Changes in blood volume and oxygenation level in a working muscle during a crank cycle

Lucia, Alejandro

Medicine & Science in Sports & Exercise: March 2002 - Volume 34 - Issue 3 - p 529
APPLIED SCIENCES: Physical Fitness and Performance: Guest Editorial to Accompany

Universidad Europea de Madrid, Madrid, Spain

Article Outline

Since the development of the bicycle ergometer by Bouny in 1896, it has been the exercise model of choice for exploring human physiological responses during exertion. The sport of cycling has also been the subject of thorough research. Surprisingly, several basic questions remain to be conclusively answered, including how the different phases of the crank cycle influence circulatory dynamics, and the optimal combination of pedalling cadence and force application. Is the pattern spontaneously adopted by humans (cyclists and noncyclists) really optimal? The outstanding performance of cycling champion Lance Armstrong in recent years suggests that the traditional approach to optimizing the “duty cycle” are not yet fully understood. During his ascent of Alpe D’Huez in the 2001 Tour de France (mean speed of 22 km·h−1 during a 14-km climb of 8% mean gradient) Armstrong’s pedalling cadence averaged ∼100 rpm (estimated power output of ∼500 W). Such an unusual, fast pedalling pattern for mountain ascents has traditionally been thought to be less economical than that commonly chosen by professional cyclists (∼70 rpm) (1).

Takaishi et al. (3–5) used surface electromyography and near infrared spectroscopy to study the effects of varying pedalling cadence on neuromuscular fatigue and metabolic variables. They also used the innovative technique of signal averaging several pedal strokes to allow acquisition of enough data to resolve muscle oxygenation during various phases of the crank cycle. These methodologies and the experimental design used by the authors showed that, in noncyclists exercising at moderate-to-high power outputs (∼200 W) and at low cadences (50 rpm), blood flow to the quadriceps is significantly restricted during the duty cycle (first third of the crank cycle). Their data also reflect a temporary increase in blood supply after the pushing phase, during which the vastus lateralis recovers from the previous contraction.

Although further research is needed, their efforts have contributed toward understanding why elite cyclists usually rely on high cadences (90 rpm or more) to maintain high absolute power outputs (>400 W) over flat terrains, minimizing the duration of blood flow restriction to the knee extensor muscles. Minimizing blood restriction to working muscles is an important concern in competitive cycling, particularly when riders adopt aerodynamic positions to reduce air resistance (e.g., during flat time trials). Besides the blood flow restriction due to increased intramuscular pressure suggested by Takaishi’s findings, the blood flow of iliac arteries (which irrigate all leg muscles) can be reduced during hip flexions (2).

The novel methodological approach reported by Takaishi et al. provides a potentially important new tool in the search for answers to the unresolved questions of cycling physiology, whether in competitive cyclists or in other models of human exercise performance.

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©2002The American College of Sports Medicine