Experimental techniques Flashcards
What is optical motion capture, what is the protocol and what are its uses?
Summary: Measurement of body movement in 3D space using a combination cameras and strategically placed reflective markers. Markerless motion capture is possible but less accurate.
Protocol:
1) Small plastic spheres with a reflective coating are attached to anatomical landmarks on the body.
2) It is usually verified that all markers can be seen by more than one camera at all times during the experiment. (needed for 3D model)
3) The subjects perform their required movements whilst the cameras record the positions of the markers.
Uses:
Kinematic measurement with a number of advantages (high spacial resolution, temporal resolution high enough for most large animals (>10Kg), non-invasive, quick and easy to use, the disadvantage being that it has to be performed in a small volume of space.
What is a force plate, what is the protocol and what are its uses?
A force plate measures GRF as an animal steps on it during some activity. It is usually level with the ground and camouflaged so the animal does not anticipate standing on it.
Protocol:
The animals runs over the plate or stands on it and performs an activity.
Use:
Terrestrial animals generate locomotion and support using external forces between their feet ad the ground.therefore GRF can be a useful measure for kinematics of movement and balance.
What is rate of oxygen consumption measurement, what is the protocol and what are its uses?
Rate of oxygen consumption can be measured and used to calculate the metabolic rate. This can either involve gathering all the expelled air and analysing it (Dougless bag technique) or using a real time gas analyser to get breath by breath measurement.
Protocol:
-Until recently all tests had to be performed with animals that could be trained to use a treadmill due to size of equipment
-Some form of mask must be fitted to the animal but not hinder movement
-As 02 consumption rate is a heavily damped function of metabolic power the animal must perform the activity for a while before measurements can be taken.
-As 02 consumption is only proportional to metabolic energy during aerobic glycolysis it is required that the animal works at less than 90%VO2max.
EMG
EMG is used to measure muscle activation by measuring electrical pulses sent along motor nerves to activate muscles. Surface EMG is attached to the skin and measures surface muscles (prone to noise). Fine wire emg is inserted into a single deep muscle.
Protocol:
1. the skin is prepared and electrodes applied. (for surface hair is removed and skin is cleaned)
2.It is necessary to ensure electrodes and equipment don’t impede movement.
3. equipment is tested by voluntary muscle contraction
4. some calibration action must be performed such as pushing on a force transducer.
5.Experimental data collection begins with subject performing some action
6. EMG data is post processed by rectifying and smoothing before interpolation.
Sonomicrometry
An invasive technique used to measure change in length of muscle. Two piezoelectric transducers are used to measure distance by emitting and receiving an ultrasound signal with a known speed of transport.
Protocol:
1. Transducers are surgically implanted into an anaesthetised animal and sutured to the muscle.
2. The animal is exercised to test that transducers work.
3. An experiment is performed where the animal performs a prescribed movement and length changes in muscle are measured.
Tendon force buckle transducers
A tendon force buckle transducer comprises of a small metal E shape around which the tendon is threaded. A strain gauge measures the strain on the middle strut of the E. The force in the tendon is proportional to the strain in the strain gauge.
Protocol:
1. Tendon force transducers are surgically implanted into the animal.
2. The animal is exercised to test the transducer.
3. The experiment is performed.
Ultrasound imaging
Medical ultrasound imaging can be used to measure distance, produce video images and reconstruct 3D structures by knowing how the density of materials in the body change.
Protocol:
This is limited as the equipment required is large and a sizeable probe has to be held to the muscle during activity.
Allometric model
1) (ideally start with a hypothesised component)
2) Collect bivariate data from a group of animals.
3) Fit the model
4) Determine the scaling exponent.
5) draw conclusions
Inverse dynamic model
The body of the animal is split into multiple rigid segments that pivot about the joints. The kinematics of each segment is recorded, often with optical motion capture. The inertial properties are calculated from morphometric data of cadavers of the same species and scaled to fit size of subject.
Inverted pendulum model of walking
A lumped mass representing the body is located at the COM of a person and connected via an incompressible strut to the position of the GRF. The model is based on the observation that the COM remains approximately constant position relative to the trunk and that the leg is approximately incompressible during walking. It is used to illustrate the exchanges of KE and PE during walking.
Spring mass model of running.
The body is modelled as a lumped mass at the COM of the body and the leg as a masses lossless linear spring. It predicts the trajectory of the body COM during the stance phase of running.
Hill model of muscle.
It consists of a perfect force generator in parallel with a perfect viscous damper hence it related tension to velocity and models the thermodynamics of the msucle. Spring elements can be added in series and parallel to model the elastic properties of the passive components of the muscle. It does not represent the internal workings of the muscle but is sufficient to model the overall workings. It can be used to create forward dynamic models.
