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Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical Appraisal of Application to Practice

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Background: Neck strength training has been advocated as a player-specific modifiable factor in the risk management for concussion in contact sports. A scoping review of the literature was undertaken to address two specific aims. The first was to identify and critically appraise the level and quality of evidence relating neck strength and resistance training to concussion incidence and risk in contact sports. The second was to compare and contrast the effectiveness of resistance neck strengthening programs and to evaluate effects of increased strength in attenuating the post-impact kinematics of the head, a proxy measure of concussion risk.
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Gilchrist et al., J Athl Enhancement 2015, 4:2
http://dx.doi.org/10.4172/2324-9080.1000195 Journal of Athletic
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Neck Muscle Strength Training
in the Risk Management of
Concussion in Contact Sports:
Critical Appraisal of Application
to Practice
Ian Gilchrist1,2, Michael Storr3, Elizabeth Chapman4 and Lucie
Pelland1,2*
Abstract
Background: Neck strength training has been advocated as
a player-specic modiable factor in the risk management for
concussion in contact sports. A scoping review of the literature was
undertaken to address two specic aims. The rst was to identify
and critically appraise the level and quality of evidence relating
neck strength and resistance training to concussion incidence and
risk in contact sports. The second was to compare and contrast
the effectiveness of resistance neck strengthening programs and
to evaluate effects of increased strength in attenuating the post-
impact kinematics of the head, a proxy measure of concussion risk.
Methods: Structured search of ve electronic databases (Ovid
MEDLINE, CINAHL, PubMED, EMBASE, and AMED), combining
MeSH and generic search terms relating neck strength to concussion
biomechanics, risk and incidence. Level of research evidence
(Oxford Centre of Evidence-based Medicine) and methodological
quality were determined (PEDro and Newcastle-Ottawa Scales).
Results: Total isometric neck strength predicted concussion
incidence in one prospective study (level 1b). The effect size of
strength on concussion incidence was small (Cohen’s d, 0.29).
Peak isometric strength did not predict the odds of sustaining a
moderate or severe head impact in contact sports (level 1b, 2b,
and 4). Short-latency anticipatory strength exerts an attenuating
effect on post-impact kinematics of the head (level 1b, 2b) and can
be facilitated by selective parameters of isotonic strength training.
Methodological quality of the research evidence ranged from 6/10
to 8/10 for controlled trials and 6/9 to 9/9 for case-series and cohort
studies.
Conclusion: Short-latency strength, developed prior to impact,
is a key modifying variable of the post-impact kinematics of the
head. By facilitating short-latency neck strength, muscle strength
training is a potential target to favorably inuence concussion
risk, but further study is required to determine the translation of
neck/head kinematics to concussion risk. Standardized methods
for assessment of multi-directional short-latency, and peak neck,
strength need to be adopted and combined with prospective studies.
Keywords
Concussions; Neck strength; Resistance training; Post-impact
head kinematics; Concussion risk; Neck stiffness
Abbreviations
HN: Head-Neck; PEDro: Physiotherapy Evidence Database;
RCT: Randomized Controlled Trial; Non-RCT: Non-randomized
Controlled Trial; NOS: Newcastle-Ottawa Scale; MDC95%: Minimum
detectable change with 95% condence; lbs: pound; Kg: kilogram;
N: Newton; MADYMO: Mathematical Dynamic Model; HIC: Head
Injury Criterion; ACSM: American College of Sports Medicine;
CI: Condence Interval; SCM: sternocleidomastoid; UFT: Upper
Fibers of Trapezius; RFD: Rate of Force Development; EMG:
Electromyography; RM: Repetition Maximum; NCAA: National
Collegiate Athletic Association
*Corresponding author: Lucie Pelland, PT, PhD, Associate Professor,
Queen’s University, School of Rehabilitation Therapy, Louise D. Acton
Building, Kingston, Ontario, Canada, K7L 3N6, Tel: +1-613-533-3237; E-mail:
Lucie.Pelland@queensu.ca
Received: July 03, 2014 Accepted: June 02, 2015 Published: June 09, 2015
Introduction
In response to increasing evidence of the severity of acute eects
of concussion on neurocognitive function and of the possibility for
their lasting impairments on health [1-3], implementation of risk
management strategies for concussion has become a priority for
sports governing bodies [4-7]. Eective risk management requires
a multi-factorial approach, with athlete preparation and sport
readiness being fundamental components [8]. Within the context
of contact sport, strength training of the neck musculature has
increasingly been advocated as a player-specic modiable factor to
lower the odds of sustaining a concussion [9-14]. As stronger muscles
generate higher peak magnitudes of isometric tension at faster rates
of force development [15], it is postulated that strength training of
the neck musculature would enhance the early resistance of the head
and neck (HN) segment to externally applied forces, attenuating the
post-impact kinematic response of the head and, thereby, lowering
the risk for concussion [9,10].
While this basic research on muscle mechanics provides
theoretical support for neck strengthening programs that are being
promoted as preventative measures for concussions in contact sports
[16-18], the research evidence specically relating neck strength to
concussion risk, incidence and severity has yet to be comprehensively
evaluated. erefore, a scoping review of the literature was undertaken
to address two specic aims. e rst was to identify and critically
appraise the level and quality of evidence relating neck strength
and resistance training of the neck musculature to the incidence of
concussion in contact sports. e second was to compare and contrast
the eectiveness of resistance training programs in producing
absolute gains in isometric neck strength in non-clinical populations,
and to evaluate eects of increased strength in attenuating the post-
impact kinematics of the head, which provides a proxy measure of
concussion risk.
Methods
e scoping review was performed using the methods outlined by
Arksey et al. [19] and Anderson et al. [20]. Five databases were searched
- Ovid MEDLINE, CINAHL, PubMED, EMBASE, and AMED –
using two structured search strategies. e rst strategy combined
MeSH and generic terms relating neck strength, measured at baseline
or following a resistance training intervention, to concussion risk and
incidence, and to concussion-relevant kinematics of the HN segment.
e second search focused on outcomes of neck training programs
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 2 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
and the relationship of these outcomes to the kinematics of the HN
segment. e search strategies are described in Table 1 and 2, and
the searches are up to date to January 2015, week 4. In agreement
with the scoping nature of the review, the search was not limited by
study design; all experimental and quasi-experimental designs, and
systematic reviews outlined by the Oxford Center for Evidence-based
Medicine were included.
Search outcomes
e rst search identied 343 articles relating neck strength
and concussion incidence and risk (Table 1). Of these, 46 titles were
redundant, leaving 297 studies for abstract review. Another 262
studies were excluded at this phase of the review process as neck
strength was either evaluated within the context of intervention
studies in clinical populations or concussion risk and incidence
were not explicitly measured outcomes. Of the thirty-ve remaining
studies, twelve were general review articles that did not include either
original or systematically reviewed data, and three studies could
not be retrieved. Five additional studies were identied by manual
search of the reference list of retrieved studies and by Google Scholar
alerts of new articles on concussion. Of this nal set of twenty-ve
articles, twelve were excluded following full review as they provided a
general context for interpreting research evidence on concussion but
did not contribute specic data relating neck strength to concussion
incidence, risk, or post-impact kinematics of the HN segment.
erefore, thirteen unique articles were included in the critical
appraisal of evidence.
e second search identied 174 articles on resistance training
programs for the neck musculature (Table 2). Of this original set, four
redundant titles were excluded and one article could not be retrieved.
Abstracts were reviewed for the remaining 169 studies, with 161
being excluded at this phase as they evaluated the eectiveness of
strength training programs of the neck and shoulder girdle in relation
to the incidence of neck pain in healthy populations, comparatively
evaluated the outcomes of dierent training modalities on strength
using repeated measures analysis within a single session, or focused
on outcomes between healthy controls and clinical populations. One
general review article was also excluded, as it did not present either
original or systematically reviewed data. ree additional strength
training studies were identied through manual search of the
reference list of retrieved studies, resulting in ten resistance training
programs included in the critical appraisal of eectiveness.
Data analysis
e guidelines of Law and MacDermid [21] were used to
appraise retrieved studies; summaries of experimental design and
methods, statistical comparison, measured outcome and ndings
Table 1: MeSH Headings and Keywords for Search on Neck Strength and Concussion Biomechanics and Risk.
Database: MEDLINE - January, Week 3, 2015
Step Search Results
1Craniocerebral trauma (MeSH)/ or brain concussion(MeSH)/ or diffuse
axonal injury (MeSH)/ or head injuries, closed (MeSH)/ 25950
2Exp Neck Muscles (MeSH)/ or sternocleidomastoid (keyword) 6007
3Muscle contraction (MeSH)/ or isometric contraction (MeSH)/ or isotonic
contraction (MeSH)/ 97865
4Exercise therapy (MeSH)/ or plyometric exercise (MeSH)/ or resistance
training (MeSH)/ 29878
5Exp Biomechanical Phenomena (MeSH)/ or biomechanics (keyword) 86333
6 Acceleration (MeSH)/ or deceleration (MeSH)/ 8423
7 Step 1 and 2 25 (Schmidt et al. [28], Fanta et al. (2014), Eckner et al. [13], Mihalik et al.
[27], Viano et al. [12], Bauer et al. [42], Merrill et al. (1984))
8 Step 1 and 3 20 (Eckner et al. [13], Almosnino et al. [47], Tierney et al. [29], Frisch et al.
(1977))
9 Step 1 and 4 25 (Cross et al. [10])
10 Step 1 and 2 and 5 7 (Schmidt et al. [28], Fanta et al. (2014), Eckner et al. [13], Mihalik et al. [27],
Viano et al. [12], Bauer et al. [42], Merrill et al. (1984))
Database: EMBASE – 1980 to 2015 week 4
Step Search Results
1Exp concussion (MeSH) / or exp brain concussion (MeSH) / 5894
2Neck muscle (MeSH) / 4415
3
Muscle contraction (MeSH) / or muscle isometric contraction (MeSH) / or
concentric muscle contraction (MeSH) / or eccentric muscle contraction
(MeSH) /
69208
4
Exp muscle strength (MeSH) / or exp resistance training (MeSH) / or exp
exercise (MeSH) / or exp training (MeSH) / or exp muscle hypertrophy
(MeSH) /
243623
5 Biomechanics (MeSH) / 76414
6Step 1 and 2 11 (Schmidt et al. [28], Eckner et al. [13], Tierney et al. [29])
7 Step 1 and 2 and 3 4 (Eckner et al. [13], Tierney et al. [29])
8 Step 1 and 2 and 4 4 (Schmidt et al. [28], Eckner et al. [13], Tierney et al. [29])
9 Step 1 and 3 8 (Eckner et al. [13], Almosnino et al. [47,57], Tierney et al. [29])
10 Step 1 and 4 and 5
12 (Hanson et al. 2014)), Schmidt et al. [28], Eckner et al. [13], Wick et al.
(2014), Benson et al. [7], Meehan III et al. (2009), Park et al. (2009), Rivara et al.
(2014))
11 Step 1 and 3 and 4 4 (Eckner et al. [13], Almosnino et al. [47,57], Tierney et al. [29])
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 3 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
were provided for all studies included in the analysis (Tables 3-6).
e Physiotherapy Evidence Database (PEDro) scale was used to
evaluate the methodological quality of experimental controlled trials
with and without randomization (RCT and non-RCT) [22,23], while
the Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of
case-series and cohort studies [24]. On the PEDro scale, the criterion
for high quality methodology is a score ≥ 6/10, with a maximum
score of 8/10 possible for non-RCTs. e NOS provides a continuous
grading of methodological quality for cohort and case-series studies
from 0 to 9, with no denition of cut-o criteria to dene high quality
methodology. e level of research evidence was determined using
the Oxford Levels of Evidence Scale. When possible from the data
reported, Cohen’s d-statistic was calculated to evaluate the eect size
of reported associations between changes in neck strength and post-
impact HN kinematics, concussion risk, and incidence. A Cohen’s d
value of 0.2 is considered to be a ‘small’ eect size, 0.5 a ‘medium’
eect size, and ≥ 0.8 a ‘large’ eect size [25]. For the strength
training programs, minimum detectable change (MDC95%) values
were calculated, when sucient data was available, to determine the
magnitude of change necessary for a resistance training program to
produce a clinically meaningful eect on neck strength [26].
Results
Evidence relating neck strength to concussion incidence and
risk
Peak isometric strength does not attenuate post-impact
kinematics of the head or lower the impact severity of hits to the
head, variables commonly used as proxy measures for concussion
risk. However, total isometric strength of the neck was found to be a
signicant predictor of concussion incidence in high school athletes.
is level 1b evidence is summarized in Table 3.
Note: Exp: Exploded search; PH: Physiology subheading. All titles listed were reviewed for relevance and fulllment of inclusion criteria. Search result titles that are
followed by the year in round brackets (e.g. Fanta et al. (2014)) were not retained, nor cited in the manuscript. Search result titles that are followed by square brackets
(e.g. Benson et al. [7]) did not meet inclusion criteria for critical review, but were cited in the manuscript. Only bold titles were retained for full critical review.
Database: AMED (Allied and Complementary Medicine) – 1985 to January 2015
Step Search Results
1 Head injuries/ or brain injuries/ or brain concussion/ 4837
2 Neck muscles/ 107
3Muscle contraction/ or isometric contraction/ or isotonic contraction/ or
muscle relaxation/ or plyometric exercise 3951
4 Exp Exercise therapy/ or exp Muscle strength/ or Exercise/ 18141
5 Biomechanics/ 16920
6Step 1 and 2 and 3 0
7 Step 1 and 2 0
8 Step 1 and 3 10 (Saari et al. (2013))
9 Step 1 and 4 94 (Kozlowski et al. (2013a), Kozlowski et al. (2013b))
10 Step 1 and 5 62 (Patton et al. (2013), Saari et al. (2013), Meaney et al. (2011), Withnall et al.
(2005), Shewchenko et al. [33,34], Johnson et al. (2005), Viano et al. (1989))
Database: CINAHL – January 25, 2015
Step Search Results
1(MeSH "Brain concussion") 1529
2(MeSH "Neck muscles") OR (MeSH "trapezius muscles") OR (MeSH
"sternocleidomastoid muscles") 1000
3(MeSH "Kinetics") OR (MeSH "kinematics") OR (MeSH "Biomechanics") 16324
4
(MeSH "Muscle contraction") OR (MeSH "eccentric contraction") OR
(MeSH "concentric contraction") OR (MH "isotonic contraction") OR
(MeSH "isometric contraction")
6318
5
(MeSH "Muscle Strength") OR (MeSH "resistance training") OR (MeSH
"muscle strengthening") OR (MeSH "muscle hypertrophy (Physiology)/
PH")
1404
6Step 1 and 2 and 3 3 (Caswell et al. (2014), Eckner et al. [13], Gutierrez et al. [30])
7 Step 1 and 3
41 (Caswell et al. (2014), Eckner et al. [13], Gutierrez et al. [30], Patton et al.
(2013), Benson et al. [7], Meehan III et al. (2011), Meaney et al. (2011), Buzzini
et al. (2006), McIntosh et al. (2000), Withnall et al. (2005))
8 Step 1 and 2 and 4 2 (Caswell et al. (2014), Eckner et al. [13])
9 Step 1 and 2 and 5 4 (Caswell et al. (2014), Eckner et al. [13], Gutierrez et al. [30], Cornwell [16])
Database: PubMed – January 25, 2015
Step Search Results
1("Brain concussion"[MeSH Terms] OR ("brain"[All Fields] AND
"concussion"[All Fields]) OR "brain concussion"[All Fields]) 5866
2
("Neck muscles"[MeSH Terms] OR ("neck"[All Fields] AND "muscles"[All
Fields]) OR "neck muscles"[All Fields] OR ("neck"[All Fields] AND
"muscle"[All Fields]) OR "neck muscle"[All Fields])
11251
3"Muscle strength"[MeSH Terms] OR ("muscle"[All Fields] AND
"strength"[All Fields]) OR "muscle strength"[All Fields] 43197
4 Step 1 and 2 and 3 7 (Schmidt et al. [28], Eckner et al. [13] Benson et al. [7], Almosnino et al.
[47], Tierney et al. [29], Viano et al. [12])
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 4 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
e specic association between peak isometric neck strength
and concussion incidence has been evaluated in one prospective
study [14]. As part of a surveillance study of concussive injuries in
three high school sports (basketball, soccer and lacrosse), Collins
et al. [14] obtained pre-season measures of peak isometric neck
strength for 6,662 high school athletes. Total neck strength was
calculated as the mean of the peak isometric force (lbs.) measured
in exion-extension and bilateral side exion. Concussion incidence
was monitored prospectively during the academic years of 2010 and
2011; a clear criterion for concussion diagnosis was not provided.
Of the study group, 179 athletes sustained a concussion, which is an
incidence rate of 2.7%. Sex- and sport-specic eects were identied.
e incidence of concussion was higher in females (P<0.001) and in
soccer, where the incidence rate was 5.2 per 10,000 athletes exposures
compared to 3.7 in lacrosse and 2.3 in basketball. Aer adjusting the
logistic regression model for sex- and sport-eects, total neck strength
remained a signicant predictor of concussion incidence (P=0.004).
e odds of sustaining a concussion were predicted to decrease by 5%
for every one lb. increase in total neck strength. e eect size of total
neck strength on concussion incidence was small (Cohen's d=0.29).
In a smaller prospective study [27], higher peak isometric neck
strength did not lower the impact severity of hits to the head in
minor hockey players. Peak isometric strength of the anterior and
anterolateral neck exors, posterolateral neck extensors and cervical
rotators muscle groups was measured prior to the start of the season
for thirty-seven elite minor ice hockey players. Participants’ hockey
helmets were instrumented with the Head Impact Telemetry (HIT)
system to record peak linear and angular acceleration of the head
during on-ice head contacts. Head impacts were monitored over 98
games and 99 practices. Post-impact head acceleration proles were
combined with data on the location and duration of impact to yield
the Head Impact Telemetry severity prole (HITsp). e HITsp score
was used as a criterion of concussion risk in the statistical analysis.
Higher peak isometric strength did not predict lower HITsp scores
(P≥0.22).
Schmidt et al. [28] conrmed the ndings of Mihalik et al. in their
prospective study of concussion risk in forty-nine high school and
collegiate football players, where again, the criterion for concussion
risk was the HITsp score. Peak isometric strength was measured in
exion, extension and bilateral side exion, with peak magnitudes
summed to provide a composite strength score. Football helmets
were instrumented with the HIT system and impact kinematics of the
head recorded over one season, including both games and practices.
HITsp scores were calculated for a total of 19,775 impacts. HITsp
scores were rank ordered and the group median used as a cuto
to classify athletes into a ‘high’ or ‘low’ head impact group. HITsp
scores were categorized as mild (HITsp<11.7, n=4775), moderate
(11.7<HITsp<15.7, n=7309) or severe (HITsp>15.7, n=7691), and
logistic regression analysis used to relate HITsp scores to composite
strength scores. Higher isometric strength scores did not modify the
Note: Exp: Exploded search, PH: Physiology subheading. All titles listed were reviewed for relevance and fulllment of inclusion criteria. Search result titles that are
followed by the year in round brackets (e.g. Fanta et al. (2014)) were not retained, nor cited in the manuscript. Search result titles that are followed by square brackets
(e.g. Benson et al. [7]) did not meet inclusion criteria for critical review, but were cited in the manuscript. Only bold titles were retained for full critical review.
Table 2: Medical Subject Headings (MeSH) and Keywords for Search on Resistance Training for the Neck Musculature in Non-Clinical Populations.
Database: MEDLINE – January Week 3, 2015
Step Search Results
1Neck Muscles (MeSH)/PH 1291
2isometric contraction (MeSH)/ or isotonic contraction (MeSH)/ 13250
3exp plyometric exercise (MeSH)/ or resistance training (MeSH)/ 3622
4exp Electromyography (MeSH)/ 67330
5Step 1 and (2 or 3) and 4 64 (Burnett et al. (2008), Portero et al. [41])
Database: EMBASE - 1980 to 2015 Week 3
Step Search Results
1Neck muscles (MeSH)/ 4415
2Resistance training (MeSH)/ 6389
3 Step 1 and 2 12 (Kramer et al. [61])
Database: AMED (Allied and Complementary Medicine) - 1985 to January 2015
Step Search Results
1Neck muscles (MeSH)/ or sternocleidomastoid (keyword)/ or splenius
capitis (keyword) 195
2Resistance training (MeSH)/ 740
3 Step 1 and 2 2 (Portero et al. [41]; Kramer et al. [61])
Database: CINAHL - January 25, 2015
Step Search Results
1(MeSH "Neck Muscles/PH") OR (MeSH "trapezius muscles/PH") OR
(MeSH "sternocleidomastoid muscles/PH") OR “splenius capitis” (keyword) 323
2(MeSH "resistance training/") OR (MeSH "muscle strengthening/") 9078
3 Step 1 and 2 48 (Caswell (2014); Cornwell [16])
Database: PubMed – January 25, 2015
Step Search Results
1 Neck muscles
2Resistance training or “strengthening”
3 Step 1 and 2 48 (Taylor et al. [39], Salmon et al. (2013), Kramer et al. [61], Mansell et al. [11],
Portero et al. [41], Conley et al. [40], Pollock et al. [59], Leggett et al. [38])
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 5 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Author(s) Experimental
Design /
rating
Participants Statistical
Comparisons
Measures of
Static Neck
Strength
External
Force
Measured Outcomes Results
Between-subject comparisons
Collins et al. [14] Prospective
cohort study
CEBM: 1b
NOS: 9/9
3,002 males
3,660 females
High school
athletes
(basketball,
soccer,
lacrosse)
Concussed vs.
uninjured athletes
Odds ratio of
concussion incidence
– neck strength
predictor variable
Logistic regression
models
Gradual
increase of
isometric
contraction to
peak (lbs.)
Natural
collisions
Strength
Peak isometric strength (lbs.) in
Flex, Ext, RSFlex and LSFlex
Concussion incidence
Athletic therapist reporting of
concussion incidence using High
School RIO system
↑ OR (1.8, P<0.0001) of concussion in females vs. males overall
↑ OR (2.7, P<0.001) of concussion in females vs. males in basketball,
↑ OR (1.8, P<0.01) in soccer; and OR (1.0, P=0.92) in lacrosse.
Isometric neck strength is a signicant predictor of concussion
(P=0.004) after controlling for gender and sport
↓ OR (0.95) of concussion incidence for every 1 lbs increase in neck
strength
Schmidt et al.
[28]
Prospective
cohort study
CEBM: 1b
NOS: 8/9
49 males
16-21 years
High school
and collegiate
football players
DS in Flex and Ext,
sagittal plane of neck
motion
High vs. low
performers (median
split)
Line positions vs.
non-line positions
OR (95% CI) of
sustaining moderate
and severe head
impacts
Increase
isometric
contraction
as quickly as
possible (Nm)
Linear
variable
mass equal
to 1.0-2.5%
body mass
dropped 15
cm via cable
attached to
the head.
Head impacts
sustained
during
practices and
game over
the 2012
season
Strength
Peak isometric torque (Nm/kg) and
RFD (Nm/s) in Flex, Ext, LSFlex,
RSFlex and Comp (sum of all
directions)
HN Kinematics
Peak angular displacement (rad) in
Flex and Ext
Peak linear head acceleration (g)
HITsp score
Dynamic stiffness (Nm/rad)
Muscle activity, SCM and UFT
muscles
Onset latency (ms), dened as
moment onset and EMG signal
upswing 11 and 6 times resting SD
(unknown trials only)
↑ 66% peak torque in Flex; ↑ 44% Ext; ↑ 62% RSFlex; ↑ 62% LSFlex;
↑ 44% Comp, high vs. low performers
↑ 114% RFD in Flex; ↑ 107% Ext; ↑ 117% RSFlex; ↑ 107% LSFlex;
↑ 82% Comp, high vs. low performers
↑ 254% dynamic stiffness in forced extension; ↑ 140% in forced
exion; ↑ 171% Comp, high vs. low performers
↑ 47% angular displacement in forced extension; ↑ 78% in forced
exion
↑ OR (1.73 – 1.78) of sustaining moderate linear head acceleration
for high performing lineman for strength predictor in RSFlex, LSFlex
and Comp
↑ OR (1.66) of sustaining severe HITsp for high performing non-
lineman for strength predictor in LSFlex
↓ OR (0.66) of sustaining moderate linear head acceleration for high
performing non-linemen for strength predictor in Flex
↑ OR (2.08 – 3.28) of sustaining severe linear head acceleration for
high performing non-lineman for strength predictor in Ext, RSFlex and
Comp
Mihalik et al.
[27]
Prospective
cohort study
CEBM: 1b
NOS: 8/9
37 males
13-16 years
AAA level
hockey players
Comparison of neck
strength capacity
(weak, moderate,
strong) to magnitude
of post-impact
kinematics of the
head
Gradual
increase of
isometric
contraction to
peak (kg)
Natural
collisions
Strength
Peak isometric strength (kg) in Flex,
L45Flex, R45Flex, L45Ext, L45Ext,
LRot, RRot and shoulder elevation
HN Kinematics
Peak linear acceleration (g)
Peak angular acceleration (rad/s2)
HITsp score
↑ 6% HITsp score in players with the strongest shoulder elevation
strength compared to players with weak shoulder elevators (P=0.011)
Greater isometric neck muscle strength does not reduce the
magnitude of post-impact HN kinematics
Table 3: Evidence relating peak isometric strength of the neck musculature and the dynamic stiffness of the HN segment.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 6 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Tierney et al.
[29]
Cohort
CEBM: 2b
NOS: 7/9
20 males
20 females
20 – 30 years
DS in Flex and Ext,
sagittal plane of neck
motion
Females to males
Gradual
increase of
isometric
contraction to
peak (lbs.)
Linear
1-kg mass,
dropped 15
cm via cable
attached to
the head
Strength
Peak isometric strength (lbs.) in Flex
and Ext
HN Kinematics
Peak angular acceleration (°/s2)
Total displacement (°)
Dynamic stiffness (lbs./ °)
Muscle activity, SCM and UFT
muscles
Peak amplitude of normalized EMG
Muscle activity area (%·ms),
dened as sum of normalized EMG
amplitudes
Onset latency (ms), dened as time
between force application and rst
upswing of EMG signal (unknown
trials only)
↓ 49% peak strength, females (P<0.001)
↑ 29% angular acceleration, females (P=0.001)
↑ 35% angular displacement, females (P=0.001)
↓ 28% DS, females (P=0.001)
↑ 81% peak amplitude of EMG, females (P=0.002)
↑ 128% muscle activity area, females (P=0.002)
↓ 29% muscle onset latency for SCM and ↓ 9% for UFT, females
(P<0.05).
Mansell et al.
[11]
Non-
randomized
control trial
CEBM: 2b
MQR: 7/10
17 males
19 females
18 - 22 years
NCAA, Division
I Soccer
DS in exion and
extension, sagittal
plane of neck motion
Females to males
Gradual
increase of
isometric
contraction to
peak (lbs.)
Linear
1-kg mass,
dropped 15
cm via cable
attached to
the head
Strength
Peak isometric strength (lbs.) in Flex
and Ext
HN Kinematics
Peak angular acceleration (°/s2)
Total displacement (°)
Dynamic stiffness (lbs./°)
Muscle activity of SCM and UFT
Peak amplitude of normalized EMG
Muscle activity area (%·ms),
dened as sum of normalized EMG
amplitudes
Onset latency (ms), dened as time
between force application and rst
upswing of EMG signal (unknown
trials only)
↓ 42% peak strength, females (P<0.001)
↑ 18% angular acceleration, females
↑ 25% angular displacement, females
↓ 29% DS, females
↑ 117% peak amplitude of EMG, females
↑ 110% muscle activity area, females
↓ 43% muscle onset latency for SCM and ↓ 28% in UFT, females
Eckner et al.
[13]
Cohort
CEBM: 2b
NOS: 7/9
24 males
22 females
8 - 30 years
DS in Flex and Ext,
sagittal plane of neck
motion, LSFlex and
RRot
Females to males
Age, continuous from
8 - 30 years
Gradual
increase of
isometric
contraction to
peak (N)
Rate of force
development
(N/s)
Linear
1-kg mass,
dropped
from variable
height relative
to body mass
via cable
attached to
the head
Anthropometrics
Neck girth (cm)
Head mass (kg)
CSA, SCM (cm2)
Strength
Peak isometric strength (N) and
RFD (N/s) in Flex, Ext, LSFlex, RRot
HN Kinematics
Peak linear velocity (m/s/J)
Peak angular velocity (°/s/J)
↓ 30% peak strength, adult females (P<0.05, Flex, Ext, LSFlex;
P<0.01, Right axial rotation)
↓ 40% peak strength, young participants
↑ 33% linear head velocity (P<0.01, Flex and Ext, females vs. males)
and ↑ 18% angular head velocity (P<0.05, Flex and right axial
rotation, females vs. males) adult female during anticipated force
application
↑ 58% linear head velocity and ↑ 45% angular head velocity, young
participants during anticipated force application
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 7 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Gutierrez et al.
[30]
Cohort
CEBM: 4
NOS: 7/9
17 females
15-17 years
High school
soccer players
Correlation of peak
isometric neck
strength to peak
resultant head
acceleration
Gradual
increase of
isometric
contraction to
peak (lbs.)
Heading of a
soccer ball
Strength
Peak isometric strength (lbs.) in
Flex, Ext, RSFlex and LSFlex
HN Kinematics
Peak linear acceleration (g)
Flex vs. forward peak resultant acceleration (r = -0.639, P<0.008); left
peak resultant acceleration (r = -0.541, P<0.03); right peak resultant
acceleration (r = -0.701, P<0.003)
Extension vs. forward peak resultant acceleration (r = -0.639,
P<0.009); left peak resultant acceleration (r = -0.545, P<0.029); right
peak resultant acceleration (r = -0.685, P<0.003)
RSFlex vs. forward peak resultant acceleration (r = -0.61, P<0.012);
left peak resultant acceleration (r = -0.500, P<0.048); right peak
resultant acceleration (r = -0.688, P<0.003)
LSFlex vs. forward peak resultant acceleration (r = -0.608, P<0.012);
left peak resultant acceleration (r = -0.621, P<0.01); right peak
resultant acceleration (r = -0.757, P<0.001)
Within-subject comparisons
Lisman et al.
[31]
Cohort
CEBM: 4
NOS: 6/9
16 males
18 - 24 years
Prior high
school football
experience
DS in Ext, sagittal
plane of neck motion
Pre-post resistance
training
Gradual
increase of
isometric
contraction to
peak (kg)
Football
tackle of a
standard
padded
tackling
dummy
Strength
Peak isometric strength (kg) in Flex,
Ext, RSFlex, LSFlex
HN Kinematics
Peak linear acceleration (g)
Peak angular acceleration (rad/s2)
Total displacement (°)
Time-to-peak angular acceleration
(ms)
Muscle activity
Peak EMG of SCM and UFT
↑ 3% peak strength in Flex, ↑ 7% Ext (P<0.05), ↑ 7% RSFlex, ↑ 10%
LSFlex (P<0.05)
Kinematics
↑ 5% linear acceleration
↑ 5% angular acceleration
↑ 18% displacement
↑ 14% time-to-peak angular acceleration
Peak muscle activity
0% right SCM, ↓ 11% left SCM; ↑ 10% right UFT (P<0.05), ↓ 31% left
UFT (P<0.05)
Mansell et al.
[11]
Non-
randomized
control trial
CEBM: 2b
MQR: 7/10
17 males
19 females
18 - 22 years
NCAA, Division
I Soccer
DS in exion and
extension, sagittal
plane of neck motion
Females to males
Gradual
increase of
isometric
contraction to
peak (lbs.)
Linear
1-kg mass,
dropped 15
cm via cable
attached to
the head
Strength
Peak isometric strength (lbs.) in Flex
and Ext
HN Kinematics
Peak angular acceleration (°/s2)
Total displacement (°)
Dynamic stiffness (lbs./°)
Muscle activity of SCM and UFT
Peak amplitude of normalized EMG
Muscle activity area (%·ms),
dened as sum of normalized EMG
amplitudes
Onset latency (ms), dened as time
between force application and rst
upswing of EMG signal (unknown
trials only)
↑ 10% peak strength in Flex (P<0.001) and ↓ 10% in Ext, males; ↑
30% Flex and ↑ 29% Ext, females (P<0.05)
↑ 130% peak angular acceleration in Flex and ↑ 68% Ext, males; ↑
74% Flex and ↑ 33% Ext, females
↓ 7% head displacement in Flex and ↑ 28% Ext, males; ↑ 20% in Flex
and ↓ 13% Ext, females
↑ 54% DS in Flex and ↑ 54% Ext, males; ↑ 68% Flex and ↓ 17% Ext,
females
↑ 24% peak amplitude of EMG, males; ↑ 1%, females
↑ 23% muscle activity area, males; ↑ 17%, females
↓ 20% muscle onset latency SCM, ↓ 16% UFT males; ↑ 15% SCM, ↑
45% UFT, females
Note: CEMB: Centre for Evidence-Based Medicine; CI: Condence interval; NOS: Newcastle-Ottawa Scale; DS: Dynamic Stiffness; HN: Head-Neck; SCM : Sternocleidomastoid; UFT: Upper Fibers of Trapezius;
EMG: Surface Electromyography; MQR: PEDro scale for methodological quality rating; NCAA: National Collegiate Athletic Association; N: Newtons; Nm: Newton meters; OR: Odds Ratio; RFD: Rate of Force
Development; Flex: Flexion; Ext: Extension; RSFlex: Right side exion; LSFlex: Left side exion; L45Flex: Flexion at 45 left from midline; R45Flex: Flexion at 45° right from midline; L45Ext : Extension at 45° left from
midline; R45Ext: Extension at 45° right from midline; RRot: Right rotation; LRot: Left rotation; Comp: Composite Strength Score; CSA: Cross-Sectional Area; rad: Radians; kg: kilograms; lbs: Pounds; g: Acceleration
of gravity; ms: Milliseconds; s: Seconds; J: Joules; m: Meters; cm: Centimeters.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 8 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
odds of sustaining a moderate or severe head impact, with an odds
ratio of 1.02 (CI95%, 0.80 to 1.32) for moderate impacts and 0.96
(CI95%, 0.67 to 1.36) for severe impacts. By including player position
as a covariate in the regression model, Schmidt et al. reported the
odds of sustaining a moderate or severe head impact to be highest
for linesmen, with an odds ratio of 1.78 (CI95%, 1.01 to 3.16) for
moderate impacts and 1.34 (CI95%, 0.29 to 6.23) for severe impacts,
despite linesmen having the highest measures of peak isometric neck
strength.
While peak isometric neck strength did not predict the odds of
sustaining a moderate or severe head impact in prospective sport-
specic cohort studies, controlled lab-based studies have described
an attenuating eect of peak isometric neck strength on the kinematic
response of the HN segment to standardized applications of
external forces to the head. ese attenuating eects were evaluated
using between-subject [11,13,29,30] and within-subject [11,31]
experimental designs. is level 2b and 4 evidence is also summarized
in Table 3.
Gutierrez et al. [30] correlated peak isometric neck strength,
measured in exion, extension and bilateral side exion, to post-
impact kinematics of the head during controlled soccer ball heading
maneuvers in 17 female high school varsity soccer players. ey
reported a negative correlation between peak measures of isometric
neck strength and peak magnitude of post-impact linear acceleration
of the head (Pearson’s r, -0.5 to -0.75). While this attenuating eect was
signicant (P≤0.04), peak isometric strength explained only between
25% and 56% of the variance of post-impact linear acceleration of the
head (level 4 evidence).
In contrast to the semi-constrained movement used by Gutierrez
et al., other studies have used a pulley system to standardize the
application of an external force to the head, either along the sagittal
(exion-extension) plane of HN motion [11,29], or along all three
planes of motion of the HN segment [13]. Eects of applied forces
were compared between male and female adults, and in athletes, both
male and female, 8 to 30 years old, with the a priori assumption that
measured dierences in post-impact HN kinematics would result
from the lower neck strength in females, as well as in children and
adolescent athletes. As predicted, adult females exhibited 29% to
49% lower peak isometric strength than adult males and 18% to 29%
higher peak post-impact angular acceleration of the head [11,13,29].
From their kinematic data, Mansell et al. [11] and Tierney et al. [29]
calculated a 29% lowering in the resistive capacity (or stiness) of the
HN segment in females (level 2b evidence). Additionally, Eckner et al.
[13] reported a signicant independent eect of age on the resistive
capacity of the neck (P<0.001). Peak isometric strength was 32% to
53% lower in athletes of high school age or younger compared to
adults, and was associated with 40% higher peak post-impact angular
velocity of the head for males and 48% for females (level 2b evidence).
From their data set, Eckner et al. [13] predicted a linear relationship
between peak isometric strength and the resistive capacity of the HN
segment along the sagittal plane of motion (P<0.02, level 2b evidence),
Figure 1: Effect size (Cohen’s d), with corresponding 95% condence intervals, is shown for the twelve resistance training programs, stratied by training
stimulus: isotonic, elastic, isometric and isokinetic. The boundaries of effect size are identied: α – “small” effect (d=0.20); δ – “medium” effect (d=0.50); φ
“large” effect (d=0.8). The data for male cohort extension strength in the study Mansell et al. [11] has been excluded from the analysis due to a large decrease
in extensor strength following the training program for which the authors do not provide an explanation.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 9 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
with peak isometric strength explaining 17% to 36% of the variance in
post-impact linear and angular velocity of the head (Pearsons r, 0.42
to 0.60). Peak isometric strength did not predict resistive capacity of
the HN segment along the frontal plane or for axial rotation.
Evidence from model-based studies
Model-based simulation provides a method to systematically
investigate the specic association between the resistive capacity
of the HN segment and post-impact kinematics of the head under
dierent scenarios of external force application. is level 5 evidence
is summarized in Table 4.
Using a physical model (Hybrid III dummy), Viano et al. [12]
measured the eects of varying the resistive capacity of the HN
segment also known as the stiness, on the post-impact kinematics of
the head. e physical force inputs applied to the head component of
the Hybrid III model were the mean three-dimensional components
of the direction and velocity of external forces recorded by video for
31 head impacts in 25 players of the National Football League who
sustained a concussion resulting from helmet-to-helmet or helmet-
to-ground collisions. Increasing the pre-impact stiness of the neck
component of the Hybrid III model from 80 N/mm, the estimated
baseline HN stiness for the 50th percentile male, to 180 N/mm
yielded a 14% attenuation of the peak post-impact linear acceleration
of the head, with a 35% lowering of the Head Injury Criterion (HIC).
e HIC, calculated as the change in acceleration of the head over
the time of force application, is a measure of the likelihood of head
injury arising from an impact [32]. e upper limit of 180 N/mm of
neck stiness used in this simulation exceeds the predicted stiness
for the 95th percentile male [12]. e relationship between neck
stiness and post-impact linear acceleration of the head was best
described by an exponential function, with relatively small changes
in stiness yielding significant attenuation effects of post-impact
head kinematics for lower baseline levels of neck stiffness, with
only minor effects for higher baseline levels of stiffness. As an
example, a 10N/mm increase from a baseline neck stiness of 30
N/mm produced a 23% lowering of the HIC compared to the 14%
lower HIC with a 40 N/mm increase from a 80 N/mm baseline of
neck stiness.
Shewchenko et al. [33] used a computational model (MADYMO,
version 6.0.1, Tass International) to characterize the relationship
between stiness of the HN segment and post-impact kinematics of
the head for a simulated soccer ball heading maneuver. In contrast
to Viano et al.’s [12] method of increasing stiness uniformly
along all directions of motion, Shewchenko et al. [33], manipulated
stiness of the HN segment indirectly and in direction-specic ways
by varying the relative levels of activation across sixty-eight pairs of
muscle elements included in the neck model. Activation levels were
attributed rst to the neck exor muscle group, with levels adjusted
to ex the head and neck toward the ball in preparation for impact.
e relative activation levels for the extensor muscle group and
sternocleidomastoid muscles were then scaled in iterative fashion
to match motions of the HN model to realistic pre- and post-impact
Author(s) Model Type Model Inputs Measured Outcomes Statistical
Comparison Results
Viano et al.
[12]
Kinematic model, based on
data obtained from laboratory-
based reconstruction of
helmet-to-helmet or helmet-
to-ground impacts resulting
in concussion in NFL players,
using 50th percentile male
Hybrid III dummy
Striking player
Peak acceleration – 70.9 g
Change in head velocity (∆V) – 5.6 m/s
Struck player
Peak acceleration – 102.5 g
Change in head velocity (∆V) – 7.1 m/s
Resultant peak force - 9700 N at 8.2 ms
Impact speed – 9.7 m/s, average of
laboratory reconstructed collisions
resulting in concussion from helmet-to-
helmet impacts applied at 0-90 (exion –
lateral side exion)
Neck stiffness (N/mm) of the struck
player was modulated prior to impact to
determine effects on ∆V and HIC.
Impact force (N)
Impact velocity (m/s)
Peak linear acceleration
(g)
Peak angular acceleration
(rad/s2)
Peak ∆V (m/s)
HIC values
Struck player
sustaining
concussion vs.
no concussion
↑ 39% peak head
acceleration (P=0.005),
concussion impacts
↑ 47% peak impact force
(P=0.017), concussion
impacts
↑ 32% head ∆V (P<0.001),
concussion impacts
↓ 14% ∆V and ↓ 35% HIC,
increasing neck stiffness
of 50% male from 80 N/
mm to 180 N/mm prior to
impact
Shewchenko
et al. [33]
Mathematical Dynamic
Model (MADYMO 6.0.1.)
50th percentile male human
model; includes 68 pairs
of neck muscles organized
into three bilateral groups:
exors, extensors and
sternocleidomastoids
Impact
Low-velocity (6 m/s)
Posture
Head angle (˚)
Back angle (˚)
Relative head-back angle (˚)
Change in relative head-back angle (˚)
Muscle activation (% MVE)
Baseline: exors – 80%, extensors 0%,
sternocleidomastoid 0%
125%: exors – 125%, extensors 10%,
sternocleidomastoid 0%
150%: exors – 80%, extensors 15%,
sternocleidomastoid 20%
Peak linear acceleration
(m/s2)
Peak angular acceleration
(rad/s2)
HIP (kW)
Neck shear (N) at C0-C1
Neck axial compression
(N) at C0-C1
Supra-maximal
neck muscle
activation
vs. baseline
activation level
↓ 1% peak linear head
acceleration; ↑ 20% peak
angular acceleration;
↑ 7% HIP; ↑ 44% A-P
shear force at C0-C1;
↑ 63% axial compression
at C0-C1, muscle pre-
activation at 125% MVE
↓ 7% peak linear head
acceleration; ↑ 48% peak
angular acceleration;
↑ 6% HIP; ↑ 79% A-P
shear force at C0C1;
↑ 119% axial compression
at C0-C1, muscle pre-
activation at 150% MVE
Table 4: Model-based evaluation of dynamic stiffness of the HN segment and post-impact kinematics of the head.
Note: NFL: National Football League; N: Newton; mm: millimeters; HIC: Head Injury Criterion; g: Acceleration of gravity; rad: Radians; s: Seconds; m: Meters; MVE:
Maximal Voluntary Effort; HIP: Head Impact Power; A-P: Anterior-Posterior; HN: Head-Neck.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 10 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
kinematics obtained from recorded performances of controlled
soccer ball heading maneuvers in seven, non-professional, male
soccer players, having ve to thirteen years of soccer experience
[34]. Resultant forces acting on the upper cervical spine were also
predicted. Model-based simulations were then used to evaluate
eects of increasing pre-impact muscle activity of the neck exors to
125% and 150% of their predicted maximum activation, adjusting co-
activation levels of extensors and sternocleidomastoid accordingly,
on the post-impact kinematics of the HN segment. Raising activation
levels to 125% yielded a 20% increase in peak angular acceleration
of the head by 20%, with an associated 7% increase in Head Impact
Power (HIP), where HIP is a composite index of the rate of energy
transfer to the head, estimated by combining peak magnitudes of
post-impact linear and angular acceleration of the head [34]. e
model also predicted an associated 44% increase in peak magnitude of
anterior-posterior shear and 63% increase in axial compression forces
at C0-C1. Raising the activation level to 150% did not further inuence
peak angular acceleration of the head and HIP, with values of 48%
and 6%, respectively. However, anterior-posterior shear forces and
axial compression forces at the upper cervical spine (i.e., C0-C1 level)
were predicted to increase to 79% and 119% of baseline, respectively.
ese model-based simulations provide evidence of the sensitivity of
HN stiness on parameters of pre-impact muscle activation.
Evidence relating short-latency neck strength to HN
kinematics
While there is no consistent evidence for a protective eect of
higher peak isometric neck strength in lowering the incidence of
concussion or in modifying the post-impact kinematics of the HN
segment, there is level 1b [28,35], 2b [11,13,29] and 4 [34,36,37]
evidence of an attenuating inuence of higher short-latency isometric
neck muscle tension, developed prior to impact, on the post-impact
kinematics of the HN segment. e attenuating eects of short-
latency neck strength have been evaluated by comparing post-impact
kinematics of the HN segment to an externally applied force when
the time of impact is either ‘anticipated’ or ‘unanticipated’, with the
assumption that knowledge of impact allows individuals to increase
isometric tension of their neck muscles and brace for the impact. is
level 1b, 2b and 4 evidence is summarized in Table 5.
e attenuating eects of anticipatory pre-tensing of neck
muscles on the post-impact kinematics of the HN segment during
game play are reported in two prospective cohort studies [28,35].
Mihalik et al. [35] reviewed video capture of on-ice collisions in their
study on concussion risk in minor hockey players to determine if
upcoming impacts were ‘anticipated’ or ‘unanticipated’. For head
impacts of moderate intensity, dened as the range between the 50th
to 75th percentile of HITsp scores, anticipation of the contact yielded
a 17% attenuation of the peak post-impact angular acceleration of the
head (P=0.006; Cohen’s d=0.37), with a 2% lowering of the HITsp
scores (P=0.03; level 1b evidence). While signicant, the eect size of
this attenuating eect was small (Cohen’s d=0.27).
In their study group of forty-nine high school and collegiate
football players, Schmidt et al. [28], similarly reported a positive
attenuating eect of higher anticipatory HN stiness. In this study,
anticipatory HN stiness was quantied pre-season using the
standard methods of Mansell et al. [11], but scaling the magnitude
of the applied external force to body weight. Players with higher
anticipatory HN stiness had lower odds of sustaining moderate
and severe head impacts over the football season, with odds ratio of
0.77 (CI95%, 0.61–0.96) for moderate impacts and 0.64 (CI95%, 0.46–
0.89) for severe impacts (level 1b evidence). e eect size of higher
anticipatory HN stiness could not be calculated from the data set
reported.
Similar positive eects of anticipation of impact on post-
impact HN kinematics were reported in soccer heading maneuvers
performed at low (6.2 m/s) and high-speed (7.5 m/s) ball impacts
[34]. For low speed head impacts, anticipatory pre-tensing of the
neck musculature yielded a 2% attenuation in peak linear acceleration
of the head (Cohen’s d=2.12) and a 5% attenuation of peak angular
acceleration (Cohen’s d=0.34). is attenuation yielded a 25%
reduction in HIP score (Cohen’s d=1.20). Anticipatory pre-tensing
of the neck musculature had no eect on post-impact HN kinematics
for high-speed impacts. erefore, anticipatory pre-tensing of neck
muscles contributes small to large protective eects on concussion
risk only for low-speed impacts (range of Cohen’s d, 0.34 to 2.12, level
4 evidence).
e positive eects of anticipatory pre-tensing of neck muscles
in attenuating post-impact kinematics of the HN segment is further
supported by level 2b and level 4 evidence from lab-based studies
[11,13,29,36,37]. Using their standard methods for quantifying HN
stiness along the sagittal plane, Mansell et al. [11] and Tierney et al.
[29] reported a 13% to 21% increase in the resistive capacity of the HN
segment with anticipatory pre-tensing of the neck (P≤0.05) [29] and an
associated 7% to 24% attenuation of peak magnitudes of post-impact
angular acceleration of the head (P≤0.001) [11,29]. Eckner et al. [13]
conrmed a positive attenuating eect of anticipatory pre-tensing of the
neck on post-impact HN kinematics along all three planes of motion
(Pearson’s r=0.42 to 0.66, P<0.001). Reported attenuating responses
represent small to large eect size of anticipatory pre-tensing, with
Cohen’s d values ranging from 0.03 to 0.70.
Evidence of eectiveness of neck strengthening programs
e second aim of our scoping review was to determine the
effectiveness of neck strength training programs in increasing
not only peak isometric strength of the neck but as well, the
anticipatory or short-latency variables of the force-time strength
response of the neck. The parameters of training for the twelve
strengthening programs identified by our search strategy are
summarized in Table 6. Figure 1 compares the mean (CI95%) eect
sizes of training on peak isometric neck strength, stratied by training
stimulus - isotonic, elastic, isometric, and isokinetic.
Calculated MDC95% values for each program are reported in
Table 7. Cohen’s d and MDC95% values could not be reliably calculated
for two strength training programs, due to insucient detail of
outcome measures [38] and small number of participants (n=5) in
the control and strength training groups [39].
In general, resistance training programs, stratied by training
stimulus, produced medium to large eect sizes of change in pre- and
post-training measures of peak isometric strength, with Cohen’s d
value of 0.65 (CI95%, 0.37 to 0.93) for isotonic, 2.10 (CI95%, 0.74 to 3.41)
for isometric, 0.48 (CI95%, 0.11 to 0.86) for isokinetic and 0.47 (CI95%,
0.16 to 0.77) for elastic programs. e widths of the CI95% indicate
that the eect size of training varied among specic programs, with
some programs producing small eects on strength and others large
eects. Of the twelve strength programs appraised in our review,
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 11 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Author(s) Experimental
Design
CEBM /
MQR / NOS
Rating
Participants Statistical
Comparisons
External Force Measured Outcomes Results
Mihalik et al.
[35]
Prospective
cohort
CEBM: 1b
NOS: 7/9
16 males
14 years
Minor hockey
players
Anticipated vs.
unanticipated
collisions
Natural on-ice
collisions
Head kinematics
Peak linear acceleration (g)
Angular acceleration (rad/s2)
Head impact severity prole
H.I.T.sp (Simbex, Lebanon, NH)
Body checking evaluation
Video review using CHECC scale
↓ 17 % peak angular acceleration (P<0.01),
anticipated medium-intensity (50-75th percentile)
impacts
↓ 2% H.I.T.sp (P<0.05), anticipated medium-
intensity (50-75th percentile) impacts
Schmidt et al.
[28]
Prospective
cohort
CEBM: 1b
NOS: 8/9
49 males
16-21 years
High school and
collegiate football
players
DS in Flex and
Ext, sagittal
plane of neck
motion
High vs. low
performers
(median split)
Line positions
vs. non-line
positions
OR (95% CI)
of sustaining
moderate
and severe
head impacts
from various
predicting
variables
Linear variable
mass equal to
1.0-2.5% body
mass dropped
15 cm via cable
attached to the
head.
Natural on-eld
collisions
Strength
Peak isometric torque (Nm) and RFD (Nm/s) in Flex, Ext,
LSFlex, RSFlex and Comp (sum of all directions)
HN Kinematics
Peak angular displacement (rad) in Flex and Ext
Dynamic stiffness (Nm/rad)
Muscle activity, SCM and UFT muscles
Onset latency (ms), dened as moment onset and EMG
signal upswing 11 and 6 times resting SD (unknown trials
only)
Head Impact Telemetry severity prole
H.I.T.sp (Simbex, Lebanon, NH)
Peak resultant linear head acceleration (g)
↓ OR (0.64 – 0.77) of sustaining severe and
moderate (respectively) HITsp for high performing
athletes for cervical stiffness predictor
↓ OR (0.64 – 0.73) of sustaining severe and
moderate (respectively) HITsp for high performing
athletes for angular displacement predictor
↑ OR (1.70 – 1.86) of sustaining moderate linear
head acceleration for high performing non-lineman
for onset latency predictor in forced Ext and Comp
↓ OR (0.68) of sustaining severe HITsp for high
performing athletes for onset latency predictor
Eckner et al.
[13]
Cohort CEBM: 2b
NOS: 7/9
24 males
22 females
8 - 30 years
DS in Flex and
Ext along sagittal
planes, LSFlex
and Right axial
rotation
Drop of a 1-kg
mass from
variable height
relative to body
mass attached
to participant’s
head via a cable
Anthropometrics
Neck girth (cm)
Head mass (kg)
CSA, SCM (cm2)
Strength
Peak isometric strength (N) and RFD (N/s) in Flex, Ext,
LSFlex, Right axial rotation
HN Kinematics
Peak linear velocity (m/s/J);
Peak angular velocity (°/s/J)
↓ 12.3% linear head velocity
↓ 10% angular head velocity
Pearson r-value, 0.417 to 0.605 (P<0.01), peak
isometric neck strength and in linear head velocity
and angular head velocity
Pearson r-values, 0.418 to 0.657 (P<0.01),
anticipatory isometric neck muscle tension and
linear head velocity and angular head velocity
Table 5: Modifying effects of anticipatory isometric neck force on dynamic stiffness of the HN segment.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 12 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Tierney et al.
[29]
Cohort CEBM: 2b
NOS: 7/9
20 males
20 females
20 – 30 years
Males vs.
females
Linear 1-kg
mass, dropped
15 cm via cable
attached to
participants’
head
Strength
Peak isometric strength (lbs.) in Flex and Ext
HN Kinematics
Peak angular acceleration (°/s2)
Total displacement (°)
Dynamic stiffness (lbs./°)
Muscle activity of SCM and UFT
Peak amplitude of normalized EMG
Muscle activity area (%·ms), dened as sum of normalized
EMG amplitudes
↓ 24% males (P<0.01), 0% females, angular
acceleration
↓ 39% males, ↓ 35% females, angular
displacement
↑ 17% males, ↑ 13% females, DS (P<0.05)
↓ 0% SCM, ↓ 11% UFT males, ↓ 15% SCM, ↑ 8%
UFT females, peak muscle activity
↑ 24% SCM, ↑ 10% UFT males, ↑ 3% SCM, ↑ 8%
UFT females, muscle activity area
Mansell et al.
[11]
Non-
randomized
control trial
CEBM: 2b
MQR: 7/10
17 males
19 females
18 - 22 years
NCAA, Division I
Soccer
Males vs.
females
Linear mass
of 1-kg mass
dropped 15
cm via cable
attached to
participants’
head
Strength
Peak isometric strength (lbs.) Flex and Ext
HN Kinematics
Peak angular acceleration (°/s2)
Total displacement (°)
Dynamics stiffness (lbs./°)
Muscle activity of SCM and UFT
Peak amplitude of normalized EMG
Muscle activity area (%·ms), dened as sum of normalized
EMG amplitudes
↑ 12% males, ↓ 7% females, angular acceleration
(P<0.01, males and females combined)
↓ 22% males, ↓ 24% females, angular
displacement (P<0.001, males and females
combined)
↓ 6% males, ↑ 21% females, DS
↓ 38% males, ↑ 5% females, peak muscle activity
SCM (P<0.05, males females combined); ↑ 23%
males, ↓ 23% females, UFT
↓ 11% males, ↑ 23% females muscle activity area
for SCM; ↑ 81% males, ↑ 27% female, UFT
Shewchenko
et al. [34]
Cohort CEBM: 4
NOS: 6/9
7 males
20 – 23 years
Previous
soccer heading
experience
Magnitude of
neck muscle
tension prior to
impact
High vs. low-
velocity impacts
Four
standardized
heading
maneuvers;
controlling,
passing,
clearing and
head rebound
applied along
the sagittal
plane in
extension
Low (6.2 m/s)
and high (7.6
m/s) impact ball
speed
Head kinematics
Peak linear acceleration (m/s2)
Peak angular acceleration (krad/s2) along the sagittal
plane, measured using an intraoral bite-plate with
accelerometer cantilevered outside of the mouth.
Head Impact Power (HIP)
HIP (calculated based on rate of energy transfer to the
head, accounts for linear and angular accelerations for all
degrees of freedom)
Muscle Activity
SCM and UFT EMG
↓ 2% peak linear acceleration, ↓ 5% peak angular
acceleration, and ↓ 25% HIP, low velocity impacts
↑ 8% peak linear acceleration, ↑ 1% peak angular
acceleration, and ↑ 5% HIP, high velocity impacts
SCM activated 280-500 ms prior to impact and
remained active 0-200 ms post-impact, low and
high velocity heading scenarios
UFT activated 120-250 ms prior to impact and
remained active 100-350 ms post-impact, low and
high velocity heading scenarios
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 13 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Kumar et al.
[36]
Cohort CEBM: 4
NOS: 7/9
5 males
9 females
23 - 30 years
Magnitude of
sled acceleration
(0.5, 0.9, 1.1 and
1.4g)
Inertial
extension force
to the head
via forward
acceleration
(pneumatic sled
impact)
Kinetics
Chair acceleration (g)
Shoulder acceleration (g)
Head acceleration (g), using tri-axial accelerometers.
↓ 18% (0.5g), ↓ 9% (0.9g), ↓ 27% (1.1g), and
↓ 37% (1.4g) extension head acceleration, males
(P<0.001)
↓ 9% (0.5g), ↓ 20% (0.9g), ↓ 34% (1.1g), and ↓
29% (1.4g) extension head acceleration, females
(P<0.001)
Ono et al.
[37]
Cohort CEBM: 4
NOS: 5/9
3 males
22 - 43 years
Magnitude of
sled acceleration
(2, 3, 4 km/h)
Known vs.
unknown force
application
Angle of sitting
posture
Head rest height
Inertial
extension force
to the head
via forward
acceleration
(pneumatic sled
impact)
Kinetics
Extension moment at C1 (Nm)
Muscle Activity
EMG of SCM and UFT
↓ 40% extension moment, relative to standard
headrest
Author(s) Experimental
Design / rating
Participants Statistical
comparison
Program Parameters Measured
Outcomes
Results
Isotonic resistance
Burnett et al.
[58]
Randomized
control-trial
CEBM: 2b
MQR: 8/10
12 males
19 - 30 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 2/wk for 10 wk
Intensity: 24 – 114% of max isometric force, 2-3 sets 10 reps
Type: MCU weight stack in Flex, Ext, RSFlex, LSFlex
Isometric neck
strength (lbs.)
↑ 64% Flex (P<0.01); ↑ 63% Ext
(P<0.01); ↑ 53% LSFlex (P<0.01);
↑ 49% RSFlex (P<0.01)
Conley et al.
[40]
Randomized
control-trial
CEBM: 2b
MQR: 6/10
22 males
20 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 4/wk for 12wk
Intensity: 10-RM, 3 sets 10 reps
Type: Free weights in Ext
Isometric neck
strength (kg)
↑ 34% Ext, 3 ×10-RM load
(P<0.05)
Pollock et al.
[59]
Randomized
control-trial
CEBM: 2b
MQR: 7/10
50 males
28 females
20 - 40 years
Pre-test vs. post-
test neck strength
assessment
DYN x1
Frequency: 1/wk for 12 wk
Intensity: 80% of 1-RM, 1 set 8-12 reps
Type: Cervical extension machine
DYN+ISO x1
Frequency: 1/wk for 12 wk
Intensity: 80% of 1-RM, 1 set 8-12 reps, plus 1 set of 5 s isometric contraction in 8
head angles
Type: Cervical extension machine
DYN x2
Frequency: 2/wk for 12 wk
Intensity: 80% of 1-RM, 1 set 8-12 reps
Type: Cervical extension machine
DYN+ISO ×2
Frequency: 2/wk for 12 wk
Intensity: 80% of 1-RM, 1 set 8-12 reps, plus 1 set of 5 s isometric contraction in 8
head angles
Type: Cervical extension machine
Isometric neck
strength a (Nm)
↑ 9.4% Ext, DYN × 1 (P<0.05)
↑ 11.5% Ext, DYN + ISO x 1
(P<0.05)
↑ 17.2% Ext, DYN × 2 (P<0.05)
↑ 11.1% Ext, DYN + ISO × 2
(P<0.05)
Table 6: Neck strengthening studies in non-clinical populations
Note: CEMB: Centre for Evidence-Based Medicine; NOS: Newcastle-Ottawa Scale; g: Acceleration of gravity; rad: Radians; H.I.T.sp: Head Impact Telemetry severity prole; CHECC : Carolina Hockey Evaluation of
Children’s Checking; m: Meters; s: Seconds; kg : Kilograms; krad: Kiloradians; ms: Milliseconds; cm: Centimeters; lbs: Pounds; HIP: Head Impact Power; EMG: Surface electromyography; SCM: Sternocleidomastoid;
UFT: Upper Fibers of Trapezius; HN: Head-Neck; DS: Dynamic Stiffness; NCAA: National Collegiate Athletic Association; Nm: Newton-meters; Flex: Flexion; Ext: Extension; LSFlex: Left side exion.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 14 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
Mansell et
al. [11]
Non-randomized
control-trial
CEBM: 2b
MQR: 7/10
17 males
19 females
18 - 20 years
NCAA Division
I soccer
players
Pre-test vs. post-
test neck strength
assessment
Frequency: 2/wk for 8 wk
Intensity: 55-70% of 10-RM, 3 set 10 reps
Type: Free weights in Flex, Ext, RSFlex, LSFlex
Isometric neck
strength (lbs.)
↑ 10% Flex, ↓ 10% Ext males
↑ 30% Flex, ↑ 29% Ext in female
training group (P=0.01)
Taylor et al.
[39]
Non-randomized
control-trial
CEBM: 3b
MQR: 6/10
10 males
30 - 50 years
US Navy
personnel
Pre-test vs. post-
test neck strength
assessment
Frequency: 3/wk for 12 wk
Intensity: 10-RM, 3 sets, 10 reps
Type: Free weight in Flex, Ext, RSFlex, LSFlex
Isometric neck
strength (lbs.)
↑ 46% Flex; ↑ 73% Ext (P<0.05);
↑ 83% RSFlex (P<0.05); ↑ 72%
LSFlex (P<0.01)
Leggett et al.
[38]
Non-randomized
control-trial
CEBM: 3b
MQR: 6/10
24 adults
18 - 30 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 1/wk for 10 wk
Intensity: 10-RM, 1 set 8-12 reps
Type: Free weights, Ext only
Isometric neck
strength (Nm)
↑ 6.3 – 14.3% Ext (P<0.05) b
Lisman et al.
[31]
Cohort study
CEBM rating: 4
NOS: 7/9
16 males
19 - 25 years
Ex-high school
football players
Pre-test vs. post-
test neck strength
assessment
Frequency: 2-3/wk for 8 wk
Intensity: 60-80% of 10-RM, 3 sets, 10 reps
Type: Pro 4-way weight stack in Flex, Ext, RSFlex, LSFlex
Isometric neck
strength (kg)
↑ 3% Flex; ↑ 7% Ext (P<0.05);
↑ 7% RSFlex; ↑ 10% LSFlex
(P<0.05)
Alricsson et
al. [60]
Cohort study
CEBM: 4
NOS: 8/9
40 males
23 - 40 years
Military ghter
pilots
Pre-test vs. post-
test neck strength
assessment
Frequency: 3/wk for 6-8 months
Intensity: Absolute masses of 1, 2, and 4 kg that could be combined to increase head
mass if required, 4 sets, 10 reps
Type: Free weights (no directions specied)
Isometric neck
strength (Nm)
↑ 11% Flex (P<0.001) and ↑ 11%
Ext (P=0.001) in reinforcement
group
↓ 2% Flex and ↓ 16% Ext in non-
reinforcement group
Elastic Resistance
Burnett et al.
[58]
Randomized
control-trial
CEBM: 2b
MQR: 8/10
9 healthy
males
19 - 30 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 2/wk for 10 wk
Intensity: Dynaband level 1-6, 2-3 sets of 10 reps
Type: Dynaband in Flex, Ext, RSFlex, LSFlex
Isometric neck
strength (lbs.)
↑ 41% Flex (P<0.05); ↑ 30% Ext; ↑
24% RSFlex; ↑ 26% LSFlex
Kramer et al.
[61]
Randomized trial
(no controls)
CEBM: 2b
MQR: 6/10
13 females
18 - 27 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 2/wk for 10 wk
Intensity: 15% of max isometric strength, 2 sets of 10-12 reps
Type: Thera-band in Flex, Ext, Rrot, Lrot
Isometric neck
strength (Nm)
↑ 10% Flex; 0% Ext; ↑ 19% Rrot
(P<0.05); ↑ 8% Lrot
Isometric Resistance
Portero et al.
[41]
Cohort study
CEBM: 4
NOS: 8/9t
7 males
24 - 30 yearst
Pre-test vs. post-
test neck strength
assessmentt
Frequency: 3/wk for 8 wk
Intensity: 80% of max isometric strength, 2 sets 8 reps of 6 second holds
Type: RSFlex, LSFlext
Isometric neck
strength (Nm)
Isokinetic neck
strength at 30º/s
(Nm)
↑ 35%, isometic bilateral side
exion (P<0.01);
↑ 20%, isokinetic bilateral side
exion (P<0.01)
Isokinetic resistance
Kramer et al.
[61]
Randomized trial
(no controls)
CEBM: 2b
MQR: 6/10
13 females
18 - 27 years
Pre-test vs. post-
test neck strength
assessment
Frequency: 2/wk for 10 wk
Intensity: 15% of max isometric strength, 2 sets 10-12 reps
Type: VR software controlled kinematic robotic system, 2 sets 10-12 reps in Flex
(start position 25° Ext – end position 40° exion), Ext (start position 40˚ Flex – end
position 25° Ext), bilateral axial rotation (start position 35° contralateral rotation – end
position 70° ipsilateral rotation, concentric phase 40°/s, eccentric phase 20°/s
Isometric neck
strength (Nm)
↑ 29% Flex (P<0.05); ↑ 8% Ext;
↑ 28% Rrot; ↑ 8% Lrot
Note: CEBM: Centre for Evidence Based Medicine; MQR: PEDro methodological rating scale; NOS: Newcastle-Ottawa Scale of methodological rating; MCU: Multi-Cervical Unit; Flex: Flexion; Ext: Extension; RSFlexion: Right side exion; LSFlexion: Left side exion;
Rrot: Right side rotation; Lrot: Left side rotation; RM: Repetitions max; DYN: Dynamic strength; ISO: Isometric strength; NCAA: National Collegiate Athletic Association; wk: Week; reps: Repetitions; lbs: Pound; kg: Kilograms; VR: Virtual reality
a
Pollock et al. [59] measured static extension strength at eight positions (0°,18°,36°,54°,72°,96°,108°,126°) of cervical sagittal-plane range of motion (end-range extension - 0°, end-range exion - 126°). Strength outputs reported are for head positioning at 54°, which
most closely represents sagittal plane neutral head posture.
b
Leggett et al. [38] measured static extension strength at eight positions (0°,18°,36°,54°,72°,96°,108°,126°) of cervical sagittal-plane range of motion (end-range extension - 0º, end-range exion - 126°.). P<0.05 for head positions at 36°,54°,72°,96°,108°,126°.
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 15 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
only three produced gains in peak isometric strength exceeding
the MDC95%threshold for clinical signicance in at least 75% of the
direction-specic measurements [39-41].
e specic eects of neck strength training on the kinematics of
the HN segment were evaluated in two studies [11,31]. e program
designed by Mansell et al. [11] produced a medium training eect
size on neck exor strength in males (Cohen’s d, 0.54) and large eect
sizes on neck exors and extensors strength in females (Cohen’s d,
1.16 to 1.83). In contrast, the program designed by Lisman et al. [31]
produced small training eects on neck strength in exion, extension
and bilateral side exion (Cohen’s d, 0.13 to 0.34). Based on within-
subject comparisons of the kinematics of the HN segment pre- and
post- strength training, neither small or large strength gains were
eective in increasing the resistive capacity of the HN segment to
externally applied forces. e data from Mansell et al. [11] shows
their program did yield a 14% to 48% lowering of the ratio of peak
angular acceleration of the head along the exion-extension plane
between ‘anticipated’ and ‘unanticipated’ conditions of external force
application. erefore, a component of their program did positively
inuence the short-latency anticipatory resistive capacity of the HN
segment.
Quality of the Research Evidence
e quality of the research evidence relating isometric neck
strength to concussion incidence and risk needs to be evaluated to
determine its application to clinical practice. e methodological
quality rating (MQR) scores from the PEDro scale and NOS are
reported in Tables 3, 5 and 6. e MQR scores could be calculated
for the strength training studies, and ranged between 6/10 and 8/10.
e main methodological limitations of these studies were non-
randomization of participants, with pre-dened allocation to control
and experimental groups due to low number of participants, inability
to conceal allocation to the experimental group from participants
and assessors, and use of within-subject pre-post assessment rather
than between-subject randomization. NOS scores for cohort and
case studies ranged between 6/9 and 9/9. Common limitations across
studies were low representation of the cohort population, lack of
non-exposed control and failure to control for potential confounding
variables in statistical models.
Interpretation of Current Evidence
e evidence relating neck strength to concussion incidence
in contact sports is very limited, with only one prospective study
reporting a small positive eect (Cohen’s d, 0.29) of total isometric
neck strength in lowering the incidence of concussion in high school
athletes [14]. Based on current evidence, inclusion of neck strength
training in the risk management for concussion in contact sports
cannot be judiciously recommended.
Research evaluating the eects of neck strength training
for concussion risk management is limited in both amount and
generalizability of ndings. Current evidence from prospective
studies is limited by the specic sex and age characteristics of the
study groups, with all three studies conducted with adolescent
and high-school athletes in whom neuromuscular coordination,
physiological cross sectional muscle area, and anthropometric ratio
of head-to-neck circumference may be markedly dierent than in
adults [14,27,28]. In a similar way, generalization of evidence relating
neck strength to the kinematics of the HN segment under controlled
lab-based conditions is inherently limited by reliance on comparative
analysis of neck strength between adult females and males [11,29]
or adults and youth athletes [13]. As an example, Mansell et al. [11]
reported a 29% lowering of the resistive capacity of the HN segment
Author (s) Direction of effort % Change
MDC %
(α=0.05,
CI95%)
%
Change>MDC95%
Isotonic resistance
Mansell et
al. [11] Flex (Male) 10 24 NO
Ext (Male) -10 23 NO
Flex (Females) 31 24 YES
Ext (Females) 28 34 NO
Lisman et al.
[31] Flex 3 23 NO
RSFlex 7 31 NO
Ext 7 20 NO
LSFlex 10 28 NO
Burnett et al.
[58] Flex 64 68 NO
RSFlex 49 53 NO
Ext 63 57 YES
LSFlex 53 58 NO
Pollock et al.
[59] Ext (DYN x1) 9 22 NO
Ext (DYN+ISO x1) 11 39 NO
Ext (DYN x 2) 17 36 NO
Ext (DYN+ISO x2) 14 56 NO
Taylor et al.
[39] Flex 46 53 NO
RSFlex 83 31 YES
Ext 72 52 YES
LSFlex 72 38 YES
Alricsson et
al. [60] Flex 10 14 NO
Ext 9 17 NO
Conley et al.
[40] Ext 34 9 YES
Elastic resistance
Burnett et al.
[58] Flex 41 63 NO
RSFlex 24 49 NO
Ext 30 54 NO
LSFlex 26 48 NO
Kramer et
al. [61] Flex 6 43 NO
Ext 0 15 NO
Rrot 5 21 NO
Lrot 16 21 NO
Isometric resistance
Portero et
al. [41] Lateral Flex 35 25 YES
Isokinetic resistance
Kramer et
al. [61] Flex 23 38 NO
Ext 625 NO
Rrot 11 20 NO
Lrot 13 28 NO
Table 7: Minimum detectable change of neck strengthening studies.
Note: Flex: Flexion; Ext: Extension; RSFlex: Right side exion; LSFlex: Left
side exion; Rrot: Right axial rotation; Lrot: Left axial rotation; DYN×1: Dynamic
strengthening, one session per week; DYN +ISO×1: Dynamic strengthening with
isometric strengthening, one session per week; DYN×2: Dynamic strengthening,
two sessions per week; DYN +ISO×2: Dynamic strengthening with isometric
strengthening, two sessions per week; MDC: Minimal Detectable Change
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 16 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
in adult females compared to males and used this between-group
dierence to infer attenuating eects of higher neck strength on the
peak magnitudes of the kinematic response of head to an externally
applied force. ese measured dierences, however, reect the
contribution of factors other than strength, including sex-specic
dierences in neuromuscular coordination and natural mechanics
of the HN segment, as for example higher head-to-neck ratio in
females [11,13,29,33,42]. Within-subject designs, using resistance
training to manipulate neck strength, should be adopted as a standard
to investigate the eects of neck strength on concussion risk. e
outcomes of the study by Mansell et al. [11] underline the importance
of within-subject designs. In this study, while between-subject
dierences in strength were related to dierences in post-impact
HN segments, a relationship between higher neck strength, resulting
from resistance training, and peak magnitudes of post-impact
HN kinematics could not be dened using within-subject analysis.
erefore, there is a need for multi-centered trials to evaluate the
association between neck strength and concussion risk and incidence
using within-subject designs in athletic populations of males and
females, both youth and adults, and across dierent contact sports.
Standards for measurement and analysis of neck strength should
be adopted to allow for systematic comparison of outcomes across
studies. In the eight studies appraised in our review, in which peak
isometric neck strength was included as an independent variable
in the analysis of concussion incidence and kinematics of the HN
segment, strength measures were obtained using a variety of methods:
hand-held dynamometry [11,27,29,30]; tensile scale [14]; and custom
or commercial xed-frame dynamometry [13,28,31]. Absence of
information regarding the sensitivity and reproducibility of strength
measures can lead to errors in interpretation of the outcomes. As an
example, from the strength data reported by Collins et al. [14], the
mean dierence in total strength between the concussed and non-
concussed athletes was calculated to be 1.7 lbs. e researchers used
a custom-designed tensile scale to quantify peak isometric neck
strength. e tension scale measurements were reported to correlate
well with a hand-held dynamometer (Pearsons r=0.83−0.94, P<0.05)
and demonstrated high inter-tester reliability between ve dierent
assessors. However, without providing information on the sensitivity
of their measurement method, it is not possible to determine if the
mean dierence of 1.7 lbs. lies outside the 95% condence interval of
the instrument’s measurement error and, therefore, if it is a clinically
meaningful dierence in strength. As a minimum, researchers need
to systematically include MDC95% cutos to allow their research
ndings to be meaningfully evaluated for practice. e positioning
of participants for strength measures also varied across assessment
protocols, with participants seated and fully restrained below the
neck [11,13,29], restrained at the pelvis [31], unrestrained in sitting
[14], and restrained and or unrestrained in prone and supine [27,28].
Dierences in test position would inuence the contribution of
other muscles to measured force variables of the neck, again possibly
leading to errors in interpretation of outcomes.
Adopting standards for identifying concussion incidence and risk
is also recommended. If concussion incidence is used as a primary
outcome to evaluate eects of neck strength in contact sports,
as in Collins et al.’s study, researchers should adhere to current
guidelines and provide a clear statement of assessment tools used
[43]. In a similar way, a standard set of kinematic variables should
be used to calculate concussion risk which is commonly used as a
primary outcome. In reviewed studies, kinematic variables used for
the calculation of concussion risk have included peak magnitudes
of linear and angular velocity and acceleration of the head, location
and duration of impact, as well as combinations of these variables
to calculate composite indices of head impact severity including the
HITsp, HIC, and the HIP [12,27,28,34,35]. Calculation of concussion
risk across these studies appears to be driven by availability of sensor
technology rather than by the validity of measures. Only one study was
identied in which measured variables of the post-impact kinematics
of the head were specically evaluated in relation to concussion
incidence [44]. Broglio et al. [44] used the HIT system to monitor
head impacts for seventy-eight high school football players over one
season. In total, 54,247 head impacts were analyzed, thirteen of which
resulted in a concussion. Using mixed design regression modeling,
the set of kinematic variables with the highest predictive value was
identied to be the combination of peak angular acceleration of the
head along the plane of axial rotation, peak linear acceleration of the
head, and location of impact to the front, top, or back of the head.
Research is needed to conrm the most appropriate set of kinematic
variables predictive of concussions and consistent use of composite
scores that incorporate this set of variables, allowing for comparison
across studies. As well, as most concussions in contact sports result
from forces transmitted to the HN segment by a hit to the body, novel
systems may need to be developed to reliably capture HN position
and motion without contact information, as well as to lower the
price to improve accessibility to systems to support increased use of
monitoring systems necessary to develop a large database for multi-
center research.
Of the twelve resistance strength training programs critically
appraised for their eectiveness in promoting increases in peak
isometric strength, only three applied the guidelines of the American
College of Sports Medicine (ACSM) for frequency, intensity, time
and type (i.e., the F.I.T.T. parameters) [45]. Eective parameters of
these programs included: training three to four times per week at a
loading intensity of 75% one repetition-maximum (1 RM) or 80%
of maximal isometric strength; and increasing the intensity when
participants could complete one or more dynamic repetitions beyond
the target number [39,40] or when there was an increase in maximal
isometric strength [41]. e training intensities used by Mansell et al.
[11] and Lisman et al. [31] were conservative by ACSM guidelines,
with training intensities of 41% to 53% 1 RM and 45% to 60% 1 RM,
respectively. In addition, these two training programs included two
training sessions per week and were four weeks shorter than the
programs of Taylor et al. [39] and Conley et al. [40]. e conservative
intensity of these protocols may not have maximized strength gains
which could explain, in part, the absence of an eect of strength
training on the resistive capacity of the HN segment. As a standard,
MDC95% values should be calculated to ascertain that reported
increases in strength with resistance training exceed the probability
of error in measurement. It may be that specic MDC95% cutos
should be established that would allow only meaningful gains in neck
muscle strength to be evaluated in terms of their potential benets in
lowering the odds for concussion in contact sports.
e ecological validity of using peak isometric strength as the
strength variable of interest in studies of concussion risk management
must be considered. Korhonen et al. [46] reported that it takes ≥ 400
ms to reach peak isometric force in skeletal muscles of the lower
extremities. Even with the shorter latencies predicted for neck muscles
[47], it is unlikely that athletes would have sucient time to develop
their maximum isometric strength in the short-latency required to
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 17 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
attenuate post-impact kinematics of the HN segment. However,
Almosnino et al. [47] did report that male athletes could develop 50%
of their maximal isometric neck strength in 135 to 148 ms. erefore,
facilitating the development of short-latency neck strength should be
a primary outcome of neck strength training programs for the risk
management of concussion. is recommendation is supported by
level 1b, 2b, 3b, and 4 evidence of small to large eects of short-latency
anticipatory neck in attenuating magnitudes of post-impact HN
kinematics and lowering the severity of head impacts [11,13,28,29,34-
37].
Facilitation of the short-latency rate of isometric force
development (RFD) was not specically addressed in any of the
strength training programs appraised. However, several studies
have reported signicant gains in RFD with resistance training for
skeletal muscles of the limbs [15,48-51]. RFD is a velocity-dependent
variable of muscle strength that reects the central activation drive
and the mechanics of muscle contraction [15,48]. erefore, training
programs that emphasize high-velocity muscle contractions (i.e.,
explosive contractions for plyometric movements) have been shown
to be eective in facilitating short-latency neuromuscular adaptations
to enhance RFD [52,53]. ese high-velocity contractions are
characterized by high motor neuron ring rates, high muscle force
production, and brief contraction times [15,49,54] which increase the
absolute magnitude of muscle tension developed in the early phases
of a muscle contraction [15,55,56]. Of importance with regards to
neck strengthening is that actual mechanical shortening of the muscle
is not necessary to elicit short-latency neuromuscular adaptations
of RFD; rather, it is the ‘intention’ to produce a high-velocity (or
ballistic) contraction that is the eective stimulus [54,55]. erefore,
isometric contractions performed with ballistic intent would be a safe
and appropriate strategy to rapidly increase anticipatory early-phase
isometric neck muscle strength along all planes of motion, including
axial rotation to increase short-latency anticipatory HN stiness. e
direct eects of training with ballistic intent contractions on short-
latency strength and muscle activation was evaluated through a 14-
week, high-intensity training strength program of the knee extensor
muscle group. e training stimulus used was 4 to 5 sets of heavy-
to-moderate training loads that ranged from 3 to 10 repetitions
maximum [15]. is training program yielded a 17% increase in peak
isometric knee extension torque (P<0.001) and a 26%, 22% and 17%
increase in RFD at time intervals of 0 to 30 ms, 0 to 50 ms, and 0 to
100 ms, respectively (P<0.05). ere was also an increase in the mean
level of activation of the quadriceps muscle group by 22% to 143%
(P<0.05) from 0 to 100 ms of force onset, and an increase of 41% and
106% from 0 to 75 ms (P<0.01).
e eects of strength training programs on RFD have yet to be
systematically investigated within the context of concussion incidence
and risk. In our scoping review, only two studies used measures of
RFD in their analysis of post-impact kinematics of the HN segment
[13,28]. In these studies, RFD was expressed as the maximum slope
of the force-time curve to peak muscle force and was reported to be
positively associated to increased resistive capacity of the HN segment
to controlled applications of external forces to the head [13] and to a
lowering of the odds of sustaining head impacts of moderate severity
during contact events in games [28]. A standard should be adapted to
report RFD measures for discrete time intervals of short-latency force
development (e.g., 0 to 25 ms, 0 to 50 ms, and 0 to 100 ms). Almosnino
et al. [47,57] demonstrated that short-latency variables of static neck
muscle strength could be reliably quantied using standardized
methods. With reliable measurement, the theorized protective eects
of RFD for concussion could be systematically evaluated.
Recommendations for Practice
Current evidence does not support a benet of resistance
training to increase peak isometric strength as a component of risk
management for concussion in contact sports. ere is evidence of
sucient level and quality to support further research to specically
evaluate the eects of RFD. At a minimum, RFD should be considered
in the evaluation of readiness for return-to-play. If resistance training
of the neck is used as a component of athlete preparation, programs
should integrate ballistic intent contractions within a motor
learning program that will facilitate recruitment of those muscles
that are optimally aligned to resist impact. To optimize outcomes,
this resistance training approach could be integrated into existing
isometric resistance programs with demonstrated eectiveness in
producing clinically meaningful changes in peak muscle strength,
as for example, the program by Portero et al. [41]. is eight-week
isometric strength training program in lateral side exion produced
a 35% increase in peak static strength in seven adult males, 24 to 30
years old, representing a large eect size of (Cohen’s d value, 2.10,
CI95%, 0.74 to 3.41). Any program of resistance training used should
adhere to ACSM guidelines.
Outcomes of the modeling study by Shewchenko et al. [33]
should be considered as a precaution in the design of resistance
training programs. Of specic importance are the predicted eects
of increasing the level of muscle activation on the anterior-posterior
shear and axial compression forces exerted on C0-C1. ere is value
and need for continued research using computational modeling
methods to systematically evaluate eects of modifying peak strength,
RFD, HN stiness, and neuromuscular control on the forces and
stability of the cervical spine as per Shewchenko et al.’s [33] approach.
e importance of adopting standardized methods for the
assessment and reporting of variables of neck strength cannot be
overlooked. As well, aordable methods need to be developed to
enhance our general capacity to instrument helmets to monitor head
impacts in contact sports. Combining standardized assessment with
monitoring into accessible databases would facilitate experimental
and computational research of this important topic in concussion
risk management.
Most important, any program should emphasis ‘sport-readiness’.
Sport intelligence and skill are principal factors that directly inuence
an athlete’s ability to avoid vulnerable positions or high-risk plays, and
to anticipate and prepare for an upcoming impact [35]. Education is
also important as athletes need to have knowledge of the specic risks
associated with sport participation. is was clearly underscored by
the ndings of Schmidt et al. [28] that linesmen in high school football
were at highest risk for sustaining moderate to severe head impacts,
even though they had the strongest necks when compared to other
player positions. Lastly, player attitude cannot be overlooked. Even
the highest level of preparation cannot lower the risk and incidence of
concussion for blindside hits to unsuspecting athletes [1]. is issue
of fair play and safe participation must be widely promoted in contact
sports. Players must be educated on their responsibilities in assuming
roles as both an ‘aggressor’, the player delivering the hit, as well as a
recipient of hits. Players should be required to develop skill to safely
assume both of these roles, including understanding the purpose of
body contact as part of the game being played, skill in delivering hits
Citation: Gilchrist I, Storr M, Chapman E, Pelland L (2015) Neck Muscle Strength Training in the Risk Management of Concussion in Contact Sports: Critical
Appraisal of Application to Practice. J Athl Enhancement 4:2.
Page 18 of 19
doi:http://dx.doi.org/10.4172/2324-9080.1000195
Volume 4 • Issue 2 • 1000195
that are both eective and safe, skill in maintaining awareness of risk
for body contact and how to safely receive a hit, and education on the
importance of reporting injuries immediately, including concussions.
Summary of Key Findings
Based on current evidence, strength training of the neck
musculature cannot be recommended as an eective strategy to
lower and incidence of concussion in contact sports. However, one
prospective study (level 1b evidence) has provided evidence that
higher absolute total isometric neck strength is a signicant predictor
of concussion incidence in contact sports in high-school athletes.
Higher short-latency isometric neck muscle tension, developed
prior to impact, can lower magnitudes of post-impact kinematics of
the head (level 1b, 2b, and 4 evidence). erefore, strength-training
programs that facilitate increased gains in short-latency rate of
isometric force development may be an important component of
neck strength training programs to lower the risk for concussion.
Isometric contractions performed with ballistic intent would
be an appropriate strategy to increase the short-latency isometric
response of the neck.
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Author Afliation Top
1School of Rehabilitation Therapy, Queen’s University, Kingston, Canada
2The Human Mobility Research Centre at Queen’s University and Kingston
General Hospital, Kingston, Canada
3Kingston General Hospital, Department of Pediatrics, Kingston, Canada
4BTE Technologies Inc., Milton, Ontario, Canada
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... However, the association between neck strength and head kinematics after purposeful headers is not well understood, and further research is required before considering specific neck and trunk strengthening programs as a risk reduction strategy (6,16,30,40). Increased neck strength facilitates increased coupling of the head and torso, thereby increasing effective mass and potentially decreasing head acceleration during and after head impacts (19,27). If this is the case, strength and conditioning professionals need to know how to best design targeted exercise programs as risk reduction measures. ...
... Another reason for the beneficial effects on strength and PLA outcomes in our trial, which are in contrast to results reported by Becker et al. (4) on a strengthening intervention in 20-year-old male soccer players, as well as in contrast to studies by Lisman et al. (25) and Mansell et al. (26) regarding PLA, could be the length of our training program. We implemented an intervention with a length of 14 weeks, as opposed to 6 weeks (4) or 8 weeks (25,26) in the above mentioned trials, which increases chances for neuromuscular adaptations that might help mitigating PLA (16). Finally, we suppose that our younger subjects probably had a greater potential for strength gains compared with 20-year-old male soccer players (4). ...
Article
Müller, C and Zentgraf, K. Neck and trunk strength training to mitigate head acceleration in youth soccer players. J Strength Cond Res XX(X): 000-000, 2020-Heading in soccer involves repetitive head accelerations that may be detrimental for brain health. One way to mitigate adverse effects may be to increase head-neck stabilization and thus reduce the kinematic response after intentional headers. This study aimed to (a) assess associations between neck strength and head kinematics and (b) evaluate an exercise intervention designed to increase strength and attenuate head acceleration during intentional heading in youth soccer players. In 22 athletes, we used accelerometers to assess associations between neck strength and peak linear acceleration (PLA). We attached the accelerometers to the occiput and sternum, allowing us to differentiate between total, trunk, and head PLA. Longitudinally, we evaluated the effects of a 14-week twice-weekly resistance training in a subsample of 14 athletes compared with regular soccer training (N 5 13). Results showed that female athletes had lower isolated neck strength (p # 0.004), lower functional neck strength (p # 0.017), and higher total PLA during purposeful headers compared with males (17.2 6 3.5 g and 13.0 6 2.3 g, respectively, at 9.6 m·s 21 ball velocity during impact; p 5 0.003). The intervention group showed moderate to large strength gains (h 2 p 5 0.16-0.42), resulting in lower PLA (total 22.4 g, trunk 20.8 g, and head 21.5 g) during headers. We conclude that a resistance training focusing on cervical and trunk musculature is practicable in youth soccer, elicits strength gains, and helps to mitigate PLA during purposeful heading. Results should encourage youth strength and conditioning professionals to incorporate neck exercises as a risk reduction strategy into their training routine.
... Rule changes [1,25], athlete technique amendment [25] and selected protective equipment [25] have been shown to mitigate the risk of injury (including incidence of head and neck injury) associated with athletic participation. Neck muscle training is another potential risk mitigating strategy [26,27]. ...
... All three studies had small sample sizes with 49, 37 and 36 participants, respectively [52][53][54]. Another possible explanation for these differences is that it may not be neck strength in and of itself which reduces injury risk, but rather the level of neck muscle activation and tension developed before a collision that may reduce linear and rotational acceleration of the head, thus reducing the risk of SRC [12,27,55]. The exercise interventions implemented by the studies included in this review may have been successful in reducing head and/or neck injury risk because they improved head-to-neck coupling and neck muscle activation through a multifaceted injury reduction program. ...
Article
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Background Sport-related head and neck injuries, including concussion, are a growing global public health concern with a need to explore injury risk reduction strategies such as neck exercises.Objectives To systematically review the literature to investigate: (1) the relationship between neck strength and sport-related head and neck injuries (including sport-related concussion (SRC); and (2) whether neck exercise programs can reduce the incidence of (a) sport-related head and neck injuries; and (b) SRC.Methods Five databases (Ovid MEDLINE, CINAHL, EMBASE, SPORTDiscus, and Web of Science) and research lists of included studies were searched using a combination of medical subject headings and keywords to locate original studies which reported the association between incidence of head and/or neck injury and neck strength data, or included a neck exercise intervention either in isolation or as part of a more comprehensive exercise program.ResultsFrom an initial search of 593 studies, six were included in this review. A narrative synthesis was performed due to the heterogeneity of the included studies. The results of two observational studies reported that higher neck strength, but not deep neck flexor endurance, is associated with a lower risk of sustaining a SRC. Four intervention studies demonstrated that injury reduction programs that included neck exercises can reduce the incidence of sport-related head and neck injuries including SRC.Conclusion Consideration should be given towards incorporating neck exercises into injury reduction exercise programs to reduce the incidence of sport-related head and neck injuries, including SRC.Systematic Review RegistrationPROSPERO (registration number: 194217).
... There is emerging theoretical and scientific evidence suggesting that higher neck strength is important for eliciting lower head accelerations (both linear and rotational accelerations) during purposeful heading in soccer. 1,3,6 While potentially important for all players, neck strengthening may be particularly beneficial for female and younger players, as these groups of players generally possess weaker neck muscles, smaller neck girth, and a lower effective mass when compared with adult male players. 1,6 The effective mass of a player is defined as the mass that is able to oppose acceleration of the head when performing a purposeful header; the higher the effective mass, the lower the acceleration of the head during heading. 1 Players can increase their effective mass by having strong, activated neck muscles, 1 with level 1b, 2b, and 4 evidence that higher short-latency isometric neck muscle tension, developed prior to impact, can lower postimpact kinematics of the head. ...
... 1,6 The effective mass of a player is defined as the mass that is able to oppose acceleration of the head when performing a purposeful header; the higher the effective mass, the lower the acceleration of the head during heading. 1 Players can increase their effective mass by having strong, activated neck muscles, 1 with level 1b, 2b, and 4 evidence that higher short-latency isometric neck muscle tension, developed prior to impact, can lower postimpact kinematics of the head. 3 This is particularly relevant in soccer, where heading is a fast, dynamic skill. United Soccer Coaches, the soccer coaches' association in the United States, have devised a number of sport-specific neck-strengthening exercises that can be integrated into a warm-up or strengthand-conditioning component of soccer training, 11 although further research is required to assess the program's shortand long-term effectiveness. ...
Article
Synopsis: Repeated purposeful heading in soccer has come under increased scrutiny as concerns surrounding the association with long-term neurodegenerative disorders in retired players continue to grow. Although a causal link between heading and brain health has not been established, the "precautionary principle" supports the notion that soccer governing bodies and associations should consider implementing pragmatic strategies that can reduce head impact during purposeful heading in youth soccer while this relationship is being investigated. This Viewpoint discusses the current evidence to support low-risk head impact reduction strategies during purposeful heading to protect young, developing players, and how such strategies could be implemented now while research and debate continue on this topic. J Orthop Sports Phys Ther 2020;50(8):415-417. doi:10.2519/jospt.2020.0608.
... Participants in the intervention group attended an average of Evaluating a Neuromuscular Neck Training Device 85% of the 14 training sessions (mean = 11.9; range = [11][12][13][14]. Of the 12 enrolled into the control group, 2 participants were lost to follow-up (1 missed posttesting and 1 was no longer on the team at the end of the study period). ...
... The aim of this training approach was to emphasize high-velocity muscle contractions and facilitate the short latency rate of force development, as described by Gilchrist et al. (11). This training approach is in line with the type of training, as suggested by prior researchers, that should be investigated as a means of training the neck to prevent concussion (11,16,17,24). ...
Article
Versteegh, TH, Dickey, JP, Emery, CA, Fischer, LK, MacDermid, JC, and Walton, DM. Evaluating the effects of a novel neuromuscular neck training device on multiplanar static and dynamic neck strength: A pilot study. J Strength Cond Res 34(2): 323-331, 2020-The neck serves an important function in damping the transference of acceleration forces between the head and the trunk, such as that occurring during contact sports or motor vehicle collisions. An inability to adequately dissipate forces has been proposed as a potential mechanism for clinical conditions such as whiplash or concussion, but current approaches to neck training may not be targeting the correct mechanisms. The purpose of this study was to explore the training effect of a novel neuromuscular strengthening protocol on dynamic and static neck strength. This was a quasiexperimental pilot study design with intervention (n = 8) and control (n = 10) groups. The intervention group was trained (twice/week, ∼10 minutes, for 7 weeks) on a training device that uses self-generated centripetal force to create a dynamic rotational resistance. This protocol is intended to target the ability of the neck muscles to perform coordinated multiplanar plyometric contractions. Both groups also continued with traditional neck strengthening that included training on a straight-plane, isotonic, 4-way neck machine. Performance on the training device showed improvement after routine practice within 1 week, as evidenced by a trend toward increased peak speed in revolutions per minute (RPM). After 7 weeks, peak RPM increased from 122.8 (95% confidence interval [CI], 91.3-154.4) to 252.3 (95% CI, 241.5-263.1). There was also a large positive effect size (Hedge's d, 0.68) in isometric composite (multiplane) neck strength favoring the intervention group over the control group (difference, 20 N; 95% CI, -8 to 48). The largest magnitude strength improvement in a single plane was in axial rotation and also favored the intervention group over the control group (Hedge's d, 1.24; difference, 46 N; 95% CI, 9-83). Future studies should explore whether the dynamic training presented here could help reduce the risk of sports concussion, whiplash, or other head-neck trauma.
... Their review shares similar aims with this review but is broader in its inclusion of head and neck injuries other than solely mTBI, addresses strengthening interventions specifically, and is narrower in its focus on only athletic populations. Other reviews on this topic have either not been systematic [32][33][34][35][36][37][38][39][40][41] or have had a more narrow scope than this review by limiting their search to either specific experimental paradigms [42,43] or specific physical neck characteristics [44]. To our knowledge, this review is the first systematic review to holistically assess physical characteristics of the head and neck and how they relate to mTBI risk in a broad range of settings. ...
Article
Full-text available
Background Investigators have proposed that various physical head and neck characteristics, such as neck strength and head and neck size, are associated with protection from mild traumatic brain injury (mTBI/concussion). Objectives To systematically review the literature and investigate potential relationships between physical head and neck characteristics and mTBI risk in athletic and military populations. Methods A comprehensive search of seven databases was conducted: MEDLINE, EMBASE, CINAHL, Scopus, SPORTDiscus, Cochrane Library, and Web of Science. Potential studies were systematically screened and reviewed. Studies on military and athletic cohorts were included if they assessed the relationship between physical head-neck characteristics and mTBI risk or proxy risk measures such as head impact kinematics. Results The systematic search yielded a total of 11,723 original records. From these, 22 studies met our inclusion criteria (10 longitudinal, 12 cross-sectional). Relevant to our PECO (Population, Exposure, Comparator, and Outcomes) question, exposures included mTBI incidence and head impact kinematics (acceleration, velocity, displacement) for impacts during sport play and training and in controlled laboratory conditions. Outcome characteristics included head and neck size (circumference, mass, length, ratios between these measures), neck strength and endurance, and rate of force development of neck muscles. Discussion We found mixed evidence for head and neck characteristics acting as risk factors for and protective factors against mTBI and increased susceptibility to head impacts. Head-neck strength and size variables were at times associated with protection against mTBI incidence and reduced impact kinematics (14/22 studies found one or more head-neck variable to be associated with protection); however, some studies did not find these relationships (8/22 studies found no significant associations or relationships). Interestingly, two studies found stronger and larger athletes were more at risk of sustaining high impacts during sport. Strength and size metrics may have some predictive power, but impact mitigation seems to be influenced by many other variables, such as behaviour, sex, and impact anticipation. A meta-analysis could not be performed due to heterogeneity in study design and reporting. Conclusion There is mixed evidence in the literature for the protective capacity of head and neck characteristics. We suggest field-based mTBI research in the future should include more dynamic anthropometric metrics, such as neck stiffness and response to perturbation. In addition, laboratory-based mTBI studies should aim to standardise design and reporting to help further uncover these complicated relationships.
... In addition, the aforementioned strength tests are performed under complete control, highlighting the need to examine the dynamic response to perturbations. Indeed, a review of 13 studies found that short-latency anticipatory strength, rather than peak isometric strength, attenuates postimpact head kinematics 24 and therefore should be assessed accordingly. Recent research by Nazarahari et al 25 used a custom-designed frame to measure head kinematics in response to controlled chest perturbations reliably. ...
Article
Full-text available
Context: Neck size and strength may be associated with head kinematics and concussion risks. However, there is a paucity of research examining neck strengthening and head kinematics in youths. Additionally, neck training is likely lacking in youth sport due to a perceived inadequacy of equipment or time. Objective: Examine neck training effects with minimal equipment on neck strength and head kinematics following chest perturbations in youth athletes. Design: Single group, pre-test-post-test case series. Setting: Athlete training center. Participants: Twenty-five (14 males, 11 females) youth soccer athletes (9.8±1.5 years) Intervention: 16 weeks of twice-weekly neck-focused resistance training utilizing bands, body weight, and manual resistance. Main Outcome Measures: Head kinematics (angular range of motion, peak anterior-posterior linear acceleration, and peak resultant linear acceleration) were measured by an inertial motion unit fixed to the apex of the head during torso perturbations. Neck flexion and extension strength were assessed using weights placed on the forehead and a plate-loaded neck harness, respectively. Neck length and circumference were measured via measuring tape. Results: Neck extension (increase in median values for all: +4.5 kg, +100%, p<0.001; females: +4.5 kg, +100%, p=0.002; males: +2.2 kg, +36%, p=0.003) and flexion (All: +3.6 kg, +114%, p<0.001; females: +3.6 kg, +114%, p=0.004; males: +3.6 kg, +114%, p=0.001) strength increased following the intervention. Males and females both experienced reduced perturbation-induced head pitch (All: -84%, p<0.001). However, peak resultant linear acceleration decreased in the female (-53%, p=0.004), but not male (-31%, p=1.0) subgroup. Pre-intervention peak resultant linear acceleration and extension strength (R2=0.21, p=0.033) were the closest-to-significance associations between head kinematics and strength. Conclusions: Young athletes can improve neck strength and reduce perturbation-induced head kinematics following a 16-week neck strengthening program. However, further research is needed to determine the effect of improved strength and head stabilization on concussion injury rates.
... Among a multitude of factors that may play a role in the causation and control of neck pain and injury, neck strength and muscle size have more demonstrable effects and are readily measurable. Studies have used dynamic impact simulations, static strength tests, and muscle measurements to explore relationships that can inform protective or interventional strategies (Collins et al., 2014;Eckner et al., 2014;Gilchrist et al., 2015;Hrysomallis, 2016;Schmidt et al., 2014). Evidence from laboratory research in this area has been consistently suggesting an inverse relationship between neck strength and head acceleration (Caccese et al., 2018;Gutierrez et al., 2014;Jin et al., 2017;Mansell et al., 2005). ...
Article
Neck muscle size and strength have been linked to lower injury risk and reduced pain. However, prior findings have been inconclusive and have failed to clarify whether there are sex differences in neck muscle size-strength relationships. Such differences may point to an underlying cause for the reported sex difference in neck pain prevalence. Thirty participants (13 males, 17 females) who underwent neck strength testing and MR imaging were analyzed. Strength was measured in three conditions that differed in posture and exertion direction. Muscle size was quantified by three metrics: anatomical cross-sectional area (ACSA), muscle volume (MV), and an estimate of physiological cross-sectional area—reconstruction-based cross-sectional area (RCSA). Inter-posture strength correlations, muscle size-strength correlations, and sex differences were analyzed with linear regression. Males were approximately 65% stronger and had significantly larger muscles. Strength varied significantly across postures, but only female strength values for different postures were significantly correlated. Observed in males only, the sternocleidomastoid (SCM) was a strong predictor of flexion strength in the neutral posture while the anterior scalene (AS) was more involved in the extended. No extensor’s size was significantly linked to extension strength. A greater amount of force variation is unexplained by muscle size alone in females than in males. Males and females exhibited distinct size-strength relationships, highlighting the need for sex-specific models and analyses and the greater potential effect of non-morphometric factors on force generating capacity in females. No advantage of one muscle size metric over another in strength prediction was evidenced.
... Additional research has attempted to review neck strength from alternative perspectives under controlled conditions. For example, one study [31] sought to examine the effect of the kinematic response of the head in controlled laboratory conditions. Kinematic studies are useful to determine responses but cannot provide support for a recommendation that strength training of the neck musculature is an effective strategy to mitigate against injury in contact sports. ...
Article
Full-text available
The objective of this systematic literature review was to evaluate the evidence regarding the development of neck strength in reducing concussion and cervical spine injuries in adult amateur and professional sport populations. PubMed, CINAHL, Science Direct, and Web of Science databases were searched systematically. The criteria for inclusion in the review were as follows: (1) a human adult (≥18 or above); (2) involved in amateur, semi-professional, or professional sports; (3) sports included involved collisions with other humans, apparatus or the environment; (4) interventions included pre- and post-neck muscle strength measures or neck stability measures; (5) outcomes included effects on increasing neck strength in participants and/or injury incidence. Database searches identified 2462 articles. Following title, abstract, and full paper screening, three papers were eligible for inclusion. All of the papers reported information from male participants, two were focused on rugby union, and one on American football. Two of the included studies found a significant improvement in isometric neck strength following intervention. None of the studies reported any impact of neck strengthening exercises on cervical spine injuries. This review has shown that there is currently a lack of evidence to support the use of neck strengthening interventions in reducing impact injury risk in adult populations who participate in sport.
Article
Synopsis: Repeated purposeful heading in soccer has come under increased scrutiny as concerns surrounding the association with long-term neurodegenerative disorders in retired players continues to grow. Whilst a causal link between heading and brain health has not been established, the 'Precautionary Principle' supports the notion that soccer governing bodies and associations should consider implementing pragmatic strategies, which can reduce head impact during purposeful heading in youth soccer whilst this relationship is being investigated. This viewpoint discusses the current evidence to support low-risk head impact reduction strategies during purposeful heading to protect young developing players; and how such strategies could be implemented now while research and debate continues on this topic. J Orthop Sports Phys Ther, Epub 22 May 2020. doi:10.2519/jospt.2020.9680.
Thesis
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Concussions have reached epidemic levels. There is no cure for concussions. Measures taken to reduce concussions have not been effective. The majority of research is focused on concussion causation and concussion management after the fact. The research continues but the number of concussions in athletics increases each year. No methodical approach to producing a specific protocol to strengthen the head and neck muscles exists and no systematic study of increase in neck musculature attributed to such a protocol is documented. Thus, this study will produce a standardized methodology for the reduction of concussive and subconcussive forces, laying the foundation for further research in this area. The research participants were healthy male and female college students, age range 18- 24. There were 30 participants. Of the 30 subjects used for this study, 18 participants were randomly assigned to the experimental group and 12 participants in the control group. The participants followed a protocol consisting of 13 movements designed to sequentially train the musculature of the head, neck and upper back. The duration of the study was 8 weeks. The strength increases were significant in the active participant group. The hypertrophy of the head and neck muscles was equally as significant and even more impressive in the male group. The females exhibited minimal muscle hypertrophy. Every active participant experienced strength increases during the eight week study; likewise each active male participant exhibited neck circumference increases. The control group experienced negligible strength or hypertrophy increases.
Article
Background and Purpose. Assessment of the quality of randomized controlled trials (RCTs) is common practice in systematic reviews. However, the reliability of data obtained with most quality assessment scales has not been established. This report describes 2 studies designed to investigate the reliability of data obtained with the Physiotherapy Evidence Database (PEDro) scale developed to rate the quality of RCTs evaluating physical therapist interventions. Method. In the first study, 11 raters independently rated 25 RCTs randomly selected from the PEDro database. In the second study, 2 raters rated 120 RCTs randomly selected from the PEDro database, and disagreements were resolved by a third rater; this generated a set of individual rater and consensus ratings. The process was repeated by independent raters to create a second set of individual and consensus ratings. Reliability of ratings of PEDro scale items was calculated using multirater kappas, and reliability of the total (summed) score was calculated using intraclass correlation coefficients (ICC [1,1]). Results. The kappa value for each of the 11 items ranged from .36 to .80 for individual assessors and from .50 to .79 for consensus ratings generated by groups of 2 or 3 raters. The ICC for the total score was .56 (95% confidence interval=.47–.65) for ratings by individuals, and the ICC for consensus ratings was .68 (95% confidence interval=.57–.76). Discussion and Conclusion. The reliability of ratings of PEDro scale items varied from “fair” to “substantial,” and the reliability of the total PEDro score was “fair” to “good.”
Book
Developed by the American College of Sports Medicine, this text offers a comprehensive introduction to the basics of strength training and conditioning based on the latest research findings. ACSM's Foundations of Strength Training and Conditioning is divided into four parts: Foundations, Physiological Responses and Adaptations, Strength Training and Conditioning Program Design, and Assessment. The text focuses on practical applications, enabling students to develop, implement, and assess the results of training programs that are designed to optimize strength, power, and athletic performance. Moreover, the text's clear, straightforward writing style makes it easy to grasp new concepts. © 2012 by American College of Sports Medicine. All rights reserved.
Article
One effect of rising health care costs has been to raise the profile of studies that evaluate care and create a systematic evidence base for therapies and, by extension, for health policies. All clinical trials and evaluative studies require instruments to monitor the outcomes of care in terms of quality of life, disability, pain, mental health, or general well-being. Many measurement tools have been developed, and choosing among them is difficult. This book provides comparative reviews of the quality of leading health measurement instruments and a technical and historical introduction to the field of health measurement, and discusses future directions in the field. This edition reviews over 100 scales, presented in chapters covering physical disability, psychological well-being, anxiety, depression, mental status testing, social health, pain measurement, and quality of life. An introductory chapter describes the theoretical and methodological development of health measures, while a final chapter reviews the current status of the field, indicating areas in which further development is required. Each chapter includes a tabular comparison of the quality of the instruments reviewed, followed by a detailed description of each instrument, covering its purpose and conceptual basis, its reliability and validity, alternative versions and, where possible, a copy of the scale itself. To ensure accuracy, each review has been approved by the original author of each instrument or by an acknowledged expert.
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There has been a remarkable increase in the past 10 years in the awareness of concussion in the sports and recreation communities. Just as sport participants,their families, coaches, trainers, and sports organizations now know more aboutconcussions, health care professionals are also better prepared to diagnose andmanage concussions. As has been stated in the formal articles in this specialissue on sport-related concussion, education about concussion is one of the mostimportant aspects of concussion prevention, with the others being data collection,program evaluation, improved engineering, and introduction and enforcement ofrules. Unfortunately, the incidence of concussion appears to be rising in manysports and thus, additional sports-specific strategies are required to reduce theincidence, short-term effects, and long term consequences of concussion. Enhancededucational strategies are required to ensure that individual participants, sportsorganizations, and health care professionals recognize concussions and managethem profciently according to internationally recognized guidelines. Therefore,this paper serves as a "brief report" on a few important aspects of concussioneducation and prevention.
Article
Background: An athlete is thought to reduce head acceleration after impact by contracting the cervical musculature, which increases the effective mass of the head. Purpose: To compare the odds of sustaining higher magnitude in-season head impacts between athletes with higher and lower preseason performance on cervical muscle characteristics. Study design: Cohort study; Level of evidence, 2. Methods: Forty-nine high school and collegiate American football players completed a preseason cervical testing protocol that included measures of cervical isometric strength, muscle size, and response to cervical perturbation. Head impact biomechanics were captured for each player using the Head Impact Telemetry System. A median split was used to categorize players as either high or low performers for each of the following outcome measures: isometric strength (peak torque, rate of torque development), muscle size (cross-sectional area), and response to cervical perturbation (stiffness, angular displacement, muscle onset latency). The odds of sustaining moderate and severe head impacts were computed against the reference odds of sustaining mild head impacts across cervical characteristic categorizations. Results: Linemen with stronger lateral flexors and composite cervical strength had about 1.75 times' increased odds of sustaining moderate linear head impacts rather than mild impacts compared with weaker linemen. Players who developed extensor torque more quickly had 2 times the increased odds of sustaining severe linear head impacts (odds ratio [OR], 2.10; 95% CI, 1.08-4.05) rather than mild head impacts. However, players with greater cervical stiffness had reduced odds of sustaining both moderate (OR, 0.77; 95% CI, 0.61-0.96) and severe (OR, 0.64; 95% CI, 0.46-0.89) head impacts compared with players with less cervical stiffness. Conclusion: The study findings showed that greater cervical stiffness and less angular displacement after perturbation reduced the odds of sustaining higher magnitude head impacts; however, the findings did not show that players with stronger and larger neck muscles mitigate head impact severity.
Article
As the number of high school students participating in athletics continues to increase, so will the number of sports-related concussions unless effective concussion prevention programs are developed. We sought to develop and validate a cost-effective tool to measure neck strength in a high school setting, conduct a feasibility study to determine if the developed tool could be reliably applied by certified athletic trainers (ATs) in a high school setting, and conduct a pilot study to determine if anthropometric measurements captured by ATs can predict concussion risk. In the study's first phase, 16 adult subjects underwent repeated neck strength testing by a group of five ATs to validate the developed hand-held tension scale, a cost effective alternative to a hand-held dynamometer. In the second phase, during the 2010 and 2011 academic years, ATs from 51 high schools in 25 states captured pre-season anthropometric measurements for 6,704 high school athletes in boys' and girls' soccer, basketball, and lacrosse, as well as reported concussion incidence and athletic exposure data. We found high correlations between neck strength measurements taken with the developed tool and a hand-held dynamometer and the measurements taken by five ATs. Smaller mean neck circumference, smaller mean neck to head circumference ratio, and weaker mean overall neck strength were significantly associated with concussion. Overall neck strength (p < 0.001), gender (p < 0.001), and sport (p = 0.007) were significant predictors of concussions in unadjusted models. After adjusting for gender and sport, overall neck strength remained a significant predictor of concussion (p = 0.004). For every one pound increase in neck strength, odds of concussion decreased by 5 % (OR = 0.95, 95 % CI 0.92-0.98). We conclude that identifying differences in overall neck strength may be useful in developing a screening tool to determine which high school athletes are at higher risk of concussion. Once identified, these athletes could be targeted for concussion prevention programs.