Abstract:
Training neck muscles in such a way as to improve responsiveness to head acceleration forces, and to help prevent concussion and/or screening subjects who are at high risk of concussion, especially from contact sports or military activities, may be accomplished by a device and/or method of training that incorporates an adjustable centripetal force about a fixed axis on the head. The centripetal force may be adjusted through varying the weight and/or length of a force arm, and neck muscle performance may be measured by a number of revolutions of the force arm completed over a set time period or a time required to complete a pre-determined number of revolutions of the force arm.

Description:
CROSS-REFERENCE 
       [0001]    This application is a Continuation-In-Part application of U.S. patent application Ser. No. 14/803,420 entitled NECK MUSCLE EXERCISER AND METHOD OF ASSESSING NECK MUSCLE PERFORMANCE filed Jul. 20, 2015, which is a Continuation of U.S. patent application Ser. No. 14/024,948 entitled NECK MUSCLE EXERCISER AND METHOD OF ASSESSING NECK MUSCLE PERFORMANCE filed Sep. 12, 2013, now U.S. Pat. No. 9,211,438 issued Dec. 15, 2015, all of which are herein incorporated by reference into the Detailed Description, herein below. 
     
    
     FIELD 
       [0002]    This application relates to physical training devices and to methods for assessing muscle performance, in particular to such devices and methods related to neck muscles. 
       BACKGROUND 
       [0003]    There are potentially very serious and lifelong consequences to suffering a concussion or other head injury. This concern is not just for professional athletes; it holds true for anyone involved in high risk sports as well as military personnel. Concussions are complex pathophysiological processes affecting the brain, induced by traumatic biomechanical forces. Research is starting to show the important role that neck muscles play in absorbing concussion forces from head impact. Recent research shows that for every pound of increased neck strength, concussion risk decreased by 5%. Previous research has also demonstrated how head peak acceleration and HIT scores, a proxy for concussion, can be drastically reduced in biomechanical models by increasing neck stiffness. What the sporting world and military lacks is an effective method of harnessing this natural shock absorption system and enhancing it. 
         [0004]    There currently exist methods of strength training the neck, and these methods may increase neck girth. However to help the neck muscles protect the brain these muscles&#39; reflexes and responsiveness should also be improved. As is known, a tense muscle provides much more resistance to acceleration than does a limp muscle. 
         [0005]    However, there remains a need in the art for devices and methods that safely strengthen the neck muscles, increase neck girth and stiffness and/or improve the neck&#39;s reflex response enhancing protection further. There also remains a need for devices and methods that can be used to evaluate a subject&#39;s pre-participation concussion risk by assessing performance and accurately predicting subjects most at risk. 
       SUMMARY 
       [0006]    Training neck muscles in such a way as to improve responsiveness to head acceleration forces to help prevent concussion and/or screening subjects who are at high risk of concussion, especially from contact sports, may be accomplished by a device and/or method of training that incorporates an adjustable centripetal force about a fixed axis on the head. A magnitude of the centripetal force may be adjusted through varying the weight and/or length of a force arm, and neck muscle performance may be measured by a number of revolutions of the force arm completed over a pre-determined time period or an amount of time required to complete a pre-determined number of revolutions of the force arm. Thus, neuromuscular and strength training of the neck muscles, as well as neck muscle performance measurement, may be accomplished using centripetal force to generate resistance. 
         [0007]    In one aspect, there is provided a neck muscle exercising or performance assessment device comprising: a substantially rigid elongated element configured to be length adjustable and/or to demountably receive one or more demountable weights selectively positionable along a length of the elongated element; a mount on which the elongated element is rotatably mounted proximate a first end of the elongated element, the elongated element rotatable around a central axis, the elongated element extending radially from the central axis; and, headwear to which the mount is rigidly attached, the headwear wearable on a subject&#39;s head so that the central axis is through the subject&#39;s head and rotational motion of the subject&#39;s head causes the elongated element to revolve around the central axis. 
         [0008]    In another aspect, there is provided a method of assessing neck muscle performance of a test subject, comprising: obtaining a neck muscle performance score of a test subject by determining a number of revolutions in a pre-determined period of time of a radially extending substantially rigid elongated element revolving around a central axis through a head of the test subject, or determining an amount of time required for a pre-determined number of revolutions of a radially extending substantially rigid elongated element revolving around a central axis through a head of the test subject, the revolutions of the elongated element being caused by action of neck muscles of the test subject; and, comparing the neck muscle performance score to a standard neck muscle performance score to assess the neck muscle performance of the test subject in relation to the standard. 
         [0009]    Adjusting the magnitude of the centripetal force acting on the elongated element may be accomplished by adjusting length of the elongated element, adjusting position of one or more demountable weights on the elongated element, adding or removing weights from the elongated element or any combination thereof. In this way, resistance may be adjusted up or down to requiring greater or lesser effort by the subject to effect revolution of the elongated element around the central axis. The elongated element has a first end proximate the mount and second end remote from the mount. Longer elongated elements, larger weights and weights positioned nearer the second end provide greater moments of inertia and larger centripetal forces. 
         [0010]    The elongated element may comprise, for example, a rod, tube or the like. Length adjustment of the elongated element may be accomplished in a number of ways, for example as follows. The elongated element may comprise telescoping members in which at least one member is housed within and slidable longitudinally in another hollow member. A locking mechanism, for example a spring-loaded pin in a pin receiving aperture may be used to lock the telescoping members together to prevent the members from sliding in or out during operation of the device. The elongated element may comprise members that are connectable longitudinally (end to end), for example with mated ends of a push-in type or a male/female thread type. Locking mechanisms may also be used to prevent the members from separating under use. The elongated element may comprise overlapping members, for example flat plates secured together by fasteners, e.g. nuts and bolts, at points along the length. The elongated element may be dismounted from the mount and replaced by an elongated element of different length. 
         [0011]    A demountable weight may be mounted on and positioned on the elongated element in a number of ways, for example as follows. The weight may be clamped on to the elongated element at a desired position. The weight may comprise a through aperture through which the elongated element may be inserted and then secured at a desired position on the length of the elongated member. In one example aspect, the elongated element is threaded with screw threads along at least a portion of the length for receiving one or more matingly threaded nuts for securing the demountable weight at one or more selected positions along the length of the elongated element. The threaded nuts themselves may be viewed as demountable weights. Alternatively or additionally, in another example aspect, the demountable weight may comprise a threaded through aperture, the weight being selectively positionable along the length of the elongated element by screwing the weight onto the elongated element until a desired position is attained. The threaded weights may be viewed as large threaded nuts. In one aspect, the elongated element comprises a rod for receiving the one or more demountable weights at the second end, and the first end of the rod is bent at an angle from the second end, the first end rotatably mounted on the mount. 
         [0012]    Rotatably mounting the elongated element on the mount may be accomplished in a number of ways, for example with a rotation bearing in a bearing block, a ball and socket joint or a pin in receiver joint. The elongated element revolves around a central axis and extends radially from the central axis. In an example embodiment, the radius formed by the elongated element is perpendicular to the central axis. 
         [0013]    In use, the subject wears the device on the head. For comfort, security and ease of operation, the mount for the elongated element is rigidly attached to the headwear. The headwear may be rigid (e.g. a plastic helmet) or semi-rigid (e.g. an array of adjustable nylon straps) device with cushioning on the underside that is in contact with the wearer&#39;s head that is able to transmit tension generated from the neck muscles up through to the rotatable mount. The mounting of the rotatable mount to the headwear may be accomplished in a variety of methods. For example, the rotatable mount may be molded to conform to the shape of a snugly fitting helmet and then held in place by bolts and nuts, straps, clips, cables, bands or some other fastening array. The helmet would then have a snugly fitting chin strap with two or more anchors to the helmet (for example in line with the temple bone and mastoid process of the skull on the helmet) to secure the device to the wearer&#39;s head and to transmit the rotation force from the neck muscles up through the device. 
         [0014]    In an example embodiment, the mount is rigidly attached to the headwear at a top of the subject&#39;s head and the elongated element revolves around the central axis above the subject&#39;s head in a plane perpendicular to the central axis running through the top of the subject&#39;s head down through the subject&#39;s torso. In use, rotation of the subject&#39;s head causes the longitudinal element to revolve around the central axis by virtue of the rotatable mounting. Such rotation of the head is due to the subject&#39;s neck muscles, which are exercised by the rotating motion. Thus, the subject uses the muscles of the neck to generate and maintain an orbital motion of the elongated element around the central axis. The elongated element may be free to revolve through a complete 360° circle and continue to revolve through an unlimited number of circles. The headwear may comprise a plurality of locations to which the mount may be rigidly attached providing different exercise options for the subject&#39;s neck muscles as the elongated element would describe circles around a different central axis and/or in a different plane than when the mount is at the top of the head. Therefore, while the mount is rigidly attached to the headwear, the mount may be dismountable from and remountable to the headwear. In one aspect, the headwear may comprise a helmet. For safety and ease of use, the headwear should fit the subject snugly and may comprise a securement element for securing the headwear to the head of the subject, for example a chin strap. 
         [0015]    In another example embodiment, there is provided a neck muscle exercising device comprising: a rigid element having a proximal end and a distal end; a mount on which the rigid element is rotatably mounted proximate the proximal end of the rigid element, the rigid element rotatable around a central axis, the rigid element extending radially from the central axis and at least the distal end of the rigid element extends substantially perpendicular to the central axis; weight located on the rigid element to define an off-central-axis center of mass; and, headwear to which the mount is attached, wherein rotational motion of the headwear causes the rigid element to revolve around the central axis. 
         [0016]    In another example embodiment, there is provided a kit of parts comprising: a plurality of rigid elements of different sizes, shapes, and/or weights, each rigid element comprising weight that is unitary with the respective rigid element, each rigid element and associated weight defining a different moment of inertia; a mount on which any selected one of the rigid elements is to be rotatably mounted, proximate a proximal end of the selected rigid element, the selected rigid element rotatable around a central axis, the selected rigid element extending radially from the central axis and at least a distal end of the selected rigid element extends substantially perpendicular to the central axis; and, headwear to which the mount is attached, wherein rotational motion of the headwear causes the selected rigid element to revolve around the central axis. 
         [0017]    The device may comprise a counter for counting a number of revolutions of the elongated element during use. The counter may comprise, for example, a position sensor, e.g. a camera, an accelerometer, an inclinometer, an RFID tag, a magnet, etc., and may be in communication with a recorder, for example a digital data processor and/or storage medium (e.g. a bicycle speedometer type counter, a computer, hard drive, flash drive, optical disc, etc.), containing software for counting the number of revolutions. The counter is, in an example embodiment, mounted on the elongated element. 
         [0018]    The device can include a detector for determining a count or speed of rotation, a processor in operable communication with the detector, and a communication subsystem which is used by the processor to wirelessly communicate data based on information detected by the detector. 
         [0019]    Assessing neck muscle performance of the subject may be achieved by one or more of varying the weight on the elongated element, the time required to perform a pre-determined number of revolutions or the number of revolutions performed during a pre-determined amount of time. This information may then be used to evaluate the neck muscle performance (e.g. strength and/or neuromuscular capabilities) of the subject. This information may be compared to a group of average and/or standardized values to determine the subject&#39;s risk of concussion, whiplash or other injury. This information may also be used to screen for participation in some sports or military or other activities as well as assess for improvement of neuromuscular strength function. 
         [0020]    Example embodiments of the device can be portable and can be used in a variety of different settings, for example clinics, playing fields or arenas, military training facilities and research facilities. Further, the ability to readily adjust the centripetal force experienced by the subject provides flexibility of operation and useability with different subjects having different neck muscle capabilities, and permits assessment of neck muscle performance. The device is useful for training the neck to improve its ability to respond to acceleration forces and protect the head and neck from injury (e.g. concussion or whiplash), rehabilitating weak or injured neck muscles, neuromuscular training and rehabilitation for neck proprioception and coordination, screening for neck strength and function for assessment of concussion risk, screening for neck strength and function for whiplash risk, rehabilitating subjects who have suffered from whiplash or concussion and training for balance. 
         [0021]    Further features will be described or will become apparent in the course of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    For clearer understanding, example embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a perspective view of a neck muscle exercising or performance assessment device; 
           [0024]      FIG. 2  depicts a bearing flange shown in  FIG. 1  with a rod rotatably mounted thereon; 
           [0025]      FIG. 3A  depicts a telescoping rod in a fully extended configuration having a plurality of weights proximate a distal end; 
           [0026]      FIG. 3B  depicts the telescoping rod of  FIG. 3A  in a fully retracted configuration and having a single weight proximate the distal end; 
           [0027]      FIG. 3C  depicts a telescoping rod in a fully extended configuration having a plurality of weights proximate a distal end secured by a wing nut on a threaded portion of the rod; 
           [0028]      FIG. 4A  depicts one embodiment of an attachment mechanism for mounting a bearing flange on headwear; 
           [0029]      FIG. 4B  depicts another embodiment of an attachment mechanism for mounting a bearing flange on headwear; 
           [0030]      FIG. 5A  depicts a front and a side view of an example neck muscle exercising or performance assessment device, in accordance with an example embodiment; 
           [0031]      FIG. 5B  depicts an example neck muscle exercising or performance assessment device, including a helmet and a rigid element for rotatably mounting to the helmet, in accordance with an example embodiment; 
           [0032]      FIG. 5C  illustrates another example rigid element for rotatably mounting to a helmet, in accordance with another example embodiment; 
           [0033]      FIG. 5D  illustrates another example rigid element for rotatably mounting to a helmet, in accordance with another example embodiment; 
           [0034]      FIG. 5E  illustrates another example rigid element for rotatably mounting to a helmet, in accordance with another example embodiment; 
           [0035]      FIG. 6A  depicts a side perspective view of another example neck muscle exercising or performance assessment device, including a helmet and a rigid element for rotatably mounting to the helmet, in accordance with another example embodiment; 
           [0036]      FIG. 6B  illustrates a perspective view of the rotatably mounted rigid element shown in  FIG. 6A ; and 
           [0037]      FIG. 6C  illustrates a top view of the rotatably mounted rigid element shown in  FIG. 6A . 
       
    
    
       [0038]    Similar reference numerals may have been used in different figures to denote similar components. 
       DETAILED DESCRIPTION 
       [0039]    Referring to  FIG. 1  and  FIG. 2 , a neck muscle exercising or performance assessment device  10  comprises a helmet  20  to the top of which a bearing flange  30  is fixedly attached by cables  35  secured to rivets  37  in the helmet  20 . Rotatably mounted on the bearing flange  30  is a rod  40  extending radially outward from an axis A through the a point of rotation B where one end of the rod  40  is rotatably secured in a rotational bearing secured in the bearing flange  30 . The rod  40  has a 90° bend  42  proximate the end secured at point of rotation B so that the rod  40  may revolve around the axis A while pointing radially outward from the axis A. The rod  40  is threaded along part of its length with screw threads  43  for matingly receiving nuts  44  that secure demountable weight  46  near a far end  47  of the rod  40 . There is one nut  44  on each side of the weight  46 , the weight  46  comprising a central aperture through which the rod  40  is inserted. The device  10  further comprises a counter including a magnet  50  from a bicycle speedometer mounted on the rod  40  in communication through wire  53  with a bicycle speedometer  55  for counting the number of full revolutions of the rod  40  around the axis A. A chin strap  60  securely holds the helmet  20  on the head of a subject.  FIG. 2  depicts a magnified view of the rod  40  rotatably mounted on the bearing flange  30  by a rotational bearing  32  in the bearing flange  30 . The bearing flange  30  comprises securement bolts  33  for securing the cables  35  to the bearing flange  30 . 
         [0040]    In use, a subject puts on the helmet  20  and secures the chin strap  60  under his chin in the same manner as donning any helmet of similar nature. By rotating his head clockwise or counter-clockwise in a rhythmic and orbital fashion, the subject can induce the rod  40  to begin revolving around the axis A by virtue of being rotatably mounted on the bearing flange  30 . The weight  46  being located proximate the far end  47  of the rod  40  provides a heightened moment of inertia and increases centripetal force on the rod  40 , which provides increased resistance to neck muscles of the subject. The increased resistance exercises the neck muscles more vigorously. More or less resistance may be provided by adding more weight or adjusting the length of the rod, some variations of which are shown in  FIGS. 3A-C . The subject may follow a prescribed regimen and the counter may be used to ensure that the subject accurately follow the regimen. 
         [0041]    The device may be used for exercise only or for performance assessment. In one aspect, the device may be used to assess the risk of concussion. Risk of concussion may be assessed and determined by correlating a subject&#39;s ability to perform on the device i.e. time needed to complete a pre-determined number of revolutions on the device at a specified weight and rotatable arm length and concussion risk. The more time a subject requires to perform the pre-determined number of revolutions, the weaker and less responsive his/her neck may be and therefore the more prone he/she may be to concussion. As an example, when assessing the performance of a team of hockey players on the device and then following this team during a hockey season, those who perform more poorly on the device may have an increased likelihood of suffering a concussion. If this is the case then it is likely that a certain performance level will be associated with the natural baseline risk for suffering a concussion and that performance levels below line this will be at higher risk for concussion. It may therefore be possible to screen players of nearly any sport to determine those that are at a high and or higher risk of concussion. In the event of an injury, a player who has suffered a concussion or whiplash may have a drop in performance on the device as the muscles of the neck are commonly injured during a concussion, and always during whiplash. Therefore, the device can be used to assess when a player is ready to return to sport after suffering a concussion by delaying return to sport until the player is able to perform on the device to the previously described baseline. 
         [0042]      FIGS. 3A and 3B  depict a telescoping rod  140  comprising an outer rod  141  having a 90° elbow  142  and an inner rod  145  that may telescope within the outer rod  141 . The outer rod  141  is rotatably mounted to a bearing flange (not shown) at a proximal end  143 . The outer rod  141  comprises a series of apertures  146  arranged along a length of the outer rod  141  for receiving a spring-loaded pin  147  situated near a proximal end of the inner rod  145 . The spring-loaded pin  147  may be engaged in any one of the apertures  146  to adjust the overall length of the rod  140 . To adjust the length of the rod  140 , the spring-loaded pin  147  is depressed to disengage the pin  147  from an aperture  146  and the inner rod  145  is slid proximally or distally within the outer rod  141  until the spring-loaded pin  147  engages the next aperture  146 . The outer rod  141  may comprise any number of apertures  146 , and each aperture represents a length setting for the rod  140 . The telescoping rod  140  may be of any desired length, for example 12 inches in the fully extended configuration ( FIG. 3A ) and 6 inches in the fully retracted configuration ( FIG. 3B ). Weights, for example two weights  151 ,  152  as seen in  FIG. 3A  or one weight  151  as seen in  FIG. 3B , may be mounted on the inner rod  145 . To secure the weights  151 ,  152  on the inner rod  145 , securement clips  153  may mounted on the inner rod  145 , the clips  153  having ends that may be inserted through clip apertures  154  on the inner rod  145 . Two clips  153  may be used on each side of the weight or weights (e.g. weights  151 ,  152  as seen in  FIG. 3A , or weight  151  as seen in  FIG. 3B ). Only one clip distally of the weight may be needed if the inner rod is retracted sufficiently that the outer rod helps secure the weight or weights in place proximally. The inner rod  145  may comprise a series of any number of clip apertures  154 , and may comprise an opposed series of clip apertures, the opposed clip aperture receiving opposite ends of the securement clips  153 . A series of clip apertures  154  permits mounting the weights  151 ,  152  at a variety of positions along the inner rod  145  in order to change the moment of inertia for the device on which the rod  140  is mounted. 
         [0043]      FIG. 3C  depicts a second embodiment of a telescoping rod  240  comprising an outer rod  241  having a 90° elbow  242  and an inner rod  245  that may telescope within the outer rod  241 . The outer rod  241  is rotatably mounted to a bearing flange (not shown) at a proximal end  243 . The telescoping rod  240  comprises a spring-loaded pin  247  near a proximal end of the inner rod  245 , and apertures  246  in the outer rod  241  to engage the spring-loaded pin  247  in a manner similar to that of the telescoping rod  140  described in relation to  FIGS. 3A-B . However, instead of the inner rod  245  possessing clip apertures, at least a portion of the inner rod  245  comprises screw threads  255  onto which weights  250 ,  251 ,  252  may be threaded. The weights may be secured at any position along the threaded portion  255  by nuts, for example a wing nut  253  distal of the weights  250 ,  251 ,  252 , and if desired, another nut on the proximal side of the weights  250 ,  251 ,  252 . The weights  250 ,  251 ,  252  may be threaded to any desired location along the threaded portion  255  to change the moment of inertia of the device. 
         [0044]      FIGS. 4A and 4B  depict different embodiments of attachment mechanisms for mounting a bearing flange on headwear, for example the helmet  20 . In  FIG. 4A , a bearing flange  130  comprising a rotational bearing  132  has straps  135  mounted therein by feeding the straps  135  through through-apertures  136  in edges of the bearing flange  130 . Alternatively, instead of two straps there could be four straps, each strap attached to the bearing flange. The straps may alternatively be secured to the bearing flange on an upper or lower surface of the flange rather than an edge or edges. The straps  135  may be configured so that straps or parts of straps are situated on opposed sides of the bearing flange  130  for better securement efficiency. The straps  135  may be secured to the headwear by bolts, rivets, stitching and the like at securement structures  137  on the straps  135 , for example at proximate ends of the straps  135 . Any number or arrangement of straps may be used to ensure proper securement of the bearing flange  130  on the headwear. 
         [0045]    In  FIG. 4B , a bearing flange  230  comprising a rotational bearing  232  has lever buckles  237  attached thereto. The lever buckles  237  comprise lever handles  239  pivotally mounted on the lever buckles  237  and operatively connected to hooks  238  through connecting straps  236 . The hooks  238  are configured to engage mounting struts  233  mounted to headwear (e.g. a helmet) (not shown). The mounting struts  233  may be secured to the headwear, for example with U-bolts or clips. The mounting struts  233  are spaced apart such that when the lever handles  239  are in an “up” position, the connecting straps  236  have sufficient length for the hooks  238  to hook over the mounting struts  233 , as seen in the lower part of  FIG. 4B . When the lever handles  239  are in a “down” position with the hooks  238  hooked over the mounting struts  233 , the connecting straps  236  are pulled toward the buckles  237  tightening the hooks  238  on the mounting struts  233 , as seen in the upper part of  FIG. 4B . Any number and arrangement of lever buckles may be used to ensure proper securement of the bearing flange  230  on the headwear. Mounting struts may be located anywhere on the headwear and a plurality of mounting struts on the headwear offer the opportunity for mounting the bearing flange in different locations. 
         [0046]    For example, the attachment mechanisms for mounting the bearing flange on headwear are readily re-moveable and re-mountable to permit exchange of headwear or to move the bearing flange to a different location on the headwear. 
         [0047]    Reference is now made to  FIG. 5A , which depicts an example neck muscle exercising or performance assessment device  350 , including the helmet  20  and a rigid element  354 , having a weight  352  mounted thereon, in accordance with an example embodiment. The device  350  further comprises a detecting device. In one example embodiment, the detecting device comprises a counter for counting the number of full revolutions of the rigid element  354  around the axis A, as shown on the helmet  20 . In another example embodiment, a detector such as a speed detector can be used to measure the speed of rotation, for example. This can be used to determine the actual real-time speed of rotation, rather than a calculated average. 
         [0048]    Still referring to  FIG. 5A , the device  350  can include an on-board computer device that includes one or more processors, memory, and a communications subsystem. The computer device is in operable communication with the detector. In some examples, the average speed of rotation can be calculated by dividing the number of counts from the counter with an applicable amount of time. The on-board computer device can be configured to wirelessly communicate over the communications subsystem with a portable mobile communication device  352 , such as a cellular phone, smart watch, or mobile tablet. Accordingly, the portable mobile communication device  352  can display the activity of the device  350  in real-time, such as the speed of rotation, the total number of revolutions, and/or the total time elapsed, for example. Games can be displayed on the mobile communication device  352  which are responsive to the performance of the device  350 . In another example embodiment, the portable mobile communication device  352  can be used for analysis and metrics (online or offline), such as comparison with previous operation of the device  350 , or comparison with other users, for example. 
         [0049]    Reference is now made to  FIG. 5B , which depicts an example neck muscle exercising or performance assessment device  300 , including the helmet  20  and a rigid element  304 , in accordance with an example embodiment. The rigid element  304  is rotatably mounted to the helmet  20  so that it can be spin around the central axis A defined by the helmet  20 . As shown in  FIG. 5B , the rigid element  304  comprises a weight  306  that is unitary with the rigid element  304 . Since the weight  306  is positioned away from the central axis A, the weight  306  defines an off-central-axis center of mass, with respect to the combined rigid element  304  and weight  306 . An example suitable moment of inertia is at least 0.05 kg·m 2 , and can depend on the desired situation or person. In the example embodiment shown, the weight  306  has a larger cross-sectional size than the remainder of the rigid element  304 . Rotational motion of the helmet  20  causes the rigid element  304  to revolve around the central axis A. 
         [0050]    In some example embodiments, in order for the weight  306  to be unitary with the rigid element  304 , the weight  306  may be cast, molded or welded with, or as part of, the rigid element  304 . 
         [0051]    In some example embodiments, the material of the rigid element  304  is of a suitably heavy material in order to provide the required centripetal force (along with the particular shape, size and/or length of the rigid element  304 ). Example metals include steel, iron, aluminum or titanium. Example non-metals and or composite materials could also be used e.g plastics, other polycarbonates, etc. In an example embodiment, different parts of the rigid element  304  are formed of two or more types of materials, and are attached together by way of casting, molding, welding, etc. 
         [0052]    Reference is now made to  FIGS. 5C and 5D , which illustrates further example rigid elements  310 ,  320  for mounting to the helmet  20 , in accordance with example embodiments. In the example embodiments shown, the rigid element  310 ,  320  may have a substantially uniform cross-section along an entire length of the rigid element  310 ,  320 . The rigid element  310 ,  320  comprises a material that has a suitably heavy weight, so that a suitable moment of inertia is provided. The weight is therefore unitary with the rigid element  310 ,  320 . As shown in the example embodiment of  FIG. 5C , the rigid element  310  may have a rectangular cross-section. As shown in the example embodiment of  FIG. 5D , the rigid element  320  may have a circular cross-section. 
         [0053]      FIG. 5E  illustrates another example rigid element  530  for mounting to the helmet  20 , in accordance with another example embodiment. In the example embodiment shown, the rigid element  330  is unitary with the weight, and uses the weight of the particular material of the rigid element  330  to provide the desired centripetal forces. The size (and therefore the weight) of the rigid element  330  increases along the length of the rigid element, towards the proximal end. The maximum weight is located at the distal end of the rigid element  330 , due to the maximal cross-sectional size. 
         [0054]      FIGS. 6A, 6B and 6C  illustrate another example rigid element  400  for rotatably mounting to the helmet  20 , in accordance with an example embodiment. In the example embodiment shown, the rigid element  400  is unitary with the weight, and uses the weight of the particular material of the rigid element  400  to provide the desired centripetal forces (along with the particular shape, size and/or length of the rigid element  304 ). The cross-sectional size (and therefore the weight) of the rigid element  400  increases along the length of the rigid element, towards the distal end and maximizing the cross-section size (and weight) proximate the proximal end. The rigid element  400  is fan-shaped in the example embodiment shown. 
         [0055]    Referring to the example embodiments shown in  FIGS. 5B, 5C, 5D, 5E and 6A, 6B, 6C , in an example embodiment, there is provided a kit of parts. The kit of parts can include: a plurality of rigid elements of different sizes, shapes, and/or weights, each rigid element comprising weight that is unitary with the respective rigid element, each rigid element and associated weight defining a different moment of inertia. 
         [0056]    Depending on the particular desired situation and desired moment of inertia, the appropriate rigid element can be selected and then mounted to the helmet  20 . Greater or lesser moments of inertia can be effected by replacing the present rigid element with a different rigid element. 
         [0057]    Variations may be made to some example embodiments, which may include combinations and sub-combinations of any of the above. The various embodiments presented above are merely examples and are in no way meant to limit the scope of this disclosure. Variations of the innovations described herein will be apparent to persons of ordinary skill in the art, such variations being within the intended scope of the present disclosure. In particular, features from one or more of the above-described embodiments may be selected to create alternative embodiments comprised of a sub-combination of features which may not be explicitly described above. In addition, features from one or more of the above-described embodiments may be selected and combined to create alternative embodiments comprised of a combination of features which may not be explicitly described above. Features suitable for such combinations and sub-combinations would be readily apparent to persons skilled in the art upon review of the present disclosure as a whole. The subject matter described herein intends to cover and embrace all suitable changes in technology.