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J Sports Med Phys Fitness. 2018 Jun 27. doi: 10.23736/S0022-4707.18.08547-X. [Epub
ahead of print]
Title: The effect of a concentrated period of soccer specific fitness training with small-sided
games on physical fitness in youth players
Authors
Darren J. Paul1, Joao B. Marques1, George P. Nassis1*
Affiliations
1National Sports Medicine Programme, Excellence in Football Project, Aspetar - Orthopedic
and Sports Medicine Hospital, Sports City, 29222 Doha, Qatar.
*Corresponding Author: George P. Nassis, PhD, georgenassis@gmail.com
Running title: Concentrated training in soccer
Abstract
BACKGROUND: It is unknown whether a concentrated period of small-sided games and
high intensity training is an effective training approach in youth soccer players. The aim of
the study was to examine the effect of a concentrated period of soccer specific training on
physical fitness in youth players. METHODS: Nineteen male soccer players, from two teams,
participated (mean ± SD age: 16.2 ± 0.8 years; body mass: 58.2 ± 7.6 kg; height: 170.8 ± 7.7
cm). One team performed 5 days of small-sided games and high intensity training (SSG &
HIT; n = 12) and the other team regular soccer training with 1 day of SSG and HIT (REG; n
= 7) weekly for 4 weeks. The 30-15 intermittent fitness test (30-15 IFT), countermovement
jump (CMJ) and change of direction (COD) performance were measured pre and post inter-
vention. Heart rate (HR) and rating of perceived exertion (RPE) were recorded and session
load calculated (RPE x minutes). RESULTS: Average % of maximum HR and session load
were 83% and 344 AU for the SSG & HIT vs 73% and 253 AU for the REG (P< 0.05). 30-
15 IFT improved for the SSG & HIT (from 17.0 ± 1.1 to 18.4 ± 0.8 km/h; p< 0.05; ES =
0.57) with no difference for the REG group (Pre: 17.9 ± 1.3, Post: 18.2 ± 1.6 km/h, ES=
0.10). CMJ and COD were unchanged in both groups and no injuries were reported. CON-
CLUSIONS: A 4-week concentrated period of daily SSG & HIT is effective for improving
endurance performance in youth soccer players. This was without injuries and without negat-
ing performance in power and change of direction.
2
Key words: Intensified, small sided games, high intensity training, junior
Introduction
Periodization is described as a framework for systematic variation of training parameters with
the goal of optimizing adaptations to a particular sport 1. The general notion is that a cumula-
tive overload of training will result in a more powerful stimulus for adaptation, given that ap-
propriate recovery periods are planned. In terms of physical training for soccer players, a typ-
ical week may be devoted to strength/power, endurance, speed, agility, injury prevention and
specific motor skills training. Arguably this may be considered an established approach that
is common in most soccer clubs 2. It has rarely been examined whether this approach is the
most optimal way for enhancing physical capacities, particularly in youth soccer players. In-
deed, whereby practitioners typically manipulate the exercise selection, intensity and volume,
changes to the training organization are often overlooked.
Players are regularly tasked with performing at high levels and during regular time periods,
as shown during congested fixture periods 3. When designing training drills therefore, it is
highly likely that coaches will gravitate towards modes of training that can simultaneously
benefit a range of fitness components. Small-sided games (SSG), for instance, are looked up-
on favourably as a way of simultaneously improving the physical, technical and tactical qual-
ities of the players 4. In a similar instance, Taylor et al. 5 found repeated sprint training might
induce small to large improvements in power, speed, repeated sprint ability and endurance.
The notion is that of hastening the training response and/or getting ‘the biggest bang for their
buck’.
Concentrated or intensified training, sometimes analogous with broadly used terms such as
block periodization or shock mesocycle, has been postulated as a viable method of enhancing
performance 6. This form of training organization is generally considered more suitable for
continuous cyclical sports (running, swimming, cycling) 7,8 rather than intermittent team (e.g.
soccer) based sports. Favourable gains in physiological and performance measures have in-
deed been reported when including a period of intensified training in other sports (e.g. skiing
and cycling). For instance, increases in VO2max have been observed in response to period of
intensified training in cyclists 7,8 and skiers, respectively 9.
Concentrated/intensified training organization has gained fewer acceptances within soccer,
although there are emerging studies examining this area 6,10,11. The rationale for it not being a
common procedure is that it may inappropriately load the players and may actually prove de-
bilitative to performance, yet this tenet appears anecdotal given the paucity of underpinning
literature. In fact, a 2-week period of intensified training (SSG and speed endurance) im-
proved repeated sprint ability (RSA) and running economy in a group of senior soccer play-
ers 10. No improvement, however, was observed in Yo Yo Intermittent Recovery Test Level 2
(YYIRTL2) 10. Another study in semi-professional soccer players has shown a 2-week period
of sprint interval training (6 sessions) to improve YYIRTL1 and VO2max by 17 and 3%, re-
spectively 12. A recent study also showed superior RSA performance after a 13-day intensi-
fied period of high-intensity training (HIT) as well as a significant improvement in YYIRTL2
11. The training comprised of interval running, SSG or a dribbling course, each consisting of
4 x 4-min bouts separated by 3min active recovery 11. Although a reduction in performance
(YYIRTL2 and RSA mean and RSA index) was observed following a 25-day period without
3
HIT (in order to test sustainability), values remained significantly higher than baseline 11. Un-
fortunately, this particular study did not include a comparative group, nor were any monitor-
ing methods used to quantify the workload (e.g. heart rate). A more recent study of similar
duration (12 days) examined the effect of a maximal shuttle run shock microcycle in hypoxia
on soccer specific performance and oxidative stress in soccer players 6. Participants were
randomly assigned to hypoxia (~3300m) or normoxia training and performed 8 maximal
shuttle run sessions within 12 days. Interestingly, YYIRT performance improved inde-
pendently of the hypoxia stimulus.
It is unknown whether a concentrated period of SSG & HIT is an effective training approach
in youth soccer players. Therefore, the aim of the present study was to investigate the effects
of a 4-week period of concentrated SSG and HIT (5 d/wk) compared to regular soccer train-
ing incorporating 1 d/wk of SSG and HIT on performance measures in youth soccer players.
Our hypothesis is that a concentrated 4-week period of SSG & HIT will improve soccer-
specific fitness more than regular soccer training.
Methods
Experimental Approach to the Problem
All participants have given their informed consent for participation in the research study. The
study has been approved by Anti Doping Lab Qatar Institutional Review Board (protocol
number: SCH-ADL-070, date of approval: 21/10/2014).
Two separate teams competing in the same professional division in Qatar national league
were approached to participate. Based on previous 3 championship rankings both teams were
classified within the top 5 in the league. The training programme of both teams included 30
min physical training followed by 60 min of technical and tactical training whereby the coach
performed drills, positional play and some small and large sided games. Performance
measures were assessed using the 30-15 intermittent field test 13, 40 m sprint, countermove-
ment jump and a modified L run change of direction test. A cluster randomisation of partici-
pants was performed to determine the selection of groups.
Subjects
Nineteen male soccer players from 2 separate teams participated in the study (team 1; mean ±
SD age: 16.2 ± 0.8 years, height: 170.8 ± 7.7 cm, body mass: 58.2 ± 7.6 kg - team 2; age:
16.4 ± 0.7 years, height: 171.2 ± 7.5 cm, body mass: 57.9 ± 7.2 kg). Their normal week
schedule consisted of five training sessions (~90 min each), comprising of 30 min physical
training and 60 min of tactical training and one 90 min competitive league match. Players
reported no significant involvement in other sports outside of their training schedule. Both
teams consisted of ~20 players and all were measured at baseline.
Procedures
Prior to the intervention and as part of the 30 min physical training, both teams performed a
combination of endurance, strength/power, speed and agility over the 5 training days. For the
intervention period one team was assigned to a 4-week period of concentrated training
whereby their designated physical training time was replaced with 4 sessions of small sided
games (SSG) and 1 high intensity training (HIT) session (5 sessions in total) per week (SSG
& HIT, n = 12). The other team continued their regular (REG, n = 7) training organisation
4
which comprised of 1 (total) SSG and HIT session as well as training of strength/power and
speed and agility, respectively. All testing and the training intervention took place within the
competitive season, between October and November and approximately 2 months after the
start of preseason.
All participants were familiar with each of the testing procedures and the training content.
The technical coach was asked to refrain from strenuous drills and players to avoid demand-
ing physical activity in the 36 h preceding testing. All pre testing was performed 5 days be-
fore the start of the intervention and post testing within 7 days after the intervention period.
Maximal aerobic velocity, countermovement jump and change of direction were performed
pre and post the 4-week training intervention period. Technical and tactical training remained
similar between groups and comprised of technical drills and match play. Heart rate (Polar
team 2, EO, Finland), and session rate of perceived exertion (RPE) were recorded.
Training
All training sessions (SSG & HIT and REG) included a similar standardized warm-up (~10
min) consisting of running, jogging, dynamic exercises and short accelerations and decelera-
tions. The SSG & HIT performed 4 SSG and 1 interval training session per week (in total 16
SSG and 4 HIT sessions, Table 1). The SSG comprised of 4 x 4 min interspersed with a 1
min passive recovery. Player configuration was 4 vs 4 while task constraints were adapted for
each session to offer variety. All of the SSG’s were performed in an area of 30 x 25 m (rela-
tive pitch area= 93.7 m2) and a large number of balls were placed around the perimeter of the
area to ensure the intensity remained high. Verbal motivation was given during all sessions to
encourage the maintenance of a high work-rate. The HIT session was based on individual 30-
15 Intermittent Field Test (30-15 IFT) performance results. Players performed 2 x 6 min
(30/15 sec) at 110% of 30-15 IFT test performance and 2 x 4 min (15/15 sec) at 120% of 30-
15 IFT test performance. The two sets were separated by a rest period of 90 sec. The players
performed 8 repetitions in each set. The SSG & HIT group performed no other form of spe-
cific designated fitness or conditioning, such as strength, power speed and agility training.
The REG group training included only 1 combined SSG & HIT session per week that con-
sisted of 4 x 4 min SSG interspersed with 1 min passive recovery and 2 x 6 min (30/15 sec) at
110% 30-15 IFT test performance (8 repetitions in total). The constraint for the SSG training
in the REG group was that no goal was included and teams had to retain possession. The
REG group also performed two strength and power sessions including resistance machine
training, plyometrics and field based strength training; 1 speed and agility (accelerations, de-
celerations and 1 vs 1 duals) and 1 injury prevention (FIFA 11+) session per week. In total
the REG group performed 4 SSG & HIT sessions during the 4-week period (Table 1).
Training intensity was classified into 5 different zones: (1) 90–100 %; (2) 80–89 %; (3) 70–
79 %; (4) 60–69 %; and (5) 50–59 % of maximal heart rate (HR). The warm up was excluded
from the analysis with only active training time analysed. Rate of perceived exertion was rec-
orded within 10 min of exercise completion using the CR-10 Borg scale, as described by Fos-
ter et al 14. The duration (min) of the entire training session was also noted and the product of
the session-RPE multiplied by session duration (min) was termed the session load. All play-
ers had been familiarized to this scale for at least one season before the start of the study.
INSERT TABLE 1 ABOUT HERE
5
Testing
The 30-15 IFT was performed outside on a grass field and players wore regular soccer boots.
The 30-15 IFT protocol consists of 30 sec shuttle runs in a forward direction between two
lines 40 m apart interspersed with 15 sec passive recovery periods 13. Running speed began at
8 km/h with increments of 0.5 km/h every 30 sec. During the 30-sec running periods, partici-
pants were instructed to run back and forth at the given pace, governed by a pre-recorded
beep and until volitional exhaustion, defined as being unable to follow the pace for 2 consec-
utive beeps. During the 15-sec recovery periods, the players were required to walk in a for-
ward direction towards the nearest line, either the two lines 40 m apart or the mid-line; next
30-sec running bout started from this line. The velocity attained during the final complete
stage was determined as the participant’s maximal aerobic velocity 13. Test reliability on a
sub sample (n = 16) was r = 0.91.
Countermovement jump (CMJ) height was assessed from time in flight using an Optojump
photocell system (Microgate, Bozen, Italy). All participants performed a standardised 10 min
warm up consisting of jogging, skipping, dynamic exercises and accelerations and 2 practice
jumps prior to test trial. Participants completed 3 countermovement vertical jumps with hands
on the hips with 30 sec of rest and the best attempt was taken for further analysis. Test relia-
bility on a sub sample (n = 16) was r = 0.89.
Change of direction (COD) performance was assessed using a modified L run COD test. Par-
ticipants placed the preferred foot 0.50 m behind the starting set of timing gates (Microgate,
Bozen, Italy). Upon instruction, they performed a maximal sprint towards a pole at 10 m be-
fore decelerating and perform a 90-degree cutting manoeuvre before sprinting through the
second set of timing gates 10 m away. The test was 20 m in length and players performed 2
trials to the left and right (4 in total) with the best performance for each side taken for analy-
sis. Test reliability on a sub sample (n = 16) was of r = 0.91.
Statistical Analysis
Descriptive statistics of the data are presented as means ± standard deviation (SD). Statistical
analysis was performed using repeated measure ANOVA (condition x time) and magnitude-
based inferences (MBI). MBI is a well-established analytic approach that provides infor-
mation on the magnitude of effects of training that is meaningful to the practitioners. Mean
effect size (ES) were calculated and the criteria to interpret the magnitude of the ES were:
0.0–0.2 trivial, 0.2–0.6 small, 0.6–1.2 moderate, 1.2–2.0 large, and >2.0 very large 15. Differ-
ences between groups with regards to average training heart rate and player load were as-
sessed with t-test for independent samples. Statistical analysis was performed using the Sta-
tistical Package for the Social Sciences (SPSS, version 21.0.) and the level of significance
was set at p< 0.05.
Results
A greater 30-15 IFT final running speed from pre to post (8.2 % improvement, p< 0.05) and a
small (ES= 0.57) beneficial effect for the SSG & HIT group was found (Table 2). A small
beneficial within group effect (COD right, ES= 0.32; COD left, ES= 0.24), though not signif-
icant decrease (improvement), was found for COD performance on the right and left side for
6
the SSG & HIT. A trivial change was reported in countermovement jump performance for the
SSG & HIT. The within group change was trivial for all measures (range: ES=0.03-0.20)
(Table 2) for the REG group.
INSERT TABLE 2 ABOUT HERE
No difference was observed between the groups for training time (90 min). Figure 1 illus-
trates the distribution of the endurance training into the different intensity zones for both
groups. Average training intensity (% HR max) and player load were greater (p< 0.05) for the
SSG & HIT (83.7 % and 344 AU) vs REG group (73.4 % and 253 AU), respectively. Attend-
ance was 89 % and 87 % for the SSG & HIT and REG group during the training intervention,
respectively. No injuries, in accordance with Fuller et al. 16 classification, were reported for
either group during the 4-week training intervention.
INSERT FIGURE 1 ABOUT HERE
Discussion
The aim of the present study was to compare the effect of a 4-week period of concentrated
SSG & HIT (4 d/wk) vs a regular training approach (SSG & HIT 1 d/wk) on fitness charac-
teristics in youth soccer players. The 4-week period of intensified training including SSG &
HIT training improved endurance performance by 8.2 % in these soccer players. Although no
improvement was seen in countermovement jump or change of direction following the SSG
and HIT neither was there any negative effect. Accordingly, it seems solely performing SSG
and HIT can provide a potent stimulus capable of inducing gains in exercise performance.
The interest towards periods of concentrated training has increased steadily over recent years.
However, it remains less studied in soccer compared to other sports such as skiing and cy-
cling 7,8,9 . The comparison of our research with similar studies, therefore, is limited 6,10,11. We
observed 4 weeks of concentrated SSG & HIT training performed 5 days per week to be su-
perior to 1 day per week. Research has shown even 14 days 6,11 of intense training to provide
a beneficial effect on performance measures in soccer players. Collectively, these studies,
including the present one, demonstrate concentrated training as a viable approach to training
of soccer players of different levels. The improvement in endurance performance reported in
the present study is in agreement with one study 11 but not wholly with another 10. Although
Christensen and colleagues 10 reported no significant improvement in YYIRTL2, significant
differences were shown from pre to post in running economy and RSA.
It is also noteworthy that no other form of specific training relating to strength, power, injury
prevention, speed and/or agility was undertaken in the present study in the SSG and HIT
group. This culminated in 20 endurance sessions over the 4-week period, compared to 4 ses-
sions for the regular group, respectively. Obviously the concern with focusing solely on one
fitness component is that of a concomitant decrease in other physical qualities. We have
shown over a relatively short term this was not the case. According to our results the concen-
trated training approach was not associated with negative effects in CMJ and/or COD. We
speculate that the high frequency of SSGs performed during the course of the 4-week period
as being a possible explanatory factor. Indeed, the positive effect of SSG on agility perfor-
mance has recently been shown in soccer players 17. Even at the elite level, whereby gains in
7
performance become more challenging, adding SSG to a training programme has proven to
be beneficial 4. Dedicated time towards improving these qualities (power, COD and speed) is
indeed important for the overall development of youth players 18. During certain stages, how-
ever, coaches should not be deterred from including a relatively short period of organised
training focusing predominantly on SSG and/or HIT. Admittedly, the medium and long-term
implications of SSG/HIT on speed, COD and power is unknown and future research should
address the sustainability or whether any negative effects are associated with this training ap-
proach. It is worth remembering, however, that Wahl et al. 11 reported fitness levels to re-
main significantly higher than baseline despite a 25-day period without HIT. According to
our results it seems that a period of concentrated training comprising of SSG & HIT is a fea-
sible option of training in youth soccer players. Its appeal is substantiated by no reported in-
juries during the intervention period. The process of intensifying training is commonly em-
ployed by athletes in an attempt to enhance performance 19. Obviously, caution must be taken
to avoid non-functional overreaching and subsequent overtraining syndrome. A degree of
functional overreaching may, however, be key to performance enhancement 20.
Players are regularly tasked with performing at high levels and during regular time periods,
as shown during congested fixture periods 3. Integrating a period of concentrated training
may facilitate this transition and possibly identify players who may excel, or struggle, in
these circumstances. Indeed, the coach also perceived a greater sense of ‘effort and resili-
ence’ amongst the players. We concede these observations lack any objective data, however,
it would be somewhat erroneous of us to dismiss such real-world feedback when examining
the feasibility and appropriateness of this concentrated period of training.
The findings of the present study raise interest in ways to further improve physical perfor-
mance in youth soccer players. This resulted in greater improvements in endurance perfor-
mance. Although commonplace, it has rarely been examined whether it (regular approach) is
optimal for enhancing physical capacities. Practitioners should be willing to adopt different
training approaches, particularly at the youth level where the focus should be more on devel-
opment rather than performance. Training modifications typically manipulate the exercise
selection, intensity and volume in an attempt to elicit greater gains in performance, changes
to the training organisation are however, often overlooked.
We acknowledge the current study has limitations. Recruiting participants from two separate
teams is particularly acknowledged, however, this is a common issue within applied research.
Although similarities were evident, it is inevitable that differences in exact technical and tac-
tical content may be a contributing factor. In addition, pre-testing values of 30-15 intermittent
fitness test might have affected at some extent the outcome of training. It is likely that future
studies will benefit from additional objective measures, such as global positioning systems, to
offer a greater insight regarding the workloads performed 21,22. Longitudinal experiments are
necessary to identify the long-term effect as well as uncover any potential confounding effect
associated with this training approach.
In conclusion, 4 weeks of daily (5 d/wk) SSG & HIT is superior to regular soccer training
incorporating 1 d/wk of SSG & HIT to improve intermittent endurance performance without
negatively impacting COD and leg power. Although no improvement was observed for leg
power and COD performance, neither was there any decrement in these parameters. In addi-
tion, no injuries were reported as a result of this training. Thus, a concentrated period of train-
8
ing, whereby focus is given to one fitness component, is effective in improving endurance
without negating other physical fitness qualities.
Practical applications
Small-sided games and high intensity running drills constitute an important part of a weekly
training programme within a soccer club setting. The tendency is for coaches to focus on ma-
nipulating the constraints (rules, instructions, etc) of these (SSG and HIT) elements. Our re-
sults may provide reassurances to coaches that changing the training organisation (i.e. includ-
ing a period of concentrated training) is an effective tool that is worth considering. Imple-
menting this approach (intensified period of training) may be particularly useful when the
preparation period is short (i.e. during preseason) or when the players need to develop and/or
maintain several physical qualities while upholding a large element of technical and tactical
involvement. Players and coaches will be highly motivated and receptive towards our find-
ings knowing that predominantly playing soccer, in a SSG format, can prove beneficial to
general physical fitness. Including an intensified period of training may also provide an, albe-
it indirect, insight into how players cope with greater training load and intensity. This may
prove useful given that the demands of soccer training and match play seem to be ever grow-
ing.
Acknowledgements
The authors would wish to thank the athletes and coaching staff for participating in the study.
We wish to confirm that there are no known conflicts of interest associated with this publica-
tion and there has been no significant financial support for this work that could have influ-
enced its outcome.
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10
Table 1. Weekly training schedule and approximate training session durations for the SSG &
HIT and REG group.
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
SSG &
HIT
group
SSG
(transition
play)
SSG (pos-
session)
HIT
SSG
SSG (in-
cluding
goal
keepers)
Match
No train-
ing
REG
group
Strength
& power
training
SSG & HIT
Strength
& power
training
Injury pre-
vention
Speed
and Agili-
ty
Match
No train-
ing
Table 2. Performance measures before and after 4 weeks of intensified SSG&HIT vs
regular training (mean (SD)).
SSG&HIT
REG
Test
Pre
Post
ES
Pre
Post
ES
30-15 IFT (km/h)
17.0(1.1)
18.4(0.8)*
0.57
17.9(1.3)
18.2(1.6)
0.10
Countermovement
Jump (cm)
33.5(5.8)
34.0(5.1)
0.04
30.8(3.8)
31.7(5.1)
0.20
Agility Right (s)
4.21(0.1)
4.08(0.2)
0.32
3.89(0.1)
3.88(0.1)
0.03
Agility Left (s)
4.23(0.2)
4.16(0.1)
0.24
3.91(0.1)
3.88(0.1)
0.11
SSG&HIT=Small sided games and high intensity training; REG= Regular training;
IFT=Intermittent field test; ES=Effect size; *p< 0.05 vs pre value
11
Fig 1. Heart rate distribution expressed in percentage of active training time in selected heart
rate zones. Average heart rate was greater (p<0.05) for the SSG&HIT (mean (SD)).
