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Abstract

The aim of the present study was to examine the effect of in-season strength maintenance training frequency on strength, jump height, and 40-m sprint performance in professional soccer players. The players performed the same strength training program twice a week during a 10-week preparatory period. In-season, one group of players performed 1 strength maintenance training session per week (group 2 + 1; n = 7), whereas the other group performed 1 session every second week (group 2 + 0.5; n = 7). Only the strength training frequency during the in-season differed between the groups, whereas the exercise, sets and number of repetition maximum as well as soccer sessions were similar in the 2 groups. The preseason strength training resulted in an increased strength, sprint, and jump height (p < 0.05). During the first 12 weeks of the in-season, the initial gain in strength and 40-m sprint performance was maintained in group 2 + 1, whereas both strength and sprint performance were reduced in group 2 + 0.5 (p < 0.05). There was no statistical significant change in jump height in any of the 2 groups during the first 12 weeks of the in-season. In conclusion, performing 1 weekly strength maintenance session during the first 12 weeks of the in-season allowed professional soccer players to maintain the improved strength, sprint, and jump performance achieved during a preceding 10-week preparatory period. On the other hand, performing only 1 strength maintenance session every second week during the in-season resulted in reduced leg strength and 40-m sprint performance. The practical recommendation from the present study is that during a 12-week period, 1 strength maintenance session per week may be sufficient to maintain initial gain in strength and sprint performance achieved during a preceding preparatory period.
EFFECTS OF IN-SEASON STRENGTH MAINTENANCE
TRAINING FREQUENCY IN PROFESSIONAL SOCCER
PLAYERS
BENT R. RØNNESTAD,
1
BERNT S. NYMARK,
1
AND TRULS RAASTAD
2
1
Lillehammer University College, Lillehammer, Norway; and
2
Norwegian School of Sport Sciences, Oslo, Norway
ABSTRACT
Rønnestad, BR, Nymark, BS, and Raastad, T. Effects of in-
season strength maintenance training frequency in professional
soccer players. JStrengthCondRes25(X): 000–000,
2011–The aim of the present study was to examine the effect
of in-season strength maintenance training frequency on
strength, jump height, and 40-m sprint performance in pro-
fessional soccer players. The players performed the same
strength training program twice a week during a 10-week
preparatory period. In-season, one group of players performed
1 strength maintenance training session per week (group 2 + 1;
n= 7), whereas the other group performed 1 session every
second week (group 2 + 0.5; n= 7). Only the strength training
frequency during the in-season differed between the groups,
whereas the exercise, sets and number of repetition maximum as
well as soccer sessions were similar in the 2 groups. The
preseason strength training resulted in an increased strength,
sprint, and jump height (p,0.05). During the first 12 weeks of
the in-season, the initial gain in strength and 40-m sprint
performance was maintained in group 2 + 1, whereas both
strength and sprint performance were reduced in group 2 + 0.5
(p,0.05). There was no statistical significant change in jump
height in any of the 2 groups during the first 12 weeks of the in-
season. In conclusion, performing 1 weekly strength mainte-
nance session during the first 12 weeks of the in-season allowed
professional soccer players to maintain the improved strength,
sprint, and jump performance achieved during a preceding
10-week preparatory period. On the other hand, performing only
1 strength maintenance session every second week during the
in-season resulted in reduced leg strength and 40-m sprint
performance. The practical recommendation from the present
study is that during a 12-week period, 1 strength maintenance
session per week may be sufficient to maintain initial gain in
strength and sprint performance achieved during a preceding
preparatory period.
KEY WORDS sprint performance, vertical jump ability, one
repetition maximum
INTRODUCTION
Conditioning for sport has usually been divided into
preparatory, in-season,and postseason phases. One
major goal for the preparatory period in team
sports like soccer is to maximize the fitness
parameters, like jumping ability, sprint performance, and
maximal dynamic strength. During the in-season, professional
soccer players have limited time available for strength training.
This is because coaches have to plan for recovery from and
preparations to 1–3 matches per week and for an increased
focus on tactical and technical training sessions. Because of the
increased demands of competition and the increased focus on
technical and tactical training, in-season strength training is
usually intended to maintain the fitness level achieved during
the preparatory period. However, already fit players are likely
to need a relatively high training stress to maintain their
maximal strength level. Consequently, it is important to
optimize the in-season strength training frequency and volume
so that strength can be maintained with as little interference on
other football-specific skills as possible. Therefore, the main
question asked by coaches might be what is the minimum
amount of strength training necessary to maintain strength and
power in leg extensors during a season? Despite a large body of
soccer-specific scientific work (e.g., Refs. (2,14,25), no one has
so far investigated the effects of in-season strength training
frequency.
Maximal strength is a basic quality that influences power
performance; an increase in maximal strength is usually
connected with an improvement of power abilities. Significant
correlations are observed between maximum strength in the
lower body and sprint and jump performance(8,24,31,32), and
an increased strength is often followed by an improved sprint
and jump performance (e.g., Refs. (6,27)). Thus, maximal
strength is an important factor that potentially affects soccer
performance. Therefore, it seems important to maintain
strength during the competition period. However, strength
Correspondence to Bent R. Rønnestad, bent.ronnestad@hil.no.
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gain achieved during the preparatory period in pubescent male
athletes has been observed to be reduced during a 12-week
competitive season without any strength maintenance training
(7). Consequently, it is necessary to perform some kind of
in-season strength maintenance training to avoid a decline in
strength and power. It is well known that when strength
training is terminated, the maximal strength declines (e.g.,
Refs. (13,29)), and it has been reported that only a small part
(0–45%) of the strength gained during a previous strength
training period is preserved after 8–12 weeks without strength
training (1,11,22). Furthermore, it has been shown that soccer
training alone has no effect on maximal strength (23,27).
In the National Collegiate Athletic Association Division I
men’s soccer, performing strength and plyometric sessions
approximately once a week during a 16-week competitive
season maintained maximal strength, sprint performance, and
vertical jump ability (28). Furthermore, Morehouse (20)
concluded that strength gains can be maintained by training
once every second week during an 8-week maintenance period
in college-aged men. However, the frequency of strength
training sessions per week is likely to be affected by the initial
training status and the length of the in-season. Furthermore, it
has been observed that adding large volumes of endurance
training to strength training may inhibit adaptations to strength
training (17). Therefore, whether it is possible to maintain an
initial gain in strength-related and power-related performance
with strength training once per week or once every second
week during the first 12 weeks of the in-season with a concurrent
large aerobic stress is unclear. Interestingly, by performing
in-season strength training twice per week during an 11-week
soccer season, a reduction in isokinetic strength, vertical jump
height, and sprint performance was observed (15). In the latter
study, a predominance of catabolic processes was observed
leading the authors to suggest that the players had a too large
stress stimulus, leading to an acute overtraining. This large stress
islikelytopartlybecausedbythe2strengthtrainingsessions
per week. It is thus important to further optimize the in-season
strength training frequency to reassure enough stimuli to
maintain the initial strength gain and, on the other hand, to
avoid a too large stimulus that might cause acute overtraining.
The aim of the present study was to investigate the effect of
performing strength maintenance training during the com-
petitive season as 1 session per week versus 1 session every
second week on strength, jump, and sprint performance in
professional soccer players. The hypothesis was that the
strength maintenance training program consisting of 1 weekly
session would preserve the increases in muscle strength sprint
and vertical jump performance achieved during the pre-
paratory period to a greater extent than the program
consisting of only 1 session every second week.
METHODS
Experimental Approach to the Problem
The present study was designed to investigate the effects of
in-season strength training frequency on strength, jump, and
sprint performance in professional soccer players. Because of
a tight match program, there is limited time available to
maintain strength during the in-season. Thus, optimizing the
in-season strength training frequency is important, and in
present study, the effect of performing 1 session of heavy
strength training once a week was compared with 1 session
every second week. Changes in the dependent variables, such
as 1 repetition maximum (RM), squat jump (SJ), and sprint
performance, were tested at 3 time points: (a) at the beginning
of a 10-week preparatory period (preintervention) that
preceded the competition season, (b) after the preparatory
period (precompetition season), and (c) at 12 weeks into the
competition season (at the middle of the competition season).
All soccer players performed the same strength training
program twice a week during the preparatory period. They
were thereafter randomly divided into 2 groups. One group
performed 1 strength training session per week during the
competition season (group 2 + 1; n=7,age2262years,body
mass 76 61 kg, height 184 63 cm), whereas the other group
performed 1 strength training session every second week
(group 2 + 0.5; n=7,age2662years,bodymass8363kg,
height 186 62 cm). Only the strength training frequency
during the competition season differed between the groups,
whereas the exercise, sets and number of RM and soccer
sessions were identical in the 2 groups.
Subjects
A total of 19 Norwegian professional male soccer players
(playing at the next highest level in Norway - the Norwegian
Championship) volunteered to participate in this study. The
players had performed in average 5–7 training sessions a week
during the past 3 years. The study was approved by the
Regional Ethics Committee of Norway. All participants
signed an informed consent form before participation. During
the preparatory period, 2 new players arrived and 2 players
departed. The new players were not included in the data
representing changes during the preparatory period (n= 12),
but they were randomly allocated into different groups and
included in the in-season data (n= 14). In addition to transfer,
injury and illness led to the dropout of 5 players. In total, 14
players completed the in-season study.
Procedures
All tests were performed in 1 test session and in the following
order: 40-m sprint, SJ, countermovement jump (CMJ), and
1RM. All test sessions were performed with the same
equipment with identical subject-equipment positioning over-
seen by the same trained investigator. The preseason and mid-
season tests were accomplished at the same time of the day as
the pretests and 3–5 daysafter the last strength-training session.
Forty-Meter Sprint
All players performed a standardized warm-up before the
sprint test byjogging for a 15-minute period at a moderate pace
and finishing with 4–5 40-m submaximal runs. After warm-up,
players performed 3–4 maximal sprints over a distance of 40 m.
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Strength Maintenance Training in Professional Soccer Players
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The sprints were performed on a hard even surfacein an indoor
facility. All players used adaptedindoor shoes. The sprints were
separated by approximately 3 minutes to ensure full recovery
between sprints. Players commenced each sprint from
a standing (static) position in which they positioned their
front foot 50 cm behind the start line. Players decided
themselves when to starteach run with the timebeing recorded
when the subject intercepted the photocell beam. Players were
instructed to sprint as fast as possible through the distance.
Times were recorded by photocells (Speedtrap 2; Brower
Timing Systems, Draper, Utah, USA) placed at the start line
and after 40 m. The best 40-m sprint time was chosen for
statistical analysis of sprint performance.
Jumping Height
The maximal vertical jump ability was tested 3 minutes after
the last sprint on a force plate (FP 4; HUR Labs Oy, Tampere,
Finland) with a sampling rate at 1,200 Hz for5 seconds. Players
performed CMJ and SJ with the hands kept on the hips
throughout the jumps. During SJ, from a knee angle of 90°of
flexion, the players were instructed to execute a maximal
vertical jump without any downward movement before the
maximal vertical jump. The force curves were inspected to
verify no downward movements before the vertical jump.
During CMJ, the angular displacement of the knees was
standardized so that the players were required to bend their
knees to approximately 90°and then rebound upward in
a maximal vertical jump. Each subject had 4 attempts
interspersed with approximately 1.5-minute rest between each
jump in both SJ and CMJ. The best jump from each subject was
used in data analysis, and all data were calculated using Matlab
(MathWorks, Natick, MA, USA). Jumping height was de-
termined as the centre of mass displacement calculated from
force development and measured body mass.
One Repetition Maximum
Maximal strength in leg extensors was measured as 1RM in half
squat. Before the 1RM squat test, players performed a stan-
dardized specific warm-up consisting of 3 sets with gradually
increasing load (40–75–85% of expected 1RM) and decreasing
number of reps (12–7–3). The depth of squat in the 1RM test
wassettoakneeangleof90°. To assure similar knee angle in all
test sessions for all the players, the squat depth was individually
marked at the pretest depth of the buttock. Thus, the subject
had to reach his individual depth in all test sessions to get the
lift accepted. The first attempt in the test was performed with
a load approximately 5% below the expected 1RM load. After
each successful attempt, the load was increased by 2–5% until
failure in lifting the same load in 2–3 following attempts. The
rest period between each attempt was 3 minutes.
Training
The 10 weeks preparatory period consisted of 2 strength
workouts per week on nonconsecutive days. Each workout
consisted of the half squat exercise only. After a 15-minute
warm-up with light jogging or cycling, players performed 2–3
TABLE 1. Strength training program during the preseason and in-season.*
Preseason In-season
Week 1–3 Week 4–6 Week 7–10 Week 11–22
1 Bout 2 Bout 1 Bout 2 Bout 1 Bout 2 Bout Bout
Half squat 3 310RM 3 36RM 3 38RM 3 35RM 3 36RM 3 34RM 3 34RM
*The strength training program was identical for both the groups. The only difference was the strength training frequency; one group
performed 1 strength maintenance training per week, whereas the other group performed 1 strength maintenance training every second
week.
TABLE 2. Weekly duration (in hours) of the training
distributed into different training intensities and
weekly number of friendly matches during the 10-
week preseason and during the first 12 weeks of
the in-season.*
Intensity distribution
Preseason
(mean 6SE)
In-season
(mean 6SE)
Low intensity 2.4 60.2 2.4 60.2
Medium intensity 3.0 60.4 2.1 60.3
High intensity 4.3 60.3 3.6 60.3
Weekly number of
friendly matches
0.9 60.1 0
Weekly number
of competitive
matches
0 1.8 60.2
*This training was performed by both the group that
performed 1 strength training session per week and the
group that performed 1 strength training session every
second week.
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warm-up sets with gradually increased load. All players were
supervisedby one of the physical trainers at all strength training
sessions during the entire intervention period. The training
load was 4–10RM and similar for the 2 groups (Table 1).
Players were encouraged to continuously increase their RM
loads during the intervention. Players were allowed assistance
on the last repetition. Based on the assumption that it is
the intended rather than actual velocity that determines
the velocity-specific training response (3), strength training
was conducted with emphasizing maximal mobilization in
concentric phase, while the
eccentric phase had a slower
speed (approximately 2–3 sec-
onds). Number of sets was
always 3. During the in-season,
group 2 + 1 performed 1
strength training session per
week, whereas group 2 + 0.5
performed 1 strength training
session every second week. The
in-season strength training con-
sisted of half squat and 3 sets of
4RM (Table 1). Only the
strength training frequency dur-
ing the competition season dif-
fered between the groups,
whereas the exercise, sets and
number of RM and soccer
sessions were similar in the
2groups.
A regular training week for
both groups consisted of 6–8
soccer sessions lasting approximately 90 minutes focusing on
physical conditioning, and technical and tactical aspects of
the game. The intensity during the soccer sessions was
divided into low, medium, and high intensity. The total
weekly training duration (including strength training) during
the preparatory period was 12.7 61.0 hours (Table 2). The
distribution of weekly duration in low, medium, and high
exercise intensity zones during the intervention period is
presented in Table 2. The mean number of soccer matches
per week during the in-season was 1.8 60.2.
Statistical Analyses
All values given in the text,
figures, and tables are mean 6
SE. During the pre-season, all
players performed the same
strength training protocol twice
per week. The data from this
period is thus pooled in 1 group
of players. Paired t-test was
used to test for changes during
the preseason. To test for
changes within groups from
the start of the in-season to 12
weeks into the in-season,
a paired t-test was used. Un-
paired t-tests were used to
compare relative changes from
before the competitive season
to mid-season between the 2 +
1 and 2 + 0.5 groups. In the
40-m sprint test, there was
a statistical power of 80% to
Figure 2. Forty-meter sprint time before the start of the in-season (Preseason) and after 12 weeks of in-season
(Mid-season) in the group that performed 1 strength maintenance training per week (group 2 + 1) and the group
that performed 1 strength maintenance training every second week (group 2 + 0.5). Individual data points are
shown, and the columns represent the mean value. *Larger than at Preseason (p,0.05).
Figure 1. One repetition maximum in half squat before the start of the in-season (Preseason) and after 12 weeks of
in-season (Mid-season) in the group that performed 1 strength maintenance training per week (group 2 + 1) and the
group that performed 1 strength maintenance training every second week (group 2 + 0.5). Individual data points are
shown, and the columns represent the mean value. *Smaller than at Preseason (p,0.05).
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Strength Maintenance Training in Professional Soccer Players
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detect differences from start of the in-season to 12 weeks into
the in-season of 0.85%, using a significance level (a) of 0.05
(2 tailed). Test-retest reliabilities (intraclass correlations) for
40-m sprint, 1RM, and SJ was 0.95, 0.97, and 0.97,
respectively, with a coefficient of variation of ,3% for all
parameters. The level of significance was set at p#0.05 for all
statistical analyses.
RESULTS
There were no differences between the groups in anthropo-
metric parameters or the test variables before the in-season.
Adaptations During the
Preparatory Period
Strength measured as 1RM in
half squat increased by 19 65%
during the preparatory period
(from 139 67kgto16368 kg;
p,0.01). Time used on 40-m
sprint decreased during the pre-
paratory period by 1.8% (from
5.39 60.07 seconds to 5.29 6
0.05 seconds; p,0.05). Regard-
ing vertical jump ability, SJ in-
creased by 3.3 61.2% during the
preparatory period (from 37.1 6
1.1 cm to 38.3 61.1 cm; p,
0.05), whereas there was a ten-
dency toward an improved CMJ
performance (from 39.3 61.6
cm to 41.1 61.3 cm; p=0.056).
In-season Adaptations
During the first 12 weeks of the
in-season, the initial gain in strength was maintained in group 2 +
1, whereas the strength was reduced by 10 64% in group 2 + 0.5
(p,0.05; Figure 1). The 40-m sprint performance was
maintained in group 2 + 1, whereas it was reduced by 1.1 60.3%
in group 2 + 0.5 (p,0.05; Figure 2). There was no statistically
significant change in SJ or CMJ in any of the 2 groups during the
first 12 weeks of the in-season (Figures 3 and 4).
DISCUSSION
Two strength training sessions per week during the pre-
paratory period resulted in an
increased strength, sprint, and
vertical jump performance in
professional soccer players. The
novel finding in this study was
that 1 strength training session
per week during the first 12
weeks of the in-season main-
tained the initial gain in
strength, sprint, and jump abil-
ity achieved during the pre-
paratory period. On the other
hand, 1 strength training ses-
sion every second week resulted
in a reduction in strength and
sprint performance, while the
vertical jumping ability was
maintained.
Theincreasein1RMhalfsquat
during the preparatory period is
in line with the 20–25% increase
reportedinotherstudieson
Figure 4. Squat jump height before the start of the in-season (Preseason) and after 12 weeks of in-season (Mid-
season) in the group that performed 1 strength maintenance training per week (group 2 + 1) and the group that
performed 1 strength maintenance training every second week (group 2 + 0.5). Individual data points are shown,
and the columns represent the mean value.
Figure 3. Counter movement jump height before the start of the in-season (Preseason) and after 12 weeks of in-
season (Mid-season) in the group that performed 1 strength maintenance training per week (group 2 + 1) and the
group that performed 1 strength maintenance training every second week (group 2 + 0.5). Individual data points are
shown, and the columns represent the mean value.
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professional male soccer players with a similar training protocol
(27,35). Maximal strength is a basic quality that influences
power performance, and an increase in maximal strength is
usually connected with an improvement of power abilities.
Significant correlations are observed between maximum
strength in the lower-body performance and sprint and jump
performance (8,24,31,32), and an increased strength is often
followed by an improved sprint and jump performance (e.g.,
Refs. (6,27,35)). The finding of concomitant improvement in
jump and sprint performance during the preparatory period
when the strength increased was therefore expected.
In other team sports like handball and volleyball, it has been
observed that 6–7 weeks without strength training in the
competitive season resulted in a reduced maximal strength
and power output (12), as well as a reduced ball throw
velocity, despite normal training sessions and competitions
were maintained (18). These findings highlight the quest for
strength maintenance training during the in-season. In the
present study, it was observed that 1 strength training session
per week during the first 12 weeks of the in-season
maintained the initial gain in strength achieved during the
preparatory period. This is in line with the previous findings
in recreationally strength-trained subjects, collegiate soccer
players, and cyclists (11,26,28). The present finding supports
the suggestion that high-intensity muscle actions and low
weekly training volume and frequency are capable of
maintaining initial strength gain (11,21). Interestingly, by
performing in-season strength training twice per week during
an 11-week soccer season, a reduction in strength, jump
height, and sprint performance was observed (15). In the
latter study, a predominance of catabolic processes was
observed leading the authors to suggest that the players got
too large stress resulting in an acute overtraining. Because of
the increased demands of competition, and technical and
tactical training, in-season strength training is usually
intended to maintain the fitness level achieved during the
preparatory period. The in-season strength training should
therefore aim to maintain the initial strength gain and, on the
other hand, to avoid a too large stimulus, thereby causing an
acute overtraining. The finding of Kraemer et al. (15)
indicates that 2 in-season strength training sessions per week
may in some cases be too much, at least when combined with
the heavy match load in that study. Furthermore, the present
study indicates that 1 strength training session every second
week is not enough to maintained the initial gain in strength
in professional soccer players.
The present finding of reduced strength after 1 strength
training session every second week is in contrast with the
finding of maintained strength by training once every second
week during an 8-week maintenance period (20). However,
this discrepancy may be explained by the fact that the latter
study was conducted on college students with no prior
strength training experience, and there was no report of any
concurrent endurance training during the maintenance period.
Professional soccer players have a larger strength training
experience and thus needs a larger strength training frequency
to maintain the initial strength, and they perform a relative
large volume of endurance training. Large volumes of
endurance training may inhibit adaptations to strength training
(17) and thus potential quest for a larger frequency of strength
maintenance training. Indeed, endurance training has been
shown to lower the maximum shortening velocity of type II
fibers, reduce motor unit discharge rates, and slightly reduce
peak tension development in all fiber types (9,10,30,33,34). In
accordance with the latter findings, endurance training has
been associated with a reduced vertical jumping ability (5),
strength (5,19), and unchanged or slightly reduced cross
sectional area (CSA) of muscle fibers (9,17,33,34). Based on the
negative effects of endurance training on explosive abilities,
and the observed reduction in strength, the impaired sprint
performance when performing strength training only once
every second week was not unexpected.
Vertical jump ability was preserved during the first 12 weeks
of the in-season in both the groups. The reason to why
strength training every second week was enough to maintain
vertical jump performance but not strength and sprint
performance remains unclear. However, 6–7 weeks without
strength training has been observed not to reduce vertical
jump ability in both recreationally strength-trained partic-
ipants and professional handball players (16,18). Further-
more, 12 weeks without strength training have been shown
to only slightly reduce jump ability despite more pronounced
reduction in strength (4). It has been suggested that
maintenance of vertical jump ability despite reduction in
other performance measurements may be because of the
importance of jump technique (16). Furthermore, it has also
been suggested that maintenance of explosive jumping
performance may be more dependent on training frequency
when more explosive-type strength or plyometric training
programs have been performed in advance (16). The present
data indicate that strength maintenance training once every
second week in addition to specific soccer practices
(including plyometric muscle actions) and matches maintains
the vertical jump ability in professional soccer players during
the first 12 weeks of the in-season.
To our knowledge, the present study is the first to
demonstrate that professional soccer players can maintain
the initial strength, sprint, and jump improvements attained
during the preparatory period with just a single low-volume
heavy strength training session per week during the first 12
weeks of the in-season, while 1 session every second week do
not maintain strength and sprint performance. It is important
to note that the present findings were done in a short
maintenance period of 12 weeks. If the maintenance period is
of a longer duration or the initial strength level is higher, then
it might be necessary with a higher strength training
frequency to maintain strength and sprint performance.
In conclusion, performing 1 weekly strength maintenance
session during the first 12 weeks of the in-season allowed
professional soccer players to maintain the improved leg
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Strength Maintenance Training in Professional Soccer Players
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strength that were attained during a preceding 10-week
preparatory period. Of even greater practical importance, the
in-season maintenance of the strength training adaptations
resulted in maintenance of performance-related factors like
40-m sprint and vertical jump ability. On the other hand,
performing 1 strength maintenance session every second
week during the in-season resulted in a reduction in leg
strength and 40-m sprint performance but maintained the
jump performance.
PRACTICAL APPLICATIONS
Our data indicate that strength training twice a week during
the preparatory period can be an important factor in
increasing maximal strength and jump and 40-m sprint
performance in professional soccer players. During the first 12
weeks of the in-season, strength maintenance training once
a week was enough to maintain the initial gain in strength,
jump, and sprint performance. On the contrary, strength
maintenance training every second week did not maintain the
initial gain in strength and sprint performance. To maintain
initial gain in strength and explosive movements achieved
during the preparatory period, we recommend using
1 strength maintenance session per week during the
in-season. Depending on the number of matches per week,
this strength maintenance session are recommended to be
performed between 1 and 2 days after a match and 2–3 days
before the next match. The specific mechanisms responsible
for the observed findings cannot be determined from the
current study. It is important to note that the present findings
were done in a short maintenance period of 12 weeks. If the
maintenance period is of a longer duration or the initial
strength level is higher, then it might be necessary with
a higher strength training frequency to maintain strength and
sprint performance.
ACKNOWLEDGMENTS
The authors thank P. T. Hans Noet for his assistance with
training procedures during the study. They also thank the
participants for their time and effort. No funding was obtained
for the present study. The authors have no professional
relationships with companies or manufacturers who will
benefit from the results of the present study and the results of
the present study do not constitute endorsement of the
product by the authors or the National Strength and
Conditioning Association.
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Strength Maintenance Training in Professional Soccer Players
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
... On average, an elite player performs about 150-250 high-intensity activities during a soccer game [16]. Different training approaches have been suggested to enhance neuromuscular [8][9][10][11][17][18][19][20][21][22][23][24][25] and recovery adaptations in soccer players [26]. It has now become apparent that strength and power training requires maximal efforts and optimal intensities to yield best effects [21]. ...
... The most commonly used exercises in the different strength programs for the "vertical direction" were the back squat [8][9][10][11][17][18][19][20][21][22] and the jump squat (JS) [8,17,18,20,23,24]; and for the "horizontal direction" the resisted sprints (i.e., sled towing) [23][24][25] and unloaded horizontal jumps [10,24]. Curiously, there were no significant differences in performance improvements between protocols that used exercises with different directions (i.e., vertical or horizontal) of force application during the training ses-▶ ▶ tables 4 and 7). ...
... Our analysis revealed a possible effect for the period of the season in which the strength training was performed (see ▶ table 4). Ronnestad et al. [19] (Norwegian Premier League), were the first authors to investigate the effects of strength training in different season periods. These authors proposed a training protocol during a pre-season of 10 weeks, two sessions per week, with 3 sets of 4-10 repetitions of vertically-oriented exercises (i.e., half squats), with 80-90 % RM overload. ...
Article
Several studies have confirmed the efficacy of strength training to maximize soccer player performance during competition. The aim of this meta-analysis was to determine the effects of different strength training protocols on short-sprint and vertical jump performance of professional soccer players from the first division of their countries. The following inclusion criteria were employed for the analysis: (a) randomized studies; (b) high validity and reliability instruments; (c) studies published in a high-quality peer-reviewed journal; (d) studies involving professional soccer players from the first division; (e) studies with descriptions of strength training programs; and (f) studies where countermovement jump and 10-m sprint time were measured pre and post training. Overall, the different strength-oriented training schemes produced similar performance improvements, which seem not to depend on the training strategy. Strength training appears to have a lower effect when applied during in-season than when applied in pre-season periods in first division soccer players. In this meta-analysis it is not possible to confirm that strength training in isolation is capable of improving the short-sprint and jump performance of elite soccer players. The congested fixture schedule and, thus, the limited time to perform complementary (non-specific) training sessions, may contribute to these reduced effects.
... Interestingly, Noya-Salces and coworkers [13] reported that injury incidence progressively increased during the football season due to chronic fatigue developed by the continuous training and competition. The gradual reduction in physical performance in football players could be attributed to the physiological stress imposed during the competitive season [14], together with a reduction in the time allocated for muscle strength training [15]. However, there is a lack of studies describing the effect of an entire season on modifiable risk factors associated with hamstring muscle injury. ...
... Of note, as indicated in the methodology, the frequency of strength training sessions was also reduced from twice per week to once per week from February until the end of the season, together with a reduction in the load set per exercise. This information suggests that the football players examined in the present investigation might have experienced a physical deconditioning towards the end of the season as the result of reduced training load during training aimed to offset cumulative fatigue [14,15]. These data suggest that, in addition to the preseason, the end-season phase may increase the likelihood of suffering a hamstring muscle injury during football practice or match-play. ...
Article
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Deficits in hamstring muscle strength and in hip range of motion (ROM) have been considered risk factors for hamstring muscle injuries. However, there is a lack of information on how chronic exposure to regular football training affects hamstring muscle strength and hip ROM. The aim of this study was to examine the longitudinal effect of football training and competition during a complete season on hamstring muscle strength and hip ROM in football players. A total of 26 semi-professional football players underwent measurements of isometric hamstring muscle strength and passive hip flexion/extension, and internal/external hip rotation (IR/ER) ROM during the football season (pre-season, mid-season, end-season). Compared to pre-season, hamstring muscle strength increased in the dominant (+11.1%, p = 0.002) and non-dominant (+10.5%, p = 0.014) limbs in the mid-season. Compared to mid-season, hamstring strength decreased in the dominant (−9.3%, p = 0.034) limb at end-season. Compared to the pre-season, hip extension ROM decreased in mid-season in the dominant (−31.7%, p = 0.007) and non-dominant (−44.1%, p = 0.004) limbs, and further decreased at end-season (−49.0%, p = 0.006 and −68.0%, p < 0.001) for the dominant and non-dominant limbs. Interlimb asymmetry for hip IR ROM increased by 57.8% (p < 0.002) from pre-season to mid-season. In summary, while hamstring muscle strength increased during the first half of the football season in football players, a progressive reduction in hip extension ROM was observed throughout the season. The reduced hip extension ROM suggests a reduced mobility of the hip flexors, e.g., iliopsoas, produced by the continuous practice of football. Consequently, hip-specific stretching and conditioning exercises programs should be implemented during the football season.
... These findings might be associated with the physical deconditioning of players and chronic fatigue developed by the continuance of training and competition across the football season [37]. As previously suggested, the reduction in physical performance in football players could be attributed to the physiological stress imposed during the competitive season [38] together with a reduction in the time allocated for muscle strength training [39]. Furthermore, fatigue is known to occur at the end of the game [40,41] and congested fixture periods due to the depletion of muscle glycogen concentrations [42], and produces reductions in physical performance (e. g., muscle strength), ability to maintain high speed running [43], and acceleration/deceleration [44]. ...
Article
The aim of this investigation was to examine the impact of the weekly training load and the match running patterns prior to a muscle injury as potential risk factors of muscle injury in professional football players. Forty male professional football players participated in the investigation. Running distances at different intensities 5 min and 15 min prior to the injury were compared to the same time-points in official matches of the same player with no injury events. Furthermore, the cummulative session rating of perceived exertion (sRPE) and training load of the week prior to the injury were compared to a control week (mean value of training weeks without injury). Nineteen players suffered 31 non-contact muscle injuries during matches. The distance covered at 21–24 km/h (p<0.001; effect size (ES)=0.62) and at>24 km/h (p=0.004; ES=0.51) over the 5-min period prior to the injury was greater than in matches without injury. The cumulative sRPE (p=0.014; ES=1.33) and training volume (p=0.002; ES=2.45) in the week prior to the injury was higher than in a control week. The current data suggest that the combination of a training week with a high load and a short period of high intensity running during the match might increase the risk of muscle injury in professional footballers.
... Detraining is very important for understanding the many changes that negatively affect the future performance of athletes with the cessation of training [20]. Although it is stated in studies that home exercises can prevent physical performance decreases in athletes during short-term detraining such as the off-season and transition period [39][40][41], it is thought that the effects of the long-term detraining may be much more detrimental due to the COVID-19 lockdown and confinement. ...
Article
Full-text available
The aim of this study is to examine how physical performance has changed after 15 weeks (109 days) long-term absence of organized training in youth soccer players imposed by the stay at home orders. A total of sixty-eight young male soccer players from different age categories (U15, U16, U17 and U19) voluntarily participated in the prospective cohort study. Body fat percentage (BF%), counter-movement jump (CMJ), 30 m sprint, change-of-direction (COD) and yo-yo intermittent recovery test level-1 (YYIRTL-1) were evaluated twice (before and after the detraining period). Subsequently, 2 × 2 repeated measures ANOVA was used to investigate group and time differences in repeated measurements. A significance level of p < 0.05 was implemented. CV and SWC values were calculated to test the reliability of the tests performed at different times. Statistical analysis was performed using the IBM SPSS statistics software (v.25, IBM, New York, NY, USA). Significant increments in BF%, 30 m sprint, and COD (left and right), and also significant decrements in CMJ and YYIRTL-1, were found after the detraining period. A long-term detraining period due to the stay at home orders has a detrimental effect on body composition, neuromuscular performances, and aerobic capacity in youth soccer players.
... For example, it has been shown that preseason strength was reduced after a 12-week in-season soccer training period without any strength training. 79 Performance of one strength training session per week during the in-season period maintained strength, 80 while strength training twice a week may decrease strength due to overtraining. 81 This indicates that injury epidemiology studies should monitor strength sessions adopted by players during the in-season period as they may affect strength imbalances relative to the preseason measurements. ...
Article
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Background For the past 30 years, the hamstrings (H) to quadriceps (Q) torque ratio (H:Q) has been considered an important index of muscle strength imbalance around the knee joint.The purpose of this systematic review has been to examine the value of H:Q strength ratio as an independent risk factor for hamstring and anterior cruciate ligament (ACL) injuries. Methods Database searches were performed to identify all relevant articles in PubMed, Medline, Cochrane Library, and Scopus. Prospective studies evaluating the conventional (concentric H:Q), functional (eccentric H: concentric Q), and mixed (eccentric H at 30°/s: concentric Q at 240°/s) H:Q ratios as risk factors for occurrence of hamstring muscle strain or ACL injury were considered. Risk of bias was assessed using the Quality In Prognosis Studies (QUIPS) tool. Results Eighteen included studies reported 585 hamstrings injuries in 2945 participants, and 5 studies documented 128 ACL injuries in 2772 participants. Best evidence synthesis analysis indicated that there is very limited evidence that H:Q strength ratio is an independent risk factor for hamstring and ACL injury, and this was not different between various ratio types. Methodological limitations and limited evidence for ACL injuries and some ratio types might have influenced these results. Conclusion H:Q ratio has limited value for the prediction of ACL and hamstring injuries. Monitoring strength imbalances along with other modifiable factors during the entire competitive season may provide a better understanding of the association between H:Q ratio and injury.
... However, after 12 weeks of training cessation, the above-mentioned specific exercise indicators decreased significantly, which is consistent with the results from a previous study [31]. Some of the previous studies showed a degree of decrease in sprinting performance and a small or moderate decrease in muscle strength [4,9,13], whereas some studies found no negative effects on sprinting performance under reduced training or training cessation [14,[32][33][34][35][36][37]. We suggest that such differences might be influenced by changes in training volume and intensity, as well as the length of the reduced training or training cessation period. ...
Article
Full-text available
Background: The global coronavirus disease pandemic (COVID-19) has had a considerable impact on athletic competition and team sports training. Athletes have been forced to train alone at home. However, the isolation training model effects are still unknown. Purpose: This study compared the effects of personal isolation training (PIT) and detraining (DT) on specific sport performances (flexibility, power, reaction time, acceleration, and aerobic capacity) and body composition in elite taekwondo athletes. Methods: Eleven elite taekwondo athletes were recruited as voluntary subjects. Athletes were randomly paired by weight into the personal isolation training group (PIT group: N = 5, age: 21.2 ± 0.4 years, BMI: 22.2 ± 0.8 kg/m2) or detraining group (DT group: N = 6, age: 19.8 ± 0.3 years, BMI: 23.1 ± 1.0 kg/m2). All subjects performed the same training content prior to the pre-test (T1). When the pre-test was completed, all subjects underwent 12 weeks of PIT or DT. Athletes were then administrated the post-test (T2). The athlete's sport performances and body composition were measured to compare the differences between the two groups (PIT and DT) and two phases (T1 and T2). Results: There were no significant differences in kicking reaction time and flexibility in both groups (p > 0.05). The PIT showed significant improvements in 10 m (10M) sprint performance (p < 0.05), and displayed a progress trend in Abalakov jump performance. In addition, the PIT resulted in a better change response in 10M sprint performance (PIT: -4.2%, DT: +2.1%), aerobic endurance performance (PIT: -10.2%, DT: -18.4%), right arm muscle mass (PIT: +2.9%, DT: -3.8%), and trunk muscle mass (PIT: +2.2%, DT: -1.9%) than DT (p < 0.05). The fat mass percentage showed a negative change from T1 to T2 in both groups (p < 0.05). Conclusions: PIT showed a trend toward better body composition (arm and trunk muscle) and sport performances (10M sprint and aerobic capacity) compared to DT. This finding may provide information on the effectiveness of a personal isolation training model for optimal preparation for taekwondo athletes and coaches. It may also serve as a useful and safe guideline for training recommendations during the coronavirus disease (COVID-19).
... The high degree of heterogeneity reflects the diversity of the training effects presented. This is likely due to the wide variation in the intervention characteristics, including training frequency [78,80], intensity [34,36,59,125], duration [76], volume [109], other training completed [62,100]), population characteristics (e.g., sex [65], baseline physical characteristics [60,110], training experience [34,80]), sprint monitoring methods (e.g., start position, environmental factors [56]), and technology (e.g., equipment [58]). Therefore, these findings should be interpreted carefully as the variation of the effect sizes demonstrates that training response is highly individualised. ...
Article
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Background Within the football codes, medium-distance (i.e., > 20 m and ≤ 40 m) and long-distance (i.e., > 40 m) sprint performance and maximum velocity sprinting are important capacities for success. Despite this, no research has identified the most effective training methods for enhancing medium- to long-distance sprint outcomes. Objectives This systematic review with meta-analysis aimed to (1) analyse the ability of different methods to enhance medium- to long-distance sprint performance outcomes (0–30 m, 0 to > 30 m, and the maximum sprinting velocity phase [ V max ]) within football code athletes and (2) identify how moderator variables (i.e., football code, sex, age, playing standard, phase of season) affected the training response. Methods We conducted a systematic search of electronic databases and performed a random-effects meta-analysis (within-group changes and pairwise between-group differences) to establish standardised mean differences (SMDs) with 95% confidence intervals and 95% prediction intervals. This identified the magnitude and direction of the individual training effects of intervention subgroups (sport only; primary, secondary, tertiary, and combined training methods) on medium- to long-distance sprint performance while considering moderator variables. Results In total, 60 studies met the inclusion criteria (26 with a sport-only control group), totalling 111 intervention groups and 1500 athletes. The within-group changes design reported significant performance improvements (small–moderate) between pre- and post-training for the combined, secondary (0–30 and 0 to > 30 m), and tertiary training methods (0–30 m). A significant moderate improvement was found in the V max phase performance only for tertiary training methods, with no significant effect found for sport only or primary training methods. The pairwise between-group differences design (experimental vs. control) reported favourable performance improvements (large SMD) for the combined (0 to > 30 m), primary ( V max phase), secondary (0–30 m), and tertiary methods (all outcomes) when compared with the sport-only control groups. Subgroup analysis showed that the significant differences between the meta-analysis designs consistently demonstrated a larger effect in the pairwise between-group differences than the within-group change. No individual training mode was found to be the most effective. Subgroup analysis identified that football code, age, and phase of season moderated the overall magnitude of training effects. Conclusions This review provides the first systematic review and meta-analysis of all sprint performance development methods exclusively in football code athletes. Secondary, tertiary, and combined training methods appeared to improve medium-long sprint performance of football code athletes. Tertiary training methods should be implemented to enhance V max phase performance. Nether sport-only nor primary training methods appeared to enhance medium to long sprint performance. Performance changes may be attributed to either adaptations specific to the acceleration or V max phases, or both, but not exclusively V max . Regardless of the population characteristics, sprint performance can be enhanced by increasing either the magnitude or the orientation of force an athlete can generate in the sprinting action, or both. Trial Registration OSF registration https://osf.io/kshqn/ .
Previous research has established the role of resistance training (RT) on muscle function in adolescents, but a lack of evidence to optimize RT for enhancing muscle quality (MQ) exists. This study examined whether RT frequency is associated with MQ in a nationally representative adolescent cohort. A total of 605 adolescents (12–15 year) in NHANES were stratified based on RT frequency. MQ was calculated as combined handgrip strength divided by arm lean mass (via dual-energy X-ray absorptiometry). Analysis of covariance was adjusted for sex, race/ethnicity, and arm fat percentage; p < 0.05 was considered significant. RT frequency was associated with MQ for 2–7 day/week but not 1 day/week. When no RT was compared to 1–2 and 3–7 day/week, associations were present for 3–7 day/week but not 1–2 day/week. When comparing no RT to 1–4 and 5–7 days/week, associations existed for 5–7 day/week but not 1–4 day/week. Next, no RT was compared to 1, 2–3, and 4–7 day/week; associations were found for 4–7 day/week, while 2–3 days/wk had a borderline association (p = 0.06); there were no associations for 1 day/week. Finally, no RT was compared to 1, 2, 3, 4, and 5–7 day/week; associations were present for all except 1 and 3 day/week. These prospective data suggest a minimum RT frequency of 2 day/week is associated with MQ in adolescents as indicated by the lack of differences in MQ between 1 day/week RT versus no RT.
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Ensuring internal validity is the key procedure when planning the study design. Numerous systematic reviews have demonstrated that considerations for internal validity do not receive adequate attention in the primary research in sport sciences. Therefore, the purpose of this study was to review methodological procedures in current literature where the effects of resistance training on strength, speed, and endurance performance in athletes were analyzed. A computer-based literature searches of SPORTDiscus, Scopus, Medline, and Web of Science was conducted. The internal validity of individual studies was assessed using the PEDro scale. Peer-reviewed studies were accepted only if they met all the following eligibility criteria: (a) healthy male and female athletes between the ages of 18-65 years; (b) training program based on resistance exercises; (c) training program lasted for at least 4 weeks or 12 training sessions, with at least two sessions per week; (d) the study reported maximum strength, speed, or endurance outcomes; and (e) systematic reviews, cohort studies, case-control studies, cross-sectional studies were excluded. Of the 6,516 articles identified, 133 studies were selected for rating by the PEDro scale. Sixty-eight percent of the included studies used random allocation to groups, but only one reported concealed allocation. Baseline data are presented in almost 69% of the studies. Thirty-eight percent of studies demonstrated adequate follow-up of participants. The plan to follow the intention-to-treat or stating that all participants received training intervention or control conditions as allocated were reported in only 1.5% of studies. The procedure of blinding of assessors was also satisfied in only 1.5% of the studies. The current study highlights the gaps in designing and reporting research in the field of strength and conditioning. Randomization, blinding of assessors, reporting of attrition, and intention-to-treat analysis should be more fully addressed to reduce threats to internal validity in primary research.
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This study examined the effects of training frequency on strength maintenance in 21 trained pubescent male baseball players (mean age 13.25 +/- 1.26 yrs). The subjects completed 12 weeks of preseason, progressive strength training 3 days a week and were assigned to 1 of 3 experimental groups for an additional 12 weeks of in-season maintenance training. Group 1 (n = 7) lifted weights 1 day a week, Group 2 (n = 8) lifted weights 2 days a week, and a control group (n = 6) did not train during this 2nd 12 weeks. The preseason strength training program revealed significant increases (p < 0.05) for all groups in upper (bench press) and lower (leg press) body strength and dynamic upper body muscular endurance (pull-up). Following the 12-week in-season maintenance program, significant differences (p < 0.05) were observed between the control group and both training groups for the bench press. However, no significant differences were revealed between groups for the leg press or pull-up. It was concluded that for pubescent male athletes, a 1-day-a-week maintenance program is sufficient to retain strength during the competitive season. (C) 1996 National Strength and Conditioning Association
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Thirty-five healthy men were matched and randomly assigned to one of four training groups that performed high-intensity strength and endurance training (C; n = 9), upper body only high-intensity strength and endurance training (UC; n = 9), high-intensity endurance training (E; n = 8), or high-intensity strength training (ST; n = 9). The C and ST groups significantly increased one-repetition maximum strength for all exercises (P < 0.05). Only the C, UC, and E groups demonstrated significant increases in treadmill maximal oxygen consumption. The ST group showed significant increases in power output. Hormonal responses to treadmill exercise demonstrated a differential response to the different training programs, indicating that the underlying physiological milieu differed with the training program. Significant changes in muscle fiber areas were as follows: types I, IIa, and IIc increased in the ST group; types I and IIc decreased in the E group; type IIa increased in the C group; and there were no changes in the UC group. Significant shifts in percentage from type IIb to type IIa were observed in all training groups, with the greatest shift in the groups in which resistance trained the thigh musculature. This investigation indicates that the combination of strength and endurance training results in an attenuation of the performance improvements and physiological adaptations typical of single-mode training.
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The study investigated changes in motor output and motor unit behavior following 6 wk of either strength or endurance training programs commonly used in conditioning and rehabilitation. Twenty-seven sedentary healthy men (age, 26.1 ± 3.9 yr; mean ± SD) were randomly assigned to strength training (ST; n = 9), endurance training (ET; n = 10), or a control group (CT; n = 8). Maximum voluntary contraction (MVC), time to task failure (isometric contraction at 30% MVC), and rate of force development (RFD) of the quadriceps were measured before (week 0), during (week 3), and after a training program of 6 wk. In each experimental session, surface and intramuscular EMG signals were recorded from the vastus medialis obliquus and vastus lateralis muscles during isometric knee extension at 10 and 30% MVC. After 6 wk of training, MVC and RFD increased in the ST group (17.5 ± 7.5 and 33.3 ± 15.9%, respectively; P < 0.05), whereas time to task failure was prolonged in the ET group (29.7 ± 13.4%; P < 0.05). The surface EMG amplitude at 30% MVC force increased with training in both groups, but the training-induced changes in motor unit discharge rates differed between groups. After endurance training, the motor unit discharge rate at 30% MVC decreased from 11.3 ± 1.3 to 10.1 ± 1.1 pulses per second (pps; P < 0.05) in the vasti muscles, whereas after strength training it increased from 11.4 ± 1.2 to 12.7 ± 1.3 pps (P < 0.05). Finally, motor unit conduction velocity during the contractions at 30% MVC increased for both the ST and ET groups, but only after 6 wk of training (P < 0.05). In conclusion, these strength and endurance training programs elicit opposite adjustments in motor unit discharge rates but similar changes in muscle fiber conduction velocity.
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