An exercise device includes an ear piece insertable within the ear canal along an ear canal axis, a plurality of light emitters located about a periphery of the ear piece and spaced apart at 120° intervals for emitting light signals perpendicular to the ear canal axis into different areas of tissue surrounding the ear canal, a plurality of light detectors located about the periphery of the ear piece for detecting reflected light signals from the different areas of tissue surrounding the ear canal, an audio speaker, an audio player for sending audio signals to the audio speaker, and a vital sign monitor for determining at least one of heart rate, blood oxygen level, and body temperature from signals of the emitters and detectors.
This application is a continuation of U.S. patent application Ser. No. 15/394,115 filed Dec. 29, 2016, which is a continuation of U.S. patent application Ser. No. 14/607,810 filed Jan. 28, 2015, which is a division of U.S. patent application Ser. No. 12/195,502 filed Aug. 21, 2008, which claims priority in U.S. Provisional Application No. 61/006,321 filed Jan. 7, 2008, the contents of these documents incorporated herein by reference.BACKGROUND TO THE INVENTION 1. Field of the Invention
The current invention relates to an exercise device for monitoring body parameters of a wearer during exercise. The invention also relates to sensor for determining sensor signals from which body parameters can be derived and to a method of determining body parameters during exercise.2. Background Information
To achieve fitness goals it is necessary to exercise in the right intensity. Heart rate is one of the most accurate measurements of the intensity or exertion level of an exercise workout. The fitness of the heart is the key to aerobic endurance. Aerobic endurance is extremely important for both general fitness training and professional athletes. Heart monitors are one of the most effective aids for tracking and developing the progress on the path to increased aerobic endurance. For example, to loss weight and bum fat, it is desirable to exercise at 60-70% of one's maximum heart rate. To improve cardiovascular fitness, it is more suitable to exercise at 70-80% of one's maximum heart rate. Exercise at the wrong intensity will just waste the effort or may even harm the body.
Heart rate can easily be checked by checking the pulses at the wrist manually for, say, 15 seconds during exercise and calculate beats per minute. However, stopping during exercise to count pulse is not only inconvenient, but also disrupts both the workout and the heart rate. This method also introduces pressure to the carotid artery which slows down the pulse. Electronic heart monitors are an effective way to track and record heart rate over the course of an entire workout. They not only provide a complete record of the heart rate for the duration of your workout, but they are also more accurate than manual methods, and can provide other information such as body temperature, SpO2 (Oxyhemoglobin saturation by pulse oximetry) are also important information to determine condition of the body.
For professional athletes, cardiovascular fitness is the most significant factor in speed. Measuring the work-rate of the heart is one of the most accurate methods of determining how much benefit an athlete derives from a workout. A heart rate monitor can also help to avoid stressing the body too much. They are a useful tool for maximize the efficiency of the training while minimizing the opportunity for injury. Heart rate monitors also enable professional athletes to exercise below a certain ceiling, i.e. avoid depleting the body's glycogen stores and ensuring that the body has the energy to perform intense workouts with vigor. For general fitness training, a heart rate monitor can function as a coach guiding the user when he or she can handle more and work harder.
Most popular heart rate monitors use ECG type chest belt with a wireless link to sports watch. The heartbeat is detected by sensing the ECG signal from the chest belt and a pulse is sent to the sports watch via wireless connection. This type of heart rate monitor is accurate and reliable, but has the disadvantage that it is not comfortable for the user to wear a plastic belt on the chest during exercise. The belt will also become very dirty after use. Another method of detecting heartbeat is to use IR LED and IR sensor through the ear lobe or finger tip. This type of detector has the intrinsic problem of motion artifact and they are simply not reliable during exercise.
There are many devices that can measure body parameters of a person. For example, by using an infrared ear thermometer, clinical thermometer, the user could get his body temperature and by using pulse oximeter the user could get his heartbeat and the amount of oxygen attached to the hemoglobin. However, none of these devices is suitable for continuous monitoring of the body parameter when the user is doing exercise. The thermometer, for example, is not suitable for use in motion. For finger pulse oximeter, study suggested the motion will result in blood volume changes that invalidate its measurement [ref—“Motion Artifact in Pulse Oximetry”, M. R. Neuman and N. Wang, Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vol. 12 No. 5, 1990].
SUMMARY OF THE INVENTION
Accordingly, is an object of the present invention to provide an exercise device for determining the body parameters of a wearer during exercise. This particular object of the present invention to provide a sensor and method of determining heartbeat from a sensor signal that overcome or at least ameliorates problems with known devices.
A noninvasive light sensor for detecting heart beat signals has a circular support member engageable circumferentially with a body part of a person. A plurality of light emitters and light detectors are located about a circumference of the circular support member for respectively emitting light signals into different areas of tissue surrounding the body part, and receiving reflected light signals from the different areas of tissue surrounding the body part. In preferred embodiments the support member is one of a ear bud insertable within an ear canal or a band locatable about a wrist or arm.
The light emitters and light detectors may comprises both red and infra-red light emitters and detectors. In preferred embodiments there are three light emitters located 120 degrees apart about the circumference of the support member and three light detectors located 120 degrees apart about the circumference of the support member. The light emitters and light detectors are preferably located in pairs consisting of one of the emitters and one of the detectors.
Further aspects of the invention will become apparent from the following description.
An exemplary form of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
Aspects of the invention will now be illustrated as practiced in a first embodiment of a personal exercise device comprising an earphone sensor for listening to audio files and also for detecting body parameters; such as heartbeat, SpO2 and temperature; during exercise, a signal processing means for resolving sensor information into heartbeat and other body parameters and a workout assistance means for providing feedback of body parameters, exercise instructions and entertainment functions such as, but not limited to, music, video, game, e-book, photo, etc. However, this is not intended to limit the scope of functionality or use of the invention. In a most basic embodiment of the invention the exercise device comprises simply an earpiece sensor and signal processing means for detecting heartbeat for feedback to the user or transmission to another device such as an exercise machine or exercise monitoring equipment. The earphones of the invention include several mechanical design characteristics that ameliorate movement inaccuracies inherent in ear sensors known hitherto. It is not essential to the invention that all such preferred mechanical design characteristics be included in all embodiments of the invention.
Some of the signal emitted from the emitters 21, 22, 23 will be reflected from the skin surface of the ear canal. The amount of the IR signals 31, 32, 33 that is reflected from the skin also varies substantially with the aforementioned x, y plane movement of the ear bud 50 within the ear canal. The reflected light is detected by the detectors and must be allowed for in later processing to determine heartbeat and other body parameters from the detected signals. The amount of referred light that is detected by the detectors can be ameliorated by locating the emitters and detectors within recess channels 35, 36, 37 below the outer peripheral surface 28 of the ear bud 50. The recess channels 35, 36, 37 can comprise air or optical glass mediums and form a narrow angle wave guide for IR signals emitted from the emitters or entering the detectors. These wave guide channels 35, 36, 37 produces a narrow angle beam to direct the light in such a way to allow the maximum amount signal by increasing the signal path of the light up and into deeper tissue before the light reflects and is captured by the detector. They also limiting large fluctuation in DC single picked up by detectors.
The outer part 38 of the ear bud 50 consists of a soft over-molding made of resiliently deformable memory foam or silicone rubber that dampens the effects of motion. The foam is compressed when the ear bud 50 is inserted into the ear canal and expands to hold the bud 50 firmly in the ear canal to ameliorate relative motion between the emitters and detectors and the ear canal wall during exercise movement. One possible optional feature is to make outer piece 38 removable and interchangeable for varying the size and shape to fit a wide variety of users having different size ear canals. The properties (elasticity, softness as known as durometer, memory or rebound rate) of this soft over-molding 38 are chosen to maximizing the damping effects.
The depth placement of the emitters and detectors inside the ear is also important, but not essential, to reducing the effects of motion introduced within the ear during exercise. The emitters and detector are placed at the end of the inner part of the ear bud 50 which is further into the ear canal to help reduce the effects of motion. This placement helps reduce the vibration as the inner ear part is more firmly attached to the bone and muscle (non-soft tissue) which does not move as much during exercise.
A first arrangement of an ear bud 50 is illustrated in
The FPC 43 comprises a hub 46 having three 120 degree radially extending arms 47. The emitter and detector pairs 21-24, 22-25, 23-26 are located at the distal ends of the FPC 43 and are encapsulated with epoxy. The encapsulation provides a round-top to avoid injury to the user when wearing the device and at the same time prevents the emitters and receivers from damage. An alternative approach is to use sensors with suitable packaging. The FPC arms 47 are made of a flexible material so that sensors follow the foam 42 when squeezed into the ear canal. Flexible wiring tracks are located along the radial arms 47 connecting the emitters and detectors to solder bonding pads 48 on the hub 46. In one embodiment the FPC and arms is formed as a flex circuit. The hub 46 is located centrally within the back of the ear bud 50 and the radial arms brought forward within slots 45 on the surface of foam 42. The depth of the slots 45 is designed to allow the sensors to be slightly above the foam surface. The foam 42 is then covered with the rubber over-molding 38 for increase comfort and protection of sensors.
The head phones 1 and arm bands 60 of embodiments of the invention use multiple pairs of emitters and detectors at symmetrical locations to aid the removal or minimization of the additive noise introduced in to the detected sensor signals by exercise motion of the wearer. The microprocessor 8 of the main unit 2 receives the detected sensor signals and analyses them to detect the wearer's heartbeat and other body parameters, such as SpO2.
The detected signals 31, 32, 33 are modeled as follows:
m2(t)=L2I02(t)(1+y2hb(t))(1+Ns2(t)+Nf2(t)+z2(t)) (2), and
m (t), m2(t), m3(t) are the signals received at the 3 detectors respectively
I01(t), I02(t), I03(t) are the transmitted signals to the IR LED emitters respectively
L1, L2, L3 are constant gain of each IR sensor
hb(t) is the heartbeat signal
y1, y2, y3 are coupling coefficients of the heartbeat signal hb(t)
Ns1(t), Ns2(t), Ns3(t) are slow varying noise in the detected signals
Nf1(t), Nf2(t), Nf3(t) are typical additive thermal noise in the detected signals, and
z1(t), z2(t), z3(t) are noise signals due to motion.
This model is based on the assumption that the motion signals z1(t), z2(t), z3(t) are in the same plane as the circular plane formed by the 3 sensors (the x-y plane) and they can be decomposed to 2 orthogonal components h(t) and v(t) as shown in
We can make the assumption that both yk εk are much smaller than 1 and we can represent the received signal as DC and AC components(mack(t), mdck(t)). By calculating the signal AC amplitude when there is no motion, we can normalize the 3 channels gain. Equations (1),(2),(3) can be approximated as:
where N′sk(t), N′fk(t), zk′(t) are scaled versions of the original signals.
The signal due to heartbeat should have similar effect on the three signals 31, 32, 33 and should be in phase in each signal and differ only by a scaling factor. The sensors are placed evenly in a circle and so the effect of motion in x-y plane should be different for the 3 symmetrically located sensors. When there is no motion, or a very small amount of motion, the maximum signal to noise ratio (SNR) of the heartbeat signal can be obtained by adding up the three AC component input signal, i.e. y(t)=mac
When there is exercise motion the noise signals z1′(t), z2′(t), z3′(t) become dominated in the received signals 31, 32, 33. We can solve this problem by finding the column vector ŵ=[w1 w2 w3]T such that y=ŵTM
and ŷ is a linear combination of input signal which maximize:
where is the cross correlation matrix of the 3 signals from motion.
ŝ=[s1 s2 s3]T is the corresponding gain of the heartbeat signal, in this ŝ=[1 1 1]T and max=MMT−σ2ŝŝT where σ2 the variance of the heartbeat signal.
Since mm is positive definite, we can write:
mm=R1/2·R1/2 and we write û=R1/2ŵ.
The problem becomes
case where all the 3 input channels are normalized.
The amplitude of 3 input heartbeat signal is normalized by calculating the variance (or standard deviation) of each channel when the user is not running.
Block 71: A simple Finite Input Response (FIR} low pass filter is used to remove all high frequency signals. Slow drifting DC offset is removed using a filter or a moving window to extract the DC offset and subtract back from the signal.
The expression is maximum when:
Block 72: The signal amplitude of the heartbeat signal on each sensor is identified when there is no user motion. This is done by calculating the standard deviation of the 3 input signals when there is no motion. The 3 signal paths are then normalized.
Block 73: We then determine whether there is motion. The signal are check in the time domain. If the heartbeat signal dominates, all the 3 signals should be synchronous and in-phase. If the motion of the user is big enough, it is expected that the signal from motion dominates and sensor signals should not be all in phase. The correlation index across the three signals is calculated. The amplitude of the signal when compared with rest time signal amplitude is a clear indicator for motion.
If there is no motion the three signals are added together (with normalized amplitude) to improve the SNR.
If there is motion: e.g. running, the acquired signals are cut into blocks of length K for calculating the covariance matrix
σ2ŝŝT can be obtained calculating the standard deviation of the 3 input signals when there is no motion. The 3 input signals are then normalized to having signal standard deviation of a when there is no motion. Then σ2ŝŝT becomes
We then calculate the vector: w=mm−1ŝ
All 3 channels are calibrated and normalized when there is no motion
w is a 3×1 column vector: ŷ=ŵM
y[n] is a linear combination of the 3 input signals
the signal due to motion should be canceled out and preserve the heartbeat signal The linear combination may also be done in frequency domain as well. The time domain waveform can be restored using an inverse Fast Fourier Transform (FFT). The signal y[n] should contain the heartbeat signal+noise.
Block 74: The heartbeat signal is detected using match filters in the time domain. The user's resting heartbeat rate signal can be recorded as templates. The corresponding heart rate of these templates can be calculated and recorded as well. For each range of the heart rate, a template is stored for each user. For the range where there is no recorded template a time wrapping approach is used to predict an approximate template. These templates are then used to build multiple matched filters for the user. The corresponding matched filter will be selected according to current heartbeat rate of the user.
Block 76: The peaks of the matched filter output are detected and they are marked as the beat time. The inter-beat intervals are calculated and stored in a buffer.
Block 77: Based on the current beat rate, an algorithm was implemented to detect missed and false alarm of the beats. In case of a miss or false alarm the inter-beat intervals will be modified accordingly to improve accuracy of the heart rate calculation.
Block 78: The heart rate is then calculated from the inter-beat intervals buffer.
The exercise device processes, displays and stores health related data, such as heart rate, blood oxygen level (SpO2), body temperature, steps walked or run, entered weight to calculate calories burned and body mass index (BMI). The user connects to the headphones that not only playback audio files but also simultaneously captures end users health related data inside the ear. The data is transferred to the portable entertainment device and workout assistant for processing, displaying/notifying and storing the data. The following various functions are available on the device. This is, however, not an exhaustive list and more or less features may be included in some embodiments. Preferred features include:—
1. Playback of the audio/video files stored on the device,
2. Determining and displaying the instantaneous heat rate and storing a heat rate profile during an exercise period.
3. Storing and displaying the number of steps taken.
4. Determining, displaying and storing the health related status of the end user, including temperature, blood oxygen level and other body parameters.
5. Providing visual and audio feedback of target exercise parameters and/or rates to help the end user optimize his physical activity—for example a pre approved beep as a sign to slow down, a pre approved different signal/sound for signaling end user to pick up the pace and a pre defined sound for providing signal on what percentage of the exercise has been completed.
6. Transfer of date to a PC for further analysis, review or summary,
7. Providing visual and audio feedback, for example via pause or stop playback, if the device detects one or more of the ear buds is not capturing a heartbeat which mean a possible detach and resume playback after the device detects a heartbeat from one or both of the ear buds.
8. Providing visual and audio feedback of target exercise parameters by changing the tempo, pitch, equalizer according to the inputted vital sign so as to raise or reduce the workout intensity of the user sub-consciously—
1. An exercise device comprising:
- an ear piece insertable within the an ear canal along an ear canal axis;
- a plurality of light emitters located about a periphery of the ear piece and spaced apart at one hundred and twenty degree intervals for emitting light signals perpendicular to the ear canal axis into different areas of tissue surrounding the ear canal;
- a plurality of light detectors located about the periphery of the ear piece for detecting reflected light signals from the different areas of tissue surrounding the ear canal;
- an audio speaker, an audio player for sending audio signals to the audio speaker; and
- a vital sign monitor that for determining at least one of heart rate, blood oxygen level, and body temperature from signals of the emitters and detectors.