The aim of the present study was to determine the effects of breathing on the three - dimensional underwater stroke kinematics of front crawl swimming. Ten female competitive freestyle swimmers participated in the study. Each subject swam a number of front crawl trials of 25 m at a constant speed under breathing and breath-holding conditions. The underwater motion of each subject's right arm was filmed using two S-VHS cameras, operating at 60 Hz, which were positioned behind two underwater viewing windows. The spatial coordinates of selected points were calculated using the DLT procedure with 30 control points and after the digital filtering of the raw data with a cut-off frequency of 6 Hz, the hand's linear displacements and velocities were calculated. The results revealed that breathing caused significantly increases in the stroke duration (t₉ = 2.764; p < 0.05), the backward hand displacement relative to the water (t₉ = 2.471; p<0.05) and the lateral displacement of the hand in the X - axis during the downsweep (t₉ = 2.638; p < 0.05). On the contrary, the peak backward hand velocity during the insweep (t₉ = 2.368; p < 0.05) and the displacement of the hand during the push phase (t₉ = -2.297; p < 0.05) were greatly reduced when breathing was involved. From the above, it was concluded that breathing action in front crawl swimming caused significant modifications in both the basic stroke parameters and the overall motor pattern were, possibly due to body roll during breathing.

• The breathing action increases the duration of the total underwater pull.

• The breathing action increases the absolute backward displacement of the hand.

• The breathing action caused significant modifications in the overall motor pattern, possibly due to body roll during breathing.