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Maximum Voluntary Activation in Nonfatigued and Fatigued Muscle of Young and Elderly Individuals

SK Stackhouse, PT, MSPT, is a doctoral student in the Interdisciplinary Graduate Program in Biomechanics and Movement Science, University of Delaware, Newark, Del
JE Stevens, PT, MPT, is a doctoral student in the Interdisciplinary Graduate Program in Biomechanics and Movement Science, University of Delaware
SCK Lee, PT, PhD, is Research Associate, Research Department, Shriners Hospitals for Children, Philadelphia Unit, Philadelphia, Pa
KM Pearce, BS, was an undergraduate biology major at the University of Delaware at the time of this study
L Snyder-Mackler, PT, ScD, SCS, is Associate Professor, Department of Physical Therapy, University of Delaware
SA Binder-Macleod, PT, PhD, is Chair and Professor, Department of Physical Therapy, University of Delaware, 301 McKinly Laboratory, Newark, DE 19716 (USA) (sbinder{at}udel.edu).

Address all correspondence to Dr Binder-Macleod

Background and Purpose. Researchers studying central activation of muscles in elderly subjects (65 years of age) have investigated activation in only the nonfatigued state. This study examined the ability of young and elderly people to activate their quadriceps femoris muscles voluntarily under both fatigued and nonfatigued conditions to determine the effect of central activation failure on age-related loss of force. Subjects and Methods. Twenty young subjects (11 men, 9 women; mean age=22.67 years, SD=4.14, range=18–32 years) and 17 elderly subjects (8 men, 9 women; mean age=71.5 years, SD=5.85, range=65–84 years) participated in this study. Subjects were seated on a dynamometer and stabilized. Central activation was quantified, based on the change in force produced by a 100-Hz, 12-pulse electrical train that was delivered during a 3- to 5-second isometric maximum voluntary contraction (MVC) of the quadriceps femoris muscle. Next, subjects performed 25 MVCs (a 5-second contraction with 2 seconds of rest) to fatigue the muscle. During the last MVC, central activation was measured again. Results. In the nonfatigued state, elderly subjects had lower central activation than younger subjects. In the fatigued state, this difference became larger. Discussion and Conclusion. Central activation of the quadriceps femoris muscle in elderly subjects was reduced in both the fatigued and nonfatigued states when compared with young subjects. Some part of age-related weakness, therefore, may be attributed to failure of central activation in both the fatigued and nonfatigued states.

Key Words: Aging • Central activation • Maximum voluntary contraction • Skeletal muscle

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