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Force Output (force + output)
Selected AbstractsCorrelation of dystrophin,glycoprotein complex and focal adhesion complex with myosin heavy chain isoforms in rat skeletal muscleACTA PHYSIOLOGICA, Issue 4 2009S. Masuda Abstract Aim:, The dystrophin,glycoprotein complex (DGC) and focal adhesion complex (FAC) are transmembrane structures in muscle fibres that link the intracellular cytoskeleton to the extracellular matrix. DGC and FAC proteins are abundant in slow-type muscles, indicating the structural reinforcement which play a pivotal role in continuous force output to maintain posture for long periods. The aim of the present study was to examine the expression of these structures across fast-type muscles containing different myosin heavy chain (MHC) isoform patterns which reflect the fatigue-resistant characteristics of skeletal muscle. Methods:, We measured the expression of dystrophin and ,1 integrin (representative proteins of DGC and FAC respectively) in plantaris, extensor digitorum longus, tibialis anterior, red and white portions of gastrocnemius, superficial portion of vastus lateralis and diaphragm, in comparison with soleus (SOL) and cardiac muscle from rats. Results:, The expression of dystrophin and ,1 integrin correlated positively with the percentage of type I, IIa and IIx MHC isoforms and negatively with that of type IIb MHC isoform in fast-type skeletal muscles, and their expression was abundant in SOL and cardiac muscle. Conclusion:, Our results support the idea that DGC and FAC are among the factors that explain the fatigue-resistant property not only of slow-type but also of fast-type skeletal muscles. [source] Motor units in cranial and caudal regions of the upper trapezius muscle have different discharge rates during brief static contractionsACTA PHYSIOLOGICA, Issue 4 2008D. Falla Abstract Aim:, To compare the discharge patterns of motor unit populations from different locations within the upper trapezius muscle during brief submaximal constant-force contractions. Methods:, Intramuscular and surface electromyographic (EMG) signals were collected from three sites of the right upper trapezius muscle distributed along the cranial-caudal direction in 11 volunteers during 10 s shoulder abduction at 25% of the maximum voluntary force. Results:, A total of 38 motor units were identified at the cranial location, 36 from the middle location and 17 from the caudal location. Initial discharge rate was greatest at the caudal location (P < 0.05; mean ± SD, cranial: 16.7 ± 3.6 pps, middle: 16.9 ± 4.0 pps, caudal: 19.2 ± 3.3 pps). Discharge rate decreased during the contraction for the most caudal location only (P < 0.05). Initial estimates of surface EMG root mean square values were highest at the most caudal location (P < 0.05; cranial: 32.3 ± 20.9 ,V, middle: 41.3 ± 21.0 ,V, caudal: 51.6 ± 23.6 ,V). Conclusion:, This study demonstrates non-uniformity of motor unit discharge within the upper trapezius muscle during a brief submaximal constant-force contraction. Location-dependent modulation of discharge rate may reflect spatial dependency in the control of motor units necessary for the development and maintenance of force output. [source] Sensorimotor memory and grip force control: does grip force anticipate a self-produced weight change when drinking with a straw from a cup?EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2003Dennis A. Nowak Abstract We examined whether self-generated weight changes are anticipated by adequate grip force adjustments when repeatedly lifting an instrumented manipulandum. Subjects lifted a cup filled with 500 mL of water prior to and following drinking two portions of water with a straw without touching it. One half of the subjects drank from and lifted an uncovered cup receiving constant visual information about its filling level and the other half of the subjects drank from a covered cup without such visual feedback. During the lifts immediately following the drinking procedures, grip force scaling was erroneously programmed for the heavier weight of the preceding lift as was obvious from an inadequately high rate of grip force development. Vision had only a minor influence on the rate of grip force increase. The influence of vision on the scaling of peak grip force was more pronounced. More accurate force scaling was obtained with an increasing number of lifts performed under each weight condition, indicating an ongoing force adjustment process probably based on sensory feedback. We conclude that self-generation of a change in the weight of an object to be lifted is not, in itself, sufficient to elicit a predictive grip force output. Rather, accurate feedback information associated with the self-generated weight change is essential to update internal models related to the mechanical object properties. This assumption was confirmed in pilot experiments; when subjects lifted the cup after having poured water from it, they accurately scaled their fingertip force to the self-produced weight change. Here, direct sensory feedback from the grasping fingers could signal the weight change and update internal models while pouring water from the cup. Our data support the hypothesis that the sensorimotor system planning and processing predictive fingertip force can operate independently of higher-level cognitive and perceptual systems. [source] Multichannel surface electromyography in ergonomics: Potentialities and limitsHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2010Marco Gazzoni Abstract The prevention of work-related musculoskeletal disorders is one of the main goals in ergonomics. Among others, surface electromyography (sEMG) is an important tool for the evaluation of risks related to work activity. Three main issues have been approached in ergonomics via sEMG: 1) the analysis of muscle activation, 2) the analysis of exerted forces and torques, and 3) the analysis of muscle fatigue. Many studies have been carried out in static conditions. In ergonomics, however, it is more relevant to study muscle activity and fatigue during real tasks that are, in general, dynamic. From isometric to dynamic contractions, the complexity of the interpretation of sEMG signals increases considerably. Changes in sEMG signals are related to the continuous modifications in force output, muscle fiber length, and relative position of surface electrodes and sources. To increase the reliability of the information extracted from sEMG, multichannel detection systems have been applied, showing the possibility of overcoming some limits of the standard technique. Some illustrative laboratory and field studies are reported in this work to illustrate the potentialities and the open problems in the use of multichannel sEMG in ergonomics. Case 1 is a laboratory study investigating the myoelectric manifestations of fatigue in the biceps brachii (BB) during dynamic elbow flexion/extension. Case 2 is a laboratory study investigating the myoelectric manifestations of fatigue during a repetitive lifting task. Case 3 is a field study, carried out in an automotive plant, investigating muscle activation during the welding of a car door. Many factors play a leading role in the correct interpretation of information provided by sEMG. Even though multichannel sEMG provides information able to improve the estimation of force and/or fatigue during working tasks, many problems related to the signal acquisition and interpretation are still open. Further improvements are necessary to develop multichannel sEMG into an effective tool supporting other methodologies for the evaluation of work-related risks. © 2010 Wiley Periodicals, Inc. [source] Load force during manual transport in Parkinson's diseaseACTA NEUROLOGICA SCANDINAVICA, Issue 6 2004X. Guo Objectives , To search for a physiological method for the measurement of upper extremity dexterity during activities of daily life in Parkinson's disease (PD). Materials and methods , We examined load force output during manual transport in seven patients with PD and 10 healthy controls. PD patients were measured in both the non-medicated and medicated states. The test movement included two continuous sub-movements: an upward-forward transport of an object from the table to the stand, and a downward-backward transport of the object from the stand to the table. Hand movements were recorded using an optoelectronic camera, and load force was measured using a force sensor installed in the test object. Results , Compared with the controls, PD patients had a different pattern of load force output characterized by slower force development and release, lower peak force, and less dynamic force generation during movement. After medication, the speed of force development and the level of peak force increased in the patients. Conclusions , These findings suggest that PD impairs the production of preprogrammed movements. The movements observed in the PD patients may result from compensatory strategies relying more on feedback mechanisms. [source] | ||||||||||