Robot-assisted assessment of muscle strength
Toigo et al. Journal of NeuroEngineering and Rehabilitation
Robot-assisted assessment of muscle strength
Marco Toigo 1
Martin Flück 1
Robert Riener 0 2
Verena Klamroth-Marganska 0 2
0 Sensory-Motor Systems Lab, Department of Health Sciences and Technology ETH Zurich , Zurich , Switzerland
1 Laboratory for Muscle Plasticity, Balgrist University Hospital, University of Zurich , Zurich , Switzerland
2 Balgrist University Hospital, University of Zurich , Zurich , Switzerland
Impairment of neuromuscular function in neurological disorders leads to reductions in muscle force, which may lower quality of life. Rehabilitation robots that are equipped with sensors are able to quantify the extent of muscle force impairment and to monitor a patient during the process of neurorehabilitation with sensitive and objective assessment methods. In this article, we provide an overview of fundamental aspects of muscle function and how the corresponding variables can be quantified by means of meaningful robotic assessments that are primarily oriented towards upper limb neurorehabilitation. We discuss new concepts for the assessment of muscle function, and present an overview of the currently available systems for upper limb measurements. These considerations culminate in practical recommendations and caveats for the rational quantification of force magnitude, force direction, moment of a force, impulse, critical force (neuromuscular fatigue threshold) and state and trait levels of fatigue.
Neuromuscular; Upper extremity; Robot; Assessment; Neurorehabilitation; Sensorimotor
Background
This work was developed in the frame of the project
“State of the Art Robot-Supported assessments (STARS)”
as part of the COST Action TD1006 “European Network
on Robotics for NeuroRehabilitation” [
1
]. STARS is
intended to equally serve clinical practitioners and
scientists working in the field of neurorehabilitation. The goal
is to give recommendations for development,
implementation, and administration of different indices of robotic
assessments, grounded on the scientific literature
available at this time.
Intact neuromuscular function is indispensable for
motor function, activities of daily living and social
participation [
2
]. Neurological disorders can result in severe
impairment of neuromuscular function. In stroke, the
muscular weakness results from changes in muscle mass,
length, muscle architecture (e.g., pennation angle)
muscle composition (i.e., fiber type, fat content,
connective tissue) and material properties [
3
]. Furthermore, an
increase in stretch reflex excitability, antagonist muscle
coactivation, and a decrease in motor unit firing rate are
observed [
4
]. Sufficient force in the upper limb is related
to the ability to adequately perform many activities of
daily living [
2
], and regaining muscle force is a major
goal in upper extremity neurorehabilitation.
Furthermore, grip strength is a major predictor of recovery and
all-cause mortality [
5, 6
]. To provide optimal therapy,
valid, reliable, sensitive, and standardized assessment
methods are crucial as they serve to quantify the extent
of impairment, to identify the most effective and time
efficient training and to progressively adapt the therapy
(exercise type, intensity and time commitment) to the
individual’s progress, needs and goals.
Force assessments with either quantitative or more
qualitative methods is an integral part of the physical
examination in neurorehabilitation such as stroke [
7
] or
spinal cord injury (SCI, [
8
]). The manual muscle test
(MMT) is the most frequently used clinical assessment.
It is integrated in the international standards for
neurological classification of spinal cord injury [
8
]. It is
classified as a semi-quantitative method with relatively low
accuracy and sensitivity. Isometric force of individual
muscles and muscle groups is subjectively rated based
on the effective performance of a movement against
gravity or resistance applied by an examiner. A number
of grading systems exist for manual muscle testing [
9–
11
]. Quantification of force or moment with continuous
variables requires instrumentation. A common method
in clinical practice is isometric dynamometry with a
handheld dynamometer [
12
]. It has good reliability and
it is sensitive for all grades. Furthermore, it is less
dependent on technique than the MMT, but it is not
suitable when movement against resistance cannot be
performed. Isometric dynamometry can be integrated in
clinical tests (e.g., the Wolf Motor Function Test [
13
]).
Novel and rapidly expanding technologies such as
rehabilitation robotics can provide objective quantification
of neuromuscular function in a standardized way. This
may help to overcome the common limitations of
clinical assessments [
14
], and advance the development of
personalized human-machine interfaces alongside
assessments and rehabilitation interventions that are
tailored to a specific patient’s anatomy an (...truncated)