U.S. patent application number 11/828513 was filed with the patent office on 2008-02-07 for muscle stimulation systems.
This patent application is currently assigned to THE UNIVERSITY OF SYDNEY. Invention is credited to Glen Macartney Davis, Che Fornusek, Peter James Sinclair.
Application Number | 20080033505 11/828513 |
Document ID | / |
Family ID | 25646823 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080033505 |
Kind Code |
A1 |
Davis; Glen Macartney ; et
al. |
February 7, 2008 |
MUSCLE STIMULATION SYSTEMS
Abstract
A control system for controlled exercise controls a functional
electrical stimulation (FES) system which applies electrical
signals to muscle groups of a user such as a user having a
disability; the user exercises on a motor driven exercise machine
such that substantially isokinetic exercise during a movement is
obtained as the user's body part moves with a motor driven
displaceable element of the machine. This element provides
resistance to applied displacement load from the user's stimulated
muscles. A feedback control system receives signals indicative of
the user's performance and a control arrangement controls
electrical stimulation to the user's muscles to achieve a desired
exercise regime.
Inventors: |
Davis; Glen Macartney;
(Petersham, AU) ; Sinclair; Peter James;
(Marrickville, AU) ; Fornusek; Che; (Randwick,
AU) |
Correspondence
Address: |
KELLY LOWRY & KELLEY, LLP
6320 CANOGA AVENUE
SUITE 1650
WOODLAND HILLS
CA
91367
US
|
Assignee: |
THE UNIVERSITY OF SYDNEY
Parramatta Road
Sydney
AU
NSW 2006
|
Family ID: |
25646823 |
Appl. No.: |
11/828513 |
Filed: |
July 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10492805 |
Sep 3, 2004 |
7280871 |
|
|
PCT/AU02/01430 |
Oct 21, 2002 |
|
|
|
11828513 |
Jul 26, 2007 |
|
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Current U.S.
Class: |
607/48 |
Current CPC
Class: |
A61N 1/36003 20130101;
A61H 1/02 20130101; A61H 2230/08 20130101 |
Class at
Publication: |
607/048 |
International
Class: |
A61N 1/04 20060101
A61N001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2001 |
AU |
PR 8376 |
Dec 11, 2001 |
AU |
PR 9427 |
Claims
1. A system including: (a) an exercise machine having displaceable
means for moving with a body part of a user; (b) a motor arranged
to drive the displaceable means at a selected but normally
substantially constant speed and providing a resistance for
resisting displacement load from the user's body part applied to
the displacement means; (c) a functional electrical stimulation
(FES) system for selected muscle groups of the user corresponding
to the body part to be exercised on the exercise machine; (d) a
feedback control system that receives signals indicative of the
user's performance during exercise; and (e) means for controlling
the FES system, by controlling the electrical stimulation to the
user's muscles to control the exercise regime.
2. A system as claimed in claim 1, wherein the FES system has means
for eliciting muscle contractions via controlling the amplitude of
electrical stimulation for a paretic or paraplegic user.
3. A system as claimed in claim 1 and wherein the FES system has
means adapted to assist muscle contraction to select muscles of a
user having impaired or voluntary muscle control.
4. A system as claimed in claim 1 and further comprising means to
measure and provide output data for recording the muscle
performance of the user.
5. A system as claimed in claim 4 and including means for
controlling an exercise regime for the user with means responsive
to the data relating to the user's muscle performance to select
different speeds for the motor and different corresponding timings
for stimulation through the FES to vary the work load.
6. A system as claimed in claim 5 wherein during an exercise
session the system initially establishes a relatively low speed of
exercise and subsequently adopts a higher speed or speeds, whereby
early fatiguing of the user's muscles is obviated and longer
exercise training sessions are provided.
7. A system as claimed in claim 6 and wherein an initial exercise
speed for a user not having voluntary muscle control or with
impaired muscle control is at about 5-25 revmin.sup.-1 and
subsequently during the exercise session the speed is increased to
of the order of 40-60 revmin.sup.-1.
8. A system as defined in claim 4 wherein the system includes an
adaptive control loop to adjust the motor to maintain constant
velocity motion in the machine and/or to regulate FES pulses to the
user's muscles to maintain a user-selected average power and/or
average torque output during exercise irrespective of any voluntary
muscle contractions of the user additional to those generated by
the electrical stimulation.
9. A system as claimed in claim 1 when the controlling means has
means allowing the user to utilise substantially isokinetic
exercise at different velocities of limb movement to elicit
different patient outcomes suitable for promoting muscular
strength, muscle fatigue-resistance or cardiorespiratory fitness
via FES muscle recruitment or voluntary muscle activation.
10. A system as claimed in claim 9, and comprising means to control
an exercise regime and having means to maintain a relatively slow
speed for an initial exercise segment followed by a relatively high
speed segment.
11.-27. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a control system and
applications of such control systems to the field of electrical
stimulation of muscles for the purpose of an exercise program. By
way of example, the invention will be illustrated with reference to
controlling a functional electrical stimulation (FES) system to
induce leg muscle contractions that permit a user with a physical
disability to benefit from such exercise. One important example is
to apply the invention to use of a machine that simulates cycling
motion, but the principles of the invention may be applied to other
machines.
BACKGROUND TO THE INVENTION
[0002] This is a continuation of co-pending U.S. Ser. No.
10/492,804, filed Sep. 3, 2004.
[0003] FES systems have been published in the prior art literature
such as U.S. Pat. No. 4,499,900 (Petrofsky et al) and U.S. Pat. No.
4,838,272 (Lieber). One system that has been commercially developed
and relates to the Petrofsky teachings is that marketed by
Electrologic of America Inc, with a system known as StimMaster
Orion, which uses FES as a form of therapeutic treatment.
Controlled electrical stimulation currents are passed through
electrodes to initiate muscle contractions, for example in the
lower extremities of a paralysed patient, thereby causing pedaling
of an exercise cycle. The Petrofsky system uses position sensors to
measure the position of pedals and these signals are used to
control the generation of stimulation signals to the user's
electrodes. The aim of these systems is to elicit a constant
pre-set velocity of pedaling as a therapeutic treatment for
disabled persons, such as paraplegics. In the event that the
velocity of cycling does not achieve the desired pedal cadence
(preset to 50 revmin.sup.-1), then the apparatus will increase or
decrease the stimulation amplitude delivered to muscles to change
the speed back to the desired pedal cadence.
[0004] Such prior art systems rely solely upon applied stimulation
to the limbs to initiate and control the exercise being undertaken.
Therefore, should the individual wish to exercise at a greater
level or intensity, the amount of stimulation applied to the limbs
must be increased to this level to achieve such intensity. The
likelihood of over-stimulation of the muscles is therefore greatly
increased and the potential of such systems to cause permanent
damage to the recipient is high. For this reason such exercise
systems have not been widely accepted as therapeutic devices.
[0005] The Lieber U.S. Pat. No. 4,838,272 discloses adaptive closed
loop electrical stimulation of muscles by a technique including
applying electrical stimulation signals to selected muscles at a
predetermined frequency, pulse width and amplitude. The work output
achieved by the muscles in response to stimulation signals is
determined over a period of time, and can be compared with target
values. The amount of electrical energy delivered to the muscles by
stimulation signals is varied in response to the results in order
to maximise the work output of the muscles during a treatment
period, this being accomplished by adjusting the frequency or pulse
width during stimulation treatment in response to the work output
measured. Such a system also has the problem that should the
individual wish to perform high intensity exercise then they are
solely reliant on increasing the amount of electrical energy
delivered to the muscles. Such an increase can therefore cause over
stimulation of the muscles and risks causing permanent damage in
much the same manner as the systems described above.
[0006] Another known class of exercise machine for therapy
purposes, particularly for paraplegics having minimal or no muscle
function, is one in which the user is passive and the machine such
as a cycle exerciser is motor driven to drive at a selected speed
whereby the user's limbs follow and are thus exercised. Such
systems, whilst reducing the risk of over stimulation of the
muscles and permanent damage associated therewith, are limited in
the amount of benefit they can provide with regard to muscle
strength and/or cardiorespiratory exercise training.
[0007] Further publications related to the present field are U.S.
Pat. No. 4,724,842 (Charters), EP 103490 (Wright State University),
U.S. Pat. No. 6,267,709 (Jacques et al), U.S. Pat. No. 4,865,315
(Paterson et al), U.S. Pat. No. 4,586,510 A (Glaser et al) and U.S.
Pat. No. 4,653,479 A (Maurer).
SUMMARY OF THE INVENTION
[0008] The present inventors consider that new and useful
alternatives to prior art proposals would be desirable and, as
described below, have conceived a new combination of features that
implement new concepts of controlled exercise for patients having a
physical disability.
[0009] The present invention, in one aspect, basically consists in
a system including: [0010] (a) a motor-driven exercise machine for
a user; [0011] (b) a functional electrical stimulation (FES) system
for selected muscle groups of a user corresponding to those to be
used on the exercise machine; [0012] (c) a feedback control system
that receives signals indicative of the user's performance during
exercise; and [0013] (d) the system being characterised by means
for controlling the FES system to the user's muscles to maintain a
desired exercise regime. More specifically an important embodiment
of the invention consists in a system including: [0014] (a) an
exercise machine having displaceable means for moving with a body
part of a user; [0015] (b) a motor arranged to drive the
displaceable means at a selected but normally substantially
constant speed and providing a resistance for resisting
displacement load from the user's body part applied to the
displacement means; [0016] (c) a functional electrical stimulation
(FES) system for selected muscle groups of the user corresponding
to the body party to be exercised on the exercise machine; [0017]
(d) a feedback control system that receives signals indicative of
the user's performance during exercise; and [0018] (e) means for
controlling the FES system, including means for controlling the
electrical stimulation applied to the selected muscle groups in
response to the user's performance detected by the feedback control
system. Embodiment of the invention include FES deployed by either
skin-surface or surgically implanted systems.
[0019] It is to be understood the invention may be implemented to
various embodiments including cycling type exercise, as well as
other exercises which may be of the nature of a push-pull motion or
indeed any motion where a relevant muscle or muscle group is
stimulated so that, apart from initial acceleration and
deceleration the muscle group is operating in a substantially
constant work mode i.e. constant velocity or constant speed mode.
In this specification exercise of this character will be for
convenience referred to as isokinetic exercise. This type of
exercise includes the case where there may be passive, assisted or
even stimulated return to an initial position for a further
exercise motion.
[0020] Embodiments of the present invention aims at overcoming the
problems associated with prior art systems by providing a control
system for a FES system that is capable of providing safe and
effective stimulation of muscles which may be described as reliant
on a combination of applied stimulation and passive
stimulation.
[0021] The present system extends the clinical efficacy of an FES
exercise system, which is a paradigm for near isokinetic training
which may be applied using a set of rules-based programs of
exercise therapy that recommend certain programs for certain
patients.
[0022] A further inventive development of the broad concept is to
embodiments wherein there is the application of slow velocity
isokinetic exercise (e.g. FES-induced cycling at 5-25
revmin.sup.-1) to build muscle strength and bulk, medium velocity
isokinetic exercise (e.g. FES-induced cycling at 25-40
revmin.sup.-1) to promote leg muscle fatigue-resistance, and fast
velocity isokinetic exercise (e.g. FES-induced cycling at 40-60
revmin.sup.-1) to promote enhanced cardiorespiratory fitness.
[0023] The present invention is directed to a system in which there
is combined the use of a motor driven exercise machine with the
user connected to an FES system via electrodes for activating
selected muscle groups corresponding to those to be used on the
exercise machine. In at least a preferred embodiment, a control
system is deployed that receives signals via closed loop feedback,
indicative of the user's performance during exercise, and the
system is thus characterised as being a means for controlling the
FES pulses to the user to maintain a substantially isokinetic
exercise regime whereby average power output and/or average torque
is the controlled outcome.
[0024] The controlling of the FES signals, advantageously, can be
by manipulating current amplitude and timing and obtaining
biofeedback to assist the user to perform exercise. Thus, one
important aspect of the invention is to the FES system eliciting
muscle contractions for a paretic or paraplegic user, but in the
alternative, the system can be applied to those with impaired or
normal voluntary muscle activation wherein the FES system simply
assists such muscle contractions via sensory biofeedback.
[0025] At least in one form, the invention may be described as
relating to a method of operation and a control system that
establishes substantially isokinetic FES-induced exercising. This
approach is believed to provide a significantly enhanced
therapeutic effect compared with the exercise regimes that follow
from use of the prior art.
[0026] The present inventors point out that their exercise regime
directly contrasts with FES isometric exercise where there is
substantially no movement of the limbs (but merely tensioning of
the muscle groups in question). The present exercise regime also
contrasts with FES concentric exercise where the velocity varies
proportionately to the amount of force generated by the muscles. In
the present regimen, the velocity of FES-induced limb movement
remains constant, regardless of the force applied by the
muscles.
[0027] When applied to a bicycle type exerciser, usually the
present invention would be implemented with the concept of
maintaining a constant speed, for example 50 revmin.sup.-1
(revolutions per minute). When muscle power is generated in excess
of that required to move the legs, the adaptive control loop
operates to adjust both current to the motor to maintain constant
velocity cycling and regulate FES pulses to the legs to maintain
constant average power output. By simultaneously controlling both
the motor and the stimulation pulses, the system can maintain both
constant velocity and constant power/torque output regardless of
whether the user can provide voluntary contractions in addition to
those generated by electrical stimulation (i.e. FES).
[0028] A further inventive proposal is to control an exercise
regime to permit muscles to perform a lengthy exercise session by
arranging for relatively low speed initially, e.g. around 15
revmin.sup.-1, with subsequent exercise at higher speed, e.g. 40-50
revmin.sup.-1. A significant proposition is that this regime
materially avoids premature fatiguing, thereby permitting more
effective muscle training over an extended period.
[0029] Further particular inventive features associated with the
present main inventive concept are operations whereby the FES
pulses are controlled according to mathematical formulae that take
into account the geometry of particular exercise machines and the
set-up of a particular user on a machine. These formulae, as
expressed in a computer model, calculate the most suitable pattern
of firing FES pulses that are to be applied to each muscle of an
individual user.
[0030] A second and independent inventive aspect associated with
the present developments concerns the use of mathematical formula
for the purposes described in the previous paragraph. However,
broadly, this concept is considered applicable to various systems
including FES systems that include those that are not motor
driven.
[0031] Furthermore, the present invention can be applied in
exercise regimes to recognise that different types of therapy can
be achieved at different velocities of limb movements. For example,
training at a relatively high speed will promote cardiorespiratory
training, whereas slower speeds enhance the development of muscular
strength. This speed-relative training can be applied to forms of
therapy that utilise FES-induced muscle contractions, or therapies
that employ voluntary muscle contractions by users.
[0032] In one aspect, the invention may be defined as consisting of
an apparatus comprising a motor-driven exercise machine (for
example, but not limited to a cycle exerciser), a functional
electrical stimulation (FES) system for delivering stimulation to
corresponding muscles of the user, and a control system to monitor
the power applied to the electrical drive system of the motor as
well as to control the timing, nature and duration of the FES
pulses. The motor and FES control system act in response to
measured performance, whereby the pedaling velocity is maintained
at a user-specified substantially isokinetic rate while the muscles
are simultaneously kept operating at a constant average
power/torque output.
[0033] In one important manifestation of the present invention,
there is provided an apparatus which includes a motor-driven
exercise machine, an FES system for providing skin/muscle sensory
biofeedback over corresponding muscles of a non-paralysed user and
a feedback control system monitoring the power/torque applied to
the electrical drive system of the motor to control the timing,
nature and duration of the low current amplitude FES pulses in
response to measured performance output by the user on the machine,
whereby the speed of operation of the exercise machine can be
pre-set to a desired constant velocity and substantially isokinetic
FES exercise is thereby achieved.
[0034] Another important embodiment of the invention is for
paralysed users; in this case, the invention may be defined as
consisting in an apparatus including a motor-driven exercise
machine such as a cycle exerciser, an FES system for the activation
of corresponding muscles of a paralysed user, and a feedback
control system monitoring the power/torque applied to the
electrical drive system of the motor to control the timing, nature
and duration of the FES pulses in response to measured performance
output by the user on the machine, whereby the speed of operation
of the exercise machine can be pre-set to a desired constant
velocity and substantially isokinetic FES exercise is thereby
achieved.
[0035] Ideally, the present invention would be implemented in a
system providing Progressive Resistance Isokinetic Training (PRIT),
typically on a cycle ergometer, although it appears that based on
present commercially available cycles, pure isokinetic training is
not achievable, but a close approximation is feasible. This
application will be described, by way of example, in the following
more detailed description. The present inventors believe that PRIT
approach allows training individuals with neuromuscular
disabilities such as spinal cord injury, hemiplegic stroke or
traumatic brain injury in a new and valuable way using FES. FES
induces leg muscle contractions, during constant-velocity leg
cycling, under control of a computer with purpose built software to
achieve substantially isokinetic exercise.
[0036] It is believed some particular disadvantages of prior art
proposals, which at least in part are overcome by embodiments of
the present invention, include the following: [0037] (a) only an
approximate-constant velocity of exercise, such as cycling, is
achieved under the prior art feedback control that alter the FES
current amplitude; [0038] (b) generally, prior art proposals use
fixed FES muscle firing patterns for all individuals and across all
muscle groups; [0039] (c) cycling velocity and muscle power could
not both be independently monitored and controlled by prior art
devices; and [0040] (d) in prior art proposals, any attempt to
quantify muscle fatigue has been imprecise due to the inability to
calculate the peak power and torque during cycling.
[0041] It is believed that the above disadvantages and limitations
have contributed to the lack of widespread acceptance of the prior
art exercise devices as part of a rehabilitation process. Thus, a
new and enhanced approach is required for there to be the perceived
value and enhance results that are desirable in many patients.
[0042] In one aspect, the present invention may be defined as
consisting in a software package for controlling and operating the
system in the forms outlined in this specification. In preferred
embodiments, newly developed algorithms control FES stimulation
parameters in real-time such as waveform, pulse frequency, current
amplitude on a pulse-by-pulse basis or muscle `firing` angles.
[0043] In a preferred system, the user or therapist may select a
desired velocity of cycling, and this will be maintained regardless
of the state of the patient's muscle weakness or degree of fatigue
during exercise. The control system thus facilitates patients
effectively using the system at home without direct supervision of
a therapist.
[0044] In the control system, the electrical stimulation to the
user's muscles can be under active control to alter the precise
timing of each stimulation pulse that can be achieved with, if
required, variation of pulse width, stimulation frequency, waveform
and current amplitude to elicit optimum stimulation of individual
muscles.
[0045] A preferred system also has means for recording information
about training sessions (e.g. FES parameters, peak and average
power/torque outputs, etc) and users or therapists can customise
the FES parameters and training sessions as desired. It is also
preferred that the software can determine, and record for later
analysis, specific timing for electrical stimulation pulses for
each individual over the duration of a training session. In
essence, the software is preferably arranged to operate in real
time to facilitate maximising the training stimulus during an
exercise session at a selected training velocity for a wide variety
of users with physical disabilities.
[0046] In the embodiment of the current invention, calculation of
exercise torque and power is achieved by monitoring the active
exercise load derived from the power applied to the electrical
motor of the machine. A significant feature of at least preferred
embodiments of this invention is the ability to calculate real
external loads of the muscles without including the passive load
provided by the motor to move the legs.
[0047] In another aspect the present invention consists in a system
to be adapted to be applied to a motor driven exercise machine, for
example a cycling type machine.
[0048] Important embodiments of the invention are directed towards
a system for achieving therapeutic exercise to paretic or
paraplegic users but embodiments can be particularly beneficial for
users having impaired or voluntary muscle control. For example,
users having injury or disease may achieve rehabilitation or
improvement in muscle performance by use of such embodiments.
[0049] Yet another aspect of the invention is directed to a
software control system for the exercise regimes.
[0050] Furthermore, the invention also manifests itself in methods
of treatment or therapy using the novel approaches described
therein.
EMBODIMENTS OF THE INVENTION
[0051] By way of example only, an embodiment of the invention will
now be described with reference to Functional Electrical
Stimulation (FES)-induced lower limb exercise using a cycle type
machine in a system suitable for patients with neuromuscular
disabilities such as (but not limited to) spinal cord injury. The
embodiment described is a design for a FES Progressive Resistance
Isokinetic Training (PRIT) cycle ergometer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] In the attached drawings:
[0053] FIG. 1 is a schematic illustration of a system embodying the
invention and including an exercise cycling machine on which a
patient is to be seated;
[0054] FIG. 2 is a flow chart illustrating the operation of system
of FIG. 1 with isokinetic cycling;
[0055] FIG. 3 is a typical display on a computer screen monitoring
operation of the system of FIG. 1;
[0056] FIG. 4 is a schematic diagram of a software program for the
FES module of FIG. 1.
[0057] FIG. 5 illustrates average data for some five patients using
the system of FIG. 1;
[0058] FIG. 6 illustrates data of power over a training or exercise
time for average data from some 5 patients and corresponding to the
exercise data of FIG. 5.
DETAILED DESCRIPTION OF THE DRAWINGS
[0059] The basic system is schematically illustrated in FIG. 1 with
a patient arranged to be seated on a commercial driven cycle module
(10), having electrical stimulation electrodes applied to the
patient's muscles and stimulated by a FES device (11) under control
of a computer (12) having novel software which monitors performance
data derived from the cycle (10). A closed loop feedback system is
provided with algorithms controlling the computer system to refine
the FES parameters for the patient before and during PRIT cycle
training.
[0060] The system may also be used with patients who do not require
use of the FES module, although the computer system monitoring the
cycle module (10) can be of value in controlling the average power
or total work during a desired exercise regime and providing
appropriate reports and monitoring. For such patients, PRIT may be
equally applied based on visual and auditory biofeedback signals
that inform the patients when to voluntarily activate their
muscles.
[0061] In an alternative embodiment, the system may also be used
with patients who require low current amplitude FES as a form of
skin/muscle sensory biofeedback (known as BioFeedback Electrical
Stimulation--"BioFES"), whereby the amplitude and timing of the FES
pulses, with the computer system monitoring the cycle module (10),
are of value in controlling the average power or total work during
a desired exercise regime and providing appropriate reports and
monitoring.
[0062] The commercial cycle (10) has its own speed control
circuitry to maintain the preset pedaling cadence, for this purpose
the cycle being driven by an electric motor. The cycle also
transmits certain performance data (e.g. pedal position, pedal
velocity and motor current) to the computer (12); such data is then
used to control and calculate FES parameters that are to be used
subsequently. The system calculates and monitors average power
output or average torque that is used to control the
exercise-training strategies.
[0063] The FES module (11) includes a micro controller that is
controlled and reconfigured by alteration of the software running
the computer system. In a preferred embodiment, alternative
algorithms are available in the controlling software so that the
therapist can vary the stimulation parameters to vary the relative
contributions of various muscles to suit the particular patient.
The principal design criteria and FES parameters of the FES module
may be summarised as follows: [0064] Six FES channels are provided
and a system is driven from a low voltage battery power supply.
[0065] A current amplitude of up to 140 mA across a 1 k.OMEGA. load
is provided. [0066] A pulse duration range of 50 .mu.s to 500 .mu.s
is provided. [0067] The pulse shape may be either square wave
monophasic, square wave biphasic or a trapezoidal biphasic shape.
[0068] Unique patterns of stimulus pulses can be delivered under
software control including (but not limited to) pulse doublets,
pulse triplets, "catch-like" pulses and variable pulse duration
"trains" of stimulation. [0069] The stimulation frequency range of
5 Hz to 60 Hz is provided. [0070] The timing of stimulation "firing
angles" (defined as the time from FES pulse onset until cessation,
for any particular muscle group) is under software or user
control.
[0071] The computer system 12 can be any suitable PC with suitable
operating software such as Microsoft Windows operating on an Intel
Pentium processor. (Microsoft and Intel are trademarks.) The
inventors have implemented an embodiment of the invention with a
computer program developed using the LabView (Trade Mark)
programming environment of National Instruments Incorporated. The
principal functionality of the program includes the following
aspects: [0072] (i) monitoring and processing the information from
the cycle ergometer module; [0073] (ii) calculation of the optimum
stimulation parameters in "real time"; [0074] (iii) determination
of optimum muscle "firing angles" based on a computer model and
mathematical equation to produce optimal FES cycling; and [0075]
(iv) delivery of the stimulation parameter information to the FES
module.
[0076] Referring now to FIG. 2, there is a flow chart for FES
isokinetic cycling which sets out the monitoring and processing of
part (i) of the program. The cycle module transmits information on
pedal position, pedal angle and motor current to the computer via a
serial cable using RS-232 handshaking protocol at a rate of 38.4
KBaud. The instantaneous pedal position triggers stimulation
delivery software. The motor current reflects the forces applied to
the pedals and the software calculates instantaneous net crank
torque. Accurate calculation of peak power, average and peak
torques during FES cycling are obtained.
[0077] FIG. 3 is a typical display for a system and the lower left
display shows a white line representing motorised passive cycling
and a grey line representing active exercising and from this data
the power and torque applied by the user is calculated in real
time. Instantaneous pedal velocity is known from the monitoring
software and is multiplied by crank torque to calculate the
instantaneous power; the average power is subsequently calculated
for the complete pedal revolution.
[0078] Average power output, which in FIG. 3 is shown as exercise
power 7.9 watts in the upper right corner of the display, is an
input variable to the second part of the software. Part (ii) of the
software calculates command and control stimulation parameters. It
is emphasised that this system contrasts with prior art systems
that only modify stimulus amplitude in response to a changing
(usually slowing) pedal cadence. The present system receives the
average power output calculated from part (i) of the program and is
compared to the desired or target value and the stimulation
parameters are altered according to an adaptive equalisation
controller algorithm. In the example shown in FIG. 3, a target
power (found on the right hand side) has a value of 7.5 watts, but
the actual exercise power determined at that time is 7.9 watts at
93.5% of peak stimulation amplitude. Accordingly, the stimulation
applied to the user is reduced to change the exercise power towards
the target value.
[0079] An alternative mode of controlling exercise with this
embodiment is using, with the adaptive controller algorithm, a
version programmed to minimise the rate of patient fatigue over
time, to maximise the peak power per stroke, or to maintain an
operator's selected average power output. The software also permits
open-loop control of FES-induced cycling by not using the adaptive
controller algorithm provided as a default feature. Thus, the
algorithms can provide control through any combination of the FES
parameters. The stimulation parameters are applied through part
(iv) of the program described below.
[0080] Part (iii) of the program in this preferred embodiment
includes a system for predicting suitable FES muscle firing angles
based on distance measurements taken from the ergometer, the seat
and having regard to the leg length of the individual user. The
preferred program enables these firing angles to be determined for
quadriceps, hamstrings and glutei muscles of paralysed persons and
this is used in the initialisation part of the system operations
depicted in FIG. 2.
[0081] Reference will now be made to FIG. 4 that illustrates the
functionality of a control program for the FES module. This
illustrates the manner in which appropriate stimulation is
given.
[0082] Use of the present system extends to a FES PRIT exercise
system, which is a paradigm for near isokinetic training using a
set of rules-based programs of exercise therapy that recommend
certain programs for certain patients. A key aspect is the
application of slow velocity isokinetic exercise (e.g. FES-induced
cycling at 10-15 revmin.sup.-1) to build muscle strength and bulk,
medium velocity isokinetic exercise (e.g. FES-induced cycling at
25-40 revmin.sup.-1) to promote leg muscle fatigue-resistance, and
fast velocity isokinetic exercise (e.g. FES-induced cycling at
40-60 revmin.sup.-1) to promote enhanced cardiorespiratory
fitness.
[0083] Tests conducted by the inventors using the present system on
patients with spinal paralysis have demonstrated that instantaneous
power and average power is greatest at faster cycling speeds,
whereas slow cycling demonstrates high torques, leading to
augmented muscle strength.
[0084] Referring to FIG. 5, average data for five patients is
illustrated, showing measured torque values over time at
respectively 15, 30 and 50 revmin.sup.-1 cycling velocity. These
data demonstrate that peak torque (which is the muscle strength
building component of exercise training) is highest at the slowest
FES PRIT cycle velocity, and this advantage is maintained over a
35-minute training session. FIG. 6 demonstrates average power over
time, and shows that average power (which is the cardiorespiratory
fitness building component of exercise training) is highest at the
fastest FES PRIT cycle velocity. This advantage is maintained over
a 35-minute session.
[0085] The rules-based approach to training, in accordance with
preferred therapy using the present invention, will assist the
therapist to recommend how much time that the user should spend in
each training session at any given cycling velocity from a wide
range of possible velocities over a 0-60 revmin.sup.-1 range.
[0086] A further inventive aspect relates to the development and
use of mathematical formulae expressed in a computer model to
determine the optimum timing of FES pulses for cycling on any
ergometer for any possible spinal cord-injured subject. This
inventive aspect may also be applicable as a development having
value in exercise systems wherein the machine does not have an
electric motor drive (e.g. the commercial cycle (10)), but is
solely driven by the user via concentric exercise.
[0087] In overview, the further inventive aspect is concerned with
analysing the geometric relationship between a particular spinal
cord-injured patient's lower limbs, the geometry of the machine and
the position at which the user is located, and developing
appropriate control-to-patterns for the timing and nature of FES
pulses. This contrasts with prior art systems where there has
simply been preset timing of FES pulses over a muscle's "firing
angle" (i.e. the time from FES pulse onset until cessation for any
particular muscle group) relative to absolute pedal crank
positions.
[0088] The mathematical modelling takes measurements from (i) the
length of the cycle crank, (ii) length of the subject's thigh from
hip to knee, (iii) length of the foreleg measured from the pedal to
the knee, (iv) horizontal and vertical distances from the cycle's
crank axle to the subject's hip when seated, and (v) speed of
FES-induced cycling. From these measurements, a unified
mathematical formula expressed as a computer model determines the
range of cycle crank angles wherein it is advantageous to have each
muscle generating force.
[0089] This geometric relationship is modified by taking into
account the time taken for paralysed muscles to contract and relax
in response to onset and cessation of FES-induced muscle
contractions. Extensive experimental evidence of the timing for
onset and cessation of FES-induced muscle contractions have been
used to determine the appropriate FES pulse durations and "firing
angles" for subjects with spinal cord injuries. The combination of
geometric formulae and timing of force development are then used to
determine the most suitable crank angles for use within the
adaptive controller algorithm.
[0090] The geometric relationship can be defined using the
following variables:
Variables Measured from the Subject and the Ergometer
[0091] seatang The angle the seat is reclined from the vertical,
[0092] dhoriz The horizontal distance between a subject's hip and
the cycle ergometer's axle, [0093] dvert The vertical distance
between a subject's hip and the cycle ergometer's axle,
[0094] lt The subjects thigh length, from hip to knee, [0095] ls
The subject's shank length, measured from the knee to the axle of
the pedal, including any thickness of the pedal and footwear,
[0096] lc The ergometer crank length. Variables Derived from
Previously Published Research [0097] dhk Moment arm of the
hamstring muscles about the knee, [0098] dhh Moment arm of the
hamstring muscles about the hip, [0099] dqk Moment arm of the
quadriceps muscles about the knee, [0100] dgh Moment arm of the
gluteal muscles about the hip.
[0101] From the measured variables, the subject's knee and hip
angles at any particular crank angle (qc) may be calculated from
the following formulae: Shank angle=Pi-ArcCos [(dhoriz 2+dvert 2+lc
2+ls 2-lt 2+2*dhoriz*lc*Cos [qc]+2*dvert*lc*Sin
[qc])/(2*ls*Sqrt[dhoriz 2+dvert 2+lc 2+2*dhoriz*lc*Cos
[qc]+2*dvert*lc*Sin [qc]])]-ArcTan [(dvert+lc*Sin
[qc])/(dhoriz+lc*Cos [qc])] Thigh angle=2*Pi-ArcCos [-((dhoriz
2+dvert 2+lc 2-ls 2-lt 2+2*dhoriz*lc*Cos [qc]+2*dvert*lc*Sin
[qc])/(2*ls*lt))]-ArcCos [(dhoriz 2+dvert 2+lc 2+ls 2-lt
2+2*dhoriz*lc*Cos [qc]+2*dvert*lc*Sin [qc])/(2*ls*Sqrt[dhoriz
2+dvert 2+lc 2+2*dhoriz*lc*Cos [qc]+2*dvert*lc*Sin [qc]])]-ArcTan
[(dvert+lc*Sin [qc])/(dhoriz+lc*Cos [qc])]
[0102] These geometric relationships, together with estimations of
the respective moment arm of each muscle about the hip and knee
joints, enable the determination of those crank angles where muscle
force will generate assist propulsion of the ergometer. For the
quadriceps, hamstring and gluteal muscles, the muscles should be
generating force at crank angles where the following formulae
produce positive values:
Quadriceps (-((lc*Csc[qs-qt]*dqk*(ls*Sin [qc+qs]+lt*Sin
[qc+qt]))/(ls*lt))) Hamstrings (lc*Csc[qs-qt]*(-(ls*dhh*Sin
[qc+qs])+ls*dhk*Sin [qc+qs]+lt*dhk*Sin [qc+qt]))/(ls*lt) Gluteals
-(lc*Csc[qs-qt]*dgh*Sin [qc+qs])/lt
[0103] Extensive measurements have been taken by the inventors with
respect to the time taken for paralysed muscles to contract and
relax in response to electrical stimulation. For each muscle a
particular time is required for the muscle to generate force after
stimulation commences, and a different time for the muscle to
relax. This experimental data, with advantage, is used to optimise
treatment regimes.
[0104] FES firing angles for each muscle may be determined for
specific individual subjects and ergometer positions by solving the
above formulae to determine crank angles where muscle force is
desired, then advancing this crank angle by the appropriate force
generation time multiplied by the velocity of cycling to give the
appropriate FES onset angle. Similarly, FES cessation angles may be
determined by using the above formulae then advancing the cessation
angle by the cycling velocity multiplied by the appropriate
relaxation time constant.
[0105] In this way, FES firing angles may be determined for use
within the adaptive controller algorithm. Once the maximum range of
suitable firing angles is calculated, the actual range used while
cycling would likely be reduced in order to increase the duration
of rest between successive muscle contractions. Use of these
formulae would enable any future knowledge of the ideal work to
rest ratio during FES induced contractions to be incorporated
within the adaptive controller algorithm.
[0106] Use of these formulae is not limited to the present system
using an isokinetic cycle ergometer and control systems based on
measurement of instantaneous crank position. These formulae may be
applied to any ergometer system where there is not substantial
movement at the ankle joint (which would produce a variable shank
length within the present definition). Furthermore, the geometric
formulae linking thigh and shank angle to crank position enable the
development of future control systems based on direct measurement
of segment positions, rather than being reliant upon feedback of
crank position from the ergometer.
* * * * *