Neuroscience Letters 383 (2005) 333–338 Dynamic stability of locomotor respiratory coupling during cycling in humans S´ ebastien Villard, Jean-Franc ¸ois Casties, Denis Mottet ∗ Universit´ e Montpellier 1, 700, av. du Pic St Loup, 34090 Montpellier, France Received 19 January 2005; received in revised form 5 April 2005; accepted 6 April 2005 Abstract We explored the locomotor respiratory coupling (LRC) during a 50-min constant-load submaximal cycling exercise. A 4-week recombinant human erythropoietin (r-HuEPO) treatment improved participants’ aerobic capabilities, but did not elicit significant changes in LRC. The distributions of the respiratory frequency over pedalling frequency ratios were systematically bimodal, with a preferred use of 1/3 and 1/2, and a progressive shift of the higher mode from 1/3 towards 1/2 with exercise duration. These results are interpreted in the framework of the sine circle map as the result of coordination dynamics between the physiological subsystems involved in the breathing pedalling cooperation. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Locomotor respiratory coupling; Sine circle map; Farey tree; Exercise duration; Dynamical systems; r-HuEPO In mammals, the capacity to sustain endurance exercises is related to their ability to efficiently integrate respiration and locomotion. Generally, this cooperation is presented as the complete entrainment of breathing cycles by the locomotion rhythm. This is especially true in quadrupeds, where gallop- ing speed performance leads to a 1/1 ratio between stride frequency and respiratory frequency [4,5,12]. However, in less constrained locomotion tasks, like in bipedal locomo- tion, the analysis of locomotor respiratory coupling (LRC) showed that the two rhythmic processes of locomotion and respiration are generally frequency locked at low integer ra- tios (such as 1/2, 1/3 or 1/4) [5]. LRC is a generic mechanism that involves mechanical and neural interactions between the two subsystems. From the point of view of mechanics, breathing entrainment can be the results of passive interactions such as impact loading of the thorax, “visceral piston” and flexion/extension movements of the axial skeleton that tend to enhance expiration [4]. Active breathing entrainment can also be the consequence of mus- cles simultaneously involved in both locomotion and respi- ∗ Corresponding author at: EA 2991 Efficience & D´ eficience Motrice, Facult´ e des Sciences du Sport, Universit´ e Montpellier 1, 700, av. du Pic St Loup, 34090 Montpellier, France. Fax: +33 467415750. E-mail address: denis.mottet@univ-montp1.fr (D. Mottet). ration, especially in tetrapods [4] and in human arm propul- sion (e.g., in rowing or wheelchair locomotion) where strong couplings are reported [2,20]. As a consequence, mechan- ical couplings are stronger in quadrupeds than in humans, for which the upright position generates less constrains and allows larger ventilatory adaptations [5]. The observed di- versity in the ratios between stride frequency and respiratory frequency in humans suggests that LRC is not simply due to a passive and active mechanical interactions between locomo- tor and respiratory systems. Moreover, Temprado et al. [21] recently showed that breathing was coordinated with simple repetitive wrist movements, a task where almost no mechan- ical coupling exists. The second mechanism that plays an important role in LRC is neurological coupling at different levels of the neural system. A common neural drive from the subthalamic and mesencephalic locomotor regions trig- gers an immediate increase in respiratory and cardiovascu- lar rhythms at the onset of locomotor exercise [9]. Such a central control seems to require the activation of spinal loco- motion generators [13,23], and Viala [23] proposed a model integrating several pattern generators to explain the coupling relationships between locomotion and respiration in rabbits. More recently, Morin and Viala [14] showed that proprio- ceptive peripheral feedback from locomotor limbs plays an important role in the modulation of LRC. All these neural 0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.04.047