A method for providing a swim fin includes providing a foot attachment member and a blade member having a predetermined blade length. The blade member has a soft portion made with a relatively soft thermoplastic material. The method includes providing a relatively harder portion and the relatively soft thermoplastic portion that is molded to the relatively harder thermoplastic portion. The method includes providing an orthogonally spaced portion of the relatively harder portion that is arranged a predetermined orthogonal direction while said swim fin is in state of rest. The method includes providing the blade member with a predetermined biasing force portion that is arranged to urge the orthogonally spaced portion while the swim fin is in a state of rest. The method includes arranging a significant portion of the blade length to experience pivotal motion a lengthwise angle of attack during use.

A method for providing a swim fin includes providing a foot attachment member and a blade member having a predetermined blade length. The blade member has a soft portion made with a relatively soft thermoplastic material. The method includes providing a relatively harder portion and the relatively soft thermoplastic portion that is molded to the relatively harder thermoplastic portion. The method includes providing an orthogonally spaced portion of the relatively harder portion that is arranged a predetermined orthogonal direction while said swim fin is in state of rest. The method includes providing the blade member with a predetermined biasing force portion that is arranged to urge the orthogonally spaced portion while the swim fin is in a state of rest. The method includes arranging a significant portion of the blade length to experience pivotal motion a lengthwise angle of attack during use.

A system, methods and apparatus for powered monofin that propels a swimmer through water uses one of two modes of power: 1. An electric-assist mode, in which the propulsor responds to a swimmer's kick by multiplying the work of the swimmer; 2. Inverse mode, in which the propulsor deactivates when the swimmer is working. In this mode, propulsion is inversely related to the work of the swimmer. As the swimmer does more work, power from the monofin is reduced, to a predetermined, average level of propulsion. As the swimmer does less work propulsion increases to the predetermined level.

A system, methods and apparatus for powered monofin that propels a swimmer through water uses one of two modes of power: 1. An electric-assist mode, in which the propulsor responds to a swimmer's kick by multiplying the work of the swimmer; 2. Inverse mode, in which the propulsor deactivates when the swimmer is working. In this mode, propulsion is inversely related to the work of the swimmer. As the swimmer does more work, power from the monofin is reduced, to a predetermined, average level of propulsion. As the swimmer does less work propulsion increases to the predetermined level.

An improved structure of a long board of a swim fin does not use a plate in gradually changing thickness, but rather uses a fiberboard in fixed thickness. The fiberboard is provided with at least a first opening and at least a second opening arranged in line from small size to large size. The first opening can be triangular, and the second opening can be n-shaped, so that the mechanical strength of fiber flat plate changes gradually from one end to the other end. The plate effective thickness is changed gradually without time consuming processing technique. As such, the manufacturing time and cost are reduced, and consistent manufacturing quality is maintained.

An improved structure of a long board of a swim fin does not use a plate in gradually changing thickness, but rather uses a fiberboard in fixed thickness. The fiberboard is provided with at least a first opening and at least a second opening arranged in line from small size to large size. The first opening can be triangular, and the second opening can be n-shaped, so that the mechanical strength of fiber flat plate changes gradually from one end to the other end. The plate effective thickness is changed gradually without time consuming processing technique. As such, the manufacturing time and cost are reduced, and consistent manufacturing quality is maintained.

A swim fin may include a foot pocket configured to receive a foot of a swimmer and a fin blade extending from the foot pocket. A relatively rigid substrate chassis may be bonded to the foot pocket. The fin blade may be relatively flexible. Fin rails may extend along the lateral edges of the fin blade. The fin rails may include a fin spine comprising a plurality of fin spine segments in linear configuration. The fin spine may be configured to provide a swim fin with predetermined hydrodynamic characteristics. The swim fin may flex within a maximum angle of attack that may be variable and dynamically changed, within a predetermined maximum attack angle range, as a function of the kicking force generated by a swimmer during a kicking cycle.

A swim fin may include a foot pocket configured to receive a foot of a swimmer and a fin blade extending from the foot pocket. A relatively rigid substrate chassis may be bonded to the foot pocket. The fin blade may be relatively flexible. Fin rails may extend along the lateral edges of the fin blade. The fin rails may include a fin spine comprising a plurality of fin spine segments in linear configuration. The fin spine may be configured to provide a swim fin with predetermined hydrodynamic characteristics. The swim fin may flex within a maximum angle of attack that may be variable and dynamically changed, within a predetermined maximum attack angle range, as a function of the kicking force generated by a swimmer during a kicking cycle.

A limb motion measurement device for swimming training includes a sense glove and a sense shoe able to measure and collect the states of moving hands and feet of a swimmer in a training practice, including strength, displacement, velocity, bearing angle, number of times, frequency and time parameters, and to generate a serial of limb motion data of arm stroking and leg kicking motions. These organized and quantified limb motion data can be transmitted outwards to an external computer for the swimmer to study and to produce useful information of more efficient movements and tempos of swimming techniques. Accordingly, the limb motion measurement device for swimming training can be applied to improve swimming techniques in a scientific way.

Aquatic activity fin (1) comprising a foot support portion (2) configured for fixing to a person's foot, and a fin portion (3) extending from the foot support portion substantially along a base plane (P). The fin portion (3) comprises a support frame (4), a plurality of hydrofoil blades (5) mounted pivotally to the support frame (4) via pivot couplings (6), and a mechanism for limiting the maximum blade pivot angle of each hydrofoil blade. The mechanism for limiting the maximum blade pivot angle comprises bidirectional angle stops (7) configured to allow pivoting of the hydrofoil blade from the a thrust position where a trailing edge (9b) of the hydrofoil blade is above said base plane (P), to a return position where the trailing edge (9b) is below said base plane (P).