1 3 Eur J Appl Physiol (2014) 114:359–364 DOI 10.1007/s00421-013-2778-5 ORIGINAL ARTICLE The effect of age on post-activation depression of the upper limb H-reflex Carlo Trompetto · Lucio Marinelli · Laura Mori · Stefania Canneva · Federica Colombano · Elisabetta Traverso · Antonio Currà · Giovanni Abbruzzese Received: 24 May 2013 / Accepted: 16 November 2013 / Published online: 1 December 2013 © Springer-Verlag Berlin Heidelberg 2013 Conclusion Our study shows that ageing does not affect the frequency-related depression of the FCR H-reflex at the frequencies of 1 Hz or lower, supporting the reliability of this method to assess PaD in the clinical practice, par- ticularly for the longitudinal assessment of spasticity. A decrease of GABA-ergic presynaptic inhibition seems to be the more likely explanation for the age-related changes that we observed at the frequency of 2 Hz. Keywords H-reflex · Ageing · Post-activation depression · Frequency-related depression · Homosynaptic depression · Presynaptic inhibition Abbreviations PaD Post-activation depression FCR Flexor carpi radialis muscle Introduction Post-activation depression (PaD) refers to the inhibition of the test response (either H-reflex or stretch reflex), elicited in a given muscle (test muscle) at rest, induced by a pre- ceding conditioning stimulus able to activate the afferents mediating the test response (e.g. a tap or a vibration applied to the tendon of the test muscle, a passive lengthening or a voluntary contraction of the test muscle, an electrical stimulation of the mixed nerve supplying the test muscle) (Crone and Nielsen 1989; Hultborn et al. 1996). In prac- tice, two methods have been used to assess PaD in humans: the frequency-related depression of the soleus and the flexor carpi radialis (FCR) H-reflex (Aymard et al. 2000; Lamy et al. 2009; Rossi-Durand et al. 1999), often reported as low-frequency depression (Ishikawa et al. 1966), or the soleus H-reflex depression following passive stretch of the Abstract Purpose Post-activation depression (PaD) refers to the inhibition of the H-reflex induced by a preceding condi- tioning stimulus able to activate the afferents mediating the H-reflex itself. PaD can be investigated assessing the fre- quency-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 related and not only disease related. The aim of this study was to investigate the possi- ble 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 (18 subjects; 69 ± 6 years) healthy subjects. PaD was evaluated by com- paring the H-reflex amplitudes obtained with a stimulation frequency of 0.1 Hz with those obtained using higher fre- quencies (0.33–0.5–1–2 Hz). Results The results showed that frequency-related depres- sion of the FCR H-reflex is similar in young and elderly subjects at all frequencies, with the exception of 2 Hz. Communicated by Alain Martin. C. Trompetto · L. Marinelli (*) · L. Mori · S. Canneva · F. Colombano · E. Traverso · G. Abbruzzese Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health, Institute of Neurology, University of Genova, Largo Daneo 3, 16132 Genoa, Italy e-mail: lucio.marinelli@unige.it A. Currà Department of Medical-Surgical Sciences and Biotechnologies, A. Fiorini Hospital, Sapienza University of Rome Polo Pontino, Via Firenze, 04019 Terracina, LT, Italy