muscle CrP 1 min after 90%-CON was also found to be similar between NMR and biochemical determinations (88 and 74% of resting value, respectively). Although no significant change in muscle ATP was found by NMR, a decrease of 29% was observed biochemically at 90%-CON. The ratio between muscle CrP and ATP was the same between NMR and biochemical determinations except for 90%-CON (1.98 and 0.78, respectively). The increase in muscle ADP determined by NMR was two-, five-, and eightfold higher than that found biochemically for 28%-, 64%-, and 90%-CON, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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Acute effects of exercise on energy intake and feeding behaviour

British Journal Of Nutrition ◽

10.1079/bjn19970053 ◽

1997 ◽

Vol 77 (4) ◽

pp. 511-521 ◽

Cited By ~ 134

Author(s):

Pascal Imbeault ◽

Sylvie Saint-Pierre ◽

Natalie AlméRas ◽

Angelo Tremblay

Keyword(s):

Total Energy ◽

Energy Intake ◽

High Intensity ◽

Negative Energy ◽

High Intensity Exercise ◽

Acute Effects ◽

Short Term ◽

Post Exercise ◽

Low Intensity ◽

Low Intensity Exercise

The main objective of the present study was to evaluate the short-term effects of exercise of different intensities on energy intake. Eleven young men were submitted to three randomly assigned sessions (one control and two exercise sessions) in which they ate, ad libitum, foods from a buffet-type meal. The energy cost of exercise was the same in the two exercise sessions. Results showed that there was no significant change in post-exercise subjective levels of hunger and fullness as well as total energy and macronutrient intakes in comparison with the control session. However, when energy intake relative to expenditure was considered by subtracting the surplus of energy expended during exercise from total energy intake, high-intensity exercise exerted a greater reducing effect on this variable compared with the control and low-intensity exercise sessions. These results suggest that for a given level of energy expenditure, high-intensity exercise favours negative energy balance to a greater extent than low-intensity exercise.

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Time Course Change in Muscle Swelling: High-Intensity vs. Blood Flow Restriction Exercise

International Journal of Sports Medicine ◽

10.1055/s-0043-118342 ◽

2017 ◽

Vol 38 (13) ◽

pp. 1009-1016 ◽

Cited By ~ 6

Author(s):

Eduardo Freitas ◽

Christopher Poole ◽

Ryan Miller ◽

Aaron Heishman ◽

Japneet Kaur ◽

...

Keyword(s):

Blood Flow ◽

Plasma Volume ◽

High Intensity ◽

Time Course ◽

Muscle Thickness ◽

Blood Flow Restriction ◽

Thigh Circumference ◽

Post Exercise ◽

Flow Restriction ◽

Low Intensity

AbstractThis study determined the time course for changes in muscle swelling and plasma volume following high (HI) and low-intensity resistance exercise with blood-flow restriction (LI-BFR). Ten male participants (22.1±3.0 yrs) completed three experimental conditions: high-intensity exercise (HI - 80% of 1RM), low-intensity exercise with BFR (LI-BFR –20% of 1RM, and 160 mmHg of BFR), and control (CON – no exercise or BFR). Muscle cross-sectional area (mCSA), muscle thickness, thigh circumference, and percentage change in plasma volume (PV%∆) were measured. mCSA was significantly greater than rest values at 15 min post-exercise (p<0.01) for HI and LI-BFR, and at 75 min post-exercise (p<0.01) for HI. Muscle thickness was significantly greater than rest immediately post-exercise (p<0.01) and 30 min post-exercise (p<0.01) for HI and LI-BFR, and at 60 min post-exercise for HI (p=0.01). Muscle thickness was greater for BFR immediately post-exercise compared to HI (p=0.01) post-exercise. Thigh circumference was significantly greater from rest at 15 min post-exercise (p=0.01) and at 75 min post-exercise for both LI-BFR (p=0.03) and HI (p<0.01). PV%∆ significantly decreased from rest immediately post-exercise for both HI (p<0.01) and LI-BFR (p<0.01). In conclusion, BFR exercise induces changes in muscle swelling and plasma volume similar to those observed at high-intensities.

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Methodological issues with the assessment of voluntary activation using transcranial magnetic stimulation in the knee extensors

10.31236/osf.io/r2vzn ◽

2018 ◽

Author(s):

Jeanne Dekerle ◽

Paul Ansdell ◽

lisa Schäfer ◽

Aaron Greenhouse-Tucknott ◽

James Graeme Wrightson

Keyword(s):

Transcranial Magnetic Stimulation ◽

Maximal Voluntary Contraction ◽

Magnetic Stimulation ◽

Voluntary Contraction ◽

Face Validity ◽

Voluntary Activation ◽

Knee Extensors ◽

Post Exercise ◽

Smallest Detectable Change ◽

Fatiguing Exercise

Purpose: The assessment of voluntary activation of the knee extensors using transcranial magnetic stimulation (VATMS) is routinely performed to assess the supraspinal function. Yet methodological scrutiny of the technique is scarce. The aim of the present study was to examine face validity and reliability of VATMS and its two main determinants (superimposed twitch during a maximal voluntary contraction [SIT100%] and estimated resting twitch [ERT]). Methods: SIT100%, ERT, and VATMS were measured on 10 healthy males (age: 24 ± 5 years) before and following intermittent isometric fatiguing exercise on two separate occasions. Results: The findings indicated issues regarding the accuracy of ERT and suggested a three-point relationship should not be used to determine ERT. Reliabilities for VATMS, SIT100% and ERT were acceptable pre- but much weaker post-exercise (especially for SIT100%). Despite statistically significant changes in main neuromuscular variables following the intermittent isometric fatiguing exercise (P<0.05), when post-exercise reliability was considered, the exercise effect on VATMS was smaller than the smallest detectable change in 18 of the 20 individual tests performed, and for the whole sample for one of two visits. Finally, Maximal voluntary contraction was reduced significantly following the neuromuscular assessment (NMA) pre-exercise but recovered during the NMA post-exercise. Conclusion: This is the first study to demonstrate a lack of sensitivity of key neuromuscular measurements to exercise and to evidence both presence of neuromuscular fatigue following the NMA in itself, and recovery of the neuromuscular function during the NMA post-exercise. These results challenge the face validity of this routinely used protocol.

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Stimulus strength related effect of transcranial magnetic stimulation on maximal voluntary contraction force of human quadriceps femoris muscle

Experimental Brain Research ◽

10.1007/s00221-001-0911-x ◽

2002 ◽

Vol 142 (1) ◽

pp. 25-31 ◽

Cited By ~ 9

Author(s):

Dietmar Urbach ◽

Friedemann Awiszus

Keyword(s):

Transcranial Magnetic Stimulation ◽

Maximal Voluntary Contraction ◽

Magnetic Stimulation ◽

Quadriceps Femoris ◽

Voluntary Contraction ◽

Stimulus Strength ◽

Related Effect ◽

Contraction Force ◽

Quadriceps Femoris Muscle ◽

Femoris Muscle

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Inhibition rather than Enhancement of Hemostatic System Activation during Initiation of Oral Anticoagulant Treatment

Thrombosis and Haemostasis ◽

10.1055/s-0038-1656034 ◽

1997 ◽

Vol 77 (04) ◽

pp. 685-689 ◽

Cited By ~ 11

Author(s):

Paul A Kyrle ◽

Johannes Brockmeier ◽

Ansgar Weltermann ◽

Sabine Eichinger ◽

Wolfgang Speiser ◽

...

Keyword(s):

High Intensity ◽

Oral Anticoagulant ◽

Protein C ◽

Venous Blood ◽

Rapid Decline ◽

Oral Anticoagulant Treatment ◽

Shed Blood ◽

Low Intensity ◽

Hemostatic System ◽

System Activation

SummaryCoumarin-induced skin necrosis is believed to be due to a transient hypercoagulable state resulting from a more rapid decline of the protein C activity relative to that of coagulation factors (F) II, IX and X during initiation of oral anticoagulant therapy. We studied hemostatic system activation during early oral anticoagulant treatment with a technique that investigates coagulation activation in the microcirculation.We determined in 10 healthy volunteers the concentrations of prothrombin fragment F1+2 (f1.2) and thrombin-antithrombin complex (TAT) in blood emerging from an injury of the microvasculature (bleeding time incision) before and after initiation of both high-inten- sity and low-intensity coumarin therapy. In addition, f1.2, TAT, activated F VII (F Vila) and the activities of FII, F VII, F X and protein C were measured in venous blood.A rapid decline of F VII and protein C was observed in venous blood with activities at 24 h of 7 ± 1% and 43 ± 2%, respectively, during the high-intensity regimen. A 20 to 30% reduction of f1.2 and TAT was seen in venous blood at 72 h with no major difference between the high- and the low-intensity regimen. F Vila levels were substantially affected by anticoagulation with a >90% reduction at 48 h during the high-intensity regimen. Following high-intensity coumarin, a >50% decrease in the fl.2 and TAT levels was found in shed blood at 48 h suggesting substantial inhibition of thrombin generation during early oral anticoagulation. An increase in the f1.2 and TAT levels was seen neither in shed blood nor in venous blood.Our data do not support the concept of a transient imbalance between generation and inhibition of thrombin as the underlying pathomechanism of coumarin-induced skin nekrosis.

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