Systems and methods for adjusting a stiffness of fitness machines

Abstract

A system for adjusting a stiffness of a fitness machine operable by a user, the fitness machine having a base and a mobile portion that moves relative to the base during operation of the fitness machine. A resilient body resists movement of the mobile portion towards the base in a height direction. The resilient body has a length defined in a length direction that is perpendicular to the height direction. The length of the resilient body increases when the mobile portion moves towards the base. An actuator is operable to adjust a set maximum for which the length of the resilient body may extend during operation of the fitness machine. A resistance provided by the resilient body to resist movement of the mobile portion towards the base is unaffected by operation of the actuator when the length of the resilient body is less than the set maximum.

What is claimed is: 
     
         1 . A system for adjusting a stiffness of a fitness machine operable by a user, the fitness machine having a base and a mobile portion that moves relative to the base during operation of the fitness machine, the system comprising:
 a resilient body that resists movement of the mobile portion towards the base in a height direction, wherein the resilient body has a length defined in a length direction that is perpendicular to the height direction, and wherein the length of the resilient body increases when the mobile portion moves towards the base; and   an actuator operable to adjust a set maximum for which the length of the resilient body may extend during operation of the fitness machine, wherein a resistance provided by the resilient body to resist movement of the mobile portion towards the base is unaffected by operation of the actuator when the length of the resilient body is less than the set maximum.   
     
     
         2 . The system according to  claim 1 , wherein the resilient body includes an elastomer. 
     
     
         3 . The system according to  claim 1 , wherein the resilient body has a parabolic shape. 
     
     
         4 . The system according to  claim 3 , wherein the mobile portion is supported at least in part by a vertex of the parabolic shape of the resilient body. 
     
     
         5 . The system according to  claim 1 , wherein a first end of the resilient body is non-translatable relative to the base. 
     
     
         6 . The system according to  claim 5 , wherein a second end of the resilient body is translatable relative to the base in the length direction and non-translatable in the height direction. 
     
     
         7 . The system according to  claim 1 , wherein operating the actuator causes the actuator to linearly extend. 
     
     
         8 . The system according to  claim 1 , wherein the actuator and the resilient body are pivotally coupled together. 
     
     
         9 . The system according to  claim 1 , wherein the mobile portion is moveable towards the base in a first phase and in a second phase, wherein in the first phase the mobile portion moves towards the base principally via bending of the resilient body, and wherein in the second phase the mobile portion moves towards the base principally via compression of the resilient body. 
     
     
         10 . The system according to  claim 1 , wherein the fitness machine is a treadmill and the mobile portion is a running deck supporting a belt on which the user runs. 
     
     
         11 . The system according to  claim 1 , wherein the resilient body is a first resilient body, further comprising at least one additional resilient body functionally equivalent to the first resilient body, and wherein the first resilient body and the at least one additional resilient body both resist the movement of the mobile portion towards the base in the height direction. 
     
     
         12 . The system according to  claim 11 , wherein the actuator is operable to adjust the set maximums for both the first resilient body and the at least one additional resilient body. 
     
     
         13 . The system according to  claim 11 , wherein the set maximum for the first resilient body is adjustable separately than the set maximum for the at least one additional resilient body. 
     
     
         14 . A method for adjusting a stiffness of a fitness machine operable by a user, the fitness machine having a base and a mobile portion that moves relative to the base during operation of the fitness machine, the method comprising:
 resisting via a resilient body movement of the mobile portion towards the base in a height direction, wherein the resilient body has a length defined in a length direction that is perpendicular to the height direction, and wherein the length of the resilient body increases when the mobile portion moves towards the base; and   operating an actuator to adjust a set maximum for which the length of the resilient body may extend during operation of the fitness machine, wherein a resistance provided by the resilient body to resist movement of the mobile portion towards the base is unaffected by operating the actuator when the length of the resilient body is less than the set maximum.   
     
     
         15 . The method according to  claim 14 , wherein the resilient body is a first resilient body, further comprising also resisting the movement of the mobile portion towards the base in the height direction via a second resilient body. 
     
     
         16 . The method according to  claim 15 , wherein operating the actuator adjusts the set maximums of the lengths of the first resilient body and the second body at the same time. 
     
     
         17 . The method according to  claim 14 , wherein operating the actuator causes the actuator to linearly extend. 
     
     
         18 . The method according to  claim 14 , wherein the movement of the mobile portion is resisted via the resilient body in a first phase in which the mobile portion moves towards the base principally via bending of the resilient body and in a second phase in which the mobile portion moves towards the base principally via compression of the resilient body. 
     
     
         19 . The method according to  claim 14 , wherein the actuator is a first actuator and the resilient body is a first resilient body, further comprising also resisting the movement of the mobile portion towards the base in the height direction via a second resilient body, further comprising operating a second actuator to adjust a set maximum for which the length of the second resilient body may extend during operation of the fitness machine, wherein a resistance provided by the second resilient body to resist movement of the mobile portion towards the base is unaffected by operating the second actuator when the length of the second resilient body is less than the set maximum. 
     
     
         20 . A fitness machine providing shock absorption for a user operating the fitness machine, the fitness machine comprising:
 a base;   a mobile portion that moves relative to the base during operation of the fitness machine;   a resilient body that resists movement of the mobile portion towards the base in a height direction, wherein the resilient body has a length defined in a length direction that is perpendicular to the height direction, wherein the length of the resilient body increases when the mobile portion moves towards the base, wherein the resilient body provides shock absorption for the user; and   an actuator operable to adjust a set maximum for which the length of the resilient body may extend during operation of the fitness machine, wherein a resistance provided by the resilient body to resist movement of the mobile portion towards the base is unaffected by operating the actuator when the length of the resilient body is less than the set maximum.