Central and Peripheral Fatigue after Electrostimulation-Induced Resistance Exercise DELPHINE BOERIO 1,2 , MARC JUBEAU 1 , RAPHAEL ZORY 1,3 , and NICOLA A. MAFFIULETTI 1 1 INSERM ERM 207, Faculty of Sport Sciences, University of Burgundy, Dijon, FRANCE; 2 Myology Institute, GH Pitie´- Salpeˆtrie´re, Paris, FRANCE; and 3 STAPS Department, University of Savoy, Chambe´ry, FRANCE ABSTRACT BOERIO, D., M. JUBEAU, R. ZORY, and N. A. MAFFIULETTI. Central and Peripheral Fatigue after Electrostimulation-Induced Resistance Exercise. Med. Sci. Sports Exerc., Vol. 37, No. 6, pp. 973–978, 2005. Purpose: To investigate central and peripheral fatigue induced by a typical session of electromyostimulation (EMS) of the triceps surae muscle. Methods: A series of neuromuscular tests including voluntary and electrically evoked contractions were performed before and immediately after 13 min of EMS (75 Hz) in 10 healthy individuals. Results: Maximal voluntary contraction torque of the plantar flexor muscles significantly decreased (9.4%; P  0.001) after EMS, and this was accompanied by an impairment of central activation, as attested by twitch interpolation results (P  0.05), whereas soleus maximal Hoffmann reflex and tibialis anterior coactivation did not change significantly. Contractile properties associated with paired stimuli and maximal M-wave amplitude for both soleus and medial gastrocnemius muscles (9.4 and 38.7%, respectively) were significantly affected by EMS (P  0.05), whereas postactivation potentiation did not change. Conclusion: A single bout of EMS resulted in fatigue attributable to both central and peripheral factors. The most obvious alteration in the function of the central nervous system is a decrease in the quantity of the neural drive to muscle from the supraspinal centers. On the other hand, neuromuscular propagation failure was more evident for the muscle with the higher percentage of Type II fibers. Key Words: TRICEPS SURAE, TORQUE, H REFLEX, EMG ACTIVITY, ACTIVATION LEVEL F atigue is defined as any exercise-induced reduction in force generating capacity of a muscle (4), and can originate from peripheral and/or central factors. Pe- ripheral fatigue is typically associated with alterations at or below the neuromuscular junction, whereas central fatigue is defined as a progressive reduction in voluntary activation of muscle during exercise (10) mediated by intrinsic mo- toneuronal, spinal, and supraspinal factors. Many authors have documented the concomitant occurrence of central and peripheral fatigue after a protocol of maximal or submaxi- mal voluntary contractions of the plantar flexor muscles (14,20,26,27). On the other hand, the acute adjustments in neuromuscular properties consecutive to a single bout of electrostimulation-induced resistance exercise, which is commonly used for muscle strengthening in sports medicine and rehabilitation settings, are poorly known. Electromyo- stimulation (EMS) is often considered a technique to sup- plement or to substitute for voluntary activation of muscle with no (apparent) involvement of the central nervous sys- tem. This assumption is, however, somewhat paradoxical because the electric stimuli applied at the skin level evoke action potentials in both motor and sensory fibers, thus generating force by direct activation of motor axons and by indirect recruitment of spinal motoneurons. Moreover, it is now well recognized that neural adaptations account for the strength gains associated with short-term EMS training pro- grams, as increases in electromyographic (EMG) activity (6,21), voluntary activation level (21,32), and significant cross-education effect (12,25) have been reported after mul- tiple sessions of EMS. It is therefore possible that a series of contractions triggered by EMS would result in fatigue not only at the muscle level (peripheral fatigue), as easily an- ticipated due to the artificial nature of the contraction, but also at the central nervous system level. Central components of triceps surae fatigue can be as- sessed in maximal voluntary contractions (MVC) with the twitch interpolation technique (23), which involves apply- ing supramaximal electrical stimuli to the posterior tibial nerve, and with surface EMG recordings, provided that raw signals are normalized to the maximal M wave (M max , that is, the EMG response due to the synchronous activation of most muscle fibers; (15)) for respective muscles. EMG recordings may also offer the possibility of investigating exercise-induced alterations in spinal reflexes, through the analysis of electrically evoked Hoffmann reflex (H reflex; (11)). However, to the best of our knowledge, twitch inter- polation and EMG recordings have not been used concom- itantly to study neural factors (spinal and supraspinal) pos- Address for correspondence: Dr. Nicola A. Maffiuletti, INSERM ERM 207, Faculty of Sport Sciences, University of Burgundy, BP 27877-21078 Dijon cedex, France; E-mail: Nicola.Maffiuletti@u-bourgogne.fr. Submitted for publication November 2004. Accepted for publication February 2005. 0195-9131/05/3706-0973/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2005 by the American College of Sports Medicine DOI: 10.1249/01.mss.0000166579.81052.9c 973