Journal of Neurophysiology, Vol 58, Issue 1 125-137, Copyright © 1987 by APS

ARTICLES

Evidence for a fatigue-induced reflex inhibition of motoneuron firing rates

J. J. Woods, F. Furbush and B. Bigland-Ritchie

1. In previous studies on the adductor pollicis and biceps brachii muscles we suggested that motoneuron firing rates are inhibited by a reflex from the muscle during fatigue, since: the firing rates decline during a sustained maximal voluntary contraction (MVC); recovery of MVC firing rates is prevented if the fatigued state of the muscle is preserved for 3 min by local occlusion of its blood supply; and full recovery occurs during this time once the blood supply to the peripheral muscle is restored. These findings were confirmed in the present study for quadriceps contractions. 2. These results do not necessarily imply an inhibitory reflex. The lower firing rates recorded from the muscle fibers during an MVC following 3 min of postfatigue ischemia may have been caused by either reduced subject effort (decreased muscle activation by the CNS) or impaired peripheral impulse transmission under these conditions. The present experiments, carried out on the quadriceps and adductor pollicis muscles, were designed to test this alternative explanation. 3. For both muscles, MVC contractions were sustained for 40 s with a blood pressure cuff inflated to 200 mmHg. This was followed by 3 min ischemic rest and a second 20-s MVC before cuff release. Three minutes after the blood supply to the muscle was restored a third 20-s MVC was made. Single shocks were delivered to the muscle throughout to record twitches from the relaxed muscle (Tr) before and after each MVC, and any twitches super-imposed on the voluntary contractions (Ts). The degree to which the muscle could be activated by voluntary effort was assessed from the ratio [1 - Ts/Tr]. For adductor pollicis, changes in the amplitude of the evoked M-waves were also measured. 4. Spike frequencies were only recorded during quadriceps experiments. These declined by 30% during the initial 40-s MVC. No recovery was seen in the second MVC following 3 min ischemic rest, but full recovery occurred within 3 min of cuff release. 5. Failure to retain full muscle activation was frequently seen in all three MVCs. However, for many well-motivated subjects twitch occlusion showed no reduction in the degree to which either the adductor pollicis or quadriceps muscles could be activated voluntarily during the MVC executed after 3 min of ischemic rest compared with that performed 3 min after the blood supply had been restored.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				G. Todd, J. L. Taylor, J. E. Butler, P. G. Martin, R. B. Gorman, and S. C. Gandevia Use of motor cortex stimulation to measure simultaneously the changes in dynamic muscle properties and voluntary activation in human muscles J Appl Physiol, May 1, 2007; 102(5): 1756 - 1766. [Abstract] [Full Text] [PDF]

				S. Racinais, O. Girard, J. P. Micallef, and S. Perrey Failed Excitability of Spinal Motoneurons Induced by Prolonged Running Exercise J Neurophysiol, January 1, 2007; 97(1): 596 - 603. [Abstract] [Full Text] [PDF]

				P. G. Martin, J. L. Smith, J. E. Butler, S. C. Gandevia, and J. L. Taylor Fatigue-sensitive afferents inhibit extensor but not flexor motoneurons in humans. J. Neurosci., May 3, 2006; 26(18): 4796 - 4802. [Abstract] [Full Text] [PDF]

				B.M. Meyers and E. Cafarelli Caffeine increases time to fatigue by maintaining force and not by altering firing rates during submaximal isometric contractions J Appl Physiol, September 1, 2005; 99(3): 1056 - 1063. [Abstract] [Full Text] [PDF]

				A. Adam and C. J. De Luca Firing rates of motor units in human vastus lateralis muscle during fatiguing isometric contractions J Appl Physiol, July 1, 2005; 99(1): 268 - 280. [Abstract] [Full Text] [PDF]

				D. Farina, L. Arendt-Nielsen, and T. Graven-Nielsen Experimental muscle pain reduces initial motor unit discharge rates during sustained submaximal contractions J Appl Physiol, March 1, 2005; 98(3): 999 - 1005. [Abstract] [Full Text] [PDF]

				P. G Martin, F. E Marino, J. Rattey, D. Kay, and J. Cannon Reduced voluntary activation of human skeletal muscle during shortening and lengthening contractions in whole body hyperthermia Exp Physiol, March 1, 2005; 90(2): 225 - 236. [Abstract] [Full Text] [PDF]

				A St Clair Gibson and T D Noakes Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans Br. J. Sports Med., December 1, 2004; 38(6): 797 - 806. [Abstract] [Full Text] [PDF]

				J. L. Taylor and S. C. Gandevia Noninvasive stimulation of the human corticospinal tract J Appl Physiol, April 1, 2004; 96(4): 1496 - 1503. [Abstract] [Full Text] [PDF]

				I. Kalezic, L. A. Bugaychenko, A. I. Kostyukov, A. I. Pilyavskii, M. Ljubisavljevic, U. Windhorst, and H. Johansson Fatigue-related depression of the feline monosynaptic gastrocnemius-soleus reflex J. Physiol., April 1, 2004; 556(1): 283 - 296. [Abstract] [Full Text] [PDF]

				D. Farina, L. Arendt-Nielsen, R. Merletti, and T. Graven-Nielsen Effect of Experimental Muscle Pain on Motor Unit Firing Rate and Conduction Velocity J Neurophysiol, March 1, 2004; 91(3): 1250 - 1259. [Abstract] [Full Text] [PDF]

				J. E. Butler, J. L. Taylor, and S. C. Gandevia Responses of Human Motoneurons to Corticospinal Stimulation during Maximal Voluntary Contractions and Ischemia J. Neurosci., November 12, 2003; 23(32): 10224 - 10230. [Abstract] [Full Text] [PDF]

				J. E. Butler and C. K. Thomas Effects of sustained stimulation on the excitability of motoneurons innervating paralyzed and control muscles J Appl Physiol, February 1, 2003; 94(2): 567 - 575. [Abstract] [Full Text] [PDF]

				S. C. Gandevia Spinal and Supraspinal Factors in Human Muscle Fatigue Physiol Rev, October 1, 2001; 81(4): 1725 - 1789. [Abstract] [Full Text] [PDF]

				L.-Q. Zhang and W. Z. Rymer Reflex and Intrinsic Changes Induced by Fatigue of Human Elbow Extensor Muscles J Neurophysiol, September 1, 2001; 86(3): 1086 - 1094. [Abstract] [Full Text] [PDF]

				N. L. Jones and K. J. Killian Exercise Limitation in Health and Disease N. Engl. J. Med., August 31, 2000; 343(9): 632 - 641. [Full Text] [PDF]

				E. M. Wojtys, B. B. Wylie, and L. J. Huston The Effects of Muscle Fatigue on Neuromuscular Function and Anterior Tibial Translation in Healthy Knees Am. J. Sports Med., September 1, 1996; 24(5): 615 - 621. [Abstract] [PDF]

				A. J. Fuglevand Neural Aspects of Fatigue Neuroscientist, July 1, 1996; 2(4): 203 - 206. [Abstract] [PDF]