The effect of age on post-activation depression of the upper limb H-reflex

Purpose Postactivation depression (PaD) refers to the inhibition of the H-reflex induced by a preceding conditioning stimulus able to activate the afferents mediating the H-reflex itself. PaD can be investigated assessing the frequency-related depression of the H-reflex. This parameter, which is highly correlated to the severity of spasticity, has been used in the longitudinal assessment of spastic patients, in particular to assess the effect of drugs and rehabilitation over the years. However, in such longitudinal assessment, changes observed might be age- and not only disease-related. The aim of this study was to investigate the possible age effects on PaD. Methods The frequency-related depression of the flexor carpi radialis (FCR) H-reflex was examined in two groups of young (20 subjects; 28±3 years) and aged (20 subjects; 70±7 years) healthy subjects. PaD was evaluated by comparing the H-reflex amplitudes obtained with a stimulation frequency of 0.1Hz with those obtained using higher frequencies (0.33-0.5-1-2Hz). Result