Why Does Power Output Decrease at High Pedaling Rates during Sprint Cycling?

SAMOZINO, PIERRE1,2; HORVAIS, NICOLAS2; HINTZY, FRÉDÉRIQUE2

Medicine & Science in Sports & Exercise: April 2007 - Volume 39 - Issue 4 - pp 680-687
doi: 10.1249/MSS.0b013e3180315246
BASIC SCIENCES: Original Investigations

Purpose: The objective of this study was to partly explain, from electromyographical (EMG) activity, the decrease in power output beyond optimal pedaling rate (PRopt) during sprint cycling.

Methods: Eleven cyclists performed four 8-s nonisokinetic sprints on a cycle ergometer against four randomized friction loads (0.5, twice 0.75, and 0.9 N·kg−1 of body mass). Power output and EMG activity of both right and left gluteus maximus, rectus femoris, biceps femoris, and vastus lateralis were measured continuously. Individual crank cycles were analyzed. Crank angles corresponding to the beginning and the peak of each downstroke and EMG burst onset and offset crank angles were computed. Moreover, crank angles corresponding to the beginning and the end of muscle force response were determined assuming a 100-ms lag time between the EMG activity and the relevant force response (or electromechanical delay).

Results: Muscle coordination (EMG onset and offset) was altered at high pedaling rates. Thus, crank angles corresponding to muscle force response increased significantly with pedaling rate. Consequently, at pedaling rates higher than the optimal pedaling rate, force production of lower-limb extensor muscles was shifted later in the crank cycle. Mechanical data confirmed that downstrokes occurred later in the crank cycle when pedaling rate increased. Hence, force was produced on the pedals during less effective crank cycle sectors of the downstroke and during the beginning of the upstroke.

Conclusion: During nonisokinetic sprint cycling, the decrease in power output when pedaling rates increased beyond PRopt may be partly explained by suboptimal muscle coordination.

1Research Unit of Physiology and Physiopathology of Exercise and Handicap, University of Saint-Etienne, Saint-Etienne, FRANCE; and 2Modelling in Sports Activities Laboratory, University of Savoie, Savoie, FRANCE

Address for correspondence: Pierre Samozino, UR Physiologie et Physiopathologie de l'Exercice et Handicap, Université de Saint-Étienne, Médecine du sport et Myologie- CHU Bellevue, 42055 Saint-Étienne Cedex 02, France; E-mail: pierre.samozino@univ-st-etienne.fr.

Submitted for publication April 2006.

Accepted for publication December 2006.

©2007The American College of Sports Medicine