| To produce the greatest horizontal distance in a punt kick the
ball must be projected at an appropriate angle. Here, we investigated the
optimum projection angle that maximises the distance attained in a punt
kick by a soccer goalkeeper. Two male players performed many maximum-effort
kicks using projection angles of between 10° and 90°. The kicks were recorded
by a video camera at 100 Hz and a 2 D biomechanical analysis was conducted
to obtain measures of the projection velocity, projection angle, projection
height, ball spin rate, and foot velocity at impact. The player's optimum
projection angle was calculated by substituting mathematical equations for
the relationships between the projection variables into the equations for
the aerodynamic flight of a soccer ball. The calculated optimum projection
angles were in agreement with the player's preferred projection angles (40°
and 44°). In projectile sports even a small dependence of projection velocity
on projection angle is sufficient to produce a substantial shift in the
optimum projection angle away from 45°. In the punt kicks studied here,
the optimum projection angle was close to 45° because the projection velocity
of the ball remained almost constant across all projection angles. This
result is in contrast to throwing and jumping for maximum distance, where
the projection velocity the athlete is able to achieve decreases substantially
with increasing projection angle and so the optimum projection angle is
well below 45°.
Key
words: Sports biomechanics, sports projectile.
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