Motor redundancy during maximal voluntary contraction in four-finger tasks

1998 ◽  
Vol 122 (1) ◽  
pp. 71-78 ◽  
Author(s):  
Zong-Ming Li ◽  
Mark L. Latash ◽  
Karl M. Newell ◽  
Vladimir M. Zatsiorsky
Keyword(s):  
Maximal Voluntary Contraction ◽  
Voluntary Contraction ◽  
Motor Redundancy

scholarly journals Corticospinal excitability of the biceps brachii is shoulder position dependent

2017 ◽  
Vol 118 (6) ◽  
pp. 3242-3251 ◽  
Author(s):  
Brandon Wayne Collins ◽  
Edward W. J. Cadigan ◽  
Lucas Stefanelli ◽  
Duane C. Button
Keyword(s):  
Evoked Potentials ◽  
Maximal Voluntary Contraction ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Voluntary Contraction ◽  
Corticospinal Excitability ◽  
State Dependent ◽  
Shoulder Flexion ◽  
Erb’S Point ◽  
Shoulder Position

The purpose of this study was to examine the effect of shoulder position on corticospinal excitability (CSE) of the biceps brachii during rest and a 10% maximal voluntary contraction (MVC). Participants ( n = 9) completed two experimental sessions with four conditions: 1) rest, 0° shoulder flexion; 2) 10% MVC, 0° shoulder flexion; 3) rest, 90° shoulder flexion; and 4) 10% MVC, 90° shoulder flexion. Transcranial magnetic, transmastoid electrical, and Erb’s point stimulation were used to induce motor-evoked potentials (MEPs), cervicomedullary MEPs (CMEPs), and maximal muscle compound potentials (Mmax), respectively, in the biceps brachii in each condition. At rest, MEP, CMEP, and Mmax amplitudes increased ( P < 0.01) by 509.7 ± 118.3%, 113.3 ± 28.3%, and 155.1 ± 47.9%, respectively, at 90° compared with 0°. At 10% MVC, MEP amplitudes did not differ ( P = 0.08), but CMEP and Mmax amplitudes increased ( P < 0.05) by 32.3 ± 10.5% and 127.9 ± 26.1%, respectively, at 90° compared with 0°. MEP/Mmax increased ( P < 0.01) by 224.0 ± 99.1% at rest and decreased ( P < 0.05) by 51.3 ± 6.7% at 10% MVC at 90° compared with 0°. CMEP/Mmax was not different ( P = 0.22) at rest but decreased ( P < 0.01) at 10% MVC by 33.6 ± 6.1% at 90° compared with 0°. EMG increased ( P < 0.001) by 8.3 ± 2.0% at rest and decreased ( P < 0.001) by 21.4 ± 4.4% at 10% MVC at 90° compared with 0°. In conclusion, CSE of the biceps brachii was dependent on shoulder position, and the pattern of change was altered within the state in which it was measured. The position-dependent changes in Mmax amplitude, EMG, and CSE itself all contribute to the overall change in CSE of the biceps brachii. NEW & NOTEWORTHY We demonstrate that when the shoulder is placed into two common positions for determining elbow flexor force and activation, corticospinal excitability (CSE) of the biceps brachii is both shoulder position and state dependent. At rest, when the shoulder is flexed from 0° to 90°, supraspinal factors predominantly alter CSE, whereas during a slight contraction, spinal factors predominantly alter CSE. Finally, the normalization techniques frequently used by researchers to investigate CSE may under- and overestimate CSE when shoulder position is changed.

Nonuniform strain of human soleus aponeurosis-tendon complex during submaximal voluntary contractions in vivo

2003 ◽  
Vol 95 (2) ◽  
pp. 829-837 ◽  
Author(s):  
Taija Finni ◽  
John A. Hodgson ◽  
Alex M. Lai ◽  
V. Reggie Edgerton ◽  
Shantanu Sinha
Keyword(s):  
Achilles Tendon ◽  
Maximal Voluntary Contraction ◽  
Three Dimensional ◽  
Motor Units ◽  
Magnetic Resonance Images ◽  
Voluntary Contraction ◽  
Force Transmission ◽  
Voluntary Contractions ◽  
Nonuniform Strain

The distribution of strain along the soleus aponeurosis tendon was examined during voluntary contractions in vivo. Eight subjects performed cyclic isometric contractions (20 and 40% of maximal voluntary contraction). Displacement and strain in the apparent Achilles tendon and in the aponeurosis were calculated from cine phase-contrast magnetic resonance images acquired with a field of view of 32 cm. The apparent Achilles tendon lengthened 2.8 and 4.7% in 20 and 40% maximal voluntary contraction, respectively. The midregion of the aponeurosis, below the gastrocnemius insertion, lengthened 1.2 and 2.2%, but the distal aponeurosis shortened 2.1 and 2.5%, respectively. There was considerable variation in the three-dimensional anatomy of the aponeurosis and muscle-tendon junction. We suggest that the nonuniformity in aponeurosis strain within an individual was due to the presence of active and passive motor units along the length of the muscle, causing variable force along the measurement site. Force transmission along intrasoleus connective tissue may also be a significant source of nonuniform strain in the aponeurosis.

scholarly journals Exercise tolerance during muscle contractions below and above the critical torque in different muscle groups

2018 ◽  
Vol 43 (2) ◽  
pp. 174-179 ◽  
Author(s):  
Leonardo Henrique Perinotto Abdalla ◽  
Benedito Sérgio Denadai ◽  
Natália Menezes Bassan ◽  
Camila Coelho Greco
Keyword(s):  
Exercise Intensity ◽  
Maximal Voluntary Contraction ◽  
Exercise Tolerance ◽  
Voluntary Contraction ◽  
Knee Extensors ◽  
Isometric Contractions ◽  
Plantar Flexors ◽  
Significant Difference ◽  
Muscle Groups

The objective of this study was to test the hypotheses that end-test torque (ET) (expressed as % maximal voluntary contraction; MVC) is higher for plantar flexors (PF) than knee extensors (KE) muscles, whereas impulse above ET (IET) is higher for KE than PF. Thus, we expected that exercise tolerance would be longer for KE than PF only during the exercise performed above ET. After the determination of MVC, 40 men performed two 5-min all-out tests to determine ET and IET. Eleven participants performed a further 4 intermittent isometric tests, to exhaustion, at ET + 5% and ET – 5%, and 1 test for KE at the exercise intensity (%MVC) corresponding to ET + 5% of PF. The IET (7243.2 ± 1942.9 vs. 3357.4 ± 1132.3 N·m·s) and ET (84.4 ± 24.8 vs. 73.9 ± 19.5 N·m) were significantly lower in PF compared with KE. The exercise tolerance was significantly longer for PF (300.7 ± 156.7 s) than KE (156.7 ± 104.3 s) at similar %MVC (∼60%), and significantly shorter for PF (300.7 ± 156.7 s) than KE (697.0 ± 243.7 s) at ET + 5% condition. However, no significant difference was observed for ET – 5% condition (KE = 1030.2 ± 495.4 s vs. PF = 1028.3 ± 514.4 s). Thus, the limit of tolerance during submaximal isometric contractions is influenced by absolute MVC only during exercise performed above ET, which seems to be explained by differences on both ET (expressed as %MVC) and IET values.

The Influence of Intermittent Fatigue Exercise on Early and Late Phases of Relaxation From Maximal Voluntary Contraction

1997 ◽  
Vol 22 (6) ◽  
pp. 573-584 ◽  
Author(s):  
Anna Jaskólska ◽  
Artur Jaskólski
Keyword(s):  
Relaxation Time ◽  
Relaxation Rate ◽  
Maximal Voluntary Contraction ◽  
Early Phase ◽  
Intermittent Exercise ◽  
Young Male ◽  
Voluntary Contraction ◽  
Hand Grip ◽  
Before And After ◽  
Late Relaxation Time

Twenty-two young male subjects were tested to estimate the behavior of the early and late phases of relaxation from a 3-s maximal voluntary contraction (MVC) under the influence of fatigue. Less demanding and more demanding protocols of intermittent hand grip exercise were used to fatigue muscle. Before and after fatigue, the early and late relaxation time, maximal relaxation rate, and half-relaxation time were measured. The results showed that during voluntary movement (a) the early phase of relaxation was independent of the mode of intermittent exercise and did not change significantly after fatigue; (b) the late relaxation time and absolute maximal relaxation rate were slower after both protocols, with the changes more pronounced following the more demanding protocol; and (c) the half-relaxation time and relative maximal relaxation rate were changed only in the more demanding protocol. It is concluded that unlike the relaxation following electrical stimulation of isolated muscle, the early phase of relaxation from voluntary contraction appears to be the most resistant to the type of intermittent fatiguing exercise used in the present study, whereas the late relaxation time was the most sensitive to this type of fatigue. Key words: hand grip exercise, late relaxation time, early relaxation time, half-relaxation time

Sex differences in forebrain and cardiovagal responses at the onset of isometric handgrip exercise: a retrospective fMRI study

2007 ◽  
Vol 103 (4) ◽  
pp. 1402-1411 ◽  
Author(s):  
Savio W. Wong ◽  
Derek S. Kimmerly ◽  
Nicholas Massé ◽  
Ravi S. Menon ◽  
David F. Cechetto ◽  
...  
Keyword(s):  
Sex Differences ◽  
Maximal Voluntary Contraction ◽  
Cardiovascular Response ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Anterior Cingulate ◽  
Exercise Heart Rate ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Ventral Medial Prefrontal Cortex

In general, cardiac regulation is dominated by the sympathetic and parasympathetic nervous systems in men and women, respectively. Our recent study had revealed sex differences in the forebrain network associated with sympathoexcitatory response to baroreceptor unloading. The present study further examined the sex differences in forebrain modulation of cardiovagal response at the onset of isometric exercise. Forebrain activity in healthy men ( n = 8) and women ( n = 9) was measured using functional magnetic resonance imaging during 5 and 35% maximal voluntary contraction handgrip exercise. Heart rate (HR), mean arterial pressure (MAP), and muscle sympathetic nerve activity (MSNA) were collected in a separate recording session. During the exercise, HR and MAP increased progressively, while MSNA was suppressed ( P < 0.05). Relative to men, women demonstrated smaller HR (8 ± 2 vs. 18 ± 3 beats/min) and MAP (3 ± 2 vs. 11 ± 2 mmHg) responses to the 35% maximal voluntary contraction trials ( P < 0.05). Although a similar forebrain network was activated in both groups, the smaller cardiovascular response in women was reflected in a weaker insular cortex activation. Nevertheless, men did not show a stronger deactivation at the ventral medial prefrontal cortex, which has been associated with modulating cardiovagal activity. In contrast, the smaller cardiovascular response in women related to their stronger suppression of the dorsal anterior cingulate cortex activity, which has been associated with sympathetic control of the heart. Our findings revealed sex differences in both the physiological and forebrain responses to isometric exercise.

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