Journal of Applied Physiology AJP: Heart and Circulatory Physiology
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J Appl Physiol (June 29, 2006). doi:10.1152/japplphysiol.00385.2006
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Submitted on March 31, 2006
Accepted on June 25, 2006

Feedback-Controlled Stimulation Enhances Human Paralyzed Muscle Performance

Richard K Shields1*, Shauna Dudley-Javoroski1, and Keith R. Cole1

1 Graduate Program in Physical Therapy & Rehabilitation Science, University of Iowa, Carver College of Medicine, Iowa City, Iowa, United States

* To whom correspondence should be addressed. E-mail: richard-shields{at}uiowa.edu.

Chronically paralyzed muscle requires extensive training before it can deliver a therapeutic dose of repetitive stress to the musculoskeletal system. Neuromuscular electrical stimulation, under feedback control, may subvert the effects of fatigue, yielding more rapid and extensive adaptations to training. The purposes of this investigation were to 1) compare the effectiveness of torque feedback controlled (FDBCK) electrical stimulation with classic open loop constant-frequency (CONST) stimulation, and 2) ascertain which of three stimulation strategies best maintains soleus torque during repetitive stimulation. When torque declined by 10%, the FDBCK protocol modulated the base stimulation frequency in three ways: by a fixed increase, by a paired pulse (doublet) at the beginning of the stimulation train, and by a fixed decrease. The stimulation strategy that most effectively restored torque continued for successive contractions. This process repeated each time torque declined by 10%. In fresh muscle, FDBCK stimulation offered minimal advantage in maintaining peak torque or mean torque over CONST stimulation. As long duration fatigue developed in subsequent bouts, FDBCK stimulation became most effective (~40% higher final normalized torque than CONST). The high frequency strategy was selected ~ 90 % of the time, supporting that excitation-contraction coupling compromise and not neuromuscular transmission failure contributed to fatigue of paralyzed muscle. Ideal stimulation strategies may vary according to the site of fatigue; this stimulation approach offered the advantage of online modulation of stimulation strategies in response to fatigue conditions. Based on stress-adaptation principles, FDBCK controlled stimulation may enhance training effects in chronically paralyzed muscle.




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L.-W. Chou, T. M Kesar, and S. A Binder-Macleod
Using Customized Rate-Coding and Recruitment Strategies to Maintain Forces During Repetitive Activation of Human Muscles
Physical Therapy, March 1, 2008; 88(3): 363 - 375.
[Abstract] [Full Text] [PDF]




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