Comments on Point:Counterpoint: Afferent feedback from fatigued locomotor muscles is/is not an important determinant of endurance exercise performance PREDOMINANCE OF CENTRAL MOTOR COMMAND IN THE REGULATION OF EXERCISE

TO THE EDITOR: Neurobiological aspects of the regulation of exercise by the central nervous system (CNS) are poorly understood and have been studied mainly to understand central fatigue (i.e., a progressive decline in the drive to motoneurons) as during prolonged strenuous exercise in humans under conditions of hyperthermia (6). The predominance of centrally originating neural signals in the perception of voluntary muscular force has been showed by data obtained in a deafferented subject who was able to accurately discriminate isometric forces solely on the basis of internal signals (3). The contribution of afferent input in sensing effort must however not be dismissed as reinforced by Amman and Secher (1). Peripheral feedback allows to modulate and calibrate the central signal of effort (2). Also, during complete paralysis by curarization, heart rate, blood pressure, and perceived effort still increase during attempted contraction of skeletal muscles, indicating that central motor command can operate independently of somatosensory inflow to the CNS (93). Finally, although Amman and Secher (1) and Marcora (4) seem to suggest that fatigue is detrimental to performance and goal-directed behavior, this may not be the case. Fatigue may provide the cognitive system with a signal that encourages the organism to lower present goals and/or seek lower effort alternative strategies. Alterations of dopamine and acetylcholine influx into the prefrontal cortex that occur with prolonged task performance is adaptative in the sense that it signals the need to abandon or change the ongoing behavior in such a way to promote energy conservation (5).