# Effects of running distance on per-step and cumulative lower-extremity loading during a simulated treadmill half marathon

## TL;DR

This study examines how running a half marathon affects biomechanical loading on the lower extremities of endurance runners.

## Contribution

The study quantifies cumulative loading on the Achilles tendon and patellofemoral joint during prolonged treadmill running.

## Key findings

- Cumulative loading on the knee and hip joints significantly increases with running distance.
- Achilles tendon and patellofemoral joint cumulative loading increases with prolonged running.
- Running mechanics shift from proximal to distal joints as running distance increases.

## Abstract

The cumulative damage impulses have been proposed as a crucial parameter for analyzing joint kinetics and tissue loading during prolonged running. Although prolonged running may have detrimental effects, research focusing on the bones and soft tissues of the lower extremity remains limited. Therefore, this study aimed to examine how treadmill half-marathons influence biomechanical variables in high-performing endurance runners. We additionally quantified per-step peak load, impulse, cumulative impulse, and cumulative weight impulse of the Achilles tendon (AT) and the patellofemoral joint (PFJ) during half marathon running.

Sixteen high-performing endurance runners (9 males and 7 females) completed a half marathon on a Zebris FDM-T pressure-sensing treadmill in a standardized biomechanics laboratory. The lower extremity kinematic and kinetic parameters were measured at every 10 km (0 km, 10 km, and 20 km) and subsequently processed using Visual3D and simulation musculoskeletal modeling. We used a one-way repeated measures ANOVA to determine the main effect of running distance on the outcome variables.

During the running stance phases, contact time and step frequency significantly increased from 10 km to 20 km (p < 0.005). Conversely, step length and stride length exhibited a significant decrease (p < 0.005). Ankle peak plantarflexion angle, ankle push-off phase range of motion (ROM), and hip braking phase ROM were significantly reduced at 10 km (p < 0.005). The cumulative loading on the ankle, knee, and hip joints was significantly greater at both 10 km and 20 km (p < 0.005). The AT force and cumulative weighted impulse value decreased at 10 km (p < 0.005) but significantly increased at 20 km running (p < 0.005). Simultaneously, the PFJ cumulative loading parameter was increased from 10 km to 20 km running (p < 0.005).

As the running distance increases, the running mechanism is significantly altered. The cumulative loading on the knee and hip significantly increased, indicating a shift in the compensatory mechanism from the proximal to the distal joint. Cumulative loading on the AT and PFJ increased with the accumulated running distance, which directly reflects that prolonged running might cause greater cumulative loading on the lower extremity.