Swing analysis method

1. A swing analysis method comprising the steps of:

measuring a swing of a golf club to which a sensor capable of measuring accelerations in directions of three axes and angular velocities or angles about the three axes is attached;

obtaining an index for classifying the swing based on a measuring result of the sensor; and

classifying the swing based on the index,

wherein the index comprises the following item (a) or (b):

(a) a grip angular velocity at least at one time during a downswing; and

(b) a grip velocity at least at one time during the downswing.

2. The swing analysis method according to claim 1 , further comprising the step of:

determining times of an address, a top, and an impact,

wherein the address is a moment of start of the swing, the impact is a moment when a head of the golf club collides with a golf ball, and the top is a moment when the head of the golf club is at a top of the swing before the impact.

3. The swing analysis method according to claim 1 , wherein the index comprises at least two selected from the following items (c), (d), and (e):

(c) a grip angular velocity in a toe-down direction;

(d) a grip angular velocity about a shaft axis; and

(e) a grip velocity in a direction toward a golfer.

4. The swing analysis method according to claim 3 , wherein the index comprises the items (c), (d), and (e).

5. The swing analysis method according to claim 1 , wherein the index comprises at least two selected from the following items (c), (d), and (f):

(c) a grip angular velocity in a toe-down direction;

(d) a grip angular velocity about a shaft axis; and

(f) a dynamic loft angle of a head.

6. The swing analysis method according to claim 5 , wherein the index comprises the items (c), (d), and (f).

7. The swing analysis method according to claim 1 , wherein the index comprises at least two selected from the following items (c), (d), and (g):

(c) a grip angular velocity in a toe-down direction;

(d) a grip angular velocity about a shaft axis; and

(g) a grip attitude angle at an impact.

8. The swing analysis method according to claim 7 , wherein the index comprises the items (c), (d), and (g).

9. A method for fitting a golf club using the swing analysis method according to claim 1 , wherein a recommended shaft is defined for each swing classification.

10. The swing analysis method according to claim 1 , wherein the index comprises the item (b),

an attitude matrix is used in the calculation of the grip velocity,

acceleration of a centrifugal component and gravitational acceleration are removed in the calculation of the grip velocity, and thereafter the acceleration is integrated.