Prefrontal cortex oxygenation is preserved and does not contribute to impaired neuromuscular activation during passive hyperthermia

2009 ◽  
Vol 34 (1) ◽  
pp. 66-74 ◽  
Author(s):  
Shawnda A. Morrison ◽  
Gordon G. Sleivert ◽  
J. Patrick Neary ◽  
Stephen S. Cheung
Keyword(s):  
Prefrontal Cortex ◽  
Cerebral Oxygenation ◽  
Isometric Force ◽  
Thermal Strain ◽  
Force Production ◽  
Knee Extension ◽  
Voluntary Activation ◽  
Passive Heating ◽  
Force Output ◽  
Passive Hyperthermia

We investigated the role of passive hyperthermia upon motor unit activation and prefrontal cortex oxygenation. Six healthy males were passively heated, using a liquid conditioning garment in a hot environment (35 °C, 50% relative humidity). Maximal force output and voluntary activation were examined during a 10 s maximal isometric knee extension. Of the initial 6 subjects, 1 experienced syncope at a rectal temperature (Tre) of 38.0 °C and was removed from the study. The remaining 5 subjects completed heating and testing to a Tre of 38.5 °C (n = 1), 39.0 °C (n = 3), or 39.5 °C (n = 1), and then were cooled back to baseline. Force production decreased from 553 ± 133 to 430 ± 176 N (p < 0.01) with passive heating, as did voluntary activation (from 90 ± 5% to 84 ± 7%). Percent heart rate reserve increased from 8 ± 5% to 59 ± 3% before returning to 4 ± 8% (p < 0.001). Although mean arterial pressure remained unchanged, there were significant decreases in diastolic blood pressure with heating (80 ± 3 to 63 ± 8 mm Hg). Passive heating did not alter prefrontal cortex oxygenation, but cooling back to baseline core temperature attenuated cerebral oxygenated and total hemoglobin levels (p < 0.05). Passive heating to the point of voluntary exhaustion elevated cardiovascular and thermal strain and subjective perceptions of thermal discomfort. However, while this resulted in a marked decrement in maximal isometric force production and central voluntary activation, no concomitant changes in cerebral oxygenation were observed, suggesting that overall cerebrovascular regulation was maintained.

scholarly journals Acute effect of tendon vibration applied during isometric contraction at two knee angles on maximal knee extension force production

PLoS ONE ◽  
2020 ◽  
Vol 15 (11) ◽  
pp. e0242324
Author(s):  
Jonathan Harnie ◽  
Thomas Cattagni ◽  
Christophe Cornu ◽  
Peter McNair ◽  
Marc Jubeau
Keyword(s):  
Isometric Contraction ◽  
Vastus Lateralis ◽  
Force Production ◽  
Knee Extensor ◽  
Acute Effect ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Tendon Vibration ◽  
Knee Angle

The aim of the current study was to investigate the effect of a single session of prolonged tendon vibration combined with low submaximal isometric contraction on maximal motor performance. Thirty-two young sedentary adults were assigned into two groups that differed based on the knee angle tested: 90° or 150° (180° = full knee extension). Participants performed two fatigue-inducing exercise protocols: one with three 10 min submaximal (10% of maximal voluntary contraction) knee extensor contractions and patellar tendon vibration (80 Hz) another with submaximal knee extensor contractions only. Before and after each fatigue protocol, maximal voluntary isometric contractions (MVC), voluntary activation level (assessed by the twitch interpolation technique), peak-to-peak amplitude of maximum compound action potentials of vastus medialis and vastus lateralis (assessed by electromyography with the use of electrical nerve stimulation), peak twitch amplitude and peak doublet force were measured. The knee extensor fatigue was significantly (P<0.05) greater in the 90° knee angle group (-20.6% MVC force, P<0.05) than the 150° knee angle group (-8.3% MVC force, P = 0.062). Both peripheral and central alterations could explain the reduction in MVC force at 90° knee angle. However, tendon vibration added to isometric contraction did not exacerbate the reduction in MVC force. These results clearly demonstrate that acute infrapatellar tendon vibration using a commercial apparatus operating at optimal conditions (i.e. contracted and stretched muscle) does not appear to induce knee extensor neuromuscular fatigue in young sedentary subjects.

Cerebral Oxygenation, Central Drive And Force Output During Passive Heating And Cooling

2005 ◽  
Vol 37 (Supplement) ◽  
pp. S195-S196
Author(s):  
Shawnda Morrison ◽  
Gordon G. Sleivert ◽  
Elizabeth Johnson ◽  
Theresa Bernhardt ◽  
Stephen S. Cheung ◽  
...  
Keyword(s):  
Cerebral Oxygenation ◽  
Passive Heating ◽  
Force Output ◽  
Heating And Cooling ◽  
Central Drive

The length dependency of maximum force development in rat medial gastrocnemius muscle in situ

2008 ◽  
Vol 33 (3) ◽  
pp. 518-526 ◽  
Author(s):  
Cornelis J. de Ruiter ◽  
Tinelies E. Busé-Pot ◽  
Arnold de Haan
Keyword(s):  
Muscle Activation ◽  
Isometric Force ◽  
Force Production ◽  
Time History ◽  
Medial Gastrocnemius ◽  
Force Output ◽  
Force Development ◽  
Activation Times ◽  
Maximal Isometric Force

During many movements (e.g., running, jumping, and kicking) there is little time for skeletal muscles to build up force, thus rapid force development is important. The length dependency of isometric force development was investigated in maximally activated rat medial gastrocnemius muscles in situ with intact blood flow at 35 °C. Depending on time available for muscle activation, the length dependency of force development was expected to differ from that of the maximal isometric force (Fmax) reached much later during the contraction. During isometric force development in intact muscle–tendon preparations, the contractile elements actually shortened. Therefore, similar to previous findings on shortening contractions, it was hypothesized that maximal rate of force development (MRFD) would be obtained at a length below the optimum (Lo) for maximal isometric force production. To measure the effect of the entire time history of activation, force time integrals (FTIs) for different activation times (10–50 ms) were also calculated. The highest MRFD was obtained 1.94 ± 0.42 mm below (p < 0.05) Lo. When expressed relative to Fmax obtained at each individual length, the optimum was found at Lo – 4.4 mm. For FTI 10 ms and FTI 20 ms, optimum length was obtained at ~2 and 1 mm above (p < 0.05) Lo, respectively, whereas the optima for FTI 30, 40, and 50 ms were ~1 mm below (p < 0.05) Lo. In addition, at short lengths (< Lo – 4 mm) and for all activation times FTIs were relatively more decreased than Fmax. In conclusion, length dependency of force output during rapid force development differed from that of maximal isometric force; specifically, MRFD was obtained 2 mm below Lo.

Modeling constraints to redundancy in bimanual force coordination

2011 ◽  
Vol 105 (5) ◽  
pp. 2169-2180 ◽  
Author(s):  
Xiaogang Hu ◽  
Karl M. Newell
Keyword(s):  
Muscle Force ◽  
Coupling Effect ◽  
Isometric Force ◽  
Force Production ◽  
Force Output ◽  
Task Constraints ◽  
Task Goal ◽  
Force Coordination ◽  
Finger Forces ◽  
Coordination Patterns

This study investigated the interactive influence of organismic, environmental, and task constraints on the organization of redundant force coordination patterns and the hypothesis that each of the three categories of constraints is weighted based on their relative influence on coordination patterns and the realization of the task goal. In the bimanual isometric force experiment, the task constraint was manipulated via different coefficients imposed on the finger forces such that the weighted sum of the finger forces matched the target force. We examined three models of task constraints based on the criteria of task variance (minimum variance model) and efficiency of muscle force output (coefficient-independent and coefficient-dependent efficiency models). The environmental constraint was quantified by the perceived performance error, and the organismic constraint was quantified by the bilateral coupling effect (i.e., symmetric force production) between hands. The satisficing approach was used in the models to quantify the constraint weightings that reflect the interactive influence of different categories of constraints on force coordination. The findings showed that the coefficient-dependent efficiency model best predicted the redundant force coordination patterns across trials. However, the within-trial variability structure revealed that there was not a consistent coordination strategy in the online control of the individual trial. The experimental findings and model tests show that the force coordination patterns are adapted based on the principle of minimizing muscle force output that is coefficient dependent rather than on the principle of minimizing signal-dependent variance. Overall, the results support the proposition that redundant force coordination patterns are organized by the interactive influence of different categories of constraints.

A comparison of central aspects of fatigue in submaximal and maximal voluntary contractions

2008 ◽  
Vol 104 (2) ◽  
pp. 542-550 ◽  
Author(s):  
Janet L. Taylor ◽  
Simon C. Gandevia
Keyword(s):  
Small Diameter ◽  
Force Production ◽  
Central Fatigue ◽  
Motor Units ◽  
Muscle Afferents ◽  
Voluntary Activation ◽  
Peripheral Fatigue ◽  
Force Output ◽  
Group Iii ◽  
Motor Cortical

Magnetic and electrical stimulation at different levels of the neuraxis show that supraspinal and spinal factors limit force production in maximal isometric efforts (“central fatigue”). In sustained maximal contractions, motoneurons become less responsive to synaptic input and descending drive becomes suboptimal. Exercise-induced activity in group III and IV muscle afferents acts supraspinally to limit motor cortical output but does not alter motor cortical responses to transcranial magnetic stimulation. “Central” and “peripheral” fatigue develop more slowly during submaximal exercise. In sustained submaximal contractions, central fatigue occurs in brief maximal efforts even with a weak ongoing contraction (<15% maximum). The presence of central fatigue when much of the available motor pathway is not engaged suggests that afferent inputs contribute to reduce voluntary activation. Small-diameter muscle afferents are likely to be activated by local activity even in sustained weak contractions. During such contractions, it is difficult to measure central fatigue, which is best demonstrated in maximal efforts. To show central fatigue in submaximal contractions, changes in motor unit firing and force output need to be characterized simultaneously. Increasing central drive recruits new motor units, but the way this occurs is likely to depend on properties of the motoneurons and the inputs they receive in the task. It is unclear whether such factors impair force production for a set level of descending drive and thus represent central fatigue. The best indication that central fatigue is important during submaximal tasks is the disproportionate increase in subjects' perceived effort when maintaining a low target force.

Cerebral Oxygenation, Central Drive And Force Output During Passive Heating And Cooling

2005 ◽  
Vol 37 (Supplement) ◽  
pp. S195???S196
Author(s):  
Shawnda Morrison ◽  
Gordon G. Sleivert ◽  
Elizabeth Johnson ◽  
Theresa Bernhardt ◽  
Stephen S. Cheung ◽  
...  
Keyword(s):  
Cerebral Oxygenation ◽  
Passive Heating ◽  
Force Output ◽  
Heating And Cooling ◽  
Central Drive

scholarly journals Voluntary Activation and Decreased Force Production of the Quadriceps Femoris Muscle After Total Knee Arthroplasty

2003 ◽  
Vol 83 (4) ◽  
pp. 359-365 ◽  
Author(s):  
Ryan L Mizner ◽  
Jennifer E Stevens ◽  
Lynn Snyder-Mackler
Keyword(s):  
Total Knee Arthroplasty ◽  
Knee Arthroplasty ◽  
Force Production ◽  
Knee Extension ◽  
Quadriceps Femoris ◽  
Voluntary Activation ◽  
Quadriceps Femoris Muscle ◽  
Extension Force ◽  
Total Knee ◽  
Femoris Muscle

Abstract Background and Purpose. Quadriceps femoris muscle weakness as manifested by a decrease in force-generating capability is a persistent problem after total knee arthroplasty (TKA). The authors hypothesized that (1) patients with a TKA would have decreased quadriceps femoris muscle performance (weakness) and impaired volitional activation when compared with a group of older adults without knee pathology, (2) pain and age would account for a large portion of the variability in volitional activation after surgery, and (3) volitional activation in the TKA group would account for a large portion of the variability in force production. Subjects. Comparison subjects were 52 volunteers (mean age=72.2 years, SD=5.34, range=64–85). The TKA group comprised 52 patients (mean age=64.9 years, SD=7.72, range=49–78) with a diagnosis of osteoarthritis who had undergone a tricompartmental, cemented TKA. Methods. Knee extension force was measured using a burst superimposition technique, where a supramaximal burst of electrical stimulation was superimposed on a maximal voluntary isometric contraction (MVIC). The amount of failure of volitional activation is determined by the amount of electrical augmentation of force beyond a person's MVIC at the instant of the application of the electrical burst. Results. The average normalized knee extension force of the TKA group was 64% lower than that of the comparison group. The average volitional activation deficit in the TKA group (26%) was 4 times as great as the comparison group's deficit (6%). Age did not correlate with quadriceps femoris muscle activation, and knee pain explained only a small portion of the variance in knee extension force (r2=.17). Volitional activation was highly correlated with knee extension force production (r2=.65). Discussion and Conclusion. Considerable quadriceps femoris muscle inhibition after surgery has several implications for recovery. Rehabilitation programs that focus on volitional exercise alone are unlikely to overcome this pronounced failure of activation. Early interventions focused at improving quadriceps femoris muscle voluntary activation may improve efforts to restore muscle force.

scholarly journals Effect of participants’ static stretching knowledge or deception on the responses to prolonged stretching

2016 ◽  
Vol 41 (10) ◽  
pp. 1052-1056 ◽  
Author(s):  
W.C. Ian Janes ◽  
Brandon B.G. Snow ◽  
Caisie E. Watkins ◽  
Elecia A.L. Noseworthy ◽  
Jonathan C. Reid ◽  
...  
Keyword(s):  
Muscle Force ◽  
Force Production ◽  
Quadriceps Muscle ◽  
Knee Extension ◽  
Static Stretching ◽  
Production Testing ◽  
Force Output ◽  
Post Intervention ◽  
Significant Impairment ◽  
Flexion Force

Much of the static stretching (SS) literature reports performance impairments with prolonged SS. However, it has been acknowledged that a limitation of these studies is participants’ knowledge or bias. Since many participants have knowledge of the literature, their performance may be subconsciously influenced by expectations. Hence, the objective of this study was to examine the effect of stretching knowledge or deception on subsequent force output following SS. Two groups of male participants who were either aware (BIASED: 14) or unaware (DECEPTION: 14) of the SS literature participated. Unaware participants were misinformed that SS increases force production. Testing involved maximal voluntary isometric contractions (MVC) of the quadriceps and hamstrings at pre-, post-, and 5 min post-intervention (three 30-s passive hamstring stretches to the point of discomfort with 30-s rest intervals) or control. While the DECEPTION group displayed impaired knee flexion force (p = 0.04; 3.6% and 10.4%) following hamstrings SS, there was no significant impairment with the BIASED (–1.1% and +0.9%) group. Both groups exhibited hamstrings F200 (force produced in the first 200 ms) impairments following SS. Whereas BIASED participants exhibited an overall decrease (p < 0.05; 1.8% and 4.2%) in knee extension MVC, DECEPTION participants showed (p = 0.005; 8.8% and 5.1%) force increases. The quadriceps F200 was not significantly affected with the BIASED group but overall there were 4.5% and 8.7% F200 impairments at 1 and 5 min post-intervention (p = 0.05) with the DECEPTION group. Thus while deception resulted in enhanced quadriceps muscle force output, there was no knowledge or deception advantage when stretching the hamstrings.

MODELING THE CONTROL OF ISOMETRIC FORCE PRODUCTION WITH PIECE-WISE LINEAR, STOCHASTIC MAPS OF MULTIPLE TIME-SCALES

2003 ◽  
Vol 03 (01) ◽  
pp. L23-L29 ◽  
Author(s):  
GOTTFRIED MAYER-KRESS ◽  
KATHERINE M. DEUTSCH ◽  
KARL M. NEWELL
Keyword(s):  
Time Scales ◽  
Isometric Force ◽  
Force Production ◽  
Human Movement ◽  
Multiple Time Scales ◽  
Force Variability ◽  
Multiple Time ◽  
Force Level ◽  
Force Output ◽  
Isometric Force Production

In human movement, the large number of system degrees of freedom at different levels of analysis of the system, joints, muscles, motor units, cells etc, naturally affords complexity and adaptability in action. It also leads to variability in movement and its outcome, even in intentional efforts to reproduce the same movement or action goal. An example is continuous isometric force output to a constant force level where the amount and structure of force variability changes with information available, force level and individual differences. In this paper we model the control of isometric force production with piece-wise linear stochastic maps of multiple time scales. At the core of our model is a piecewise linear function, depending on three parameters that can be estimated from the observed data that is perturbed by additive Gaussian noise at a given level. The result of the stochastic forcing is that outside of a threshold interval the system behaves like a discrete Ornstein-Uhlenbeck process and inside it performs a Brownian motion. The model is shown to simulate the basic findings of the structure of human force variability that decreasing variability is correlated with increased dynamical complexity as measured with the "Approximate Entropy (ApEn)" statistic.

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