Relationship Between the Patterns of Time-Course Changes in Running Pace and Running Mechanics in a Full Marathon.

In full marathons, a considerable slowdown that typically occurs after 30 km, often referred to as "hitting the wall," is well known, but the underlying biomechanical mechanism remains unclear. This study aimed to elucidate pacing patterns and kinematic changes in marathon runners. Hierarchical clustering of running pace per kilometer of 297 participants, obtained from 58 marathon races, identified 3 groups, each exhibiting different biomechanical changes tracked by wearable sensors. Two groups that experienced a slowdown showed decreases in step length (effect size [ES] = 0.40-1.43), step frequency (ES = 0.30-0.34), and vertical stiffness (ES = 0.55-0.65), along with an increase in contact time (ES = 0.56-0.86). The group that slowed down suddenly after 30 km displayed unchanged vertical oscillation, in contrast to the group that began slowing down earlier. The relationship among contact time, step length, and vertical stiffness observed differs from findings in laboratory tests with constant speed, suggesting that changes in step length in response to decreased vertical stiffness may contribute to the slowdown. The mechanism of sudden slowdown after 30 km, which is unique to marathon running, should be distinguished from slowdowns that occur earlier.