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Is the experience of bodily effort caused by outflowing nerve signals—by the central nervous system sending a “command” to do work? Or is it caused by inflowing signals providing feedback from just-performed work? This debate dates to the 1860s, when it drew in figures like Helmholtz, Wundt, Mach, James, Ferrier, and Bastian. Recently, philosophers and physicians have claimed that new experimental work answers this old question (Bergevin et al. 2023, Bermúdez and Massin 2023, Pageaux and Gaveau 2016);(also see Barbosa et al. 2016, Fernandes et al. 1990). I show that the new experimental work is in fact inconclusive, and for precisely the same reasons that empirical evidence proved incapable of settling this issue going back to the 19th century.
The recent experiments record perceived effort in exercising subjects who are under epidurally-administered anesthesia. The rate of perceived exertion is claimed to be unaffected by this anesthetic protocol, and this is supposed to show that the feeling of effort cannot be due to peripheral factors.
But the latter claim is unconvincing. First, the epidural injections are invariably made in the lumbar region of the spine, typically between either L2-L3 or L3-L4. This means subjects have been desensitized roughly below the waist, and afferent feedback is only being blocked from some of the muscles actually employed during exercise. Afference from core muscle groups involved has not been blocked, which is what afference theorists have typically hypothesized is a key source of the feeling of effort. Second, all these experiments specifically block group III/IV muscle afferents only, leaving afferent feedback in the legs from groups Ia/II intact. Group III/IV afferents modulate cardiovascular response during exercise (Amann 2012); group Ia/II afferents, in contrast, give proprioceptive feedback of the position and speed of change of the muscles (Taylor 2009). The results do not block the peripheralist theory from claiming that Ia/II (proprioceptive) afferents are key to perceived effort.
Strikingly, the 19th century centralism/peripheralism debate also deadlocked over similar limitations in experimental design. Centralists often pointed to clinical evidence that patients with paresis in an arm or an eyeball (to take two key examples) perceive an increase in effort when attempting to move the paretic appendage, counter to what the peripheralist theory might predict. But the old debate was interminable because there are a galaxy of afferent nerve signals, and it is impossible to block them all.
The two sides stalemated, with centralists proffering evidence that the feeling of effort persists even when this specific afferent signal is blocked, and peripheralists responding with that afferent signal that the experiments had not blocked, and thus could not rule out as a factor in producing perceived effort. I shall argue that the failure to settle the matter is structurally the same, today.


Amann, M. 2012. "Significance of Group Iii and Iv Muscle Afferents for the Endurance Exercising Human." Clin Exp Pharmacol Physiol 39 (9):831-5.
Barbosa, Thales C., Lauro C. Vianna, Igor A. Fernandes, Eliza Prodel, Helena N. M. Rocha, Vinicius P. Garcia, Natalia G. Rocha, Niels H. Secher, and Antonio C. L. Nobrega. 2016. "Intrathecal Fentanyl Abolishes the Exaggerated Blood Pressure Response to Cycling in Hypertensive Men." The Journal of Physiology 594 (3):715-25.
Bergevin, Maxime, James Steele, Marie Payen de la Garanderie, Camille Feral-Basin, Samuele M. Marcora, Pierre Rainville, Jeffrey G. Caron, and Benjamin Pageaux. 2023. "Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-Analysis." Sports Medicine 53 (2):415-35.
Bermúdez, Juan Pablo, and Olivier Massin. 2023. "Efforts and Their Feelings." Philosophy Compass 18 (1):e12894.
Fernandes, A, H Galbo, M Kjaer, J H Mitchell, N H Secher, and S N Thomas. 1990. "Cardiovascular and Ventilatory Responses to Dynamic Exercise During Epidural Anaesthesia in Man." The Journal of Physiology 420 (1):281-93.
Pageaux, Benjamin, and Jeremie Gaveau. 2016. "Studies Using Pharmacological Blockade of Muscle Afferents Provide New Insights into the Neurophysiology of Perceived Exertion." The Journal of Physiology 594 (18):5049-51.
Taylor, J. L. 2009. "Proprioception." In Encyclopedia of Neuroscience, edited by Larry R. Squire, 1143-49. Oxford: Academic Press.