Flexible dumbbell

A flexible dumbbell comprises a cylindrical body of elastic material such as rubber formed in predetermined length and diameter suitable for various kinds of physical exercises or running, and a flexible core element of predetermined weight suitable for a user's physique contained within the cylindrical body to provide radial resiliency of the dumbbell. The cylindrical body is closed in an appropriate manner at the opposite ends thereof to retain the core element in place.

BACKGROUND OF THE INVENTION 
The present invention relates to a dumbbell for use in various kinds of 
sports, and more particularly to a flexible dumbbell suitable for use in 
physical exercises, running or the like. 
A conventional dumbbell is made of cast iron, which is used by grasping the 
central portion thereof to train muscles of a wrist, an arm, a shoulder 
and the like. In case a user grasps one end of the dumbbell and swings its 
other end at a constant rhythm in a vertical direction, he will feel a 
pain at his carpal bones due to excessive weight of the dumbbell acting on 
his arm joint. In case a user grasps the central portion of the dumbbell 
and swings it in running, the weight load of the dumbbell acting on his 
wrist, arm and shoulder will increase due to his feet impacting on the 
ground to cause muscle binding of his swing arm. For these reasons, the 
dumbbell of cast iron is unsuitable for use in physical exercises, running 
and the like. Furthermore, the dumbbell of cast iron will injure the 
user's hand or an adjacent instrument in its careless use, and in winter 
the user will hesitate to use the dumbbell of cast iron because of a cold 
feel. 
SUMMARY OF THE INVENTION 
It is, therefore, the primary object of the present invention to provide a 
flexible dumbbell suitable for use in various kinds of physical exercises, 
running and the like and in its use capable of effecting appropriate shock 
absorption and excitement on the user's wrist, arm and shoulder. 
Another object of the present invention is to provide a flexible dumbbell 
which is adjustable in weight suitable for user's physique in the same 
size. 
According to the present invention, the foregoing objects are accomplished 
by providing a flexible dumbbell which comprises a cylindrical body of 
elastic material such as rubber formed in predetermined length and 
diameter suitable for various kinds of physical exercises, a flexible core 
element of predetermined weight suitable for a user's physique contained 
within the cylindrical body to provide radial resiliency of the dumbbell, 
and means for closing the opposite ends of the cylindrical body to retain 
the core element in place. It is preferable that the flexible core element 
consists of a number of metallic plates assembled longitudinally in a 
predetermined length within the cylindrical body. Alternatively, the 
flexible core element may be a single molded core element of rubber mixed 
therein with an amount of metallic powder. The flexible dumbbell may be 
modified in the form of a flexible dumbbell which comprises a cylindrical 
body of elastic material such as rubber formed in a piece with a pair of 
end walls, a flexible core element of predetermined weight contained 
within the cylindrical body and retained in place by engagement at its 
opposite ends with the end walls of the cylindrical body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, FIG. 1 illustrates a flexible dumbbell 20 
which comprises a cylindrical body 21 of elastic material such as rubber, 
a core element 10 of predetermined weight contained within the cylindrical 
body 21, and a pair of end caps 22, 22 secured to the opposite ends of 
cylindrical body 21. The core element 10 consists of a number of iron 
disks 11 each of which has a predetermined thickness T.sub.1. The iron 
disks 11 are assembled longitudinally in a predetermined length L.sub.1 
and radially displaceable in the cylindrical body 21 to effect an 
appropriate resiliency of the dumbbell 20. As can be well seen in FIG. 2, 
the cylindrical body 21 is formed at its inner wall with longitudinal ribs 
21a which are circumferentially equi-spaced to provide first air gaps 
A.sub.1 between the outer periphery of the core element assembly 10 and 
the inner periphery of cylindrical body 21. Each of end caps 22 is made of 
relatively hard rubber and is formed at its inner end wall with annular 
ribs 22a which are concentrically arranged to provide second air gaps 
A.sub.2 at each end of the core element 10. 
In such a construction as described above, the total weight of the flexible 
dumbbell 20 can be adjusted by replacement of the core element 10 with 
another core element assembly each disk of which is different in weight 
from the iron disk 11. For example, in the case that heavy metallic disks 
are adapted to the core element 10, the flexible dumbbell 20 is provided 
as a heavy dumbbell in the same size. When the flexible dumbbell is 
grasped by a user at its one end or central portion and swung up and down, 
the disks 11 of core element 10 displace slightly in a radial direction to 
cause appropriate flexure of the dumbbell 20 at its other end or opposite 
ends. This effects appropriate resiliency and shock absorption on the 
user's wrist. In use of the flexible dumbbell 20, the elasticity of 
cylindrical body 21 is useful to eliminate a feel of cold to the user in 
winter and to prevent an adjacent instrument from damage caused by 
abutment with the dumbbell 20. Furthermore, the provision of the air gaps 
A.sub.1 and A.sub.2 in the dumbbell 20 is useful to enhance the 
advantageous effects described above. 
In FIG. 3 there is illustrated a modification 120 of the flexible dumbbell 
which comprises a cylindrical body assembly 121 and a flexible core 
element 110 contained within the cylindrical body assembly 121. The core 
element assembly 110 consists of a number of lead disks 111 each of which 
has a predetermined thickness T.sub.2. The lead disks 111 are assembled 
longitudinally in a predetermined length L.sub.2 and radially displaceable 
in the cylindrical body assembly 121 to provide an appropriate resiliency 
of the dumbbell 120. The cylindrical body assembly 121 is closed by a pair 
of end caps 122, 122 adhered to the opposite ends thereof. The cylindrical 
body assembly 121 includes an outer cylindrical member 121A of rubber and 
an inner cylindrical member 121B of sponge rubber. The outer cylindrical 
member 121A is formed at the opposite end portions thereof with a pair of 
annular projections 121a, 121a, while each of end caps 122, 122 is made of 
relatively hard rubber and formed at its inner wall with an annular recess 
122a which is coupled with each annular projection 121a of cylindrical 
body 121. Furthermore, a soft rubber disk 123 is interposed between each 
inner wall of end caps 122, 122 and each end of the core element 110. In 
such a construction of the dumbbell 120, the inner cylindrical member 121B 
and the soft rubber disks 123 are useful to provide advantageous effects 
substantially as same as those in the dumbbell 20 of FIG. 1, and the lead 
disks 111 heavier than the iron disks 11 are adapted to form the dumbbell 
120 in a smaller size. 
FIG. 4 illustrates another modification 220 of the flexible dumbbell which 
comprises a flexible core element 210 contained within a single 
cylindrical body 221 of elastic material such as rubber. The core element 
210 consists of a number of iron disks 211 each of which has the same 
thickness T.sub.1 as that of disk 11 in the dumbbell 20 of FIG. 1. The 
iron disks 211 are assembled longitudinally in the same length L.sub.1 as 
that of the core element 10 in the dumbbell 20 and radially displaceable 
in the cylindrical body 221. In this modification, the disks 211 are 
respectively formed with a central hole 211a through which a core rod 230 
is inserted during the process of molding the cylindrical body 220. The 
core rod 230 is previously inserted into the central holes 211a of disks 
211 in an appropriate manner and positioned in a molding die (not shown). 
Subsequently, an amount of raw rubber material is put into the molding die 
and sulfurized, and thereafter the core rod 230 is drawn out of the 
molding die to complete the dumbbell 220. In such a construction described 
above, the iron disks 211 with central through holes 211a are adapted to 
form the dumbbell 220 in light weight but yet in the same size as that of 
the dumbbell 20 of FIG. 1. 
In the actual practices of the present invention, the cylindrical body 21, 
121 or 221 may be formed at its outer periphery with nonskid treatments 
such as straight, mesh or bias pattern ridges, and the metallic disks 11, 
111 or 211 may be replaced with multiangular plates of different thickness 
or weight. The metallic core element 10, 110 or 210 may be also replaced 
with a predetermined amount of metallic particle and/or powder. In the 
actual practices of the dumbbell 20 of FIG. 1, the iron disks 11 located 
at an intermediate portion of the dumbbell may be replaced with disks of 
wood, synthetic resin, light weight metal or the like, while the iron 
disks 11 located at the opposite end portions of the dumbbell may be 
replaced with a pair of heavy metallic blocks. Alternatively, the iron 
disks 11 located at the intermediate portion of the dumbbell may be 
replaced with an amount of sand, light weight metallic particle or powder, 
while the iron disks 11 located at the opposite end portions of the 
dumbbell may be replaced with heavy metallic disks such as lead disks. It 
is further noted that the cylindrical body may be modified in its 
peripheral wall thickness and its outer configuration to enhance the 
design of the dumbbell. 
In FIG. 5 there is illustrated another flexible dumbbell in accordance with 
the present invention which comprises a single molded flexible core 
element 320 contained within a flexible cylindrical body 321 which is 
provided at the opposite ends thereof with a pair of end caps 322 adhered 
thereto. The single molded flexible core element 320 is made of rubber 
mixed therein with an amount of heavy metallic powder, and the cylindrical 
body 321 is made of elastic material such as rubber. The end caps 322 are 
also made of soft synthetic resin. The cylindrical body 321 has a circular 
cross-section, and its length and diameter are respectively determined in 
appropriate dimension for use in physical exercises or running. 
Preferably, the heavy metallic powder is selected from lead monoxide 
(PbO), lead red (Pb.sub.3 O.sub.4) or barium sulfate (BaSO.sub.4). During 
the process of manufacturing the flexible core element 320, a 
predetermined amount of raw rubber material is mixed therein with an 
amount of the heavy metallic powder (PbO, Pb.sub.3 O.sub.4 or BaSO.sub.4) 
and is sulfurized in a molding die. In this instance, the maximum amount 
of the heavy metallic powder mixed in the raw rubber material should be 
determined to obtain appropriate flexibility of the core element 310. For 
example, in manufacturing of a flexible core element of approximately 26 
cm in length, 3.6 cm in diameter and 260 ml in volume, the maximum amount 
of the heavy metallic powder has been determined to be 52% in volume 
ratio. In use of lead monoxide (PbO), a flexible core element of 1.6 kg in 
weight has been obtained, and in use of barium sulfate (BaSO.sub.4), a 
flexible core element of 1.0 kg has been obtained. 
From the above description, it will be understood that a flexible core 
element of different weight in the same size can be manufactured by 
selection of kinds of the heavy metallic powder and its amount. That is to 
say, lead monoxide is useful to obtain a flexible core element of maximum 
weight, and barium sulfate is useful to obtain a flexible core element of 
minimum weight. Additionally, the raw rubber material for the flexible 
core element may be replaced with thermoplastic elastomer . In use of 
thermoplastic elastomer, the core element can be formed by injection 
molding or extrusion molding without any sulfurizing process. 
Having now fully set forth preferred embodiments of the concept underlying 
the present invention, various other embodiments as well as certain 
variations and modifications of the embodiments herein shown and described 
will obviously occur to those skilled in the art upon becoming familiar 
with said underlying concept. It is to be understood, therefore, that 
within the scope of the appended claims, the invention may be practiced 
otherwise than as specifically set forth herein.