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1 Groupe Analyse du Mouvement, Unité de Formation et de Recherche en Sciences et Techniques des Activités Physiques et Sportives, Université de Bourgogne, 21078 Dijon Cedex, France; 2 Centre for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager ST7 2HL, United Kingdom; 3 Centro Studi Attività Motorie, Fondazione S. Maugeri, 27100 Pavia, Italy; and 4 Division Metabolic Diseases, Istituto Auxologico Italiano, Instituto di Ricovero e Cura a Carattere Scientifico, 28900 Piancavallo, Italy
The purpose of this study was to investigate whether the voluntary neural drive and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-wk strengthening program on plantar flexor voluntary activation (VA) and on the maximum Hoffman reflex (Hmax)-to-maximum M wave (Mmax) ratio were investigated in 14 elderly men (65-80 yr). After training, isometric maximum voluntary contraction (MVC) increased by 18% (P < 0.05) and weight-lifting ability by 24% (P < 0.001). Twitch contraction time decreased by 8% (P < 0.01), but no changes in half relaxation time and in peak twitch torque were observed. The VA, assessed by twitch interpolation, increased from 95 to 98% (P < 0.05). Pretraining VA, also evaluated from the expected MVC for total twitch occlusion, was 7% higher (P < 0.01) than MVC. This discrepancy persisted after training. The interpolated twitch torque-voluntary torque relationship was fitted by a nonlinear model and was found to deviate from linearity for torque levels >65% MVC. Compared with younger men (24-35 yr), the Hmax- to Mmax ratio and nerve conduction velocity (H index) of the older group were significantly lower (42%, P < 0.05; and 29%, P < 0.001, respectively) and were not modulated by training. In conclusion, older men seem to preserve a high VA of plantar flexors. However, the impaired functionality of the reflex pathway with aging and the lack of modulation with exercise suggest that the decrease in the Hmax- to Mmax ratio and H index may be related to degenerative phenomena.
twitch interpolation; triceps surae; aging; exercise
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