Tracking of Individual Motor Units Following Concentric and Eccentric Exercise‐induced Fatigue Reveals Contraction‐type Specific Changes in Discharge Properties

1. The tension produced by the combined stimulation of two to four single motor units of the cat tibialis posterior muscle was compared with the algebraic sum of the tensions produced by each individual motor unit. Comparisons were made under isometric conditions and during imposed changes in muscle length. 2. Under isometric conditions, the tension resulting from combined stimulation of units displayed marked nonlinear summation, as previously reported in other cat hindlimb muscles. On average, the measured tension was approximately 20% greater than the algebraic sum of the individual unit tensions. However, small trapezoidal movements imposed on the muscle during stimulation significantly reduced the degree of nonlinear summation both during and after the movement. This effect was seen with imposed movements as small as 50 microns. 3. The degree of nonlinear summation was not dependent on motor unit size or on stimulus frequency. The effect was also unrelated to tendon compliance because the degree of nonlinear summation of motor unit forces was unaffected by the inclusion of different amounts of the external tendon between the muscle and the force transducer. 4. Our results support previous suggestions that the force measured when individual motor units are stimulated under isometric conditions is reduced by friction between the active muscle fibers and adjacent passive fibers. These frictional effects are likely to originate in the connective tissue matrix connecting adjacent muscle fibers. However, because these effects are virtually eliminated by small movements, linear summation of motor unit tensions should occur at low force levels under nonisometric conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

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The innervation and organization of motor units in a series-fibered human muscle: the brachioradialis

Journal of Applied Physiology ◽

10.1152/japplphysiol.01163.2009 ◽

2010 ◽

Vol 108 (6) ◽

pp. 1530-1541 ◽

Cited By ~ 12

Author(s):

Zoia C. Lateva ◽

Kevin C. McGill ◽

M. Elise Johanson

Keyword(s):

Human Subjects ◽

Standing Waves ◽

Motor Units ◽

Human Muscle ◽

Motor Unit Action Potential ◽

Distal Muscle ◽

Normal Human ◽

Motor Unit Action ◽

Unit Action ◽

Individual Motor

We studied the innervation and organization of motor units in the brachioradialis muscle of 25 normal human subjects. We recorded intramuscular EMG signals at points separated by 15 mm along the proximodistal muscle axis during moderate isometric contractions, identified from 27 to 61 (mean 39) individual motor units per subject using EMG decomposition, and estimated the locations of the endplates and distal muscle/tendon junctions from the motor-unit action potential (MUAP) propagation patterns and terminal standing waves. In three subjects all the motor units were innervated in a single endplate zone. In the other 22 subjects, the motor units were innervated in 3–6 (mean 4) distinct endplate zones separated by 15–55 mm along the proximodistal axis. One-third of the motor units had fibers innervated in more than one zone. The more distally innervated motor units had distinct terminal waves indicating tendonous termination, while the more proximal motor units lacked terminal waves, indicating intrafascicular termination. Analysis of blocked MUAP components revealed that 19% of the motor units had at least one doubly innervated fiber, i.e., a fiber innervated in two different endplate zones by two different motoneurons, and thus belonging to two different motor units. These results are consistent with the brachioradialis muscle having a series-fibered architecture consisting of multiple, overlapping bands of muscle fibers in most individuals and a simple parallel-fibered architecture in some individuals.

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Resistance-Trained Individuals Are Less Susceptible to Oxidative Damage after Eccentric Exercise

Oxidative Medicine and Cellular Longevity ◽

10.1155/2018/6857190 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11 ◽

Cited By ~ 3

Author(s):

Ypatios Spanidis ◽

Dimitrios Stagos ◽

Christina Papanikolaou ◽

Konstantina Karatza ◽

Andria Theodosi ◽

...

Keyword(s):

Oxidative Damage ◽

Eccentric Exercise ◽

Radical Scavenging Activity ◽

Radical Scavenging ◽

Reducing Power ◽

Protein Carbonyls ◽

Oxidation Reduction ◽

Oxidation Reduction Potential ◽

Exercise Induced ◽

Training Background

It has been proposed that exercise-induced oxidative stress and adaptations are dependent on training status. In this study, we examined the effects of training background on free radical generation and adaptations after eccentric exercise. Forty volunteers were divided into two groups (trained and untrained) and were asked to perform eccentric exercise. Then, their blood samples were collected pre, 24, 48, and 72 hours postexercise. Biomarkers indicating oxidative damage and the antioxidant profiles of the participants were measured in plasma and erythrocyte lysate both spectrophotometrically and chromatographically. The results revealed that the untrained group depicted more severe oxidative damage (protein carbonyls, malondialdehyde), weaker antioxidant status (reduced glutathione, static and capacity oxidation-reduction potential), and weaker radical-scavenging activity (superoxide radical scavenging and reducing power) compared to the trained participants. Our findings show that trained individuals are less susceptible to oxidative damage and suggest that generalized nutritional recommendations regarding recovery after exercise should be avoided.

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Effect of two maximal isometric contractions on eccentric exercise-induced muscle damage of the elbow flexors

European Journal of Applied Physiology ◽

10.1007/s00421-012-2581-8 ◽

2013 ◽

Vol 113 (6) ◽

pp. 1545-1554 ◽

Cited By ~ 31

Author(s):

Trevor C. Chen ◽

Hsin-Lian Chen ◽

Ming-Ju Lin ◽

Che-Hsiu Chen ◽

Alan J. Pearce ◽

...

Keyword(s):

Muscle Damage ◽

Eccentric Exercise ◽

Isometric Contractions ◽

Elbow Flexors ◽

Exercise Induced

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Eccentric exercise‐induced morphological changes in the membrane systems involved in excitation—contraction coupling in rat skeletal muscle

The Journal of Physiology ◽

10.1111/j.1469-7793.2001.0571a.x ◽

2001 ◽

Vol 533 (2) ◽

pp. 571-583 ◽

Cited By ~ 125

Author(s):

Hiroaki Takekura ◽

Nahoko Fujinami ◽

Tomie Nishizawa ◽

Hitomi Ogasawara ◽

Norikatsu Kasuga

Keyword(s):

Skeletal Muscle ◽

Eccentric Exercise ◽

Morphological Changes ◽

Membrane Systems ◽

Rat Skeletal Muscle ◽

Excitation Contraction Coupling ◽

Contraction Coupling ◽

Exercise Induced

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Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus

Journal of Applied Physiology ◽

10.1152/japplphysiol.00580.2007 ◽

2007 ◽

Vol 103 (5) ◽

pp. 1706-1714 ◽

Cited By ~ 5

Author(s):

Keith N. Bishop ◽

J. Ross McClung ◽

Stephen J. Goldberg ◽

Mary S. Shall

Keyword(s):

Motor Units ◽

Lateral Rectus ◽

Contraction Time ◽

Fatigue Index ◽

Muscle Twitch ◽

Abducens Nucleus ◽

Single Motor Unit ◽

Twitch Contraction ◽

Whole Muscle ◽

Individual Motor

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.

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