Biomechanics and neural control of movement, 20 years later: what have we learned and what has changed?
Nordin et al. Journal of NeuroEngineering and Rehabilitation
Biomechanics and neural control of movement, 20 years later: what have we learned and what has changed?
Andrew D. Nordin 0
William Z. Rymer
Andrew A. Biewener
Andrew B. Schwartz
Daofen Chen
Fay B. Horak
0 University of Florida , PO Box 116131, Gainesville, FL 32611 , USA
We summarize content from the opening thematic session of the 20th anniversary meeting for Biomechanics and Neural Control of Movement (BANCOM). Scientific discoveries from the past 20 years of research are covered, highlighting the impacts of rapid technological, computational, and financial growth on motor control research. We discuss spinal-level communication mechanisms, relationships between muscle structure and function, and direct cortical movement representations that can be decoded in the control of neuroprostheses. In addition to summarizing the rich scientific ideas shared during the session, we reflect on research infrastructure and capacity that contributed to progress in the field, and outline unresolved issues and remaining open questions.
Biomechanics; Motor control; Locomotion; Cortex; Spinal cord; BANCOM
Background
At the 20th anniversary meeting for Biomechanics and
Neural Control of Movement (BANCOM), the opening
thematic session was chaired by Dr. Fay Horak (Oregon
Health & Science University). Presentations and discussions
covered insights from 20 years of research in the field of
motor control, delivered by Drs. Zev Rymer (Rehabilitation
Institute of Chicago), Andy Biewener (Harvard University),
Andy Schwartz (University of Pittsburgh), and Daofen
Chen (National Institute of Neurological Disorders and
Stroke). Presentation themes included the impact of
technological advancements on motor control research,
unresolved issues in muscle biology and
neurophysiology, and changes in the scientific funding landscape.
This brief review summarizes content presented by
each speaker, along with discussions from the audience.
Considerable changes have occurred in the fields of
biomechanics and motor control over the past 20 years,
changes made possible by rapid technological advances
in computing power and memory along with reduced
physical size of biotechnology hardware. Because of
these changes, research approaches have been reshaped
and new questions have emerged. Previously, motor
control research was constrained to laboratory-based
assessments of individual neurons, muscles or joints,
captured from low sample sizes. In the past, reliance on
large, expensive, external recording devices, such as
optical motion capture systems, understandably limited
the feasibility of large-scale, multivariate research. Today,
whole-body kinematic recordings using body-worn inertial
measurement units, wireless electromyography (EMG),
electroencephalography (EEG), and functional near
infrared spectroscopy (fNIRS) systems, and electrode arrays for
neural network recordings are increasingly commonplace.
Alongside these technical leaps, sociocultural bounds have
expanded research inclusion, as evidenced in the
representation of speakers at the 2016 BANCOM meeting. In
contrast to the 1996 meeting, which included three invited
female speakers, 13 women were included as speakers in
2016. Such advancements will continue to shape our
scientific landscape, driving innovation through new
technologies and perspectives.
Neuromuscular control: unfinished business
Although considerable progress has been made in the
field of biomechanics and motor control over the past
20 years, there remains unfinished business on many
fronts. Many tasks were halted because of technical
obstacles that led to redirected research questions,
though in some instances, loose ends have remained due
to perceptions that remaining problems have already
been solved. For example, a notable open question
remains: “What do muscle spindle receptors sense?” We
know that muscle spindles regulate muscle contraction
by responding to changes in muscle length via changes
in joint angle. However, the elaborate nature and more
complex sensory function of these organs cannot be
overstated. Matthews and Stein [
1
] revealed
velocitysensitivity of spindle afferents in detecting muscle length
changes, but also identified non-linearities across stretch
amplitudes. In response, Houk, Rymer, and Crago [
2
]
tested the dynamic responsiveness of muscle spindle
receptors during large stretches, revealing surprisingly
weak velocity sensitivity. Instead, discharge rates were
dependent on low fractional power of muscle lengthening
velocity [
2
]. Houk and colleagues [
2
] also described
friction-like features in the nonlinear dynamic response of
loaded muscle spindles. The authors speculated that
muscle control while moving inertial loads might be
simplified by novel frictional damping, without the need for
adjusting feedback gain [
2
]. Further research examining
the nature of muscle length-velocity coding by muscle
spindles is sti (...truncated)