Influences of chemically-induced muscle pain on power output of ballistic upper limb movements Marco Bonifazi a , Guido Ciccarone a , Raimondo della Volpe b , Raffaele Spidalieri b , Alessandro Rossi b, * a Dipartimento di Fisiologia, Via Aldo Moro 4, Siena, Italy b Dipartimento di Scienze Neurologiche e del Comportamento, Policlinico Universitario Le Scotte, Viale Bracci 1, Universita ` degli Studi di Siena, I-53100 Siena, Italy Accepted 7 March 2004 Available online 6 May 2004 Abstract Objective: To analyse the conditioning effects of localised acute muscle pain on power output during ipsi- and contra-lateral ballistic arm extensions. Methods: Eight male subjects performed right arm (ipsilateral) and left arm (contra-lateral) bench press movements. The power output (and force and velocity) of the concentric phase of movement was measured before and during muscle pain induced by a standardised intramuscular injection of levo-ascorbic acid in the right pectoralis major muscle (prime mover muscle) and in the lateral head of the right triceps brachii muscle (synergist). Results: The power output of ipsi- and contra-lateral arm bench press movements was significantly decreased during pain of the right pectoralis major muscle, but not during pain of the right lateral triceps muscle. The velocity and force were both affected and contributed to the decrease in power output. Conclusions: Acute muscle pain of a prime mover muscle reduces ipsi- and contra-lateral motor performance of ballistic upper limb extension. This is not a generalised or non-specific inhibitory effect on the motor system, since pain failed to modify motor performance when applied to a synergist, non-prime mover, muscle. A basically bilateral executive cortical plan for ballistic upper limb extension could explain the conditioning effect of muscle pain on both ipsi- and contra-lateral arm. Significance: The results presented here contributes to the understanding of the conditioning effects of muscle pain on movement performance. q 2004 Published by Elsevier Ireland Ltd on behalf of International Federation of Clinical Neurophysiology. Keywords: Muscle pain; Muscle performance; Motor system; Ballistic movement 1. Introduction Neurophysiological pain research has concentrated principally on processes involved in the transfer of nociceptive information to the brain and to conscious perception. The effects of nociceptive afferent discharge on the motor system have largely been ignored. Since Sherrington (1910), the stereotyped ‘nocifensive’ flexion reflex has been assumed to be the fundamental motor action evoked by nociceptive afferents. Recent investigations using experimental pain in humans have revealed intricate implications of nociceptive afferents in the control of movements. There is evidence in humans that discharge from high-threshold nociceptive afferents interacts with spinal and trigeminal motor pathways (Arendt-Nielsen et al., 1996; Decchi et al., 1997; Graven-Nielsen et al., 1997; Kofler, 2003; Kofler et al., 2001; Kranz et al., 1973; Le Pera et al., 2000; Lund et al., 1991; Matre et al., 1998; Rossi and Decchi, 1995, 1997; Rossi et al., 1999a,b; Rossi et al., 2003a,b; Sohn et al., 2000; Svensson et al., 1999; Wang et al., 2000; Westberg et al., 1997) as well as with primary somatosensory and motor cortex (Kofler et al., 2001; Le Pera et al., 2000; Romaniello et al., 2000; Rossi et al., 1998, 2003b; Valeriani et al., 1999; Valeriani et al., 2001). These complex actions can be expected to contribute to adaptive motor strategies during pain (Graven-Nielsen et al., 1997), 1388-2457/$30.00 q 2004 Published by Elsevier Ireland Ltd on behalf of International Federation of Clinical Neurophysiology. doi:10.1016/j.clinph.2004.03.014 Clinical Neurophysiology 115 (2004) 1779–1785 www.elsevier.com/locate/clinph * Corresponding author. Tel.: þ 39-577-233-484; fax: þ39-577-40327. E-mail address: rossiale@unisi.it (A. Rossi).