Three-dimensional rocking chair with variable curvature base for abdominal exercise

An omnidirectional rocking chair for abdominal exercise has a rectangular support base with a convex lower support surface with variable radii of curvature. The chair back supports only the user's lower back. Rocking the chair develops outward momentum in the mass of the user's upper back, arms and head. The minimum lower support surface radius of curvature is in its central portion and the center of that curvature is above the center of gravity of the seated user and chair. The peripheral portions of the lower support surface have larger radii of curvature. The corner portions of the lower support surface have maximum radii of curvature. The effect of progressive increase in support surface radius of curvature is to increase righting moment in the rocking motion where the respective larger radii portions contact the floor. This acts to decelerate outward rocking motion in the chair seat and user's lower back in opposition to the developed outward momentum in the mass of the user's upper back, arms, and head, which engages user abdominal trunk muscles.

BACKGROUND OF THE INVENTION

The present invention relates to rocking chairs and abdominal exercise apparatus. In the prior art of rocking chairs, it is long known that it is the arcuate form of the rockers contacting a floor that provides the characteristic rhythmical user experience. Here the vertical distance between the seated user center of gravity and the rocker center of curvature functions as a pendulum with a specific natural frequency of oscillation. This is how rocking chairs continue to rock back and forth between user actuations, as does a swinging pendulum. The continuity of this motion is what adds valuable vestibular stimulation to the user experience.

The object of the chair invention disclosed here is to provide an exercise means to maintain or improve abdominal core strength in a low-intensity, comfortable, and secure way. Chronic lower back pain and increased fall risk with age have significant negative impacts on quality of life. Exercises to increase abdominal core strength are known to mitigate both. The chair's enjoyable natural rocking rhythm with vestibular stimulation makes the exercise easier to perform for long periods of time, for example while watching television. For infirm persons, it may be performed without constant professional assistance once seated.

The improvement of the present invention is in the particular form of a three-dimensional chair base that can rock in all directions, with distinct radii of curvature in the central, peripheral and corner portions.

In the prior art, U.S. Pat. No. 5,887,944 to Boost discloses a chair with a round base and a ballast member under the seat. The ballast member prevents the chair from tipping over during use. U.S. Pat. No. 3,041,070 to Kerstein discloses a hemispherical shell compartment for multiple users, also with ballast to keep the shell upright. U.S. Pat. No. 4,084,273 to Hayes disclosed a playpen for children with a round spherical base. The round and hemispherical base shapes of these inventions also rock in all directions, but do not have distinct radii of curvature in the central, peripheral and corner portions.

In a non-chair balancing device, U.S. Pat. No. 7,494,446 to Weck et al. discloses a spherical bladder attached to a platform, the so-called “BOSU BALL”. Users may invert this devise and stand upon the platform with the spherical bladder contacting the floor. In this position the devise is inherently unstable and requires dynamic user body control to keep upright, and so is not suitable for long duration exercise sessions.

U.S. Pat. No. 4,595,234 to Kjersem discloses a chair base with two straight sections at an angle to each other and a fulcrum portion between them. A user may tip the chair to rest upon one section or the other, but this action does not provide a continuous rocking motion with a natural frequency of oscillation.

The related prior art also includes tipping devices with circular bases as disclosed in U.S. Pat. No. 5,643,165 to Klekamp and US Pat. Appl. 2003/01646633A by Jakus et al. These have in common a round base platform with a central downward projection. A user may tip them from one side of the base platform circumference to another, or roll around the central projection so the central vertical axis sweeps a conical path. These devices also do not provide the aesthetic benefit of a natural rocking motion.

U.S. Pat. No. 9,586,084 to Duke discloses a rocking chair with conventional two dimensional motion with rockers with an increased radius of curvature only in their rear portions.

SUMMARY OF THE INVENTION

The chair of the present invention supports only the user's lower back, and has a preferably rectangular base to enable a three dimensional rolling motion rather than the two dimensional motion in the longitudinal plane of a conventional rocking chair. The lower base surface has a distinct variable radius of curvature shape. First, the minimum base radius of curvature is in the central portion. Here the height of the center of this minimum radius of curvature is above the center of gravity of the seated user and chair, which provides an integral positive righting moment without added ballast. Second, the form of the base transitions smoothly to a larger radius of curvature outside the central portion, which progressively increases the chair righting moment with greater angles of inclination in all directions. Within this portion, the radii of curvature in the transverse sectors is less than in the forward and rear sectors. Lastly, the maximum radius of curvature is in the corner portions of the base rectangle. When a user rolls forward and back along a side portion of the base, this provides an increase in transverse righting moment when the corner portions of the chair base contact the floor.

In operation, the above low righting moment in the central portion facilitates initiation of rolling motion by some user body movement. This develops momentum in the user's upper body. The above progressive peripheral increase in righting moment then decelerates that rocking motion. This deceleration is translated from the chair seat to the user's lower back. The user's abdominal trunk muscles are then engaged in translating that deceleration from the user's lower back to the user's upper back. This abdominal trunk muscle engagement is an isometric reaction type without potentially injurious large angle spinal flection. The above increase in transverse righting moment when the corner portions of the chair base contact the floor has a particular benefit in strengthening lateral abdominal muscles, which are critical to user fall prevention reflexes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows a perspective view of the chair with a floor5upon which a base8rests. Base8has a forward end10, an aft end11, a left side12, a right side13not shown, an upper base surface14and a lower base surface15not shown. Upper surface14supports a forward left leg20, a forward right leg22, an aft left leg24, and an aft right leg26. A transverse handle tube30projects through an upper portion of forward left leg20and an upper portion of forward right leg22. The left end of handle tube30supports a left hand grip32and the right end of handle tube30supports a right hand grip34not shown. The upper ends of legs20,22,24, and26support a user body support surface40with a seat portion42and back portion44.

FIG. 2is a left side view of the invention further showing lower base surface15. A forward chine54is at the intersection of front end10and lower base surface15. An aft chine56is at the intersection of aft end11and lower base surface15. The side projection of lower base surface15is a compound curve tangent to floor5. The longitudinal axes of hand grip32and hand grip34not shown are substantially parallel to the plane of seat portion42. The plane of seat portion42is inclined upward-forward at an angle of approximately 21 degrees with respect to upper base surface14. The lower section of back portion44is inclined upward-aftward approximately perpendicular to seat portion42, and the upper section of back portion44curves convexly aftward to follow the lordosis curve of the lumbar region of the back of a typical user. The upper extent of the back portion44is approximately to the top of the lumbar region of the back of a typical user. The thoracic region of the back of a typical seated user therefore extends above the top of back portion44.

FIG. 2further shows the side view projection of the forward-aft complex curvature of lower base surface15, where the tangent contact between lower base surface15and floor5is within a central segment of lower base surface15bound by a pair of radial rays X1and X2. The position of user body support surface40is such that the center of gravity of a seated user with feet held above floor5is substantially above this central segment of lower base surface15. An angle S is the angle between rays X1and X2. A radius A is the radius of curvature of the forward-aft silhouette of lower base surface15within the segment bound by rays X1and X2. Rays X1and X2originate at the center of radius A. A radius B is the radius of curvature of the forward-aft silhouette of lower base surface15forward of ray X1. A radius C is the radius of curvature of the forward-aft silhouette of lower base surface15aft of ray X2. The length of radius A is less than the lengths of radii B and C. The portion of lower base surface15bound by rays X1and X2is tangent to both the adjacent portion forward of ray X1and the adjacent portion aft of ray X2. A left chine50is the intersection of left side12and lower base surface15. A right chine52not shown is the intersection of right side13and lower base surface15. Left chine50and right chine52are substantially symmetric with respect to the chair's forward-aft vertical centerline plane. A radius D is the radius of curvature of chine50within the segment bound by rays X1and X2. A radius E is the radius of curvature of chine50forward of ray X1. A radius F is the radius of curvature of chine50aft of ray X2. The length of radius D is less than the lengths of radii E and F. Transversely, the length of radius A is less than the length of radius D, the length of radius B is less than the length of radius E, and the length of radius C is less than the length of radius F.

FIG. 3is a front view further showing right base side13, right hand grip34, and right chine52. The front projection of base8shows the transverse complex curvature of lower base surface15, where a central segment of lower base surface15is bound by a pair of radial rays Y1and Y2. An angle T is the angle between rays Y1and Y2. A radius J is the radius of curvature of the transverse silhouette of lower base surface15within the segment bound by rays Y1and Y2. Rays Y1and Y2originate at the center of radius J. A radius K is the radius of curvature of the transverse silhouette of lower base surface15rightward of ray Y1. A radius L is the radius of curvature of the transverse silhouette of lower base surface15leftward of ray Y2. Radius K is substantially equal to radius L. The length of radius J is less than the lengths of radii K and L. The portion of lower base surface15bound by rays X1and X2is tangent to both the adjacent portion rightward of ray Y1and the adjacent portion leftward of ray Y2. Chine54and chine56are substantially straight.

In the preferred embodiment radius A is less than radius J and angle S is greater than angle T.

FIG. 4shows a bottom view of the chair with a series of dashed equal vertical interval contour lines60,62,64,66, and68on lower base surface15. In the central lower portion of lower base surface15, contour lines60and62are elongated transversely, reflecting the relation of radius A less than radius J. Next upward, contour line64transitions to a quasi-rectangular form with straighter longitudinal and straighter transvers portions. Further upward, contour lines66and68intersect base sides12and13and are progressively straighter closer to chines54and56. Contours60,62,64,66, and68indicate how, in the preferred embodiment, the fabrication of lower base surface15is a lofted three dimensional shape that conforms to the particular side and front projection views shown inFIG. 2andFIG. 3respectively. Those views show tangent transitions from distinct smaller radii of curvature in the central portion of lower base surface15to larger radii of curvature in the peripheral portions. In an alternative embodiment, the form of lower base surface15may be specified as a blended loft of continuously variable radii of curvature.

In the preferred embodiment, the lowest portion of body support surface40is nine inches above floor5, and the above measures of the complex curvature of base surface15are as follows: Angle S equals twelve degrees, radius A equals twenty-one inches, radii C and B equal thirty inches, radius D equals 53 inches, radii E and F equal fifty-five inches, angle T equals 6 degrees, radius J equals 25 inches, and radii K and L equal 35 inches.

In the preferred mode of operation, a user sits upon support surface40and extends her or his legs to hold her or his heels above floor5. In that stationary position, upper base surface14is substantially horizontal and the point of tangent contact between lower base surface15and floor5is within the area of base surface15bounded longitudinally between rays X1and X2and transversely between rays Y1and Y2, as shown inFIGS. 2 and 3. While a user is comfortable is this stationary position, there is an isometric exercise benefit in supporting the cantilever loads of his or her leg extension forward of seat portion42and his or her thoracic back extension aft of the top end of the inclined back portion44.

A user then acts to shift her or his center of gravity horizontally. This action may result from one or a combination of the following motions: Tipping the head forward, aftward or sideward, extending one or both arms forward, aftward or sideward, retracting the legs, swinging one or both legs sideward, flexing the abdominal muscles to pull the upper body forward, grasping hand grips32and34and exerting a same direction horizontal or vertical force to which the upper body reacts by tipping forward, aftward or sideward, and grasping hand grips32and34and exerting respective opposing horizontal or vertical forces, which develops a force couple to which the upper body reacts by tipping forward, aftward or sideward. Because the radius of curvature of lower base surface15is smallest within its central portion bound by rays X1, X2, Y1, and Y2, the above shift in user center of gravity easily initiates a chair rocking motion of lower base surface15upon floor5away from the above initial stationary position. This chair rolling motion then develops forward, aftward, or sideward horizontal momentum in the user's upper body mass above the top of seat back44.

Next, the above chair rolling motion shifts the point of tangent contact between base surface15and floor5to a peripheral portion where the radius of curvature of base surface15is greater than within the central portion bound by rays X1, X2, Y1, and Y2. This larger peripheral radius of curvature increases the gravitational righting moment on the chair, which is a restoring force that acts to arrest the above forward, aftward, or sideward rolling motion. This increased restoring force translates from the chair to the user's lower body through the body's sitting connection to support surface40. At this moment, one or more of the user's abdominal core muscles then contract to translate this increased restoring force from the user's lower body to the user's upper body. This abdominal core muscle engagement is greater than it would be if the curvature of lower base15were constant. In this way, a first benefit of the chair's variable curvature base is increased abdominal muscle engagement in upper body mass deceleration.

Human muscles react dynamically as springs. In the above initial chair roll, after the forward, aftward or sideward upper body momentum has been opposed, the same muscle contraction causes a small angle deflection of the user's abdomen in the opposite direction, which then shifts the user's center of gravity to initiate the next roll in the opposite direction. In this way, a second benefit of the chair's variable curvature base is to help establish a rhythmical cycle of to and fro rolling, which is inherently enjoyable.

A third benefit of the chair's variable curvature base is the consequent restriction of the amplitude of the above to and fro rolling cycle, which enhances actual and perceived user security in the chair.

The above listed multiple means by which a user may shift her or his center of gravity, combined with the freedom to roll the chair in any direction, provide a diverse set of potential exercise routines.

A particular exercise that benefits from the chair's variable curvature base results in a quasi-rectangular motion about the chair's vertical axis. Here there is a particular benefit in lateral trunk muscle engagement due to the reduction in lower base15curvature adjacent to forward end10and aft end11, near where chines54and56are straight. In this mode of operation, the user initially tips the chair to a first side, and then initiates a rocking motion along that side. The transverse radius of curvature along the sides is less at the ends of the base than in its midsection, as radii K and L transition to straight chines54and56. Therefore, when rocking along one side, as the user's forward or aftward motion stops, the radius of curvature of lower base15at its point of contact with floor5is less in the transverse direction than in the forward-aft direction. This results in an abrupt reverse tip to the opposite side, which engages the lateral core muscles to accelerate the user's upper body towards the opposite side. The return longitudinal rocking motion is then veers to that opposite side. Continuation of this exercise results in a quasi-rectangular motion. The user may alternate this cycle in clockwise and counter-clockwise directions with or without use of handles32and34.

The chair primarily engages abdominal core muscles to oppose horizontal momentum in the user's upper body that results from the chair's rolling motion. This has a significant advantage to persons with spinal injuries or back pain, because it does not require large angle spinal flexure and the user's vertebrae remain within their neutral zone of relative motion. The spine as a whole moves with the chair. This is in contrast to crunch type exercises in which the abdominal muscles act to bend the spine. A related advantage of this mode of core engagement is in fall prevention. Here the controlled rolling motion of the whole upper body in the chair is geometrically similar to sway in a person's upper body that may presage a fall. In using the chair, the neurological pathways that act to stabilize the spine are repeatedly used to resist the rolling induced upper body momentum. These are the same neurological pathways activated in balance keeping reflexes. In these ways, the chair both strengthens muscles needed to keep balance and trains the neurological reflexes that activate them.

A further engagement of a user's abdominal core muscles is in the abdominal reaction to arm extension and contraction when pulling or pushing on hand grips32and34.