Dynamic properties of partially denervated muscle

Abstract

The mechanical and electrical properties of the partially denervated first dorsal interosseous muscle were measured in 14 patients and 14 normal control subjects. The following variables were studied during isometric contraction: maximum voluntary contraction; maximum rate of rise of tension in a rapid voluntary contraction; amplitude, rate of rise, time to peak, and duration of peak of the compound muscle action potential; twitch force, maximum rate of rise, contraction time, and half-relaxation time; and tetanic (50 Hz) force, rate of rise, and tetanus/twitch ratio. The force produced during repetitive stimulation of the ulnar nerve at 10, 20, 50, and 100 impulses per second was also analyzed. The major findings were: (1) decreased load bearing (voluntary contraction, twitch, and tetanus), (2) prolonged twitch contraction times and half-relaxation times, (3) decreased tetanus/twitch ratio, and (4) preserved rate of rise of tension.

Central fatigue during isometric exercise in amyotrophic lateral sclerosis

“…Poor performance on these measures is consistent with incomplete motor unit recruitment, less-than-maximal discharge rates and/or poor modulation of rate and recruitment. 4,14,21 Similar impairments have been observed in other disorders of the UMN. 21,28 A limitation of our method of assessing central activation failure includes the possible influence of volitional factors on our measures.…”

“…Prior to exercise, central activation was also assessed by quantitating the speed of voluntary force development (df/ dt), measured during a rapid, submaximal (40% MVC) isometric contraction. 4,14 Several trials were given, until the subject was able to rapidly and reliably hit the target tension. To control for the effects of any changes in peripheral muscle contractile speed in ALS, the rate of voluntary force development was normalized to the rate of TF development.…”

Simple Foot Tapping Test as a Quantitative Objective Assessment of Cervical Myelopathy

“…11 Slowing of voluntary contraction speed was not seen in patients with lower motor neuron diseases. 22 Slowness of foot tapping was reported to be a more useful sign than Babinski sign for identifying UMN weakness. 23 Cervical compressive myelopathy is one of the UMN syndromes and the gait disturbance is mainly caused by UMN weakness, which includes spasticity, hyperrefl exia, and slowness of voluntary movements not in proportion to muscle weakness.…”

Lower energy cost of skeletal muscle contractions in older humans

“…RFD and RFR are expressed as a percentage of the peak force achieved during the contraction. This approach accounts for the fact that the RFD is higher when force production is higher and allows direct comparison among individuals with different torque-generating capacities (39). The force-frequency relationship was fit with a sigmoid function, and the f 50 was calculated as the frequency that would produce 50% of maximal force.…”