Design
and function of muscular systems for locomotion and sound production
The general goal of my research program is to answer basic
questions about the design of muscle and its function during locomotion
and sound production. In addition, my research focuses on the
effect of temperature on motor performance.
This research has required both integrative and comparative
approaches. The integrative approach has required us to obtain
information at different levels of organization from molecular
biophysics to whole-animal biomechanics. This is necessary because:
1) one cannot understand how a muscle is designed without knowing
exactly what it does during normal behavior and 2) the adaptation
of muscle for different motor activities takes place at the molecular
level.
This integrative approach requires measurements at all levels
of organization and hence an animal model where all these measurements
can be performed. Fish have led the way in this regard. In contrast
to the mixing of different fiber types such as occurs in the muscles
of mammals and most other vertebrates, the different muscle fiber
types in fish are organized into large, homogenous, and anatomically
separated regions, that are visible to the naked eye. In fish,
as opposed to mammals, we can monitor which motor activities are
powered by each fiber type because we can implant electromyography
electrodes in these anatomically separate regions. In addition,
one can dissect bundles of fibers, that are all of the same type,
so that the mechanical, biochemical and ultrastructural properties
of each muscle fiber type can be determined. We have also concentrated
on frogs, because although their different fiber types are not
separated as in fish, it turns out that the large extensor muscles
used in jumping are almost pure in fiber type.
fish swimming — frog jumping
Using swimming fish and jumping frog, we have been able to elucidate
2 rules of muscle design. First, myofilament length and fiber
orientation in the animals seem to be set so that active muscle
fibers always operate on the optimal part of the sarcomere length-tension
curve, and second, the maximum velocity of shortening of the muscles
(Vmax) and the gear ratio of the fibers are set so no matter
how fast an animal moves the active fibers will operate at a V/Vmax
(where V is the velocity at which the fibers shorten) of
about 0.2 to 0.4 where maximum power is generated with optimal
efficiency. Given these constraints, to achieve a full repertoire
of movement, animals must have different fiber types with different
Vmax's, so that a wide range of V's can be attained.
The process of activation and relaxation (i.e., turning muscle
off and on, respectively) can greatly effect the power muscle
generates during locomotion. To obtain critical information, we
determined the length changes and stimulation pattern the muscles
undergo during locomotion, and then imposed these conditions on
isolated muscle and measure the resulting force and power production.
We found that in fish, relaxation rate is set to be relatively
slow and hence the muscle is actually in the process of relaxing
during the power stroke so that it can be subsequently relengthened
without resistance. By contrast, in the one-shot jump of the frog,
the muscle remains maximally activated throughout the jump so
it can produce maximum power.
calling in fish
Up to now we have approached muscle design in a fairly phenomenological
manner, but over the last 4 or 5 years my laboratory has been
using biophysical approaches to better understand how modifications
are made at the molecular level for different functions.
We have used toadfish Opsanus tau as an experimental model
because they contain the greatest range of contractile properties
of any vertebrate. These animals rest on the bottom and wait for
a fish or crustacean to pass; then they grab the prey with their
immense jaws. Toadfish’s swimming muscles reflect this sluggish
behavior. Their slow twitch red muscle, which in most fish are
used for steady swimming, are almost non-existent; the few that
do occur are among the slowest ever measured–they work at
~1 Hz. Toadfish "fast"-twitch white muscle, used in
a short burst of activity to capture prey, are also unimpressive–
they have about the same speed as slow-twitch muscle in other
fish.
But when it comes to calling for a mate, the male toadfish is
an athlete of Olympic stature. The muscles that surround his heart-shaped
swimbladder, alternately contract down on the organ and relax
at up to 200 hertz to produce the "boat-whistle" mating
call. In fact, the swimbladder muscle is the fastest vertebrate
muscle known.
By using a series of biophysical approaches such as Ca2+
transients, caged Ca2+ and single muscle fiber ATPase,
we determined that the immense speed of the swimbladder is principally
due to its extremely fast relaxation rate, which in turn is due
to three specific adaptations: the swimbladder removes Ca2+
from the cytoplasm 50-fold faster than the red muscle (Step 4),
swimbladder troponin has a far faster Ca2+ off-rate
than red muscle (Step 5), and swimbladder crossbridges have a
50-fold faster detachment rate constant than red muscle (Step
6):
The diversity of muscles in toadfish strikingly illustrate how
muscle can be so exquisitely tuned for one behavior, that it can’t
be used for another. Neither the red nor white swimming muscles
can physically produce high frequency sounds because they can't
relax fast enough. By contrast, at the low frequencies of steady
swimming, the swimbladder muscle’s extremely low mechanical
power output make it unable to power locomotion.
As we examine the biophysics of the muscle in more detail, we
are also studying the fish’s behavior. During our summer
research in Woods Hole, we go into the field with a boat, and
record the calls of toadfish with a hydrophone. Our goal is to
understand how the fish produce the calls—all the way from
muscle biophysics to the whole animal.
scaling of muscle mechanics and energetics with body size
in mammals
The high cost of locomotion in small mammals has been attributed
to fibers from small animals using more ATP to generate force
than fibers from large animals. To test this hypothesis, we have
developed a quantitative realtime fluorescently coupled assay
to measure ATP utilization by single skinned fibers during contraction
and we have used this to determine the energetic cost of muscle
contraction from animals of different body sizes.
musculo-skeletal model of jumping frogs
The ultimate goal of our approach is to integrate muscle function
from the molecular to the whole animal level. Although we can
make molecular biophysical measurements and whole animal measurements,
there is still a significant obstacle to integrating from muscle
to locomotion. The musculo-skeletal system of any animal is extremely
complex. For instance in our previous studies of frog jumping,
we related the results from one muscle to movement of the whole
frog. But frog hindlimbs have in excess of 15 muscles which may
be performing different types of contractions. Musculo-skeletal
modeling, however, can be an enormous help in keeping track of
forces and torques generated by many muscles simultaneously.
Our first step in developing a virtual frog model was to disarticulate
the bones and scan them with a 3-D laser scanner into a computer.
The next step was to determine the origins, insertions, and tracks
of the muscles which are represented by red lines. In addition,
we measured the anatomical properties of the muscle: their mass,
angle of pinnation, fiber length, sarcomere length etc. We also
divided the frog into a number of segments and determined the
masses and moments of inertia. Further the joints were defined,
and the contractile properties of the muscles were input into
the model:
The last step was to run a forward dynamic simulation. This involves
turning on the muscles with the same time course found in vivo.
The muscles generate force and accelerates the frog into a jumping
movement. It is important to point out that this is not an animation–rather
the movement is due to generation of virtual forces and virtual
torques accelerating the frog’s body.
The model will become most exciting, when we can couple it with
a molecular model of muscle contraction. We should then be able
to answer "what if" questions–such as how
would frog jumping performance be altered if the crossbridge kinetics
were changed in a specific manner. This would give us terrific
opportunity to test our understanding of the muscular system.
In addition, this virtual frog will be a great discovery learning
tool for physiology and bioengineering students. The students
will be able to modify any parameter (cross-bridge kinetics, muscle
mass, angle of pinnation, point of attachment) and see how this
will effect whole animal movement.
selected
publications
fish swimming
Rome, L. C. and D. M. Swank. 2001. The influence of
thermal acclimation on power production during swimming (I &
II) I: Acclimation of the scup nervous systems and Red Muscle
(cover article). Journal of Experimental Biology204:409-418,
419-430.
Rome L. C., Swank D. & Corda D. 1993. How fish power
swimming. Science261:340-343.
Rome L. C., Funke R. P., Alexander R. McN., Lutz G.,
Aldridge H., Scott F., Freadman M.A. 1988. Why animals have
different muscle fiber types? Nature355:824-827.
frog jumping
Lutz, G. & Rome, L. C. 1996. Muscle function during
jumping in frogs (I & II):The influence of temperature on
muscle length change, recruitment pattern, jumping performance
and mechanical properties of muscle AJP: Cell Physiology271:C563-C570, C571-C578.
Lutz G. J. & Rome L. C. 1994. Built for jumping:
the design of the frog muscular system. Science263:370-372.
toadfish
Rome, L. C., Klimov, A. A. 2000. Superfast Contractions
Without Superfast Energetics:ATP Usage by SR-Ca2+
Pumps and Crossbridges in the Toadfish Swimbladder Muscle (cover
article). Journal of Physiology526:279-298.
Rome, L. C., Klimov, A. A., and Young, I. S. 1999. A
new approach for measuring real-time calcium pumping and SR
function in muscle fibers. Biological Bulletin197:227-228.
Rome, L. C., Cook, C., Syme, D., Connaughton, M., Ashley-Ross,
M., Klimov, A., Tikunov, B. and Goldman, Y. E. 1999. Trading
force for speed: Crossbridge kinetics of super-fast muscle fibers.
Proceedings of the National Academy of Science96:5826-5831.
Rome, L. C., Syme D., Hollingsworth S., Lindstedt S.,
& Baylor S. 1996. The whistle and the rattle: the design
of sound producing muscles. Proceedings of the National Academy
of Sciences93:8095-8100.
scaling
Rome, L. C. 1992. Scaling of muscle fibres and locomotion.
Journal of Experimental Biology168:243-252.
Rome, L. C., Sosnicki A. A., Goble D. O. 1990. The maximum
velocity of fiber typed horse muscle fibers: some implications
of scaling Vmax with body size. Journal of Physiology31:173-185.
Rome, L. C., Lindstedt, S. L. 1997. Mechanical and Metabolic
design of the vertebrate muscular system. Handbook of Physiology.
Section 13, Comparative Physiology pp. 1587-1651, W.
H. Dantzler, ed. Oxford University Press.
Rome, L. C. 1997. Testing a muscle's design. American
Scientist85:356-363.
education
Ph.D., Biology, Harvard University, Cambridge, Massachusetts
Advisors: C. Richard. Taylor and Martin. J. Kushmerick, 1976-1981
People