Upper extremity kinematics and body roll during preferred-side breathing and breath-holding front crawl swimming.

Front crawl swimmers often restrict the number of breaths they take during a race because of the possible adverse effects of the breathing action on resistance or stroke mechanics. The aim of this study was to determine whether differences exist in the kinematics of the trunk and upper extremity used during preferred-side breathing and breath-holding front crawl swimming. Six male swimmers performed trials at their 200 m race pace under breathing and breath-holding conditions. The underwater arm stroke was filmed from the front and side using video cameras suspended over periscope systems. Video recordings were digitized at 50 Hz and the three-dimensional coordinates of the upper extremity obtained using a direct linear transformation algorithm. Body roll angles were obtained by digitizing video recordings of a balsa wood fin attached to the swimmers' backs. The swimmers performed the breathing action without any decrement in stroke length (mean +/- s: breathing 2.24 +/- 0.27 m; breath-holding 2.15 +/- 0.22 m). Stroke widths were similar in the breathing (0.28 +/- 0.07 m) and breath-holding (0.27 +/- 0.07 m) trials, despite swimmers rolling further when taking a breath (66 +/- 5 degrees) than when not (57 +/- 4 degrees). The timing of the four underwater phases of the stroke was also unaffected by the breathing action, with swimmers rolling back towards the neutral position during the insweep phase. In conclusion, the results suggest that front crawl swimmers can perform the breathing action without it interfering with their basic stroke parameters. The insweep phase of the stroke assists body roll and not vice versa as suggested in previous studies.

Estimating propulsive forces in swimming from three-dimensional kinematic data.

Propulsive forces are important determinants of swimming performance. The aim of this study was to quantify the measurement error (uncertainty) in propulsive forces calculated from kinematic data. Ten operators digitized underwater video recordings of a breaststroke swimmer's right arm action. Four landmarks on the hand were digitized at 50 Hz and their three-dimensional coordinates obtained using a DLT algorithm. Two angles (alpha and psi) defining the orientation of the hand relative to the fluid flow were calculated following the procedures of Schleihauf et al. (1983). The hydrodynamic force acting on the hand (FR) was calculated using the force coefficients of Schleihauf (1979). Errors in single measurements of hand speed, alpha and psi were estimated for each video field analysed. Errors in alpha and psi led to average errors in the lift and drag coefficients of 27 and 20% respectively, which, when combined with an average hand speed error of 6%, produced an average error in FR of 26%. Each of these errors was reduced by a factor of square root 10 when the mean of 10 measurements was used to calculate FR. Researchers should report both the estimated errors in their hydrodynamic data and the procedures used to reduce them.