Kari Huseth: From foot to trunk – how the body adapts after an Achilles tendon rupture
Kari Huseth's thesis concerns the interaction in the body – how movement and function are linked in a complex chain. As a leading example, she has studied how the body is affected by an Achilles tendon rupture. The results show that rehabilitation should primarily focus on the Achilles tendon's own capacity, and rebuilding nearby segments in the ankle. During rehabilitation, focus can be placed on integrating structures further up the body to optimize the function of the entire chain.
KARIN HUSETH
Dissertation defense: 14 April 2025 (click for details)
Doctoral thesis: An exploration of the biomechanical chain in walking and running -Neuromechanical function from the feet up to the trunk
Research area: Orthopaedics
Sahlgrenska Academy, The Institute of Clinical Sciences
Human gait and posture depend on a long sequence of coordinated events in the body. This occurs through what is known as the biomechanical chain1, where movement and force are transferred from the feet up through the legs to the trunk. The purpose of this dissertation was to investigate how changes in foot kinematics2 affect motor behavior along this chain during walking and running. The focus was on Achilles tendon ruptures3.
– Can we, through rehabilitation, influence other parts of the body by training one area that in turn may reduce problems elsewhere? I have focused particularly on which positions activate the trunk, how the feet and trunk interact, and how an injury in the foot and ankle region can have effects further up the body, says Kari Huseth, physical therapist specialized in orthopedic manual therapy, and a doctoral student at the Institute of Clinical Sciences.
To study this, she conducted methodological investigations of how foot position affects muscle activation, using EMG (electromyography) measurements, where EMG detects the electrical signal generated when the nervous system activates a muscle. She then studied individuals one year after an Achilles tendon rupture and analyzed how the injured side compared to the non-injured side during walking and running.
Healing of the Achilles tendon is slow and requires gradual adaptation
The results showed that foot position primarily influenced muscle activity in the legs and feet, while the trunk was affected to a lesser extent. After an Achilles rupture, long-term changes were observed in ankle function.
Illustration from thesis: The green curves illustrate the path of the ground reaction forces (GRFs) throughout stance. The red arrow indicates the direction and magnitude of the GRF at intial contact (IC). The yellow stick figures trace the movement of the body segments, following the motion of the ankle, knee, and hip joints. Compared with walking, running produces GRFs of greater magnitude and different orientation.
During the stance phase of walking and running: In walking, the injured side showed increased activation in the outer calf muscle (gastrocnemius lateralis) toward the end of the stance phase, while ankle mobility was reduced early in the step. The injured side also demonstrated lower force production in both the ankle and knee, and a lower total support moment during both heel strike and push-off. During running, no significant side differences were observed in muscle activity or joint force, but ankle mobility was slightly reduced toward the end of the stance phase, and the total support moment was lower during push-off. However, there were large individual variations.
Focus on the Achilles tendon's own capacity
– Rehabilitation after an Achilles tendon rupture should be based on clinical reasoning –– that is, on the facts and symptoms related to the individual patient’s injury — and on individualized, progressive, task-specific loading with continuous evaluation according to the patient’s goals. Healing of the tendon is slow and requires gradual adaptation to promote durability and strength.
The focus should therefore be directed toward the Achilles tendon’s own capacity, the rebuilding of nearby segments, and effective integration of proximal structures to optimize the function of the entire chain.
– The goal is not merely symmetry or a return to previous gait patterns, but the development of a resilient and dynamic tendon–muscle–nerve system that can adapt to the varying demands of sports, work, and daily life.
Making the invisible visible and understanding the body in depth
What has been most rewarding and most challenging about the PhD project?
– Muscles and movements can be seen with the naked eye, but with biomechanical tools another layer is revealed – we can measure them, make the invisible visible, and understand the body in depth. Working in the biomechanics laboratory requires precision at every step but also brings that special sense of excitement while waiting to see what the results will show. It has been both educational and enjoyable, and equally valuable has been the collaboration with other researchers, as well as the opportunity to combine clinical practice with research, where both experiences enrich each other in everyday work.
Text: Susanne Lj Westergren
1. In biomechanics, kinetics2 is used to understand the forces and moments acting within the body and between the body and its surroundings.
2. Kinematics – describes how the body moves, for example how fast, in which direction, or with what pattern, and why it moves in that way.
3. An Achilles tendon rupture causes acute pain (...) leading to reduced ankle stability, decreased muscle strength, and difficulty pushing off during walking. This alters gait patterns. If untreated, it affects balance, reduces muscular endurance, and causes cramping in the calf and surrounding muscles, as well as recurring swelling. The altered gait and uneven load distribution can lead to secondary problems, for example in the back (...). Source: The National Board of Health and Welfare (Socialstyrelsen).