Estimates of individual muscle power production in normal adult walking
Bogey and Barnes Journal of NeuroEngineering and Rehabilitation
Estimates of individual muscle power production in normal adult walking
Ross A. Bogey 0
Lee A. Barnes 1
0 Physical Medicine and Rehabilitation Residency Program, Casa Colina Hospital and Centers for Healthcare , 255 East Bonita Avenue, Pomona, CA 91769 , USA
1 B&L Engineering , 1901 Carnegie Avenue, Suite Q Santa Ana, Santa Ana, CA 92705 , USA
Background: The purpose of this study was to determine the contribution of individual hip muscles to the net hip power in normal adult self-selected speed walking. A further goal was to examine each muscle's role in propulsion or support of the body during that task. Methods: An EMG-to-force processing (EFP) model was developed which scaled muscle-tendon unit (MTU) force output to gait EMG. Active muscle power was defined as the product of MTU forces (derived from EFP) and that muscle's contraction velocity. Passive hip power was estimated from passive moments associates with hip position (angle of flexion (extension)) and the hip's angular velocity. Net hip EFP power was determined by summing individual active hip muscle power plus the net passive hip power at each percent gait cycle interval. Net hip power was also calculated for these study participants via inverse dynamics (kinetics plus kinematics, KIN). The inverse dynamics technique - well accepted in the biomechanics literature - was used as a “gold standard” for validation of this EFP model. Closeness of fit of the power curves of the two methods was used to validate the model. Results: The correlation between the EFP and KIN methods was sufficiently close, suggesting validation of the model's ability to provide reasonable estimates of power produced by individual hip muscles. Key findings were that (1) most muscles undergo a stretch-shorten cycle of muscle contraction, (2) greatest power was produced by the hip abductors, and (3) the hip adductors contribute to either hip adduction or hip extension (but not both). Conclusions: The EMG-to-force processing approach provides reasonable estimates of individual hip muscle forces in self-selected speed walking in neurologically-intact adults.
Background
The role of individual hip muscles in normal walking
has not been fully described. A more complete
understanding of each muscle’s role could be established by
knowledge of that muscle’s force output and power
generation. However, direct measurements of muscle force
has been obtained for only a few lower extremity
muscles (i.E. Achilles tendon [
1, 2
]), and the techniques used
to directly record muscle forces – even when possible –
are not practical in a clinical environment. Muscle
power is related to muscle force, in that it is the product
of force output and muscle-tendon unit (MTU)
contraction velocity. Joint power – that is, the power produced
by synergistic muscles – may be used to establish the
capacity of muscle groups to generate or restrain
movement [
3–12
]. Concentric power typically produces
motion, while negative power implies motion restraint. A
possible confound is that the presence of muscle power
has been used as a proxy for muscle activity, yet studies
of amputee locomotion [
13
] demonstrate non-zero power
at the prosthetic ankle. Further, isometric contractions
have zero power, due to a contraction velocity of zero.
Nonetheless, the power produced by any muscle cannot be
directly determined. Hence other methods are required.
An impediment to easy determination of muscle power
– and the potential role of individual hip muscles – is that
the hip has more muscles than are necessary to perform
basic movements. This overabundance of muscles leads to
statistical indeterminacy (more unknown muscle forces
than solution set of equations). Power calculation
approaches thus are based on inverse dynamics techniques.
This method solves the actuator-redundancy problem.
However, conventional power analysis cannot define the
unique power contribution of a single muscle, except in
uncommon cases where only a single muscle is
responsible for the observed movement. Co-contraction of
agonists and antagonists is a further confound. As a
result there may not be a direct link between a muscle’s
power output (via inverse dynamics techniques) and
that muscle’s true role in gait. These factors show that
the muscle power estimates from inverse dynamics can
include muscle force, joint angular velocities and other,
undefined variables.
Neuromuscular modeling techniques have produced
reasonable estimates of in vivo ankle muscle power [
14
].
It was the purpose of this study to examine if those
techniques could be applied to at the more proximal hip
joint to determine individual hip muscle power
production in normal, self-selected-speed walking.
Methods (overview)
Hip power values at self-selected speed walking were
determined by (i) inverse dynamics (kinematics plus kinetics,
KIN) and (ii) an EMG-to-force processing (EFP) model
during the same (...truncated)