Equipment
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The lean and release mechanism is a custom-built
device used to provide destabilizing balance disturbances by leaning
participants forward via a waist-supporting cable and breaking the
cable’s connection to evoke a step response. This device features a trigger mechanism that initially grips the
end of the cable when closed, and is opened by activating a 12 V DC
solenoid. A load cell is
incorporated in order to monitor cable tension, and lean angle may be
adjusted with a rope cleat attached near the participant’s waist (coarse
adjustment) or by turning a ball screw on which the trigger assembly is
mounted (fine adjustment). |
The waist-pull mechanism is a custom-built device
used to provide destabilizing or non-destabilizing pulls at the waist in
the posterior or lateral directions. This is accomplished by dropping weights with a computer-controlled
mechanism while engaging a cleat that grips the cable used to transfer the
postural disturbance to the subject. Disturbance magnitude may be varied by adjusting the amount of
weight or the dropping height used, and cable force may be measured with
an incorporated custom-built 2-channel load cell. |
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Three AMTI OR6-series force plates are used for
balance experiments.These
plates feature 500 lb shear force capacity and 1000 lb vertical force
capacity; and 10,000 in-lb and 5000 in-lb moment capacities about the
horizontal (x and y) and vertical (z) axes, respectively. The plates also feature horizontal force and moment sensitivities
of 3 μV/(V-lb) and 0.18 μV/(V-lb), respectively; and vertical
force and moment sensitivities of 0.75 μV/(V-lb) and 0.382 μV/(V-lb),
respectively. The natural
frequencies of the OR6-6 model (primarily used for pre-perturbation stance
measurements) are 430 Hz and 900 Hz for the horizontal and vertical
forces, respectively; and the natural frequencies for the OR6-7 model
(primarily used for post-perturbation step landing measurements) are 300
Hz and 480 Hz for the horizontal and vertical forces, respectively. |
The Optotrak model
3020 position sensor features 0.1 mm RMS accuracy for x and y coordinates and 0.15 mm
RMS accuracy for z coordinates. The
system can resolve differences in 3D position as small as 0.01 mm (at 2.25
m distance) and has a sensor resolution of 1:200,000. The camera system is used to locate infrared-emitting diode (IRED)
markers that are strobed at a rate of up to 3500 Hz, and frames may be
sampled as fast as 750 Hz. This
system may also be used with a 6-marker digitizing probe to locate
individual points of interest. |
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This bench is used to provide upper extremity
exercises used in muscular fatigue experiments. The bench features a rotating lever arm with weights placed on one
end in order to provide a quasi-isokinetic fatigue exercise. The bench’s adjustable arm may be configured for exercises
ranging from full range of motion biceps contraction (elbow flexion) to
full range of motion triceps contraction (elbow extension). The bench also features a padded restraint to restrict upper arm
movement during exercise. |
A treadmill (True model 500, O’Fallon, MO, USA) is used in the lab to facilitate lower-extremity fatigue. The treadmill features manual speed control ranging from 0 to 10 mph and grade control ranging from 0 to 15%. It also includes four pre-programmed workouts designed to target various fitness areas including hill interval, weight loss, cardiovascular, and speed interval; and three available user-defined programs. It is also equipped with a heart rate monitor that may be used to control the treadmill’s speed and grade in order to maintain a desired heart rate. |
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The EMG system is a Bagnoli 8-channel system
manufactured by Delsys, Inc. Each
output channel has selectable gains of 100, 1000, and 10,000 V/V with a
frequency bandwidth of 20 – 450 Hz. Output voltage is ± 5V, which is accessible through BNC or
composite connectors. This system is used with Delsys DE-3.1 double-differential
surface electrodes, which feature 10 +2% V/V gain and supply voltage
ranging from ± 4.5 V to ± 15 V at ± 2.5 mA. |
This bench is used to facilitate biceps maximum
voluntary contraction (MVC) by means of an isometric pulling task. Typically used for performing biceps curls, this bench has been
modified to include a load cell (Futek, Inc.) that measures biceps muscle
force during the MVC. |
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The motor control apparatus consists of a
large square panel that is equipped with four light-emitting diodes (LEDs),
each of which corresponds to one of four circular targets, a smaller panel
equipped with a "home plate" positioned below and behind the larger
panel, and a stylus that is held by the participant and used to make
electrical contact with the targets and the home plate. Each of the targets, home plate, lights, and stylus are connected
to a separate I/O pin on a Basic Stamp microcontroller (Parallax, Inc.,
Rocklin, CA, USA). The
microcontroller may be programmed with light sequences that illuminate
LEDs at random. When an LED is illuminated, the participant is instructed to
move the stylus from the home plate to that LED’s corresponding target,
and then back to the home plate. The
microcontroller is programmed such that it will not initiate the next
cycle until the participant makes contact with the home plate after having
made contact with theintended target plate. Each of the I/O pins may be connected to separate channels of a
data acquisition system in order to collect target and LED voltage data
that is subsequently used to calculate participants’ reaction times,
target dwell times, and travel times. |
Computer Hardware and Software
The laboratory in Learned Hall is equipped with two 350 MHz PCs and a
500 MHz Pentium III PC for kinematic, kinetic, and electromyographic data
acquisition. The PC dedicated
for electromyographic data acquisition is equipped with a 16 bit, 32
channel A/D DAQ card, and the PC used for kinetic data acquisition is
equipped with a 16 bit, 64 channel A/D DAQ card. An additional 500 MHz Pentium III PC and a 1.8 GHz Pentium IV PC
are dedicated for data analysis and report generation. All computers are equipped with LabVIEW and MATLAB for data
acquisition and analysis, respectively, as well as Microsoft Office and CD
R/W drives and Iomega ZIP drives for storage purposes. |
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