The Transition Period in Soccer: A Window of Opportunity

Abstract

The aim of this paper is to describe the physiological changes that occur during the transition period in soccer players. A secondary aim is to address the issue of utilizing the transition period to lay the foundation for the succeeding season. We reviewed published peer-reviewed studies if they met the following three selection criteria: (1) the studied population comprised adult soccer players (aged >18 years), (2) time points of physiological and performance assessments were provided, and (3) appropriate statistics for the calculation of effect sizes were reported. Following two selection phases, 12 scientific publications were considered, involving a total sample of 252 players. The transition period elicits small to moderate negative changes in body composition, a moderate decline in sprint performance with and without changes of direction, and small to moderate decrements in muscle power. Detraining effects are also evident for endurance-related physiological and performance outcomes: large decrements in maximal oxygen consumption (\( \dot{V} \)O2max) and time to exhaustion, and moderate to very large impairments have been observed in intermittent-running performance. Off-season programs should be characterized by clear training objectives, a low frequency of training sessions, and simple training tools in order to facilitate compliance. The program suggested here may constitute the ‘minimum effective dose’ to maintain or at least attenuate the decay of endurance- and neuromuscular-related performance parameters, as well as restore an adequate strength profile (reduce muscle strength imbalances). This periodization strategy may improve the ability of players to cope with the elevated training demands of pre-season training and therefore reduce the risk of injury. Moreover, this strategy will favor a more efficient development of other relevant facets of performance during the pre-competition phase (e.g., tactical organization). We contend that the transition period needs to be perceived as a ‘window of opportunity’ for players to both recover and ‘rebuild’ for the following season.

Full text

CURRENT OPINION
The Transition Period in Soccer: A Window of Opportunity
Joao Renato Silva
1,2
•Joao Brito
3
•Richard Akenhead
1
•George P. Nassis
1
Published online: 3 November 2015
ÓSpringer International Publishing Switzerland 2015
Abstract The aim of this paper is to describe the
physiological changes that occur during the transition
period in soccer players. A secondary aim is to address
the issue of utilizing the transition period to lay the
foundation for the succeeding season. We reviewed pub-
lished peer-reviewed studies if they met the following
three selection criteria: (1) the studied population com-
prised adult soccer players (aged [18 years), (2) time
points of physiological and performance assessments were
provided, and (3) appropriate statistics for the calculation
of effect sizes were reported. Following two selection
phases, 12 scientific publications were considered,
involving a total sample of 252 players. The transition
period elicits small to moderate negative changes in body
composition, a moderate decline in sprint performance
with and without changes of direction, and small to
moderate decrements in muscle power. Detraining effects
are also evident for endurance-related physiological and
performance outcomes: large decrements in maximal
oxygen consumption (
_
VO
2max
) and time to exhaustion,
and moderate to very large impairments have been
observed in intermittent-running performance. Off-season
programs should be characterized by clear training
objectives, a low frequency of training sessions, and
simple training tools in order to facilitate compliance. The
program suggested here may constitute the ‘minimum
effective dose’ to maintain or at least attenuate the decay
of endurance- and neuromuscular-related performance
parameters, as well as restore an adequate strength profile
(reduce muscle strength imbalances). This periodization
strategy may improve the ability of players to cope with
the elevated training demands of pre-season training and
therefore reduce the risk of injury. Moreover, this strategy
will favor a more efficient development of other relevant
facets of performance during the pre-competition phase
(e.g., tactical organization). We contend that the transition
period needs to be perceived as a ‘window of opportunity’
for players to both recover and ‘rebuild’ for the following
season.
Key Points
The transition period should be viewed as a ‘window
of opportunity’ for players to recover and to ‘rebuild’
for the following season.
Coaches should adopt a holistic view (e.g., social
factors, training background) when defining the
individual training variables (e.g., frequency,
volume, intensity) and modality of the exercise
intervention.
An individualized training program during the off
season may represent an adequate methodological
and physiological strategy favoring a more efficient
periodization of the subsequent pre-season phase.
&Joao Renato Silva
jm_silv@hotmail.com; joao.silva@aspetar.com
1
National Sports Medicine Programme, Excellence in Football
Project, Aspetar-Qatar Orthopaedic and Sports Medicine
Hospital, PO Box 29222, Doha, Qatar
2
Center of Research, Education, Innovation and Intervention
in Sport (CIFI2D), Porto, Portugal
3
Health and Performance Unit, Portuguese Football
Federation, Lisbon, Portugal
123
Sports Med (2016) 46:305–313
DOI 10.1007/s40279-015-0419-3

1 Introduction
The soccer season is commonly planned in three distinct
periods: the pre-competition, competition, and transition
periods. The duration of each period is influenced by
intrinsic (e.g., environmental conditions) and extrinsic
factors (e.g., international competitions). For instance,
some leagues comprise two distinct cycles of pre-compe-
tition, competition, and transition periods. Nevertheless,
the most frequent scenario is that after 10–11 months of
training and competition [1], players undertake a period of
rest typically lasting 4–6 weeks; the so-called transition or
off-season period.
Despite the general increase of training and competition
demands over time, the transition period is generally
characterized by a complete cessation of, or substantial
reduction in, training [2,3]. In some cases, players might
be involved in sport activities and/or voluntary non-peri-
odized training. The duration of the cessation period, the
magnitude of decrement in training impulses, and the
players’ fitness levels will modulate the kinetics of alter-
ations to body composition and physiological functions;
ultimately, this may lead to a partial or complete loss of
some training-induced adaptations [2,3].
According to Mujika et al. [2], detraining can be divided
into short term (\4 weeks) and long term ([4 weeks).
Importantly, detraining effects may influence how players
prepare during pre-competition and potentially affect their
performance levels in the first matches of the competition
period [4]. In fact, pre-competition periodization is affected
by players’ physical performance and physiological status
at the start of the season. For instance, following significant
detraining during the transition period, additional physical
training may be required, which may be detrimental to
other dimensions of performance (e.g., team tactical
organization). Furthermore, the pre-competition period is
commonly characterized by a high frequency of training
sessions. Players are typically exposed to friendly games
after a short period of returning to training (7–10 days) and
are subjected to more rapid increases in training load
compared with other periods [5,6]. Moreover, clubs’
commercial obligations may see many players travelling
and competing frequently within the pre-season, limiting
structured training and recovery opportunities within this
important period; all these factors contribute to substan-
tially increasing the psychological and physiological stress
of the pre-season period [7–9]. The development of fatigue
during such intensified phases impacts players’ responses
to training demands (e.g., how players understand the
tactical tasks within the global team organization). More-
over, excessive fatigue may also compromise the capacity
of players to tolerate and recover from the typically higher
training loads, and consequently affect the odds of injury. It
should be noted that rapid increases in training load (e.g.,
training load =rating of perceived exertion 9training
duration), particularly during pre-season training, have
been associated with increased risk of injury [10]. More-
over, training intensity [e.g., accumulated time spent
[85 % of maximal heart rate (HR
max
)] and volume (ac-
cumulated training hours) are key variables in character-
izing players’ training load and have been recently
associated with injury incidence in professional football
players [6]. Assuming complete cessation of training dur-
ing the transition period, the pre-season period represents a
triad of risk factors: high training volumes, high training
intensity, and a rapid increase in training load relative to
recent exposure [6,11].
Despite the consensus that ‘optimal’ fitness develop-
ment requires variability in training stimuli, elite players
may be persistently exposed to high training loads during
pre-competition; internal and external load variables have
been reported as being constant within the different pre-
competition microcycles during pre-season periodization
[12]. Notwithstanding these data, the transition period
remains the least examined and understood phase of the
soccer season. Here, we discuss the physical, physiological,
biochemical, and performance alterations that occur during
transition periods. We contend that the transition period
should be viewed as a window of opportunity for players to
recover and to ‘rebuild’ for the following season. A com-
plete cessation or near absence of training stimuli might not
be beneficial or appropriate for all players. We begin by
examining the magnitude of decrements in physical per-
formance and physiological parameters observed from pre-
to post-transition. Following this, we present evidence-
based guidelines for a periodized transition program.
2 Methods
2.1 Search Strategy: Databases and Inclusion
Criteria
We selected studies in two consecutive screening phases.
The first phase consisted of identifying articles through a
systematic search using the US National Library of Med-
icine (PubMed), MEDLINE, and SPORTDiscus databases.
Literature searches comprised scientific publications from
April 2000 to January 2015. The following keywords were
used in combination: ‘elite soccer’, ‘professional soccer’,
‘highly trained players’, ‘seasonal alterations’, ‘perfor-
mance analysis’, ‘soccer physiology’, ‘football’, ‘detrain-
ing’, and ‘training cessation’. We further searched the
relevant literature using the ‘related citations’ function of
306 J. R. Silva et al.
123

PubMed and by scanning reference lists. In the second
phase, we reviewed published peer-reviewed studies if they
met the following three selection criteria: (1) the studied
population comprised adult soccer players (aged
[18 years), (2) time points of physiological and perfor-
mance assessments were provided, and (3) appropriate
statistics for the calculation of effect sizes were reported.
Following the two selection phases, 12 scientific publica-
tions (ten journal articles, one PhD thesis, and one con-
ference communication) were considered, involving a total
sample of 252 adult soccer players.
2.2 Data Extraction and Presentation
Data related to the players’ physiological parameters
(e.g., % body fat) and performance parameters (e.g., soc-
cer-specific endurance tests and jump tests) were extracted
and presented as the percentage of change (PC) =(post-
test mean -pretest mean)/pretest mean 9100. We
assessed the magnitude of the changes using effect sizes
(ES) =(post-test mean -pretest mean)/pretest standard
deviation [13]. We obtained 52 ESs, threshold values for
which were ‘trivial’ (\0.2), ‘small’ (0.2–0.6), ‘moderate’
(0.6–1.2), ‘large’ (1.2–2.0), and ‘very large’ ([2.0) [14].
3 Physiological and Performance Changes
3.1 Body Composition
It is common that the off-season break negatively influ-
ences players’ body composition. Trivial to small increases
in the percentage of body fat (%BF) in professional
(PC =0.8–3.0 %; ES =0.2–0.5; Fig. 1)[15–18] and in
semi-professional (PC =0.6 %; ES =0.2) [19] players
have been reported. Moreover, moderate decreases in lean
body mass (LBM; PC =-3%; ES=-0.5) [15] and
large decrements in fat-free mass (FFM) were detected in
professional players (PC =-6.6 %; ES =-1.3) [20].
However, the ability of off-season training programs to
prevent these changes has received little attention. A
4-week off-season multi-component training program
comprising 22 sessions of general strength training and
gymnastic exercises, low-intensity running, and stretching
routines might prevent negative changes in body compo-
sition compared with no structured training program [16].
Body mass increased from 78.1 ±4.8 to 78.7 ±5.0 kg
(PC =0.8 %; ES =0.1) in the training group, but greater
increases were detected in the control group (from
76.5 ±2.7 to 77.9 ±2.8 kg; PC =1.9 %; ES =0.5)
[16]. Similarly, %BF increased by 0.3 % (ES =0.2) in the
training group and by 0.8 % (ES =0.5) in the control
group [16].
3.2 Neuromuscular Performance
In terms of long-term neuromuscular detraining, trivial to
small changes in force production at low and moderate
angular velocities occur after 4 weeks of detraining
(30 min jogging at approximately 60 % HR
max
, three times
a week) in professional players [21]. Nevertheless, the
deleterious effects may be more pronounced at higher
shortening velocities (60°s
-1
and 180°s
-1
;PC=0.1 %
and ES =0.01 vs. PC =–3.4 % and ES =-0.3, respec-
tively) [21]. This position is further supported when con-
sidering other reports tracking seasonal alterations in force
production capacity of professional players [22]. Trivial
changes in jumping ability evaluated by the counter-
movement and squat jump tests have also been reported
(PC =-0.3 % and ES =-0.03 vs. PC =1 % and
ES =0.1, respectively) [21]. Nevertheless, 6–8 weeks of
detraining was associated with moderate reductions in
countermovement jump (PC =-4.6 to -6.3 %; ES =
-0.5 to -0.8) and squat jump height (PC =-6.1 to
-7.1 %; ES =-0.7 to -0.9) in professional players [17].
Short distance (10-m sprint time: PC =2.9 %;
ES =0.7–0.8; 20-m sprint time: PC =1.3–1.7 %,
ES =0.7–0.8) [17] and long-distance sprint performance
(50-m sprint time: PC =7.4 %, ES =1.0) [18] seem to be
moderately impaired after 3–6 weeks of detraining in
professional players. Similar trends were also observed in
semi-professional players after 8 weeks’ detraining (15-m
sprint time: PC =3.3 %; ES =0.9) [19]. Additionally,
assessment of change of direction ability using the Illinois
agility test revealed moderate performance declines in
semi-professional players (PC =1.6 %; ES =0.7) [19].
3.3 Aerobic Fitness
Detraining during the off-season period is also detrimental
to other physiological and performance measures (Fig. 1).
The transition period leads to a decrease in maximal oxy-
gen consumption (
_
VO
2max
;PC=-3.5 to -6.1 %;
ES =-0.5 to -3.0) [16,17,19,23]. Sotiropoulos et al.
[16] reported that a 4-week transition period training pro-
gram undertaken by professional players did not prevent
decreases in
_
VO
2max
. However, players who did not per-
form any structured training during the transition period
had a greater decline in
_
VO
2max
than those who followed
the structured training (PC =-6.1 % and ES =-1.4 vs.
PC =-1.4 % and ES =-0.3, respectively). In contrast,
Slettalokken et al. [24] recently showed that the off-season
decline in aerobic fitness can be prevented by adding a low-
frequency high-intensity training stimulus (five bouts
of 4 min at 87–97 % of peak heart rate) during a 6-week
off-season period in semi-professional players. One
Detraining in Soccer 307
123

high-intensity training (HIT) session every second week
(PC =1%, ES=0.1) or one HIT session per week
(PC =-2%,ES=-0.6) effectively prevented a signif-
icant decrease in
_
VO
2max
in soccer players [24]. Off-season
deconditioning is also reflected in decreased time to
exhaustion during incremental tests (PC =-3.9 %;
ES =-1.2) [23], as well as a reduced ability to perform at
sub-maximal intensity. Christensen et al. [25] observed that
only 2 weeks of inactivity during the off-season period
resulted in lower
_
VO
2
kinetics (at 75 % maximal aerobic
speed) as evidenced by an increased time constant (s)
(PC =10.7 %; ES =0.9). This general attenuation of the
_
VO
2
response dynamic reduces the contribution of oxida-
tive phosphorylation for adenosine triphosphate (ATP)
resynthesis [26] and increases the accumulation of fatigue-
related metabolites (H
?
and P
i
)[27]. In addition, Mohr
et al. [23] observed that the off-season resulted in an
increased heart rate at running speeds of 10, 14, and
17 kmh
-1
(PC =6.1 % and ES =2.0; PC =4.4 % and
ES =1.4; and PC =2.8 % and ES =1.7, respectively).
Therefore, coaches should expect an altered external:
internal load ratio when players return to training, which
has obvious consequences in the high-loading phase of pre-
competition (e.g., reduced economy, increased fatigue and
psychophysiological responses to a given training load).
For this purpose, HIT impulses during the off-season
period might be needed to counteract decrements in soccer-
specific fitness. Long-term detraining impairs performance
during soccer-specific endurance tests such as the Yo–Yo
Intermittent Recovery Test—level 2 (YYIR2, PC =
10.7 %; ES =-2.2) [28] and the Yo–Yo Intermittent
Endurance Test—level 2 (YYIE2, PC =28 %; ES =
-1.0) [29]. In fact, a short-term 2-week detraining period
significantly impaired YYIR2 performance (PC =-23 %,
Fig. 1 a The effect of
detraining (3–8 weeks)
presented as mean percentage of
change and/or average weighted
mean percentage of change. b
Overall effect sizes (mean) for
body mass (BM) [15–17];
percentage body fat (%BF) [15–
17,19]; lean body mass (LBM)
[15,20]; 10-m [17], 15-m [19],
20-m [17], and 50-m sprint
times (T10–T50) [18]; change
of direction ability (COD) [19];
countermovement jump without
(CMJ) [17,21] and with arm-
swing (CMJWAS) [19]; squat
jump (SJ) [17,21]; maximal
oxygen consumption (
_
VO
2
max)
[16,17,19,23]; time to
exhaustion (TE) [23]; Yo–Yo
Intermittent Recovery Test—
level 2 (YYIR2) [28]; Yo–Yo
Intermittent Endurance Test—
Level 2 (YYIE2) [29]
308 J. R. Silva et al.
123

ES =-1.2) and total time to perform a repeated sprint
(RS) test (10 920 m/15-s recovery; PC =2.1 %;
ES =0.7) [25]. This decreased ability to perform high- to
very high-intensity exercise (e.g., RS) may result from the
aforementioned impairments in some neuromuscular (e.g.,
sprint speed) and endurance determinants of high-intensity
exercise (e.g.,
_
VO
2
kinetics) [30]. Given the established
associations between physical match performance and Yo–
Yo tests, it is assumed that the reduction in Yo–Yo test
performance translates into lower match running perfor-
mance [31].
The benefits of performing an off-season organized
training plan is indirectly supported by a study by Boullosa
et al. [32]. During the final 5 weeks of the transition period,
after 18 days’ rest, players performed 21 individualized
conditioning sessions (strength, endurance, and proprio-
ceptive-based exercises). After 8 weeks of pre-season
training, no pre- to post-preseason improvements were
observed in either specific (YYIR1: 2475 vs. 2600 m;
PC =5.1 %; ES =0.3) and non-soccer-specific [maximal
aerobic speed (MAS); 18.1 vs. 18.2 kmh
-1
;PC=0.6 %;
ES =0.1) endurance performance. Therefore, it can be
concluded that organized, individualized conditioning ses-
sions were as key to enabling players to maintain their ability
to perform intermittent endurance exercise as their physio-
logical determinants (e.g.,
_
VO
2max
and running economy). In
fact, players started the season with high levels of soccer-
specific endurance (YYIR1, 2475 ±421 m); pre-season
values of professional players have been reported to range
from 1510 to 2000 m [33–35] and from 15.9 to 16.1 kmh
-1
[35,36] for YYIR1 and MAS, respectively.
4 Biochemical Changes
Detraining can lead to changes in the cellular and blood
biochemical milieu. Short-term detraining (2 weeks)
decreased muscle oxidative capacity, via reduced muscle
pyruvate dehydrogenase activity (17 %), and maximal
activities of citrate synthase (12 %) and 3-hydroxyacyl-
CoA (18 %) [25]. A decrease in muscle oxidative capacity
may have a detrimental effect on players’ ability to perform
and recover from intense exercise via reduction in phos-
phocreatine (PCr) resynthesis rate and increasing the con-
tribution from anaerobic sources [25–27,30]. Alterations in
blood redox states indicative of a decrease in antioxidant
status capacity have also been observed; a decrease in the
first line of antioxidant enzymatic defense against super-
oxide radicals (superoxide dismutase activity) has also been
reported after a 6-week off-season period [37].
Biochemical monitoring has shown that long-term
detraining resulted in lower concentrations of biomarkers
of tissue damage (e.g., creatine kinase, malondialdehyde)
[37]. This may not be surprising given that the kinetics of
these bio-markers have been associated with the metabolic
and mechanical demands associated with eccentric muscle
contractions, ischemia-reperfusion events during power-
related actions, excessive trauma (e.g., contact actions),
and increased
_
VO
2
, which are all typical of soccer
activities. No changes in C-reactive protein have been
reported [15,37], but increases in creatinine, granulo-
cytes, total interleukin-8, serum nitrate, ferritin, and
bilirubin have been reported during the off-season phase
[15]. This apparent increase in catabolism observed after
long-term detraining periods [15] is also partially sup-
ported by an increase in cortisol levels and a decrease in
testosterone/cortisol ratio during the off-season [37].
Accordingly, Reinke et al. [15] observed that the transi-
tion period induced significant decrements in tissue-level
stress, but that periods longer than 4 weeks may be
required before full recovery is achieved. Nevertheless,
training exposure throughout the off-season was not
recorded, particularly during the final weeks of the tran-
sition period. Thus, a stress reaction related to physical
loads before the start of pre-season cannot be excluded as
a factor that may have influenced results [37]. However,
players with higher match exposure during the season
(starters vs. non-starters) may be prone to higher catabolic
states as evidenced by the kinetics of hormonal-related
parameters (increased cortisol) and their association with
match exposure [4,37]. Being so, this further reinforces
the need for a holistic approach when defining the indi-
vidual training variables of the exercise intervention (e.g.,
frequency and intensity).
Long-term detraining did not affect sex steroid levels
at rest. Non-significant changes have been reported in
sex steroid concentration, as total testosterone [17,37],
free testosterone, dehydroepiandrosterone-sulfate, D4-an-
drostenedione, estradiol, luteinizing hormone, follicle-
stimulating hormone, and prolactin [17]. However, it is
clear that the scarcity of studies examining the multi-fac-
torial nature of physiology and performance hamper
extensive conclusions on the biochemical changes
observed during transition periods. Moreover, difficulties
interpreting the meaningfulness of alterations in biological
markers due to the complexity of the network of biological
interactions (e.g., spontaneous oscillations) and the lack of
clear control of the activity of players during transition
periods all increase the complexity of drawing precise
conclusions.
Detraining in Soccer 309
123

5 How to Alleviate the Changes Due to Reduced
Training
As previously discussed, the transition period is commonly
devoted to recovery from the physiological and psycho-
logical stress of the competitive season [37,38]. Therefore,
off-season programs should be characterized by clear
training objectives, a low frequency of training sessions,
and simple training tools in order to increase compliance.
The practitioner should adopt a holistic view (e.g., social
factors, family obligations, a need for mental regeneration)
when defining the individual training variables (e.g., fre-
quency, volume, intensity) and modalities of the exercise
intervention. Player training background, accumulated
training and match exposure, injury history, player’s per-
sonality and preferences, and off-season length, among
others, are all factors that must be carefully considered
during training prescription. The best exercise intervention
is one that fits a player’s specific needs. At the end of the
season, individual members within a squad will likely
occupy a broad range of different physical and physio-
logical states (e.g., from detraining to over-reaching) [4,
38–44]. Therefore, individualized training programs may
be warranted, with consideration of the aforementioned
factors. As a practical guideline, to avoid a substantial
decrement in endurance- and neuromuscular-related per-
formance, we believe that off-season structured training
programs should involve a minimum of two sessions per
week, separated by 48–72 h [16,24,45,46]. We believe
that the design presented here constitutes a ‘minimal
effective dose’ to allow maintenance, or a reduced decay of
physical and physiological features relevant to football
performance [16,24,45,46].
Our proposal includes one HIT session per week (e.g.,
594 mins at 87–97 % peak heart rate) [24]. Distinct HIT
formats have been shown as a time-efficient stimulus;
positive effects on cardiopulmonary and neuromuscular
function can be achieved with a low volume of training
[47–50]. Moreover, evidence suggest that a lower volume
of high-intensity exercise is required to maintain key
physiological features (
_
VO
2max
)[51]. In addition, the hor-
monal responses associated with low-volume HIT (e.g.,
testosterone, androstanediol glucuronide, growth hormone)
favors the anabolic processes to a greater degree than high-
volume protocols [52–56] and so may at least partly
counteract the negative changes in body composition pro-
file that occur during the transition period (e.g., increa-
sed %BF and decreased LBM).
The selection of the off-season HIT session should
consider an acute physiological response/strain effect [49].
Overall, the physical and physiological changes observed
during the transition period (Fig. 1) recommend HIT
sessions that combine high metabolic requirements from
the O
2
transport and utilization systems with a substantial
anaerobic glycolytic contribution whilst also considering
the desired neuromuscular load. Individualized HIT ses-
sions should be prioritized, and these sessions should take
into account the physiological and neuromuscular profile of
each player since the acute impact of HIT is highly variable
and population dependent (age, sex, training status, and
background) [49]. Moreover, the practitioner should con-
sider that manipulation of the different HIT variables (e.g.,
bout duration and intensity and duration of recovery,
number of intervals) will affect the acute physiological
responses and so model the short- to long-term training
adaptations [57].
The second training session should focus on muscle
strength and power. A combination of resistance exercises,
plyometric, and sport-specific strength exercises (e.g.,
accelerations and deceleration drills) is recommended to
target a broad range of the force–velocity spectrum [58].
The aim is to maintain the essential aspects of intra- and
inter-muscular coordination during soccer-specific motor
tasks where force production is a key factor. As an
example, the injury-prevention training program proposed
by the Fe
´de
´ration Internationale de Football Association
(FIFA) Medical Assessment and Research Centre, the
‘11?’, may represent a practical and feasible strategy [59,
60]. It is easy to implement, requiring only simple tools and
few resources. The program is focused on injury preven-
tion, but we believe the ‘11?’ has the necessary compo-
nents to also serve as a detraining prevention program. We
recommend adding a multi-joint exercise such as the squat
[e.g., [80–95 % 1 repetition maximum (1RM), 3–4 sets,
4–8 reps] to the ‘11?’ training program to address the
basic requirements of the high-force low-velocity rela-
tionship of the neuromuscular system. The plyometric
section of the ‘11?’ will provide a complementary stim-
ulus to address other parts of the force–velocity spectrum
(low-force high-velocity relationship). This training struc-
ture may partially counteract the reported negative effects
that long-term detraining (4 weeks) has on some morpho-
logical (muscle cross-sectional area) and mechanical fac-
tors (tendon stiffness), which are important in force
production and application [61]. We believe this design
may reduce the observed detraining effect in important
muscle power abilities (e.g., sprint ability). Interestingly,
one strength training session per week involving squats
(3 94RM) during the competition period may be suffi-
cient to maintain strength, jump, and sprint performance in
professional players [45]. However, a lower training
stimulus (single set vs. multiple sets) may also be effective
for maintaining strength levels during the initial stage of
the transition period [62,63]. Again, the practitioner must
310 J. R. Silva et al.
123

consider each player (e.g., single set programs prescribed
for players exposed to high training loads at the end of the
season). Nevertheless, we believe the relatively high neu-
romuscular stress imposed during training sessions and
games throughout the competitive season also provides a
meaningful stimulus and contributes to preserving a play-
er’s neuromuscular performance [39,64]. This supports our
proposal of combining HIT sessions with strength/power
training as a strategy to maintain high neuromuscular
involvement during the transition period.
The transition period also represents a window of
opportunity to intervene on modifiable risk factors associ-
ated with injury occurrence. In terms of injury prevention,
off-season training should focus on reducing the risk of the
most common injuries (e.g., hamstring strains). Players
with untreated strength imbalances may be four- to fivefold
more susceptible to sustaining a hamstring injury than
players showing normal strength profiles [65], therefore
off-season interventions should target the restoration of
normal strength profiles. Eccentric muscle loading has been
recommended for the prevention of hamstring injuries [66,
67]. Training interventions might have a time-dependent
effect on promoting eccentric strength and reducing the
negative influence of fatigue observed during matches [68].
Although scarcely investigated [69], we believe that vari-
ation is key: strength exercises and proprioception exer-
cises should be performed at both the start and the end of
training sessions to expose players to non-fatigued and
fatigued conditions, respectively. This might help condi-
tion players to cope with high-intensity periods in the final
stages of the training sessions and/or friendly matches
during pre-season. Similarly, although the mechanisms of
adaptation are currently not fully understood, eccentric
exercise elicits a protective adaptation often referred to as
the ‘repeated-bout effect’. Inducing this protective effect
via eccentric exercise might reduce the magnitude of
subsequent muscle soreness that is frequently reported
during the pre-competition period. As well as the clear
physiological benefits, this approach may also provide
psychological benefits such as a reduced perception of
effort and increased perceived tolerance and so favor
players’ commitment during training practices [70,71].
An appropriate off-season training program may con-
stitute, at least in part, a superior methodological and
physiological strategy favoring a more efficient periodiza-
tion of the subsequent pre-season phase. For instance,
given the detrimental effect of high endurance loading on
power development, a periodized program during the
transition period may avoid or reduce the interference
effect between power and endurance adaptations during
pre-season in professional players, allowing practitioners to
focus more on a certain component of a player’s perfor-
mance (e.g., muscle power) due to a greater ‘baseline’ of
aerobic fitness [72]. Indeed, the role of the different
training variables in the interference effect should be
considered [73]. The frequency, duration, and volume of
endurance training are key determinants of the develop-
ment and maintenance of strength and power [74,75]. This
provides support for the adoption of an HIT format for the
purposes of maintaining endurance qualities due to the low
frequency and volume of training required. Moreover,
strength, power, and HIT are characterized by brief and
intense muscle contractions [58] and provide synergistic
contributions to the overall training stimulus [74].
We recommend that the scientific community engage in
active collaboration with applied practitioners and coaches
to examine in detail the periodization during the transition
period. For instance, which assessments of pre- and post-
transition adaptation are the most useful: physical, physio-
logical, psychological, or a combination [76–78]? Moreover,
examining the effect of different off-season periodization
programs on subsequent injury incidence, match perfor-
mance, physical fitness, and psychometric markers
throughout the season is warranted. We believe that
addressing these questions may help practitioners develop
more effective periodization models in the future, and ulti-
mately result in tangible benefits for players and teams.
6 Conclusion
Overall, detraining during the transition period results in
meaningful performance impairments in a range of physi-
ological and performance measures. Both short- and long-
term detraining leads to small-to-moderate negative chan-
ges in body composition profile and moderate changes in
sprint ability. In addition, small-to-moderate decrements in
muscle power might occur. The effect of detraining may be
more evident in the ability to produce force at high angular
velocities. Dynamic, multi-joint actions can be affected,
primarily those requiring high levels of motor coordination.
The detraining effects are also extended to endurance-
related physiological and performance outcomes. Large
reductions in
_
VO
2max
and time to exhaustion, and moderate
to very large impairments in soccer-specific endurance,
have been described. The resultant reductions in training
status may negatively affect periodization during the pre-
season, compromising performance levels during the initial
stages of the competition phase.
We believe that the transition period needs to be per-
ceived as a window of opportunity for players to recover
and ‘rebuild’ for the start of the following season. This
does not necessarily imply a complete or near cessation of
training. On the contrary, cessation of training may nega-
tively impact performance and increase susceptibility to
injury when restarting structured training. We recommend
Detraining in Soccer 311
123

that clubs, coaches, and clinical departments should con-
sider the points discussed when prescribing individualized
training programs for the transition period.
Compliance with Ethical Standards
Funding No sources of funding were used to assist in the prepa-
ration of this article.
Conflicts of interest Joao Renato Silva, Joao Brito, Richard
Akenhead, and George P. Nassis declare that they have no conflicts of
interest relevant to the content of this review.
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