United States Patent [19]
`Ebeling et al.
`
`US006145389A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,145,389
`Nov. 14, 2000
`
`[54] PEDOMETER EFFECTIVE FOR BOTH
`WALKING AND RUNNING
`
`[76] Inventors: W. H. Carl Ebellng, 6212 39th Ave.
`NE., Seattle, Wash. 98115; Amara
`Ebeling, 4002 Burke Ave. N., Seattle,
`Wash. 98103
`
`[
`1
`pp
`21 A 1. N .1 08 970174
`0
`/
`’
`Nov. 13, 1997
`[22]
`Filed:
`
`Related U-S- APPIiCZItiOII Data
`Provisional application No- 60/030,743, Nov- 12, 1996-
`[60]
`[51] Int C17
`A61B 5/00
`...................................................... ..
`.
`.
`'
`[52] US. Cl. ........................................ .. 73/865.4, 73/8654
`58
`F, M f S
`h
`73 865 4_ 364 565
`[
`]
`1e
`0
`earc """"""""""""" "
`/ 5' ’ 5 / 5 ’
`364/ 69’ 66’ 61
`
`[56]
`
`4:578:769
`4,855,942
`5,485,402
`
`.
`References Clted
`US, PATENT DOCUMENTS
`_
`ilgsreit
`364/565
`3/1986 Frederick
`364/561
`8/1989 BiaIlCO ....... ..
`1/1996 Smith et al. .......................... .. 364/566
`
`"""""""""""
`
`5,574,669 11/1996 Marshall ............................... .. 364/569
`5,724,265
`3/1998 Hutchings ............................. .. 364/565
`Primary Examiner—Benj amin R. Fuller
`Assistant Examiner_JeWe1 V Thompson
`
`[57]
`
`ABSTRACT
`
`A pedometer is disclosed that accurately calculates the
`len th of the strides taken b a user When Walkin and
`g
`Y
`g
`running. The length of each stride is calculated using mea
`surements of the acceleration of the Wearer’s foot during
`each stride. This acceleration is measured by an accelerom
`eter attached either directly or indirectly to the Wearer’s foot.
`The calculation of the stride length is performed by a data
`processor Which analyZes the accelerations of the foot as
`measured by the accelerometer‘ The acceleration Values for
`.
`.
`.
`.
`.
`.
`each stride are identi?ed, and these are used in con]unct1on
`With a set of coefficients to calculate the length of each
`stride. These coefficients are determined for each user by
`means of a calibration process during Which the pedometer
`measures the characteristics of the Wearer’s stride for a
`variety of different Walking and running speeds. Since the
`length of each stride is calculated independently, the user
`can change Walking and running speeds and gaits Without
`affecting the accuracy of the distance calculation.
`
`12 Claims, 6 Drawing Sheets
`
`Memory
`1 O4
`
`Timer
`108
`
`Data Processor
`1 O2
`
`Accelerometer
`1 1 0
`
`Output Device
`1 O6
`
`Input Device
`1 12
`
`Power Source
`1 14
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`U.S. Patent
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`Nov. 14,2000
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`Sheet 1 0f6
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`6,145,389
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`Memory
`104
`
`T1'r88er
`
`Data Processor
`102
`
`Accelerometer
`110
`
`Output Device
`106
`
`Input Device
`112
`
`Power Source
`114
`
`Fig. 1
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`U.S. Patent
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`Nov. 14,2000
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`Sheet 2 0f6
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`6,145,389
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`ACéELERATION
`
`,,
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`n
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`“
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`U.S. Patent
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`Sheet 3 0f6
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`6,145,389
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`AICCELEFIlATION
`10.4 g
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`1 SEC
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`U.S. Patent
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`Nov. 14, 2000
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`Sheet 4 0f 6
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`6,145,389
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`I
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`ACCELERATION
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`I
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`I
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`0.4 g
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`I
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`(404
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`I
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`I
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`I
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`/— 408
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`410 _/
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`L
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`05 SEC
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`_|
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`Fig. 4
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`U.S. Patent
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`Sheet 5 0f 6
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`ACCELERATION '
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`0.4 g
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`504
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`508
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`521
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`/_ 522
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`Fig. 5
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`U.S. Patent
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`Nov. 14,2000
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`Sheet 6 0f6
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`6,145,389
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`110
`
`Accelerometer
`
`V
`Accelerometer
`Data Stream
`
`602
`
`604
`
`Data
`Conditioning
`
`Acceleration
`Data Array
`
`606
`
`Stride Analysis
`
`608
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`Stride
`Profile Data
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`_
`
`610
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`Stride Length
`Calculation
`
`612
`
`Stride
`Length
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`614
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`6,145,389
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`1
`PEDOMETER EFFECTIVE FOR BOTH
`WALKING AND RUNNING
`
`CROSS-REFERENCES TO RELATED
`APPLICATIONS
`
`2
`particular, these pedometers alloW the user to change gaits
`While Walking and running. HoWever, the accuracy of these
`pedometers is still limited to the accuracy of the preset stride
`length.
`Some recent pedometers do not rely on a preset stride
`length, but use the rate at Which steps are taken to estimate
`the length of each stride. (See US. Pat. No. 5,583,776 to
`Levi, et. al., Dec. 10, 1996.) The stride length is correlated
`to some extent to the step rate, but this correlation does not
`hold for different gaits and is not generally accurate for
`running speeds greater than 7 or 8 mph. US. Pat. No.
`5 ,583,776 further discloses a pedometer that incorporates an
`accelerometer, Which is used as a more accurate alternative
`to the pendulum mechanism of ordinary pedometers. This
`patent discloses tWo methods for counting the number of
`steps taken. One method detects peaks in the acceleration
`data measured by the accelerometer Which correspond to
`individual steps taken. A second method uses signal pro
`cessing algorithms to extract the fundamental step frequency
`from the accelerometer data. The number of steps taken is
`then calculated by multiplying the elapsed time by the step
`frequency. The step frequency is also used to estimate the
`average stride length, relying on the correlation betWeen step
`frequency and stride length. In this regard, US. Pat. No.
`5,583,776 is similar to other prior art because it counts the
`users steps and estimates the stride length from the rate at
`Which steps are taken. In particular, it does not measure the
`acceleration of the foot itself, and provides no advantage
`over other prior methods for counting steps or estimating
`stride length.
`US. Pat. No. 4,371,945 to Karr, et. al., Feb. 1, 1983
`discloses a device that directly measures the stride length by
`means of an ultrasonic distance measuring device that
`measures the distance betWeen the Wearer’s feet When taking
`a step. This requires an ultrasonic transmitter strapped to one
`leg and an ultrasonic receiver strapped to the other leg, each
`connected to a processor that performs the distance calcu
`lation. This device is both cumbersome for the user to Wear
`and more expensive than ordinary pedometers because of
`the ultrasonic devices required. US. Pat. No. 4,703,445 to
`Dassler, Oct. 27, 1987 discloses a device that operates in a
`similar manner using ultrasonic transmitters in both shoes.
`US. Pat. No. 4,736,312 to Dassler, et. al., Apr. 5, 1988
`discloses a device that measures the stride length of a runner
`by measuring the elapsed time betWeen the time When one
`foot lifts off the ground and the time When the other foot hits
`the ground during a stride. This provides a more accurate
`estimation of stride length than possible using the step
`frequency alone. HoWever, the shoes on both feet are
`equipped With sensors, and the data from both must be
`communicated to a central processor Which performs the
`distance calculation. Thus this arrangement is not a self
`contained unit that can be Worn by the user. Since it is
`comprised of three different components, it is also more
`expensive to make than a single unit.
`US. Pat. No. 5,485,402 to Smith, et. al., Jan. 16, 1996
`discloses a gait activity monitor that records the number of
`steps taken by the Wearer. This monitor incorporates an
`accelerometer attached to the ankle of the Wearer, Which
`measure the acceleration of ankle. A data processor pro
`cesses this acceleration data, counting and recording the
`number of steps taken during each measurement time inter
`val. This monitor, hoWever, does not calculate any distance
`traveled. Moreover, it is not a self-contained unit that the
`user can portably Wear.
`
`This application claims the bene?t of Provisional Patent
`Application Ser. No. 60/030,743 ?led Nov. 12, 1996.
`
`BACKGROUND
`
`1. Field of Invention
`This invention relates to pedometers, speci?cally to
`pedometers that measure the stride length of the Wearer.
`2. Description of Prior Art
`Pedometers are devices for measuring the distance trav
`eled by a person When Walking and running. By using a
`device for measuring time in conjunction With the
`pedometer, the elapsed time taken to travel a distance can be
`measured and the average speed can be determined by
`dividing the distance traveled by the time taken to travel that
`distance.
`In most of the prior art, pedometers do not determine the
`length of each individual step, but instead rely on a preset
`average stride length of the Wearer. These pedometers count
`the number of steps and then compute the distance traveled
`by multiplying the step count by the preset average stride
`length. The accuracy of these pedometers depend on accu
`rately counting the number of steps taken and accurately
`setting the preset stride length to the average stride length
`actually taken by the user. Since the stride length can vary
`greatly for different Walking speeds and gaits, this method
`can be very inaccurate unless the person is careful to
`maintain the particular speed and gait that yields the preset
`average stride length. Running gaits vary even more Widely
`in stride length than Walking gaits and thus this method
`cannot accurately compute the distance traveled by runner.
`Pedometers count the number of steps taken by the Wearer
`using a variety of methods. Typical pedometers sense the up
`and doWn motion of the Wearer caused by each stride by
`means of a Weighted pendulum. The inertia of the pendulum
`causes it to move With relation to the pedometer. In mechani
`cal pendulums, this motion is typically sensed using a
`ratchet mechanism, Which advances a counter With each
`sWing of the pendulum. (See US. Pat. No. 4,560,861 to
`Kato, et. al., Dec. 24, 1985 Electrically instrumented
`pendulums typically use a sWitch contact Which is closed by
`each sWing of the pendulum. (See US. Pat. No. 5,117,444
`to Sutton, et. al., May 26, 1992.) In either case, the pedom
`eter must be adjusted according to the stride characteristics
`of the Wearer. Some pedometers have a sWitch that can be set
`to “Walk” or “run” While others alloW a range of adjust
`ments. AdraWback to pedometers that rely on pendulums is
`this requirement that they be adjusted to the user’s gait. This
`means that the Wearer must maintain approximately the
`same gait or the pedometer Will not count the steps taken by
`the user accurately.
`Some pedometers count steps more directly by means of
`a sensor or sensors embedded in the shoe that are connected
`directly to a counter. This can be done mechanically Where
`each step depresses a mechanism that causes a mechanical
`counter to increment. More frequently electrical means are
`used Whereby an electrical sWitch is closed by each step,
`creating an electrical signal that causes an electronic counter
`to increment. (See US. Pat. No. 5,640,786 to BuyayeZ, Jun.
`24, 1997.) This method counts the number of steps more
`accurately than pedometers that rely on pendulums. In
`
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`OBJECTS AND ADVANTAGES
`Accordingly, several objects and advantages of the
`present invention are:
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`3
`(a) to provide a pedometer Which accurately measures the
`distance traveled over a Wide range of Walking and
`running speeds;
`(b) to provide a pedometer Which accurately measures the
`distance traveled even if the Wearer changes speeds and
`gaits during use;
`(c) to provide a pedometer Which is small and light enough
`to be Worn on the shoe Without encumbering the Wearer;
`(d) to provide a pedometer Which is small and light enough
`to be manufactured as part of a shoe; and
`(e) to provide a pedometer Which can be easily and accu
`rately calibrated for the individual user.
`Further objects and advantages of our invention Will
`become apparent from a consideration of the draWings and
`ensuing description.
`
`DRAWING FIGURES
`
`FIG. 1 is a block diagram of the components contained
`Within the pedometer.
`FIG. 2 is a graph of the forWard acceleration of the foot
`for several representative Walking strides.
`FIG. 3 is a graph of the forWard acceleration of the foot
`for several representative running strides.
`FIG. 4 is a graph of the forWard acceleration of the foot
`for one representative Walking stride.
`FIG. 5 is a graph of the forWard acceleration of the foot
`for one representative running stride.
`FIG. 6 is a ?oWchart shoWing the data How by Which the
`acceleration data measured by the accelerometer is pro
`cessed to determine the stride length.
`
`Reference Numerals in Drawings
`
`102 data processor
`106 output device
`110 accelerometer
`114 poWer source
`402 quiescent region
`404 Walking lift phase
`408 Walking kick phase
`502 running impact region
`504 running lift phase
`508 running kick phase
`
`521 acceleration increase in
`running impact
`impact region
`602 accelerometer data stream
`606 acceleration data array
`610 stride pro?le data
`
`614 stride length data
`
`104 memory
`108 timer
`112 input device
`
`403 beginning of Walking stride
`406 Walking coast phase
`410 end of Walking stride
`503 beginning of running stride
`506 running coast phase
`520 end of running stride/?rst
`acceleration decrease in
`running impact region
`522 second acceleration decrease
`in running
`impact region
`604 data conditioning procedure
`608 stride analysis procedure
`612 stride length calculation
`procedure
`
`SUMMARY
`
`The present invention is a device that measures the stride
`length of a person When Walking or running. The device
`comprises a data processor coupled to an accelerometer
`attached to the user’s foot. This device determines the length
`of each stride from the acceleration data measured by an
`accelerometer. This device can thus accurately calculate the
`distance traveled by the user, regardless of Walking or
`running speed or gait.
`
`DESCRIPTION
`The present invention is a pedometer that operates by
`calculating the distance traveled by a person’s foot When
`
`65
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`6,145,389
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`4
`that person is Walking or running. The length of each stride
`is calculated accurately from data provided by an acceler
`ometer that measures the acceleration of the Wearer’s foot.
`The total distance traveled is computed as the sum of the
`individual stride lengths. Since the length of each stride is
`calculated independently, this pedometer calculates the dis
`tance traveled accurately even if the person changes speed
`and gait While Walking or running. It is necessary to measure
`the stride length for only one foot, since both feet travel the
`same distance.
`Our invention comprises an accelerometer (110) and a
`data processor (102) connected together as depicted in FIG.
`1. The data processor is further connected to an output
`device (106) Which is used to display information to the user.
`In the preferred embodiment, this output device is a liquid
`crystal display (LCD) that is placed on the instep of the shoe
`or on the toe of the shoe so that it is easily visible to the user.
`The Walker can read the information While Walking When
`ever the foot With the display is on the ground and therefore
`stationary With respect to the eye.
`Also connected to the data processor is a memory (104)
`comprising both volatile and non-volatile memory. The
`non-volatile memory is used to store the program instruc
`tions and data. The non-volatile memory is further used to
`store coef?cient data that specialiZes the distance calculation
`formula for a particular user. This coef?cient data is Written
`to the memory during a calibration process and thus at least
`part of the non-volatile memory must be Writeable. This can
`be accomplished using EEPROM memory as is Well-knoWn
`in the art. The volatile memory is used by the data processor
`as temporary storage While performing the distance calcu
`lation.
`The data processor is further connected to a timer (108)
`Which provides a means of measuring the elapsed time. This
`elapsed time is used to calculate the speed of travel. The
`timer can optionally be used in addition to provide a clock
`function.
`The data processor may be further connected to an input
`device (112) Which provide the user the means of operating
`the pedometer. Such operations may include turning the
`pedometer on and off; enabling the display of different
`information such as the total distance traveled, the speed of
`travel or the elapsed time; and restarting or pausing the
`distance measurement. In the preferred embodiment, the
`user additionally operates the pedometer using a simple
`communication method based on tapping the toe on the
`ground. For eXample, tapping the toe tWice in rapid succes
`sion could be used to reset the distance measurement and
`time. A single tap could be used to pause the time and
`distance measurement and another tap to resume measure
`ment. This tapping is performed by raising the foot so that
`the sole is perpendicular to the ground and tapping the toe
`on the ground. This produces foot accelerations that are
`distinctly different from that produced by Walking or
`running, and these are easily recogniZed by the data proces
`sor.
`ApoWer source (114) is also provided to provide electri
`cal poWer to the pedometer. In the preferred embodiment, a
`lithium battery is used for the poWer source.
`Microprocessors are currently available that combine a
`data processor, volatile and non-volatile memory, including
`EEPROM memory, and a timer in a single integrated chip.
`An eXample is the Atmel AT89S8252 8-bit microcontroller.
`The remaining components are sufficiently small that the
`entire pedometer can be put into a package the siZe of a small
`WristWatch. The pedometer is thus small enough and light
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`enough to be Worn on the shoe or in the shoe Without
`impeding the Wearer. It Will be appreciated that the pedom
`eter as described need not be assembled in a single package,
`but could comprise discrete parts connected together.
`The accelerometer (110) is attached to the foot of the
`Wearer and measures the acceleration of the Wearer’s foot in
`the direction of travel. The accelerometer can be attached to
`the foot by a number of means, including by means of a band
`to attach it to the ankle, or by attaching it to the shoe, or by
`embedding it directly in the shoe itself. The accelerometer is
`attached to the foot so that the aXis of acceleration measure
`ment is aligned more or less With the direction of travel. This
`alignment does not have to be precise and can be as much
`as 30 degrees, or more, out of alignment With respect to the
`direction of travel. The accelerometer measures the rate of
`change in velocity of the foot along the aXis of measurement.
`If this aXis is not aligned With the direction of travel, the
`acceleration measured is a combination of the acceleration
`in the forWard and lateral directions. Since there is little or
`no lateral movement of the foot While Walking and running,
`the value measured is A‘=A cos 0, Where A is the accelera
`tion in the direction of travel and 0 is angle betWeen the aXis
`of acceleration measurement and the direction of travel. If
`the accelerometer is securely fastened, then this angle 0 is
`constant, and the measured value A‘ is the actual acceleration
`scaled by a constant factor. If the device is Worn the same
`Way each time it is used, the values from one session to the
`neXt Will differ only slightly for the same motions of the foot.
`If the accelerometer is mounted so that the aXis is nearly
`aligned With the direction of travel, then differences in
`mounting Will cause little difference in the measured value
`since the cosine of small angles is very nearly 1.0.
`In the currently preferred embodiment, the accelerometer
`(110) is a silicon accelerometer such as the Analog Devices
`ADXL05. The accelerometer used in this invention should
`have a range of measurement of about —4 g/+4 g and be
`capable of measuring instantaneous acceleration at a rate of
`up to 250 samples/second With an accuracy of about 0.03 g.
`In the currently preferred embodiment, the Analog Devices
`ADXL05 outputs the measured acceleration as an analog
`value that is directly proportional to the measured accelera
`tion. This analog value is ?rst converted to an 8-bit digital
`value using an analog-to-digital (A-D) converter before
`being used by the data processor. Many microprocessors
`have analog-to-digital (A-D) converters integrated on the
`same integrated circuit, obviating the need for a separate
`A-D converter. FIG. 2 shoWs an eXample of the forWard
`acceleration of the foot of a person Walking as measured by
`the Analog Devices ADXL05 accelerometer attached to the
`shoe. FIG. 3 shoWs an eXample of the forWard acceleration
`of the foot of a person running.
`The data processor (102) is connected to the accelerom
`eter (110) to receive the acceleration data measured by the
`accelerometer. In the currently preferred embodiment, the
`data processor and accelerometer are combined into a single
`unit attached to the foot. This unit is attached to the foot by
`some means, for example, by means of a strap or elastic
`band attached to the ankle, by means of attachment to the
`shoe or by means of embedding directly in the shoe itself.
`The means of attachment is not important insofar as the
`accelerometer is positioned in such a Way that it measures
`the acceleration of the foot in the direction of travel, as
`described previously. The preferred means of attachment is
`to attach the device to, or embed the device in, a Walking
`shoe or running shoe in such a Way that it can be removed
`and used for different shoes. Since silicon accelerometers are
`fabricated using the same integrated circuit technology as
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`microprocessor s, the accelerometer can be integrated onto
`the same integrated circuit as the microprocessor.
`Analysis of foot acceleration data
`The data processor receives data from the accelerometer,
`Which measures the instantaneous acceleration of the foot in
`the direction of travel. This acceleration is sampled many
`times per second. This data is processed and analyZed in
`order to calculate the distance traveled by the foot by each
`stride. It is necessary to calculate the distance traveled by
`only one foot since both feet travel the same distance.
`We call the acceleration data collected during a single
`stride the stride pro?le. FIG. 4 shoWs the stride pro?le for a
`representative Walking stride. The stride pro?le is similar for
`different people and for different Walking speeds. FIG. 5
`shoWs the stride pro?le for a representative running stride.
`The stride pro?le for running is someWhat different from the
`Walking pro?le, but it too is similar for different people and
`for different running speeds. The acceleration data is ?rst
`analyZed to identify the beginning and end of each stride.
`The acceleration data is then further analyZed to identify
`speci?c events that occur during the course of a stride. This
`analysis produces a set of values that characteriZe each
`stride. This set of values is used to directly calculate the
`length of each stride.
`FIG. 6 gives the overall data How of the process that
`analyZes the acceleration data measured by the accelerom
`eter (110) and calculates the length (614) of each stride. The
`data processor samples the data provided by the accelerom
`eter at a rate sufficient to produce a Well-de?ned stride
`pro?le. In the preferred embodiment, a sample rate of 150
`HZ. is used. This sampling process produces a stream of
`acceleration data values (602).
`Before these data values (602) are stored and analyzed,
`the data is conditioned (604) by removing the acceleration
`bias caused by gravity and the Way the accelerometer is
`mounted on the shoe. This bias is removed by subtracting
`from each data sample the mean value of the acceleration
`data sampled during the time period immediately preceding
`the data sample. In the preferred embodiment, the length of
`this time period is ?ve seconds. The data measured by the
`accelerometer may be further conditioned by ?ltering to
`remove noise introduced by the accelerometer or by the Way
`it is attached to the foot.
`After conditioning, the acceleration data samples are
`stored sequentially in the processor memory in a data
`structure called the acceleration data array (606). The accel
`eration data array contains the data that has been sampled,
`but not yet processed. As data is sampled, it is added to the
`end of this data array, and When data is ?nished being
`processed, it is removed from the beginning of the array.
`Thus only data not yet processed remains in the acceleration
`data array. Those skilled in the art Will recogniZe that a data
`structure called a softWare FIFO can be used to implement
`the acceleration data array (606).
`The data in the acceleration data array is processed by a
`process (608) that eXamines the data sequentially starting at
`the beginning, examining it ?rst for the features that distin
`guish a Walking stride from a running stride. The Walking
`stride pro?le is distinguished by a region of relatively
`constant acceleration (402) Which occurs When the foot is on
`the ground betWeen steps. We call this region the “quies
`cent” phase of the stride. Running step pro?les are distin
`guished by a region of very high change in acceleration
`(502) Which is caused by the foot hitting the ground at the
`end of a step. This region starts With a large but brief
`decrease in acceleration (520), folloWed by a large but brief
`increase in acceleration (521), folloWed by a large but brief
`
`IPR2017-01058
`Garmin EX1026 Page 10
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`decrease in acceleration (522). We call this region the
`“running impact” phase of the stride. Walking strides can be
`thus distinguished from running strides.
`The stride analysis process (608) examines the data
`starting at the beginning of the acceleration data array for the
`?rst instance of either a quiescent region or a running impact
`region. If a quiescent region is found, then the input data is
`analyZed under the assumption that a Walking step has taken
`place. If a running impact region is found, the data is
`analyZed under the assumption that a running step has taken
`place.
`Walking Stride Pro?le Analysis
`FIG. 4 shoWs the acceleration data pro?le for a represen
`tative Walking stride. This stride begins With the foot on the
`ground during the quiescent phase (402). The quiescent
`phase ends When the foot is lifted from the ground (403).
`This lifting of the foot is marked by a large forWard
`acceleration of the foot Whose maximum marks the “lift”
`phase of the stride (404). The lift phase is folloWed by a
`decreased acceleration of the foot, called the “coast” phase
`(406) during Which the foot experiences much less forWard
`acceleration as it sWings forWard. The coast phase is fol
`loWed by the “kick” phase (408), during Which the foot
`again experiences a large forWard acceleration prior to being
`placed on the ground. The forWard acceleration of the foot
`decreases rapidly as the foot is placed on the ground (410).
`The phases of the Walking stride are further de?nes as
`folloWs. The quiescent phase (402) is de?ned as an interval
`of at least 0.25 seconds during Which the acceleration of the
`foot changes by no more than 0.2 g, indicating that the foot
`is stationary.
`The lift phase is de?ned as the ?rst peak (404) in the
`acceleration data after the quiescent phase. This peak must
`have an acceleration value at least 0.4 g greater than the
`average acceleration value during the quiescent phase, and
`the peak must be folloWed by a decrease in acceleration of
`at least 0.4 g. Aprocedure for ?nding the peak is to examine
`the data in sequence beginning With the quiescent phase,
`maintaining the maximum value found so far. If data is
`found Which is less than this maximum value by 0.4 g, and
`the current maximum value is suf?ciently large, then the
`procedure terminates and the maximum value is called the
`lift value and the time at Which this maximum value occurs
`relative to the beginning of the stride (403) is called the
`“time of the lift value”. The beginning of the stride (403) is
`further de?ned as the time from Which the acceleration
`values increase monotonically in value until the lift value,
`subject to the constraint that the acceleration value at the
`beginning of the stride (403) must be no more than 0.1 g
`greater than the average acceleration value in the quiescent
`region (402).
`The coast phase (406) is de?ned as the ?rst trough in
`acceleration data after the lift phase (404). This trough must
`have an acceleration value less than 0.4 g less than the lift
`value, and must be folloWed by an increase in acceleration
`of at least 0.4 g. A procedure for ?nding the coast trough is
`to examine the data in sequence beginning at the lift phase,
`maintaining the minimum value found so far. If data is found
`Which is greater than this minimum value by 0.4 g, and the
`current minimum value is suf?ciently small, then the mini
`mum value is called the coast value and the time at Which
`this minimum value occurs relative to the beginning of the
`stride (403) is called the “time of the coast value”.
`The kick phase (408) is de?ned as the ?rst peak in the
`acceleration data after the coast phase. This peak must have
`an acceleration value at least 0.4 g greater than the coast
`value, and the peak must be folloWed by a decrease in
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`acceleration of at least 0.4 g. Aprocedure for ?nding the kick
`peak is to examine the data in sequence beginning at the
`coast phase, maintaining the maximum value found so far. If
`data is found Which is less than this maximum value by 0.4
`g, and the maximum value is suf?ciently large, then the
`maximum value is de?ned as the kick value and the time at
`Which this maximum value occurs relative to the beginning
`of the stride (403) is called the “time of the kick value”.
`The ?rst trough after the kick phase marks the end of the
`stride (410). This trough must have an acceleration value at
`least 0.4 g less than the kick value and must be folloWed by
`an increase in acceleration of at least 0.1 g. Aprocedure for
`?nding the end of stride trough is to examine the data in
`sequence beginning With the kick peak, maintaining the
`minimum value found so far. If data is found Which is greater
`than this minimum value by 0.1 g, and the minimum value
`is suf?ciently small, then the time at Which this minimum
`value occurs relative to the beginning of the stride (403) is
`called the time of the end of stride.
`This analysis of the Walking stride results in several
`values that characteriZe the Walking stride precisely. These
`include:
`1) The duration of the stride, de?ned as the elapsed time
`betWeen the start of the stride (403) and the end of the
`stride (410).
`2) The lift acceleration value.
`3) The time of the lift value.
`4) The coast acceleration value.
`5) The time of the coast value.
`6) The kick acceleration value.
`7) The time of the kick value.
`8) The sum of the acceleration values from the start of the
`stride to the time of coast. This represents the area under
`the curve in FIG. 4 from (403) to (406).
`9) The sum of the acceleration values from the time of coast
`to the end of the stride. This represents the area under the
`curve in FIG. 4 from (406) to (410).
`This set of nine data values resulting from the stride
`analysis process (608) forms a data vector called the stride
`pro?le data (610). This stride pro?le data is used by the
`stride length calculation (612) to calculate the stride length
`(614). It Will be appreciated that this set of nine data values
`are those used in the currently preferred embodiment, but
`that other data derived from the stride analysis could be
`used, including a subset of these values.
`Running Stride Pro?le Analysis
`FIG. 5 shoWs the acceleration data pro?le for a represen
`tative running stride. The quiescent phase as de?ned for the
`Walking stride does not appear in the running stride pro?le
`because the foot is on the ground for a shorter period and
`maintains movement even While the foot is in contact With
`the ground. The distinguishing feature of the running stride
`is the running impact region (502), Which occurs When the
`foot hits the ground at the end of a stride. The running
`impact region is de?ned by three large changes in accelera
`tion: First, there is a decrease in acceleration (520) of at least
`0.6 g., folloWed by an increase in acceleration (521) of at
`least 0.6 g., folloWed by a decrease in acceleration of 0.8 g.
`(522). These three changes in acceleration must occur Within
`0.2 seconds.
`The remainder of the run