Postactivation Potentiation of Force Is Independent of H-Reflex Excitability

2008 ◽  
Vol 3 (2) ◽  
pp. 219-231 ◽  
Author(s):  
Matthew J. Hodgson ◽  
David Docherty ◽  
E. Paul Zehr
Keyword(s):  
Isometric Force ◽  
Plantar Flexion ◽  
Force Production ◽  
H Reflex ◽  
Postactivation Potentiation ◽  
Neural Excitability ◽  
Reflex Excitability ◽  
Before And After ◽  
History Of ◽  
A Minor

The contractile history of muscle can potentiate electrically evoked force production. A link to voluntary force production, related in part to an increase in reflex excitability, has been suggested.Purpose:Our purpose was to quantify the effect of postactivation potentiation on voluntary force production and spinal H-reflex excitability during explosive plantar fexion actions.Methods:Plantar flexor twitch torque, soleus H-reflex amplitudes, and the rate of force development of explosive plantar fexion were measured before and after 4 separate conditioning trials (3 × 5 s maximal contractions).Results:Twitch torque and rate of force production during voluntary explosive plantar flexion were significantly increased (P < .05) while H-reflex amplitudes remained unchanged. Although twitch torque was significantly higher after conditioning, leading to a small increase in the rate of voluntary force production, this was unrelated to changes in reflex excitability.Conclusion:We conclude that postactivation potentiation may result in a minor increase in the rate of voluntary isometric force production that is unrelated to neural excitability.

Cyclic H-Reflex Modulation in Resting Forearm Related to Contractions of Foot Movers, Not to Foot Movement

2003 ◽  
Vol 90 (1) ◽  
pp. 81-88 ◽  
Author(s):  
Gabriella Cerri ◽  
Paola Borroni ◽  
Fausto Baldissera
Keyword(s):  
Plantar Flexion ◽  
Motor Command ◽  
H Reflex ◽  
Reflex Modulation ◽  
Phase Coupling ◽  
Foot Kinematics ◽  
Reflex Excitability ◽  
Movement Frequency ◽  
Before And After ◽  
Foot Loading

During rhythmic voluntary oscillations of the foot, the excitability of the H-reflex in the Flexor Carpi Radialis (FCR) muscle of the resting prone forearm increases during the foot plantar-flexion and decreases during dorsiflexion. It is known that, when the two extremities are moved together, isodirectional (in-phase) coupling is the preferred form of movement association. Thus the above pattern of the H-reflex excitability modulation may favor the preferred coupling between the two limbs. To gain some clues about its origin, FCR H-reflex excitability was tested before and after modifying the phase relations between the activation [electromyogram (EMG)] of foot movers and foot movement, either by loading of the foot or by changing the movement frequency. After foot loading, the movement cycle was consistently delayed with respect to the onset of the EMG in Soleus (Sol) or Tibialis Anterior (TA) muscles. Simultaneously, the FCR H-reflex modulation advanced by that same amount with respect to the foot movement, thus remaining phase-locked to the EMG onsets. Similarly, when movement frequency was varied step-wise between 1.0 and 2.0 Hz, the foot movement was progressively delayed with respect to both the EMG onset (Sol and TA) and the FCR H-reflex modulation, so that the phase relation between the motor command to the foot and the H-modulation in the forearm remained constant. These results suggest that modulation of H-reflex in the forearm is tied to leg muscle contraction, rather than to foot kinematics, and point to a central, rather than kinesthetic, origin for the modulation.

Pliometric contraction-induced injury of mouse skeletal muscle: effect of initial length

1997 ◽  
Vol 82 (1) ◽  
pp. 278-283 ◽  
Author(s):  
Kam D. Hunter ◽  
John A. Faulkner
Keyword(s):  
Skeletal Muscle ◽  
Fiber Length ◽  
Isometric Force ◽  
Force Production ◽  
Initial Length ◽  
Average Force ◽  
Mouse Skeletal Muscle ◽  
Before And After ◽  
Work Input ◽  
Initial Fiber

Hunter, Kam D., and John A. Faulkner. Pliometric contraction-induced injury of mouse skeletal muscle: effect of initial length. J. Appl. Physiol. 82(1): 278–283, 1997.—For single pliometric (lengthening) contractions initiated from optimal fiber length ( L f), the most important factor determining the subsequent force deficit is the work input during the stretch. We tested the hypothesis that regardless of the initial length, the force deficit is primarily a function of the work input. Extensor digitorum longus muscles of mice were maximally activated in situ and lengthened at 2 L f /s from one of three initial fiber lengths (90, 100, or 120% of L f) to one of three final fiber lengths (150, 160, or 170% of L f). Maximal isometric force production was assessed before and after the pliometric contraction. No single mechanical factor, including the work input ( r 2= 0.34), was sufficient to explain the differences in force deficits observed among groups. Therefore, the force deficit appears to arise from a complex interaction of mechanical events. With the data grouped by initial fiber length, the correlation between the average work and the average force deficit was high ( r 2= 0.97–0.99). Consequently, differences in force deficits among groups were best explained on the basis of the initial fiber length and the work input during the stretch.

Acoustic myography for investigating human skeletal muscle fatigue

1991 ◽  
Vol 71 (4) ◽  
pp. 1422-1426 ◽  
Author(s):  
M. J. Stokes ◽  
P. A. Dalton
Keyword(s):  
Isometric Force ◽  
Maximum Voluntary Contraction ◽  
Force Production ◽  
Rectus Femoris ◽  
Quadriceps Muscle ◽  
Voluntary Contraction ◽  
Fatigued Muscle ◽  
Before And After ◽  
Acoustic Myography ◽  
Voluntary Contractions

Sounds produced during voluntary isometric contractions of the quadriceps muscle were studied by acoustic myography (AMG) in five healthy adults. With the subject seated, isometric force, surface electromyography (EMG), and AMG were recorded over rectus femoris, and the EMG and AMG signals were integrated (IEMG and IAMG). Contractions lasting 5 s each were performed at 10, 25, 50, 60, 75, and 100% of maximum voluntary contraction (MVC) force. Fatigue was then induced by repeated voluntary contractions (10 s on, 10 s off) at 75% MVC until only 40% MVC could be sustained. After 15 min of rest, the different force levels were again tested in relation to the fresh MVC. Both before and after fatiguing activity the relationships between force and IEMG [r = 0.99 +/- 0.01 (SD), n = 10] and force and IAMG (r = 0.98 +/- 0.02) were linear. After activity, however, the slopes of the regression lines for force and IEMG increased (P less than 0.01) but those for force and IAMG remained the same (P greater than 0.05). The present results clarify the relationship between AMG and isometric force in fatigued muscle without the problem of fatigue-induced tremor, which hampered previous studies of prolonged activity. This study contributes to the validation of AMG and shows that it is a potentially useful method for noninvasive assessment of force production and fatigue. Further studies to establish the origin of AMG activity are required before AMG can be accepted for use in neuromuscular physiology or rehabilitation.

Threshold for force potentiation associated with skeletal myosin phosphorylation

1993 ◽  
Vol 265 (6) ◽  
pp. C1456-C1462 ◽  
Author(s):  
R. Vandenboom ◽  
R. W. Grange ◽  
M. E. Houston
Keyword(s):  
Isometric Force ◽  
Conditioning Stimulus ◽  
Force Production ◽  
Peak Force ◽  
Phosphate Content ◽  
Before And After ◽  
Skeletal Myosin ◽  
Fast Twitch Muscle ◽  
Isometric Twitch ◽  
Fast Twitch

Phosphate incorporation by the phosphorylatable light chains (P-LC) of myosin is associated with isometric twitch force potentiation in intact fast-twitch muscle. The purpose of this study was to examine the association between myosin P-LC phosphorylation and force potentiation at higher stimulation frequencies (1-150 Hz) using mouse extensor digitorum longus (EDL) muscles at 25 degrees C. Peak isometric force and the peak rate of isometric force development (+dF/dtmax) were measured at selected test frequencies before and after the application of a 5-Hz 20-s conditioning stimulation known to increase P-LC phosphate content. Associated with a ninefold elevation in myosin P-LC phosphate content (to 0.72 mol phosphate/mol P-LC), +dF/dtmax was increased at all test frequencies (mean 27%, range 20-37%). After the conditioning stimulus, peak isometric force was increased by approximately 15% for frequencies 1-15 Hz. However, at 20-150 Hz, the increase in +dF/dtmax was not associated with force potentiation, since peak force was diminished by 5-40%. These data reveal that the stimulation frequency limit for the potentiation of peak force production associated with myosin P-LC phosphorylation is < 20 Hz in mouse EDL at 25 degrees C. Furthermore, the data suggest that increases in the rate constant describing the rate of cross-bridge transition from a non-force-generating to a force-generating state mediated by myosin P-LC phosphorylation may be responsible for the general increase in +dF/dtmax and for the force potentiation at 1-15 Hz.

scholarly journals Redox modulation of maximum force production of fast-and slow-twitch skeletal muscles of rats and mice

2001 ◽  
Vol 90 (3) ◽  
pp. 832-838 ◽  
Author(s):  
David R. Plant ◽  
Paul Gregorevic ◽  
David A. Williams ◽  
Gordon S. Lynch
Keyword(s):  
Skeletal Muscles ◽  
Isometric Force ◽  
Force Production ◽  
Dependent Manner ◽  
Redox Modulation ◽  
History Of ◽  
Slow Twitch ◽  
Fast Twitch ◽  
Rats And Mice ◽  
Isometric Force Production

We used intact fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles from rats and mice to test the hypothesis that exogenous application of an oxidant would increase maximum isometric force production (Po) of slow-twitch muscles to a greater extent than fast-twitch skeletal muscles. Exposure to an oxidant, hydrogen peroxide (H2O2; 100 μM to 5 mM, 30 min), affected Po of rat muscles in a time- and dose-dependent manner. Po of rat soleus muscles was increased by 8 ± 1 (SE) and 14 ± 1% ( P < 0.01) after incubation with 1 and 5 mM H2O2, respectively, whereas in mouse soleus muscles Po was only increased after incubation with 500 μM H2O2. Po of rat EDL muscles was affected by H2O2 biphasically; initially there was a small increase (3 ± 1%), but then Po diminished significantly after 30 min of treatment. In contrast, all concentrations of H2O2 tested decreased Po of mouse EDL muscles. A reductant, dithiothreitol (DTT; rat = 10 mM, mouse = 1 mM), was added to quench H2O2, and it reversed the potentiation in Po in rat soleus but not in rat EDL muscles or in any H2O2-treated mouse muscles. After prolonged equilibration (30 min) with 5 mM H2O2 without prior activation, Po was potentiated in rat soleus but not EDL muscles, demonstrating that the effect of oxidation in the soleus muscles was also dependent on the activation history of the muscle. The results of these experiments demonstrate that Po of both slow- and fast-twitch muscles from rats and mice is modified by redox modulation, indicating that maximum Po of mammalian skeletal muscles is dependent on oxidation.

scholarly journals Effect of Ankle Angles on the Soleus H-Reflex Excitability During Standing

Motor Control ◽  
2020 ◽  
Vol 24 (2) ◽  
pp. 189-203
Author(s):  
Aviroop Dutt-Mazumder ◽  
Richard L. Segal ◽  
Aiko K. Thompson
Keyword(s):  
Plantar Flexion ◽  
H Reflex ◽  
Spinal Reflex ◽  
System Control ◽  
M Wave ◽  
Reflex Excitability ◽  
Limb Loading ◽  
Upright Standing ◽  
Neurological Injuries ◽  
Full Body

This study investigated effects of ankle joint angle on the Hoffman’s reflex (H-reflex) excitability during loaded (weight borne with both legs) and unloaded (full body weight borne with the contralateral leg) standing in people without neurological injuries. Soleus H-reflex/M-wave recruitment curves were examined during upright standing on three different slopes that imposed plantar flexion (−15°), dorsiflexion (+15°), and neutral (0°) angles at the ankle, with the test leg loaded and unloaded. With the leg loaded and unloaded, maximum H-reflex/maximum M-wave ratio of −15° was significantly larger than those of 0° and +15° conditions. The maximum H-reflex/maximum M-wave ratios were 51%, 43%, and 41% with loaded and 56%, 46%, and 44% with unloaded for −15°, 0°, and +15° slope conditions, respectively. Thus, limb loading/unloading had limited impact on the extent of influence that ankle angles exert on the H-reflex excitability. This suggests that task-dependent central nervous system control of reflex excitability may regulate the influence of sensory input on the spinal reflex during standing.

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