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Journal of Science and Medicine in Sport 12 (2009) 662–666

Original paper

Evaluation of specific anaerobic power in 12–14-year-old male rowers Pavle Mikuli´c ∗ , Lana Ruˇzi´c, Goran Markovi´c Zagreb University School of Kinesiology, Zagreb, Croatia Received 31 August 2007; received in revised form 15 May 2008; accepted 16 May 2008

Abstract No previous study had applied the modified Wingate rowing test to young athletes (i.e. children and adolescents). The aims of this study were to evaluate the trial-to-trial reliability of a rowing-modified Wingate test in a group of 12–14-year-old rowers (n = 98) and to compare anaerobic power values among the 12-, 13-, and 14-year-old rowers after accounting for differences in physical maturity and body size. Each subject performed two “all-out” 30-s trials on a Concept II rowing ergometer. The trials were separated by a 15-min active recovery period, which included walking and stretching and ensured the participants’ full recovery. The test proved to be highly reliable, with coefficients of variations of 2.4 and 2.9% (CI = 2.1–3.4%) and intraclass correlation coefficients of 0.994 and 0.996 (CI = 0.991–0.997) for mean power and peak power, respectively. The ANCOVA analyses accounting for differences in body size and level of physical maturity (assessed using indices of pubic hair) and the Bonferroni post hoc tests identified the 14-year-olds as having significantly greater adjusted mean power and peak power values (P < 0.01) than the other two age groups, while the differences between the 12- and 13-year-olds in terms of mean power and peak power were not significant. Our findings indicate (1) that the rowing-modified Wingate test may be reliably used for the assessment of specific anaerobic performance in 12–14-year-old rowers and (2) that factors other than physical maturity and body size are partly responsible for the increase in anaerobic power during growth. © 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. Keywords: Rowing; Modified Wingate test; Reliability; Anaerobic power; Maturation; Allometric scaling

1. Introduction Rowing is primarily a strength-endurance sport demanding high levels of both aerobic and anaerobic capacities for successful performance.1 Anaerobic effort has been found to contribute a total of 20–30% of the energy needed to complete a 2000 m race.2 Some recent studies3,4 have clearly demonstrated the importance of muscle strength, muscle power production, and anaerobic capacity for successful rowing performance. For the purpose of selection in rowing, it is important to define those tests that may be used in order to evaluate characteristics that are relevant to successful performance. The Wingate anaerobic test has emerged as the most widely used test for the assessment of anaerobic performance in children and adolescents.5 In its original form, the test allows for the determination of cycling peak and mean power over a 30∗

Corresponding author. E-mail address: [email protected] (P. Mikuli´c).

s period. The test was found to be a highly reliable, valid measurement of anaerobic performance in both adults and children (for review, see [6]). However, alternate unilateral movement using only the lower limbs does not correspond well to the coordinated bilateral movements accomplished when the upper and lower limbs are used in rowing. This observation stresses the importance of using sport-specific ergometers for an anaerobic power assessment of rowers.7 There are few anaerobic tests available specifically designed to assess this type of power.4,7 Recently, Riechman et al.4 applied a modified Wingate “sprint test” on a Concept II rowing ergometer and reported very high trial-to-trial reliability for mean and peak power in a group of trained female rowers. However, to our knowledge, no previous study had applied the modified Wingate rowing test to young athletes (i.e. children and adolescents). Because this specific anaerobic performance test could be particularly important for the selection and profiling of young rowers, it would be important in both scientific and practical terms to examine the reliability of the test in a sample of young rowers. Hence, the primary

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P. Mikuli´c et al. / Journal of Science and Medicine in Sport 12 (2009) 662–666

aim of this study was to evaluate the reliability of a modified Wingate test using a relatively large group of rowers aged 12–14 years. Evidence shows that maximal anaerobic performance may improve with an increase in chronological age and physical maturity during childhood and adolescence (for review, see [8]). Moreover, it has been demonstrated that most of the improvement in maximal anaerobic performance during growth may be due to dimensional changes.5,9 Therefore, when differences in anaerobic performance between young athletes of different ages are analysed, both physical maturity and body size should be considered. Hence, the secondary aim of this study was to compare differences in specific rowing anaerobic performance among 12–14-year-old rowers after accounting for differences in physical maturity and body size.

2. Method All 12–14-year-old members of the “rowing schools” affiliated with five rowing clubs in Zagreb, Croatia were invited to participate in the study. A total of 128 rowers, representing 82% of all eligible members according to official rowing club records, volunteered. The prerequisites for inclusion in this study were as follows: (1) they participated in rowing training for at least 6 months before testing, which ensured that the rowers possessed sufficient technical skills for the completion of a maximal test on a rowing ergometer10 ; (2) they reported regular attendance (>75% of the total number of practices within the past 6 months), and (3) they reported no medical problems. The sample for this study eventually comprised 98 rowers aged 13.3 ± 0.8 years (mean ± S.D.; range: 12.0–14.9 years). While in rowing school, young rowers typically train three times per week for 75–90 min per training session. Each training session combines a rowing-specific approach, which includes “on-water,” ergometer, and tank rowing, with cross-training methods that mainly involve running, ball games, swimming, and body weight strength training (squats, push-ups, sit-ups, lunges, etc.). Each subject’s parents (or legal guardians) and coaches were asked to give their consent following an explanation, in compliance with the Declaration of Helsinki, of the nature and purpose of the experiment and of any possible risks associated with participation. All experimental procedures were approved by the Ethics Committee of the University of Zagreb School of Kinesiology. The participants’ ages were calculated using date of birth and date of examination and then rounded to the nearest decimal. Sexual maturity was visually assessed using indices of pubic hair developed by Tanner.11 All observations were made by the same pediatrician. Body height, body mass, triceps and subscapular skinfolds (using the Harpenden caliper) were measured by an experienced anthropometrist according to IBP recommendations.12 The percentage of body fat was

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estimated using a method described by Slaughter et al.13 Lean body mass was calculated by subtracting estimated body fat from total body mass. Each subject was given 10 min to stretch and warm-up on the Concept II model B rowing ergometer according to his usual habits. After these warm-up exercises, the ergometer was programmed for a 30-s trial at the maximum damper setting (10 on the resistance control dial, which corresponds to a drag factor of 158–160). The participants then performed an “all-out” 30-s effort with verbal encouragement from coaches and laboratory staff members. The same ergometer was used, and the same investigators conducted the procedure for all participants. Power output was calculated and displayed by the Concept II computer and was recorded by the investigators. Mean power (MP) was the average individual stroke power over this 30-s trial. Peak power (PP) was the mean value of the five highest consecutive strokes during this 30-s trial. This methodology, used to conduct the modified Wingate test, is described in Riechman et al.4 In order to estimate the reliability of the test in the population of 12–14-year-old rowers, a second trial was conducted after a 15-min active recovery period (walking and stretching), which ensured the participants’ full recovery. A considerably shorter rest period (4 min) was used in a previous reliability study.4 Measures of centrality and spread are reported as mean ± S.D. Differences in MP and PP between the two trials were tested using a paired t-test. The reliability of both MP and PP assessment was expressed using intraclass correlation coefficients (ICCs) and coefficients of variation (CVs). ICCs were calculated from repeated ANOVA measurements, while CVs were established using a two-way ANOVA as follows: the participants represented a random effect; the number of tests in a sequence was a fixed effect, while the log-transformed performance measurement was a dependent variable. The mean CV was calculated based on the root mean square error (RMSE) using the following formula: CV = 100(eRMSE − 1) ≈ 100RMSE.14 The 95% confidence intervals (CIs) for both ICCs and CVs were also calculated. Differences in anthropometric characteristics, as well as in MP and PP among the three age groups (i.e. 12-, 13-, and 14year-olds), were compared using a one-way ANOVA. MP and PP were expressed using absolute units (W) and ratio standard mass-related units (W kg−1 ). However, several authors have demonstrated that simple ratio standard fails to produce a dimensionless power output variable5,9,15,16 and thus have suggested the use of a non-linear allometric approach in order to normalise muscle power for body size in both children and adults.9,15,16 Therefore, comparisons of MP and PP, independent of body size (either body mass or body height) and physical maturity, were established using ANCOVA based on the following allometric model: MP (or PP) = massk · exp(a + b · level of physical maturity)

(1)

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Table 1 Age, anthropometric, maturity, and anaerobic performance characteristics of 12–14-year-old rowers Variable

12-year-olds

13-year-olds

14-year-olds

Statistics

N Age (years) Body height (cm)

37 12.4 ± 0.3 159.7 ± 8.3

31 13.5 ± 0.3 168.1 ± 7.9a

30 14.3 ± 0.2 174.5 ± 7.7b

– – F

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an important rowing performance predictor,4 this test may also be an efficient means of identifying talent. For example, within the observed age group, young rowers with the necessary prerequisites for high-level competitive rowing may be identified using the modified Wingate anaerobic test. Furthermore, the modified Wingate anaerobic test may also be used to determine the effectiveness of various training procedures. For this purpose, however, the “test–retest” reliability of the test should also be quantified. This might, however, be interpreted as a limitation of our study, as it is known that a test–retest on the same day leads to a higher reliability coefficient than is yielded by a test–retest on separate days. The secondary aim of our study was to compare differences in specific rowing anaerobic performance among different age groups. This objective was tackled using both absolute and normalised (either ratio or allometric scaling) values. In terms of absolute values, significant differences are observed among all age groups, with increases in chronological age accompanied by a corresponding rise in both MP and PP. This finding was expected, as it is well known that muscle mass, for example, increases with age, and this accumulation of muscle mass directly affects the amount of absolute anaerobic power output that can be generated.8 In terms of relative values (ratio scaling) the differences in MP and PP between groups are smaller, yet still significant, except for the difference between the 13- and 12-year-olds, where no significant difference was observed. Obviously, not only does anaerobic power in young rowers increase with age, but a similar pattern of improvement also emerges when power outputs are expressed in mass-specific units. This observation is hardly surprising, since it is a widely held belief that improvements in anaerobic fitness typically outpace growth rates.8 In addition to this increase in muscle mass, other factors that may affect anaerobic performance, such as ATP, creatine phosphate, and glycogen content, also become more prevalent as young rowers grow.8 Similar increments in both absolute and relative values corresponding to increases in chronological age were observed by other authors.6,19,20 It should be noted that, in general, 14-year-old rowers may be expected to be more experienced and technically more efficient than their younger counterparts, so this expectation may likely account for some of the difference in performance levels. When the differences between age groups are considered using allometric scaling as a more appropriate normalisation procedure,15,16 they are reduced even further but are still significant between the 14- and 13-year-old rowers, as well as between the 14- and 12-year-old rowers. Interestingly, the differences between the observed age groups of rowers in terms of the MP and PP values obtained using ANCOVA, although even smaller, do not differ substantially from the differences obtained using traditional ratio scaling methods. There appear to be qualitative differences in the factors that determine performance in the rowingspecific anaerobic power test. Those differences appear to

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be quite unrelated to differences in body size and in levels of physical maturity. Armstrong et al.5 indicate that chronological age exerts a positive influence (independent of body size) on short-term power output. This effect may be mediated over time by improvements in neural activation and anaerobic rephosphorylation.21 Moreover, our approach is perhaps limited by the fact that stages of puberty were used as indicators of physical maturity. Sexual maturation is a continuous process and the use of only five discrete stages of puberty suggests that the approach is, in fact, incomplete, thus implying that some important information may be lacking.8 We admit that a more continuously distributed indicator of physical maturity (e.g. skeletal age) would have provided additional information regarding the young rowers’ levels of physical maturity, thus permitting a more thorough analysis. Finally, the obtained body size scaling coefficients are worthy of discussion. The scaling coefficients for body mass yielded values of k = 0.66 (CI = 0.45–0.87) and k = 0.67 (CI = 0.48–0.87) for MP and PP, respectively. According to the theory of geometric similarity, muscle power should be proportional to body mass raised to the power of 0.67,15,16 which puts our results in line with that theory and also in line with the findings of Nevill et al.16 and Martin et al.22 However, Armstrong et al.23 reported higher mass scaling coefficients of k = 0.82 and k = 1.02 for MP and PP, respectively. The authors explained this notable deviation from the theoretical value by citing the possible limitations of using the Wingate anaerobic test to assess anaerobic performance in young people (insufficient resistance for producing true maximal values for PP and a test duration that may be suboptimal for assessing MP). With respect to body height, the scaling coefficients yielded values of k = 2.76 (CI = 1.76–3.76) and k = 2.75 (CI = 1.77–3.72) for MP and PP, respectively. Furthermore, the theory of geometric similarity predicts that scaling coefficients for body height are three times higher than scaling coefficients for body mass. Although our results deviate somewhat from that prediction, with the coefficients for body height being approximately four times higher than those for body mass, the corresponding 95% confidence intervals for both MP and PP cover the theoretically predicted values. Some authors15 argue that body height, when considered alone, cannot serve as a proper index of body size for normalising physiological functions because the relationship observed between muscle power and body height is generally weak. In conclusion, our results show that the modified Wingate anaerobic test performed on the Concept II rowing ergometer may be a highly reliable test of anaerobic performance in 12–14-year-old rowers on a “trial-to-trial” basis, although this conclusion still needs to be investigated on a “test–retest” basis. Furthermore, 12–14-year-old rowers exhibit an increase in specific anaerobic power that corresponds to increases in chronological age; however, physical maturity and body size only partly explain the obtained differences between the age groups.

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Practical implications • The modified Wingate anaerobic test performed on the Concept II rowing ergometer may be reliably used to assess anaerobic performance in young rowers. • Given that anaerobic power significantly contributes to overall rowing performance, this test may be used to identify talent in rowing. • Body size and physical maturity may only partly explain the rise in anaerobic rowing performance that occurs as chronological age increases in 12–14-year-old rowers. Acknowledgement The third author (GM) was supported in part by a MSES grant (no. 034-0342607-2623). This project received no external financial or material support. References 1. Shephard RJ. Science and medicine of rowing: a review. J Sports Sci 1998;16:603–20. 2. Secher NH. Rowing. In: Reilly T, Secher N, Snell P, Williams C, editors. Physiology of sports. London: E&FN Spon; 1990. 3. Ingham SA, Whyte GP, Jones K, et al. Determinants of 2000 m rowing ergometer performance in elite rowers. Eur J Appl Physiol 2002;88:243–6. 4. Riechman SE, Zoeller RF, Balasekaran G, et al. Prediction of 2000 m indoor rowing performance using a 30 s sprint and maximal oxygen uptake. J Sports Sci 2002;20:681–7. 5. Armstrong N, Welsman JR, Chia MYH. Short term power output in relation to growth and maturation. Br J Sports Med 2001;35:118–24. 6. Bar-Or O. Pediatric sports medicine for the practitioner. New York: Springer-Verlag; 1983. 7. Mandic S, Quinney HA, Bell GJ. Modification of the Wingate anaerobic power test for rowing: optimization of the resistance setting. Int J Sports Med 2004;25:409–14.

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