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Torque Production (torque + production)

Distribution by Scientific Domains

Medical Sciences	80%

Selected Abstracts

Acute botulinum toxin-induced muscle weakness in the anterior cruciate ligament-deficient rabbit

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2005
David Longino
Abstract We established botulinum type-A toxin (BTX-A) injections as a powerful tool to cause knee extensor weakness in New Zealand White (NZW) rabbits. The purpose of this study was to determine if BTX-A induced quadriceps weakness causes muscle dysfunction beyond that caused by anterior cruciate ligament (ACL) transection in the knee of NZW rabbits. Twenty animals were randomly divided into four study groups (n = 5 each); uninjected controls, BTX-A injection alone, ACL transection alone, BTX-A injection and ACL transection combined. Isometric knee extensor torque, quadriceps muscle mass, and vertical and anterior,posterior ground reaction forces were measured four weeks post single (BTX-A and ACL), unilateral intervention. Muscle weakness, muscle atrophy and decrease in ground reaction forces were all significantly greater for the experimental compared to the untreated contralateral legs. BTX-A injection produced a greater deficit in quadriceps mass and knee extensor torque than ACL transection alone, but produced smaller deficits in the ground reaction forces. ACL transection superimposed on BTX-A injection did not change either knee extensor torque production or muscle mass. Together these results suggest that BTX-A injection causes great force and muscle mass deficits, and affects functional gait in a significant manner, but it has no measurable functional effect when superimposed on ACL transection, at least not in the acute protocol tested here. Hopefully, BTX-A injection for acutely enhancing the degree of muscle weakness in otherwise untreated animals, or in experimental models of osteoarthritis, will help in investigating the role of muscle weakness in joint degeneration. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source]

Impact of varying pulse frequency and duration on muscle torque production and fatigue,

MUSCLE AND NERVE, Issue 4 2007
Chris M. Gregory PhD
Abstract Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue. Muscle Nerve, 2007 [source]

The Effect of Using Variable Frequency Trains During Functional Electrical Stimulation Cycling

NEUROMODULATION, Issue 3 2008
Simona Ferrante PhD
ABSTRACT Objectives., This paper describes an experimental investigation of variable frequency stimulation patterns as a means of increasing torque production and, hence, performance in cycling induced by functional electrical stimulation. Materials and Methods., Experiments were conducted on six able-bodied subjects stimulating both quadriceps during isokinetic trials. Constant-frequency trains (CFT) with 50-msec interpulse intervals and four catchlike-inducing trains (CIT) were tested. The CITs had an initial, brief, high-frequency burst of two pulses at the onset of or within a subtetanic low-frequency stimulation train. Each stimulation train consisted of the same number of pulses. The active torques produced by each train were compared. Parametric main effect ANOVA tests were performed on the active torque-time integral (TTI), on the active torque peaks and on the time needed to reach those peaks (T2P). Results., The electrical stimulation of the quadriceps produced active torques with mean peak values in the range of 1.6,3.5 Nm and a standard error below 0.2 Nm. CITs produced a significant increase of TTI and torque peaks compared with CFTs in all the experimental conditions. In particular, during the postfatigue trials, the CITs with the doublet placed in the middle of the train produced TTIs and torque peaks about 61% and 28% larger than the CFT pattern, respectively. In addition, the CITs showed the lowest reduction of the performance between prefatigue and postfatigue conditions. Conclusions., The use of CITs improves the functional electrical stimulation cycling performance compared with CFT stimulation. This application might have a relevant clinical importance for individuals with stroke where the residual sensation is still present and thus the maximization of the performance without an excessive increase of the stimulation intensity is advisable. Therefore, exercise intensity can be increased yielding a better muscle strength and endurance that may be beneficially for later gait training in individuals with stroke. [source]

The Effect of Fatigue on the Timing of Electrical Stimulation-Evoked Muscle Contractions in People with Spinal Cord Injury

NEUROMODULATION, Issue 3 2004
Peter J. Sinclair PhD
Abstract This study investigated the activation dynamics of electrical stimulation-evoked muscle contractions performed by individuals with spinal cord injury (SCI). The purpose was to determine whether electrical stimulation (ES) firing patterns during cycling exercise should be altered in response to fatigue-induced changes in the time taken for force to rise and fall with ES. Seven individuals with SCI performed isometric contractions and pedaled a motorized cycle ergometer with stimulation applied to the quadriceps muscles. Both exercise conditions were performed for five minutes while the patterns of torque production were recorded. ES-evoked knee extension torque fell by 75% under isometric conditions, and the rate of force rise and decline decreased in proportion to torque (r = 0.91, r = 0.94, respectively). There was no change in the time for torque to rise to 50% of maximum levels. The time for torque to decline did increase slightly, but only during the first minute of exercise. Cycling power output fell approximately 50% during the five minutes of exercise, however, there was no change in the time taken for torque to rise or fall. The magnitude of ES-evoked muscle torques decline substantially with fatigue, however, the overall pattern of torque production remained relatively unchanged. These results suggest there is no need to alter stimulation firing patterns to accommodate fatigue during ES-evoked exercise. [source]