The effect of leg kick on sprint front crawl swimming.

The aim of this study was to examine the influence of leg kick on the pattern, the orientation and the propulsive forces produced by the hand, the efficiency of the arm stroke, the trunk inclination, the inter-arm coordination and the intra-cyclic horizontal velocity variation of the hip in sprint front crawl swimming. Nine female swimmers swam two maximal trials of 25 m front crawl, with and without leg kick. Four camcorders were used to record the underwater movements. Using the legs, the mean swimming velocity increased significantly. On the contrary, the velocity and the orientation of the hand, the magnitude and the direction of the propulsive forces, as well as the Froude efficiency of the arm stroke were not modified. The hip intra-cyclic horizontal velocity variation was also not changed, while the index of coordination decreased significantly. A significant decrease (13%) was also observed in the inclination of the trunk. Thus, the positive effect of leg kick on the swimming speed, besides the obvious direct generation of propulsive forces from the legs, could probably be attributed to the reduction of the body's inclination, while the generation of the propulsive forces and the efficiency of the arm stroke seem not to be significantly affected.

Acute effect of front crawl sprint resisted swimming on the propulsive forces of the hand.

The purpose of the current study was to investigate the acute effect of sprint resisted front crawl swimming on the propulsive forces of the hand. Eight female swimmers swam 25 m with maximal intensity, with and without added resistance. A bowl with a capacity of 2.2, 4 and 6 L was used as low, moderate and high added resistance, respectively. The underwater motion of the swimmer's right hand was recorded using 4 cameras (60 Hz) and the digitization was undertaken using the Ariel Performance Analysis System. Repeated-measures ANOVA revealed that the velocity of the hand, the pitch and the sweepback angles of the hand, as well as the magnitude and the relative contribution of the drag and lift forces were not significantly modified and thus the magnitude of the resultant force did not change. Moreover, the magnitude of the effective force, as well as the angle formed between the resultant force and the axis of the swimming propulsion were not significantly affected. Thus, it could be concluded that resistance added as in this study did not alter the pattern of the propulsive hand forces associated with front crawl sprinting.

Kinematic characteristics of the stroke and orientation of the hand during front crawl resisted swimming.

The aim of this study was to examine the acute effect of front crawl sprint resisted swimming with different added resistances on the kinematic characteristics of the stroke and the orientation of the hand. Ten female swimmers swam four maximal trials (25 m) with small, moderate, large, and no added resistance respectively. Four camcorders were used to record the underwater motion of the right hand and digitizing was undertaken using the Ariel Performance Analysis System. Stroke rate, the stroke length, and mean swimming velocity were significantly decreased, whereas the total duration of the stroke and the relative duration of the pull and push phases were significantly increased during resisted swimming. The increase in the total duration of the stroke was accompanied by an increase in absolute pull length, while no alterations were observed in relative pull length or medial-lateral displacements of the hand. Moreover, the mean resultant velocity of the hand, as well as the pitch and the sweepback angles of the hand were not modified. In conclusion, resisted swimming appears to be a specific form of training, at least regarding its acute effect, although long-term effects should be investigated further.

The influence of hand paddles on the arm coordination in female front crawl swimmers.

The purpose of the research was to determine the influence of hand paddles on the arm coordination in female front crawl swimmers. Ten female swimmers swam at a maximal intensity 25 m without, with small hand paddles (116 cm), and with large hand paddles (286 cm). Four S-VHS cameras were used to record the underwater motion of both arms, and the digitizing of selected points onto the subject's body was undertaken using the Ariel Performance Analysis System. The mean swimming velocity, the stroke length, the stroke rate, the relative duration of the separate phases of the stroke, and the index of coordination were then calculated. The index of coordination was defined as the time interval between the propulsive phases of the 2 arms expressed as a percentage of the mean duration of the stroke cycle. The results showed that when the hand paddles were worn, the mean swimming velocity (p < 0.05) and the stroke length (p < 0.05) were significantly increased, whereas the stroke rate was significantly decreased (p < 0.05). When large paddles were worn, the relative duration of the whole propulsive phase was significantly decreased (p < 0.05), and the relative duration of the nonpropulsive phase was significantly increased (p < 0.05). However, the index of coordination was remained unchanged under the 3 measurement conditions (p = 0.895). It was concluded that in front crawl hand-paddled swimming, significant increases of the swimming velocity was not caused by modifications in the pattern of arm coordination. Thus, hand-paddled swimming should not be used as a tool to alter the time sequence of the application of propulsive forces generated from the 2 arms.

Estimation of hand forces and propelling efficiency during front crawl swimming with hand paddles.

The aim of the study was to investigate possible modifications caused by hand paddles in the relative contribution of the lift and drag forces of the hand and in the propelling efficiency, during front crawl swimming. Eight female swimmers swam 25 m with maximal intensity without paddles, with small (116 cm(2)) and with large paddles (268 cm(2)). Four cameras operating at 60 Hz were used to record the images and the Ariel Performance Analysis System was used for the digitisation. The results showed that, although during swimming with hand paddles the hand's velocity decreased, the greater propulsive area of the hand paddle caused an increase in the drag, lift, resultant and effective forces of the hand. However, the relative contribution of lift and drag forces on swimming propulsion was not modified, nor was the direction of the resultant force. Hand paddles also increased the propelling efficiency, the stroke length and the swimming velocity, mainly because of the larger propulsive areas of the hand in comparison with free swimming. However, the significant decrease of the stroke rate, might argue the effectiveness of hand paddle training, particularly when large paddles are used in front crawl swimming.

Reconstruction accuracy in underwater three-dimensional kinematic analysis.

Accuracy of kinematic data is of decisive importance in motion analysis particularly when they are to be used for the calculation of kinetic parameters, like the propulsive forces in swimming. The present study investigated the accuracy of underwater three-dimensional (3-D) kinematic analysis using periscope systems and calibration volumes with different size. Two analogue cameras (60Hz) were used to record the images, along with two stationary periscope systems for the underwater recordings. The calibration of the recording space was performed using two different-sized calibration frames. The reconstruction accuracy was determined in static and dynamic conditions, both under water and out of the water. In static conditions, the reconstruction accuracy was determined by calculating the root mean square (RMS) error for the reconstruction of eight validation points on the calibration frames, and in dynamic conditions it was determined by the percentage of RMS error of the reconstructed length of a moving rod. The results revealed that in static conditions the RMS error was greater during underwater analysis, due to refraction, and it was increased particularly in the longitudinal axis as the dimensions of the calibration volume were increased. The reconstruction errors observed during underwater recordings with both calibration volumes (transverse axis, 1.61-2.35mm; longitudinal, 2.99-4.64mm; vertical, 2.83-2.59mm) may be considered suitable for three-dimensional kinematic analysis of swimming.

Underwater Stroke Kinematics During Breathing and Breath-holding Front Crawl Swimming.

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. Key pointsThe 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.

Effect of a submaximal half-squats warm-up program on vertical jumping ability.

The purpose of the current research was to study the effect of a warm-up program including submaximal half-squats on vertical jumping ability. Twenty physically active men participated in the study. Each subject performed 5 sets of half-squats with 2 repetitions at each of the following intensities: 20, 40, 60, 80, and 90% of the 1 repetition maximum (1RM) load. Prior to the first set and immediately after the end of the last set, the subjects performed 2 countermovement jumps on a Kistler force platform; the primary goal was to jump as high as possible. The results showed that mean vertical jumping ability improved by 2.39% after the warm-up period. Subjects were then divided into 2 groups according to their 1RM values for the half-squat. Subjects with greater maximal strength ability improved their vertical jumping ability (4.01%) more than did subjects with lower maximal strength (0.42%). A warm-up protocol including half-squats with submaximal loads and explosive execution can be used for short-term improvements of vertical jumping performance, and this effect is greater in athletes with a relatively high strength ability.