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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).
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Tab
leI.
Des
crip
tive
stat
isti
csfo
rth
eto
tal
sam
ple
(n¼
73
),re
sult
so
fK
olm
ogo
rov-
Sm
irn
ov
test
for
chec
kin
gth
en
orm
alit
yo
fth
ed
istr
ibu
tio
n,
biv
aria
teco
rrel
atio
ns
bet
wee
nb
od
ym
ass
and
fitn
ess
vari
able
s,an
db
exp
on
ents
der
ived
from
anal
ysis
of
cova
rian
ce(A
NC
OV
A)
of
log-t
ran
sfo
rmed
dat
a.
Ran
ge
(min
–m
ax)
Mea
n+
sK
olm
ogo
rov-
Sm
irn
ov
Z(P
)
Co
rrel
atio
nb
etw
een
bo
dy
mas
san
dfi
tnes
s
Mas
s
exp
on
ents
Co
rrel
atio
n
bet
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nb
od
ym
ass
and
scal
edfi
tnes
s
rP
bS
Er
P
Ch
ron
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gic
alag
e[C
A],
year
s1
4.5
–1
6.5
15
.4+
0.6
0.9
6(0
.31
7)
Skel
etal
age
[SA
],ye
ars
(n¼
57
)*1
3.1
–1
7.9
16
.4+
1.5
1.1
9(0
.11
3)
Bo
dy
mas
s,kg
38
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8.6
63
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11
.30
.59
(0.8
78
)
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ture
,cm
14
3.6
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82
.21
69
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6.9
0.7
2(0
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2)
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0.3
36
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þ0
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16
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76
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-up
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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.
Discrimination of U-17 hockey players by competitive level 1799
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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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