Effect of trunk muscles fatigue on lower limb mechanical work and stiffness in recreational runners

During running, trunk muscles contribute to generation and transmission of mechanical power and work. The effect of trunk muscle fatigue on lower limb mechanical work and leg stiffness (K_leg) is not well known. This study aimed to examine the effects of trunk muscle fatigue on K_leg and lower limb mechanical work in recreational runners. Thirty recreational rearfoot-strike runners completed overground running trials before and after trunk muscle fatigue. From a biomechanical assessment, we calculated the K_leg, positive and negative mechanical work, and the relative contribution of mechanical work of the hip, knee, and ankle joints across the three anatomical planes. After trunk muscle fatigue, an increase in K_leg was observed. At the ankle joint, trunk muscle fatigue increased negative and positive works in the sagittal plane, while increased knee joint positive work in the sagittal and frontal planes. In the sagittal plane, trunk muscle fatigue decreased knee joint negative work relative contribution and hip joint positive work relative contribution, and increased ankle joint positive work relative contribution. Increases in knee joint positive work relative contribution in the frontal plane, and hip joint positive work relative contribution in the horizontal plane were observed. It is evident from the findings that compensatory changes in lower-limb biomechanics occur in response to trunk muscle fatigue. This could include increased stiffness and redistribution of joint mechanical work, particularly toward distal joints. Such adaptations highlight the role of trunk stability in running performance and injury prevention, emphasizing the importance of trunk endurance in training programs.