WO2018050773A1

WO2018050773A1 - Wearable device

Info

Publication number: WO2018050773A1
Application number: PCT/EP2017/073187
Authority: WO
Inventors: Jack PICKARD; Nephtali MARINA; Alexander GOURINE
Original assignee: Ucl Business Plc
Priority date: 2016-09-14
Filing date: 2017-09-14
Publication date: 2018-03-22
Also published as: GB201615605D0

Abstract

A wearable device to improve exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation. The device includes an earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear; a generator connected to the stimulating electrode for generating the electrical stimulation signal; and a controller connected to the generator, for determining the form of the electrical stimulation signal and the pattern of stimulation.

Description

WEARABLE DEVICE

FIELD OF THE INVENTION

The present invention relates to wearable electronic devices providing electrical stimulation to the skin surface of the outer ear, in order to improve exercise capacity. BACKGROUND OF THE INVENTION

A sedentary lifestyle is considered to be an important modifiable risk factor for human morbidity and mortality. Regular exercise has been well documented to protect against many disorders such as cardiovascular disease, type II diabetes, several cancers and obesity. Physical activity thus forms a key component of a healthy lifestyle. During exercise, cardiac output increases in order to provide adequate supply of oxygenated blood and metabolic substrates to the working skeletal muscles. This change in cardiac output is mediated in part via the autonomic nervous system, with a combination of parasympathetic (vagal) withdrawal and sympathetic activation. During recovery from physical exercise, parasympathetic reactivation and sympathetic withdrawal will cause heart rate and cardiac output to return to resting levels. Heart rate recovery from exercise (HRR) is a powerful indicator of autonomic health that reflects the beneficial effect of exercise training on overall cardiovascular health. Indeed, elite athletes display an incredibly high rate of HRR. Conversely, a slower rate of HRR is an independent predictor of cardiovascular mortality. Moreover, patients suffering from autonomic dysfunction, for example in heart failure, will display low physical fitness and exercise capacity. The ability to exercise is thus correlated with the strength and the health of the autonomic nervous system.

In particular, the vagus nerve forms a key part of systemic sensory and motor innervation, with branches projecting to almost every internal organ of the body.

Sensory parasympathetic (vagal) nerves terminate in the nucleus of the solitary tract (NTS) in the brainstem, which integrates the information received and controls the autonomic balance. The NTS is responsible for many systemic autonomic functions, for example: gastrointestinal peristalsis, glucose production in the liver, and most importantly for the present invention, control of cardiac output. SUMMARY OF THE INVENTION

The present invention employs non-invasive techniques for transcutaneous electrical stimulation of afferent (sensory) branches of cranial nerves innervating the outer ear, for the purpose of improving exercise capacity. These include afferents of the vagus, trigeminal and facial nerves projecting to the NTS.

More specifically, the present invention aims to achieve an improvement in exercise capacity by autonomic modulation, induced via electrical non-invasive stimulation of parasympathetic sensory pathways. At its broadest, the present invention does so by stimulating sensory afferent cranial nerves innervating the external ear, including the tragus, cymba conchae and cochlea.

Specifically, experimental data demonstrate that a particular group of autonomic neurones residing in the dorsal brainstem is especially important in determining an individual's ability to exercise, or in other words, an individual's exercise capacity. Rats having had this group of neurons genetically silenced were rendered unable to exercise. Conversely, when the activity of these neurons was artificially enhanced by optogenetic stimulation (for 15 minutes a day for 4 days) the exercise capacity was significantly increased to a level similar to that seen in control rats subjected to normal exercise training. This experiment is discussed in greater detail later on in this application.

Low-level electrical stimulation applied to the skin of the outer ear, including the tragus and cymba concha, has been demonstrated in the literature to activate systemic autonomic neural pathways. In particular, electrical stimulation of the tragus has been demonstrated to activate sensory neural pathways that lead to the same dorsal brainstem centres which are shown in the present invention to be critically important in determining the exercise capacity. These findings are harnessed in the present invention, a first aspect of which provides a wearable device to improve exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation, the device including: an earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear,

a generator connected to the stimulating electrode for generating the electrical stimulation signal, and a controller connected to the generator, for determining both the form of the electrical stimulation signal and the pattern of stimulation.

Throughout this application, the term "determine the electrical stimulation signal" should be understood to mean, and is used interchangeably with terms such as "determine the form of the electrical stimulation signal", "determine the pattern of the electrical stimulation signal", "determine the pattern of electrical stimulation", and "determine the pattern of stimulation".

In this way, a user's exercise capacity is expected to be improved by wearing the device and receiving stimulation as outlined in the previous paragraphs. Preferably, the stimulating electrode is configured to provide an electrical stimulation signal to one or more of: the auricular branch of the vagus nerve (ABVN), the greater auricular nerve (GAN), the auriculotemporal nerve (ATN) and the lesser occipital nerve (LON).

In preferred embodiments of the present invention, the wearable device further includes a physiological sensor which is configured to measure the value of a physiological parameter, to generate a sensor signal. The physiological sensor is preferably located on the earpiece of the wearable device, perhaps in close proximity to the stimulating electrode. Such a physiological sensor is preferably a heart rate sensor, which records a heart rate signal. In preferred embodiments, the heart rate sensor may be a high- sensitivity infrared sensor. The sensor signal may be used to determine the output to the controller, for example for determination of the form of the electrical stimulation signal and the pattern of stimulation. Specifically, the controller may be configured to determine the electrical stimulation signal based at least in part on the sensor signal. This is described in more detail, later on in the application.

In some embodiments of the present invention, the earpiece is in the form of a headphone, with the stimulating electrode and, optionally, the physiological sensor preferably located at a tip of said headphone. In some embodiments, the headphone is shaped to provide an ergonomic fit inside a user's ear. For example, the tip of the headphone may be shaped using a mould of a user's outer ear. This is advantageous for delivery of electrical pulses and for precise monitoring of physiological parameters such as heart rate, while minimizing motion-related artefacts in the sensor signal (or physiological signal such as heart rate). It should be noted that in embodiments of the present invention incorporated in a headphone, it is preferred that the electrical stimulation capability does not replace the music-playback capability of the headphone. Accordingly, the headphone preferably also includes a speaker, and may be configured to play sound simultaneously with the provision of the electrical stimulation signal and recording of the physiological variables. Alternatively, in other embodiments, the headphone may be configured only to play sound when there is no electrical stimulation taking place. It should be noted that in the present application, the term "headphone" is used to refer to all devices which may be worn on or around the ear to play sound into the ear. In particular, the term "headphone" is used to refer to devices which may be worn inside the ear (which may also be referred to as "earphones"), and those devices which are worn over the ear, and sometimes joined by a band which is worn over the top or the back of the head. The wearable device of the present invention may include just one earpiece (which may be a headphone), or may include two earpieces (one or both of which may be headphones). In embodiments having two earpieces, there may be a stimulating device and, optionally, a physiological sensor in each earpiece, to provide sensory stimulation of both outer ears, again preferably the sensory projections of ABVN, GAN, ATN, and/or LON of each ear. In other embodiments, including two earpieces, the stimulating electrode may be located (preferably at the tip) of one earpiece, and the physiological sensor may be located (preferably at the tip) of the other earpiece. Such embodiments are simpler to manufacture, and thus more cost effective. The wearable device may also include a reference electrode on the earpiece, in addition to the stimulating electrode and physiological sensor. In embodiments in which the stimulating electrode is located on a headphone, the reference electrode is preferably also located on the headphone. Furthermore, in devices having a pair of earpieces, there is preferably a reference electrode associated with a stimulating electrode on each (respective) earpiece. The device may include a plurality of stimulation electrodes on one earpiece, and may include a reference electrode associated with each stimulation electrode, or a single reference electrode associated with the plurality of stimulation electrodes on a given earpiece. Specifically, there may be a plurality of stimulating electrodes configured to provide an electrical stimulation signal to a single ear, or a plurality of stimulating electrodes per earpiece. Each stimulating electrode may be associated with a respective reference electrode.

The wearable device of the present invention preferably includes securing means configured to secure the earpiece in place in a user's ear. In embodiments including a headphone, the securing means preferably secure the earpiece or headphone in the user's ear.

The securing means may include a clip or the earpiece itself may take the form of a clip. For example, in some embodiments, the clip may be a tragus clip, configured to secure the earpiece (or headphone) in place by gripping a user's tragus, with a first gripping portion and a second gripping portion on respective sides of the tragus. Where this is the case, the stimulating electrode may be located on the first gripping portion, and a reference electrode may be located on the second gripping portion. One or both of the first gripping portion and the second gripping portion may extend into the ear canal, in order to provide additional anchoring. The physiological sensor may also be located on the clip, and is preferably also located on the first gripping portion or the second gripping portion. Alternatively, the physiological sensor may be present on part of the device which is not the clip.

Alternatively, the securing means may be a shaped portion of the earpiece, which is shaped to fit snugly inside a user's ear. For example, that portion may be shaped to fit snugly inside the cavity conchae, or inside the opening to the ear canal, behind the tragus. In embodiments including a headphone, the headphone may include the shaped portion. By ensuring a snug fit, the user may place the earpiece or headphone in his or her ear, and it will be securely in place. The shape of the portion may be formed by first taking a mould of the user's ear, and preparing a bespoke earpiece. Any or all of the stimulating electrode, a reference electrode and physiological sensor may be located on the shaped portion as described in this paragraph.

The controller and the generator may be located within the same component, which may be a portable electronic device. The portable electronic device is preferably able to run applications or apps, and is preferably a laptop computer, a tablet or a smartphone. Alternatively, the controller may be in the form of a portable electronic device, and the generator may be a separate component. The earpiece of the wearable device is preferably connected to the controller and/or generator via an electric cable, or via a wireless connection such as Bluetooth. As is described above, the controller is for determination of the electrical stimulation signal. More specifically, the controller may be for the determination of parameters relating to the electrical stimulation signal, such as pulse width, pulse frequency, waveform and pattern. The generator preferably produces the electrical stimulation signal (current or amplitude) based on the signal determined by and received from the controller. The controller is preferably for determining the strength of the electrical stimulation signal based on the sensor signal. This determination may take place in two ways: user-controlled, or automatic.

For user-controlled determination of the electrical stimulation signal, the signal may be determined based on a user input, which is provided by a user using the controller. The user input may include values of parameters such as pulse width, pulse pattern, frequency, and waveform. The user could also choose the length and pattern of stimulation within a predetermined range. The user input may then be transmitted to the generator whereupon it is used to generate the electrical stimulation signal. The user input may include values of stimulation amplitude (i.e. current) determined by the generator. In order to inform the user's decision when selecting values of the

parameters, a portable electronic device may include a display for displaying a visual representation of the sensor signal. Parameters relating to the sensor signal may be also be displayed alongside the visual representation, such as heart rate, heart rate variability, heart rate recovery after cessation of exercise, and exercise tolerance. These or other relevant parameters may be displayed using an application which may be run on the portable electronic device.

In other embodiments, the electrical stimulation signal (or the parameters relating to it) may be determined by the controller itself, based on the sensor signal, preferably a physiological sensor signal. For example, the electrical stimulation signal may be determined based on parameters such as resting heart rate, heart rate variability, heart rate recovery after cessation of exercise and exercise tolerance. The determination of the electrical stimulation signal may also take into account factors such as the user's age and body mass index (BMI). The controller may either transmit the determined electrical stimulation signal to the generator automatically, or alternatively, via an app or otherwise, display a suggested waveform for the electrical stimulation signal (and perhaps any relevant parameters) on the display of the portable electronic device. Then, a user may be able to modify the suggested waveform or parameters, before deciding to transmit the modified suggested electrical stimulation waveform to the generator. In some embodiments, an application modality will suggest the optimal duration and frequency of stimulation according to the progress made by the user as judged by resting heart rate, heart rate variability, heart rate recovery after cessation of exercise and exercise tolerance. The application or app may have the capacity to derive a heart rate signal to provide a direct measure of heart rate recovery following exercise, as a direct indicator of autonomic health. The user may thus be able to track improvements in their exercise capacity (via proxy of measuring the rate of heart rate recovery) during successive training/outer ear stimulation sessions. The application or app may also help the user to set cardiovascular fitness goals by comparing their heart rate recovery rate to the population average according to their gender, age and BMI. The application or app may also be able to pool useful data to assess the relationship between heart rate recovery, BMI and exercise capacity. Furthermore, the application or app may be able to link with other fitness-based applications or apps, in order to provide the user with a

comprehensive profile and record of their fitness regime and physical health.

In some embodiments, the generator is a device capable of generating pulses of electrical stimulation of no less than 0.01 mA, and no more than 80 mA. In

embodiments in which the generator is also included on the portable electronic device, the portable electronic device is preferably a smartphone, laptop computer or a tablet with a bipolar output and a maximum output of 80 mA.

According to a second aspect of the invention, there is provided an earpiece to improve exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation, the earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear, wherein:

the stimulating electrode is connectable to a generator for generating the electrical stimulation signal, and

the earpiece is connectable to a controller for determining the form of the electrical stimulation signal and the pattern of stimulation.

The earpiece may be connectable to the controller via the generator. Where compatible, all of the optional features set out above relating to the earpiece, stimulating electrode, generator, controller and the like of the first aspect of the invention apply equivalently to the second aspect of the invention. In particular, the controller and the generator may be the same component, or different components.

According to a third aspect of the invention, there is provided a wearable device to improve exercise capacity via electrical stimulation applied to the skin of the outer ear to produce autonomic modulation, the device including:

an earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear, and

a generator connected to the stimulating electrode for generating the electrical stimulation signal, wherein

the earpiece and the generator are connectable to a controller for determining the form of the electrical stimulation signal and the pattern of stimulation.

The earpiece may be connectable to the controller via the generator. Where compatible, all of the optional features set out above relating to the earpiece, stimulating electrode, generator, controller and the like of the first aspect of the invention apply equivalently to the third aspect of the invention.

According to a fourth aspect of the invention, there is provided a method of improving exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation, the method including the steps of: determining the form of an electrical stimulation signal and the pattern of stimulation; generating the electrical stimulation signal; and providing the electrical stimulation signal to sensory fibres innervating the outer ear.

In preferred embodiments, the method of the fourth aspect of the invention is performed using the wearable device of the first aspect of the invention. Accordingly, the optional features discussed above with respect to the wearable device also apply equivalently to the method of the second aspect of the invention, where compatible. Again, preferably the electrical stimulation signal is applied to the skin of the outer ear to provide stimulation of one or more of the: auricular branch of the vagus nerve (ABVN), the greater auricular nerve (GAN), the auriculotemporal nerve (ATN) and the lesser occipital nerve (LON).

Further optional features of the invention are set out below. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figs. 1 A to 1 C show a diagram of the anatomy and autonomic innervation of the human outer ear.

Fig. 2 shows an embodiment, in use, of the earpiece of a device according to the first aspect of the present invention. Fig. 3 shows an alternative embodiment, in use, of the earpiece of a device according to the first aspect of the present invention.

Fig. 4 shows an embodiment of a device, including the controller, according to the first aspect of the present invention.

Fig. 5 shows an alternative embodiment of a device, including the controller, according to the first aspect of the present invention.

Fig. 6 shows the expression of the light sensitive protein ChlEF in neurones of the dorsal brainstem.

Fig. 7 shows a schematic diagram of a method to stimulate the dorsal brainstem of a rat.

Fig. 8 shows the different regimes used in experiments on rats, relating to the present invention.

Figs. 9A and 9B show experimental results from various experiments on rats, relating to the present invention.

Fig. 10 shows the results of an alternative experiment relating to the present invention. DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES OF THE INVENTION Fig. 1 A illustrates the anatomy of the outer ear. The regions of particular interest for the present invention are the tragus, the antitragus, the cavity of conchae and the cymba conchae. Figs. 1 B and 1 C show the autonomic innervation of the outer ear. Four main branches provide the innervation: the auricular branch of the vagus nerve (ABVN), the greater auricular nerve (GAN), the auriculotemporal nerve (ATN) and the lesser occipital nerve (LON). Afferent (sensory) fibres from each nerve are distributed in a distinct spatial pattern throughout the outer ear. Devices of the present invention enable one or more of these nerves to be electrically stimulated. Fig. 2 shows an embodiment of a wearable device according to the present invention, in place in the ear of a user. Specifically, earphone 200 is in the form of a tragus clip, which has two lobes 204a, 204b which are biased to provide a gripping force on the tragus 205 of the user of the device. Lobe 204b includes a stimulating electrode 201 , and a reference electrode 202 in close proximity to the stimulating electrode 201 , which are arranged to provide an electrical stimulation signal e.g. to the ABVN, in the configuration shown in Fig. 2. The earphone 200 also includes a heart rate monitor 203 which is configured to record the heart rate from the ear canal. Not shown in Fig. 2, the earphone 200 also includes a speaker, so that the wearable device can be used as a normal earphone, rather than only as a neural stimulator. Earphone 200 is connected to a controller (not shown) by lead 206. The output from the heart rate monitor 203 is sent to the controller via lead 206, and also an input signal which may be used to generate the electrical stimulation signal is received at the stimulating electrode 201 from the controller, via the lead 206. In an alternative embodiment, shown in Fig. 3, the main body 304 of the earphone 300 is chosen to fit snugly inside the trigon of the cavity conchae. For example, it may be shaped using a mould. Again, the earphone 300 includes a stimulating electrode 301 and a reference electrode 302 in close proximity thereto. There is a heart rate sensor 303 also located in the main body 304. As with the embodiment shown in Fig. 2, earphone 300 is connected to a controller (not shown) by connecting lead 306, which performs the same function as in the previous embodiment.

The present invention preferably includes headphones which have sound-playing capability in addition to the ability to provide electrical stimulation to the outer ear. An embodiment demonstrating this is shown in Fig. 4, in which earphone 401 is connected to a music-playing device, such as a smartphone 403, optionally via amplifier 402. In addition to receiving music from smartphone 403, a program or an app running on the smartphone 403 may also control the pattern of electrical stimulation signal, depending on the input from a heart rate monitor on the headphone. In Fig. 4, the heart rate monitor and electrodes are not shown. A slightly different embodiment is shown in Fig. 5, in which the headphone 501 is connected to the generator or amplifier 502. In this embodiment, however, the amplifier or generator 502 is connected to smartphone 503 via Bluetooth. Experimental evidence - selective activation of the dorsal brainstem in experimental animals.

Given the importance of autonomic health in maintaining the exercise capacity, this experiment investigated whether specific recruitment of autonomic neural circuits in the dorsal brainstem of experimental animals improves their ability to exercise.

Specific recruitment of these dorsal brainstem autonomic neurons was achieved, using viral vectors, via expression of the light-sensitive optogenetic protein ChlEF. Selective activation of neurons expressing ChlEF was induced by delivery of 445nm light pulses via an optic fibre implanted in the dorsal brainstem region. Fig. 6 shows that highly specific expression of the optogenetic actuator was achieved in a region of autonomic control within the dorsal brainstem (shown in red). Rats were selected on the basis of relatively poor baseline exercise endurance and randomised in three experimental groups: (1 ) rats expressing the optogenetic protein ChlEF, and subjected to 15 minute stimulation of their dorsal brainstem region with 445nm light for 4 consecutive days (shown schematically in Fig. 7), (2) rats expressing the control transgene eGFP subjected to the same stimulation protocol described above over 4 days, and (3) naive, non-transduced rats subjected to daily 15 minute treadmill exercise training sessions. These protocols are shown in Fig. 8.

Exercise capacity was determined twice: on day 1 (baseline) and on day 6 to determine the effect of treatment. Stimulation of the dorsal brainstem over 4 days was sufficient to double exercise capacity, to a comparable level observed in the normally trained naive rats (see Fig. 9A). As shown in Fig. 9B, echocardiographic assessment of the left ventricular function revealed that dorsal brainstem stimulation increased baseline ejection fraction and enhanced the cardiac contractile response to β-adrenoceptor stimulation to a similar level observed in rats with classical exercise training.

These data indicate that the activity of the dorsal brainstem can be recruited to improve the exercise capacity. Regular stimulation of these neurons can mimic classical exercise training and improve exercise capacity via improving cardiovascular performance and autonomic balance. Transcutaneous vagus nerve stimulation enhances exercise tolerance in healthy human volunteers A study has been conducted to determine the effect of transcutaneous vagus nerve stimulation (tVNS) applied for 30 min each day over 5 days on exercise capacity in humans. Ten healthy subjects (6 male, 4 female) with previous experience of treadmill running and varying levels of ability were recruited to the study. One subject was excluded from the study due to pregnancy. A Conconi treadmill test was used to assess exercise capacity. This test includes an incremental protocol using a calibrated treadmill with 1.5% inclination. The treadmill speed begins at 3 km.hr¹ and increases by 1 km.hr¹ each minute. Subjects would continue to run on the treadmill until exhaustion-limited fatigue. Heart rate was continuously recorded throughout the protocol and for 2-min after cessation of exercise. Heart rate recovery was assessed over this period. Subjects performed a baseline exercise test, before once-daily tVNS for 30-min (200 ms, 30 Hz, 30-80mA) over 5 consecutive days. A second exercise test was then performed. In fig. 10 data are presented as the duration of the exercise test in seconds. The data obtained showed that five days of tVNS improved exercise capacity by 6% (Baseline = 850 ± 46s vs Stimulation = 890 ± 59s, paired t-test p = 0.02, n=9).

While the invention has been described in conjunction with the exemplary embodiments and experimental setups described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

All references referred to above are hereby incorporated by reference.

Claims

A wearable device to improve exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation, the device including:

an earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear;

a generator connected to the stimulating electrode for generating the electrical stimulation signal;

a controller connected to the generator, for determining the form of the electrical stimulation signal and the pattern of stimulation.

A wearable device according to claim 1 , wherein the stimulating electrode is configured to provide the electrical stimulation signal to one or more of:

the auricular branch of the vagus nerve (ABVN),

the greater auricular nerve (GAN),

the auriculotemporal nerve (ATN), and

the lesser occipital nerve (LON).

A wearable device according to claim 1 or claim 2, further including a physiological sensor configured to measure the value of a physiological parameter to generate a sensor signal, which is transmitted to output to the controller.

A wearable device according to claim 3, wherein the controller is configured to determine the electrical stimulation signal at least in part based on the sensor signal.

A wearable device according to claim 3 or claim 4, wherein the physiological sensor is a heart rate sensor, and the sensor signal is a heart rate signal.

A wearable device according to claim 5, wherein the heart rate sensor is an infrared heart rate sensor.

A wearable device according to any one of claims 3 to 6, wherein the physiological sensor is located on the earpiece.

8. A wearable device according to any one of claims 1 to 7, wherein the earpiece is a headphone.

9. A wearable device according to claim 8, wherein the stimulating electrode is located at a tip of said headphone.

10. A wearable device according to claim 8 or claim 9, wherein the headphone

includes a speaker.

1 1. A wearable device according to any one of claims 1 to 10, including two

earpieces, each having a stimulating electrode thereon.

12. A wearable device according to any one of claims 1 to 10, including two

earpieces, a stimulating electrode located on one, and a physiological sensor located on the other.

13. A wearable device according to any one of claims 1 to 12, further including a reference electrode on the earpiece.

14. A wearable device according to any one of claims 1 to 13, further including a securing means configured to secure the earpiece in the ear of a user.

15. A wearable device according to claim 14, wherein the securing means includes a clip.

16. A wearable device according to claim 15, wherein the clip has a first gripping portion and a second gripping portion which are biased into contact with each other.

17. A wearable device according to claim 16, wherein the stimulating electrode is located on the first gripping portion.

18. A wearable device according to claim 16 or claim 17, wherein a reference

electrode is located on the second gripping portion.

19. A wearable device according to any one of claims 15 to 18, wherein a

physiological sensor is located on the clip.

20. A wearable device according to claim 14, wherein the securing means includes a shaped portion of the earpiece, configured to fit snugly inside the ear of a user.

21. A wearable device according to claim 20, wherein the shaped portion is shaped to fit inside the cavity conchae.

22. A wearable device according to claim 20 or claim 21 , wherein the shaped portion is formed by taking a mould of a user's ear.

23. A wearable device according to any one of claims 20 to 22, wherein any or all of the stimulating electrode, the physiological sensor, and a reference electrode are located on the shaped portion.

24. A wearable device according to any one of claims 1 to 23, wherein the controller and the generator are the same component.

25. A wearable device according to any one of claims 1 to 23, wherein the controller and the generator are separate components.

26. A wearable device according to any one of claims 1 to 25, wherein the controller is configured to determine the electrical stimulation signal and the pattern of stimulation based on a user input received at the controller.

27. A wearable device according to claim 26 wherein the user input includes at least one of the pulse width, waveform, pulse frequency, pulse pattern and current of the electrical stimulation signal.

28. A wearable device according to claim 26 or claim 27, wherein the controller includes a display for displaying a visual representation of the sensor signal.

29. A wearable device according to any one of claims 3 to 25, wherein the controller is configured to determine the electrical stimulation signal based on the sensor signal.

30. A wearable device according to claim 29 wherein the electrical stimulation signal is based on one or more of: resting heart rate, heart rate variability, heart rate recovery after cessation of exercise and exercise tolerance.

31. A wearable device according to claim 29 or claim 30 wherein the controller is configured to determine the electrical stimulation signal taking into account one or more of a user's age and body mass index (BMI).

32. A wearable device according to any one of claims 1 to 31 , wherein the controller is a portable electronic device.

33. A wearable device according to claim 32, wherein the portable electronic device is able to run applications.

34. A wearable device according to claim 33, wherein the portable electronic device is a smartphone, a tablet or a laptop computer.

35. A wearable device according to any one of claims 32 to 34 wherein the earpiece is connected to the portable electronic device via an electronic cable or a wireless connection.

36. An earpiece to improve exercise capacity via electrical stimulation applied to the skin of the outer ear in order to produce autonomic modulation, the earpiece having thereon a stimulating electrode configured to provide an electrical stimulation signal to sensory fibres innervating the outer ear, wherein:

37. A wearable device to improve exercise capacity via electrical stimulation applied to the skin of the outer ear to produce autonomic modulation, the device including:

38. A method of improving exercise capacity via electrical stimulation of the outer ear in order to produce autonomic modulation, the method including the steps of: determining the form of an electrical stimulation signal and the pattern of stimulation;

generating the electrical stimulation signal; and

providing the electrical stimulation signal to sensory fibres innervating the outer ear.