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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Deciphering the metabolic and mechanical contributions to the exercise-induced circulatory response: insights from eccentric cycling

¹Service de Physiologie et d'Explorations Fonctionnelles, Hôpital Civil and Département de Physiologie, Faculté de Médecine, Strasbourg, France; ²Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex, United Kingdom; ³Institut de Chimie Biologique, Faculté de Médecine, Strasbourg, France; ⁴Hôpital de la Robertsau, Strasbourg, France; ⁵and Service de Cardiologie, Hôpitaux Civils, Colmar, France

Submitted 9 August 2006 ; accepted in final form 4 December 2006

Metabolic demand and muscle mechanical tension are closely coupled during exercise, making their respective drives to the circulatory response difficult to establish. This coupling being altered in eccentric cycling, we implemented an experimental design featuring eccentric vs. concentric constant-load cycling bouts to gain insights into the control of the exercise-induced circulatory response in humans. Heart rate (HR), stroke volume (SV), cardiac output (), oxygen uptake (O₂), and electromyographic (EMG) activity of quadriceps muscles were measured in 11 subjects during heavy concentric (heavy CON: 270 ± 13 W; O₂ = 3.59 ± 0.20 l/min), heavy eccentric (heavy ECC: 270 ± 13 W, O₂ = 1.17 ± 0.15 l/min), and light concentric (light CON: 70 ± 9 W, O₂ = 1.14 ± 0.12 l/min) cycle bouts. Using a reductionist approach, the circulatory responses observed between heavy CON vs. light CON (difference in O₂ and power output) was ascribed either to metabolic demand, as estimated from heavy CON vs. heavy ECC (similar power output, different O₂), or to muscle mechanical tension, as estimated from heavy ECC vs. light CON (similar O₂, different power output). 74% of the response was determined by the metabolic demand, also accounting for 65% and 84% of HR and SV responses, respectively. Consequently, muscle mechanical tension determined 26%, 35%, and 16% of the , HR, and SV responses, respectively. was significantly related to O₂ (r² = 0.83) and EMG activity (r² = 0.82; both P < 0.001). These results suggest that the exercise-induced circulatory response is mainly under metabolic control and support the idea that the level of muscle activation plays a role in the cardiovascular regulation during cycle exercise in humans.

metabolic demand; muscle mechanical tension; heart rate; stroke volume; circulatory control

This article has been cited by other articles:

				F. N. Daussin, J. Zoll, S. P. Dufour, E. Ponsot, E. Lonsdorfer-Wolf, S. Doutreleau, B. Mettauer, F. Piquard, B. Geny, and R. Richard Effect of interval versus continuous training on cardiorespiratory and mitochondrial functions: relationship to aerobic performance improvements in sedentary subjects Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2008; 295(1): R264 - R272. [Abstract] [Full Text] [PDF]

				Rebuttal from Drs. Richard, Zoll, Mettauer, Piquard, and Geny J Appl Physiol, February 1, 2008; 104(2): 563 - 564. [Full Text] [PDF]