Biofeedback system for monitoring the motion of body joint

A biofeedback system for self-monitoring of selected body motions includes configurable mounting appliances, compatible twist, stretch and flexure sensors, coded means for positioning and orienting sensors at any location of the body, and a small, self contained signal processing and feedback module. Multi-level instant audible feedback is employed to provide a quick learning environment. The motion sensors include low force, high compliance, long extension sensors.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
This invention relates to instrumentation for monitoring of motion and 
flexure of body joints and real time biofeedback to the user. In 
particular, it relates to a system of body mounted appliances, sensors and 
specialized signal processors with audible and other biofeedback 
capabilities. 
2. Discussion of Prior Art 
The art of user fitment with medical devices for injury avoidance and 
rehabilitation therapy is not new. However, as with medical care and 
treatment in general, it used to be conducted with a somewhat cavalier 
attitude about cost. The `if it doesn't cost a lot in can't be any good` 
attitude, was driven home to the applicant some years ago when a new state 
of the art oscillometer product costing a conservative $300 was offered to 
a surgeon who quipped, "I paid that for the light I wear in the operating 
room," and declined to consider it further. 
Now, however, we have entered an era of great emphasis on reduction of 
medical care and treatment costs. There is a new willingness by the 
medical care delivery establishment to consider and even search for lower 
cost products that offer bonifide medical benefits. The need for lower 
cost medical products extends to injury prevention and rehabilitation 
devices. 
There are at least two patented body suit implementations for general 
measurement of body activities for injury avoidance and/or rehabilitation. 
The first body suit, disclosed in U.S. Pat. No. 4,729,377, requires points 
of electrode contact with the skin and requires soaking the garment with 
conductive fluid to select the measurement points of interest. The second 
suit, disclosed in U.S. Pat. No. 5,375,610, encompasses the entire body 
and measures by a plurality of mercury switches. Both are costly examples 
of accomplishing generalized monitoring at the expense of ease of use and 
do not lend them selves to casual use as in sports training or for 
prolonged use in the field of action. These types of devices are more 
appropriate for specific data collection sessions rather than for everyday 
wearing to monitor body motion for injury prevention or rehabilitation in 
the industrial setting. 
Professional and recreational training activities for kinetic sports share 
the requirement for low cost, effective monitoring of body motion. Common 
problems facing both industries are the need for a system or inventory of 
low cost associated devices to meet the needs of athetes and patients of 
different sizes; the need for a flexible scheme for universal fitments 
adaptable to each part of the body; the need for a self-monitoring system 
and methodology that is easy for the athlete or patient to remove and 
reinstall daily, and to use and interpret so as to realize the full 
benefit. 
More specifically, industry data clearly indicates a large amount of pain, 
suffering, lost time and lost productivity results from back injuries that 
occur on and off the job from lack of training or improper training in 
lifting and related activities. Lifting is a general problem, and twisting 
while lifting or repetitive twisting such as when moving parts along a 
production line are statistically very significant contributors to 
employee injuries. 
One example of a recently introduced body motion monitoring device is the 
Spine Tuner.TM. by Clear Sky Products, a posture monitor consisting of a 
belt that goes around the back approximately half way between the waist 
and shoulder that holds a small system module against the spine. The 
system module consists of a pressure activated switch that is actuated by 
pressure, forcing the housing to compress front to back, actuating the 
switch. When the switch is closed, a battery is connected directly to a 
small motor with unbalanced weight, to cause vibrations that are noticable 
to the user. The system sensitivity is set by adjusting the contact 
spacing on a stamped metal switch by turning an adjustment screw. This 
operation cannot be performed while the device is being worned, which 
requires the user to use an awkward trial and error approach to obtain a 
useful setting. 
One example of the need for body motion monitoring in the sports training 
category is in golf. The new `buzzword` in the golf industry for the last 
five years is the "X" factor, a rotation of the shoulders relative to the 
hips. The need to monitor spinal twisting in this instance is similar to 
the industrial requirements cited above. 
It is common for workers in some companies and industries to be required to 
wear back support belts. Home DePot and the Merriot Chain are among 
companies with this requirement. Interviews with workers that are required 
to wear these belts produce answers ranging from, "Now that I have support 
I can lift heavier things", which defeats the purpose, or comments like "I 
have to wear it but I don't think it does anything." There seems to be an 
acceptance and confidence problem with these commonly required devices 
that defeats or reduces their intended benefit. 
Much of the technology for medical and sports requirements rely on braces. 
A sport brace called The Secret.TM., endorsed by golf pro Greg Norman, 
sells at a premium price, but constrains the user to a particular position 
of the wrist, an approach that is not likely to promote good muscle 
memory. 
Braces in general have a number of problems, they are uncomfortable, 
frequently they do not quite fit the subject or the need, in training they 
do not promote good muscle memory, they can cause injury by constraining 
too well during a required activity, particularly in athletics, and they 
can promote "false" confidence causing users to try to overperform. 
What is needed, for both medical and athletic fields, is a low cost system 
and methodology of devices, sensors and biofeedback mechanisms that is 
flexible and adaptable to various body motions, comfortable to wear, and 
easy to understand and use. 
SUMMARY OF THE INVENTION 
A biofeedback system is herein disclosed that allows for a universal 
monitoring methodology to be applied to the physical therapy needs for the 
human body, by combining configurable mounting appliances, compatible 
motion sensors, coded means for positioning and orienting sensors at any 
location of the body, with a small self contained signal processing and 
feedback module. Multi-level instant audible feedback is employed to 
provide a quick learning environment. Motions of the back, torso, limb 
joints and digits can be monitored. Specific subset systems employing the 
concepts and methodology focus the back and a second subset focuses limb 
joints (wrist, elbow, knee and ankle). Special versions concentrate on 
proper lifting and on avoiding twisting of the back while performing 
common repetitive industrial movements that have a proven history of 
harming the performer. 
To strengthen the system concepts, two low force, high compliance, long 
extension sensors have been disclosed. These enhance the functionality, 
simplicity and cost of the resulting system implementation. 
An object of this invention is to provide a universal physical therapists 
biofeedback kit capable of providing the doctor or therapist with an in 
office fitting-breadboard that can be custom set and adjusted, for a 
number of different patients and for a number of different patient 
problems, then used as a final product that the patient wears out of the 
office. 
An object of this invention is to provide mounting appliance systems allow 
motion sensors to be placed anywhere on the body with a chosen orientation 
and that is comfortable to wear and non-confining. Many of the athletic 
training devices on the market are uncomfortable constraining braces that 
force the user to a particular per-determined move that may not be correct 
for every user. 
An object of this invention is to provide a monitoring system that allows a 
user to isolate on a single motion of the body (e.g. flexing the wrist in 
a particular plane), providing sensing and instant feedback to cue for 
proper motion performance and warn against improper motions. To promote 
proper training methodology including "one thing at a time" and natural 
learning. 
An object of this invention is to include in the training system, a means 
for adjusting the system sensitivity to accommodate different levels of 
skill, performance, application or severity, in a manner that is simple to 
set up and adjustment. Many existing training systems for athletic 
activities compare and force the user to a pre-determined average motion. 
An object of this invention is to provide a limb/body sensing and 
monitoring system that enables very low cost implementation. Medical 
systems that help a patient with recovery and rehabilitation, 
historically, have been expensive and frequently require fitting and 
ordering of a custom device. The disclosed invention provides a means for 
in office setup of the system so that the patient can leave with a 
properly fitted custom aid, and where the fitting breadboard and the final 
device are one in the same for cost and stock reduction. 
An object of this invention is to provide training systems easy to wash, 
clean, or sterilize. 
Further objects and advantages of this invention will become apparent from 
a consideration of the drawings and ensuing description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention is basically a biofeedback system for monitoring the motion 
of selected body joints. The appliances and sensors of the system are 
uniquely adaptable to fit individual users, for converting a selected 
motion or combination of motions of particular body joints into a 
particularized set of audible tones for coaching, warning and range of 
motion self-monitoring. The invention is susceptible of many variations. 
Accordingly, the preferred embodiments described hereafter should not be 
construed as limitations to the scope of the invention. 
The preferred embodiments described herein utilize a common, self-contained 
electronic system signal processing and feedback module or subsystem 
(approximately 2".times.2".times.0.75") that has a single system 
sensitivity adjustment control. The module is mounted or attached to any 
of the several universal mounting appliances, and is electrically 
connected to one or more system sensors. The module generates a limited 
sequence of stepped audible tones in response to sensor input, from which 
the incremental range of motion is easily interpreted. In the general 
case, an appliance set is selected appropriate the body joint of interest. 
The placement and orientation of a sensor on or within the appliance is 
guided by a coded scheme of markings or pockets, selectable depending on 
the motion of interest and easily identified in instructions for 
repeatability. The feedback module is connected to the sensor and mounted 
to the appliance. 
Sensors are disclosed, that are mechanically soft (high compliance) 
elements that can measure motions over extended ranges and perform 
satisfactorily where developed forces may be very low. A variety of 
mounting appliances are disclosed, that together provide a one-to-one 
fitment capability for one or more of the various joints of the body, 
(i.e. there is a preferred appliance for the back, wrist, knee, etc.). 
Each appliance is universal in that it provides coded location or anchor 
points and orientations for mounting the sensor for the intended 
application. The coded location or anchor points facilitate a close 
description of the fitment and promote easy repeatability from written or 
verbal instructions. 
The doctor, therapist, or user fits the system to a particular need by 
selecting planes of motion at the joint of interest via a sensor mounting 
point and orientation, and chosing the range of motion using the 
sensitivity adjustment. As the user moves through the range of motion, a 
limited sequence of stepped audible tones provide instant feedback with 
easily interpreted resolution. Alternate and addition forms of feedback 
may include lights, displays, vibration, and so forth. Position and motion 
data can also be transmitted between sensors or to a ground station data 
logger. 
Preferred System Embodiment for monitoring the motion of the Back 
Referring now to FIG. 6, there is disclosed a preferred biofeedback system 
embodiment of the invention suitable for monitoring the back and torso for 
twisting, windup, rolling, and hunching motions. Suspender system 60 
includes suspenders 61, which are attached between collar 53 and belt 42, 
at selected anchor points 62 and 63. Suspenders 61 are configured with 
respective sensor elements 32, connected mechanically in series to carry 
the load of the suspenders in tension. Sensor elements 32 are electrically 
connected to the biofeedback module 143 of FIGS. 14 and 15, (not shown in 
FIG. 6), which in use can be mounted to belt 42. Sensor elements 32 may be 
specified to be compliant oval sensor 20 of FIG. 2, or a conventional 
sensor such as a potentiometer, encoder or switch. Alternate 
configurations for this application are shown in FIGS. 3, 4, 5 and 7. 
Preferred System Embodiment for monitoring the motion of Limb Joints 
Referring now to FIG. 10, there is disclosed a preferred biofeedback system 
embodiment of the invention for monitoring the motion of limb joints, 
including the elbow, wrist, ankle and knee. Wrist joint system 100 
includes wrist appliance 92 with coded mounting pockets 101, flexure 
sensor 93 mounted on shaped backbone 141, with signal leads 94 connecting 
to a signal processing and feedback module such as module 143 of FIG. 14 
(not shown in FIG. 10). In practice, the biofeedback module would be 
attached to wrist appliance 92 in the manner illustrated in FIG. 14. FIG. 
9 illustrates another system configuration variation for wrist motion 
monitoring. 
Mounting Appliances 
Referring generally to FIGS. 3, 4, 5, 6, and 7, suspender style mounting 
appliances are disclosed for use with suitable sensors for measuring 
various motions of the back and spinal column. Referring to FIG. 3, 
suspender system 30 consists of waist belt 42, collar 53, and connecting 
vertical suspender 31 configured so as to be aligned with the user's 
spinal column. Suspender 31 is constructed of an elastic material so as to 
stretch in compliance with the user's motion without noticable effort. Low 
force, large elongation sensor 32 is attachable to suspender 31 so as to 
be placed in tension in proportion to the linear extension of the 
suspender length. 
Referring to FIG. 4, suspender system 40 includes belt 42 to which is 
attached a pair of over the shoulder suspenders 41. Suspenders 41 are 
constructed of an elastic material so as to stretch in compliance with the 
user's motion without noticable. Low force, large elongation sensors 32 
are attachable to suspenders 41, the outputs connectable as a sum or 
different to a biofeedback module of the invention, to detect tilting or 
lifting of one or both shoulders. 
Referring to FIG. 5, suspender system 50 includes belt 42, which is 
configured with multiple attach points 52 arranged at uniform intervals 
along its length. Collar 53 is similarly equipped with attach points 52. 
Suspender 51 is adjustable, stretchable, and connectable at any 
combination of belt and collar attach points to be aligned and compliant 
with the motion of interest. A low force, large elongation sensor 32 is 
applied to suspender 51 and connected to a biofeedback module of the 
invention in the manner described above. Suspender 51 is illustrated here 
in the over-the-spine, vertical position. 
Referring to FIG. 6, suspender system 60 includes compliant suspenders 61, 
configured with respective low force, large elongation sensors 32, 
arranged in an inverted V form and attached at selected anchor points 62 
and 63 between collar 53 and belt 42. Anchor points 62 and 63 are three of 
a multitude of selectable anchor points arranged at uniform intervals 
along the length of the belt and collar, each point coded so as to be 
easily designated in instructions or reports. As in previous embodiments, 
the sensors are electrically connected to a biofeedback module. 
It will be apparent from the embodiments of FIGS. 5 and 6 that by choosing 
the appropriate anchor points and suspender elements, different motions of 
the back such as rolling, hunching, and twisting, can be selectively 
favored. 
Referring to FIG. 7, suspender system 70 illustrates a variation on the 
systems of FIGS. 5 and 6, suspender 73 with sensor 32 being configured and 
attached to anchor points 71 and 72 on collar 53 and belt 42 so as to wrap 
around the torso of the user. 
Referring to FIG. 11, back roll belt system 110 includes a belt 111 sized 
and intended to be mounted chest high on the user, to which sensor 112 can 
be mounted over the spine in compliant mass 114, so the sensor 112 is 
placed between belt 111 and the body. The sensor and operation of back 
roll belt system 110 is further described below. 
Referring to FIG. 13, there is disclosed a back motion monitoring system 
130, which includes belt 42 and collar 53 of previous embodiments, worn 
with anchor points aligned over the spine. The sensors and operation of 
back motion monitoring system 130 are further described below. 
Referring to FIGS. 9, 10 and 14, there are disclosed wrist appliances that 
incorporate mounting options and coding for selection and placement of 
sensors. Wrist appliance 90 of FIG. 9 has coding marks 93 with which 
sensor 93 on trident backbone 91 can be selectively aligned. Wrist 
appliance 100 of FIG. 10 has coded pockets 101 into which sensor 93 and 
backbone 95 may be selectively fitted. In use, signal leads 94 are 
connected to a biofeedback module of the invention, which may be attached 
directly to the appliance. 
Similar to FIGS. 9 and 10, wrist appliance 140 of FIG. 14 is configured 
with pocket 141 and coding marks 142. Biofeedback module 143 is attached 
by a clip to the wrist appliance and connected by leads 94 to a sensor in 
pocket 141. 
Knee and ankle appliances of the invention closely correspond in construct 
and use to the appliances of FIGS. 9, 10 and 14, with mounting and coding 
features consistent with the details described above. 
Sensing Elements 
There are four distinct sensor systems that have been invented to 
accommodate the system compliance, coded mounting and low force high 
elongation needs of the system embodiments. 
Referring to FIG. 1, sensor system 10 is a compliant half oval link sensor 
consisting of half oval link 11, attached to flexible band 14 by fasteners 
13, with a single sensor element 12 affixed to half oval link 11. Link 11 
has spring-like response to tension applied at its end points, gradually 
straightening under increasing tension and recoiling to its original shape 
when the tension is released. Link 11 may be a plastic or metal member 
formed in the shape of a half oval, with attachment tabs 15 extending from 
each end. 
Referring to FIG. 2A, sensor system 20 is a compliant oval sensor 
consisting of a flexible band 21 with a second flexible band 26 attached 
to it by fasteners 22 around compliant oval member 24. Oval member 24 is 
formed from a sponge-like compressible material that deforms readily under 
increasing band tension or lateral compression to an elongated form, but 
expands to its origin shape when the tension or lateral compression is 
released. Strain sensors 25 are affixed to bands 21 and 26 on each side of 
the oval; each having individual signal leads 27, which can be connected 
in aiding or opposing polarity to serve processing objectives in related 
multi-sensor configurations, or wired individually into a signal 
processing and feedback module of the invention. 
Referring now to FIG. 2B, compliant oval sensor 24A has two leads 27A 
embedded and extending from opposing ends and two leads 27B embedded and 
extending from opposing sides. It is constructed from a conductive 
elastomer that changes resistance with change in pressure (or tension), 
and is employed directly as the sensor element of a compliant oval sensor 
system similar in utility to sensor system 20 of FIG. 2. Suitable 
electronics and audio output capability and a battery may be embedded in 
oval sensor 24A or otherwised incorporated into a localized sensor system 
configuration, resulting in a fully self-contained sensor/biofeedback 
device that in combination with the appropriate appliance, functions in 
the manner of the invention. 
Referring to FIGS. 8, 9, 10 and 14, as has been disclosed in earlier 
applications by this applicant, the flexure sensors illustrated consist of 
a strain gage instrument beam, piezoelectric sensor or other means for 
measuring flexure over a relatively large area. In the current 
embodiments, Kynar piezoelectric film is used and the sensing area is 
approximately 0.4 by 1 inch. The area measured can be extended by 
increasing the beam dimension, the sensing dimension or both. It is also 
possible to instrument the beam with other variable resistance elements, 
magnetic systems and the like, all within the scope of the invention. 
The bending beam or backbone of the various sensor assemblies of the 
invention can take the form of a simple rectangle, coded and sized to fit 
into the pockets of the various appliances of the invention. 
Alternatively, a trident form of sensor backbone, as illustrated in FIG. 
9, provides a convenient form factor for fitment to some belt-like 
appliances. 
Referring to FIG. 8, to enable the hinge-like action of hinge sensor system 
80, sensor element 82 is mounted on backbone 81, and has leads 27 
connectable to a biofeedback module of the invention. Backbone 81 is 
preconfigured for compliant bending at its central zone 83, with stiffer 
end zones 84 that are secured to the respective members of the joint of 
interest. 
The flexible mounting appliances and methodology of the invention are also 
adaptable to accomodate conventional sensor elements such as strain gages, 
switches, potentiometers, and encoders. However, the sensors disclosed 
herein significantly enhance the functionality and help meet the invention 
objectives of low cost implementation, comfortable to wear and easily 
sanitizible. Rotary potentiometers and encoders are desirable sensors for 
integration within certain system configurations to measure rotation or 
twisting of the back or wrist, as for variants of the several embodiments 
disclosed in the figures. 
Addition embodiments for monitoring back motion 
Referring again to FIG. 11, back roll belt system 110 is a more specific 
implementation of the invention for measuring rolling of the back such as 
in lifting a weight from the floor. Sensor 112 and compliant mass 114 may 
be the compliant oval sensor system 20 of FIG. 2, or the compliant oval 
sensor 24A of FIG. 2A, or another flexure sensor mounted in a specially 
shaped sponge-like mass and placed between belt 111 and the body. The 
compliant characteristic of the sensor installation acts to integrate out 
the "noise" component of the motion or flexure signal that results from 
irregularities in the spine or in the placement of the sensor on the 
spine, making the location and orientation of the appliance and sensor 
less critical. The output of the sensor is connected to a biofeedback 
module of the invention. 
Referring to FIG. 13, there is disclosed a back motion monitoring system 
130 configured for isolating and measuring twisting motions of the back. 
The system includes belt 42 and collar 53 of previous embodiments, worn 
with anchor points aligned over the spine. An absolute position sensing 
rotary switch 136, which may be an encoder or potentiometer, the stator of 
which is attached to belt 42. Motion transfer strut 132 extends from the 
rotor of rotary switch 136 to collar 53 at anchor point 131, and is 
encased in a guiding shroud 133. Rotary motion is transferred between the 
upper body as referenced by collar 53 and the lower body as referenced by 
belt 42 to absolute position sensing rotary switch 136, and hense to a 
biofeedback module of the invention. 
An alternate configuration of the back motion monitoring system of FIG. 13 
for monitoring linear contraction and extensions of back bending, 
incorporates a static overlay cabability that provides one or more 
absolute position references which can be used to reset an integrator or 
zero out drift in a dynamic measurement systems such as the compliant oval 
sensor system of FIG. 2A. Referring again to FIG. 13, but in the context 
of a static overlay device, the body of switch 136 is connected to belt 
42. One end of motion transfer strut 132 is connected to collar 53 at 
anchor point 131, and the other end is slideably connected to switch 136 
so that the switch is acutated when the transfer strut reaches the 
predetermined reference position. Shroud 133 restricts and protects 
transfer strut 132 from bucking under compression as in an autothrottle 
cable assembly. 
Signal Processing 
Piezofilm sensors offer the best fit to the objectives of this invention, 
however there are disadvantages to the piezofilm sensors, they do not have 
static or d.c. response. While the low frequency response can be very low, 
0.01 hz or less, practical considerations move this lower limit to the 
0.1-0.3 hz range. Two mechanisms 1) dynamic compensation and 2) a static 
overlay system, overcome this disadvantage, and can be combined with the 
measuring systems to significantly improve performance. 
1) Dynamic compensation: 
The inherent non zero low frequency cutoff in piezofilms will, the 
magnitude of the signal lags the actual by a calculatable amount. Said lag 
or time droop in incoming signals can be compensated for by analog signal 
processing or by numerical means within signal processing and feedback 
module 143 of FIG. 14. However the static overlay system 130 FIG. 13 
(disclosed below) offers a significant alternative. 
2) Static overlay system: 
It is common practice to use signal and or integrator reset circuits to 
yield quasi-static or quasi-d.c. response. When a system is not capable of 
zero frequency response, drift and signal lag occur. Integration of 
offsets and a.c. coupling and non static sensors preclude true static 
(zero frequency) response. Reset switches are commonly used to establish a 
new absolute reference at a point(s) in time or position. 
Note that the static reset system shown in FIG. 13 can be used alone to 
provide a single point of reference. Also, the switch can replaced by a 
linear potentiometer or a linear encoder (indexed incremental or 
quadrature) to function as an absolute analog system over a limited range. 
It is however, very effective as a low cost static overlay that is used 
with one of the dynamic systems disclosed in the other figures. When these 
systems are combined there is good synergy. The dynamic system provides 
necessary refinements of signals for early warnings to be sounded so that 
an improper lift is aborted or a range of motion is not exceeded. The 
static overlay cabability reinserts a static reference and can be used to 
provide an absolute limit. While a dynamic sensing system with static zero 
frequency response could be used, the combined non-zero response 
sub-system in concert with the static overlay sub-system is a much better 
choice for the system inventions disclosed herein. 
Adding Fuzzy Logic and AI (artificial intelligence) 
The system elements and system configurations discussed to this point are 
very effective in measuring most motions that would be useful to monitor. 
There are specific motions that are subject to many extraneous inputs from 
"motion noise" sources. The methodology discussed above uses multiple 
sensors, symmetry and selective attachment to sort out the particular 
motion that one desires to monitor. Sometimes however, the extraneous 
motions are at a level where still more discrimination is needed. It is 
disclosed that AI (artificial intelligence) and Fuzzy Logic algorithms can 
be used to separate the signal from the noise. These algorithms would 
employ A-priori knowledge of the application and empirical data derived 
from directed experimentation to study the signals and rule out "probable 
noise". 
Consider the application where the design intends to measure back motion 
during a lifting operation to detect improper technique. The system 
determines that the lifter is rolling his back to pick up an object rather 
than to keep his back straight while using the legs for the lift. The 
system monitors the motion, makes a decision, and sounds warning tones if 
an improper lift is about to be performed. Such a system can be used to 
train new employees to develop correct technique, or can monitor them 
continuously where risk is high, to sound a warning each time an improper 
lift is attempted. In this application there are many sources of motion 
that are not important to lifting, however these sometimes cannot be 
eliminated from the sensors measurement and therefore will appear in the 
output signal. The output signal is being monitored to make a decision to 
sound a warning tone. 
What intelligence can be employed to minimize false alarms? The sources of 
motion noise can include: breathing, raising hands over the head, 
twisting, vertical roll of the shoulders, hunching of the shoulders, or 
unusual body configurations such as a particularly large stomach. To come 
up with a reliable monitoring system in the presence of these "motion 
noise" factors, intelligence applied to the resulting sensor signal may be 
required. The intelligence can use A-priori information and make 
judgements about the probable cause. 
Referring now to FIG. 12, there is disclosed a model graph demonstrating 
some of the signal characteristics used by the biofeedback module 
electronics to improve the measurement discrimination, quality and 
applicability of the sensor inputs. 
Voltage versus time curves are illustrated for lifting signal 126 and arm 
position signal 124. In the simplest case a peak motion threshold 123 is 
applied to lifting signal 126, sounding a warning that an improper lift is 
about to be performed. Further discrimination can be had by comparing the 
length of time that lifting signal 126 is above threshold 123 by examining 
the time between points 121 and 122 of the signal, making a decision only 
if the signal is above the threshold 123 for the correct range of time. 
This can avoid occurrence of a significant number of false alarms. 
More protection against false alarm warnings can be attained by considering 
the characteristics of both the lifting signal 126 and the arm position 
signal 124. For this method of discrimination the electronics makes sure 
that both lifting signal 126 is above its threshold 123, and that the arms 
are in the lift position as determined by arm position signal 124, where a 
warning tone would be aborted if the arm position signal 124 was positive. 
Various conditions can be applied to one or more signal waveforms to 
improve the biofeedback system performance significantly. 
Feedback and Data Collection 
The preferred embodiment of the invention disclosed herein uses instant 
audible feedback. The feedback is in the form of stepped tone pitches that 
correspond one-to-one with selected or programmed signal thresholds. The 
tone that corresponds to the greatest motion threshold reached is held for 
a fraction of a second (0.1 to 0.5 sec). The effect of holding the peak 
motion is that the method assures that the user can both remember and make 
sense of the feedback. 
The signal spacing between thresholds can be linear or non-linear so that 
early warning, or degrees of warning, can be achieved when an undesired 
body movement is occurring. It can be in bands so that training can be 
aimed at a central point. The feedback can take any other usable form 
either separately or in parallel with the audible feedback. 
The information collected by the system can also be transmitted to a data 
logger or ground based computerized data collection system for post 
analysis and for establishing norms and correlating motion histories with 
future injury or other physical problems. Statistical data collection can 
be performed as a histogram of threshold events. 
The preferred embodiment uses five tones, however more or fewer are 
possible, the resolution of the collected data corresponds to the number 
of thresholds and feedback tones. The Applicant's research indicates that 
a methodology using a relatively few descrete tone steps is significantly 
easier for the average person to detect, resolve and remember on a real 
time basis, than are continuously varying or many incrementally small step 
changes in frequency or amplitude. 
Referring here to FIG. 15, a block diagram of the preferred embodiment of 
the system electronics of the signal processing and feedback module of the 
invention is disclosed. An input signal from the sensor would connect to 
impedance matching block 151, the output of block 151 is connected to 
signal processing block 152, which in turn connects to threshold selection 
and programming block 153. The output of block 153 feeds to both the 
threshold detection block 154 and the peak detection block 155, both block 
154 and 155 outputs connect to the discrete tone generator block 156 which 
drives the audible output or speaker block 157. A sensitivity control 
block 158 allows the user to set the system gain and sensitivity by 
rotating the knob, the output of the sensitivity block 158 is connected to 
signal processor block 152 to accomplish this. 
The circuitry necessary to accomplish the functionality of the biofeedback 
module is easily achieved by anyone skilled in the art, and need not be 
elaborated on here. 
Operation of Invention 
In operation, the system converts motions to multi-level audible feedback. 
Research has demonstrated that the multi-level instant feedback has the 
attribute of providing a memorable history of an event that might 
otherwise be too fast to be able to make a connection between the desired 
effect and the feedback. The methodology of the system integration 
provides total measurement flexibility encompassing back and torso, as 
well as for limb joints and digits. 
A large part of the gain of measurement flexibility comes from the concepts 
imbedded in the mounting appliance. Each system has a mounting appliance 
that supports all of the measurements that one would want to make for the 
wrist or the back or other points where complex motions are possible. The 
appliances are soft and comfortable to wear, they are fitted with coded 
attachment points for sensors or for other members of the mounting system 
(e.g. an elastic suspender strap can be attach to a number of location on 
a belt or collar). The coding for the placement and orientation of the 
sensor on the mounting appliance might take the form of a Velcro strip 
upon which a mating Velcro strip affixed to the sensor can be aligned, or 
the use of placement marking which may be color coded can be incorporated 
into the mounting appliance, or the mounting appliance may be fitted with 
multiple pockets for the sensor to be fit into, where the selection of the 
pocket automatically selects the point of placement of the sensor and its 
orientation. The support electronics in its preferred embodiment takes the 
form of a signal processing and feedback subsystem or module, which at 1.4 
ounces and approximately 2".times.2".times.0.75" can be attached directly 
to the clothing or to a convenient place on the sensor mounting subsystem, 
yielding a self-contained system. 
One version works as a modified pair of suspenders, by removing 
restrictions on where the bands go on the body, as in FIGS. 3-7. The user 
or therapist card isolate one specific mode of movement (e.g. twisting of 
the back or pronation of the wrist) while ignoring the other motions that 
are occurring. This isometric selection can be further enhanced through 
the use of multiple sensors and by connecting them in different ways and 
processing the, information accordingly (i.e. the sensor can be connected 
in series or parallel, or they can be connected in a polarity opposing or 
polarity additive mode). 
The signal processing and feedback module can be factory set to have 
specific dynamic frequency response that helps to enhance the activity 
that is being targeted for training by sorting out "noise" motions that 
occur but are not a part of the training. The sensitivity of the 
electronics can be adjusted through a wide range to account for 
differences in application and to account for wide differences in skill 
level or motion capability of the user. 
The advantages of all of the subsystems described herein, including the 
mounting appliances, sensors, and signal processing and feedback 
electronics, work together to meet the numerous objectives of the 
invention. 
The suspender system depends on a balance of compliant members to function 
properly, to this need, the compliant sensors described were invented. 
These elements convert low forces in the elastic suspender straps into a 
deformation of a half oval or full oval member which can be instrumented 
with large area strain gages. A system that is easy to use, comfortable to 
wear and does not impede the performance of the activity results from the 
application of the principles. 
The invention is susceptible to many varations, all within the scope of the 
appended claims. For example, there is an appliance system for mounting 
the sensors of a biofeedback system that converts a selected body torso 
motion into audible tones, where the appliance system has multiple 
components, each component having at least one coded anchor point, the 
components being configurable on a user's body for establishing a suitable 
reference line for placement of a sensor relative to the desired motion. 
As another example, the multiple components of a system may include a 
collar, a waist belt, and at least one interconnecting member attachable 
to the waist belt and the collar at the coded anchor points. The 
interconnecting member may be configured to accept the mounting of a 
sensor. 
As a further example, the sensor may be a spring member that deforms under 
tension and reforms when released, with a measurable electrical impedance 
that varies with the degree of deformation applied to the spring member, 
and electrical leads by which the impedance can be measured. 
Further, the spring member may be a half oval shaped structure the ends of 
which are attached to an elastic base member that would be subjected to a 
tension load, and the electrical impedance may be a strain gage sensor 
bonded to the half oval shaped structure. Alternatively, the spring member 
may be a deformable core member contained in a pliable loop structure 
having opposing end tabs that measure a tension load, and the electrical 
impedance may be a strain gage sensor bonded to the pliable loop 
structure. A further alternative may have the spring member be a 
deformable core member contained in a pliable loop structure having at 
least two opposing sides subjected to deforming pressure, where the 
electrical impedance is present in the deformable core member's structure 
by being fabricated with a distributed electrical impedence quality 
proportionally affected by deformation of the core member, and the 
electrical leads are connected to at least two opposing sides of the core 
member. 
As a yet further example, there is an appliance system where the 
interconnecting member is configured with an elongation sensor for 
detecting and resolving the degree of linear motion between the anchor 
points. The interconnecting member may be capable of detecting and 
resolving the degree of rotational motion between the collar and the waist 
belt. Further, the interconnecting member may include an elongation motion 
static reset switch and cable assembly. 
As an even yet further example, there may be a low force compliant sensor 
for a biofeedback system for converting a selected motion of a selected 
body joint into audible tones, where the sensor consists of a spring 
member that deforms under tension and reforms when released, with a 
measurable electrical impedance that varies with the degree of deformation 
applied to the spring member, and electrical leads by which the resistance 
can be measured. The compliant sensor may be a spring member consisting of 
a half oval shaped structure the ends of which are attached to an elastic 
base member subject to a tension load, where the electrical impedance 
consists of a strain gage sensor bonded to the half oval shaped structure. 
The spring member may consist of a deformable core member contained in a 
pliable loop structure having opposing end tabs subject to a tension load, 
where the electrical impedance consists of at least one strain gage sensor 
bonded to the pliable loop structure. 
As yet another example, the compliant sensor may be a spring member 
consisting of a deformable core member contained in a pliable loop 
structure which has at least two opposing sides being subjected to 
deforming pressure, where the electrical impedance consists of the 
deformable core member fabricated with a distributed electrical impedence 
quality proportionally affected by deformation of the core member, and the 
electrical leads connected to the two opposing sides of the core member. 
As still yet another example, the invention may consist of a biofeedback 
system for converting a selected motion of a selected body joint into 
audible tones, where the system includes a sensor for sensing body 
flexure, a signal processor and biofeedback module for receiving and 
processing input from the sensor and for transmitting one tone at a time 
from among a limited set of tones of stepped audio frequency, where each 
tone represents a different amount of body flexure. The system would 
include an adaptable appliance system for afixing the sensor in a suitable 
position to detect the selected motion. 
An additional example of the invention is a biofeedback system where the 
appliance system consists of multiple components, each component having at 
least one coded anchor point, and the components are configurable on a 
user's body for establishing a suitable reference line for placement of 
the sensor relative to the subject motion. The multiple components can 
consist of a collar, a waist belt, and at least one interconnecting member 
attachable to the waist belt and to the collar at the coded anchor points, 
the sensor being attachable to the interconnecting member. 
Another additional example is a biofeedback system where the sensor 
consists of a spring member that deforms under tension and reforms when 
released, a measurable electrical impedance that varies with the degree of 
deformation applied to the spring member, and electrical leads by which 
the resistance can be measured. The spring member consists of a half oval 
shaped structure the ends of which are attached to an elastic base member 
subject to a tension load. The electrical impedance consists of a strain 
gage sensor bonded to the half oval shaped structure. 
Yet another example is a biofeedback system where the sensor consists of a 
spring member that deforms under tension and reforms when released, a 
measurable electrical impedance that varies with the degree of deformation 
applied to the spring member, and electrical leads by which the resistance 
can be measured. The spring member consists of a deformable core member 
contained in a pliable loop structure having opposing end tabs subject to 
a tension load, and the electrical impedance consists of at least one 
strain gage sensor bonded to the pliable loop structure.