Age Related Differences in Motor Output Variability During Isometric, Concentric and Eccentric Quadriceps Femoris Muscle Contractions
Christou, Evangelos Andrea
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Permalink
https://hdl.handle.net/2142/86429
Description
Title
Age Related Differences in Motor Output Variability During Isometric, Concentric and Eccentric Quadriceps Femoris Muscle Contractions
Author(s)
Christou, Evangelos Andrea
Issue Date
2000
Doctoral Committee Chair(s)
Carlton, Les G.
Department of Study
Kinesiology and Community Health
Discipline
Kinesiology and Community Health
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
The purpose was to examine the ability of young and elderly individuals to produce maximum voluntary contractions (MVC) and control submaximum levels of force during continuous isometric, discrete isometric, discrete concentric and discrete eccentric contractions of the quadriceps femoris. Of particular interest was to model variability of force during continuous and discrete isometric contractions. Participants were 24 young (25.3 +/- 2.8 years) and 24 elderly individuals (73.3 +/- 5.5 years) that were active, healthy and mentally fit. Participants were to match a criterion force-level during continuous isometric contractions, and a parabolic force-time function with time-to-peak force of 200 ms during discrete contractions. Target-forces ranged from 5 to 90% MVC for continuous and discrete isometric contractions, and 20 to 90% MVC for concentric and eccentric contractions. Quadriceps strength for the elderly was on average 40% lower of that of young participants and eccentric strength was affected the least. The standard deviation (SD) and coefficient of variation (CofV) of force was greater during discrete than during continuous isometric contractions. During discrete contractions, eccentric contractions exhibited greater variability than isometric or concentric contractions for peak force, impulse and impulse duration. During continuous isometric contractions, young and elderly participants exhibited similar CofV of force. During all discrete contractions, however, elderly participants exhibited greater CofV for peak force and impulse and greater SD and CofV for temporal characteristics than young adults. Variability of force was modeled as a sigmoidal logistic function for continuous isometric contractions, whereas, it was modeled as a sigmoidal Gompertz function for discrete isometric contractions. For continuous isometric contractions, model parameters were different between the two age groups; however, for discrete isometric contractions, model parameters were similar between the two groups. Results support the hypothesis that eccentric contractions are controlled uniquely by central nervous system, and lack of muscle control in elderly might be due to deteriorations at the spinal level or discharge rate of motor units.
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