Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Original article 5 ABSTRACT The aim of the present study was to compare the buoyancy assessed by floating tests with the buoyancy calculated using the variables measured during underwater weighing. We also aimed to evaluate the relationship between assessed buoyancy and body composition. Twenty-seven women (age: 20 ± 3 years, height: 1.66 ± 0.34 m, weight: 62 ± 7 kg; body mass index: 22 ± 2; vital capacity: 4.26 ± 0.47 l) and twenty-six men (age: 19 ± 2 years, height: 1.81 ± 6.76 m, weight: 79 ± 10 kg body mass index: 24 ± 3; vital capacity: 6.05 ± 0.7 l) volunteered to participate in the study. They performed floating tests, underwater weighing, pulmonary function measurement, and body composition procedure on the same day in random order with a 30-minute break. Floating testing consisted of one horizontal (HT) and two vertical tests with different arm positions, i.e., arms adducted to the body (VT1) or arms extended overhead (VT2). We assessed participants' buoyancy (B-HT, B-VT1, and B-VT2). In addition, we calculated participants' body volume and buoyancy (B-c) using variables measured during underwater weighing. Results showed that B-c was moderately correlated with B- VT1 (Spearman's ρ = 0.51; p < 0.001) and B-VT2 (Spearman's ρ = 0.55; p < 0.001), but not with B-HT. Multiple regression analysis showed that vital capacity and muscle mass had a positive and negative effect, respectively, on the scores of buoyancy assessed by vertical floating tests. In addition, the mass of the arms correlated negatively with the scores of buoyancy assessed by VT2 (β = -6.26; p = 0.005). According to the obtained results, we can conclude that both vertical floating tests i.e. with arms adducted to the body or arms extended overhead are suitable substitutes for underwater weighing to determine buoyancy, which is strongly related to vital capacity and lesser extent to muscle mass. Muscle mass is not a factor that can be changed immediately, while the amount of inspiration can be regulated. Therefore, the control of breathing and thus the reduction or increase of buoyancy is an important skill that novice swimmers should acquire as part of the learn-to-swim program. Keywords: swimming beginners, learn-to swim, floating ability 1University of Ljubljana, Faculty of Sport, Ljubljana, Slovenia 2Primary School Ivan Cankar, Trbovlje, Slovenia IZVLEČEK Cilj raziskave je bil primerjati vrednosti plovnosti, ki so ocenjene s testi z vrednostmi, ki so izračunane iz podatkov podvodnega tehtanja. Želeli smo ugotoviti tudi učinek telesne sestave na plovnost. Sedemindvajset žensk (starost: 20 ± 3 leta, višina: 1,66 ± 0,34 m, teža: 62 ± 7 kg; indeks telesne mase: 22 ± 2; vitalna kapaciteta: 4,26 ± 0,47 l) in šestindvajset moških (starost: 19 ± 2 leti, višina: 1,81 ± 6,76 m, teža: 79 ± 10 kg indeks telesne mase: 24 ± 3; vitalna kapaciteta: 6,05 ± 0,7 l) je sodelovalo v raziskavi. V istem dnevu smo opravili teste plovnosti in meritve podvodnega tehtanja, vitalne kapacitete ter telesne sestave. Testiranje plovnosti je bilo sestavljeno iz testa v vodoravnem položaju (HT) in dveh testov v navpičnem položaju, pri katerih so bile roke bodisi priročeno (VT1), bodisi vzročeno (VT2). S temi testi smo ocenili plovnost preiskovancev (B-HT, B-VT1 in B-VT2). Poleg tega smo s podatki, izmerjenimi s podvodnim tehtanjem, izračunali tudi njihovo telesno prostornino in vzgon (B-c). Rezultati so pokazali, da je bil B-c zmerno povezan z B-VT1 (Spearmanov ρ = 0,51; p < 0,001) in B-VT2 (Spearmanov ρ = 0,55; p < 0,001), vendar ne z B-HT. Multipla regresijska je pokazala, da imata vitalna kapaciteta in mišična masa pozitiven oziroma negativen učinek na rezultate plovnosti, ocenjene s testoma v navpičnem položaju. Poleg tega je bila masa rok negativno povezana z rezultati plovnosti, ocenjenimi z VT2 (β = -6,26; p = 0,005). Glede na dobljene rezultate lahko sklepamo, da sta za ugotavljanje plovnosti oba testa v navpičnem položaju (priročeno in vzročeno) primerno nadomestilo testiranju s podvodnim tehtanjem. Plovnost je močno povezana z vitalno kapaciteto in v manjši meri z mišično maso. Mišična masa ni dejavnik, ki bi ga lahko hipno spreminjali, medtem ko količino vdiha lahko nadziramo. Zato je nadzor dihanja in s tem zmanjševanje ali povečanje plovnosti pomembna veščina, ki naj bi jo plavalni začetniki osvojili v okviru programa začetnega učenja plavanja. Ključne besede: plavalni začetniki, učenje plavanja, sposobnost lebdenja na vodi Corresponding author*: Jernej Kapus, University of Ljubljana, Faculty of Sport Gortanova 22, 1000 Ljubljana, Slovenia E-mail: jernej.kapus@fsp.uni-lj.si https://doi.org/10.52165/kinsi.30.1.5-19 Jernej Kapus 1,* Jure Jazbec 2 Petra Prevc 1 Samo Rauter 1 Igor Štirn 1 BUOYANCY ASSESSED WITH FLOATING TESTS AND UNDERWATER WEIGHING. A PILOT STUDY PLOVNOST OCENJENA S TESTI PLOVNOSTI IN PODVODNIM TEHTANJEM. PILOTSKA RAZISKAVA Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 6 INTRODUCTION When our body is immersed in water, we experience weightlessness. The degree of weightlessness we experience varies depending on the part of the immersed body (Yanai, 2002). It is determined by the balance between the magnitudes of two opposing forces acting on the body, namely the buoyant force (Fb) and the weight of the body. When a body displaces enough water to create a Fb equal to or greater than the body's weight, the body experiences complete weightlessness and floats. This shows buoyancy, which is the tendency or ability of the body to stay afloat, often referred to as our floating ability (Llana-Belloch, LucasCuevas, Perez- Soriano, and Prigo Quesada, 2013). On the contrary, if the weight is greater than Fb, the body accelerates downward and sinks to the bottom. The Fb is calculated as follows (Halliday, Resnick, and Walker, 2011): Fb = ρ ⋅ g ⋅ V where Fb is the buoyant force in [N], ρ is the density of water in [kg.m-3], g is the acceleration due to gravity in [m.s-2], and V is the volume of the displaced body in the fluid [m3]. With respect to the human body, the volume of the displaced body of liquid, and consequently Fb, depends largely on the volume of the lungs. On inhalation, V and hence Fb increase, while on exhalation they decrease. Indeed, most people float at maximal inhalation and sink after exhalation (Stallman 1997; Llana-Belloch, LucasCuevas, Perez-Soriano, and Prigo Quesada, 2013). In addition to lung volume, Fb of the human body also depends on its density, which is not homogeneous due to the different densities of the biological tissues that compose the human body (Clauser, McConville, and Young, 1969). While bone tissue is the most dense, with a density between 1400 kg/m3 (cancellous or spongy bone) and 1800 kg/m3 (cortical or compact bone), other tissues such as muscles, tendons, or ligaments are somewhat denser than water, with a density between 1020 kg/m3 and 1050 kg/m3. The only tissue that is less dense than water is adipose tissue with a density of 940-950 kg/m3. Overall, these data show that buoyancy or floating ability varies in different people due to differences in lung volume and body composition. Swimming instructors dealing with beginners, as well as coaches training competitive swimmers at various levels, should consider this natural fact. Beginners being less buoyant are likely to need more time to gain confidence, break contact with the bottom of the pool, and should perform more effective propulsive movements to stay on the surface alone than beginners having higher buoyancy. In addition, controlling buoyancy by manipulating lung volume is a fundamental skill that beginners should Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 7 learn in the water. In fact, the acceptance of buoyancy is the turning point in initial learning (Stallman, Moran, Quan, and Langendorfer, 2017). In addition, buoyancy is an important ability for competitive swimmers. It can influence the swimmer's perceived drag, efficiency, and metabolic cost of swimming (Chatard, Collomp, Maglischo, and Maglischo, 1990; Chatard, Lavoie, and Lacour, 1990; McLean and Hinrichs, 1998; Zamparo, et al., 1996a). Therefore, it is not surprising that swimming instructors and coaches often use different tests to assess the hydrostatic profile of learners or swimmers. The swimmer's hydrostatic profile (Fb through measuring body volume (Vb)) can be measured using several validated techniques such as: underwater weighing (Yanai, 2004, Zamparo et al., 1996a) and measurement of water displacement (Katch, Hortobagyi, and Denahan, 1989). Underwater weighing is a method commonly used for body composition assessment (Behnke, Feen, and Welham, 1995), but it can also be used to indirectly measure buoyancy. In this method, a person is submerged in water while being weighed. The weight of the person in water is compared to their weight in air, and the difference is used to calculate his or her buoyancy. In addition, a swimmer's buoyancy can be measured by determining the amount of water they displace when submerged. We can do it by measuring the volume of water before and after the person enters the water (Katch, Hortobagyi, and Denahan, 1989). By using the weight of the swimmer to the volume of water displaced, swimmer's buoyancy can be estimated. However, these methods are expensive and require complex techniques to measure. For this reason, swimming instructors and coaches use various floating tests that are inexpensive and easy to perform and, therefore, are often used in learn-to-swim programs and in regular training of competitive swimmers (Kapus et al., 2002). Some of them (turtle and vertical float after maximum inhalation) have been used only to distinguish floaters from sinkers (Carter, 1973). However, in others (vertical and horizontal floating test), researchers used a scale to measure participants’ floating ability (Stallman, 1971; Barbosa et al., 2012). We use two vertical and one horizontal floating tests in Slovenia (Kapus et al., 2002). In the vertical tests, the swimmer takes a deep breath and remains in a vertical position with different arm positions, i.e., arms adducted to the body or arms extended overhead in deep water. It is assumed that a greater proportion of the swimmer's surfaced body represents greater buoyancy (Barbosa et al., 2012; Kapus et al., 2002). In horizontal floating tests, the swimmer takes a deep breath and remains supine with arms extended overhead on the water surface. The swimmer slowly pulls the arms toward the body. It is assumed that the later the swimmer's legs begin to sink, the greater the buoyancy (Kapus et al., 2002). However, to our knowledge, there are no studies in the literature on the validity of the presented floating tests. Therefore, the aim of the present study was to compare the buoyancy assessed by floating tests Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 8 with the buoyancy calculated using the variables measured during underwater weighing. We also aimed to evaluate the relationship between assessed buoyancy and body composition. METHODS Experimental approach to the problem Participants performed floating tests, underwater weighing, pulmonary function measurement, and body composition procedure on the same day in random order with a 30-minute break. Floating testing consisted of one horizontal (HT) and two vertical tests with different arm positions, i.e., arms adducted to the body (VT1) or arms extended overhead (VT2). We assessed participants' buoyancy (B-HT, B-VT1, and B-VT2). In addition, we calculated participants' Vb and buoyancy (B-c) using variables measured during underwater weighing. The floating tests and underwater weighing were performed in a heated pool. The water temperature, set at 31-32 °C, was noted with an accuracy of 0.1 °C and used to calculate water density. The pulmonary function measurement and body composition procedure took place under controlled environmental conditions in the laboratory (21°C, 40–60% RH, 970–980 mbar). Participants Twenty-seven women (age: 20 ± 3 years, height: 1.66 ± 0.34 m, weight: 62 ± 7 kg; body mass index: 22 ± 2; vital capacity (VC): 4.26 ± 0.47 l) and twenty-six men (age: 19 ± 2 years, height: 1.81 ± 6.76 m, weight: 79 ± 10 kg body mass index: 24 ± 3; VC: 6.05 ± 0.7 l) volunteered to participate in the study. None of the participants were smokers and none had respiratory disease. Participants were fully informed of the purpose and potential risks of the study before giving written informed consent to participate. The study was approved by the National Ethics Committee of the Republic of Slovenia. Body Composition Procedure Participant's body composition was measured by bioelectrical impedance using the InBody 720 (Biospace Co., Seoul, Korea). Before each measurement, participant' palms and soles were wiped with an electrolyte tissue. Then, participant stood on the InBody 720 scale with the soles of his or her feet in contact with the foot electrodes, and body weight was measured. Gender, age, and height (which were determined using a wall-mounted stadiometer [SECA 220; Seca, Ltd., Hamburg, Germany]) were manually entered into the device by the experimenter. The Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 9 participant then grasped the handles, with the palm, fingers, and thumb of each hand in contact with the hand electrodes. Body composition analysis was initiated while the participant remained as immobile as possible. The 8-electrode InBody 720 system measured body composition on the entire body and on 5 segments (arms, legs, and trunk) by emitting multiple frequencies at 5, 50, 250, and 500 kHz from the 8-pole contact points. The scan time for the InBody 720 system was approximately 2 minutes per participant. Pulmonary function A pneumotachograph spirometer (Vicatest P2a, Mijnhardt, The Netherlands) was used for measurement VC. Pulmonary function measurements were performed according to the recommendations of the European Respiratory Society (Miller et al., 2005). Residual lung volume was estimated by multiplying the average VC by the constant 0.28 and 0.24 for women and men, respectively (Wilmore, 1969). Floating tests Vertical floating tests Participant performed two vertical floating tests with different arm positions: VT1 and VT2. Participant took and hold a deep breath and remained in the vertical position without moving. When the participant had assumed a stable position, we assessed his or her buoyancy in relation to the water surface. In the VT1 test, if the water surface was near (Cazorla, 1993): a) the vertex (score 1); b) the forehead (score 2); c) the eyes (score 3); d) the nose (score 4); and e) the mouth (score 5). In the VT2 test, if the water surface was near (Kapus et al., 2002): a) the ends of the fingers (score 1); b) the wrists (score 2); c) the middle of the forearm (score 3); d) the elbows (score 4); and e) the middle of the upper arms (score 5). In both tests, buoyancy at immersion was scored as zero. If the water surface was midway between two anatomical landmarks, the higher one was selected. The vertical floating tests lasted approximately 30-60 seconds until the swimmer achieved stable position. Horizontal floating test The participant held deep breath and remained supine with arms extended overhead on the surface of the water (HT). Then the participant slowly pulled his or her arms toward the body. We assessed his or her buoyancy in relation to the moment the legs began to sink (Kapus et al., 2002): a) with arms extended overhead (score 1); b) with arms extended obliquely upward Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 10 (score 2); c) with arms extended to the side (score 3); d) with arms extended obliquely downward (score 4); and e) with arms adducted to the body (score 5). All floating tests were repeated three times. The highest score was used for further analysis. Underwater weighing The participant was weighed in his bathing suit before entering the pool. During underwater weighing, the participant sat on a submerged chair suspended from the hanging scale so that his entire body, except for his head, was underwater. After maximal exhalation, the participant submerged his head under water and after a stable position was reached, the value of the certified hanging scale (Salter Brecknell 235 10S, United Kingdom) was read. This procedure was repeated until three weights within 50 g were recorded. The highest value was used for further analysis. Data analysis Calculations After underwater weighing, we calculated the B-c for each participant in several steps based on the loss of body weight during weighing underwater, water density, and VC (Williams, Anderson, and Currier, 1983). First, we calculated the body volume at residual lung volume (VRLV) using the loss of body weight during underwater weighing and corrected the density of water according to the water temperature at the time of weighing. In this experiment, the water density was 0.995 kg/L at a water temperature of 31° to 32°C. Therefore, we derived VRLV from the following equation (Williams, Anderson, and Currier, 1984): VRLV = (Wair- Wwater)/(water density) where VRLV is the body volume at residual lung volume, Wair is the weight measured on land, and Wwater is the weight measured in water. Second, since the floating tests were performed at full lung capacity, the Vb was determined by the sum of VRLV and VC. Third, we calculated Fb by multiplying the Vb by the water density. To do this, we used the following equation (Williams, Anderson, and Currier, 1984): Fb = Vb × water density where Fb and Vb are the buoyant force and the body volume, respectively. Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 11 Finally, B-c was calculated for each participant by dividing body weight on land by Fb (Llana- Belloch, LucasCuevas, Perez-Soriano, and Prigo Quesada, 2013). A B-c higher than 1, i.e., Fb was greater than weight, meant that the participant was floating on the water surface. If B-c was 1, it meant that the participant remained at the same depth. When buoyancy was lower than 1, i.e., exerted a net downward force, the participant sank to the bottom of the pool. Statistical analyses The validity of the floating tests was determined by examining the Spearman correlations between the buoyancy assesed with floating tests (B-HT, B-VT1, and B-VT2) and the buoyancy calculated from the underwater weight measurement (B-c). In addition, we used the scores obtained in the floating tests, for which a significant correlation was confirmed, as the dependent (criterion) variable for further regression calculations. Two linear regression models were tested. VC and tissue masses were used as independent (predictor) variables in the first regression model. A separate model was created for VC and body segment masses to determine the relationship of the variables with their respective assesed buoyancy. A p value ≤ 0.05 was considered statistically significant. SPSS for Windows version 18.0 (SPSS Inc; Chicago, IL) was used for all analyses. RESULTS Descriptive statistics for body composition variables, buoyancy assessed by VT1, VT2, and HT, and calculated buoyancy from variables measured during underwater weighing are presented separately for female and male participants in Table 1. Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 12 Table 1. Measured and calculated variables presented for female and male participants. Female Male Fat Mass (kg) 12.70 (4.6) 8.13 (3.06) Mineral Mass (kg) 3.46 (0.57) 4.59 (0.74) Muscle Mass (kg) 27.61 (3.96) 40.54 (5.86) Arms mass (kg) 5.12 (0.7) 8.45 (1.46) Trunk mass (kg) 21.77 (2.15) 31.42 (4.15) Legs mass (kg) 15.53 (2.05) 21.2 (2.9) B-HT (score) 2 (2-2) 2.5 (1-2) B-VT1 (score) 3 (2.5-3) 2.75 (2-4) B-VT2 (score) 4 (3-4) 1.5 (0.75-4) Wair (kg) 62.26 (7.46) 78.53 (10.33) Wwater (kg) 1.89 (0.63) 3.47 (1.16) VRLV (l) 60.36 (7.39) 75.04 (9.67) VC (l) 4.26 (0.47) 6.05 (0.7) V (l) 64.62 (7.69) 81.09 (10.1) Fb (kg) 64.23 (7.64) 80.61 (10.04) B-c 1.01 (0.01) 1.01 (0.01) Note. Means are shown with standard deviations in parentheses for the majority of variables. Median scores from floating testing are shown with quartile range in parentheses. B-HT – buoyancy assessed by horizontal floating test; B-VT1 – buoyancy assessed by vertical floating tests with arms adducted to the body; B-VT2 – buoyancy assessed by vertical floating tests with arms extended overhead; Wair – body weight measured at dry land; Wwater - body weight when weighed underwater; VRLV –body volume at residual lung volume calculated with the loss of body weight when weighed underwater and corrected the density of the water; VC – vital capacity; V – body volume determined by the sum of the body volume at residual lung volume and vital capacity; Fb – buoyant force calculated by multiplying the body volume by the water density; B-c – calculated buoyancy by dividing body weight on land by the buoyant force. We calculated a positive B-c for most participants (Table 1). The average lift was 1.98 kg (19.42 N) for women and 2.07 kg (20.3 N) for men. Twelve participants (4 women and 8 men) had a B-c lower than 1 and received scores between 0 and 2 on the floating tests. The results in Table 2 show that B-c was moderately correlated with B-VT1 (r = 0.51; p < 0.001) and B-VT2 (r = 0.55; p < 0.001), but not with B-HT. In addition, there was a strong correlation between B-VT1 and B-VT2 (r = 0.81; p < 0.001). Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 13 Table 2. Spearman's correlations (rho) between calculated buoyancy from variables measured at underwater weighing and buoyancy assessed by floating testing. B-c B-HT B-VT1 B-VT2 B-c 1.00 0.17 0.51** 0.55** B-HT 1.00 0.4** 0.50** B-VT1 1.00 0.81** B-VT2 1.00 Note. ** - significant correlation between the variables (p < 0.01). Based on the results in Table 2, B-VT1 and B-VT2 were used as dependent (criterion) variables for further regression calculations (Tables 3 and 4). We calculated two linear regression models. The first model included VC and tissue masses as predictor variables (Table 3). Table 3. Analysis of the first linear regression model with B-VT1 and B-VT2 as criterion variables. Criterion variable Predictor variables b SE of b β t p-value B -V T 1 VC 1.06 0.22 1.14 4.78 0.00 Fat Mass -0.03 0.03 -0.13 -1.04 0.30 Mineral Mass 0.07 0.20 0.06 0.34 0.73 Muscle Mass -0.17 0.03 -1.39 -5.16 0.00 R = 0.63; R2 = 0.4; Adjusted R2 = 0.35; F = 8.04; p < 0.001; St. Error of estimate: 0.8 B -V T 2 VC 1.08 0.30 0.82 3.60 0.00 Fat Mass 0.02 0.04 0.07 0.58 0.57 Mineral Mass 0.38 0.28 0.23 1.38 0.17 Muscle Mass -0.24 0.04 -1.40 -5.38 0.00 R = 0.67; R2 = 0.45; Adjusted R2 = 0.4; F = 9.69; p < 0.001; St. Error of estimate: 1.09 Note. B-VT1 – buoyancy assessed by vertical floating tests with arms adducted to the body; B-VT2 – buoyancy assessed by vertical floating tests with arms extended overhead; VC – vital capacity, R – coefficient of the multiple correlation; R2 – coefficient of the determination; β – standardized regression coefficient; b – unstandardized regression coefficient. The linear regression model that included VC and tissue masses as predictor variables (Table 3) explained 35% and 40% of the variation in B-VT1 and B-VT2, respectively. VC had a positive (β = 1.14; p < 0.001 in VT1 and β = 0.82; p < 0.001 in VT2) and muscle mass had a negative (β = -1.39; p < 0.001 in VT1 and β = -1.4; p < 0.001 in VT2) effect on the scores of Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 14 buoyancy assessed by vertical floating tests. The second linear regression model included VC and body segment masses as predictors (Table 4). Table 4. Analysis of the second linear regression model with B-VT1 and B-VT2 as criterion variables. Criterion variable Predictor variables b SE of b β t p-value B -V T 1 VC 1,04 0,22 1,12 4,65 0,00 Arms mass -2,47 1,62 -5,01 -1,52 0,13 Trunk mass 0,76 0,62 4,46 1,23 0,23 Legs mass -0,20 0,12 -0,77 -1,62 0,11 R = 0,64; R2 = 0,41; Adjusted R2 = 0,36; F = 8,41; p < 0,001; St. Error of estimate: 0,8 B -V T 2 VC 1.02 0.30 0.78 3.44 0.00 Arms mass -4.37 2.16 -6.26 -2.02 0.05 Trunk mass 1.40 0.83 5.80 1.69 0.10 Legs mass -0.30 0.17 -0.80 -1.78 0.08 R = 0.69; R2 = 0.48; Adjusted R2 = 0.43; F = 10.97; p < 0.001; St. Error of estimate: 1.06 Note. B-VT1 – buoyancy assessed by vertical floating tests with arms adducted to the body; B-VT2 – buoyancy assessed by vertical floating tests with arms extended overhead; VC – vital capacity, R – coefficient of the multiple correlation; R2 – coefficient of the determination; β – standardized regression coefficient; b – unstandardized regression coefficient. Table 4 showed that the second linear regression model explained 36% and 43% of the variation in B-VT1 and B-VT2, respectively. VC had the greatest influence on the scores of buoyancy assessed by vertical floating tests (β = 1.12; p < 0.001 for VT1 and β = 0.78; p < 0.001 for VT2). In addition, the mass of the arms correlated negatively with the scores of buoyancy assessed by VT2 (β = -6.26; p = 0.05). DISCUSSION The results of the present study showed that buoyancy assessed by both vertical floating tests i.e. with arms adducted to the body or arms extended overhead correlated with the buoyancy calculated using the variables measured during underwater weighing. This was not confirmed for the HT. Moreover, the scores of buoyancy obtained with the vertical floating tests were strongly related to VC (positive correlation) and to muscle mass (negative correlation) of the participants. Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 15 Descriptive statistics of the variables selected were within the range of values reported in the literature from similar group according to gender and chronological age (Psycharakis, and Yanai, 2018; Roberts, Kamel, Hedrick, McLean, and Sharp, 2003; Siders, Lukaski, and Bolonchuk, 1993). Therefore, we can concluded that both vertical floating tests are suitable substitutes for underwater weighing to distinguish the participants according to theirs buoyancy. However, the magnitude of the correlations between B-c and B-VT1 or B-VT2 was significant (Table 2), but only moderate, i.e., not sufficient to make clear what they really mean. Due to easy implementation, we suggest that these test can be used only for rough assessments of pupils' buoyancy. Stallman (1971) recommended that teachers screen all learners as early as possible using a floating test to identify poor floaters. Early identification, attention, and patience with learners with poor buoyancy can help them reach a skill level that will allow them to overcome buoyancy deficiencies very early. On the other hand, the implementation of vertical floating test for testing competitive swimmers is more questionable. Indeed, Barbarosa et al. (2012) showed that the vertical floating test with arms adducted to the body did not present any relationship with anthropometrical and biomechanical variables nor with the prone gliding test. Therefore, they concluded that this test was not appropriate techniques to assess the swimmers’ hydrostatic profile. Even more, Yanai (2008) argued against the suggestion that swimmers’ buoyancy or ability for static floating has significant influence on theirs swimming performances. He disagree with the widely accepted mechanism that a swimmer with less (static) buoyancy swims deeper, has more drag and must exert more effort to overcome the drag while swimming than a swimmer who floats higher in the water (Chatard, Bourgoin, Lacour, 1990). He suggested that faster swimmers use buoyancy more effectively to generate body roll. This reduces the waste of generated hydrodynamic forces in non-propulsive directions and maximises forward propulsion. There are several reports in the literature describing that buoyancy is related to respiratory variables (e.g., lung volume, VC, residual volume, and tidal volume) (Zamparo et al., 1996b). For this reason, we included VC in both regression models, in which the buoyancy scores assessed with vertical floating tests were used as dependent (criterion) variables. In the first model, we considered VC and tissue masses as predictor variables. The results of the present study supported the above suggestion. The assessed scores of buoyancy were closely related to VC (positive correlation) and muscle mass (negative correlation) of the participants. However, the later results differed from the results of previous studies, in which a higher percentage of fat mass correlated with a higher B value (Zamparo et al., 1996b). The reason for this difference Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 16 could be the selection of participants. In the present study, the students from the Faculty of sport participated. Therefore, we can assume that they were physically active in various sports on recreational or competitive level. They were homogeneous and heterogeneous in terms of fat and muscle mass, respectively. According to these results and from the perspective of learning to swim, we should emphasize that muscle mass is not a factor that can be changed immediately, while the amount of inspiration can be regulated. Therefore, the control of breathing and, consequently, the reduction or increase of buoyancy is an important skill that novice swimmers should acquire as part of the swimming learning program (Stallman, Moran, Quan, and Langendorfer, 2017). In the second model, we included VC and body segment mass as predictor variables. The assessed scores for buoyancy were closely related to VC (positive correlation) and to arm mass (negative correlation) for VT2 but not for VT1. This difference is related to the fact that participants extended their arms above their heads and thus out of the water for VT2, whereas they were adducted to the body for VT1. Limitation of the study The magnitude of the obtained correlations between the buoyancy assessed with floating tests and the buoyancy calculated from the underwater weight measurement does not allow to draw clear conclusions. The reason for this may lie in some limitations that should be addressed in future studies. We calculated buoyancy using underwater weight measurements. However, these testing procedure was carried out in a manner for determining body composition (percent of body fat particularly), where participant fully exhaled during weighing (Williams, Anderson, and Currier, 1984). Therefore, our calculation of Fb was based on the sum of VRLV and VC, which can only be an approximation of real Vb. On the other hand, Stallman (1971) determined functional buoyancy as body density at full inspiration, uncorrected for residual lung volume. A replication of this study should use a spirometer connected to the valve and measure the participant's VC and Vb while weighing underwater at total lung volume (Stallman, 1971). Additional mass (usually 6.5 kg) should be added to ensure full immersion when the participant holds their breath at full inspiration (McLean, and Hinrichs, 1998). Moreover, in the floating tests, we used the arbitrary unit scale to measure participants’ floating ability (Barbosa et al., 2012). Like any ordinal measure, the scale used describes a ranking rather than a relative magnitude or degree of difference between the items measured. It is possible to exist some significant limitations in using an ordinal scale to measure this physical Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 17 phenomenon. Therefore, the ordinal scale should be replaced by an interval scale. This means that you measure the distance between the highest point of the head (in VT1) or the ends of the fingers (in VT2) and the water surface in centimetres and standardise these values with the head and arm length. Several techniques for determining residual volume are described in the literature. Helium rinse oxygen rebreathing, nitrogen washout, volume expansion, and plethysmography are some of those used. However, all of these techniques require special equipment. Therefore, several researches have used estimates of residual lung volume as we did in the present study. CONCLUSION According to the obtained results, we can conclude that both vertical floating tests i.e. with arms adducted to the body or arms extended overhead are suitable substitutes for underwater weighing to determine buoyancy, which is strongly related to vital capacity and less to muscle mass. Muscle mass is not a factor that can be changed immediately, while the amount of inspiration can be regulated. Therefore, the control of breathing and thus the reduction or increase of buoyancy is an important skill that novice swimmers should acquire as part of the learn-to-swim program. Funding This research was supported by the Slovenian Research Agency (ARRS) as Project No. PS- 0147 entitled the Kinesiology of Micro-Structured, Poly-Structured and Conventional Sports. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. REFERENCES Barbosa, T. M., Costa, M. J., Morais, J. E., Moreira, M., Silva, A. J., & Marinho, D. A. (2012). How Informative are the Vertical Buoyancy and the Prone Gliding Tests to Assess Young Swimmers' Hydrostatic and Hydrodynamic Profiles?. Journal of human kinetics, 32, 21–32. https://doi.org/10.2478/v10078-012-0020-x Behnke, A. R., Jr, Feen, B. G., & Welham, W. C. (1995). The specific gravity of healthy men. Body weight divided by volume as an index of obesity. 1942. Obesity research, 3(3), 295–300. https://doi.org/10.1002/j.1550- 8528.1995.tb00152.x Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 18 Carter, E.C. (1973). A Comparison of Natural Body Bouyancy of Negro and Caucasian Boys. Master's Thesis, University of Tennessee. https://trace.tennessee.edu/utk_gradthes/6351 Cazorla, G. (1993). Tests spécifiquesd’évaluation du nager. Paris: Editions Vigot. Chatard, J. C., Collomp, C., Maglischo, E., & Maglischo, C. (1990). Swimming skill and stroking characteristics of front crawl swimmers. International journal of sports medicine, 11(2), 156–161. https://doi.org/10.1055/s-2007- 1024782 Chatard, J. C., Bourgoin, B., & Lacour, J. R. (1990). Passive drag is still a good evaluator of swimming aptitude. European journal of applied physiology and occupational physiology, 59(6), 399–404. https://doi.org/10.1007/BF02388619 Chatard, J. C., Lavoie, J. M., Bourgoin, B., & Lacour, J. R. (1990). The contribution of passive drag as a determinant of swimming performance. International journal of sports medicine, 11(5), 367–372. https://doi.org/10.1055/s-2007-1024820 Clauser, C. E., McConville, J., & Young, J. W. (1969). Weight, volume and center of mass of the human body. Aerospace Medical Research Laboratory. Halliday, D., Resnick, R., & Walker, J. (2011). Fundamentals of physics. New York: John Wiley & Sons, Inc. Kapus, V., Štrumbelj, B., Kapus, J., Jurak, G., Šajber-Pincolič, D., Bednarik, J., Vute, R., Šink, I., Čermak, V., & Kapus, M. (2002). Plavanje, Učenje. Ljubljana: Univerza v Ljubljani, Fakulteta za šport. Katch, F.I., Hortobagyi, T., & Denahan, T. (1989) Reliability and Validity of a New Method for the Measurement of Total Body Volume, Research Quarterly for Exercise and Sport, 60:3, 286-291, DOI: 10.1080/02701367.1989.10607452 Llana-Belloch, S., Lucas-Cuevas, A.G., Pérez-Soriano, P., & Priego Quesada, J.I. (2013). Human body floating and organic responses to water immersion. Journal of Physical Education and Sport 13(3), 354 – 361. http://dx.doi.org/10.7752/jpes.2013.03057 McLean, S. P., & Hinrichs, R. N. (1998). Sex differences in the centre of buoyancy location of competitive swimmers. Journal of sports sciences, 16(4), 373–383. https://doi.org/10.1080/02640419808559365 Miller, M. R., Crapo, R., Hankinson, J., Brusasco, V., Burgos, F., Casaburi, R., Coates, A., Enright, P., van der Grinten, C. P., Gustafsson, P., Jensen, R., Johnson, D. C., MacIntyre, N., McKay, R., Navajas, D., Pedersen, O. F., Pellegrino, R., Viegi, G., Wanger, J., & ATS/ERS Task Force (2005). General considerations for lung function testing. The European respiratory journal, 26(1), 153–161. https://doi.org/10.1183/09031936.05.00034505 Psycharakis, S. G., & Yanai, T. (2018). How does buoyancy affect performance during a 200m maximum front crawl swim? Journal of Sports Sciences, 36(18), 2061–2067. https://doi.org/10.1080/02640414.2018.1436188 Roberts, B. S., Kamel, K. S., Hedrick, C. E., McLean, S. P., & Sharp, R. L. (2003). Effect of a FastSkin suit on submaximal freestyle swimming. Medicine and science in sports and exercise, 35(3), 519–524. https://doi.org/10.1249/01.MSS.0000053699.91683.CD Siders, W. A., Lukaski, H. C., & Bolonchuk, W. W. (1993). Relationships among swimming performance, body composition and somatotype in competitive collegiate swimmers. The Journal of sports medicine and physical fitness, 33(2), 166–171. Stallman, R. K. (1971). The Relationship Of Body Density And Selected Anthropometric Measures To The Acquisition Of Beginning Swimming Skills (Order No. 7121238). Available from ProQuest Dissertations & Theses Global. (302605703). Retrieved from http://nukweb.nuk.uni- lj.si/login?url=https://www.proquest.com/dissertations-theses/relationship-body-density-selected- anthropometric/docview/302605703/se-2 Stallman, R. K. (1997). The functional buoyancy of European and African children and youth. In Proceedings of the 3rd Conference of the Africa Association for Health, Physical Education, Recreation, Sport & Dance. Kinesiologia Slovenica, 30, 1, 5-19 (2024), ISSN 1318-2269 Buoyancy Assessed With Floating Tests 19 Stallman, R. K., Moran, K., Quan, L., & Langendorfer, S. (2017). From swimming skill to water competence: Towards a more inclusive drowning prevention future. International Journal of Aquatic Research and Education, 10(2). http://doi:10.25035/ijare.10.02.03 Wilmore, J.H. (1969). The use of actual, predicted and constant residual volumes in the assessment of body composition by underwater weighing. Medicine and Science in Sports and Exercise, 1, 87-90. Williams, D., Anderson, T., & Currier, D. (1984). Underwater weighing using the Hubbard tank vs the standard tank. Physical therapy, 64(5), 658–664. https://doi.org/10.1093/ptj/64.5.658 Yanai, T. (2002). Weightlessness in Water: Its Unexpected Mechanical Effects on Freestyle Swimming. Korean Journal of Applied Biomechanics, 12 (2), 393-405. Yanai T. (2004). Buoyancy is the primary source of generating bodyroll in front-crawl swimming. Journal of biomechanics, 37(5), 605–612. https://doi.org/10.1016/j.jbiomech.2003.10.004 Yanai, T., & Wilson, B.D. (2008). How does buoyancy influence front-crawl performance? Exploring the assumptions. Sports Technology, 1, 89-99. https://doi.org/10.1002/jst.23 Zamparo, P., Capelli, C., Termin, B., Pendergast, D. R., & di Prampero, P. E. (1996). Effect of the underwater torque on the energy cost, drag and efficiency of front crawl swimming. European journal of applied physiology and occupational physiology, 73(3-4), 195–201. https://doi.org/10.1007/BF02425476 Zamparo, P., Antonutto, G., Capelli, C., Francescato, M. P., Girardis, M., Sangoi, R., Soule, R. G., & Pendergast, D. R. (1996). Effects of body size, body density, gender and growth on underwater torque. Scandinavian journal of medicine & science in sports, 6(5), 273–280. https://doi.org/10.1111/j.1600-0838.1996.tb00470.x