• J. Paulo VILAS-BOAS


Purposes of this study were to evaluate: (i) gender differences in maximum breaststroke propulsive force and (ii) relationships between breaststroke maximum propulsive force and maximum propulsive resultant horizontal impulse during the stroke cycle. Subjects were 12 Portuguese top level breaststroke swimmer(6 females and 3 males). After a 30 min slow pace free warm-up period, subjects period, subjects performed three times 6 sec.of maximum breaststroke tethered swimming, with a 5 min. rest period. Immediately before each 6 sec. effort, swimmers performed a 5 to 10 sec. of preparing sub maximal exercise. Maximum tethered swimming force was registered trough a Lafayete-Jackson force transducer. model 32528, mounted in a special designed support. Maximum propulsive resultant impulses per stroke phase were calculated trough speed fluctuation profiles, that were assessed using a photo-optical method. This was based on extended exposure photographic (Canon T70, lOOOASA film) light traces of a pulse light device placed in the-waist of the swimmer, at a middle distance between the two hip joints. After digitising of photographs (CaIComp table and Sigma Scull software), pairs of values for time (t) and speed (v) were modelled using polynomial regression procedures with two constraints: same first (v,, o) and last (v, =T) speed values of the stroke cycle and same first derivative values of speed in order of time in the same moments. Using the model, t values for maximum and minimum speed values during the stroke cycle were determined trough derivation (PC-Matlab, 3.13). and acceleration values per phase were determined. These values were then multiplied by the swimmer's body mass, and again by the time duration of each stroke cycle phase, in order to allow the assessment of horizontal resultant impulses per phase. Maximum horizontal propulsive resultant impulses per phase were then correlated with individual maximum propulsive tethered forces. Results showed that: (i) males mean values of maximum propulsive force were significantly higher than female ones (pi0.05); (ii) maximum breaststroke propulsive resultant impulse per phase was associated with the leg kick and (iii) maximum propulsive force and maximum propulsive resultant: impulse per stroke phase were positively and significantly (pi0.0Sj correlated (1- = 0.851).
Coaching and Sports Activities