Adjustment of muscle coordination during an all-out sprint cycling task.
Dorel S, Guilhem G, Couturier A, Hug F.
This study was designed to assess muscle coordination during a specific all-out sprint cycling task (Sprint). The aim was to estimate the EMG activity level of each muscle group by referring to the submaximal cycling condition (Sub150 W) and to test the hypothesis that a maximal activity is reached for all of the muscles during Sprint.
Fifteen well-trained cyclists were tested during submaximal and sprint cycling exercises and a series of maximal voluntary contractions (MVCs) in isometric and isokinetic modes (MVC at the three lower limb joints). Crank torque and surface EMG signals for 11 lower limb muscles were continuously measured.
Results showed that Sprint induced a very large increase of EMG activity level for the hip flexors (multiplied by 7-9 from 150 W to Sprint) and the knee flexors and hip extensors (multiplied by 5-7), whereas plantar flexors and knee extensors demonstrated a lower increase (multiplied by 2-3). During Sprint, EMG activity level failed to reach a maximal value for hamstrings, tibialis anterior, tensor fasciae latae, and gluteus maximus (i.e., <70% to 80% of peak EMG activity during MVC, P < 0.05 to P < 0.001), and individual EMG patterns demonstrated a significant earlier onset and/or later offset for the majority of the muscles (P < 0.01 to P < 0.001).
Results clearly suggest a change in the relative contribution of the different muscles to the power production between Sub150 W and Sprint, and provide evidence that EMG activity level is not systematically maximal for all muscles involved in the all-out sprint cycling task. The longer period of activity induced during Sprint is likely to represent an interesting coordination strategy to enhance the work generated by all of the muscle groups.
COMMENT: This study looks at what happens to the pedaling coordination as cyclists increase from "cruising" to maximum sprinting power. While it is a common belief that to improve power the rider should just push harder this study demonstrates that what actually happens when riders need maximum power is most of the work increase comes by increasing the upstroke portion of the pedaling stroke. Unfortunately, other studies (Sanderson, Dorel) have shown that these are the muscles that fatigue the most at the end of a race, when the rider is exhausted. If one is interested in minimizing how these muscles fatigue in order to maximize sprint power at the end of the race one needs to better train the hip flexor and hamstring muscles. This is exactly what the PowerCranks do.