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J Appl Physiol (June 12, 2008). doi:10.1152/japplphysiol.90421.2008
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Submitted on March 18, 2008
Revised on May 22, 2008
Accepted on June 10, 2008

Impaired Neuromuscular Function During Isometric, Shortening and Lengthening Contractions After Exercise-Induced Damage to Elbow Flexor Muscles

Tanya S. Turner1, Kylie J. Tucker1, Nigel C. Rogasch1, and John G. Semmler1*

1 University of Adelaide

* To whom correspondence should be addressed. E-mail: john.semmler{at}adelaide.edu.au.

The purpose of this study was to examine the effect of exercise-induced damage of the elbow flexor muscles on steady motor performance during isometric, shortening and lengthening contractions. Ten healthy individuals (age 22 ± 4 years) performed four tasks with the elbow flexor muscles: a maximum voluntary contraction (MVC), a one-repetition maximum (1-RM), an isometric task at 3 joint angles (short, intermediate and long muscle lengths), and a constant-load task during slow (~7 °/s) shortening and lengthening contractions. Task performance was quantified as the fluctuations in wrist acceleration (steadiness), and electromyography (EMG) was obtained from the biceps and triceps brachii muscles at loads of 10, 20 and 40% 1-RM. Tasks were performed before, immediately and 24-hrs after eccentric exercise that resulted in indicators of muscle damage. MVC force and 1-RM load declined by ~45% immediately after exercise and remained lower at 24-hrs (~30% decrease). Eccentric exercise resulted in reduced steadiness and increased biceps and triceps brachii EMG for all tasks. For the postural task, steadiness was impaired at the short compared with the long muscle length immediately after exercise (P < 0.01). Furthermore, despite no differences before exercise, there was reduced steadiness for the shortening compared with the lengthening contractions after exercise (P = 0.01), and steadiness remained impaired for shortening contractions 24-hrs later (P = 0.01). These findings suggest that there are profound effects for the performance of these types of fine motor tasks when recovering from a bout of eccentric exercise.




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T. J. Dartnall, N. C. Rogasch, M. A. Nordstrom, and J. G. Semmler
Eccentric Muscle Damage Has Variable Effects on Motor Unit Recruitment Thresholds and Discharge Patterns in Elbow Flexor Muscles
J Neurophysiol, July 1, 2009; 102(1): 413 - 423.
[Abstract] [Full Text] [PDF]




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