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Sport selection in under-17 male roller hockeyManuel J. Coelho-E-Silva a , Vasco Vaz a , Filipe Simões a , Humberto M. Carvalho a , JoãoValente-Dos-Santos a , António J. Figueiredo a , Vanildo Pereira b , Roel Vaeyens c , RenaatPhilippaerts c , Marije T. Elferink-Gemser d e & Robert M. Malina f ga University of Coimbra, Portugalb Maringa State Univesity, Brazilc Faculty of Medicine and Health Sciences, Ghent University, Belgiumd University Medical Center Groningen, University of Groningen, The Netherlandse HAN University of Applied Sciences, Nijmegen, The Netherlandsf Tarleton State University, Stephenville, TX, USAg University of Texas, Austin, TX, USAPublished online: 07 Aug 2012.

To cite this article: Manuel J. Coelho-E-Silva , Vasco Vaz , Filipe Simões , Humberto M. Carvalho , João Valente-Dos-Santos , António J. Figueiredo , Vanildo Pereira , Roel Vaeyens , Renaat Philippaerts , Marije T. Elferink-Gemser & RobertM. Malina (2012) Sport selection in under-17 male roller hockey, Journal of Sports Sciences, 30:16, 1793-1802, DOI:10.1080/02640414.2012.709262

To link to this article: http://dx.doi.org/10.1080/02640414.2012.709262

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Sport selection in under-17 male roller hockey

MANUEL J. COELHO-E-SILVA1, VASCO VAZ1, FILIPE SIMOES1,

HUMBERTO M. CARVALHO1, JOAO VALENTE-DOS-SANTOS1,

ANTONIO J. FIGUEIREDO1, VANILDO PEREIRA2, ROEL VAEYENS3,

RENAAT PHILIPPAERTS3, MARIJE T. ELFERINK-GEMSER4,5, & ROBERT M. MALINA6,7

1University of Coimbra, Portugal, 2Maringa State Univesity, Brazil, 3Faculty of Medicine and Health Sciences, Ghent

University, Belgium, 4University Medical Center Groningen, University of Groningen, The Netherlands, 5HAN University of

Applied Sciences, Nijmegen, The Netherlands, 6Tarleton State University, Stephenville, TX, USA, and 7University of Texas,

Austin, TX, USA

(Accepted 2 July 2012)

AbstractCharacteristics of 32 international and 41 local under-17 (U-17) (14.5–16.5 years) roller hockey players were consideredin the context of discrimination by competitive level using training history, anthropometry, skeletal maturation, and severallaboratory and field performance tests. More international (42%) than local (22%) players were advanced in maturitystatus. International players had slightly less hockey experience (years), but had more practice sessions and match time(minutes) during the season. Local players were shorter and attained better performance in the 25-m dash, whileinternational players performed better in sit-ups, ball throw and 20-m shuttle run. The fatigue index derived from theWingate anaerobic test was higher among local players, while peak torques of knee extension and flexion were greater ininternational players. Stepwise discriminant function correctly classified 85% of players by competitive level based on gripstrength, ratio of eccentric and concentric knee extension, number of training sessions, playing time and fatigue index.The results suggested an interaction among strength, anaerobic fitness and training plus game time as factors indiscriminating international from local level players and by inference in the selection and development of youth rollerhockey players.

Keywords: talent, maturation, isokinetic strength, Wingate, maximal oxygen uptake

Introduction

Roller (rink) hockey is played on a level, smooth

rectangular rink (40 m620 m) surrounded by a

barrier one metre high. Games have two periods of

20-minutes duration and are played by two teams

of five players (two defenders, two attackers, one

goalkeeper). The front frame of the goal cage has a

distance from the floor to the inner edge of the

cross-bar of 105 cm and the distance between the

inner edges of the goal-posts of 170 cm. The

official ball (23 cm circumference, 155 g) is made

of pressed cork. Players must wear four-wheeled

squad skates (in contrast to inline hockey skates)

and use a two-sided stick to play the ball. The

sport is popular in nearly 60 countries worldwide

and was included in the programme of the 1992

Barcelona Olympic Games; it was not considered

in subsequent Games. Nevertheless, the popularity

of the sport continues to grow in Europe. Roller

hockey is part of the Portuguese Skating Federa-

tion with figure skating and in-line skate racing.

Registered participants numbered 7,335 pre-juniors

and 1,341 juniors in 2003 (IDP – Instituto do

Desporto de Portugal, 2005). Field hockey is one

of the smallest Portuguese sport federations with

only 754 participants, while ice hockey is not

institutionally organised in Portugal.

As in other team sports, the performance

structure of the game is complex (Mendo &

Argilaga, 2002). Match analysis of seniors indicated

high intensity non-continuous action; rolling ac-

counted for 71% of match time while sprinting and

pushing accounted for 4% and 14%, respectively

(Kingman & Dyson, 1997). Rolling was defined as

one or two utility strides used to maintain speed or

Correspondence: Manuel J Coelho-e-Silva, University of Coimbra, Portugal, Faculty of Sport Science and Physical Education, Estadio Universitario de

Coimbra, Pavilhao III, Coimbra, 3040-156 Portugal. E-mail: mjcesilva@fcdef.uc.pt

Journal of Sports Sciences, December 2012; 30(16): 1793–1802

ISSN 0264-0414 print/ISSN 1466-447X online � 2012 Taylor & Francis

http://dx.doi.org/10.1080/02640414.2012.709262

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to adjust position with almost no additional effort

and pushing as a forward or backward propulsive

movement. Estimated total skating distance was,

on average, 16 km; differences between attackers

and defenders were negligible. Literature on the

energetic-metabolic requirements of roller hockey is

limited. Under simulated game conditions among

14 Spanish players 20–32 years of age, lactate

concentration and heart rate were, on average,

4.20+ 0.95 mmol � l71 and 163.5+ 10.4 beats �min71, respectively (Bonafonte, Perez, & Marrero,

1994).

The literature dealing with youth team sports has

considered relationships among growth and matur-

ity status on one hand, and indicators of function

and sport-specific skill, on the other. Among soccer

players aged 11–14 years, for example, skeletal

maturation had a significant influence on body size,

vertical jump, speed (repeated sprints) and aerobic

capacity (endurance shuttle run), but did not

influence soccer-specific skills (Figueiredo, Gon-

calves, Coelho-e-Silva, & Malina, 2009a). Among

12-to 13-year-old basketball players, stature and

adiposity had an inverse relationship with perfor-

mances on manipulative-skill tests, while sport-

specific skills were positively and linearly related to

a combination of abdominal muscular strength

reflected in 60-second sit-ups and aerobic endur-

ance assessed with a 20-m shuttle run (Coelho-

e-Silva et al., 2010a). The studies are limited to

traditional field-based fitness batteries and did not

include laboratory assessments of strength, short-

term anaerobic efforts and maximal oxygen uptake.

The objectives of this study were twofold: [i] to

profile the experience, size, adiposity and biological

maturity characteristics and functional perfor-

mances of under-17 (U-17) Portuguese male roller

hockey players using both field and laboratory

tests; and [ii] to evaluate the contributions of these

variables to the discrimination of players by

competitive level (international versus local). Given

the available information, it was hypothesised that

the growth and maturity status would differ

between international and local roller hockey

players.

Methods

The study was approved by the Scientific Com-

mittee of the University of Coimbra and was

conducted in accordance with recognised ethical

standards (Harriss & Atkinson, 2009). The Portu-

guese Skating Federation, clubs and parents

provided written consent, while players provided

assent. Participants were also informed that colla-

boration was voluntary and that they could with-

draw at any time.

Sample

The sample included 73 competitive roller hockey

players aged 14.5 to 16.5 years at the time of the

study. The players were classified as juveniles (15–16

years) in the structure of Portuguese youth hockey

and as local (n¼ 41) or international (n¼ 32). The

latter were selected for the national team. The

distribution of players (local/international) by posi-

tion was as follows: goalkeepers (6/7), defenders

(16/13) and attackers (19/12), and did not differ by

position and competitive level (w(2)2 ¼ 0.87, P¼

0.645). International players (15.4+ 0.4 years)

competed with their respective clubs during the

season and were included among the Portuguese

selections for the 2007 and 2008 U-17 European

League. Local players (15.4+ 0.7 years) competed

at the club level in the Aveiro, Coimbra and Leiria

districts and in the metropolitan area of Porto. The

national team finished second in 2007 and first in

2008 in the U-17 European league.

Training information

All players participated in regular training sessions

(2–5 sessions; *180–510 min �week71) with their

clubs and typically played one game per week. Clubs

participated in a 9-month competitive season

(September–May) through the Portuguese Skating

Federation. Training sessions for the international

group were irregularly scheduled during school

holidays, specifically Carnival and Easter. European

league competition usually occurred in September.

The national coach collected information about

practice sessions and minutes of training and

competition on a weekly basis for the international

players. Corresponding data for local players were

obtained by research assistants (master’s level

students) who contacted the clubs and respective

coaches on a weekly basis across the season.

Skeletal maturation

Chronological age (CA) was calculated to the nearest

0.1 year by subtracting birth date from the date on

which a posterior-anterior radiograph of the left

hand-wrist was taken. The Fels method (Roche,

Chumlea, & Thissen, 1988) was used to estimate

skeletal age (SA). It requires assessment of specific

criteria for each bone of the hand-wrist and ratios of

linear measurements of epiphyseal and metaphyseal

widths. Ratings are entered into a specific program

(Felshw 1.0 Software) to calculate SA and its

standard error of estimate. SA is not assigned when

an individual has reached skeletal maturity; he is

simply indicated as skeletally mature. Radiographs

were assessed by a single observer trained by an

experienced assessor. Comparison of independent

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assessments of 14 radiographs by the observer and

experienced assessor indicated a small difference

(0.1+ 0.3 years) and high inter-observer intra-class

correlation (0.93). The total number of indicators

(stages, grades and linear widths of epiphyses and

diaphyses) involved in the assessment of the 14 films

was 391. Disagreement between assessors occurred

on 26 occasions; all differences were by one stage/

grade or by 0.5 mm for metaphyseal and epiphyseal

widths. The difference between SA and CA was used

to classify players into four groups: [1] Late or

delayed: SA younger than CA by41.0 year; [2] On

time or average: SA within+1.0 year CA; [3] Early

or advanced: SA older than CA by41.0 year; [4]

Mature: SA skeletally mature (Malina, 2011).

Anthropometry

A single trained observer measured body mass,

stature and four skinfolds (triceps, subscapular,

suprailiac, medial calf) following standard proce-

dures (Lohman, Roche, & Martorell, 1988). Body

mass was measured to the nearest 0.1 kg with a

balance (SECA model 770, Hanover, MD, USA).

Stature was measured to the nearest 0.1 cm with a

Harpenden stadiometer (model 98.603, Holtain Ltd,

Crosswell, UK). Skinfolds were measured to the

nearest mm with a Lange caliper (Beta Technology,

Ann Arbor, MI, USA), and were summed to provide

an estimate of overall subcutaneous adiposity. Intra-

observer technical errors of measurement for stature

(0.27 cm), body mass (0.47 kg), and skinfolds (0.47

to 0.72 mm) were within the range of intra- and

inter-observer errors in several surveys in the United

States and a variety of field surveys (Malina, 1995).

Field tests

Lower limb strength was assessed with the vertical

jump using the ergo-jump (Globus, Glo1.etest, Italy)

which includes two components: squat and counter-

movement jumps (Bosco, Luhtanen, & Komi,

1983). Each protocol was performed twice and the

best scores were retained for analysis (flight time

in seconds, estimated jump height). Static grip

strength was assessed with an adjustable dynam-

ometer (Lafayette model, Lafayette, IN, USA). Run-

ning speed was measured with a 25-m sprint from a

standing start. Time was measured with photoelectric

cells (Globus Ergo Timer Timing System, Codogne,

Italy). Two trials were administered and the best was

retained for analysis. Abdominal muscular strength

and endurance was assessed as the number of sit-ups

completed in 60 seconds. The 20-metre shuttle run

was the measure of aerobic endurance (Leger,

Mercier, Gadoury, & Lambert, 1988). Participants

were familiar with the respective protocols because the

tests are included in the Portuguese Physical Educa-

tion curriculum. Based on a test-retest protocol (one

week apart), technical errors of measurement (se)

and reliability coefficients (R) were determined

(Mueller & Martorell, 1988): [1] squat jump

(n¼ 41): se¼ 1.8 cm, R¼ 0.89; se¼ 0.021 s, R¼0.76 [2] counter-movement jump (n¼ 41): se¼ 1.6

cm, R¼ 0.92; se¼ 0.018 s, R¼ 0.81; [3] 2-kg ball

throw (n¼ 41): se¼ 0.47 m, R¼ 0.90; [4] hand grip

strength (n¼ 41): se¼ 1.6 kg, R¼ 0.97; [5] 25-m dash

(n¼ 41): se¼ 0.06 s, R¼ 0.95; [6] 60-s sit-ups

(n¼ 21): se¼ 2.9 repetitions, R¼ 0.84; [7] 20-m

shuttle run (n¼ 21): se¼ 6.3 runs, R¼ 0.86.

Laboratory tests

Laboratory testing was completed within one week

and with at least 48 hours between sessions. Maximal

oxygen uptake was determined using an incremental

running test on a motorised treadmill (Quasar, HP

Cosmos, Germany). Participants started with 2 min-

utes at 8 km � h71 with subsequent increments of

2 km � h71 every minute until 16 km � h71. Exercise

intensity was subsequently increased through in-

creasing the treadmill grade by 28 every minute until

exhaustion. This protocol was suggested for the

physiological assessment of field hockey players

(Lawrence & Polgalze, 2000). Criteria for attainment

of peak oxygen uptake were: RER (Respiratory

Exchange Ratio) 4 1.00 and heart rate (HR) within

5% of the age predicted maximum (Armstrong &

Welsman, 2001). Expired oxygen (O2) and carbon

dioxide (CO2) flow and concentrations were mea-

sured every 10 seconds using a mixing chamber

system (MetaMax System, Cortex Biophysics, Leip-

zig, Germany). Calibration and ambient air mea-

surements were conducted before each testing

session according to the manufacturer’s guidelines.

Before each test, flow and volume were calibrated

using a 3-L capacity syringe (Hans Rudolph, Kansas

City, USA). Gas analysers were calibrated using

gases of known concentrations. HR was measured

throughout exercise with a commercially available

HR-monitor (Polar Electro, Finland).

After a standardised warm-up, athletes completed

the 30-s Wingate test (WAnT) on a friction-loaded

cycle ergometer (Monark 824 E, Monark AB,

Vargerg, Sweden) that was interfaced with a micro-

computer and calibrated for pedal speed and applied

resistance that was set at 0.075 kg (0.74 N) per unit

of body mass. The WAnT test began with minimal

resistance (basket supported) at 60 rev �min71. On

the command ‘‘go’’, the resistance was abruptly

applied and the computer was simultaneously

activated. To measure flywheel velocity, an optical

sensor counted pulses using 16 markers that were

mounted on the side of the flywheel in front of the

Discrimination of U-17 hockey players by competitive level 1795

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sensor (Opto Sensor 2000, Sports Medicine Indus-

tries Inc, St. Cloud, MN). Peak and minimum

outputs were calculated by averaging the five con-

secutive seconds. Test outputs included peak output

(P-WAnT, highest generated mechanical output in

watt), mean output (M-WAnT, average for the 30-s

period, watt) and a fatigue index (FI-WAnT), which

corresponds to the peak output minus lowest output

divided by peak (Inbar, Bar-Or, & Skinner, 1996).

Coefficients of variation based on replicate tests in 20

participants were 2.8%, 3.2% and 8.7% for P-WAnT,

M-WAnT and FI-WAnT, respectively.

Isokinetic concentric and eccentric knee extension

and flexion were measured using a calibrated

dynamometer (Biodex System 3, Shirley, NY,

USA) at angular velocities of 60 rad � s71 after a

10-min warm-up on a cycle ergometer (Monark

814 E, Varberg, Sweden) with minimal resistance

(basket supported) at 60 rev �min71 and 2 min of

static stretching of the hamstring and quadriceps

muscles. Participants were in a seated position in a

standardised 858 hip flexion from the anatomical

position. Range of motion was set using voluntary

maximal full knee extension (08) to knee flexion

(908). Cushioning was set using a hard deceleration

(according to manufacturer guidelines) and therefore

908 constituted the range of motion tested. In the

concentric action, the participant was instructed to

push the arm lever during extension and pull during

flexion as hard and fast as possible. In the eccentric

action, the participant was instructed to resist the

lever arm during extension and flexion as hard as

possible. Each participant performed five continuous

maximal repetitions on each mode and leg. Visual

feedback of moment versus time was provided

during the test, but no verbal feedback was given

(Baltzopoulos, Williams, & Brodie, 1991). Isokinetic

assessments were completed within a one week

period that included a familiarisation and testing

session with at least 48-h between sessions; intra-

observer reliability estimates (coefficient of variation)

for the tested muscular actions ranged from 3.9 to

6.0%. Maximal knee flexion and extension peak

torque of the best repetition in both concentric and

eccentric muscular actions were retained and ex-

pressed as Nm. Eccentric knee extension (ECCKE)

divided by concentric knee extension (CONKE) peak

torques (ECCKE/CONKE), and concentric knee

flexion (CONKF) divided by eccentric knee flexion

(ECCKF) peak torques were calculated as a predictor

of the thigh musculature stability (Aagaard, Simon-

sen, Magnusson, Larsson, & Dyhre-Poulsen, 1998).

Statistical analyses

Descriptive statistics were calculated for the total

sample (minimum, maximum, mean and standard

deviation) and Kolmogorov-Smirnov tests used to

check normality. Pearson correlation coefficients

were calculated between body mass and functional

tests. Allometric equations, Y¼ a �Xb � e, where a is

the intercept of the regression line on the Y-axis and

b is the slope of the line, were used to model the

relationship between functional variables and body

size. Values of a and b were derived from linear

regressions of the logarithmic regression transforma-

tions, in the form of log Y¼ log aþ b � log Xþ log e,where Y was the dependent variable (e.g., maximal

oxygen uptake) of functional tests measures (log-

transformed) and body size descriptor (log body

mass). Regression diagnostics (Nevill, Ramsbottom,

& Williams, 1992) were performed to check whether

the allometric models were successful in partitioning

out the influence of body size on the functional tests.

All models resulted in size-independent scores of the

functional tests (data not shown). The size-adjusted

measurements were subsequently considered in

comparisons of players by competitive level. Before

comparing local and international players, the

Levene test was used to check equality of variances.

Student t-tests were used to compare competitive

groups on CA, SA, training experience, anthropo-

metric characteristics, and field and laboratory tests.

The effect size correlations (ES-r) were estimated

using the square root of the ratio of the t-value

squared and the difference between the t-value

squared and degrees of freedom (Rosnow & Ro-

senthal, 1996). Coefficients were interpreted as

follows: trivial (r5 0.1), small (0.15 r5 0.3) mod-

erate (0.35 r5 0.5), large (0.55 r5 0.7), very

large (0.75 r5 0.9), nearly perfect (r4 0.9) and

perfect (r¼ 1). Using those variables that were

significantly influenced by competitive level, discri-

minant function analysis was used to obtain a

predictive model that permitted classification of

hockey players as local or international, i.e., the

original groupings. It was possible to order the

predictors by the magnitude of correlations with

the linear function. Subsequently, a stepwise model

was used to test the hypothesis of extracting an

alternative predictive model based on a smaller set of

variables without losing explained variance. Percen-

tages of players who were correctly classified based

on the discriminant linear functions were noted.

Significance level was less than 5%. Analyses were

performed using SPSS version 17.0 software (SPSS,

Chicago, IL).

Results

Descriptive statistics for the total sample are sum-

marised in Table I. Chronological ages ranged from

14.5 to 16.5 years, but variation in skeletal ages was

6.8 years (16 players were skeletally mature).

1796 M.J. Coelho-e-Silva et al.

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Characteristics of players by competitive level are

summarised in Tables II and III. Local and interna-

tional players did not differ in CA but differed in SA

[t¼72.43, P¼ 0.018]. Proportionally more inter-

national level players were advanced and proportion-

ally more local players were delayed and on time in

skeletal maturation [w(3)2 ¼ 7.93, P¼ 0.021]. The

proportion of skeletally mature players did not differ

between international and local players. Interna-

tional players were less experienced in competitive

hockey [t¼ 2.15, P¼ 0.035], but accumulated more

training sessions during the monitored season

[t¼72.95, P¼ 0.004] and played more minutes

(t¼73.22, P¼ 0.002). International players were,

on average, 4.4 cm taller [t¼73.02, P¼ 0.004] and

4.3 kg heavier (although the difference was not

significant, t¼71.69, P¼ 0.095). Local players

had significantly greater subcutaneous adiposity

(sum of skinfolds, t¼ 2.22, P¼ 0.030). Local and

international players did not differ in the two jumps.

Local players performed better in the 25-m dash test

[t¼72.51, P¼ 0.014], while international players

attained better performances in 60-s sit-ups

[t¼73.11, P¼ 0.003], hand grip strength

[t¼74.98, P5 0.001] and aerobic endurance [t ¼72.88, P¼ 0.005]. Since performance in hand grip

strength test was significantly related with body mass

(r¼ 0.54, P5 0.01, Table I), it was allometrically

normalised. Nevertheless, the difference in grip

strength between groups persisted (t¼74.33,

P5 0.001). International and local players did not

differ in the 2-kg ball throw before and after

normalising for body mass. The other fitness tests

were size independent and did not require allometric

scaling. Body mass was significantly correlated with

short-term outputs with the WAnT protocol (Peak

output: r¼þ 0.71, P5 0.001; Mean output: r¼0.73, P5 0.001) and the isokinetic peak torques:

CONKE (r¼þ 0.52, P5 0.001), ECCKF (r¼0.40, P5 0.001), CONKF (r¼þ 0.44, P5 0.001),

ECCKE (r¼þ0.37, P¼ 0.001). These variables were

thus normalised for variation in body mass (Table I).

The WAnT fatigue index [t¼ 3.35, P¼ 0.002] was

higher among local players (higher values correspond

to poorer performance), while peak torque in

concentric knee extension was greater in the inter-

national players [t ¼ 72.57, P¼ 0.012]. The latter

had a significantly lower ECCKE/CONKE ratio

compared to local players [t ¼ 4.08, P5 0.001].

An equation predicting group membership was

derived using the variables that differed between

international and local players [rc¼ 0.76, Eigenvalue

1.32, Wilks’ Lambda¼ 0.439, w2(11)¼ 54.37, P5

0.001]. Of the 73 players, 66 (90%) were correctly

classified as local or international. Four local players

presented a profile that did not differ from

international players (one goalkeeper, one attacker,

two defenders). Correlations between predictors

and the linear function used to re-classify the

players were ordered as follows: grip strength

(þ0.49), ECCKE/CONKE ratio (70.42), WAnT

fatigue index (70.36), 20-m shuttle run (þ0.35),

playing time (þ0.33), 60-s sit-ups (þ0.32), annual

number of training sessions (þ0.31), stature

(þ0.29), peak torque CONKE (þ0.25), 2-kg ball

throw (þ0.22), peak torque CONKF (0.20). When

the stepwise protocol was used in the discriminant

analysis, a linear combination of five variables

correctly predicted 85% of the players into the

original groups [rc¼ 0.70, Eigenvalue¼ 0.953,

Wilks’ Lambda¼ 0.51, w2(4)¼ 46.20, P5 0.001].

After six steps, the final model included grip

strength, ECCKE/CONKE ratio, annual number of

training sessions, playing time, and WAnT fatigue

index (Table IV). Six local players were classified as

international, while five international players were

classified as local. Incorrectly classified players

included two goalkeepers, five defenders and four

attackers.

Discussion

Players selected for the Portuguese national U-17

roller hockey team tended to be more advanced in

skeletal maturation and taller with less subcutaneous

adiposity. The hypothesis of the study dealing with

growth and maturity status was partially supported

and consistent with previous studies examining youth

male athletes in other team sports (Coelho-e-Silva

et al., 2010b; Figueiredo, Goncalves, Coelho-e-Silva,

& Malina, 2009b; Malina, 2011; Mohamed et al.,

2009; Vaeyens et al., 2006). In addition, maximal

oxygen uptake of hockey players was comparable to

male athletes of similar age in several team sports but

lower than participants in endurance-based individual

sports-triathlon, long-distance running, cross country

skiing, and swimming (Bunc, 2004). Compared to

athletes of the same age and young adults in several

other team sports (Apostolidis, Nassis, Bolatoglou, &

Geladas, 2004; Hoffman, Epstein, Einbinder, &

Weinstein, 2000; Potteiger, Smith, Maier, & Foster,

2010), hockey players had poorer short-term outputs

(i.e., squat and counter-movement jumps, 25-m

sprint and 30-s WAnT). On the other hand, maximal

isokinetic strength was comparable to young male

athletes in basketball (Buchanan & Vardaxis, 2003,

2009; Gerodimos et al., 2003) and soccer (Forbes

et al., 2009a; Forbes, Sutcliffe, Lovell, McNaughton,

& Siegler, 2009b; Iga, George, Lees, & Reilly, 2009).

International U-17 roller hockey players were, on

average, 4.4 cm taller and 4.3 kg heavier than local

U-17 players (Table II, although the difference in

body mass was not statistically significant: t¼71.69,

P¼ 0.095, effect size¼ 0.19). Such variation in

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stature and body mass is often overlooked in

comparisons of fitness tests between players of

different competitive level. Maximal oxygen uptake

is routinely expressed as a ratio standard (e.g., ml �min71 � kg71), despite theoretical and statistical

limitations (Armstrong & Welsman, 1994; Nevill

et al., 1992; Tanner, 1949). The current study used

allometric scaling for comparisons of measurements

correlated with body mass. The differentiation of

effects due to size, maturation, training and selection

is complex.

Local roller hockey players attained better perfor-

mances in the squat jump and 25-m sprint.

Of interest, international adolescent players had

Table II. Descriptive statistics for players by competitive level, results of Levene’s test for equality of variances and student t-tests

comparing groups (chronological age, skeletal age, training variables, morphology and field tests).

Local (n¼ 41) International (n¼32)

Levene-test Student’s t

Effect size rF P t P

Chronological age [CA], years 15.41+ 0.77 15.42+0.42 7.41 0.008 70.09 0.929 0.01

Skeletal age [SA], years* 16.1+ 1.6 16.8+1.1 12.81 0.001 72.43 0.018 0.29

Skeletal maturity status, f

Delayed 6 1

On time 18 8

Advanced 9 15

Mature 8 8

Training experience, years 8.9+ 1.2 8.3+1.0 8.26 0.005 2.15 0.035 0.24

Annual training sessions, n 106+ 14 117+18 1.88 0.175 72.95 0.004 0.33

Annual playing time, minutes 720+ 261 964+385 1.97 0.165 73.22 0.002 0.36

Body mass, kg 62.1+ 12.7 66.4+9.0 5.04 0.028 71.69 0.095 0.19

Stature, cm 168.0+ 7.7 172.4+4.7 4.65 0.035 73.02 0.004 0.32

Sum of skinfolds, mm 54.5+ 26.1 43.5+16.3 4.35 0.041 2.22 0.030 0.24

Squat jump, cm 31.7+ 5.2 29.3+4.7 0.73 0.395 2.04 0.045 0.24

Squat jump – flight time, s 0.507+ 0.043 0.488+0.049 0.07 0.796 1.72 0.090 0.20

Counter-movement jump, cm 33.1+ 5.6 32.7+6.4 0.24 0.624 0.24 0.812 0.03

Counter-movement jump – flight time, s 0.518+ 0.043 0.508+0.038 0.01 0.948 1.03 0.306 0.12

Sit-ups, repetitions 27.7+ 4.0 30.8+4.4 0.03 0.863 73.11 0.003 0.35

Hand grip strength, kg 36.7+ 8.2 44.6+5.2 4.88 0.030 74.98 50.001 0.49

Hand grip strength, kg � kg70.64 2.63+ 0.47 3.05+0.33 1.72 0.194 74.33 50.001 0.46

2-kg ball throw, m 7.50+ 1.44 8.00+1.19 1.93 0.169 71.59 0.117 0.19

2-kg ball throw, m � kg70.45 1.18+ 0.20 1.21+0.16 4.22 0.044 70.88 0.382 0.10

25-m dash, s 3.99+ 0.25 4.13+0.20 1.34 0.251 72.51 0.014 0.29

20-m shuttle run, m 1624+ 332 1839+291 0.05 0.832 72.88 0.005 0.32

*An SA is not assigned to skeletally mature players; subsample were 33 local and 24 international.

Table III. Descriptive statistics for players by competitive level, results of Levene’s test for equality of variances and student t-tests

comparing groups (laboratory tests).

Local (n¼ 41) International (n¼ 32)

Levene-test Student’s t

Effect size rF P t P

Peak oxygen uptake, L �min71 3.90+ 0.69 3.87+0.52 2.66 0.107 0.20 0.840 0.02

Peak oxygen uptake, mL � kg70.60 �min71 32.88+ 4.02 31.32+3.75 0.27 0.605 1.69 0.096 0.20

WAnT: peak output, watt 583+ 152 613+91 11.20 0.001 71.06 0.295 0.12

WAnT: peak output, watt � kg70.95 11.55+ 2.25 11.43+1.21 4.00 0.049 0.29 0.776 0.03

WAnT: mean output, watt 489+ 116 529+67 10.39 0.002 71.83 0.072 0.20

WAnT: mean output, watt � kg70.89 12.43+ 2.11 12.69+1.12 5.36 0.024 70.68 0.500 0.07

WAnT: fatigue index 33.3+ 5.4 27.8+8.0 5.03 0.028 3.35 0.002 0.38

Peak Torque CON(KE), Nm 168.1+ 40.7 188.1+25.5 4.99 0.029 72.57 0.012 0.28

Peak Torque CON(KE), Nm � kg70.59 14.78+ 2.90 15.90+2.08 4.05 0.048 71.93 0.058 0.21

Peak Torque ECC(KF), Nm 240.4+ 62.0 251.8+78.6 2.38 0.127 70.69 0.490 0.08

Peak Torque ECC(KF), Nm � kg70.57 22.95+ 5.09 23.07+6.81 1.92 0.170 70.08 0.936 0.01

Peak Torque CON(KF), Nm 98.4+ 23.2 108.0+17.7 2.31 0.133 71.96 0.055 0.23

Peak Torque CON(KF), Nm � kg70.48 13.63+ 2.83 14.45+2.14 5.47 0.022 71.40 0.165 0.16

Peak Torque ECC(KE), Nm 155.6+ 35.8 148.7+32.9 0.15 0.702 0.85 0.398 0.10

Peak Torque ECC(KE), Nm � kg70.39 31.20+ 6.15 28.99+6.08 0.32 0.573 1.53 0.130 0.18

Ratio: CON(KF)/ECC(KF) 0.42+ 0.06 0.46+0.13 6.76 0.011 71.78 0.082 0.22

Ratio: ECC(KE)/CON(KE) 0.94+ 0.15 0.79+0.15 0.22 0.644 4.08 50.001 0.44

*An SA is not assigned to skeletally mature players; subsample were 33 local and 24 international.

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less experience in the sport as reflected in years of

training. Given the cross-sectional design of the

present study, a causal relationship between training

experience (years of training, annual number of

sessions, playing time) and development in particular

functional aspects cannot be assumed. In parallel,

differences in body size may have contributed to

better performances attained by international hockey

players in hand-grip strength, although differences

persisted when the analysis was done after scaling for

body mass. International and local U-17 roller

hockey players did not differ in maximal oxygen

uptake, but the former covered a greater distance in

the 20-m endurance shuttle run. A study of

adolescent basketball players noted a gradient by

stage of sexual maturation in aerobic endurance

measured in a continuous 20-m shuttle run test

(Coelho-e-Silva, Carvalho, Figueiredo, & Malina,

2008). Among 14-year-old basketball players, those

in pubic hair stage 5 (PH 5, mature) were 17 cm

taller and 31.3 kg heavier compared to players in PH

3 (mid-puberty); the former, however, attained

poorer performances in the shuttle run test

(1498 m and 1176 m, respectively, for participants

in PH 3 and 5). Consistent trends were also noted

among soccer players of 11–12 years of age. Players

advanced in maturation based on the difference

between skeletal and chronological ages were 8.5 kg

heavier, 9.0 cm taller but covered 566 m less

distance in the yoyo test compared to players delayed

in skeletal maturation relative to chronological age

(Figueiredo et al., 2009a).

A comparison of youth soccer players who

dropped out, continued at the club level or moved

to a higher level indicated differences at baseline, 11–

12 and 13–14 years (Figueiredo et al., 2009a).

Players who moved to a more elite level were

advanced in skeletal maturation, larger in body size

and performed better in three functional (vertical

jump, endurance shuttle run, sprint speed) and three

soccer-specific skill tests compared to those who

dropped out or who remained at the club level. More

recently, a study of U-14 soccer players considered

variables that discriminated local club and regional

elite players (Coelho-e- Silva et al., 2010b). A linear

combination of stature, 30-m dash, 106 5-m agility

shuttle run, squat jump and years of training

correctly identified 90% of defenders, 89% of

midfielders and 79% of forwards regardless of

competitive level. Among this sample of U-17 youth

roller hockey players, a larger set of both laboratory

and field tests of functional capacities and two

models were used. When all variables were entered,

the 20-m endurance shuttle run, sit-ups and annual

number of training session were among predictors

with the highest coefficients. With the stepwise

method using a smaller set of predictors, the final

model included grip strength, ECCKE/CONKE ratio,

annual number of training sessions, playing time and

WAnT fatigue index (Table IV). Local and interna-

tional hockey players did not significantly differ in

WAnT peak and mean outputs. There is a need for

further study with concurrent short-term protocols

assessing the force-velocity characteristics of players.

Although the WAnT has been used extensively and

in a variety of settings in children and adolescents

and was highly reliable and sensitive (Bar-Or, 1987),

a lack of valid, reliable and standardised methods of

assessing maximal short-term outputs in youth has

been suggested (Van Praagh & Dore, 2002). More-

over, the specificity of WAnT for athletes in non-

cycling sports has not been established.

During rapid knee extension and towards full

extension, eccentrically acting hamstrings have been

shown to produce a braking joint flexor moment that

is equal to or greater than the extensor moment

exerted by the quadriceps (Aagaard et al., 1998).

Thus, an ECCKE/CONKE ratio of 1.0 indicates that

the eccentrically acting hamstrings have the ability to

fully brake the action of the concentrically contract-

ing quadriceps (Coombs & Garbutt, 2002). A low

CONKF/ECCKF ratio also indicates that the specific

length tension and force-velocity properties are

impaired for the hamstring muscles and enhanced

for the quadriceps muscles during fast forceful knee

flexion (Coombs & Garbutt, 2002). Results for the

torque ratios in the present study suggested an effect

of competitive level: elite players tended to produce

lower values for the ECCKE/CONKE ratio and higher

values of ECCKF/CONKF ratio. Longitudinal study

Table IV. Summary of stepwise discriminant analyses to predict competitive level (local versus international).

Step

Variables

Wilks’ Lambda df1 df2 df3 Exact F df1 df2 PEntered Removed

1 Hand grip strength 0.761 1 1 71 22.26 1 71 50.01

2 Ratio: ECC(KE)/CON(KE) 0.599 2 1 71 23.46 2 70 50.01

3 Annual training sessions 0.555 3 1 71 18.47 3 69 50.01

4 Playing time 0.525 4 1 71 15.37 4 68 50.01

5 WAnT: fatigue index 0.493 5 1 71 13.80 5 67 50.01

6 Annual n8 of training sessions 0.512 4 1 71 16.21 4 68 50.01

1800 M.J. Coelho-e-Silva et al.

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is needed to examine potential inter-relationships

between the amount and variability of training and

torque ratios among adolescent roller hockey players

and athletes in other sports.

It is likely that other variables not considered in this

analysis are important in player selection. There is a

need to consider sport-specific skills (Coelho-e-Silva

et al., 2008), tactical skills (Elferink-Gemser,

Visscher, Richart, & Lemmink, 2004b), and match-

related and other behavioural variables, especially

perceptual abilities related to visual search and playing

spaces (Vaeyens, Lenoir, Williams, & Philippaerts,

2007) and psychological characteristics. Variables not

ordinarily considered in athlete selection, but which

should also be considered, include coach character-

istics, behaviours and expectations; coach-athlete

interactions; and the overall training environment.

Acknowledgments

Fundacao para a Ciencia e a Tecnologia [PTDC/DTP-

DES/1178/2012, SFRH/BD/64648/2009]. The con-

tribution of Rui Soles Goncalves in the assessment of

isokinetic strength was appreciated. Humberto Car-

valho contributed in the early discussion of the

manuscript.

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