Systems and methods for adjusting a stiffness of fitness machines

Abstract

A system for adjusting a stiffness of a fitness machine having a base and a mobile portion that moves relative to the base. A resilient body that resists movement of the mobile portion towards the base in a height direction. The resilient body has a length defined in a length direction perpendicular to the height direction, which increases when the mobile portion moves towards the base. An end stop prevents the length from increasing beyond a set maximum, the end stop being fixed relative to the base in the length direction. An actuator is operable to adjust the set maximum at which the end stop prevents the length of the resilient body from increasing. 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;   an end stop that prevents the length of the resilient body from increasing beyond a set maximum, the end stop being fixed relative to the base in the length direction; and   an actuator operable to adjust the set maximum at which the end stop prevents the length of the resilient body from increasing, 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 has a parabolic shape. 
     
     
         3 . The system according to  claim 2 , wherein the mobile portion is supported at least in part by a vertex of the parabolic shape of the resilient body. 
     
     
         4 . The system according to  claim 1 , wherein the mobile portion includes a running deck supporting a belt on which the user may run, wherein the belt moves parallel to the length direction of the resilient body during use of the fitness machine, and wherein operating the actuator moves the resilient body in the length direction. 
     
     
         5 . The system according to  claim 1 , wherein the resilient body is coupled to the actuator via an arm, wherein the arm is configured such that moving the actuator in a first direction causes the resilient body to move in a second direction opposite the first direction. 
     
     
         6 . The system according to  claim 1 , wherein the resilient body is coupled to the actuator via an arm, wherein the mobile portion includes a running deck supporting a belt on which the user may run, and wherein the arm has an opening through which the belt extends without contacting the arm. 
     
     
         7 . The system according to  claim 1 , wherein the resilient body is coupled to the actuator via an arm, wherein the resilient body is coupled to a first pivot point of the arm, the actuator is coupled to a second pivot point of the arm different than the first pivot point, and wherein operating the actuator causes the arm to pivot about a third pivot point of the arm that is different than the first pivot point and the second pivot point of the arm. 
     
     
         8 . The system according to  claim 7 , wherein the first pivot point is positioned between the second pivot point and the third pivot point such that the arm acts as a class 2 lever between the actuator and the resilient body. 
     
     
         9 . The system according to  claim 7 , wherein the arm is positioned such that the mobile portion is between the resilient body and the third pivot point in the height direction. 
     
     
         10 . The system according to  claim 1 , wherein the resilient body is a first resilient body, the length is a first length, the end stop is a first end stop, and the set maximum is a first set maximum, further comprising:
 a second resilient body functionally equivalent to the first resilient body, wherein the resilient body has a second length defined in the length direction; and   a second end stop that prevents the second length of the resilient body from increasing beyond a second set maximum;   wherein the actuator is operable to adjust the second set maximum at which the second end stop prevents the second length of the second resilient body from increasing, wherein a resistance provided by the second resilient body to resist movement of the mobile portion towards the base is unaffected by operation of the actuator when the second length of the resilient body is less than the second set maximum.   
     
     
         11 . The system according to  claim 10 , wherein the first resilient body and the second resilient body are offset from each other in a width direction perpendicular to the length direction and perpendicular to the height direction. 
     
     
         12 . The system according to  claim 1 , wherein the resilient body resists the mobile portion moving 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. 
     
     
         13 . The system according to  claim 12 , wherein operating the actuator to adjust the set maximum at which the end stop prevents the length of the resilient body from increasing changes when the resilient body changes resistance from the first phase to the second phase. 
     
     
         14 . 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 may run. 
     
     
         15 . The system according to  claim 1 , wherein the actuator comprises a lever manually moveable to adjust the set maximum at which the end stop prevents the length of the resilient body from increasing. 
     
     
         16 . The system according to  claim 15 , wherein the actuator is configured to be retained in at least a first position and a second position, and wherein the actuator is moved between the first position and the second position by pivoting via the lever. 
     
     
         17 . The system according to  claim 16 , wherein the lever pivots about a pivot axis, wherein the actuator is retained in the first position and in the second position via a spring, and where the spring moves from a first side of the pivot axis to a second side of the pivot axis when the actuator is moved from the first position to the second position. 
     
     
         18 . The system according to  claim 16 , wherein the mobile portion includes a running deck supporting a belt on which the user may run, wherein the belt moves parallel to the length direction of the resilient body during use of the fitness machine, wherein the lever pivots in a plane parallel to the length direction. 
     
     
         19 . The system according to  claim 15 , wherein the resilient body is coupled to the actuator via an arm, and wherein the lever is pivotally coupled to the arm via a linkage therebetween. 
     
     
         20 . 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;   preventing the length of the resilient body from increasing beyond a set maximum via an end stop that is fixed relative to the base in the length direction; and   operating an actuator to adjust the 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.