Fig 1.
A robotic actuator was used to apply pulling forces to three separate interface locations. The subject stabilized themselves in a custom scaffold (not depicted for clarity; see Appendix). Inset: Desired tension force (blue) vs. actual tension force (green). The peak force of the triangle profile increased incrementally by 50 N from the beginning value. The triangle wave force profile was determined by the specified loading rate. The initial peak force value (peak value of the first triangle) and the rate of force application (high vs. low) were randomized for each segment, subject and session. For the shoulders, the high force rate was 300 Ns-1 and the low force rate was 100 Ns-1; for the shank and thigh, the high force rate was 3000 Ns-1 and the low force rate was 1000 Ns-1.
Fig 2.
Boxplots depict individual subject results. Boxplots indicate subject median (cyan line), 25th and 75th quartiles (dark blue box), whiskers (extending to the farthest data point or 1.5x the interquartile range, whichever is nearer the median) and outliers (red cross markings). Three subjects (denoted with ^) only completed the first two sessions of testing on the shank. Percentage of trials that reached the maximum approved force limit are depicted in green boxes above each column. The 1200 N maximum approved force limit is denoted with a dashed gray line. The group mean comfort limit is denoted with a dotted green line. The gray boxes indicate the approximate range of forces applied by exosuits in prior literature during dynamic tasks [1], [2], [14–16]; the gray solid lines indicate maximum peak forces applied by individual studies during static tasks [4], [13].
Fig 3.
A) Group results. Boxplots depict group results for each testing day. Percentage of trials that reached the maximum approved force limit are depicted in green boxes above each column. B) Subject-specific results. Each marker (colored shape) depicts the median comfort limit for a single subject across multiple days. The 1200 N maximum approved force limit is denoted with a dashed gray line.
Fig 4.
Effect of force rate on comfort limits.
Boxplots depict group results for each force rate across days. High force rate results are in dark blue (“H”), and low force rates are depicted in light green (“L”). Percentage of trials that reached the maximum approved force limit are depicted above each column. The 1200 N maximum approved force is denoted with a dashed gray line.