Devices systems and methods are disclosed. Among other things, the devices systems and methods can facilitate ergonomic gripping of a handle; conform to the shape of a wrist; enhance golf techniques or performance; enhance racket sport technique or performance; protect a head of a user engaged in contact sports or other hazardous activities; identify concussions, in some cases in substantially real time; provide sterilization of garments; control surgical robots; allow for medical treatment of multiple subjects without disrobing; provide biometric or other data; and/or be used to train muscles or body parts for, for example, performing specified tasks using a body part.

Devices systems and methods are disclosed. Among other things, the devices systems and methods can facilitate ergonomic gripping of a handle; conform to the shape of a wrist; enhance golf techniques or performance; enhance racket sport technique or performance; protect a head of a user engaged in contact sports or other hazardous activities; identify concussions, in some cases in substantially real time; provide sterilization of garments; control surgical robots; allow for medical treatment of multiple subjects without disrobing; provide biometric or other data; and/or be used to train muscles or body parts for, for example, performing specified tasks using a body part.

A golf club shaft connection assembly comprising first and second shaft sections, male and female adaptors, a hollow retainer, a spring, and a plurality of balls is disclosed herein. The male and female adaptors are each attached to the first and second shaft sections, respectively, preferably with a permanent adhesive. The male adaptor comprises a protrusion that fits within a keyed interior of the female adaptor, and moving the hollow retainer towards the male adaptor reversibly fixes the two adaptors together, while moving the hollow retainer towards the female adaptor allows the male adaptor to be removed from the female adaptor.

A hollow wall composite tube for improving performance in sports shafts and lightweight structural members is disclosed that includes: a constituent tube, for forming the wall, that comprises: a flexible core component, for providing an adjustable shape on which to wind or braid filaments or fabric; and an adjustable shape hollow structure, for reducing weight, providing a path for the core to be evacuated, tightly conformed to the core, and tow, braid filaments or fabric, for providing a reinforcing fiber matrix for saturation with epoxy, spirally wrapped, applied or braided on the constituent tube. Methods of producing contemplated composite tubes are also disclosed.

A hollow wall composite tube for improving performance in sports shafts and lightweight structural members is disclosed that includes: a constituent tube, for forming the wall, that comprises: a flexible core component, for providing an adjustable shape on which to wind or braid filaments or fabric; and an adjustable shape hollow structure, for reducing weight, providing a path for the core to be evacuated, tightly conformed to the core, and tow, braid filaments or fabric, for providing a reinforcing fiber matrix for saturation with epoxy, spirally wrapped, applied or braided on the constituent tube. Methods of producing contemplated composite tubes are also disclosed.

A golf club 2 includes a head 4, a shaft 6 and a grip 8. The shaft 6 includes a plurality of layers, a tip end Tp and a butt end Bt. If a distance between a center of gravity of the shaft and the butt end Bt is defined as Lg (mm), a shaft full length is defined as Ls (mm), and a ratio of the distance Lg to the shaft full length Ls is defined as a ratio of the center of gravity of the shaft, the ratio of the center of gravity of the shaft is 44.5% or less. If a torsional rigidity at a point of 90 mm distant from the tip end Tp is defined as GJt (kgf.Math.m.sup.2), and a torsional rigidity at a point of 210 mm distant from the butt end Bt is defined as GJb (kgf.Math.m.sup.2), GJb/GJt is 5.5 or less.

A golf club 2 includes a head 4, a shaft 6 and a grip 8. The shaft 6 includes a plurality of layers, a tip end Tp and a butt end Bt. If a distance between a center of gravity of the shaft and the butt end Bt is defined as Lg (mm), a shaft full length is defined as Ls (mm), and a ratio of the distance Lg to the shaft full length Ls is defined as a ratio of the center of gravity of the shaft, the ratio of the center of gravity of the shaft is 44.5% or less. If a torsional rigidity at a point of 90 mm distant from the tip end Tp is defined as GJt (kgf.Math.m.sup.2), and a torsional rigidity at a point of 210 mm distant from the butt end Bt is defined as GJb (kgf.Math.m.sup.2), GJb/GJt is 5.5 or less.

A golf club 2 includes a head 4, a shaft 6, and a grip 8. A club inertia moment about a swing axis is defined as Isw. A club inertia moment about a grip end is defined as Ige. Ige is 2920 (kg.Math.cm.sup.2) or greater and less than 2970 (kg.Math.cm.sup.2). Isw/Ige is equal to or less than 2.48. A club weight is defined as Wc (kg), an axial direction distance from the grip end to a center of gravity of the club is defined as Lc (cm), and a club inertia moment about the center of gravity of the club is defined as Ic (kg.Math.cm.sup.2). Isw is calculated by Equation (1) below. Ige is calculated by Equation (2) below.
Isw=Wc×(Lc+60).sup.2+Ic  (1)
Ige=Wc×(Lc).sup.2+Ic  (2)

A golf club 2 includes a head 4, a shaft 6, and a grip 8. A club inertia moment about a swing axis is defined as Isw. A club inertia moment about a grip end is defined as Ige. Ige is 2920 (kg.Math.cm.sup.2) or greater and less than 2970 (kg.Math.cm.sup.2). Isw/Ige is equal to or less than 2.48. A club weight is defined as Wc (kg), an axial direction distance from the grip end to a center of gravity of the club is defined as Lc (cm), and a club inertia moment about the center of gravity of the club is defined as Ic (kg.Math.cm.sup.2). Isw is calculated by Equation (1) below. Ige is calculated by Equation (2) below.
Isw=Wc×(Lc+60).sup.2+Ic  (1)
Ige=Wc×(Lc).sup.2+Ic  (2)

Embodiments of golf clubs and methods to manufacture golf clubs are generally described herein. In one example, a golf club may include a golf club head having an interior cavity and a shaft attached to the golf club head. At least a portion of the shaft may be filled with an elastic polymer material, and the interior cavity may be at least partially filled with an elastic polymer material. Other examples and embodiments may be described and claimed.