Abstract
Purpose: This study aimed to determine the changes in lower extremity biomechanics during running-induced fatigue intervention. Methods: Fourteen male recreational runners were required to run at 3.33 m/s until they could no longer continue running. Ground reaction forces (GRFs) and marker trajectories were recorded intermittently every 2 min to quantify the impact forces and the lower extremity kinematics and kinetics during the fatiguing run. Blood lactate concentration (BLa) was also collected before and after running. Results: In comparison with the beginning of the run duration, (1) BLa significantly increased immediately after running, 4 min after running, and 9 min after running; (2) no changes were observed in vertical/anterior–posterior GRF and loading rates; (3) the hip joint range of motion (θROM) significantly increased at 33%, 67%, and 100% of the run duration, whereas θROM of the knee joint significantly increased at 67%; (4) no changes were observed in ankle joint kinematics and peak joint moment at the ankle, knee, and hip; and (5) vertical and ankle stiffness decreased at 67% and 100% of the run duration. Conclusion: GRF characteristics did not vary significantly throughout the fatiguing run. However, nonlinear adaptations in lower extremity kinematics and kinetics were observed. In particular, a “soft landing” strategy, achieved by an increased θROM at the hip and knee joints and a decreased vertical and ankle stiffness, was initiated from the mid-stage of a fatiguing run to potentially maintain similar impact forces.
Highlights
Long-distance running has many benefits, including reducing the risk of cardiovascular disease [1]. there is not sufficient literature demonstrating that injuries are inevitable for all runners, running-related musculoskeletal injuries are still very common
The repetitive impact forces occurred during touchdown can reach a magnitude ranging from 2- to 3-times body weight [7], and are considered as high risk factors of lower limb injury [6]
In comparison with joint range of motion at the beginning, θROM of the knee joint significantly increased at 33% and 67% of the run duration, and θROM, ∆θ, θ0, and θmax-ext of the hip joint significantly increased at 33%, 67%, and 100% of the run duration (Figure 4 and Table 2)
Summary
Long-distance running has many benefits, including reducing the risk of cardiovascular disease [1]. There is not sufficient literature demonstrating that injuries are inevitable for all runners, running-related musculoskeletal injuries are still very common. More than 74% of long-distance runners adopt the heel strike pattern [6]. The repetitive impact forces occurred during touchdown can reach a magnitude ranging from 2- to 3-times body weight [7], and are considered as high risk factors of lower limb injury [6]. Long-term and high-intensity running inevitably induces neuromuscular fatigue, which further influences musculoskeletal system of the lower limbs. The movement control of the lower extremity decreases after fatigue, which is an important cause of running injury [8,9]
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