scholarly journals Complexity of force output during static exercise in individuals with Down syndrome

2009 ◽  
Vol 106 (4) ◽  
pp. 1227-1233 ◽  
Author(s):  
Kevin S. Heffernan ◽  
Jacob J. Sosnoff ◽  
Edward Ofori ◽  
Sae Young Jae ◽  
Tracy Baynard ◽  
...  
Keyword(s):  
Down Syndrome ◽  
Spectral Power ◽  
Temporal Structure ◽  
Voluntary Contraction ◽  
Premature Aging ◽  
Force Variability ◽  
Force Output ◽  
Isometric Handgrip ◽  
Similar Time ◽  
Output Variability

Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS ( n = 29, age 26 yr), and healthy young ( n = 26, age 27 yr) and older ( n = 33, age 70 yr) individuals. Mean, standard deviation (SD), and coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls ( P < 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls ( P < 0.05). The DS group had a significantly greater proportion of spectral power within the 0-to 4-Hz bandwidth than the young and older controls ( P < 0.05). The DS group had significantly lower ApEn values than the young controls ( P < 0.05), but there were no differences in ApEn between the DS group and the old controls ( P > 0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.

Intermittency in the Control of Continuous Force Production

2000 ◽  
Vol 84 (4) ◽  
pp. 1708-1718 ◽  
Author(s):  
Andrew B. Slifkin ◽  
David E. Vaillancourt ◽  
Karl M. Newell
Keyword(s):  
Visual Feedback ◽  
Visual Information ◽  
Spectral Power ◽  
Force Production ◽  
Motor Output ◽  
Force Variability ◽  
Force Output ◽  
Feedback Information ◽  
Information Processes ◽  
Feedback Frequency

The purpose of the current investigation was to examine the influence of intermittency in visual information processes on intermittency in the control continuous force production. Adult human participants were required to maintain force at, and minimize variability around, a force target over an extended duration (15 s), while the intermittency of on-line visual feedback presentation was varied across conditions. This was accomplished by varying the frequency of successive force-feedback deliveries presented on a video display. As a function of a 128-fold increase in feedback frequency (0.2 to 25.6 Hz), performance quality improved according to hyperbolic functions (e.g., force variability decayed), reaching asymptotic values near the 6.4-Hz feedback frequency level. Thus, the briefest interval over which visual information could be integrated and used to correct errors in motor output was approximately 150 ms. The observed reductions in force variability were correlated with parallel declines in spectral power at about 1 Hz in the frequency profile of force output. In contrast, power at higher frequencies in the force output spectrum were uncorrelated with increases in feedback frequency. Thus, there was a considerable lag between the generation of motor output corrections (1 Hz) and the processing of visual feedback information (6.4 Hz). To reconcile these differences in visual and motor processing times, we proposed a model where error information is accumulated by visual information processes at a maximum frequency of 6.4 per second, and the motor system generates a correction on the basis of the accumulated information at the end of each 1-s interval.

scholarly journals Long-Term Microgravity Effects on Isometric Handgrip and Precision Pinch Force with Visual and Proprioceptive Feedback

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Ilario Puglia ◽  
Michele Balsamo ◽  
Marco Vukich ◽  
Valfredo Zolesi
Keyword(s):  
Maximum Voluntary Contraction ◽  
Space Station ◽  
Voluntary Contraction ◽  
Force Output ◽  
Isometric Handgrip ◽  
Short Term ◽  
Space Flights ◽  
Pinch Force ◽  
Long Duration

The study and analysis of human physiology during short- and long-duration space flights are the most valuable approach in order to evaluate the effect of microgravity on the human body and to develop possible countermeasures in prevision of future exploratory missions and Mars expeditions. Hand performances such as force output and manipulation capacity are fundamental for astronauts’ intra- and extravehicular activities. Previous studies on upper limb conducted on astronauts during short-term missions (10 days) indicated a temporary partial reduction in the handgrip maximum voluntary contraction (MVC) followed by a prompt recovery and adaptation to weightlessness during the last days of the mission. In the present study, we report on the “Crew’s Health: Investigation on Reduced Operability” (CHIRO) protocol, developed for handgrip and pinch force investigations, performed during the six months increment 7 and increment 8 (2003-2004) onboard International Space Station (ISS). We found that handgrip and pinch force performance are reduced during long-term increments in space and are not followed by adaptation during the mission, as conversely reported during short-term increment experiments. The application of protocols developed in space will be eligible to astronauts during long-term space missions and to patients affected by muscle atrophy diseases or nervous system injury on Earth.

scholarly journals Recruitment Order of Motor Units in Human Vastus Lateralis Muscle Is Maintained During Fatiguing Contractions

2003 ◽  
Vol 90 (5) ◽  
pp. 2919-2927 ◽  
Author(s):  
Alexander Adam ◽  
Carlo J. De Luca
Keyword(s):  
Motor Unit ◽  
Time Course ◽  
Vastus Lateralis ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Vastus Lateralis Muscle ◽  
Force Output ◽  
Similar Time ◽  
Lateralis Muscle ◽  
Recruitment Order

Motor-unit firing patterns were studied in the vastus lateralis muscle of five healthy young men [21.4 ± 0.9 (SD) yr] during a series of isometric knee extensions performed to exhaustion. Each contraction was held at a constant torque level, set to 20% of the maximal voluntary contraction at the beginning of the experiment. Electromyographic signals, recorded via a quadrifilar fine wire electrode, were processed with the precision decomposition technique to identify the firing times of individual motor units. In repeat experiments, whole-muscle mechanical properties were measured during the fatigue protocol using electrical stimulation. The main findings were a monotonic decrease in the recruitment threshold of all motor units and the progressive recruitment of new units, all without a change of the recruitment order. Motor units from the same subject showed a similar time course of threshold decline, but this decline varied among subjects (mean threshold decrease ranged from 23 to 73%). The mean threshold decline was linearly correlated ( R2 ≥ 0.96) with a decline in the elicited peak tetanic torque. In summary, the maintenance of recruitment order during fatigue strongly supports the notion that the observed common recruitment adaptations were a direct consequence of an increased excitatory drive to the motor unit pool. It is suggested that the increased central drive was necessary to compensate for the loss in force output from motor units whose muscle fibers were actively contracting. We therefore conclude that the control scheme of motor-unit recruitment remains invariant during fatigue at least in relatively large muscles performing submaximal isometric contractions.

scholarly journals Motor control differs for increasing and releasing force

2016 ◽  
Vol 115 (6) ◽  
pp. 2924-2930 ◽  
Author(s):  
Seoung Hoon Park ◽  
MinHyuk Kwon ◽  
Danielle Solis ◽  
Neha Lodha ◽  
Evangelos A. Christou
Keyword(s):  
Older Adults ◽  
Force Control ◽  
Discharge Rate ◽  
Maximum Voluntary Contraction ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Force Variability ◽  
Force Output ◽  
Force Increase ◽  
Change In Mean

Control of the motor output depends on our ability to precisely increase and release force. However, the influence of aging on force increase and release remains unknown. The purpose of this study, therefore, was to determine whether force control differs while increasing and releasing force in young and older adults. Sixteen young adults (22.5 ± 4 yr, 8 females) and 16 older adults (75.7 ± 6.4 yr, 8 females) increased and released force at a constant rate (10% maximum voluntary contraction force/s) during an ankle dorsiflexion isometric task. We recorded the force output and multiple motor unit activity from the tibialis anterior (TA) muscle and quantified the following outcomes: 1) variability of force using the SD of force; 2) mean discharge rate and variability of discharge rate of multiple motor units; and 3) power spectrum of the multiple motor units from 0–4, 4–10, 10–35, and 35–60 Hz. Participants exhibited greater force variability while releasing force, independent of age ( P < 0.001). Increased force variability during force release was associated with decreased modulation of multiple motor units from 35 to 60 Hz ( R2 = 0.38). Modulation of multiple motor units from 35 to 60 Hz was further correlated to the change in mean discharge rate of multiple motor units ( r = 0.66) and modulation from 0 to 4 Hz ( r = −0.64). In conclusion, these findings suggest that force control is altered while releasing due to an altered modulation of the motor units.

Modulation of sympathetic nerve activity during posthandgrip muscle ischemia in humans

1994 ◽  
Vol 266 (1) ◽  
pp. H79-H83 ◽  
Author(s):  
C. A. Ray ◽  
N. H. Secher ◽  
A. L. Mark
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Sensory Nerve ◽  
Vascular Occlusion ◽  
Voluntary Contraction ◽  
Central Command ◽  
Isometric Handgrip ◽  
Nerve Activity ◽  
Muscle Ischemia

To evaluate modulation of muscle sympathetic nerve activity (MSNA) during posthandgrip muscle ischemia (PHGMI), subjects performed 2 min of isometric handgrip at 33% of maximal voluntary contraction (MVC) followed by 2 min of PHGMI produced by forearm vascular occlusion. The response to PHGMI was studied in the absence and again during the addition of contralateral rhythmic handgrip (RHG; 40 times/min) at 15% (n = 6) and 30% (n = 10) MVC during the second minute of the PHGMI. Additionally, to isolate the effect of central command, response to PHGMI was studied during attempted RHG after sensory nerve blockade (n = 5). RHG for 2 min at 15 and 30% MVC and attempted RHG for 2 min did not increase MSNA. Isometric handgrip elicited an 130 +/- 48% increase in MSNA (P < 0.05), which was maintained during PHGMI. RHG at 15 and 30% MVC elicited an attenuation of MSNA (-10 +/- 7% and -14 +/- 6%, respectively) when performed during the second minute of PHGMI (P < 0.05). In contrast, attempted RHG did not significantly affect MSNA during PHGMI. The findings demonstrate modulation of MSNA during activation of the muscle metaboreflex. The attenuation of metaboreceptor-mediated increases in MSNA appear to be the result of mechanosensitive muscle afferents and not central command.

Forearm endurance training attenuates sympathetic nerve response to isometric handgrip in normal humans

1992 ◽  
Vol 72 (3) ◽  
pp. 1039-1043 ◽  
Author(s):  
V. K. Somers ◽  
K. C. Leo ◽  
R. Shields ◽  
M. Clary ◽  
A. L. Mark
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Endurance Training ◽  
Sympathetic Nerve ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Isometric Handgrip ◽  
Nerve Response ◽  
The Right ◽  
Muscle Chemoreflex

Recent evidence indicates that muscle ischemia and activation of the muscle chemoreflex are the principal stimuli to sympathetic nerve activity (SNA) during isometric exercise. We postulated that physical training would decrease muscle chemoreflex stimulation during isometric exercise and thereby attenuate the SNA response to exercise. We investigated the effects of 6 wk of unilateral handgrip endurance training on the responses to isometric handgrip (IHG: 33% of maximal voluntary contraction maintained for 2 min). In eight normal subjects the right arm underwent exercise training and the left arm sham training. We measured muscle SNA (peroneal nerve), heart rate, and blood pressure during IHG before vs. after endurance training (right arm) and sham training (left arm). Maximum work to fatigue (an index of training efficacy) was increased by 1,146% in the endurance-trained arm and by only 40% in the sham-trained arm. During isometric exercise of the right arm, SNA increased by 111 +/- 27% (SE) before training and by only 38 +/- 9% after training (P less than 0.05). Endurance training did not significantly affect the heart rate and blood pressure responses to IHG. We also measured the SNA response to 2 min of forearm ischemia after IHG in five subjects. Endurance training also attenuated the SNA response to postexercise forearm ischemia (P = 0.057). Sham training did not significantly affect the SNA responses to IHG or forearm ischemia. We conclude that endurance training decreases muscle chemoreflex stimulation during isometric exercise and thereby attenuates the sympathetic nerve response to IHG.

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.

Corticofugal Modulation of the Tactile Response Coherence of Projecting Neurons in the Gracilis Nucleus

2007 ◽  
Vol 98 (5) ◽  
pp. 2537-2549 ◽  
Author(s):  
Nazareth P. Castellanos ◽  
Eduardo Malmierca ◽  
Angel Nuñez ◽  
Valeri A. Makarov
Keyword(s):  
Electrical Stimulation ◽  
Tactile Stimulation ◽  
Spectral Power ◽  
Temporal Structure ◽  
Neural Response ◽  
Spike Timing ◽  
Sensory Stimulus ◽  
Functional Coupling ◽  
Tactile Response ◽  
Stimulation Of

Precise and reproducible spike timing is one of the alternatives of the sensory stimulus encoding. We test coherence (repeatability) of the response patterns elicited in projecting gracile neurons by tactile stimulation and its modulation provoked by electrical stimulation of the corticofugal feedback from the somatosensory (SI) cortex. To gain the temporal structure we adopt the wavelet-based approach for quantification of the functional stimulus–neural response coupling. We show that the spontaneous firing patterns (when they exist) are essentially random. Tactile stimulation of the neuron receptive field strongly increases the spectral power in the stimulus and 5- to 15-Hz frequency bands. However, the functional coupling (coherence) between the sensory stimulus and the neural response exhibits ultraslow oscillation (0.07 Hz). During this oscillation the stimulus coherence can temporarily fall below the statistically significant level, i.e., the functional stimulus–response coupling may be temporarily lost for a single neuron. We further demonstrate that electrical stimulation of the SI cortex increases the stimulus coherence for about 60% of cells. We find no significant correlation between the increment of the firing rate and the stimulus coherence, but we show that there is a positive correlation with the amplitude of the peristimulus time histogram. The latter argues that the observed facilitation of the neural response by the corticofugal pathway, at least in part, may be mediated through an appropriate ordering of the stimulus-evoked firing pattern, and the coherence enhancement is more relevant in gracilis nucleus than an increase of the number of spikes elicited by the tactile stimulus.

Cardiovascular and nitric oxide response after maximal voluntary isometric contraction in adolescents with and without Down Syndrome v1

2021 ◽  
Author(s):  
Geiziane Leite Rodrigues Melo ◽  
Dahan Cunha Nascimento ◽  
Weldson Abreu ◽  
Rafael Olher ◽  
Lysleine Deus ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Down Syndrome ◽  
Isometric Contraction ◽  
Cardiovascular Response ◽  
Exercise Session ◽  
Isometric Handgrip ◽  
Maximal Voluntary Isometric Contraction ◽  
Post Exercise ◽  
Muscle Groups ◽  
Familiarization Session

Background This study was designed to compare the cardiovascular and nitric oxide (NO) responses to maximal voluntary isometric contraction (MVIC) with different muscle groups (leg press [LEP] and isometric handgrip [IHG] exercise) of adolescents with Down syndrome (DS) and age-matched non-DS peers. We also aimed to compare the absolute and relative IHG strength between groups. MethodsEleven adolescents with DS (14.1 ± 1.0 years) and ten without DS (13.7 ± 1.25 years)participants performed two experimental sessions of LEP and IHG exercises: 1) familiarization session and 2) 3 attempts x 5-sec contraction at MVIC with 3-min rest interval. Blood pressure (BP), heart rate (HR) and NO were collected at rest, immediately post-exercise session, and 10-min post-exercise. Results There were no differences for cardiovascular and NO responses between groups for MVIC test using different muscle groups. However, DS group displayed a lower but not significantly cardiovascular response at rest and after MVIC tests than controls. Furthermore, DS group displayed a higher NO- concentration at rest, recovery and after IHG when compared to controls (P< 0.05). In addition, DS adolescents displayed a significantly lower level in absolute and relative IHG strength when compared to controls (P = 0.001). Conclusions Individuals with DS display a lower cardiovascular response at rest and after MVIC tests than controls and higher NO response after exercise.

Abstract 266: Neural Circulatory Responses to Isolated Muscle Metaboreflex Activation in Postmenopausal Women

Hypertension ◽  
2013 ◽  
Vol 62 (suppl_1) ◽  
Author(s):  
Jody L Greaney ◽  
Evan L Matthews ◽  
Paul J Fadel ◽  
William B Farquhar ◽  
Megan M Wenner
Keyword(s):  
Blood Pressure ◽  
Postmenopausal Women ◽  
Young Women ◽  
Blood Pressure Response ◽  
Muscle Sympathetic Nerve Activity ◽  
Feedback Mechanism ◽  
Voluntary Contraction ◽  
Pressure Response ◽  
Isometric Handgrip ◽  
Muscle Metaboreflex

Understanding the neural circulatory responses to exercise in postmenopausal women (PMW) is important given their greater risk for developing hypertension. During exercise, blood pressure is controlled, in part, by the exercise pressor reflex, which is a feedback mechanism originating in skeletal muscle and compromised of mechanically and metabolically sensitive afferents. A recent study reported an enhanced blood pressure response during exercise in normotensive PMW due to greater muscle metaboreflex activation, but the mechanism(s) underlying these responses are unknown. Herein, we tested the hypothesis that metaboreflex activation elicits exaggerated sympathetic nervous system responses in PMW compared to young women, contributing to the enhanced blood pressure response during exercise. Methods: Blood pressure (BP, Finometer) and muscle sympathetic nerve activity (MSNA, peroneal microneurography) were continuously measured in 7 PMW (age 59±2 years; BMI 24±1 kg/m 2 ) and 7 young women (age 23±2 years; BMI 22±2 kg/m 2 ) during 2-minutes of isometric handgrip exercise performed at 30% of maximal voluntary contraction followed by 3-minutes of forearm ischemia (post-exercise ischemia, PEI) to isolate muscle metaboreflex activation. Results: Resting mean arterial pressure (MAP) was similar between PMW (85±3 mmHg) and young women (82±2 mmHg; P>0.05). During exercise, the increase in MAP was greater in PMW (Δ18±2mmHg) compared to young women (Δ 12±2 mmHg; P<0.05), and this was maintained during PEI (Δ13±1 mmHg PMW vs. Δ 6±1 mmHg young women; P<0.05). Resting MSNA was higher in PMW (24±4 bursts/min) compared to young women (9±3 bursts/min; P<0.05). Interestingly, the increase in MSNA during exercise was comparable between groups (P>0.05), whereas during PEI, the increase in MSNA was approximately 50% greater in PMW compared to young women (Δ13±2 burst/min PMW vs. 7±2 bursts/min young women; P<0.05). Conclusions: These preliminary data suggest that compared to young women, PMW exhibit an exaggerated MSNA response to isolated muscle metaboreflex activation.

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