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Photobiomodulation therapy as a tool to prevent hamstring strain injuries by reducing soccer-induced fatigue on hamstring muscles

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Muscle fatigue is a potential risk factor for hamstring strain injuries in soccer players. The aim of this study was to verify the effect of photobiomodulation therapy (PBMT) on the hamstrings’ muscle fatigue of soccer players during a simulated match. Twelve male amateur soccer players (~ 25 years) participated in this randomized, crossover, double-blinded, placebo-controlled trial. The volunteers were evaluated in two sessions, with a minimum 7-day interval. At each session, volunteers received either PBMT (300 J per thigh) or placebo treatment on the hamstrings prior to the simulated soccer match. Muscle strength and functional capacity were evaluated through isokinetic dynamometry and countermovement jump (CMJ) tests, respectively, before and immediately after the simulated soccer match. Players had lower reductions on hamstring eccentric peak torque [4.85% (ES = 0.31) vs. 8.72% (ES = 0.50)], hamstring-to-quadriceps torque ratio [3.60% (ES = 0.24) vs. 7.75% (ES = 0.50)], and CMJ height [1.77% (ES = 0.09) vs. 5.47% (ES = 0.32)] when treated with PBMT compared to placebo. Magnitude-based inference supports that PBMT promoted 75%, 69%, and 53% chances for beneficial effects on hamstring eccentric peak torque, hamstring-to-quadriceps torque ratio, and CMJ height, respectively, compared to placebo treatment. In conclusion, PBMT applied before a simulated soccer match proved to be effective in attenuating the hamstrings’ muscle fatigue. These findings support PBMT as a promising tool to prevent hamstring strain injury in soccer players.
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ORIGINAL ARTICLE
Photobiomodulation therapy as a tool to prevent hamstring strain
injuries by reducing soccer-induced fatigue on hamstring muscles
Maurício Pinto Dornelles
1
&Carolina Gassen Fritsch
1
&Francesca Chaida Sonda
2
&Douglas Scott Johnson
3
&
Ernesto Cesar Pinto Leal-Junior
4
&Marco Aurélio Vaz
2
&Bruno Manfredini Baroni
1
Received: 1 November 2018 /Accepted: 14 December 2018
#Springer-Verlag London Ltd., part of Springer Nature 2019
Abstract
Muscle fatigue is a potential risk factor for hamstring strain injuries in soccer players. The aim of this study was to verify the effect
of photobiomodulation therapy (PBMT) on the hamstringsmuscle fatigue of soccer players during a simulated match. Twelve
male amateur soccer players (~ 25 years) participated in this randomized, crossover, double-blinded, placebo-controlled trial. The
volunteers were evaluated in two sessions, with a minimum 7-day interval. At each session, volunteers received either PBMT
(300 J per thigh) or placebo treatment on the hamstrings prior to the simulated soccer match. Muscle strength and functional
capacity were evaluated through isokinetic dynamometry and countermovement jump (CMJ) tests, respectively, before and
immediately after the simulated soccer match. Players had lower reductions on hamstring eccentric peak torque [4.85% (ES =
0.31) vs. 8.72% (ES = 0.50)], hamstring-to-quadriceps torque ratio [3.60% (ES = 0.24) vs. 7.75% (ES = 0.50)], and CMJ height
[1.77% (ES= 0.09) vs. 5.47% (ES= 0.32)] when treated with PBMTcompared to placebo. Magnitude-based inference supports
that PBMT promoted 75%, 69%, and 53% chances for beneficial effects on hamstring eccentric peak torque, hamstring-to-
quadriceps torque ratio, and CMJ height, respectively, compared to placebo treatment. In conclusion, PBMT applied before a
simulated soccer match proved to be effective in attenuating the hamstringsmuscle fatigue. These findings support PBMT as a
promising tool to prevent hamstring strain injury in soccer players.
Keywords Phototherapy .Muscle injury .Prevention .Football
Introduction
The hamstring strain injury (HSI) is one of the major problems
soccer players face in sports practice. A 13-year longitudinal
analysis of European elite soccer teams reported that 22% of
the players sustained at least one hamstring injury in each
season [1]. It means that a soccer team with a 25-player squad
can expect about 56 injured players per season. In addition,
the recurrence rate is high (12 out of 10 injured players
usually sustain a re-injury within 2 months of return to play)
and the average absence time per injury is about 17 days [1].
Despite the persistent deficits after a HIS [2], players Boff the
pitch^due to injuries compromise the team performance [3]
and negatively affect the club finances [4]; hence, prevention
is the primary goal. Soccer clubs have invested in a range of
tests for screening players who might be prone to injury and in
specific prevention programs [5,6], but HSI rates have not
decreased throughout the years [1].
HSI is typically a non-contact injury (high-speed running is
responsible for 6080% of soccer HSIs) [7,8]. Therefore, the
scientific community has paid great attention to the intrinsic
risk factors associated with HIS [9,10]. Age and previous
injuries are well-accepted non-modifiable risk factors [9,
10]. Among the modifiable risk factors, there is great attention
on the hamstring eccentric strength [8,11,12]andthe
hamstring-to-quadriceps (H:Q) strength ratio [11,13,14]. It
is important to note that both factors are expected to be affect-
ed by fatigue during a soccer match. Studies with intermittent
exercise protocols designed to mimic demands of competitive
*Bruno Manfredini Baroni
bmbaroni@yahoo.com.br
1
Universidade Federal de Ciências da Saúde de Porto Alegre
(UFCSPA), Porto Alegre, RS, Brazil
2
Exercise Research Laboratory, Universidade Federal do Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
3
Multi Radiance Medical, Solon, OH, USA
4
Laboratory of Phototherapy and Innovative Technologies in Health,
Universidade Nove de Julho (UNINOVE), São Paulo, SP, Brazil
Lasers in Medical Science
https://doi.org/10.1007/s10103-018-02709-w
soccer have found significant decreases (up to 31%) in ham-
string eccentric strength with few or no impact on quadriceps
strength [1518], thus affecting the agonistantagonist
strength balance. The link between eccentric weakness and
increased HSI risk suggests that players would be more sus-
ceptible to injury in fatigue situations, and this hypothesis is
supported by the fact that most HSIs sustained during matches
occurred during the last third of the first and second halves of
the match (3145and 7690,respectively)[7]. Therefore,
muscle fatigue has been commonly stated as a potential risk
factor for HSI [9].
Photobiomodulation therapy (PBMT), also known as pho-
totherapy, is a non-invasive and non-pharmacological therapy
largely employed to treat a series of musculoskeletal disorders
[19]. Positive effects on pain [20], inflammation [20], and
tissue repair [21] have been reported with application of
low-level LASERs or light-emitting diodes (LEDs) over a
target tissue [22]. Along the last decade, a growing body of
evidences has been published regarding the PBMT action on
muscle fatiguefor a review, see Vanin et al. [23]. Improved
exercise performance and/or reduced fatigue markers have
been found with a single application of PBMT immediately
before a range of exercise protocols, such as exercise with free
weights [24], isokinetic exercise [25], cycling [26], running
[27], and intermittent sprints test [28].
In summary, the ability of PBMT to reduce muscle fatigue
in different types of exercise has elevated this therapy to the
category of potential ergogenic agent in sports. Considering
the relationship between fatigue and HSI in soccer players, it
seems plausible that PBMT may also be a promising tool for
this injury prevention. The first step in the application of
preventive-based PBMT is to find therapy parameters capable
of minimizing the loss of hamstring strength generated by
soccer practice. Therefore, the aim of the current study was
to verify the effect of PBMTon the hamstringsmuscle fatigue
of amateur soccer players during a simulated match.
Methods
Study design
The study is characterized as a randomized, crossover, double-
blinded, placebo-controlled trial. The volunteers were evalu-
ated in two sessions, with a minimum 7-day interval. Both
sessions were performed at the same hour of day and with
similar climatic conditions. At each session, volunteers re-
ceived either PBMT or placebo treatment on the hamstrings
prior to a soccer match simulation protocol. The order of the
PBMT and placebo sessions was randomized through the
random.org website. Muscular performance tests were
applied before and after a simulated soccer match. The
following sequence of events was performed within each
session: (1) general warm-up, (2) countermovement jump
(CMJ) test, (3) isokinetic test, (4) PBMT or placebo therapy,
(5) simulated soccer match, (6) CMJ re-test, and (7) isokinetic
re-test (Fig. 1). The study was previously approved by the
Ethics and Research Committee of the University where the
study was conducted (no. 63299416.4.0000.5345), and all
participants signed an informed consent.
Participants
Twelve male amateur soccer players were recruited to
participate in the study (age, 25.17 ± 4.04 years; body
mass, 73.75 ± 5.85 kg; height, 1.74 ± 0.04 m). All partic-
ipants followed a minimum routine of one soccer match
per week (1.75 ± 0.86 h per week of sports practice) and
had competitive experience in amateur soccer leagues.
Exclusion criteria for participation in the study were as
follows: (1) the presence of any musculoskeletal injuries
during the study period, (2) history of muscle injuries on
lower limbs (e.g., hamstrings, quadriceps, groin) in the
6 months prior to the evaluations, (3) recent history of
any lower limbs injuries that could interfere with the stud-
ied outcomes (e.g., anterior cruciate ligament rupture,
Fig. 1 Flowchart of study
Lasers Med Sci
meniscus injury, patellofemoral pain syndrome), (4) any
contraindication to performing maximum exercises, and
(5) difficulty in understanding and/or executing the testing
protocols.
CMJ test
After general warm-up (5-min run at moderate intensity), low-
er extremity functional capacity was assessed through the
CMJ test [29]. The rater explained and demonstrated the
CMJ proper execution. The volunteer should be standing with
hands on hips and feet aligned respecting the same distance
from the shoulders, then squat until a position of approximate-
ly 90° of knee flexion and perform a vertical jump as high as
possible. Submaximal CMJs were performed to familiarize
the volunteer with the movement. A smartphone was posi-
tioned 1.5 m away from the volunteer to record the execution
of three maximal CMJs [29]. The volunteer was instructed to
use the hip, knee, and ankle flexion movements to dampenthe
landing. The jump height analysis was done through the mo-
bile application named Jumpo (available for free download).
This application works similar to the previously validated ap-
plication named My Jump [29]. Jumpo was chosen because it
was the only available application for the iOS operating sys-
tem when our data were collected. The highest height obtained
between the jumps was considered for analysis. The CMJ re-
test started 3 min after ending the simulated soccer match.
Isokinetic dynamometry
The volunteer was positioned on the isokinetic dynamometer
Biodex System 3 Pro (Biodex Medical Systems, USA) ac-
cording to the manufacturers recommendations for evalua-
tion of the knee flexionextension movements with the dom-
inant limb. Ten submaximal repetitions of knee flexion
extension in the concentric mode at an angular velocity of
90° s
1
were used as specific warm-up. The volunteer was
familiarized with the execution of isokinetic concentric and
eccentric tests through submaximal contractions. Two sets of
three maximal knee extensors concentric contractions and two
sets of three maximal kneeflexors eccentric contractions were
performed [30]. The 60° s
1
angular velocity was used for all
tests, and a 1-min rest period was observed between sets [30].
The volunteer was verbally encouraged to produce as much
strength as possible in all contractions. The highest peak
torques in each contraction type were considered for analysis.
The H:Q functional torque ratio was calculated as follows:
hamstring eccentric peak torque/quadriceps concentric peak
torque [31]. The isokinetic re-test started 5 min after the sim-
ulated soccer match end due to the time required for the vol-
unteers positioning at the dynamometer.
PBMT/ placebo treatments
Interventions with PBMT or placebo were administered im-
mediately before the soccer match simulation protocol. A sin-
gle researcher was responsible for the treatmentsallocation
(PBMT or placebo) in each session. The researchers respon-
sible for the CMJ and isokinetic dynamometry assessments,
and for the soccer match simulation protocol, were not inside
the room during the PBMT/placebo application. The volun-
teers were blindfolded and used headphones plugged into a
music player device during treatments to avoid identification
of sounds emitted by the PBMT device. Since PBMT is a
modality that does not promote any thermic, sensitive, and/
or painful stimulus, participants did not know whichtreatment
was applied in each session.
LEAP SportsPOD (prototype by Multi Radiance Medical,
Solon, OH, USA) was used for administration of PBMT and
placebo treatments (Fig. 2). This device contains 152 infrared
LEDs (880 nm) distributed evenly over an area of 252 cm
2
(10.5 cm × 24 cm); thus, it was possible to treat most of the
posterior thigh area with a single application (differently than
conventional cluster probes that are smaller and require mul-
tiple application sites). The PBMT device used here is a flex-
ible pad, so it was coupled appropriately to the convexity of
the posterior thigh. In addition, the researcher exerted a slight
pressure with the hands to ensure the diodes contact with the
Fig. 2 Volunteer receiving PBMT/placebo treatment (top) and PBMT
parameters used in this study (bottom)
Lasers Med Sci
volunteers skin. The parameters used for PBMT application
are shown in Fig. 2. The PBMTwas applied for 60 s, totalizing
an energy dose of 300 J in each of the volunteershamstring
muscle. This pre-exercise energy dose provided the best re-
sults in a previous trial with high-level soccer players [32].
The placebo application was carried out in the same way as the
active therapy, but with the equipment turned off.
Simulated soccer match
Based on movement analysis of the English Football League,
Small et al. [18] designed and validated the protocol entitled
soccer-specific aerobic field test (SAFT
90
). The protocol con-
sists of a sequence of activities that mimics the physiological
demands of a soccer match within a 15-min module of inter-
mittent exercise. To represent the 90 min of a soccer match,
this module is repeated six times with a 15-min interval be-
tween the 3rd and 4th execution. Therefore, SAFT
90
accurate-
ly represents the physiological load associated with a soccer
match, including multi-directional movements with different
intensities and requiring changes in direction and speed (ac-
celerations and decelerations) [18].
Since the present study included only amateur soccer
players, the original protocol of SAFT
90
was adapted to a
45-min protocol (i.e., three executions of the intermittent ex-
ercise module that represents the first half of a soccer match).
A single researcher provided commands and verbal encour-
agement during the simulated soccer match for all volunteers.
At the end of each 15-min module, the volunteers ingested
regular water ad libitum to avoid any influence of
hypohydration on their fatigue level. The rating of perceived
exertion (RPE) provided by the volunteer after completing the
simulated soccer match was multiplied by the time duration
(~ 45 min) to determine the internal workload generated by
the exercise protocol in each volunteer [33].
Statistical analysis
Sample size was calculated through G*Power software (ver-
sion 3.1.9.2) using results provided by a previous study that
assessed the effect of simulated soccer match on the hamstring
eccentric peak torque of amateur soccer players [15]. A sam-
ple of nine participants was estimated to provide a statistical
power over 0.90. As we expected a dropout rate of approxi-
mately 20%, 12 subjects were initially included in the trial.
Data normality was verified using the ShapiroWilk test.
Internal workloads promoted by the simulated soccer match
in placebo and PBMT sessions were compared through a
paired sample Studentsttest.
Subjectsbehaviors within each session (PBMT and place-
bo) were analyzed with the following calculations: mean per-
cent change (Δ% =post-exercise / pre-exercise 1); paired
sample ttest (pre-exercise vs. post-exercise), with a
significance level set as 5% (α< 0.05); and effect size (ES)
through Cohensd[ES = (M
post
M
pre
)/SD
pooled
,whereM
post
is the mean post-exercise measure, M
pre
is the mean pre-
exercise measure, and SD
pooled
is the pooled standard devia-
tion of the pre- and post-exercise]. Effect sizes were consid-
ered as Btrivial^(ES < 0.2), Bsmall^(ES > 0.2), Bmoderate^
(ES > 0.5), or Blarge^(ES > 0.8) [34].
Longitudinal percent changes (pre- to post-exercise) were
used for comparison between PBMT and placebo treatments.
Data were analyzed for practical significance using
magnitude-based inferences because traditional statistical ap-
proaches often do not indicate the magnitude of an effect,
which is typically more relevant to sports medicine than sta-
tistical significance [35]. The magnitude of between-
treatments differences (PBMT vs. placebo) was calculated
and expressed as standardized mean differences, considering
the Cohens criteria for the analysis (> 0.2 = small; > 0.5 =
moderate; > 0.80 = large). The chances that the true
(unknown) mean changes were trivial, harmful, or beneficial
[i.e., greater than the smallest worthwhile change (0.2 multi-
plied by the between-participant standard deviation)] were
determined. Quantitative chances of a beneficial or harmful
effect were assessed qualitatively, as follows: < 1%, almost
certainly not; 15%, very unlikely; 525%, unlikely; 25
75% = possibly; 7595% = likely; 9599% = very likely; and
> 99% = almost certain [36]. When the harmful and beneficial
values were both > 5%, the inference was classified as unclear
[36].
Results
The simulatedsoccer match represented similar internal work-
loads in PBMT (368.18 ± 60.06 a.u.) and placebo (363.34 ±
85.08 a.u.) sessions (p=0.863).
Quadriceps concentric peak torque was not affected by the
simulated soccer match in any experimental condition
(p> 0.05; trivial effect size; Table 1). Hamstring eccentric
peak torque decreased significantly in both conditions
(p< 0.05), while a significant fall of H:Q torque ratio was
observed only in placebo session (p< 0.05). Greater effect
sizes were observed with placebo treatment for both hamstring
eccentric peak torque and H:Q torque ratio (Table 1). There
was no statistically significant reduction on jump height
(p> 0.05 for both conditions), but a small effect size was ob-
served only with placebo treatment (Table 1).
As shown in Fig. 3, PBMT promoted 75%, 69%, and 53%
chances for beneficial effects on hamstring eccentric peak
torque, H:Q torque ratio, and CMJ height, respectively, com-
pared to placebo treatment. PBMT had no beneficial or harm-
ful effects compared to placebo treatment on quadriceps con-
centric peak torque (Fig. 3).
Lasers Med Sci
Discussion
The main finding of the current study was that PBMTapplied
before a simulated soccer match reduced the losses of ham-
string eccentric strength, H:Q functional ratio, and CMJ
height. Our results become relevant to clinical practice from
the following rationale: hamstring fatigue generated by a soc-
cer match is a potential risk factor for HSI, and PBMT can
reduce soccer-induced fatigue on hamstring muscles; thus,
PBMT may be an innovative tool for HSI prevention.
Fatigue is frequently pointed out as a strong risk factor for
non-contact injuries in soccer players [5,6], specially the HSI
[9]. Fatigue perhaps explain, at least partially, why most HSIs
sustained during matches occurred during the last third of the
first and second halves of the match [7]. However, the rela-
tionship between soccer-induced fatigue and HSI is only sup-
ported by indirect evidences, such as the fall of hamstring
maximal eccentric strength promoted by simulated soccer
matches [15,16,18]. Like our findings, Small et al. [18]and
Jones et al. [15] found 58% reduced hamstring eccentric
strength after 45 min of the SAFT
90
in semi-professional
and amateur soccer players, respectively. That strength loss
seems to be higher than 16% after the full SAFT
90
protocol
[15,18], and up to 31% with another simulated soccer match
protocol called Loughborough intermittent shuttle test [16].
Prospective studies have evidenced that eccentric knee flexor
weakness increases the risk of hamstring injury in soccer [8,
11] and other sports [12]. For instance, Timmins et al. [8]
found a significant inverse relationship between pre-season
hamstring eccentric strength and the incidence of HSIs along
the season in premier league soccer players; for every 10-N
increase in hamstring eccentric strength, the risk of HSI was
reduced by 9%. Therefore, it is expected that a player with
greater deficits on hamstring eccentric strength during a soccer
Fig. 3 Standardized mean
differences and 95%CI for PBMT
effect compared to placebo effect
(forest plot); and chances of
harmful, trivial, or beneficial
effects with PBMT treatment
(right columnpercent values
and magnitude-based inferences)
Table 1 Soccer playersisokinetic and jump performance in photobiomodulation (PBMT) and placebo sessions
Pre Post Δ%pvalue ES
Quadriceps CON PT (Nm)
PBMT 229.95 ± 40.56 226.74 ± 43.72 1.40 0.407 0.08
Placebo 229.06 ± 41.31 224.21 ± 41.11 2.12 0.200 0.12
Hamstring ECC PT (Nm)
PBMT 188.33 ± 29.20 179.19 ± 32.32 4.85 0.005* 0.31
Placebo 190.78 ± 35.01 174.13 ± 34.85 8.72 0.001* 0.50
H:Q torque ratio (a.u.)
PBMT 0.83 ± 0.13 0.80 ± 0.13 3.60 0.056 0.24
Placebo 0.85 ± 0.17 0.78 ± 0.12 7.75 0.008* 0.50
CMJ height (cm)
PBMT 35.06 ± 7.04 34.44 ± 7.46 1.77 0.531 0.09
Placebo 35.29 ± 5.87 33.36 ± 6.65 5.47 0.085 0.32
CON concentric, ECC eccentric, PT peak torque, CMJ countermovement jump, Δ%mean percent change, ES effect size
*Significant difference (p<0.05)
Small effect size (ES> 0.2)
Lasers Med Sci
match may be closer to experiencing a HSI, although there is
no data available in the literature to consistently support this
hypothesis.
In contrast to the consistent loss of hamstring strength, the
soccer match leads to a small (or even insignificant) fall on
quadriceps maximal strength [16,18]. Consequently, the H:Q
torque ratio is also negatively affected throughout the soccer
match, as supported by our results. It means that a player with
proper strength balance between knee flexor and extensor
muscles during laboratory tests (performed at a non-fatigued
condition) may present an H:Q ratio increasingly poor
throughout the soccer match. Although prospective studies
have found conflicting results regarding the predictive value
of the H:Q ratios for HSIs in soccer players [11,13,37],
isokinetic dynamometry is largely used as a screening tool
and muscle imbalance is considered one of the main risk fac-
tors for non-contact injuries by premier league soccer teams
[5,6]. The H:Q functional ratio (i.e., hamstring eccentric peak
torque divided by quadriceps concentric peak torque) has been
considered a Bmore functional^way to screen for injury risk in
soccer players compared to the H:Q conventional ratio (i.e.,
hamstring concentric peak torque divided by quadriceps con-
centric peak torque). However, the usual landmark of 1.0 is
rarely reached by professional male soccer players when
assessed at the most traditional testing angular velocity (i.e.,
60° s
1
)for a review, see Baroni et al. [31]. Independently of
the accuracy and predictive value of any landmark, a poor
H:Q functional ratio suggests a reduced hamstring capacity
of Bbreaking^knee extension and hip flexion during the ter-
minal swing phase of running [9], precisely the movement
responsible for most HSIs in soccer [7,8].
To the best of our knowledge, there is no evidence to sup-
port the CMJ performance as predictive of HSI. Jump tests are
largely used to assess lower extremity power, and we added
CMJ to the current study to verify the PBMTeffect on a motor
task closer to the multi-articular complex movements required
in a soccer match. The primary hip extensor during CMJ is the
gluteus maximus, but other hip extensors (including the ham-
string muscles) are also activated during the CMJ stretch-
shortening cycle [38]. Hamstrings execute a rapid eccentric
contraction during squat phase, when energy is stored within
the elastic components of the muscle-tendon unit and muscle
spindle is activated; next, a powerful concentric contraction
during jump phase is generated through a sum of muscle vol-
untary activation, myotatic reflex response, and elastic energy
release [38]. Fatigue impairs all these factors, and consequent-
ly reduces the CMJ height [39]. Our findings support that
PBMT minimized the fatigue effects on hamstring muscles
and, consequently, the soccer match-induced impair on CMJ.
Fatigue is classically defined as an exercise-induced reduc-
tion in the muscles maximal force capacity [40], so reduction
in the maximal strength that a person can produce provides a
straightforward demonstration of fatigue level [41]. However,
other fatigue-related deficits (not assessed in the current study)
may contribute to a player experiencing a HSI. Animal exper-
iments demonstrated that fatigued muscles absorbed less en-
ergy before failure when compared with unfatigued muscles
[42], making fatigued hamstring muscles more likely to suffer
a strain injury due to a reduced capacity to resist to over-
lengthening. At the same time, fatigue negatively affects knee
joint position sense [43] and execution of soccer-specific mo-
tor tasks [44]. These findings suggest decreased function in
afferent output of the sensory organs, including the muscle
spindles and their protective action against over-lengthening.
Consequently, the player may perceive a normal hamstring
muscle action during running, while in reality, repeated
over-lengthening of the hamstrings is occurring [9]. That re-
peated over-lengthening leads to microscopic muscle damage
that may accumulate to become macroscopic damage (i.e.,
muscle strain injury) [45].
To date, the usage of PBMT as a preventive tool against
sport injuries remains unexplored. Previous studies have al-
ready evidenced that a single PBMTsession, applied immedi-
ately before exercise, can minimize the muscle damage levels
in animals [46] and humans [47], but the preventive goal of
PBMT suggested here is totally new. Of course, a long-term
prospective study is needed to verify if PBMT can reduce the
HSI rate along a soccer season. The current study was just the
kick-off for employing PBMT as a preventive tool in sports
medicine, and our findings support that PBMT parameters
used here may be applied to reduce the soccer-induced fatigue
on hamstring muscles, exactly the primary effect to seek HSI
prevention through PBMT.
The reduced fatigue after PBMT was firstly demonstrated
in animal model [48], and a robust body of evidence has
supported this ergogenic effect in humans [23]. The mecha-
nisms responsible for this effect are not fully understood, and
the current study had no intention to investigate how PBMT
affects muscle fatigue from a physiological point of view.
Evidences suggest that the absorption of light energy by spe-
cific chromophores at mitochondria lead to intracellular reac-
tions that increase the ATP production and cellular metabo-
lism [49], as well as improve microcirculation (and, conse-
quently, oxygen supply to irradiated tissue) due to nitric oxide
release [50], among other responses that may optimize the
muscle cell functioning [22].
Given the typical biphasic doseresponse effect of PBMT
treatments [22], finding the optimal parameters of PBMT is a
key factor for the treatment success. We cannot state that
PBMT parameters used in the current study are the most ef-
fective ones because we tested a single dosage, which can be
pointed out as a study limitation. However, the total energy
dose applied per muscle group (i.e., 300 J) is within the range
recommended to treat large muscle groups by the most recent
meta-analysis [23]. In addition, previous findings support that
pre-exercise PBMT with 300 J is better than lower dosages
Lasers Med Sci
(60180 J) to improve performance and biochemical markers
related to skeletal muscle damage and inflammation in soccer
players [32]. Finally, the PBMT device used in the current
study required 60 s to deliver that energy amount to each
hamstring muscle (i.e., a 2-min treatment per player), so it is
a feasible therapy for application before a soccer match or
even during the half-time interval. The applicability of
PBMT as proposed here to the real-world of competitive soc-
cer (and other sports) is a strength of the current study.
Conclusion
PBMT applied on the posterior thigh muscles immediately
before a simulated soccer match proved to be effective in
attenuating fatigue-related impairments on hamstring maxi-
mal eccentric strength, H:Q strength ratio, and CMJ perfor-
mance. Given the relation between soccer-induced ham-
stringsfatigue and HSI, this study is pioneer to highlight
PBMT as a promising tool to prevent HSI in soccer players.
Long-term prospective studies are needed to verify if PBMT
will be effective in reducing the HSI rate along a soccer
season.
Acknowledgements Marco Aurélio Vaz and Ernesto Cesar Pinto Leal-
Junior thank CNPq-Brazil for the research productivity fellowships.
Maurício Pinto Dornelles and Carolina Gassen Fritsch thank CAPES-
Brazil for the scholarships.
Compliance with ethical standards
The study was previously approved by the Ethics and Research
Committee of the Universidade Federal de Ciências da Saúde de Porto
Alegre (no. 63299416.4.0000.5345), and all participants signed an in-
formed consent.
Conflict of interest Professor Ernesto Cesar Pinto Leal-Junior receives
research support from Multi Radiance Medical (Solon - OH, USA) and
Douglas Scott Johnson is an employee and shareholder of Multi Radiance
Medical, a photobiomodulation/laser device manufacturer. They didnt
have any participation in data collection or data analysis in this study.
Furthermore, Multi Radiance Medical didnt have any participation in
any aspect related to this study. The remaining authors declare that they
have no conflict of interests.
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Lasers Med Sci
... To date, de Oliveira et al, 6 Denis et al, 7 and Dornelles et al 8 have investigated the effect of LLLT on muscular performance and soreness recovery. 30,31,39 However, none of them have focused on physically active athletes. ...
... The elimination process left 24 eligible trials. [2][3][4][5][6][7][8][9][10]12,[16][17][18][19][20][21][22][25][26][27]32,35,37,39 The characteristics of the 24 included trials are shown in Appendix Table A1 (available in the online version of this article). Ten of them were RCTs, [2][3][4]6,9,10,19,27,36,40 whereas others were crossover trials. ...
... In summary, 14 trials were graded as low risk for overall bias risk 2,3,5,6,8,[17][18][19][20][21][22]27,32,38 ; the other 10 trials had overall bias risk. 4,7,9,10,12,16,25,26,36,40 ...
Article
Context Athletes must maintain their peak state of strength. Previous studies have investigated the effect of low-level laser therapy (LLLT) on muscular performance. A previous systematic review and meta-analysis has investigated this issue in healthy participants but not in physically active athletes. Objective To investigate whether LLLT can improve muscular performance and soreness recovery in athletes. Data Sources PubMed, EMBASE, and Cochrane Library. Study Selection Published randomized controlled trials and crossover studies till December 2020. Study Design Systematic review and meta-analysis. Level of Evidence Level 3. Data Extraction Assessment of study quality was rated using the risk of bias assessment method for randomized trials (Cochrane Handbook for Systematic Reviews of Interventions). Results A total of 24 studies were included. LLLT application before exercise significantly improved lower-limb muscle strength in 24-hour, 48-hour, 96-hour, and 8-week follow-up groups. Furthermore, decreased soreness index, serum creatine kinase concentrations, interleukin-6, and thiobarbituric acid reactive substance concentrations and a trend toward the improvement of contract repetition number and VO 2 kinetic outcomes were observed. Conclusion Although a definite therapeutic effect of LLLT is yet to be established, the current evidence supports that LLLT use improves muscular performance in physically active athletes. Additional trials with large sample sizes and robust design should be conducted before strong recommendations are made.
... Studies that have examined the effects of PBMT on recovery and performance following exercise protocols include simple open-chain isolated single-joint exercises, such as knee extension (Antonialli et al., 2014;Baroni et al., 2015;de Paiva et al., 2016;Rossato et al., 2018) and elbow flexion (Larkin-Kaiser et al., 2015;Machado et al., 2017;Nausheen et al., 2017;Rigby and Hagan, 2019;Vieira et al., 2019). Studies have progressed to more dynamic protocols, such as such as in-game competitions (De Marchi et al., 2019;Dornelles et al., 2019), sport-specific tests (Pinto et al., 2016), running (Malta et al., 2016(Malta et al., , 2018Dellagrana et al., 2018;Peserico et al., 2019), plyometrics (Fritsch et al., 2016), and cycling (Teles et al., 2015;Malta et al., 2018). In addition, research has examined highly-trained sample populations, such as athletes in jiu-jitsu (Follmer et al., 2018), judo (Orssatto et al., 2019), volleyball (Ferraresi et al., 2015;da Cunha et al., 2019;Vieira et al., 2019), rugby (Pinto et al., 2016), water polo (Zagatto et al., 2016), and futsal (De Marchi et al., 2019). ...
... In addition, research has examined highly-trained sample populations, such as athletes in jiu-jitsu (Follmer et al., 2018), judo (Orssatto et al., 2019), volleyball (Ferraresi et al., 2015;da Cunha et al., 2019;Vieira et al., 2019), rugby (Pinto et al., 2016), water polo (Zagatto et al., 2016), and futsal (De Marchi et al., 2019). Much of the data support the ergogenic effect of PBMT, including reduced CK post-competition (De Marchi et al., 2019), improved time to exhaustion (Follmer et al., 2018), reduced muscle fatigue (Dornelles et al., 2019), improved rate of perceived exertion, and improved running economy . ...
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Photobiomodulation therapy (PBMT) can be applied to the whole body as compared to the application of using single hand-held devices that isolate a smaller muscle area. The purpose of this study was to examine the effects of an acute dose of whole-body PBMT pre- and post-high-intensity resistance training on creatine kinase (CK) and salivary interleukin-6 (IL-6) in a sample of trained males. Twelve males (31 ± 8.3 years, 177.2 ± 5.4 cm, and 86.0 ± 7.5 kg) were part of a randomized, counterbalanced, cross-over design, whereby each participant performed a high-intensity resistance training session that consisted of the bench press, chin-up, and repeated sprints on two separate occasions. Each participant was assigned to either the PBMT or control condition on two separate weeks, with a 10-days washout period between the weeks. Creatine kinase was measured at baseline, 24, 48, and 72 h post-exercise. Salivary IL-6 was measured at baseline, 60, 90, and 120 min. A paired t-test showed no significant difference (p = 0.669) in the area under the curve (AUC) for CK during the PBMT (191.7 ± 48.3) and control conditions (200.2 ± 68.0). A Wilcoxon signed-rank test also showed no significant median difference (p = 0.155) in the AUC for salivary IL-6 during the PBMT (Mdn = 347.7) and control conditions (Mdn = 305.8). An additional Wilcoxon signed-rank test for CK percentage change from 24 to 72 h showed the PBMT condition (Mdn = −45%) to have a −18% median difference as compared to the control condition (Mdn = −41%). As such, whole-body PBMT does not significantly reduce the activity of salivary IL-6 or CK concentration during the 24 to 72-h recovery post-high-intensity resistance training.
... Because muscle tiredness is an inherent hazard for hamstring stretch lesions in soccer players, Dornelles et al. [17] investigated the effects of PBMT (300 J per thigh or placebo on the hamstrings, before the match) on twelve young male amateur soccer players in a randomized, crossover, double-blinded, placebo-controlled trial, assessed in two sessions at least at 7-day apart. Muscle endurance and useful workout were evaluated through isokinetic dynamometry and countermovement jump (CMJ) tests, respectively, before and immediately after the match. ...
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Benefits of photobiomodulation (PBM) have been known for several decades. More recently, PBM applied in sports offers a special chance to support the modeling of the performance and recovery. Increasingly complex physical activities and fierce competition in the world of sports generate a state of psycho-emotional and physical stress that can induce chronic fatigue syndrome, failure in physical training, predisposition to muscle damage, physical and emotional exhaustion etc., for which PBM could be an excellent solution. To evaluate and identify all risk factors and the influence of PBM on health and performance in sport and for a better understanding of its effects, we did a search for “Photobiomodulation and Sports” on PubMed, to update the PBM science applied in sports, and we retained for analysis the articles published from 2014 to date. The term “PBM” is recent, and we did not include previous studies with “low level laser therapy” or “LLLT” before 2014. In the present research, PBM has been shown to have valuable protective and ergogenic effects in 25 human studies, being the key to success for high performance and recovery, facts supported also by 22 animal studies. PBM applied creatively and targeted depending on sport and size of the level of physical effort could perfectly modulate the mitochondrial activity and thus lead to remarkable improvements in performance. PBM with no conclusive results or without effects from this review (14 studies from a total of 39 on humans) was analyzed and we found the motivations of the authors from the perspective of multiple causes related to technological limitations, participants, the protocols for physical activity, the devices, techniques and PBM parameters. In the near future, dose–response experiments on physical activity should be designed and correlated with PBM dose–response studies, so that quantification of PBM parameters to allow the energy, metabolic, immune, and neuro-endocrine modulation, perfectly coupled with the level of training. There is an urgent need to continuously improve PBM devices, delivery methods, and protocols in new ingenious future sports trials. Latest innovations and nanotechnologies applied to perform intracellular signaling analysis, while examining extracellular targets, coupled with 3D and 4D sports motion analysis and other high-tech devices, can be a challenge to learn how to maximize PBM efficiency while achieving unprecedented sports performance and thus fulfilling the dream of millions of elite athletes.
... In recent years, this therapy has shown positive effects in the management of several musculoskeletal disorders and inflammatory conditions to promote pain relief and wound healing [5][6][7][8][9][10][11]. Many studies have reported that PBMT increases muscle performance, reduces fatigue, and improves muscle recovery in athletes, physically active, and sedentary individuals [12][13][14][15][16][17][18][19][20][21][22]. The main mechanism of action of PBMT include the interaction of photons with cytochrome c-oxidase, a mitochondrial photoreceptor [2], leading to greater transfer of electrons and consequently mitochondrial respiratory chain activation, which increases mitochondrial adenosine triphosphate (ATP) production [23]. ...
Article
Full-text available
Background: The direct application of photobiomodulation therapy (PBMT) using low-level laser therapy (LLLT) and light emitting diodes (LEDs) combined with a static magnetic field (sMF) (PBMT-sMF) to target tissues is shown to improve muscle performance and recovery. Studies have reported possible PBMT effects when a local distant to the target tissue is irradiated. Notably, the extent of these effects on musculoskeletal performance and the optimal site of irradiation remain unclear, although this information is clinically important since these aspects could directly affect the magnitude of the effect. Therefore, we investigated the effects of local and non-local PBMT-sMF irradiations on musculoskeletal performance and post-exercise recovery before an eccentric exercise protocol. Methods: This randomized, triple-blind (participants, therapists and assessors), placebo-controlled trial included 30 healthy male volunteers randomly assigned to the placebo, local, and non-local groups. Active or placebo PBMT-sMF was applied to 6 sites of the quadriceps muscle of both legs. An eccentric exercise protocol was used to induce fatigue. The primary outcome was peak torque assessed by maximal voluntary contraction (MVC). The secondary outcomes were delayed onset muscle soreness (DOMS) measured by visual analogue scale (VAS), muscle injury assessed by serum creatine kinase activity (CK), and blood lactate levels. Evaluations were performed before the eccentric exercise protocol (baseline), as well as immediately after and 1, 24, 48, and 72 h upon protocol completion. Results: Ten volunteers were randomized per group and analysed for all outcomes. Compared to the placebo and non-local groups, irradiation with PBMT-SMF led to statistically significant improvement (p < 0.05) with regard to all variables in the local group. The outcomes observed in the non-local group were similar to those in the placebo group with regard to all variables.The volunteers did not report any adverse effects. Conclusion: Our results support the current evidence that local irradiation of all exercised muscles promotes ergogenic effects. PBMT-sMF improved performance and reduced muscle fatigue only when applied locally to muscles involved in physical activity. Trial registration: NCT03695458. Registered October 04th 2018.
... In addition to promoting ergogenic effects, PBMT also had a protective effect on the skeletal muscles of the animals, as creatine kinase activity was significantly lower in the irradiated animals than in the non-irradiated animals. Subsequently, a series of clinical trials involving athletes from different sports and healthy individuals conducted by our research group and other groups showed that, when applied before an exercise session, both PBMT and PBMT combined to static magnetic field (PBMT/sMF) can increase the number of repetitions performed, 10-12 lengthen the time to exhaustion, 10 13-15 increase peak torque 12 16-19 and even improve performance of athletes in field tests, 20 and in simulated 21 and real matches. 22 In many of these clinical trials, when PBMT or PBMT/sMF were applied before exercises, it also had protective effects on the skeletal muscle tissue, allowing a faster recovery. ...
Article
Full-text available
Introduction In recent years, it has been demonstrated that photobiomodulation therapy (PBMT) using low-level laser therapy and/or light-emitting diode therapy combined to static magnetic field (sMF) has ergogenic effects, improving muscular performance and accelerating postexercise recovery. However, many aspects related to these effects and its clinical applicability remain unknown. Therefore, the aim of this project is to evaluate the ergogenic effects of PBMT/sMF in detraining after a strength-training protocol. Methods and analysis The study will be a randomised, triple-blind, placebo-controlled clinical trial. Healthy male volunteers will be randomly distributed into four experimental groups: PBMT/sMF before training sessions + PBMT/sMF during detraining, PBMT/sMF before training sessions + placebo during detraining, placebo before training sessions + PBMT/sMF during detraining and placebo before training sessions + placebo during detraining. Strength-training sessions will be carried out over 12 weeks, and the detraining period will occur during the 4 weeks after. The muscular strength and the structural properties of quadriceps will be analysed. Ethics and dissemination This study was approved by the Research Ethics Committee of Nove de Julho University. The results from this study will be disseminated through scientific publications in international peer-reviewed journals and presented at national and international scientific meetings. Trial registration number NCT03858179 .
... Subsequently, a series of clinical studies involving athletes from different sports and healthy individuals conducted by our research group and others showed that, when applied before an exercise session, PBMT can increase the number of repetitions performed, [2][3][4] lengthen the time to exhaustion, [2,[5][6][7] increase peak torque, [4,[8][9][10][11] and even improve performance of athletes in field tests, [12] in simulated [13] and real matches. [14] Moreover, studies have also shown that PBMT can potentiate gains in different training protocols, such as strength training [15,16] and aerobic training. ...
Article
Full-text available
Introduction: Over the last 10 years, it has been demonstrated that photobiomodulation therapy (PBMT), also known as phototherapy, using low-level laser therapy (LLLT) and/or light-emitting diode therapy (LEDT) has ergogenic effects, improving athletic performance and also accelerating post-exercise recovery. However, many aspects related to these effects and its clinical applicability remain unknown. Therefore, the aim of this project is to evaluate the ergogenic effects of PBMT in detraining after an aerobic endurance training protocol. Methods and analyzes: A randomized, triple-blind, placebo-controlled clinical trial will be carried out. Healthy male volunteers will be randomly distributed into 4 experimental groups: PBMT before and after training sessions + PBMT during detraining, PBMT before and after training sessions + placebo during detraining, placebo before and after training sessions + PBMT during detraining, and placebo before and after training sessions + placebo during detraining. The aerobic endurance training sessions will be carried out using motorized treadmills during 12 weeks, and the detraining period will consist in the next 4 weeks after that. It will be analyzed the time until exhaustion, maximal oxygen uptake (VO 2max), and fat percentage of volunteers. Discussion: Despite the increasing body of evidence for the use of PBMT as an ergogenic agent, several aspects remain unknown. The findings of this study will contribute to the advance of knowledge in this field regarding clinical applications. Ethics and dissemination: This study was approved by the Research Ethics Committee of Nove de Julho University. The results from this study will be further disseminated through scientific publications in international peer-reviewed journals and presentations at national and international scientific meetings. Trial registration number: NCT03879226. Abbreviations: ANOVA = analysis of variance, Hz = hertz, ISAK = International Society for the Advancement of Kineanthropometry, J = joules, km/h = kilometers per hour, LEDs = light-emitting diodes, LEDT = light-emitting diode therapy, LLLT = low-level laser therapy, mW = milliwatt, nm = nanometers, PBMT = photobiomodulation therapy, PO 2 = partial pressure of oxygen, RCT = randomized controlled trial, SaO 2 = oxygen saturation, VO 2max = maximum oxygen uptake, W = Watt.
Article
The intravascular or transcutaneous application of PBM over blood vessels (vascular photobiomodulation, VPBM) has been used for the treatment of inflammatory and chronic conditions with promising systemic results. This study evaluated the VPBM effects on a model of muscle regeneration after acute injury and compared the outcomes of preventive and therapeutic VPBM. Transcutaneous VPBM was administered over the rat's main tail vein. Serum levels of creatine kinase (CK), aspartate aminotransferase (AST) and lactate were evaluated and muscles were processed for macroscopic and microscopic analysis. Preventive and therapeutic VPBM led to decreased inflammatory infiltrate, edema, and myonecrosis but with an increase in immature muscle fibers. CK, AST and lactate levels were lower in the groups treated with VPBM (lowest concentrations in preventive VPBM application). Preventive and therapeutic VPBM were capable of exerting a positive effect on acute muscle injury repair, with more accentuated results when preventive VPBM was administered. This article is protected by copyright. All rights reserved.
Article
Full-text available
The aim of this study was to investigate the effect of fatigue on the lower limb muscle electromyography frequency spectrum in teen weightlifters during the snatch and the clean and jerk move. This study was semi-experimental. 15 teen weightlifters with an age range of 12 to 17 years with purposive sampling were selected in coordination with the Ardabil province weightlifting board. A wireless electromyography system with 8 pairs of bipolar surface electrodes used to record the electromyography activity of lower limb muscles during the running (sample rate: 1000 Hz). For doing functional fatigue, each subject performed squat motion as much as possible to load equal to 50% of body weight. Two-way ANOVA was used for statistical analysis(P<0.05). Results showed that the median frequency of vastus medialis muscle duringsnatch after fatigue protocol was greater than before it (P=0.023; large effect size).Moreover, the median frequency of semi tendinosus muscle during snatch was greater than clean and jerk (P=0.047; Medium effect size). Also, the median frequency of rectus femoris (P=0.021; medium effect size) and biceps femoris (P=0.033; medium effect size) during clean and jerk increased significantly after fatigue compared to before fatigue. The results showed that the frequency spectrum of the lower limb muscles has different responses in two movements of clean and jerk and snatch before and after fatigue. For this reason, the necessity of performing special exercises for each muscle is necessary for various techniques. Keywords: Clean and jerk, Fatigue, Frequency Spectrum, Snatch, Weightlifters.
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Recently, phototherapies, such as low reactive level laser therapy (LLLT) and light emitting diode therapy, have been referred to as photobiomodulation therapies (PBMT). It has been reported that PBMT is effective not only in the treatment and prevention of sports-related disorders but also in improving the performance of athletes by delaying muscle fatigue. This study summarizes previous published reports that examined PBMT-induced performance improvement effects in athletes of different sport types.
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When conservative treatments fail, hip osteoarthritis (OA), a chronic degenerative disease characterized by cartilage wear, progressive joint deformity, and loss of function, can result in the need for a total hip arthroplasty (THA). Surgical procedures induced tissue trauma and incite an immune response. Photobiomodulation therapy (PBMt) using low-level laser therapy (LLLT) and/or light-emitting diode therapy (LEDT) has proven effective in tissue repair by modulating the inflammatory process and promoting pain relief. Therefore, the aim of this study was to analyze the immediate effect of PBMt on inflammation and pain of patients undergoing total hip arthroplasty. The study consisted of 18 post-surgical hip arthroplasty patients divided into two groups (n = 9 each) placebo and active PBMt who received one of the treatments in a period from 8 to 12 h following THA surgery. PBMt (active or placebo) was applied using a device consisting of nine diodes (one super-pulsed laser of 905 nm, four infrared LEDs of 875 nm, and four red LEDs 640 nm, 40.3 J per point) applied to 5 points along the incision. Visual analog scale (VAS) and blood samples for analysis of the levels of the cytokines TNF-α, IL-6, and IL-8 were recorded before and after PBMt application. The values for the visual analog scale as well as those in the analysis of TNF-α and IL-8 serum levels decreased in the active PBMt group compared to placebo-control group (p < 0.05). No decrease was observed for IL-6 levels. We conclude that PBMt is effective in decreasing pain intensity and post-surgery inflammation in patients receiving total hip arthroplasty.
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Photobiomodulation therapy (PBMT) has been investigated because of its intimate relationship with tissue recovery processes, such as on peripheral nerve damage. Based on the wide range of benefits that the PBMT has shown and its clinical relevance, the aim of this research was to carry out a systematic review of the last 10 years, ascertaining the influence of the PBMT in the regeneration of injured peripheral nerves. The search was performed in the PubMed/MEDLINE database with the combination of the keywords: low-level laser therapy AND nerve regeneration. Initially, 54 articles were obtained, 26 articles of which were chosen for the study according to the inclusion criteria. In the qualitative aspect, it was observed that PBMT was able to accelerate the process of nerve regeneration, presenting an increase in the number of myelinated fibers and a better lamellar organization of myelin sheath, besides improvement of electrophysiological function, immunoreactivity, high functionality rate, decrease of inflammation, pain, and the facilitation of neural regeneration, release of growth factors, increase of vascular network and collagen. It was concluded that PBMT has beneficial effects on the recovery of nerve lesions, especially when related to a faster regeneration and functional improvement, despite the variety of parameters.
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The goal of this review was to determine the isokinetic hamstring-to-quadriceps (H/Q) torque ratios of professional male soccer players. Systematic searches were independently carried out by 2 researchers in 7 electronic databases. Only studies with teams from the first or second national leagues were included. From these studies, we extracted the players’ H/Q conventional (concentric/concentric) and/or functional (eccentric/concentric) ratios. The initial search resulted in 2,128 articles that were filtered to 30 articles (1,727 players) meeting the inclusion criteria. The H/Q conventional ratio was assessed in 27 studies (1,274 players), whereas the H/Q functional ratio was assessed in 15 studies (1,082 players). The H/Q conventional ratio mean scores of professional male soccer players were close to 60% when tested at low to intermediate angular velocities (12°·s−1 = 52 ± 7%; 30°·s−1 = 52 ± 8%; 60°·s−1 = 65 ± 12%; 90°·s−1 = 57 ± 6%; 120°·s−1 = 65 ± 16%; 180°·s−1 = 67 ± 17%) and around 70–80% at fast angular velocities (240°·s−1 = 80 ± 40%; 300°·s−1 = 70 ± 15%; 360°·s−1 = 80 ± 13%). The H/Q functional ratio mean scores of professional male soccer players were close to 80% at 60°·s−1 (79 ± 19%), around 100–130% at intermediate to fast angular velocities (120°·s−1 = 127 ± 42%; 180°·s−1 = 96 ± 19%; 240°·s−1 = 109 ± 22%; 300°·s−1 = 123 ± 18%), and near or above 130% when angular testing velocities were mixed (eccentric hamstring < concentric quadriceps; 30/240°·s−1 = 132 ± 26%; 60/180°·s−1 = 129 ± 20%; 60/240°·s−1 = 153 ± 30%). In conclusion, considering the tested isokinetic angular velocity, professional male soccer players do not meet the traditional reference landmarks used to assess the strength balance between quadriceps and hamstring muscles (i.e., 60 and 100% for H/Q conventional and functional ratios, respectively), which supports a need for specific reference values according to the angular velocity selected for testing H/Q torque ratios.
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This study was aimed at verifying effects of photobiomodulation therapy (PBMT) with different energy doses (15, 30, and 60 J per site) on physiological and performance parameters during running tests. Fifteen male recreational runners participated in a crossover, randomised, double-blind, and placebo-controlled trial. They performed testing protocol in 5 sessions with different treatments: control, placebo, and PBMT with 15, 30 or 60 J per site (14 sites in each lower limb). Physiological and performance variables were assessed during submaximal (at 8 km·h-1 and 9 km·h-1) and maximal running tests. PBMT with 30 J significantly (p<0.05) improved running economy (RE) at 8 and 9 km·h-1 (3.01% and 3.03%, respectively), rate of perceived exertion (RPE) at 8 km·h-1 (7.86%), velocity at VO2MAX (3.07%), peak of velocity (PV) (1.49%), and total time to exhaustion (TTE) (3.41%) compared to placebo. PBMT with 15 J improved RE at 9 km·h-1 (2.98%), RPE at 8 km·h-1 (4.80%), PV (1.33%), TTE (3.06%), and total distance (4.01%) compared to the placebo; while PBMT with 60 J only increased RE at 9 km·h-1 (3.87%) compared to placebo. All PBMT doses positively affected physiological and/or performance parameters; however magnitude-based inference reported that PBMT applied with 30 J led to more beneficial effects than 15 J and 60 J.
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Researches have been performed to investigate the effects of phototherapy on improving performance and reduction of muscular fatigue. However, a great variability in the light parameters and protocols of the trials are a concern to establish the efficacy of this therapy to be used in sports or clinic. The aim of this study is to investigate the effectiveness, moment of application of phototherapy within an exercise protocol, and which are the parameters optimally effective for the improvement of muscular performance and the reduction of muscular fatigue in healthy people. Systematic searches of PubMed, PEDro, Cochrane Library, EMBASE, and Web of Science databases were conducted for randomized clinical trials to March 2017. Analyses of risk of bias and quality of evidence of the included trials were performed, and authors were contacted to obtain any missing or unclear information. We included 39 trials (861 participants). Data were reported descriptively through tables, and 28 trials were included in meta-analysis comparing outcomes to placebo. Meta-analysis was performed for the variables: time until reach exhaustion, number of repetitions, isometric peak torque, and blood lactate levels showing a very low to moderate quality of evidence and some effect in favor to phototherapy. Further investigation is required due the lack of methodological quality, small sample size, great variability of exercise protocols, and phototherapy parameters. In general, positive results were found using both low-level laser therapy and light-emitting diode therapy or combination of both in a wavelength range from 655 to 950 nm. Most of positive results were observed with an energy dose range from 20 to 60 J for small muscular groups and 60 to 300 J for large muscular groups and maximal power output of 200 mW per diode.
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Objectives: The purpose of this study was to investigate whether preseason isokinetic strength measures were predictive of future HSI among professional football players. Design: Prospective cohort study, Level of evidence 2. Methods: A total of 169 professional players participated in a preseason isokinetic strength screening, followed by a 10-month competitive season. Testing protocol included the concentric performance of both knee flexion and extension at 60degs-1 and 240degs-1 and the eccentric performance of the knee flexor at 30degs-1. Strength deficits, bilateral differences, and hamstring to quadriceps strength ratios were computed. Univariate and multivariate logistic regressions were used to identify potential risk factors of HSI. Receiver operating characteristic (ROC) curves were used to investigate the sensitivity and specificity of the strength measures. Results: Forty-one acute HSIs were sustained, and 12% (n=5) reoccurred within the study period. In the multivariate analysis, we have shown an association between the injury risk and eccentric hamstring peak torque below 2.4Nmkg-1 (OR=5.59; 95% CI, 2.20-12.92); concentric H/Q ratio below 50.5% (OR=3.14; 95% CI, 1.37-2.22); players with previous injury of HSI (OR=3.57; 95% CI, 3.13-8.62). ROC analysis displayed an area under curve (AUC) of 0.77, indicating fair combined sensitivity and specificity of the overall predicting model. Conclusions: Professional football players with significant lower isokinetic hamstring strength, lower hamstring-to-quadriceps strength ratio, and a previous injury of HSI were linked to an increased risk of acute HSI.
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Background Hamstring injuries remain prevalent across a number of professional sports. In football, the incidence has even increased by 4% per year at the Champions League level over the last decade. The role of muscle strength or strength ratios and their association with risk of hamstring injury remain restricted by small sample sizes and inconclusive results. Purpose The purpose of this study is to identify risk factors for hamstring injury in professional football players in an adequately powered, prospective cohort study. Using both established (isokinetic) and novel (eccentric hamstring test device) measures of muscle strength, we aimed to investigate the relationship between these strength characteristics over the entire range of motion with risk of hamstring injury. Methods All teams (n=18) eligible to compete in the premier football league in Qatar underwent a comprehensive strength assessment during their annual periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar. Variables included isokinetic strength, Nordic hamstring exercise strength and dynamic hamstring: quadriceps ratios. Results Of the 413 players included (68.2% of all league players), 66 suffered a hamstring injury over the two seasons. Only isokinetic quadriceps concentric at 300°/s (adjusted for bodyweight) was associated with risk of hamstring injury when considered categorically. Age, body mass and playing position were also associated with risk of hamstring injury. None of the other 23 strength variables examined were found to be associated with hamstring injury. Conclusion The clinical value of isolated strength testing is limited, and its use in musculoskeletal screening to predict future hamstring injury is unfounded.
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Objectives: To describe the physiotherapists perceptions and the current practices for injury prevention in elite football (soccer) clubs in Brazil. Design: Cross-sectional study. Setting: Group of Science in Sports & Exercise, Federal University of Healthy Sciences of Porto Alegre (Brazil). Participants: 16 of the 20 football clubs involved in the Brazilian premier league 2015. Main outcome measures: Physiotherapists answered a structured questionnaire. Results: Most physiotherapists (∼88%) were active in design, testing and application of prevention programs. Previous injury, muscle imbalance, fatigue, hydration, fitness, diet, sleep/rest and age were considered "very important" or "important" injury risk factors by all respondents. The methods most commonly used to detect athletes' injury risk were: monitoring of biochemical markers (100% of teams), isokinetic dynamometry (81%), questionnaires (75%), functional movement screen (56%), fleximetry (56%) and horizontal jump tests (50%). All clubs used strength training, functional training, core exercises and balance/proprioception exercises in their injury prevention program; and Nordic hamstring exercise and other eccentric exercises were used by 94% of clubs. "FIFA 11+" prevention program was adapted by 88% of clubs. Conclusion: Physiotherapists perceptions and current practices of injury prevention within Brazilian elite football clubs were similar to those employed in developed countries. There remains a gap between clinical practice and scientific evidence in high performance football.
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The Nordic hamstring exercise (NHE) is a field-based exercise designed for knee-flexor eccentric strengthening, aimed at muscle strains prevention. However, possible effects of NHE programmes on other hamstring injury risk factors remain unclear. The purpose of this study was to investigate the effects of a NHE training programme on multiple hamstring injury risk factors. Twenty physically active young adults were allocated into two equal sized groups: control group (CG) and training group (TG). The TG was engaged in a 4-week NHE programme, twice a week, 3 sets of 6-10 repetitions; while CG received no exercise intervention. The knee flexor and extensor strength was assessed through isokinetic dynamometry, the biceps femoris long head muscle architecture through ultrasound images, and the hamstring flexibility through sit-and-reach test. The results showed that CG subjects had no significant change in any outcome. TG presented higher percent changes than CG for hamstring isometric peak torque (9%; effect size=0.27), eccentric peak torque (13%; effect size=0.60), eccentric work (18%; effect size=0.86), and functional hamstring-to-quadriceps torque ratio (13%; effect size=0.80). The NHE programme led also to increased fascicle length (22%; effect size=2.77) and reduced pennation angle (-17%; effect size=1.27) in biceps femoris long head of the TG, without significant changes on muscle thickness. In conclusion, a short-term NHE training programme (4 weeks; 8 training sessions) counteracts multiple hamstring injury risk factors in physically active young adults.