Effects of age and gender on the propelling efficiency of the arm stroke.

The propelling efficiency of the arm stroke (etaP) was estimated in a group of 63 male and female subjects (9-59 years of age) of good technical skill, swimming the front crawl at sub-maximal speeds. etaP was calculated on the basis of values of speed (v), stroke frequency (SF) and shoulder-to-hand distance (l, calculated from measures of arm length and elbow angle during the in-sweep) as proposed by Zamparo et al. (Eur J Appl Physiol 94:134-144, 2005). In both genders, the distance covered per stroke (Ds = v/SF) is similar before puberty, reaches its maximum at about 20 years of age and then steadily declines. l is significantly larger in males than in females and this difference tended to offset the differences in Ds so that etaP is almost the same in male and female swimmers of the same age group and swimming ability: about 0.31 before puberty, 0.38-0.40 at about 20 years of age and about 0.25 in swimmers older than 40 years of age. The development of etaP and Ds during the life span is similar to the changes in muscle strength and power reported in the literature suggesting that these parameters are related to the ability to exert forceful (and hence effective) strokes in water. Since the energy cost of swimming (C) depends essentially on etaP and the hydrodynamic resistance (Wd), these data further suggest that differences in C between genders are mainly to be attributed to differences in Wd, whereas differences across ages can be attributed also to changes in etaP.