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Muscular strength in male adolescents and premature death: Cohort study of one million participants

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To explore the extent to which muscular strength in adolescence is associated with all cause and cause specific premature mortality (<55 years). Prospective cohort study. Sweden. 1 142 599 Swedish male adolescents aged 16-19 years were followed over a period of 24 years. Baseline examinations included knee extension, handgrip, and elbow flexion strength tests, as well as measures of diastolic and systolic blood pressure and body mass index. Cox regression was used to estimate hazard ratios for mortality according to muscular strength categories (tenths). During a median follow-up period of 24 years, 26 145 participants died. Suicide was a more frequent cause of death in young adulthood (22.3%) than was cardiovascular diseases (7.8%) or cancer (14.9%). High muscular strength in adolescence, as assessed by knee extension and handgrip tests, was associated with a 20-35% lower risk of premature mortality due to any cause or cardiovascular disease, independently of body mass index or blood pressure; no association was observed with mortality due to cancer. Stronger adolescents had a 20-30% lower risk of death from suicide and were 15-65% less likely to have any psychiatric diagnosis (such as schizophrenia and mood disorders). Adolescents in the lowest tenth of muscular strength showed by far the highest risk of mortality for different causes. All cause mortality rates (per 100 000 person years) ranged between 122.3 and 86.9 for the weakest and strongest adolescents; corresponding figures were 9.5 and 5.6 for mortality due to cardiovascular diseases and 24.6 and 16.9 for mortality due to suicide. Low muscular strength in adolescents is an emerging risk factor for major causes of death in young adulthood, such as suicide and cardiovascular diseases. The effect size observed for all cause mortality was equivalent to that for well established risk factors such as elevated body mass index or blood pressure.
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Muscular strength in male adolescents and premature
death: cohort study of one million participants
OPEN ACCESS
Francisco B Ortega research associate
1 2 3
, Karri Silventoinen research associate
4
, Per Tynelius
statistician
5
, Finn Rasmussen professor
5
1
Department of Physical Education and Sport, School of Sport Sciences, University of Granada, Granada, Spain;
2
Department of Biosciences and
Nutrition at NOVUM, Karolinska Institutet, Huddinge, Stockholm, Sweden;
3
Department of Medical Physiology, School of Medicine, University of
Granada;
4
Population Research Unit, Department of Social Research, University of Helsinki, Helsinki, Finland;
5
Child and Adolescent Public Health
Epidemiology Group, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden
Abstract
Objectives To explore the extent to which muscular strength in
adolescence is associated with all cause and cause specific premature
mortality (<55 years).
Design Prospective cohort study.
Setting Sweden.
Participants 1 142 599 Swedish male adolescents aged 16-19 years
were followed over a period of 24 years.
Main outcome measures Baseline examinations included knee
extension, handgrip, and elbow flexion strength tests, as well as
measures of diastolic and systolic blood pressure and body mass index.
Cox regression was used to estimate hazard ratios for mortality according
to muscular strength categories (tenths).
Results During a median follow-up period of 24 years, 26 145
participants died. Suicide was a more frequent cause of death in young
adulthood (22.3%) than was cardiovascular diseases (7.8%) or cancer
(14.9%). High muscular strength in adolescence, as assessed by knee
extension and handgrip tests, was associated with a 20-35% lower risk
of premature mortality due to any cause or cardiovascular disease,
independently of body mass index or blood pressure; no association
was observed with mortality due to cancer. Stronger adolescents had a
20-30% lower risk of death from suicide and were 15-65% less likely to
have any psychiatric diagnosis (such as schizophrenia and mood
disorders). Adolescents in the lowest tenth of muscular strength showed
by far the highest risk of mortality for different causes. All cause mortality
rates (per 100 000 person years) ranged between 122.3 and 86.9 for
the weakest and strongest adolescents; corresponding figures were 9.5
and 5.6 for mortality due to cardiovascular diseases and 24.6 and 16.9
for mortality due to suicide.
Conclusions Low muscular strength in adolescents is an emerging risk
factor for major causes of death in young adulthood, such as suicide
and cardiovascular diseases. The effect size observed for all cause
mortality was equivalent to that for well established risk factors such as
elevated body mass index or blood pressure.
Introduction
Knowledge about different risk factors at early stages of life for
later premature mortality is needed for disease prevention and
early treatment. In addition to traditional risk factors, such as
obesity and hypertension, a low cardiorespiratory fitness level
during middle or older ages has been proposed as a powerful
predictor of mortality.
1 2
Another important health related
component of fitness is muscular strength, which has been
shown to be positively related to cardiorespiratory fitness.
3
Although muscular strength has received far less attention than
cardiorespiratory fitness, recent studies support the hypothesis
that low muscular strength in adulthood also predicts all cause
mortality, as well as mortality due to cardiovascular disease and
cancer in healthy and diseased people.
4-13
Whether muscular
strength in childhood, adolescence, or both is a predictor of
mortality is unknown. Mortality rates in young adulthood are
very low in developed counties; consequently, large samples
sizes and long follow-up periods are needed to accumulate
enough cases to ensure appropriate statistical power in the
analyses.
Suicide is the leading cause of death in young adults (25-44
years old) and a major public health concern in developed and
developing countries.
14 15
Identification of early modifiable risk
factors for suicide is therefore important for the design of
successful strategies for suicide prevention.
In this study, we followed up more than one million male
adolescents (16-19 years of age) recruited from the Swedish
military conscription register to explore the extent to which
Correspondence to: F Rasmussen Finn.Rasmussen@ki.se
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Research
RESEARCH
muscular strength in adolescence is associated with all cause
premature mortality (defined as death before 55 years of age),
as well as cause specific premature mortality due to
cardiovascular disease (coronary heart disease and stroke) and
cancer. A second major aim was to study muscular strength in
relation to mortality due to suicide. To obtain meaningful
information about the clinical relevance of our results, we
compared the effect sizes observed for associations between
muscular strength and premature mortality with those for
traditional disease risk factors such as body mass index and
blood pressure.
16-18
The associations of body mass index and
blood pressure with mortality have previously been examined
in depth in this population,
17 18
and they are included in this
study only for comparison purposes.
Methods
Study sample and design
We used data from the Swedish military conscription register
for male adolescents born in Sweden between 1951 and 1976,
according to the multi-generation register.
19 20
Conscription
examinations are mandatory by law for all young male Swedish
citizens, and they predate active military service; that is, they
are also done for boys who do not later enter military service.
21
During the years covered by this study, only boys with severe
handicap or a chronic disease were exempted from the
conscription. A total of 1 194 359 participants with valid data
on age at conscription were available. Inclusion criteria were
age 19 years or less (98.4% of the original sample) and
availability of valid data on the main exposures (three strength
tests, body mass index, and blood pressure), main confounders
(year of birth, conscription age, conscription office), and main
study outcomes (mortality). We defined premature death as
death before the age of 55 years, following criteria used in
previous studies on premature death.
16
The entire study sample
met these criteria. To minimise the risk of reverse causality, we
excluded participants with less than one year of follow-up from
the analyses (n=985).
13 22
Finally, we excluded those with
extreme values for height (valid range 150-210 cm), weight
(valid range 40-150 kg), body mass index (valid range 15-60),
or diastolic and systolic blood pressure (valid ranges 40-100
mm Hg and 100-180 mm Hg) (n=1669). A total of 1 142 599
male adolescents (95.8% of the sample) aged 16 to 19 years
(mean age 18.3 (SD 0.5) years) met all the aforementioned
criteria and were therefore included in main analyses (see
appendix fig A). The Centers for Disease Control and Prevention
defines the age range for adolescence as 10-19 years.
Accordingly, the baseline period studied here is considered late
adolescence.
Baseline examination
During the conscription (baseline) examination, knee extension
strength, handgrip strength, elbow flexion strength, diastolic
and systolic blood pressure, and height and weight were
measured, as previously described.
18 23
These muscular strength
tests have been shown to have high reliability in young men
(r=0.88-0.98).
24
The Swedish Defence Recruitment Agency
regarded the exact measurement protocol to be confidential
information and did not reveal it to us. However, we observed
in preliminary analyses that no systematic differences existed
in the mean values of the measures between conscription offices,
suggesting that a uniform protocol was used. The values of
elbow flexion, handgrip, and knee extension strength in these
data were similar to values in a previous study of young Finnish
men, supporting the notion that standard protocols were used.
24
We calculated body mass index as weight (kg) divided by
squared height (m). Parental socioeconomic position in
childhood came from population and housing censuses 1960-80
and parental level of education from the 1970 census. We
retrieved participants’ own highest achieved educational level
from the educational register 1990-2004 (see sample sizes and
study categories in appendix table A).
25
Follow-up and ascertainment of mortality
We calculated the follow-up period as from the age of
conscription until the earliest of three possible events: death,
date of emigration, or end of follow-up (31 December 2006),
whichever came first. The median follow-up period was 24.2
(range 1.0-37.3) years.
We used the cause of death register,
26
and we categorised the
underlying cause of death according to the eighth, ninth, and
tenth revisions of the Swedish version of the international
classification of diseases as coronary heart disease (410-414 for
ICD-8 and ICD-9; I20-I25 for ICD-10), stroke (430-438, 344
for ICD-8, 430-438, 342, 344 for ICD-9; I60-I66, G45 for
ICD-10), cancer (140-239 for ICD-8 and ICD-9; C00-D48 for
ICD-10), suicide (E950-E959, E980-E989 for ICD-8 and ICD-9;
X60-X64, Y10-Y34 for ICD-10), and non-intentional accidents
(800-929 for ICD-8 and ICD-9; V01-X59 for ICD-10), as
previously described.
18 25 27-29
Information about causes of death
was available until 31 December 2004.
Statistical analysis
We used Cox proportional hazards regression to estimate hazard
ratios and 95% confidence intervals for mortality according to
exposure categories (tenths) of the three muscular strength tests
separately. We did similar analyses for body mass index and
blood pressure. We set the lowest tenth for muscular strength
variables and the highest tenth for body mass index and blood
pressure as reference groups, so that the hazard ratios would
mostly range between 0 and 1 for all the exposures, allowing
easier comparison among exposures. The main outcomes were
all cause mortality and mortality due to cardiovascular disease,
cancer, and suicide. We adjusted all the models for year of birth,
conscription age, and conscription office. Additionally, we used
adjusted models for simultaneous analysis of significant
predictors—that is, muscular strength (knee extension, handgrip,
or elbow flexion), body mass index, and blood pressure
(diastolic or systolic). We used SPSS statistical software, version
19.0.0, for all statistical analyses.
Results
Appendix table A shows baseline characteristics of the whole
study cohort, and appendix table B shows body mass index and
blood pressure stratified by categories of muscular strength.
Appendix fig B shows the distribution of muscular strength
variables. Over the follow-up period (24.2 years), 26 145 (2.3%)
participants died. Information on underlying causes of death
was available for 22 883 participants. Among these 22 883
deaths, 1254 (5.5%) were caused by coronary heart disease, 526
(2.3%) by stroke, 3425 (14.9%) by any type of cancer, 5100
(22.3%) by suicide, and 5921 (25.9%) by non-intentional
accidents. We categorised the remaining deaths (6657; 29.1%)
as other causes of mortality. A combination of coronary heart
disease and strokes (that is, cardiovascular disease) resulted in
1780 (7.8%) deaths. Figures 1, 2, 3, and 4 show hazard
ratios and 95% confidence intervals for all cause mortality and
mortality due to cardiovascular disease, suicide, and cancer.
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RESEARCH
All cause mortality
Higher levels of muscular strength were significantly associated
with lower risk of all cause mortality. The association was
stronger for knee extension and handgrip strength than for elbow
flexion strength (fig 1). Compared with the weakest group
(first tenth), higher levels (second, third, and fourth tenths) of
muscular strength were monotonically associated with
progressively reduced mortality risk. From the fourth tenth on,
a plateau was achieved, with an approximate 20% risk reduction
for premature mortality for knee extension and handgrip—that
is, hazard ratios ranged from 0.78 to 0.84 and confidence
intervals from 0.74 to 0.88. We saw a similar effect size (~20%
risk reduction) for body mass index and diastolic blood pressure,
whereas the effect of systolic blood pressure was weaker than
that of diastolic blood pressure (fig 1). Mutually adjusted
analyses showed that muscular strength (knee extension or
handgrip), body mass index, and diastolic blood pressure were
independently associated with premature all cause death (fig
5). Analyses stratified by body mass index categories showed
that muscular strength was inversely associated with all cause
mortality within all body mass index categories—that is,
underweight, normal weight, overweight, and obese adolescents
(fig 6). All cause mortality rates per 100 000 person years were
122.3 for adolescents with very low muscular strength, 98.9 for
those with low to middle muscular strength, and 86.9 for those
with and middle to very high muscular strength, as measured
by the knee extension test (appendix table C). The corresponding
rates for handgrip muscular strength were 114.5, 96.5, and 90.9
(appendix table C).
Cardiovascular disease mortality
Body mass index and blood pressure (both diastolic and systolic)
were strongly associated with premature mortality due to
cardiovascular disease (fig 2). Muscular strength was not
clearly associated with premature mortality due to cardiovascular
disease in Cox models adjusted only for year of birth, age at
conscription, and conscription office (fig 2), but it became
significantly associated with cardiovascular disease mortality
after additional adjustments for body mass index and diastolic
blood pressure (see knee extension and handgrip strength in fig
5). The risk reduction was approximately 35% in high muscular
strength groups, 60-70% in low body mass index groups, and
35-45% in low diastolic blood pressure groups, compared with
the reference groups. We saw similar patterns when we did the
analyses separately for coronary heart disease and stroke (data
not shown). Mortality rates per 100 000 person years due to
cardiovascular disease were 9.5 for adolescents with very low
muscular strength, 7.3 for those with low to middle muscular
strength, and 5.6 for those with middle to very high muscular
strength, as measured by the knee extension test (appendix table
C). The corresponding rates for handgrip muscular strength
were 8.3, 7.3, and 5.6 (appendix table C).
Suicide mortality
High muscular strength (knee extension and handgrip) was
associated with a 20-30% lower risk of death from suicide (fig
3). We found a monotone and inverse association between
body mass index and mortality due to suicide, whereas no clear
association was apparent between systolic and diastolic blood
pressure and suicide, as previously reported by our group.
30
The
results persisted in the fully adjusted model (fig 5). Mortality
rates per 100 000 person years due to suicide were 24.6 for
adolescents with very low muscular strength, 20.3 for those
with low to middle muscular strength, and 16.9 for those with
middle to very high muscular strength, as measured by the knee
extension test (appendix table C). The corresponding rates for
handgrip muscular strength were 22.4, 19.7, and 17.9 (appendix
table C).
Cancer mortality
Body mass index was the only significant predictor of premature
mortality due to cancer (fig 4), with a risk reduction of 25-35%
in participants with low body mass index compared with those
with high body mass index. The results persisted after mutual
adjustment for the other exposures (appendix fig E).
Additional analyses
Appendix figures C and D show hazard ratios for mortality due
to non-intentional accidents or other causes, to provide the full
spectrum of cause specific mortality, but we do not discuss this
further, as it is outside the scope of this study. In exploratory
analyses, we observed that adolescents with a higher muscular
strength level were 15-65% less likely to have any psychiatric
diagnosis (that is, schizophrenia, other non-affective psychosis,
mood disorders, neurotic and somatoform disorders, adjustment
disorders, personality disorders, or alcohol related disorders,
according to ICD-8/ICD-9 or ICD-10, as previously described
31
)
at baseline (cross sectional association) and years later
(longitudinal association) (see appendix fig F). We did this
analysis after excluding participants with a psychiatric diagnosis
before conscription. When we additionally adjusted the
association between muscular strength and mortality due to
suicide for psychiatric diagnoses either at baseline or years later,
the association was attenuated and became non-significant (data
not shown). Overall, little or no effect was apparent after further
adjustment for socioeconomic factors (data not shown).
Discussion
Three major findings relevant for clinical practice and public
health monitoring emerged from this prospective study. Firstly,
muscular strength in adolescence, as assessed by handgrip and
knee extension tests, is strongly associated with premature death
from any cause, independently of body mass index or diastolic
blood pressure. The effect sizes of these associations are similar
to those of classic risk factors such as body mass index and
blood pressure. Secondly, muscular strength is also associated
with premature death from cardiovascular disease, independently
of body mass index and blood pressure. Thirdly, stronger
adolescents have a lower risk of mortality due to suicide,
whereas no association is apparent with mortality due to cancer.
After doing several systematic reviews and validation studies
(as part of the ALPHA project: www.thealphaproject.net), we
concluded that the handgrip test and tests of lower body muscle
strength (jump tests, leg extension) are the most reliable, valid,
and health related muscular strength tests.
32
This could at least
partially explain why the associations were stronger for handgrip
and knee extension strength than for elbow flexion strength.
All cause mortality and cardiovascular
disease mortality
Previous studies in adults or older adults have supported an
association between muscular fitness and all cause mortality,
cardiovascular disease mortality, or both.
4-13
Our study provides
new evidence for the importance of muscular strength in
adolescence as predictor of premature mortality due to any cause
or cardiovascular disease. In addition, our results suggest that
the lowest tenth of population distribution of muscular strength
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RESEARCH
in late adolescence has the greatest risk of all cause mortality
in late life. Higher levels of strength are associated with
additional risk reduction, and the risk reduction levels off close
to the median (fourth to fifth tenths). This indicates that people
with a muscular strength level equal to or higher than the
population average have the same 20% risk reduction in all
cause mortality, suggesting the need to target those with very
low strength. Likewise, results from other cohort studies have
reported similar reductions in the risk of mortality in men with
middle versus high muscular strength,
11
suggesting that having
high levels of muscular strength does not provide additional
“protection” against death compared with middle levels of
muscular strength. The findings of this study also suggest that
muscular strength in adolescence is as important as body mass
index or blood pressure in terms of all cause mortality, whereas
body mass index has a greater role than muscular strength or
blood pressure in terms of mortality due to cardiovascular
disease.
Suicide mortality
Unfortunately, we cannot discuss our results in relation to
previous literature, as we have not found studies examining the
association between muscular strength and suicide or between
muscular strength and later psychiatric diagnosis. A few
investigations, however, have focused on another component
of physical fitness (that is, cardiorespiratory fitness) and suggest
that high cardiorespiratory fitness in adulthood predicts a lower
risk of depression, both in cross sectional and longitudinal
studies.
33 34
Likewise, adolescents with a lower cardiorespiratory
fitness level are more likely to have a diagnosis of psychosis or
schizophrenia.
35-37
Taken together, these findings support a link
between cardiorespiratory fitness and mental health, which could
in turn be related to suicidal behaviour.
In addition, we observed that adolescents with a higher muscular
strength were less likely to have a psychiatric diagnosis at
baseline and years later, which seemed to partly explain the
lower risk of premature mortality due to suicide seen in this
study. These findings suggest that physically weaker people
might be more mentally vulnerable. Outlining a biological
explanation for this association that could be reproduced in
other studies is difficult. Reverse causation might partially
explain this association. People with more mental problems
(such as depression or schizophrenia) might be less likely to
become involved in any social activity, including physical
activities, which in turn would result in decreased physical
fitness and lower muscular strength due to inactivity. On the
other hand, depression and many other psychiatric disorders are
highly related with a poor self concept and self esteem.
38-41
Likewise, low physical fitness in general, and low muscular
fitness in particular, has been found to be closely related to
lower self concept/self esteem.
42
Therefore, we could reasonably
hypothesise that people with a very low muscular fitness have
a worse self concept/self esteem, which may put them at higher
risk of psychiatric disorders and suicide. This hypothesis is
supported by several studies.
43 44
Cancer mortality
The available literature is contradictory with respect to mortality
due to cancer. Although some authors have observed an
association between muscular strength and mortality due to
cancer,
6 11
others have found no association.
5 10
Muscular strength
was not associated with premature cancer mortality in our study.
The large sample size in this study, and the resulting high
statistical power of the analyses, strengthens the confidence in
the null hypothesis (that is, no association between muscular
strength and mortality due to cancer).
Limitations
This study is based on conscription data from 1969-94, and no
information is available for female adolescents during this time
period. Although some studies have observed significant effects
in both men and women,
7
most of available literature seems to
supports the notion that low muscular strength might be a
stronger predictor of mortality in men than in women.
4-6 10
This
study is based on muscular strength of male adolescents and
premature mortality among those who came to the conscription
examination; we cannot know to what extent our findings apply
to other populations. Unfortunately, cardiorespiratory fitness
and physical activity data were not available, so we were unable
to examine whether muscular strength is associated with
premature mortality independently of these two factors.
Nevertheless, several studies in adults and elderly people have
reported that muscular strength is associated with mortality after
adjustment for cardiorespiratory fitness or physical activity,
7 11 13
suggesting that this might also be the case among adolescents.
Strengths
We followed more than one million male adolescents for 24
years. The large sample size and high statistical power allowed
us to study cause specific mortality over the whole range of the
distribution of muscular strength. To our best knowledge, this
is the first study that links muscular strength assessed in an
adolescent population with all cause and cause specific mortality
many years later. Only a small study in female adolescents aged
17 years (n=510) has linked cardiorespiratory fitness (the most
studied fitness component) in early ages to all cause mortality.
45
The inverse association between muscular strength and mortality
due to suicide is a novel finding. Availability of information
about psychiatric diagnoses from the conscription examination
and also from psychiatric inpatient care during many years of
follow-up allowed cross sectional and longitudinal analyses,
which shed further light on the association between muscular
strength and mortality due to suicide. Thanks to these data, we
found that the association between muscular strength and
mortality due to suicide seems to be partly mediated by
psychiatric disorders.
Clinical and public health implications
Although several tests of muscular strength are available, the
strongest evidence in relation to mortality has been reported for
the handgrip strength test.
4-10 12
As handgrip strength can be
assessed with good reliability in almost any place without
additional costly equipment, it is a useful tool for clinical
settings and for preventive services in schools and workplaces,
for example. The study of premature mortality is of special
relevance as a result of many years of life lost and also large
productivity losses at the societal level. Although this study
cannot disentangle causal pathways, physical training from
childhood and adolescence seems to be needed. People at
increased risk of long term mortality, because of lower muscular
strength, should be encouraged to engage in exercise
programmes and other forms of physical activity. In appendix
tables D and E, we propose reference values and “healthy”
muscular fitness zones based on the results of this study and
reference values of European adolescents from the HELENA
study.
46
However, we acknowledge that these reference values
are tentative and that further research in younger adolescents
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RESEARCH
and female adolescents is needed before firm conclusions can
be drawn.
Conclusions
This study provides strong evidence that a low level of muscular
strength in late adolescence, as measured by knee extension and
handgrip strength tests, is associated with all cause premature
mortality to a similar extent as classic risk factors such as body
mass index or blood pressure. Muscular strength is also
associated with premature mortality due to cardiovascular
disease but not that due to cancer. Finally, our data suggest that
low muscular strength is associated with an increased risk of
mortality due to suicide, supporting the notion that physically
weaker people might also be mentally more vulnerable. Low
muscular strength should be considered an emerging risk factor
for major causes of death in young adulthood.
We are grateful to Jonatan R Ruiz, Manuel J Castillo, Michael Sjöström,
and Steven Blair’s group for constructive scientific discussions. We are
also indebted to Charlotte Goodrose-Flores for the English revision.
Contributors: FR was responsible for the concept and design of the
study. FR and PT acquired the data. PT created the dataset, and FBO
did the statistical analysis and prepared the first draft of the manuscript.
All authors were involved in further analysis and interpretation of data,
drafting the manuscript, and critical revision of the manuscript for
important intellectual content. They are all guarantors.
Funding: The study was supported by a grant to FR from the Swedish
Research Council (grant 2007-5942). FBO was supported by grants
from the Spanish Ministry of Science and Innovation (RYC-2011-09011).
The funding bodies had no role in the preparation of this manuscript.
Competing interests: All authors have completed the ICMJE uniform
disclosure form at www.icmje.org/coi_disclosure.pdf (available on
request from the corresponding author) and declare: the study was
supported by a grant to FR from the Swedish Research Council, and
FBO was supported by grants from the Spanish Ministry of Science and
Innovation; no financial relationships with any organisations that might
have an interest in the submitted work in the previous three years; no
other relationships or activities that could appear to have influenced the
submitted work.
Ethical approval: The study was approved by the Ethical Review Board,
Stockholm, Sweden.
Data sharing: No additional data available.
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Sports Med 2011;45:20-9.
Accepted: 19 October 2012
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What is already known in this topic
Muscular strength in adulthood is associated with all cause mortality and cardiovascular disease mortality
Whether low muscular strength in adolescence is associated with mortality is unknown; a long follow-up period and very large sample
size would be needed to explore this
A higher cardiorespiratory fitness is associated with better mental health in adults, but whether muscular strength at any age is associated
with future mental health and suicide mortality is unknown
What this study adds
Muscular strength in adolescence, as assessed by knee extension and handgrip tests, was associated with a 20-35% lower risk of all
cause and cardiovascular disease premature mortality (<55 years), independently of body mass index or blood pressure
Stronger adolescents had a 20-30% lower risk of death from suicide and were 15-65% less likely to have any psychiatric diagnosis
(such as schizophrenia and mood disorders)
Adolescents in the lowest tenth of muscular strength showed by far the highest risk of mortality due to different causes
Cite this as: BMJ 2012;345:e7279
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any medium, provided the original work is properly cited, the use is non commercial and
is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-
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Figures
Fig 1 Hazard ratios (95% CI) for relation of muscular strength, body mass index, and blood pressure with all cause premature
death. Models were adjusted for birth cohort, conscription age, and conscription office (n=1 142 599)
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Fig 2 Hazard ratios (95% CI) for relation of muscular strength, body mass index, and blood pressure with premature death
from cardiovascular disease. Models were adjusted for birth cohort, conscription age, and conscription office (n=1 118 154)
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Fig 3 Hazard ratios (95% CI) for relation of muscular strength, body mass index, and blood pressure with premature death
from suicide. Models were adjusted for birth cohort, conscription age, and conscription office (n=1 121 480)
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Fig 4 Hazard ratios (95% CI) for relation of muscular strength, body mass index, and blood pressure with premature death
from cancer. Models were adjusted for birth cohort, conscription age, and conscription office (n=1 119 790)
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Fig 5 Hazard ratios (95% CI) for relation of muscular strength, body mass index, and blood pressure, mutually adjusted,
with all cause premature death and death from cardiovascular disease and suicide. Models were additionally adjusted for
birth cohort, conscription age, and conscription office
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Fig 6 Hazard ratios (95% CI) for relation of muscular strength with all cause premature death, stratified by body mass index
(BMI) categories. Models were adjusted for birth cohort, conscription age, and conscription office
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Supplementary resource (1)

... 9 10 Such a poor physical fitness status heralds an increased risk of adverse health effects and premature death. [11][12][13][14] This is in line with patients with SUD exhibiting an increased occurrence of lifestyle-related diseases (ie, diabetes, hypertension and cardiovascular disease and some types of cancer). 4 15-17 Moreover, having SUD is associated with a 15-30 years shorter life expectancy compared with the general population, attributed to poor mental and somatic health in addition to psychosocial comorbidities. 4 17 18 It is noteworthy that premature mortality is commonly caused by lifestyle-related diseases. ...
... Muscular strength is inversely linked to the prevalence of somatic illness such as cancer, 14 cardiovascular disease, 46 47 type II diabetes, 48 impaired skeletal health 49 and being an independent predictor of all-cause mortality. 13 47 50 51 Muscular strength is typically measured as 1-repetition maximum (1RM) in a defined concentric task, which denotes the highest possible force or torque generated in one muscle contraction. Also, muscular strength is commonly measured using large muscle mass with dynamic movement patterns (eg, bench press or leg press), but single joint movements (eg, arm flexion or knee extension) or static contractions (eg, hand grip) are also used. ...
... Also, muscular strength is commonly measured using large muscle mass with dynamic movement patterns (eg, bench press or leg press), but single joint movements (eg, arm flexion or knee extension) or static contractions (eg, hand grip) are also used. 13 14 46-48 50 51 High-intensity physical training Physical endurance and strength training at higher intensities are shown to elicit larger increases in VO 2max and 1RM than low-intensity or moderate-intensity training, in both healthy and patient populations. 36 52-58 Highintensity physical training denotes endurance and strength workloads of 85%-95% of maximum heart rate (HR max ) and 85%-90% of 1RM, respectively. ...
Article
Full-text available
Introduction Patients with substance use disorder (SUD) have high prevalence of lifestyle-related comorbidities. Physical exercise is known to yield substantial prophylactic impact on disease and premature mortality, and there seems to be an inverse association between physical fitness and adverse health outcomes. High-intensity training is regarded as most effective for improving physical fitness, but less is known concerning the ideal training dose necessary to achieve clinically relevant effects in these patients. The aim of this study is to compare the effect of low-dose and high-dose, high-intensity training, on physical fitness in patients diagnosed with SUD. Methods and analysis This study will recruit 40 in-patients of mixed genders, aged 18–70 years. Participants will be block allocated to low-dose or high-dose training, encompassing 24 high-intensity interval and maximal strength training sessions (3/week × 8 weeks). After a 10 min warm-up, the low-dose group will perform 1×4 min intervals at ⁓90% of maximal heart rate and 2×4 repetitions strength training at ⁓90% of 1 repetition maximum. The high-dose group will perform 4×4 min intervals at ⁓90% of maximal heart rate and 4×4 repetitions strength training at ⁓90% of 1 repetition maximum. Clinical measurements and physical tests will be conducted at baseline, midway and on completion and a questionnaire on physical activity will be administered at baseline. Ethics and dissemination This protocol is in accordance with the Standard Protocol Items: Recommendations for Interventional Trials statement. All participants will sign a written informed consent. The Regional Committee of Medical Research Ethics, Norway has approved the study. A study of this kind is warranted, and the results will be published in an open access journal to ensure public access, and presented at national and international conferences. Trial registration number NCT04065334 .
... In terms of physical fitness, cardiorespiratory fitness (CRF) has been reported to have an inverse association with cIMT in young individuals [11][12][13]. There have only been a few studies on the associations between muscular strength (MusS) and cIMT in children [10] and premature CVD death in adolescents [14], despite the fact that several studies have found associations between MusS and diabetes mellitus, CVD death, sudden cardiac death, and heart failure in middle-aged or elderly individuals [15][16][17][18][19][20][21]. Notably, the association could vary by sex, and was dependent on which MusS was assessed [22]. ...
... Notably, the association could vary by sex, and was dependent on which MusS was assessed [22]. In addition, many studies were not adjusted for CRF levels to clarify the independent role of MusS in the prevention of atherosclerosis [14,15,22]. Today, the association of MusS with cIMT in young adults remains unclear and has not been previously studied. ...
... Several studies have demonstrated better CRF to be a protector against subclinical atherosclerosis, CVD events, and related death in the general population across a wide age range [10][11][12][13][14]. However, there have been relatively fewer studies with regard to the associations between MusS, atherosclerosis severity, and the risk of CVD-particularly among the youth and young adults [11,14]. ...
Article
Full-text available
Background: Greater muscular strength (MusS) has been found to have an inverse association with subclinical atherosclerosis in children, as well as with mortality from cardiovascular diseases (CVDs) in middle-aged and elderly individuals. However, the association of the degree of MusS with atherosclerosis may differ by sex and has not been clarified in young adults. Methods and Results: A total of 1021 Taiwanese military personnel, aged 18-40 years, participated in annual health examinations in 2018-2020. MusS was separately assessed by 2-minute push-up and 2-minute sit-up numbers. Subclinical atherosclerosis was measured by the left carotid bulb intima-media thickness (cIMT) using high-resolution ultrasonography. Multiple linear regression with adjustments for age, sex, alcohol intake, cigarette smoking, anthropometric indices, blood pressure, and lipid profiles was utilized to determine the correlation between MusS and cIMT. Both 2-minute push-up and 2-minute sit-up numbers were inversely correlated with cIMT (standardized β: −0.089 and −0.072, respectively; both p-values < 0.05). In men, both 2-minute push-up and 2-minute sit-up numbers were inversely correlated with cIMT (standardized β: −0.076 and −0.086, respectively; both p-values < 0.05), while in women, 2-minute push-up numbers but not 2-minute sit-up numbers were inversely correlated with cIMT (standardized β: −0.204 and −0.01; p = 0.03 and 0.99, respectively). Conclusions: Among young adults, there was an inverse association between MusS and cIMT, emphasizing the beneficial impact of MusS on the regression of atherosclerosis. The study also revealed a sex difference and suggested that training of the upper arm muscles may be an effective preventive measure for young women to reduce the risk of early cardiovascular diseases.
... In addition, CRF levels are a stronger predictor of cardiovascular disease risk factors among youth than objectively measured physical activity levels [17]. Longitudinal epidemiological studies have shown that physical fitness levels persist (i.e., track) across the life course [18][19][20][21], and that high CRF and MSF in childhood, adolescence, or early adulthood is prospectively associated with a healthier cardiovascular profile [13,[22][23][24], reduced disability [25,26], and a decreased risk of premature mortality [27,28] in adulthood. An individual's physical fitness level, especially their CRF, provides a reasonable objective indication of their moderate to vigorous intensity physical activity levels in recent months, as it summarizes the physiological response to their physical activity profile [29]. ...
... In recent decades, several longitudinal studies have established that physical fitness in adolescence is a significant inverse and independent predictor of disease outcomes, including premature mortality in adulthood [13,[23][24][25][26][27][28]. Some studies on adolescents investigated changes in fitness levels (i.e., CRF and MSF) and associations with health outcomes using follow-up periods of several years [42][43][44], whilst others identified that improvements in MSF from childhood to adolescence were associated with reduced adiposity [13,45]. ...
... Some studies on adolescents investigated changes in fitness levels (i.e., CRF and MSF) and associations with health outcomes using follow-up periods of several years [42][43][44], whilst others identified that improvements in MSF from childhood to adolescence were associated with reduced adiposity [13,45]. There is a need for future studies to link fitness (both CRF and MSF) measured in young childhood (of both sexes) with clinical outcomes in adulthood in nationally representative cohorts to establish longitudinal links with key health outcomes [13,22,24,27]. Such studies could provide valuable insights into physical fitness and the associated risk of developing and dying from a chronic disease (i.e., relative risk), that could be used to calculate the population attributable fraction. ...
Article
Full-text available
Background The measurement of physical fitness has a history that dates back nearly 200 years. Recently, there has been an increase in international research and surveillance on physical fitness creating a need for setting international priorities that could help guide future efforts. Objective This study aimed to produce a list of the top 10 international priorities for research and surveillance on physical fitness among children and adolescents. Methods Using a twin-panel Delphi method, two independent panels consisting of 46 international experts were identified (panel 1 = 28, panel 2 = 18). The panel participants were asked to list up to five priorities for research or surveillance (round 1), and then rated the items from their own panel on a 5-point Likert scale of importance (round 2). In round 3, experts were asked to rate the priorities identified by the other panel. Results There was strong between-panel agreement (panel 1: r s = 0.76, p < 0.01; panel 2: r s = 0.77, p < 0.01) in the priorities identified. The list of the final top 10 priorities included (i) “conduct longitudinal studies to assess changes in fitness and associations with health”. This was followed by (ii) “use fitness surveillance to inform decision making”, and (iii) “implement regular and consistent international/national fitness surveys using common measures”. Conclusions The priorities identified in this study provide guidance for future international collaborations and research efforts on the physical fitness of children and adolescents over the next decade and beyond.
... Accumulating evidence shows that lower grip strength, as a proxy for muscle strength, imposes serious limitations on dependency, disability, and quality of life in older age [4,5]. Individuals with weak grip strength are at higher risk of adverse health consequences like mobility, frailty, falls, hospitalization, and all-cause mortality [6,7]. ...
... Among all 30 behavioral measures, 15 have baseline data that were collected approximately 8.96 ± 1.82 years prior to MRI scanning (N = 3152-40,784). As in prior studies [39,40], a classic two-wave cross-lagged panel model [6] was estimated using structural equation modeling in Mplus (version 8.3) [41] to determine the longitudinal relationship between grip strength and behavioral outcomes. Specifically, the model examines the relative strength of the cross-lagged correlations between baseline grip strength and each of the 15 phenotypes at 10-year follow-up, as well as between baseline behavioral measures and subsequent grip strength, while adjusting for confounding covariates and the baseline behavioral or grip strength measurements. ...
Article
Full-text available
Background Grip strength is a widely used and well-validated measure of overall health that is increasingly understood to index risk for psychiatric illness and neurodegeneration in older adults. However, existing work has not examined how grip strength relates to a comprehensive set of mental health outcomes, which can detect early signs of cognitive decline. Furthermore, whether brain structure mediates associations between grip strength and cognition remains unknown. Methods Based on cross-sectional and longitudinal data from over 40,000 participants in the UK Biobank, this study investigated the behavioral and neural correlates of handgrip strength using a linear mixed effect model and mediation analysis. Results In cross-sectional analysis, we found that greater grip strength was associated with better cognitive functioning, higher life satisfaction, greater subjective well-being, and reduced depression and anxiety symptoms while controlling for numerous demographic, anthropometric, and socioeconomic confounders. Further, grip strength of females showed stronger associations with most behavioral outcomes than males. In longitudinal analysis, baseline grip strength was related to cognitive performance at ~9 years follow-up, while the reverse effect was much weaker. Further, baseline neuroticism, health, and financial satisfaction were longitudinally associated with subsequent grip strength. The results revealed widespread associations between stronger grip strength and increased grey matter volume, especially in subcortical regions and temporal cortices. Moreover, grey matter volume of these regions also correlated with better mental health and considerably mediated their relationship with grip strength. Conclusions Overall, using the largest population-scale neuroimaging dataset currently available, our findings provide the most well-powered characterization of interplay between grip strength, mental health, and brain structure, which may facilitate the discovery of possible interventions to mitigate cognitive decline during aging.
... Maximal muscle strength and power are key components affecting functional performance in everyday life and have both been acknowledged as independent risk factors of all-cause mortality [58][59][60]. Maximal muscle strength is typically measured as the heaviest weight one can lift once in a given movement (1RM) and decreases by approximately 1% per year from the fourth decade of life [61]. Power is a sub-component of maximal muscle strength and a product of work over time, i.e., force × velocity [25]. ...
Article
Full-text available
Background Individuals with severe mental disorders (SMDs; schizophrenia spectrum disorders, bipolar disorder, and major depressive disorder) are not only suffering from their mental conditions; they also have an attenuated physical health, augmenting their overall critical condition. Objectives We review and critically appraise the evidence based on (1) key physiological factors relating to aerobic endurance and skeletal muscle strength; (2) implications for physical function and health; and (3) effects of training interventions with different intensities evaluated in individuals with SMDs. Findings Reductions in aerobic endurance factors, peak oxygen uptake (VO2peak) and walking work efficiency, are paralleled by reductions in maximal skeletal muscle strength and power. In turn, the poor aerobic endurance and muscle strength lead to impaired physical function, increased risk of lifestyle-related diseases, and ultimately early death. Exercise has the potential to counteract the attenuated physical health in people with SMDs. While aerobic endurance training is shown to increase VO2peak due to plasticity of the oxygen transport system, strength training is documented to improve maximal muscle strength, power, and walking work efficiency as a result of adaptations in neuromuscular force developing factors. Conclusions In conclusion, improvements in these key determinants for physical health appear to be achievable in people with SMDs despite many being challenged by motivational difficulties with attending regular exercise and have beneficial implications for physical function during activities of daily living, lifestyle-related diseases, and early death.
... Several studies have shown that PF can predict the future probability of cardiovascular disease or all-cause mortality [9]. Better PF can improve the health of the skeletal muscular system [10], prevent a range of psychological disorders (e.g., depression, anxiety, psychological stress) [11], and reduce the risk of premature death [12]. Recently, a growing body of research has shown that PF is strongly associated with students' cognitive and academic performance [13]. ...
Preprint
Full-text available
Purpose Many studies have investigated the effects of Physical Activity (PA), Sedentary Time (ST), and Physical Fitness on human’s physical health and well-being. However, these findings have been inconsistent. In view of the significantly lower PA and PF levels of females than males in China, as well as limited research is available investigating a population of college female students who are influenced by Eastern culture and context. This study therefore explored the association between Physical Activity (PA), Sedentary Time (ST), and Physical Fitness (PF) in female college students in China. Methods 512 female college students from China participated in this study. The international PA questionnaire was used to investigate the PA and ST of participants. Participants were classified into (a) active versus inactive groups according to WHO PA Guidelines and as (b) low versus high sedentary groups according to the median of their sedentary time. Subsequently, participants were divided into four sub-groups: (a) active/low sedentary, (b) active/high sedentary, (c) inactive/low sedentary, and (d) inactive/high sedentary. The Chinese National Student Physical Fitness Test (CNSPFT) was used to assess participants’ body composition, cardiorespiratory fitness, speed, flexibility, muscular endurance, explosive power, and overall fitness. Based on the CNSPFT results, participants were then divided into fit versus unfit groups. The association between PA, ST, and PF was examined and analyzed using independent samples t-test, binary logistic regression, and multinomial logistic regression methods. Results Participants in the active group showed significantly higher cardiorespiratory fitness(p < 0.05) and overall fitness (p < 0.01) than the inactive group. Compared to the inactive group, participants in the active group were also less likely to be classified as unfit in terms of cardiorespiratory fitness (odds ratio (OR), 0.572; 95% confidence interval (CI), 0.384–0.852; p < 0.05). Relative to the inactive/high sedentary group, those in the active/low sedentary group (OR, 0.436; 95% CI, 0.251–0.755; p < 0.01) and the active/high sedentary group (OR, 0.544; 95% CI, 0.319–0.929; p < 0.05) were less likely to be classified as unfit in terms of cardiorespiratory fitness. Furthermore, those in the active/high sedentary group (OR, 1.658; 95% CI, 1.018-2.700; p < 0.05) and the inactive/low sedentary group (OR, 2.086; 95% CI, 1.155–3.768; p < 0.05) were more likely to be classified as unfit in terms of their flexibility. Conclusions There was a positive association between PA, cardiorespiratory fitness and overall fitness. There was also an association between PF and the combination of PA and ST. Specifically, the combination of more PA and less ST was associated with better cardiorespiratory fitness. The combination of more PA and more ST or the combination of less PA and less ST were also associated with worse flexibility. These findings suggest that increasing PA and decreasing ST simultaneously can improve the PF of Chinese female college students.
... Many studies have shown a downward continuous trend in muscular fitness among school children in different countries or regions such as the U.S. [19], Britain [20], Canada [21], Spain [22], China [23], and New Zealand [24]. Low muscular strength in teenagers is a developing risk factor for major causes of mortality in early adulthood, such as suicide and cardiovascular diseases [25], and muscular strength in males is inversely and independently associated with death from all causes and cancer [26]. Poor muscular fitness has been linked to pediatric dynapenia in modern-day youth [27] and sarcopenia in elder individuals (i.e., the loss of skeletal muscle mass associated with aging, neuromuscular factors independent of muscle size contribute to muscle weakness, fall risk, declining quality of life, and loss of functional movement) [28,29]. ...
Article
Full-text available
Purpose: This research was to see how effective and feasible school-based comprehensive strength training programs are in improving muscular fitness and perceived physical competence in Chinese male adolescents. Methods: A total of 123 participants (13.46 ± 0.60 years) were randomized to comprehensive strength training intervention group (CST) (n = 62) and the control group (CON) (n = 61). The training sessions were performed three times a week for ten weeks in CST. Muscular fitness (i.e., muscular strength, power, and muscular endurance) and perceived physical competence were assessed at initial testing and final testing. Results: The subjects in the CST significantly improved their mean performance in standing long jump (p < 0.05), vertical jump (p < 0.05), 1 min push-ups (p < 0.05), 1 min sit-ups (p < 0.05), handgrip strength (p < 0.05), and perceived physical competence (p < 0.05) after the intervention. Moreover, the CST were greater in standing long jump (p < 0.05), vertical jump (p < 0.05), 1 min sit-ups (p < 0.05), handgrip strength (p < 0.05), and perceived physical competence (p < 0.05) compared to the CON, but no in 1 min push-ups (p > 0.05). Conclusions: The comprehensive strength training interventions designed in this study can significantly increase male adolescents' muscular fitness, especially in the lower extremity muscle power and abdominal core endurance, and can enhance their perceived physical competence.
Article
Purpose : To examine the effects of a 14-week gamification-based physical education teaching program on fitness in college students. Method : A convenience sample of 112 college students (21.22 ± 2.55 years) was distributed among a gamification-based group or a control group (i.e., traditional teaching). College students from the gamification group used a game-based mobile app under the narrative of “STAR WARS™” with a countdown, so they had to gain lifetime. Cardiorespiratory fitness was assessed by the 20-m shuttle run test. Muscular fitness was measured by the handgrip strength and the standing broad jump tests. Results : Participants from the gamification program reported a significantly higher cardiorespiratory fitness and upper and lower body muscular fitness at postintervention, indicated by an effect size of 0.86 ( p < .001), 0.18 ( p = .018), and 0.52 ( p < .001), respectively. Conclusion : Gamification can have an important implication on students’ motivation toward higher fitness.
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