An Investigation of Fatigue During the Flexion and Extension of the Knee as a Function of Velocity

This paper describes the work intended to supplement a previous study of Extravehicular Mobility Unit (EMU) strength fatigue data, collected from a variety of joints at a fixed velocity (60 degrees/second), by collecting torque data of a single joint (knee) over time, unsuited, under a condition of multiple fixed velocities. Knee flexion and extension torque values were evaluated for 8 subjects at 60, 120, 180, and 240 degrees per second. Subjects were considered “fatigued” when they reached 30% of the maximal voluntary contraction (MVC), or after 5 minutes of testing had elapsed. Results indicated that over the five-minute testing period, subjects’ available torque output decreased to 40% of their MVC, and then reached a plateau at this level. For lower velocities, subjects gradually decreased from their MVC, but their overall decrease in torque over the fiveminute period was high. For higher velocities, subjects experienced a sharp decline in torque output at the beginning of the trial, but quickly reached a plateau and had an overall smaller decrease in torque compared with lower velocities. Subjects were able to maintain a more constant torque at higher velocities at the beginning of a trial. These results will be correlated to the EMU data when it has been collected and processed, and a mathematical fatigue model will be built to aid designers and mission planners in evaluating EVA activities.