Comfort during prolonged exposure to repetitive forces mimicking exoskeleton use

Exoskeletons can be used for rehabilitation, as assistive device for patients,
or to support workers during strenuous tasks. To fulfil their purpose, they
need to apply forces to the user*s musculoskeletal system. The forces are
transmitted at skin level through an interface, often in the form of cuffs.
Adverse events causing discomfort and injuries to the skin and underlying
tissue can be attributed to those interaction forces. While there is some
information about safe limit values for impact forces or pressure and shear
applied for short durations, little is known regarding comfort and safety
thresholds for repetitive forces applied over long durations as is the case in
exoskeleton use. This study therefore aims at gaining new knowledge on safe and
comfortable limit values for continuous repetitive shear and normal forces
applied through a cuff.

The primary objective is to determine comfort thresholds for prolonged exposure
to repetitive normal and shear stress exerted to the human thigh via a cuff
with straps, using different force patterns comparable to those exerted during
exoskeleton use. The secondary objectives are to determine the feasibility of
the experiment, the influence of subject characteristics on comfort thresholds,
the occurrence of skin injuries or other negative signs, and whether
characteristics of muscle activity can be related to discomfort.

The study is a cross-sectional intervention study with one measurement session,
where participants will provide a continuous comfort rating during exposure to
repetitive normal and shear forces.

A pre-defined set of prolonged repetitive force patterns will be applied to
each participant*s thigh though a contact force which is similar to cuffs
commonly used in gait exoskeletons. The forces will be applied by a custom made
actuated test device and are based on normal use of exoskeletons.

The study is non-therapeutic, so no direct benefits for the participants are
involved. The procedures are non-invasive and safety measures are taken to
avoid excessive force exertion to the participants or other unsafe situations.
Therefore, subjects suffer no negative effects or disadvantages, except for the
invested time and the discomfort experienced during the force execution. Pain
will be avoided as participants can trigger a release of the forces at any
time. Any changes to the participants* skin or other negative signs will be
monitored and followed up on until they have resolved.