Leg exercise machine

A leg exercise machine includes a frame having a seat connected thereto for supporting a user in a seated position thereon. A foot engaging member is adapted for engaging the feet of a user and receiving force from the user leg. The foot engaging member is pivotally mounted on the frame by a four-bar linkage which includes first and second lever arms pivotably mounted on the frame. The pivotal mounting of the lever arms provides for back and forth movement along a path of travel and about an instantaneous (changing) axis of rotation for changing the angle of inclination of the foot engaging member so that a force substantially normal to the foot engaging member is directed substantially up the leg and tibia during corresponding movement of the user. The second lever arm is operatively connected to a weight stack for transmitting the pivotal back and forth movement of the leg engaging member to movement of the weight stack to thereby exercise the legs of a user.

FIELD OF THE INVENTION 
This invention relates to a leg exercise machine, and more particularly, to 
a leg exercise machine having a foot engaging member, in the form of a 
footboard, movable along an eccentric path of travel about an 
instantaneous (changing) axis of rotation so that the angle of inclination 
of the foot engaging member is constantly changed wherein forces are 
directed only up the lower leg and tibia of a user during corresponding 
movement of the footboard by the user. 
BACKGROUND OF THE INVENTION 
On most prior art exercise machines, when exercising the leg muscles, the 
user engages a foot engaging member, typically in the form of a plate or 
footboard on which the user rests his feet, and exerts back and forth 
movement thereagainst for exercising the legs. The foot engaging member is 
operatively connected to a resistance in the form of a stack of metal 
plates for providing resistance against movement of the foot engaging 
member during exercise movement Typically, during movement, as the leg 
extends and pushes the foot engaging member along its eccentric path of 
travel, the angle of inclination of the lower leg and tibia constantly 
changes. 
Heretofore, most prior art machines for exercising the leg have been 
constructed to include a foot engaging member which is movable in a back 
and forth somewhat arcuate or eccentric path of travel where the rate of 
angle change of the foot engaging member during pivotal movement is 
substantially constant so that the imposed forces are not properly 
directed up the lower leg and tibia. For example, in commonly assigned 
U.S. Pat. No. 4,511,137 to Jones, the foot engaging member is attached to 
the lower portion of a lever arm. The lever arm is pivotally mounted in a 
medial location thereon between two frame members. During back and forth 
exercise movement, the lever and foot engaging member attached thereto 
rotate about a fixed axis of rotation. The maximum exercise efficiency is 
not obtained because during extension and retraction of the lower leg 
during exercise, the forces normal to the footboard and exerted against 
the leg are not always exerted up the lower leg and tibia. The 
semi-circular movement of the foot engaging member does not compensate for 
the constantly changing angle in movement of the lower leg and tibia 
during exercise. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a leg 
exercise machine which overcomes the deficiencies of the prior art. 
Another object of the present invention is to provide a leg exercise 
machine which includes a foot engaging member adapted for engaging the 
feet of a seated user and receiving force from the legs for exercising the 
legs, and wherein the foot engaging member is movable along a back and 
forth path of travel so that an instantaneous (changing) axis of rotation 
is generated for changing the angle of inclination of the foot engaging 
member so that a force substantially normal to the foot engaging member is 
directed substantially along the lower leg and tibia during corresponding 
movement of the legs of the seated user. 
The leg exercise machine in accordance with the present invention includes 
a frame and a seat connected to the frame for supporting a user in a 
seated position thereon. The seat is slidably mounted on the frame for 
varying the distance of the seat from the foot engaging member for varying 
the range of starting positions of a user seated on the frame. 
First and second substantially vertically extending lever arms are 
pivotally mounted at their lower ends on the frame in spaced relation to 
each other. A support shaft is transversely mounted on the upper end of 
each lever arm. Each shaft is approximately equal in length and has 
aligned opposing ends. A pair of spaced, substantially parallel support 
arms are pivotally mounted on the support shafts and are mounted so that 
the distance between the lower lever arm ends is greater than the distance 
between the upper lever arm ends so that when the lever arms are pivotally 
moved in a back and forth movement, the motion of the lever arms defines 
an instantaneous (changing) axis of rotation. 
A foot engaging member, in the form of a footboard, on which the user rests 
his feet is fixed to the parallel support arms for engaging the feet of a 
user and receiving force from the legs of the user to pivot the first and 
second lever arms so as to move the footboard in a back and forth movement 
along a predetermined path of travel about an instantaneous (changing) 
axis of rotation. This movement changes the angle of inclination of the 
footboard so that a force substantially normal to the footboard is 
directed substantially along the leg and tibia during corresponding 
movement of the user. A shaft is rotatably mounted on the frame and a 
variable radius cam is fixedly mounted on the shaft for rotatable movement 
therewith. A chain is entrained about the variable radius cam and has one 
end is fixed to the cam and the other end is attached to the second lever 
arm. A sprocket is fixed to the shaft and rotatable therewith and includes 
a chain interconnecting the sprocket and resistance means in the form of a 
stack of weights. During back and forth movement of the footboard, the 
force exerted by a user's legs is transmitted to the stack of weights 
thereby lifting and lowering the stack of weights and exercising the legs 
of the user.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, there is illustrated a preferred embodiment 
of the leg exercise machine, broadly indicated at 10. As best shown in 
FIG. 4, the leg exercise machine includes a frame, broadly indicated at 
11, and having respective front and rear frame portions, broadly indicated 
at 12 and 14. The frame 11 includes a lower horizontal base frame 16 with 
two substantially parallel, horizontally extending side frame rails 18 
fixed in position to each other by reinforcing cross bars 22. Two inverted 
and parallel, upstanding, substantially U-shaped support braces 24 are 
fixed on the forward end of the side frame rails 18. The inverted, 
U-shaped support braces 24 incline downward toward the rear portion 14 of 
the machine and form legs 26 for supporting the front portion of the side 
frame rails 18 on a flat surface such as an exercise floor. Longitudinal 
transversely extending reinforcing braces 28 are fixed to the inverted 
U-shaped support braces 24 and provide rigidity thereto. Two substantially 
parallel and opposing lever arm mount braces 32 are affixed to the 
respective inverted, U-shaped support braces 24 and extend downward in a 
rearward direction. 
A larger, inverted, U-shaped weight support frame member 36 is fixed to the 
lower portion of the transversely extending braces 28 and extends upward 
adjacent the front portion 12 of the leg exercise machine 10. Resistance 
means is supported for vertical movement on the frame member 36 and 
includes a plurality of weight plates forming a weight stack 40 which is 
supported for sliding movement between the rear leg of the weight support 
frame member 36 and a vertically extending leg member 42 which is fixed at 
its upper end to the weight support frame member 36 by a transverse cross 
bar 44 fixed to the weight support frame member 36. The weight plates 40 
are supported for vertical sliding movement between the leg of the weight 
support frame member 36 and the vertically extending leg member 42 (FIG. 
5). Additionally, spaced guide rods (now shown) can be included for aiding 
sliding movement and preventing the weight stacks from falling. A vertical 
selector guide and weight lifting rod 46 extends through the center 
portion of the weight stack 40. The individual weight plates 40 in the 
weight stack are provided each with horizontal openings 48 for reception 
of a selector pin 50 so that varying amounts of weight can be selected by 
the user to be lifted and lowered when exercising with the machine. As 
shown in FIG. 1, a two-piece molded cover 52 is mounted on opposite sides 
of the inverted U-shaped weight support frame member 36 and includes a 
slot opening 54 for gaining access to the selector pin 50 and choosing a 
desired weight. 
A seat, illustrated broadly at 60 (FIGS. 1 and 4), is supported for 
longitudinal adjustable movement along the rear portion 14 of the frame 
11. The seat 60 includes a guide roller support member 62 having front 
guide rollers 64 and rear guide rollers 66 which are supported to roll 
along the upper surfaces of the side rails 18 of the base frame 16. As 
better illustrated in FIG. 1, upper side rail members 68 are affixed in 
spaced relation to the lower side rails 18 a distance about the diameter 
of the guide rollers 66 and 68 to provide additional stability to the 
guide rollers 66 and 68 and prevent the seat 60 from being raised from the 
frame. 
A pivot pin 70 extends through the guide roller support members 62 (FIG. 8) 
and has a lever bar 74 affixed thereto and rack teeth 76 for engaging 
teeth 78 positioned on a longitudinal support rack 80 fixed on the lower 
side rail 18 (FIGS. 6, and 8). A handle 72 extends through the guide 
roller support members 62 and has a lifting pawl 73 fixed thereto. The 
lifting pawl 73 is adapted to raise the lever bar 74 when the handle 72 is 
lowered. The guide roller support member 62 can be longitudinally adjusted 
in a position along the frame 11 by lifting the handle 72 to disengage the 
lever bar 74 rack teeth 76 from the teeth 78 of the longitudinal support 
rack 80 for allowing the guide roll support member to be rolled along the 
side frame rails 18. After the guide roll support member 62 has been 
longitudinally rolled to a desired position, the control handle 72 is 
raised to an intermediate position to move the rack teeth 76 of the lever 
bar 74 into engagement with the teeth 78 of the rack 80 and lock the seat 
60 in a desired position. The seat 60 can be moved forwardly, one tooth 78 
of the rack 80 at a time, by repeatedly raising the control handle 72 to 
the uppermost position. 
A seat frame, indicated broadly at 82, is supported by the guide roll 
support members 62 and includes a back support rest member 84 pivotally 
mounted on its lower end to the guide roll support members 62 (FIG. 8). A 
two-piece, adjustable, and vertically extending back support brace, 
indicated broadly at 86, includes a lower outer sleeve 88 and an upper 
inner movable member 90 received in the sleeve. The lower outer sleeve 88 
is pivotally mounted at its lower end to the guide roll support members 62 
and the upper end of members 90 is pivotably mounted to a clevis member 92 
fixed to the back support rest member 84. The back support brace 86 is 
adjustable in height by means of a selector pin 93 (FIG. 7) which can be 
removed out of guide holes for adjusting the extension distance of the 
upper inner member 90 relative to the lower outer sleeve member 88 and 
thus pivotally lowering and raising the same to a desired position for the 
back support rest member 84. An inclined buttock support frame member 94 
is mounted on the guide roll support members 62. Padded cushions 95 are 
attached to the buttock support frame member 94 and the back support rest 
member 84. 
A foot engaging member 100, in the form of a rectangular footboard, is 
adapted for engaging the feet of a user and receiving force therefrom for 
isolating and exercising the leg muscles. The footboard 100 is mounted for 
movement on the frame by a four-bar linkage which creates an instantaneous 
(changing) axis of rotation, as is conventional with four-bar linkage 
mechanisms. The four-bar linkage includes vertically extending first and 
second spaced lever arms 102, 104 which are pivotally mounted on 
respective lever arm shafts 106, 107, fixed at opposite ends to the lever 
arm mount braces 32. Respective first and second support shafts 108, 109 
extend through the upper ends of each lever 102 104. Each support shaft 
108, 109 is substantially similar in length and has its ends pivotably 
supported in a pair of spaced, substantially parallel support arms 110. 
The shafts 108, 109 and are mounted so that the distance between the lower 
first ends of the lever arms 102, 104 is greater than the distance between 
the upper second ends of the lever arms 102, 104. When the parallel 
support arms 110 are pivotally moved in a back and forth movement along a 
predetermined path of travel, the arm movement defines an instantaneous 
(changing) axis of rotation. The footboard 100 is affixed to the rear ends 
of the parallel support arms 110, and includes on one side thereof a 
handle 114 for grasping by a user and a bossed ridge 116 to define 
positions for left and right feet. 
Means operatively connects the second lever arm 104 to the weight stack 40 
for transmitting pivotal back and forth movement of the footboard 100 to 
movement of the weight stack to thereby exercise the legs of the user. 
This connecting means includes a force transmittance shaft 118 rotatably 
mounted between the lever arm mount braces 32. A variable radius cam 120 
is supported by the shaft 118 and rotatable therewith. A chain 122 is 
entrained about the variable radius cam 120 and has one end fixed to the 
variable radius cam 120 and the other end fixed to the reinforcing cross 
brace member 28. The chain 122 extends upward from the variable radius cam 
120 and is entrained about another idler sprocket and shaft assembly 124 
and extends upward around a clevis and sprocket assembly 126 affixed to 
the second lever arm 104. 
As better illustrated in FIG. 5, a sprocket 128 is fixedly mounted on the 
shaft 118 supporting the variable radius cam 120 and rotatable therewith. 
A second chain 130 is affixed at one end to the sprocket 128 and extends 
upward along the inverted U-shaped weight support frame member 36 and is 
connected at its other end to the weight lifting rod 46 extending through 
the weight plates 40. The second chain 130 passes over a pair of idler 
sprockets 132 supported above the transverse cross bar 44 (FIG. 6). For 
protecting a user or bystander from injury resulting from moving parts, 
and for general aesthetic appearance, a two-piece cover 134 extends over 
the parallel support arms 110 (FIGS. 1-3) and another two-piece cover 136 
also extends over and between the inverted U-shaped support braces 24. 
METHOD OF OPERATION 
In the use of the leg exercise machine, the user is positioned in the seat 
60. The user initially adjusts the longitudinal position of the seat 60 on 
the side rails by lowering the handle 72 and moving the lever bar rack 76 
out of engagement with the teeth of the support rack teeth 80. The user 
then moves and adjusts the seat and locks the seat in the desired 
position. The user selects the desired resistance by inserting the 
selector pin 50 into the desired opening 48 to engage the weight stack 40 
with the weight lifting rod 46. The user places his feet on the footboard 
100 and begins exercise by pushing against the footboard 100 and lifting 
the weight stack 40. During movement, the four-bar linkage mechanism, 
formed by first and second lever arms 102 and 104 keeps the forces 
directed axially up the tibia and lower leg substantially normal to the 
footboard 100 at all times. The instantaneous (changing) axis of rotation 
of the footboard 100 is varied by the four-bar linkage throughout the 
range of motion allowing the exercise machine to keep the forces properly 
directed as desired. The user repeats the cycle for as many repetitions as 
necessary during the exercise program. 
The present invention offers several benefits over other prior art exercise 
machines. The four-bar linkage structure of the lever arms generates an 
instantaneous (changing or moving) axis of rotation of the footboard 100 
so that the forces are directed axially up the lower leg and tibia at all 
times during an exercise movement. Thus, exercise efficiency is increased 
and the possibility of injury during the exercise movement is lessened 
because there is not a net force transverse to the muscle groups of the 
lower leg. Additionally, the seat can be adjusted longitudinally on the 
frame for varying the starting position of a user. This is especially 
beneficial for those users which are rehabilitating old injuries when the 
full range of exercise movement is not desirable. 
In the drawings and specification there has been set forth the best mode 
presently contemplated for the practice of the present invention and 
although specific terms are employed, they are used in a descriptive sense 
only and not for purposes of limitation, the scope of the invention being 
defined in the claims.