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Articles in PresS, published online ahead of print February 8, 2002
J Appl Physiol, 10.1152/jap.00367.2001
Submitted on April 19, 2001
Accepted on January 30, 2002
1 Groupe Analyse du Mouvement (G.A.M.), Universite de Bourgogne, Dijon, Dijon, France; Centre for Biophysical and Clinical Research into Human Movement (CRM), Manchester Metropolitan University, Alsager, Cheshire, United Kingdom; Centro Studi Attivita Motorie(C.S.A.M.), S.Maugeri Foundation, Pavia, Pavia, Italy
2 Centre for Biophysical and Clinical Research into Human Movement (CRM), Manchester Metropolitan University, Alsager, Cheshire, United Kingdom; Centro Studi Attivita Motorie(C.S.A.M.), S.Maugeri Foundation, Pavia, Pavia, Italy
3 Groupe Analyse du Mouvement (G.A.M.), Universite de Bourgogne, Dijon, Dijon, France
4 Centro Studi Attivita Motorie(C.S.A.M.), S.Maugeri Foundation, Pavia, Pavia, Italy
5 Division of Metabolic Diseases, Italian Institute of Auxology, Piancavallo, Verbania, Italy
* To whom correspondence should be addressed. E-mail: m.narici{at}mmu.ac.uk.
The reduction in muscle strength with aging is not only associated with sarcopenia, but may also be related to changes in neural drive. The objective of this study was to investigate whether the voluntary neural drive to the muscle and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-week strengthening program on plantarflexors' activation capacity, and on the Hmax/Mmax ratio were investigated in a population of 14 elderly males (aged 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 (Pt) were observed. Voluntary activation, assessed by the twitch-interpolation, increased from 95% to 98% (p<0.05). Pre-training, activation capacity, also evaluated from the expected MVC for total twitch occlusion, was 7% higher (p<0.01) than the observed MVC. This discrepancy persisted after training. The relationship between the interpolated twitch amplitude and voluntary torque was curvilinear with marked deviation from linearity for torque levels > 65% MVC. When compared to a group of younger males (aged 24-35 yr) the maximal Hoffmann reflex to maximum M wave ratio (Hmax/Mmax) 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, fairly active older men seem to preserve a high activation capacity of the plantar flexor muscles. However, the impaired functionality of the reflex pathway with aging and the lack of modulation with exercise suggest that the decrease in Hmax/Mmax ratio and conduction velocity may be essentially related to degenerative phenomena. These observations may be specific to the plantar flexors since different findings have been previously reported for other muscle groups.
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