Civil Engineering Reference
In-Depth Information
In vivo dynamometry is well suited for the study of chronic muscle injury and adaptation and studies of
this kind would be beneficial in elucidating the physiological response to repetitive biomechanical
loading. Biomechanical loading parameters, such as number of repetitions per day, the velocity and
acceleration of the movement, the range of motion of the movement, muscle force or torque during
each movement, and the rest interval between sets, should be controlled during experiments. Controlling
and quantifying the biomechanical loading profile is essential for rigorous study of muscle injury and
adaptation for both acute and chronic exposure studies. Also, it is important to have the ability to
vary the biomechanical inputs to study the effects of different inputs, and how the level of those
inputs, such as more or less repetitions, higher or lower velocities or acceleration, and so on, affects
the physiological response after a single exposure and
or multiple exposures.
In addition to controlling the biomechanical inputs, it is also important in volitional models to not
only provide an apparatus to facilitate controlled movement, but to appropriately instrument the appar-
atus to monitor movement dynamics in real time. This will allow for quantitation of the biomechanical
loading profile within each exposure session for the study of both acute and chronic muscle response.
This approach is similar to in vivo dynamometry in that the biomechanical loading signature is recorded
during each exposure, but different from in vivo dynamometry in that the movement profile is not
controlled by an external source like a servomotor, but controlled by the animal.
In vivo models, whether volitional or nonvolitional, can provide a wealth of information about the
effects of biomechanical loading inputs on acute and chronic physiological responses. Refinement of
these models to control and monitor the biomechanical loading signature has been done in nonvolitional
models and is currently being accomplished in volitional models.
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15.6.2 The Need for Tissue Mechanobiology Studies
There is a clear need for tissue mechanobiology studies to determine the failure or injury mechanics of
soft tissues and ultimately the repair kinetics after acute or chronic injury. From a muscle perspective,
dose-response models would be important to develop in both an acute and chronic framework.
In the acute framework, the effect of number of repetitions, rest between sets of exposures, range of
motion, movement kinematics such as velocity, acceleration, and jerk, and force on the amount of
soft-tissue injury should be fully investigated. The changes in soft tissue at the cellular level commensu-
rate with injury should also be investigated. Defining damage at the tissue level is important to develop a
consensus about what is soft-tissue injury. The time course of these changes after an acute exposure and
the mechanisms of repair should also be fully characterized. Factors such as level of conditioning,
age, and gender, and other relevant comorbid factors on injury susceptibility and rate of repair are
also important considerations.
In the chronic framework, the threshold for injury under sustained or repeated loading should be
determined. This should be based on the foundation developed by acute injury studies regarding the
effect of different biomechanical parameters and any intrinsic interplay. Additional parameters such as
exposure duration (number of days, weeks, or months) and the duty cycle (rest period between
exposures) should also be considered. Using this framework, the time frame for injury to develop, the
sustainment of injury, and any repair that can take place during repeated exposures should be
studied. Functional measurements as well as noninvasive biological measurements should be made to
monitor the status of the animal. Patterns of rest and reuse after injury are also important to consider.
15.6.3 Summary
There has been much work in the area of exercise-induced muscle injury over the past 30 years. The
relation between factors such as force, range of motion, number of repetitions, exposure duration,
velocity, age, gender, and training on muscle injury have been studied and have a clear occupational
relevance. Also, the cellular mechanisms responsible for the injury and repair processes have been well
studied to date. The relation between muscle function, myofiber damage, pain, and molecular indicators
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