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Changes with age in the voluntary static and dynamic strength of the quadriceps muscle group have been well characterized, and the importance of the muscle group for locomotion and independent living have been highlighted in both normal human aging and in clinical studies. Surprisingly few studies of this muscle group have described age-related changes in(More)
The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 +/- 0.8 yr) and six old men (82.0 +/- 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with(More)
The purpose of this study was to determine whether the loss of muscle strength in the elderly could be explained entirely by a decline in the physiological cross-sectional area (PCSA) of muscle. Isometric force, muscle activation (twitch interpolation), and coactivation (surface electromyograph) were measured during maximal voluntary contractions (MVCs) of(More)
This study examined, in nine old men (82 +/- 4 yr), whether there is an association between the magnitude of change in motor unit discharge rate and the amount of twitch potentiation after a conditioning contraction (CC). The evoked twitch force and motor unit discharge rate during isometric ramp-and-hold contractions (10-18 s) of the triceps brachii muscle(More)
Muscle weakness, studied in 4 patients with multiple sclerosis (MS), was compared with values from normal subjects. Twitch occlusion showed that normal subjects could activate their muscles maximally, but patients rarely achieved greater than 60% activation. In both groups, motoneuron firing rates increased linearly with force. Consistent with the reduced(More)
This chapter explores the hypothesis that fatigue is not caused uniquely by any common set of factors, but rather that the amount of stress placed on each site depends on the type of exercise from which fatigue develops. Evidence supporting this idea is presented by comparing results from various studies in which fatigue was caused by different exercise(More)
It has been proposed that during brief voluntary contractions, twitch potentiation may sustain force output despite a decline in motor unit discharge rate. This study examined the evoked twitch force and motor unit discharge rates during submaximal voluntary contractions of the triceps brachii muscle before and after a 5 s conditioning contraction (CC) at(More)
A study was made of motoneuron firing rates and mechanical contractile parameters during maximum voluntary contraction of human hand muscles. A comparison of muscles that had been fatigued after a 60-s maximum voluntary contraction (MVC) with muscles that were cooled by approximately 5 degrees C showed that the contractile properties, in particular the(More)
Many tasks require synergistic activation of muscles that possess different architectural, mechanical, and neural control properties. However, investigations of the motor unit (MU) mechanisms which modulate force are mostly restricted to individual muscles and low forces. To explore the pattern of MU recruitment and discharge behavior among three elbow(More)