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J Physiol 349:519–534ĭoherty TJ (2003) Invited review: aging and sarcopenia. Arch Phys Med Rehabil 86:318–327ĭay BL, Marsden CD, Obeso JA, Rothwell JC (1984) Reciprocal inhibition between the muscles of the human forearm. J Neurophysiol 53:805–820Ĭhung SG, Van Rey EM, Bai Z, Rogers MW, Roth EJ, Zhang LQ (2005) Aging-related neuromuscular changes characterized by tendon reflex system properties. J Neurophysiol 53:786–804Ĭheney PD, Fetz EE, Palmer SS (1985) Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey. J Physiol 349:249–272Ĭheney PD, Fetz EE (1985) Comparable patterns of muscle facilitation evoked by individual corticomotoneuronal (CM) cells and by single intracortical microstimuli in primates: evidence for functional groups of CM cells. Exp Brain Res 120:223–232Ĭheney PD, Fetz EE (1984) Corticomotoneuronal cells contribute to long-latency stretch reflexes in the rhesus monkey. J Physiol 445:1–24Ĭapaday C, Devanne H, Bertrand L, Lavoie BA (1998) Intracortical connections between motor cortical zones controlling antagonistic muscles in the cat: a combined anatomical and physiological study. J Appl Physiol 89:61–71īutler EG, Horne MK, Rawson JA (1992) Sensory characteristics of monkey thalamic and motor cortex neurones. J Physiol 511:947–956īurnett RA, Laidlaw DH, Enoka RM (2000) Coactivation of the antagonist muscle does not covary with steadiness in old adults. The data also indicate the need to use age-matched control subjects when comparing individuals with abnormalities resulting from disorders that occur at an old age.īertolasi L, Priori A, Tinazzi M, Bertasi V, Rothwell JC (1998) Inhibitory action of forearm flexor muscle afferents on corticospinal outputs to antagonist muscles in humans. Activation of agonist and antagonist muscle pairs are most likely organized around a dual system of cortically and spinally mediated reciprocal inhibition that is altered by age. These data confirm the existence of cortical reciprocal inhibition reported previously in young humans and show that age reduces this inhibition similarly to the previously reported reduction of spinal reciprocal inhibition reported in old adults. The MEPs remained at control level in the FCR and were also unaffected in the first dorsal interosseus. The age by conditioning interval interaction ( P=0.001) showed that the MEPs in the ECR were significantly depressed at 14, 15, 16, 17, 18, and 19 ms (range 55.5-65.9% of control, all P<0.05) compared with control value of 100% and with old adults who showed no depression.
The size of the control MEP in the ECR was also similar in young (0.98☐.10 mV) and old subjects (0.90☐.14 mV, P=0.686). The absolute TMS intensity, expressed as the percent of stimulator output, used to produce 1-mV control MEPs in the ECR was similar in young (mean 58.5, standard deviation ☑2.8%) and old adults (60.3☒0.3%, P=0.855). The test stimulus, delivered by transcranial magnetic stimulation (TMS) at 1-ms increments between 11 and 24 ms after the electrical conditioning stimulus, evoked motor potentials (MEP) in the extensor carpi radialis (ECR) and flexor carpi radialis (FCR). In young (age 27, n=6) and old (age 73, n=6) adults a mild conditioning electrical stimulus was delivered to the median nerve at the elbow. We examined the possibility that age also modifies cortical reciprocal inhibition. A widely observed age-related adaptation is the heightened activation of the antagonist muscles during voluntary movements. Age alters the control of voluntary movement.