The participants in this symposium were invited to
speak on Recent Research in Muscle Mechanics. Although it was expected
that each speaker would focus on the latest research conducted in his
own laboratory, the exact topics to be presented were left for them to
decide. Two chose to speak on the measurement of muscle forces -- one
with particular reference to the function of skeletal muscles in normal
movements and the other with respect to the integration of theories of
neural control and direct measurements of muscle force outputs. The
third chose to speak on the mechanics of delayed-onset muscle soreness
following exercise involving eccentric muscle actions -- a topic of
importance from both basic and applied standpoints.
W. Herzog
The in vivo measurement of muscle forces is a "hot
topic" in the area of muscle mechanics and a review of recent
literature on the subject is timely. We have recorded electromyographic
activity and made measurements of muscle forces and of muscle length and
fibre length changes in situ and in vivo. Experimental
results from this work on the deformation of muscle during contraction
and on force,muscle and fibre length changes during normal movement will
be presented. I believe this work provides important insights into the
function of skeletal muscles during normal movements.
R. J. Gregor
Motor output strategies guiding human performance through various
perturbations and loading paradigms have traditionally been evaluated
using EMG alone, and in some cases muscle length changes synchronized to
the EMG and environmental force patterns. The addition of actual muscle
force measurements (i.e. tendon force transducers, reported primarily in
animal models) has advanced our knowledge in the field of
musculoskeletal biomechanics and neural control in their collective
attempts to understand movement control. The fact that the end organ of
the nervous system (i.e. the muscle) can be evaluated directly and its
motor output quantified as opposed to estimated through EMG has resulted
in useful information related to both fields of study. Interfacing
direct muscle force measurements with theories in neural control,
investigators now present a wide-range of motor output parameters that
have advanced our understanding of the strategies employed by the
nervous system in the control of limb movements.
D. L. Morgan
When muscle is stretched while generating tension, it displays a
number ofphenomena which are quite difficult to explain. Perhaps the
most familiar of these is the stiffness and soreness in muscles that
occur after unaccustomed exercise involving such eccentric contractions.
This begins the day after the exercise, and recovers over about a week.
It is accompanied by measurable changes in muscle mechanics,
particularly a fall in tension and a shift to longer lengths in the
optimum length for tension generation. The damage is greater for longer
stretches and for more stretches. However there has been conflicting
evidence how it depends on the range of muscle lengths over which the
stretch occurs. Our recent experiments in a number of preparations have
shown that muscle length is in fact a very strong determinant of damage,
which is much greater at longer muscle lengths. This finding is in
accord with theories on the cause of the damage that involve
non-uniformity of sarcomere lengths due to instability on the descending
limb of the length-tension curve. It also highlights the need to
determine the part of the length-tension curve over which experimental
eccentric contractions are applied.
