Abstract
INTRODUCTION: In unstationary swimming (changing velocity), some of the water around the swimmer is set in motion. This can be thought of as an added mass (AM) of water. Previously only one other study (Klauck, 1999) has investigated added mass on swimmers during passive gliding, and reported added mass values in a range of 30-70kg. The purpose of this study was to find added mass on human swimmers and the effects of age and genders on added mass. METHODS: 31 subjects between the ages of 12 to 36 years were included. They where recruited into three groups; boys (aged 13.7±1.1years), women (21.8±3.4years) and men (25.2±4.9years) with body mass of 52.6±10,6kg, 63.9±5.3kg and 78.2±6.3kg, respectively. The subjects were connected to a 2.8m long bar with handles, attached with springs (stiffness k=318N/m) and a force cell. By oscillating this system vertically and registering the period of oscillations it was possible to find the added mass of the swimmer, given the known masses of the bar and swimmer. RESULTS: Added mass for the three groups were 14.5±3.1kg, 15.1±1.2kg and 21.1±2.5kg for boys, women and men, respectively. This corresponds to relative added mass (AM%) of, respectively 27.8±2.9%, 23.6±1.5% and 27±2.2% of the subjects¿ body mass. This study reported significant difference in AM (p<0.01) and AM% (p<0.01) between men and women. In boys and men significant differences were found for AM (p<0.01), but not for AM% (p<0.01). DISCUSSION: The added mass in this study seems to be lower and within a smaller range than previously reported (Klauck, 1999). An added mass of about 27% of body mass will influence inertial forces during passive gliding phases in a swimming race, but must also be considered in intracyclic velocity fluctuations. The subjects¿ lack of experience to hold the optimal and best position on the bar during oscillation, could lead to increased AM. Boys and men reported similar values for AM%. This indicates that AM is in some way dependent on body mass. Lower AM% values for women could mean that they are influenced by other effects of body size such as height, CD, frontal surface area or % body fat compared men. This study indicates an effect of gender between men and women, but no effect on AM by age between boys and men. If age can be viewed to represent experiences (and skill), added mass seem not to be reduced by swimming training or skill enhancement.