Exp Brain Res (2002) 146:394–398 DOI 10.1007/s00221-002-1186-6 RESEARCH NOTE Julie N. CôtØ · Pierre A. Mathieu · Mindy F. Levin · Anatol G. Feldman Movement reorganization to compensate for fatigue during sawing Received: 10 April 2002 / Accepted: 14 June 2002 / Published online: 22 August 2002 # Springer-Verlag 2002 Abstract Peripheral (muscle) aspects of fatigue are well documented. However, little is known about the central aspects of fatigue that could influence, in particular, multijoint coordination. To investigate the central aspects offatigue,wecomparedthemultijointkinematicsofnon- fatigued and fatigued individuals while sawing. Muscle fatiguewasassociatedwithdecreasesinsawingforceand movement amplitude at the elbow whereas the basic characteristics of the saw trajectory, including the move- ment direction, extent and duration, remained invariant. This invariance was maintained by increasing the move- ment amplitude at the wrist, shoulder and trunk. The system thus takes advantage of the redundancy of the motor apparatus to maintain the endpoint trajectory despite fatigue. Keywords Motor control · Multijoint coordination · Redundancy problem · Human Introduction When a movement is performed repetitively, muscle fatigue has been shown to translate into changes in local parameters of movement. Such changes may include decreased range of motion at the main agonist joint, decreased movement velocity and muscle force, and changes in the spectrum of muscle electromyogram (Enoka and Stuart 1992). The possibility that muscle fatigue can lead to multimuscle and multijoint coordina- tion changes and, in particular, movement reorganization has received little attention in previous studies. Forestier and Nougier (1998) found that in ball throwing, the temporal sequence of the arm joint peak velocities was modified with fatigue, with shorter delays between the peak velocities of movement at different body segments. Inastudyofrepetitivehoppinginhumans,Bonnardetal. (1994) found that subjects used two strategies to adapt to fatigue:one,aredistributionofthemuscularcontributions across different joints involved in the motor task, and the other,changesinthecontributionofsinglejoints.Another study of repetitive load lifting (Sparto et al. 1997) reported decreased postural stability with fatigue, as well as decreased motion at distal joints (knee and hip) compensated by increased trunk motion. There is also considerable evidence of increased multimuscle coacti- vationwithfatigueinpatientswithlow-backpain(Potvin and O’Brien 1998). In the present study, we investigated thepossibilityofreorganizationofmultijointcoordination with fatigue during repetitive sawing. We chose this whole-body, forceful motion since fatigue is an inherent part of the task when it is performed in repetition. We hypothesized that the system could take advantage of its redundancy by modifying the relative contributions of various joints to compensate for fatigue. Materials and methods Experimental protocol Thirty subjects (25 men, 5 women, average age = 34€11 years) signed informed consent forms approved by the institutional Ethics Committee. Nine infra-red-emitting markers were placed on the proximal extremity of a saw and on the following anatomical landmarks of the dominant side of the body: head of the third metacarpal(hand),styloidprocessoftheulna(wrist),epicondyleof thehumerus(elbow),anterolateralborderofthescapula(shoulder), spinous process of the seventh cervical vertebrae (neck), manubri- umofthesternum(torso),greatertrochanterofthefemur(hip),and head of the fibula (knee). A system for the analysis of movement (Optotrak,samplingrate100Hz)wasusedtorecordthekinematics J.N. CôtØ ( ) ) · P.A. Mathieu · M.F. Levin · A.G. Feldman Department of Physiology, Institute of Biomedical Engineering, University of Montreal, Montreal, Quebec, Canada e-mail: cotej@igb.umontreal.ca Tel.: +1-514-3402078 Fax: +1-514-3402154 M.F. Levin · A.G. Feldman Center for Multidisciplinary Research in Rehabilitation (CRIR), Montreal, Quebec, Canada A.G. Feldman Institute for Rehabilitation of Montreal, 6300 Darlington ave., Montreal, Canada H3S 2J4