The Influences of Turning on Hip Muscle Forces

Abstract Body : Human locomotion is a complex phenomenon that requires muscular force both to propel the individual forward and to stabilize the trunk over the stance limb. In straight path walking, stabilization of the trunk typically depends on the activation of hip abductors (gluteus medius and minimus) during single stance, with little need for hip adductor forces. Not all walking is in a straight path, however. Turning is a feature that happens constantly and seamlessly as an individual moves through their environment. How the hip muscles respond to, or create, these directional changes is unclear. In this work, we ask: do hip muscle forces during a turn differ from those of straight path walking?

Five adults (ages 19-55 years) walked unshod at their self-selected normal velocity in four conditions: straight line, 45° turn with and without a crossover-event, and 90° turn. Kinematic and kinetic data were collected using a Qualisys motion capture with four Kistler force plates. A musculoskeletal model (AnyBody Managed Model Repository v2.3.0, AnyBody Technology, Denmark) was used to calculate muscle forces in the pelvis and lower limb (42 muscles; 169 muscle elements in each limb). Maximum muscle forces for the hip abductors and hip adductors were examined during both the braking and propulsion phases of stance via Students t-test to determine if differences exist between the turning conditions and straight path walking. No difference was seen in gluteus medius, gluteus minimus, or tensor fasciae latae. During propulsion, three adductor muscles, adductor brevis, adductor magnus, and gracilis, showed a significant difference between straight path and turning conditions (all p’s< 0.05). During a 45° turn, maximum forces produced by adductor brevis (87N versus 51N) and adductor magnus (169N versus 66N) are higher than in straight path walking. During a 90° turn, adductor brevis (93N versus 51N) and gracilis (63N versus 31N) produce higher maximum muscle forces.

These data suggest that adductor muscles assist in stabilizing the trunk at the hip as the body makes a turn. Additionally, these data show that adductor brevis, adductor magnus, and gracilis produce higher forces during a turn than in straight path walking. Mechanical forces, and the strains that they induce in musculoskeletal elements, play a critical role in bone function and development. Given that bones and soft tissues respond to applied forces, turning conditions should be included to understand how lower limb morphology has adapted to accommodate for these force profiles.