Analysis of Swimming Performance From Physical, Physiological, and Biomechanical Parameters in Young Swimmers

Pediatric Exercise Science, 2007, 19, 70-81 2007 Human Kinetics, Inc. Analysis of Swimming Performance From Physical, Physiological, and Biomechanical Parameters in Young Swimmers Jaak Jürimäe, Kaja Haljaste, Antonio Cicchella, Evelin Lätt, Priit Purge, Aire Leppik, and Toivo Jürimäe The purpose of this study was to examine the influence of the energy cost of swimming, body composition, and technical parameters on swimming performance in young swimmers. Twenty-nine swimmers, 15 prepubertal (11.9 ± 0.3 years; Tanner Stages 1 2) and 14 pubertal (14.3 ± 1.4 years; Tanner Stages 3 4) boys participated in the study. The energy cost of swimming (C s ) and stroking parameters were assessed over maximal 400-m front-crawl swimming in a 25- m swimming pool. The backward extrapolation technique was used to evaluate peak oxygen consumption (VO 2peak). A stroke index (SI; m 2 s 1 cycles 1 ) was calculated by multiplying the swimming speed by the stroke length. VO 2peak results were compared with VO 2peak test in the laboratory (bicycle, 2.86 ± 0.74 L/min, vs. in water, 2.53 ± 0.50 L/min; R 2 =.713; p =.0001). Stepwise-regression analyses revealed that SI (R 2 =.898), in-water VO 2peak (R 2 =.358), and arm span (R 2 =.454) were the best predictors of swimming performance. The backward-extrapolation method could be used to assess VO 2peak in young swimmers. SI, arm span, and VO 2peak appear to be the major determinants of front-crawl swimming performance in young swimmers. Key Words: energy cost of swimming, stroke index, in-water oxygen consumption, arm span Many factors that affect swimming performance have been studied extensively in adults (1,3,7,12,14,25). Performance in swimming has been related to different anthropometrical, physiological, and biomechanical parameters (12,18,22,25). Specifically, maximal performance in swimming depends on the amount of metabolic energy (C s ) spent in transporting the body mass of the athlete and on the economy of locomotion over the unit of swimming distance (3,26). It has been reported that C s varies largely from one swimmer to another, mainly depending on the specific anthropometrical (6) and technical (16) characteristics of the athlete. J. Jürimäe, Haljaste, Lätt, Purge, Leppik, and T. Jürimäe are with the Institute of Sport Pedagogy and Coaching Sciences, University of Tartu, Tartu Estonia. Cicchella is with the Faculty of Exercise and Sport Science, University of Bologna, Bologna, Italy. 70

Analysis of Swimming Performance 71 C s increases as a function of speed (3,9,26) and has usually been assessed from the ratio of oxygen consumption (VO 2 ) to the corresponding speed (v) in adult athletes swimming within the aerobic range of intensities (25). In a few studies, C s has also been estimated at maximal speeds wherein the anaerobic-energy contribution had to be considered in the calculation of the overall energy balance of the exercise (3,26). Oxygen-consumption values measured during recovery have been used to extrapolate backward to determine the VO 2peak during a maximal swimming bout (7). This method of determining VO 2peak during maximal swimming has been reported to be valid in adult swimmers, offering a specific in-water assessment of the oxygen consumption during swimming (7). To our knowledge, however, no studies have been conducted to assess the suitability of this methodology in young children. Besides the anthropometrical and physiological parameters mentioned earlier, biomechanical aspects should also be considered as determinants of the best swimming performance (25). Most of the biomechanical studies have been concerned with the relationship between stroke rate, stroke length (SL), and swimming performance (4,13,14,18,19,24). In addition, Costill et al. (7) used stroke index (SI) as an indicator of swimming economy because it describes the ability to move at a given velocity with the fewest number of strokes. It can be speculated that, as in highly trained adult swimmers (7), SI could be the major indicator of swimming economy in prepubertal and pubertal children. Very few studies have investigated the importance of different anthropometrical, physiological, and technical parameters to determine swimming performance in children. Poujade et al. (18) and Zamparo et al. (26) used children older than 12 years of age and determined the C s during maximal 400-m front-crawl swimming. To our knowledge, no studies have investigated C s in prepubertal swimmers. Furthermore, the changes from prepuberty to puberty are important and include different anthropometrical, physiological, and mechanical parameters (18). Poujade et al. (18) have suggested that morphological characteristics in children are still of the utmost importance when it comes to predicting adult swimming performance. Accordingly, the purposes of the present investigation were to (a) assess and compare the C s in prepubertal and pubertal boys, (b) compare indirect in-water measurement of VO 2peak with laboratory-based measurement of VO 2peak, and (c) examine the influence of C s, anthropometrical, body composition, and technical parameters on swimming performance in prepubertal and pubertal boys. Participants Methods Twenty-nine swimmers, 15 prepubertal (11.9 ± 0.3 years; Tanner stages 1 2) and 14 pubertal (14.3 ± 1.4 years; Tanner stages 3 4) boys, participated in the study. All swimmers had a training background of 3.0 ± 1.1 years and had trained for 8.4 ± 1.7 hr/week for at least the last 2 years. During the testing period (i.e., September), the mean weekly training volume was 19.4 ± 5.5 km performed mainly at an aerobic pace. Biological age was measured according to the method of Tanner (20). All

72 Jurimae et al. procedures were approved by the medical ethics committee of the University of Tartu and explained to the children and their parents, who signed consent forms. Study Design Measurements were taken on three different occasions during the study period. On the first visit main anthropometrical parameters, biological age, and VO 2peak on the bicycle ergometer were measured. The second measurement session consisted of maximal 400-m front-crawl swimming tests in the pool. During the third measurement session body-composition parameters were measured using dual-energy X-ray absorptiometry (DXA). The first and second measurement sessions were separated by at least 48 hr, and the third measurement session depended on the participantsʼ schedules and DXA availability at the hospital. Anthropometrics and Body Composition Height was measured with a Martin metal anthropometer to the nearest 0.1 cm according to a standard technique, and body mass was measured with minimal clothing to the nearest 0.05 kg with a medical electronic scale (A&D Instruments, UK). Body-mass index (BMI) was calculated as body mass (in kg) divided by height (in m 2 ). Arm span was measured to the nearest 0.1 cm according to the standard recommendations (17). Whole-body fat, fat-free mass (FFM), and bone-mineral (BM) mass were measured by DXA using the DPX-IQ densitometer (Lunar Corp., Madison, WI) equipped with proprietary software, version 3.6. Participants were scanned in light clothing while lying flat on their backs with their arms at their sides. The fast-scan mode and standard participant positioning were used for total-body measurements, and participants were analyzed with the use of the extended-analysis option. Bonemineral density (BMD) was determined as the total body BMD and at the site of the posterior-anterior spine. Peak Oxygen Consumption VO 2peak was directly measured on an electronically braked cycle ergometer (Tunturi T8, Finland). Swimmers performed at an initial work rate of 80 W with increments of 20 W every 2 min in order to attain a test approximately 8 10 min in duration. At the end of the last work rate, participants were required to sprint as fast as possible for 1 min. Participants pedaled at a cadence of 70 ± 5 rpm, and they were actively encouraged to continue until voluntary exhaustion. Heart rate was recorded every 5 s during the test using a Sporttester Polar Vantage NV (Kempele, Finland). Gasexchange variables were measured throughout the test in a breath-by-breath mode, and data were stored in 10-s intervals. During the test, participants breathed through a face mask. Oxygen consumption (VO 2 ), carbon-dioxide output (VCO 2 ), minute ventilation (V E ), breathing frequency, and tidal volume were continuously measured using a portable open-circuit system (MedGraphics VO200, St. Paul, MN). The mean respiratory-exchange ratio and ventilatory equivalents in O 2 (V E /VO 2 ) and CO 2 (V E /VCO 2 ) values were calculated from the recorded measurements. The analyzer was calibrated with the gases of known concentration before the test. All

Analysis of Swimming Performance 73 data were processed by computer analysis using standard software. To establish that VO 2peak was reached, the attainment of a plateau in VO 2 with increasing work rate was used as a criterion. When this plateau in VO 2 was not observed, a respiratory-exchange ratio exceeding 1.05 and a theoretical maximal cardiac frequency were used. All participants satisfied these criteria. Energy Cost of Swimming and Stroking Parameters The energy cost of swimming and stroking parameters in boys were assessed over maximal 400-m freestyle swimming in a 25-m pool (26). Each swimmer performed 400-m front-crawl swimming at a maximal evenly paced effort (7). The swimmers started without diving from the starting block and did not perform regular turning motions at the end of the lane but instead resumed swimming immediately without gliding underwater after the turn (26). After the trial, capillary blood samples were analyzed for blood-lactate levels using Dr. Langeʼs enzymatic photometric method (Berlin, Germany) at the third, fifth, and seventh minute of recovery to obtain a peak value (3,25). The net increase of blood lactate (ΔLa) was obtained by subtracting the pretrial value (equal to 1 mmol/l) from the peak value attained during the recovery phase (25,26). The backward-extrapolation technique was used to evaluate VO 2peak during the 400-m front-crawl swimming bout (7,22,25,26). Each swimmer was instructed to exhale the last breath into a breathing mask as soon as it was fitted over his head (approximately 1 3 s after finishing) (7,25). Metabolic values of VO 2 were determined by a portable metabolic unit (MedGraphics VO200) during the first 20 s of recovery at the end of the 400-m swimming bout (7,22,25,26). Gas sensors and a ventilatory-flow transducer were calibrated using gases of known concentrations before each experimental run, following the procedure indicated by the manufacturer. To exclude the influence of turning, the effective swimming speed (v; m/s) maintained by each swimmer during the trial was measured over 15 m within two points 5.0 m distance from each end of the pool (v = D/t 15, where D = 15 m and t 15 = time for the 15 m) (18). A video camera (Sony DCR-TRV 130E, Japan) filmed the trials of each swimmer with a profile view from above the pool. This camera also measured the time over a distance of 15 m (14). The video recording covered at least five stroke cycles for each trial (14). Average stroke rate (cycles/min) was the average number of strokes completed by the swimmers during the 15-m distance (1,14). The distance per stroke (SL; m/cycle) was calculated by dividing the average speed by the corresponding stroke rate (1,14,18). Finally, in an effort to gauge the economy of a swimmerʼs technique, a stroke index (SI; m 2 s 1 cycles 1 ) was calculated by multiplying the swimming v by the SL (7). All studied parameters were measured during the first 25 m of each 50 m of the 400 m, and the average values for 400-m distance are presented (1). The energy cost of swimming (C s ; kj/m) was calculated by dividing the difference between measured VO 2 and VO 2 at rest, assumed to amount to 5 ml O 2 min 1 kg 1 (4), by the average v (9,18). The C s was converted to kilojoules per meter, assuming that the metabolic energy that equals 1 L O 2 (at standard temperature and pressure) amounts to 20.9 kj (3,22,25). Anaerobic contribution to the overall energy expenditure was obtained from the energetic value of ΔLa, which was calculated

74 Jurimae et al. on the basis of an equivalent of 0.0689 kj kg 1 mm 1 (9). Finally, the energetic value of ΔLa was divided by the overall distance covered and added to the aerobicenergy cost obtained, as already described, to yield the overall C s (25). Statistical Analysis Statistical analysis was performed with SPSS 11.0 for Windows (Chicago, IL). Means and standard deviations were calculated for all measured and calculated parameters. An unpaired, two-tailed t test was used to assess differences between groups. Pearsonʼs product moment correlations were used to determine the degree of association among selected variables. Regression analyses were also used to evaluate the potential associations among selected variables. Limits of agreement between directly measured VO 2peak on a bicycle ergometer and indirectly calculated VO 2max were derived following the procedures recommended by Bland and Altman (2). Significance was set at p <.05. Results Pubertal boys had significantly higher values (p <.05) for height, body mass, BMI, FFM, BM, total BMD, spine BMD, and arm span than did prepubertal boys (Table 1). No differences (p >.05) between groups were observed in fat-mass values. Absolute VO 2peak measured on a bicycle ergometer was significantly higher in pubertal boys (4.36 ± 1.11 L/min) than in prepubertal boys (2.86 ± 0.74 L/min), but relative VO 2peak values were not different between groups (pubertal, 71.26 ± 13.35 ml min 1 kg 1, and prepubertal, 68.33 ± 13.93 ml min 1 kg 1 ). Performance time, v, SL, SI, C s, and VO 2 values for the maximal 400-m front-crawl swimming test were significantly higher in pubertal boys than in prepubertal boys (Table 2). Stroke rate and ΔLa values were not different between the two groups. To validate the indirect in-water measurement of VO 2peak in the whole group of studied boys, we compared the results with the VO 2peak results obtained on a bicycle-ergometer test in the laboratory (bicycle, 2.86 ± 0.74 L/min, vs. in water, 2.53 ± 0.50 L/min; r =.850, p =.0001). Regression analysis of the recovery VO 2 data resulted in the following equation for the prediction of swimming VO 2peak : y = 1.014x + 0.337 (adjusted R 2 =.713, p =.0001), where x is the VO 2 during the first 20 s of recovery and y is the predicted VO 2peak during the swim (Figure 1[a]). Figure 1 shows the results of the Bland Altman analysis for both measurements of VO 2peak. The agreement between directly measured VO 2peak on a bicycle ergometer and indirectly calculated VO 2peak after swimming was high (Figure 1[b]). Correlation analysis demonstrated that stroking parameters (v, SL, SI), C s, and VO 2peak were significantly related to height, body mass, BMI, FFM, BM, total BMD, spine BMD, arm span, and Tanner stage in young swimmers (Table 3). Stroke rate was not related to any measured anthropometric or body-composition parameters. ΔLa was negatively related to percentage body fat and positively related to FFM, BM, total BMD, spine BMD, and Tanner stage. No significant relationship was observed between C s and the stroking parameters studied (r <.316, p >.095). Performance time for 400-m front-crawl swimming was negatively correlated with SL (r =.862, p =.0001), SI (r =.949, p =.0001), and VO 2peak (r =.618,

Analysis of Swimming Performance 75 Table 1 Body-Composition Parameters in Prepubertal and Pubertal Swimmers, M ± SD Variable Prepubertal (n = 15) Pubertal (n = 14) Total (N = 29) Age (years) 11.9 ± 0.3 14.3 ± 1.4* 13.0 ± 1.8 Height (cm) 154.9 ± 7.50 172.9 ± 7.9*0 163.6 ± 11.9 Body mass (kg) 42.5 ± 7.0 61.3 ± 10.6* 51.6 ± 13.0 BMI (kg/m 2 ) 17.5 ± 1.9 20.3 ± 2.1* 18.9 ± 2.4 Body fat% 13.0 ± 6.3 11.2 ± 3.90 12.1 ± 5.3 FM (kg) 5.5 ± 3.7 6.2 ± 1.8 5.8 ± 2.9 FFM (kg) 34.5 ± 4.3 50.4 ± 10.3* 42.2 ± 11.2 BM (kg) 1.7 ± 0.3 2.7 ± 0.6* 2.2 ± 0.7 Total BMD (g/cm 2 ) 0.95 ± 0.06 1.13 ± 0.11* 1.04 ± 0.12 Spine BMD (g/cm 2 ) 0.77 ± 0.10 1.06 ± 0.24* 0.91 ± 0.23 Arm span (cm) 158.4 ± 7.90 179.9 ± 9.0*0 168.8 ± 13.7 Tanner stage 1 2 3 4 2.3 ± 1.0 Note. BMI = body-mas index; FM = whole-body fat; FFM = fat-free mass; BM = bone-mineral mass; BMD = bone-mineral density. Table 2 Biomechanic and Bioenergetic Values Obtained From the Maximal 400-m Front-Crawl Swim in Prepubertal and Pubertal Swimmers, M ± SD Variable Prepubertal (n = 15) Pubertal (n = 14) Total (N = 29) Time (s) 401.5 ± 53.80 353.6 ± 42.2*0 378.3 ± 53.5 v (m/s) 0.99 ± 0.12 1.12 ± 0.13* 1.05 ± 0.14 SL (m/cycle) 0.87 ± 0.11 0.99 ± 0.10* 0.92 ± 0.12 SR (cycle/min) 69.3 ± 5.90 68.0 ± 4.800 68.7 ± 5.3 SI (m 2 s 1 cycles 1 ) 0.87 ± 0.20 1.11 ± 0.22* 0.99 ± 0.24 C s (kj/m) 2.38 ± 0.41 3.29 ± 0.67* 2.82 ± 0.71 VO 2 (L/min) 2.53 ± 0.50 3.92 ± 0.90* 3.20 ± 1.0 ΔLa (mmol/l) 4.1 ± 2.0 5.2 ± 2.90 4.6 ± 2.5 Note. v = speed; SL = stroke length; SR = stroke rate; SI = stroke index; C s = energy cost of swimming; VO 2 = oxygen consumption; La = net increase of blood lactate. *Significantly different from prepubertal children, p <.05. p =.0001). Stepwise-regression analyses revealed that SI (R 2 =.898, p =.0001), in-water measurement of VO 2peak (R 2 =.358, p =.0001), and arm span (R 2 =.454, p =.0001) were the best predictors of 400-m front-crawl swimming performance from measured stroking, bioenergetic, and body-composition parameters in young swimmers.

76 Jurimae et al. Figure 1 Relationship between in-water and ergometer measurements of peak oxygen consumption (VO 2peak ) in young swimmers.

Analysis of Swimming Performance 77 Table 3 Correlation Coefficients of Stroke Parameters, C s, VO 2 and ΔLa With Body-Composition Characteristics in Young Swimmers Time (s) v (m/s) SL (m/cycle) SR (cycle/min) SI (m 2 s 1 cycles 1 ) C s (kj/m) VO 2 (L/min) ΔLa (mmol/l) Height (cm) 0.658* 0.675* 0.707* 0.107 0.721* 0.718* 0.856* 0.291 Body mass (kg) 0.620* 0.655* 0.693* 0.100 0.714* 0.693* 0.839* 0.285 BMI (kg/m 2 ) 0.479* 0.520* 0.562* 0.087 0.582* 0.540* 0.669* 0.173 Body fat% 0.1360 0.11300 0.065 0 0.121 0.100 0 0.2600 0.2420 0.378* FM (kg) 0.1610 0.1970 0.2450 0.132 0.2280 0.013 0.106 0.215 FFM (kg) 0.593* 0.609* 0.689* 0.155 0.690* 0.656* 0.780* 0.377* BM (kg) 0.563* 0.588* 0.682* 0.185 0.675* 0.680* 0.789* 0.404* Total BMD (g/cm 2 ) 0.454* 0.481* 0.583* 0.188 0.569* 0.726* 0.778* 0.415* Spine BMD (g/cm 2 ) 0.516* 0.550* 0.562* 0.033 0.592* 0.657* 0.749* 0.415* Arm span (cm) 0.688* 0.707* 0.746* 0.105 0.758* 0.675* 0.839* 0.282 Tanner stage 0.430* 0.437* 0.538* 0.207 0.512* 0.759* 0.781* 0.459* Note. v = speed; SL = stroke length; SR = stroke rate; SI = stroke index; C s = energy cost of swimming; VO 2 = oxygen consumption; ΔLa = net increase of blood lactate; BMI = body-mas index; FM = whole-body fat; FFM = fat-free mass; BM = bone-mineral mass; BMD = bone-mineral density. *p <.05.

78 Jurimae et al. Discussion Many studies have investigated different bioenergetic and biomechanical characteristics of adult swimmers (1,3,7,14,25). Very few have investigated the physiological aspects of younger swimmers older than 12 years of age (11,18,26). To our knowledge, this is the first study that has also included prepubertal children in the study of various bioenergetic and biomechanical characteristics in young swimmers. Swimmers usually start serious training before the onset of puberty and achieve international competitive level at a relatively early age (8). Accordingly, it is necessary to study different parameters that might affect swimming performance in complex, taking into account various anthropometrical, physiological, and biomechanical aspects of swimming before puberty. Furthermore, it is important to analyze physiological and biomechanical characteristics in conditions similar to those of free swimming in a pool (18,26). In the present study, C s in our prepubertal and pubertal swimmers was assessed at the maximal speed maintained during actual 400-m front-crawl swimming competition (7,26). We used the backward-extrapolation technique of VO 2peak values recorded immediately after the 400-m maximal trial to calculate the value of C s (7,26). The backward-extrapolation technique has been validated in front-crawl swimming, and it has been demonstrated as a reliable method for assessing VO 2peak in adults (15). The results of our study show that backward extrapolation could be used in prepubertal and pubertal swimmers, and it allows us to consider the biomechanical parameters of swimming technique in the assessment of VO 2peak in young swimmers. It has to be noted, however, that the VO 2peak obtained using the backward-extrapolation technique was compared with VO 2peak measured using a maximal bicycle-ergometer test. Although the VO 2peak estimated from the bicycleergometer test might underestimate VO 2peak attained in an in-water swimming test, the results of different VO 2peak tests in our young swimmers were highly comparable (see Figure 1). The VO 2peak values obtained using the backward-extrapolation technique in pubertal (3.92 ± 0.90 L/min) and prepubertal (2.53 ± 0.50 L/min) boys were similar and lower, respectively, to those found in a mixed-age group of 12- to 17-year-old swimmers (3.66 ± 0.54 L/min) after maximal 400-m front-crawl swimming (26). The results of our study demonstrate that, as in adult swimmers (7,25), accurate and reliable measurements of VO 2 during free swimming in the pool can be made from expired gas samples collected in the first 20 s of recovery in prepubertal and pubertal boys who do not present very high absolute VO 2 values. In the past, C s has usually been assessed at speeds substantially slower than those actually attained during competition in adults (4,25) and children (18). In adult swimmers, Costill et al. (7) reported an average C s of 1.16 kj/m at a mean v of 1.42 m/s in maximal 400-m front-crawl swimming. In comparison, the average values of C s during the maximal 400-m front-crawl swimming were 2.38 and 3.29 kj/m at a mean v of 0.99 and 1.12 m/s in our prepubertal and pubertal boys, respectively. The mean v values during 400-m front-crawl swimming in our participants were relatively lower than those measured in 12-year-old boys (1.23 m/s) (18) and 14-year-old boys (1.21 m/s) (5). The metabolic requirement per unit distance in swimming has been described as the result of the energy spent in overcoming drag, in moving water for propulsion, in accelerating the body, and of mechanical efficiency (21). This suggests that the lower C s in our prepubertal swimmers

Analysis of Swimming Performance 79 than in our pubertal swimmers could also be related to the differences in specific anthropometrical parameters (see Table 1). Furthermore, differences in C s might also be a result of the differences in the level of maturation between prepubertal (Tanner Stages 1 2) and pubertal (Tanner Stages 3 4) young swimmers because we found a significant relationship between C s and Tanner stages in our young swimmers (r =.759, p <.05). According to Van Praagh (23), the differences in C s could result from qualitative changes that occur during growth, such as muscle-fiber characteristics, hormonal effects, or neuromotor maturation. It can be assumed that pubertal children are already mature enough to produce more energy from anaerobic pathways, compared with prepubertal children (23). In accordance with this, a significant relationship between Tanner stages and ΔLa was observed (r =.459, p <.05). It is known that children accumulate less blood lactate than adults do during swimming (18). According to the results of our study, it appears that C s increases from prepubertal (mean chronological age 11.9 years) to pubertal (mean chronological age 14.3 years) stages in young swimmers. In accordance to our results, Poujade et al. (18) reported that C s increases between the ages of 12 and 14 years, whereas Chatard et al. (5) found no differences in C s between the ages of 14 and 17 years. In contrast, it must be noted that stroke mechanics decrease C s in children with increasing age (18). Energy expended during swimming pays the cost needed to maintain the body on the surface of the water and to generate the force required to overcome the waterʼs resistance to motion (7). It is well known that body mass in water is highly related to the body drag created by the movement of the body through water (7,10). Furthermore, FFM has been reported to better represent the body drag created by the movement of the body through water in highly trained adult swimmers (7), but no relationship between anthropometric parameters and energy cost to swim a given distance was found in 12-year-old swimmers (18). We found, however, significant relationships (p <.05) between C s and body mass (r =.693), FFM (r =.656), and BM (r =.680) in prepubertal and pubertal swimmers. This would suggest that, for our studied group of young swimmers, specific body-composition parameters are also important determinants of C s. It is interesting to note that measured BMD values in our study had a significant influence on C s during swimming. In contrast, no significant relationship was observed between C s and calculated stroking parameters. This is in accordance with other studies in young swimmers (18) and in contrast to the results obtained from adult swimmers (3,24,25). Taken together, the results of our study demonstrate that anthropometric, body-composition, and maturation characteristics are all important determinants of C s in contrast to stroking parameters in prepubertal and pubertal swimmers. It should be noted that the evaluation of C s for young swimmers allows the estimation of energy expenditure during swimming training and could be used to evaluate the training load (18). It is apparent that several body-composition, biomechanic, and bioenergetic parameters influenced 400-m front-crawl swimming in prepubertal and pubertal swimmers (see Table 3). We were interested in which of these factors had more influence on swimming performance, and we performed separate regression analyses for measured body-composition, biomechanic, and bioenergetic parameters that showed a significant relationship with swimming performance. According to our results, biomechanical factors (89.8%, R 2 100) contribute most to the swimming performance in young swimmers, followed by body-composition (45.4%)

80 Jurimae et al. and bioenergetic (35.8%) factors. Therefore, as in adult swimmers (7), SI was chosen from biomechanic parameters characterizing best swimming performance in our young swimmers. Arm span and VO 2peak after 400-m swimming were the best indicators of swimming performance from body-composition and bioenergetic factors, respectively. Of course, the efficient and continuous application of force accounts significantly for the variance in performance during swimming distance. This explains the importance of SI, arm span, and VO 2peak parameters in swimming performance. Similar to our results, arm span (19) and VO 2peak after 400-m front-crawl swimming (7,15) have been related to swimming performance time in adult swimmers. Taken together, these results suggest that it is very important to consider specific stroke-technique parameters when predicting success in young swimmers. In summary, the results of our study suggest that the backward-extrapolation method of assessing VO 2peak after maximal 400-m front-crawl swimming in prepubertal and pubertal swimmers could be used in the training and testing programs for competitive young swimmers. The evaluation of C s in young swimmers allows us to estimate energy expenditure during swimming training and could be used to evaluate the training load, taking into account both aerobic and anaerobic pathways of energy production. SI, arm span, and VO 2peak appear to be the major determinants of front-crawl swimming performance in young swimmers. References 1. Alberty, M., M. Sidney, F. Huot-Marchand, et al. Reproducibility of performance in three types of training test in swimming. Int. J. Sports Med. 27:623-628, 2006. 2. Bland, J.M., and D.G. Altman. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1:307-310, 1986. 3. Capelli, C., D.R. Pendergast, and B. Termin. Energetics of swimming at maximal speeds in humans. Eur. J. Appl. Physiol. 78:385-393, 1998. 4. Capelli, C., P. Zamparo, A. Cigalotto, et al. Bioenergetics and biomechanics of front crawl swimming. J. Appl. Physiol. 78:674-679, 1995. 5. Chatard, J.C., C. Collomp, E. Maglischo, and C. Maglischo. Swimming skill and stroking characteristics of front crawl swimmers. Int. J. Sports Med. 11:156-161, 1990. 6. Chatard, J.C., S. Padilla, G. Cazorla, and J.R. Lacour. Influence of body height, weight, hydrostatic lift and training on the energy cost of the front crawl. N. Z. Sports Med. 13:82-84, 1985. 7. Costill, D.L., J. Kovaleski, D. Porter, J. Kirwan, R. Fielding, and D. King. Energy expenditure during front crawl swimming: predicting success in middle-distance events. Int. J. Sports Med. 6:266-270, 1985. 8. Costill, D.L., B.W. Maglischo, and A.B. Richardson. Swimming. Oxford, UK: Blackwell Scientific Publications, 1992. 9. Di Prampero, P.E. The energy cost of human locomotion on land and in water. Int. J. Sports Med. 7:55-72, 1986. 10. Dobelin, W.V. Human standard and maximal metabolic rate in relation to fat free body mass. Acta Physiol. Scand. 126:7-26, 1956. 11. Geladas, N.D., G.P. Nassis, and S. Pavlicevic. Somatic and physical traits affecting sprint swimming performance in young swimmers. Int. J. Sports Med. 26:139-144, 2005.

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