an illustrative embodiment of the exercise device 10 according to the invention includes two principal parts , as shown in fig1 and fig2 : a rotatable base 20 having a central opening 23 , and a bar 50 equipped with hand grips 21 a and 21 b ( preferably of rubber or other elastic material ) removably insertable into the central opening . the rotatable base 20 includes a lower base section 22 that rests upon an exercise surface . the rotatable base 20 also includes an upper base section 24 rotatably mounted on the lower base section 22 . the rotation of the upper base may be provided by conventional ball bearings captured in races . preferably the lower base section 22 and the upper base section 24 are round , generally flat pieces ; and in some embodiments the upper base section 24 is a round , generally flat piece about 41 to 46 centimeters or about 16 to 18 inches in diameter , with the height of the base being about 3 . 8 cm or about 1 . 5 inches . the rotatable base 20 has a central opening 23 in its upper surface with a bar releasably inserted therein . the bar 50 fits within the opening 23 so that the bar may be moved relative the rotatable base 20 . the bar 50 or the opening 23 ( or both ) may be fitted with a rubber or other conformable surface ; this may take the form of a thimble - shaped insert or boot 30 , preferably of rubber or other elastic material , placed within the opening 23 . the opening 23 is formed in the upper surface of the upper base section 24 and is a depression of sufficient depth to aid the user in maintaining the position of the bar 50 in the depression if so desired for a particular exercise . the upper base section 24 may be mounted on the lower base section 22 by means of conventional bearings and races and is secured to the lower base section by bolt 34 and nut 32 , or alternatively means of clips or screws , to prevent the upper base section 24 from separating from the lower base section 22 . in the embodiment illustrated in fig1 and fig2 , the bolt 34 and nut 32 are augmented by washer 36 and spacer 38 . optionally bearings and races are supported by frame 26 . optionally lower base section 22 has a ribbed pattern and includes circular channels 23 a , 23 b , and 23 c in which bearings from frame 26 will run . optionally the lower base section 22 may include a support frame for supporting a plurality of bearings for rotatably supporting the upper base section on the lower base section . optionally the top surface of base 20 is topped by contoured rubber pad 28 . the user may exercise by placing the rotatable base 20 on an exercise surface , standing on the rotatable base 20 , and inserting the bar 50 into the central opening 23 . the user twists his or her upper body and lower body relative to one another ; while doing so with the bar 50 inserted in the central opening 23 , the user may use the bar 50 to aid balance or to aid the relative twisting of the upper and lower body . the user may also remove the bar 50 from the central aperture 23 and use movement of the bar 50 to provide additional exercise for user &# 39 ; s upper body . optionally , as shown in fig3 a and 3b , a bar 90 may comprise a first releasably coupled bar segment 92 and a second releasably coupled bar segment 94 , with the coupling device comprising a spring - loaded protruding button 96 that mates with an aperture 98 to fasten the two segments together . also optionally , the bar 90 may include hand grips 91 a and 91 b . the bar segments 92 and 94 may in other embodiments be connected by other means . optionally , as shown in fig4 and fig5 , male threaded coupling 76 at one end bar segment 72 is fitted to a corresponding threaded coupling 78 of bar segment 74 . optionally and again as shown in fig4 and fig5 , the bar 70 may include additional weights 80 and 82 , which are circular disks each having a central aperture allowing them to be slipped over male threaded coupling 76 and secured between bar segments 72 and 74 . the lengths and weights of the bar segments 72 and 74 may be essentially identical or may differ significantly . for example , each bar segment may be about 76 cm to 100 cm or about 2 . 5 to 3 feet in length , with a total assembled bar length of about 150 to 200 cm or about 5 to 6 feet . a first bar segment may weigh about 0 . 9 kilograms or 2 pounds and be supplied with a second bar segment weighting about 2 . 3 kg or about 5 pounds . bar segments that are relatively close in length and weight are preferred for allowing the user to hold one bar segment in each hand ; bar segments that differ significantly in length or weight allow the user to use only one bar segment or the other to provide a desired weight and length for exercising . optionally the device may include a conventional timer or calorie counter of the type that calculates a number of calories burned based on the user &# 39 ; s weight and elapsed exercise time . optionally , the device may include a counter that displays the number of “ twists ” or movements completed by the user . if a timer , calorie counter , or other counter is provided , a display 65 , as shown in fig4 , or a display 125 , as shown in fig6 , may be mounted on the base or elsewhere . preferably the upper base section 22 and the lower base section 24 are constructed from aluminum , plastic , or other sturdy material , with the upper surface of the upper section having a surface providing some traction for the feet of the user , such as provided by use of a friction material such as rubber pad 28 shown in fig1 and fig2 , or by use of protrusions , depressions , grooves , as shown in fig6 , or other contours formed on the surface . an alternative embodiment of a base 120 is shown in fig6 . in that embodiment , opening 123 could have a depth of less than 1 . 3 cm , or about 0 . 5 inches . while the invention has been described by illustrative embodiments , additional advantages and modifications will occur to those skilled in the art . therefore , the invention in its broader aspects is not limited to specific details shown and described herein . modifications may be made without departing from the spirit and scope of the invention . for example , modifications may be made to the weight or length of bar segments , to the size of the rotatable base sections ; to the mechanism used to support the upper base section on the lower base section or to couple those two sections together ; and to the materials of construction . accordingly , it is intended that the invention not be limited to the specific illustrative embodiments , but be interpreted within the full spirit and scope of the appended claims and their equivalents .
a device for exercising the abdominal and other core muscles of a user comprises a rotatable base having a central opening therein , and a bar removably insertable into the opening . the bar may comprise two or more separable segments and may have provide for the attachment and removal of weights to provide resistance to a user . also disclosed is a method of exercising using such a device .