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Progressive Resistance Training for Concomitant Increases in Muscle Strength and Bone Mineral Density in Older Adults: A Systematic Review and Meta‑Analysis

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Background Older adults experience considerable muscle and bone loss that are closely interconnected. The efficacy of progressive resistance training programs to concurrently reverse/slow the age-related decline in muscle strength and bone mineral density (BMD) in older adults remains unclear. Objectives We aimed to quantify concomitant changes in lower-body muscle strength and BMD in older adults following a progressive resistance training program and to determine how these changes are influenced by mode (resistance only vs. combined resistance and weight-bearing exercises), frequency, volume, load, and program length. Methods MEDLINE/PubMed and Embase databases were searched for articles published in English before 1 June, 2021. Randomized controlled trials reporting changes in leg press or knee extension one repetition maximum and femur/hip or lumbar spine BMD following progressive resistance training in men and/or women ≥ 65 years of age were included. A random-effects meta-analysis and meta-regression determined the effects of resistance training and the individual training characteristics on the percent change (Δ%) in muscle strength (standardized mean difference) and BMD (mean difference). The quality of the evidence was assessed using the Cochrane risk-of-bias tool (version 2.0) and Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) criteria. Results Seven hundred and eighty studies were identified and 14 were included. Progressive resistance training increased muscle strength (Δ standardized mean difference = 1.1%; 95% confidence interval 0.73, 1.47; p ≤ 0.001) and femur/hip BMD (Δ mean difference = 2.77%; 95% confidence interval 0.44, 5.10; p = 0.02), but not BMD of the lumbar spine (Δ mean difference = 1.60%; 95% confidence interval − 1.44, 4.63; p = 0.30). The certainty for improvement was greater for muscle strength compared with BMD, evidenced by less heterogeneity (I2 = 78.1% vs 98.6%) and a higher overall quality of evidence. No training characteristic significantly affected both outcomes (p > 0.05), although concomitant increases in strength and BMD were favored by higher training frequencies, increases in strength were favored by resistance only and higher volumes, and increases in BMD were favored by combined resistance plus weight-bearing exercises, lower volumes, and higher loads. Conclusions Progressive resistance training programs concomitantly increase lower-limb muscle strength and femur/hip bone mineral density in older adults, with greater certainty for strength improvement. Thus, to maximize the efficacy of progressive resistance training programs to concurrently prevent muscle and bone loss in older adults, it is recommended to incorporate training characteristics more likely to improve BMD.
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Vol.:(0123456789)
Sports Medicine (2022) 52:1939–1960
https://doi.org/10.1007/s40279-022-01675-2
SYSTEMATIC REVIEW
Progressive Resistance Training forConcomitant Increases inMuscle
Strength andBone Mineral Density inOlder Adults: ASystematic
Review andMeta‑Analysis
StevenJ.O’Bryan1 · CatherineGiuliano1 · MaryN.Woessner1 · SaraVogrin2,4 · CassandraSmith1,2,3 ·
GustavoDuque2,4 · ItamarLevinger1,2,4
Accepted: 12 March 2022 / Published online: 24 May 2022
© The Author(s) 2022
Abstract
Background Older adults experience considerable muscle and bone loss that are closely interconnected. The efficacy of
progressive resistance training programs to concurrently reverse/slow the age-related decline in muscle strength and bone
mineral density (BMD) in older adults remains unclear.
Objectives We aimed to quantify concomitant changes in lower-body muscle strength and BMD in older adults following
a progressive resistance training program and to determine how these changes are influenced by mode (resistance only vs.
combined resistance and weight-bearing exercises), frequency, volume, load, and program length.
Methods MEDLINE/PubMed and Embase databases were searched for articles published in English before 1 June, 2021.
Randomized controlled trials reporting changes in leg press or knee extension one repetition maximum and femur/hip or
lumbar spine BMD following progressive resistance training in men and/or women 65years of age were included. A
random-effects meta-analysis and meta-regression determined the effects of resistance training and the individual training
characteristics on the percent change (∆%) in muscle strength (standardized mean difference) and BMD (mean difference).
The quality of the evidence was assessed using the Cochrane risk-of-bias tool (version 2.0) and Grading of Recommendation,
Assessment, Development, and Evaluation (GRADE) criteria.
Results Seven hundred and eighty studies were identified and 14 were included. Progressive resistance training increased
muscle strength (∆ standardized mean difference = 1.1%; 95% confidence interval 0.73, 1.47; p ≤ 0.001) and femur/hip BMD
(∆ mean difference = 2.77%; 95% confidence interval 0.44, 5.10; p = 0.02), but not BMD of the lumbar spine (∆ mean differ-
ence = 1.60%; 95% confidence interval − 1.44, 4.63; p = 0.30). The certainty for improvement was greater for muscle strength
compared with BMD, evidenced by less heterogeneity (I2 = 78.1% vs 98.6%) and a higher overall quality of evidence. No
training characteristic significantly affected both outcomes (p > 0.05), although concomitant increases in strength and BMD
were favored by higher training frequencies, increases in strength were favored by resistance only and higher volumes, and
increases in BMD were favored by combined resistance plus weight-bearing exercises, lower volumes, and higher loads.
Conclusions Progressive resistance training programs concomitantly increase lower-limb muscle strength and femur/hip
bone mineral density in older adults, with greater certainty for strength improvement. Thus, to maximize the efficacy of
progressive resistance training programs to concurrently prevent muscle and bone loss in older adults, it is recommended to
incorporate training characteristics more likely to improve BMD.
* Steven J. O’Bryan
steven.obryan@vu.edu.au
1 Institute forHealth andSport (IHeS), Victoria University,
Footscray Park Campus, Melbourne, VIC3134, Australia
2 Australian Institute forMusculoskeletal Science (AIMSS),
The University ofMelbourne andWestern Health,
Melbourne, VIC, Australia
3 Institute forNutrition Research, School ofHealth
andMedical Sciences, Edith Cowan University, Perth, WA,
Australia
4 Department ofMedicine-Western Health, Melbourne
Medical School, The University ofMelbourne, Melbourne,
VIC, Australia
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1940 S.J.O’Bryan et al.
Key Points
Progressive resistance training programs concomitantly
increase muscle strength and bone mineral density in
older adults and, therefore, may be used to prevent mus-
cle and bone loss in old age
Most evidence demonstrated an increase in muscle
strength irrespective of differences within common
training characteristics whereas bone mineral density
improvement was more uncertain
To maximize dual improvements in muscle and bone
strength with progressive resistance training programs
for older adults, it may be beneficial to complete three
sessions per week, incorporate weight-bearing/impact
loading exercises (e.g., jumping, stepping), perform one
or two sets per exercise, and adopt a load corresponding
to 75–80% 1 repetition maximum
1 Introduction
Life expectancy almost doubled in the last 100years owing
to advances in technology and medical treatments [1],
with the global number of people aged over 65years pro-
jected to rise from 703 million in 2019 to 1.5 billion by the
year 2050 [2]. Unfortunately, aging is associated with the
development of many chronic diseases, including sarcope-
nia (the loss of muscle mass, strength, and function) and
osteoporosis (severe bone loss), which respectively costs
the USA ~ $40 billion [3] and ~ $17 billion [4] annually in
healthcare. Between the ages of 65 and 80years, the annual
percentage loss in muscle strength is ~ 1–4% for both sexes
[5, 6], whereas the decline in bone mineral density (BMD)
is accelerated in women (~ 1–3% vs ~ 0.25–1.5% for men)
[5]. The reduction in muscle strength and BMD with age
decreases the capacity to perform activities of daily living
and increases the susceptibility to falls and fractures [7, 8].
The factors associated with age-related osteoporosis and sar-
copenia are multi-faceted [9, 10] and range from lifestyle
(e.g., inactivity, nutritional intake) [11, 12], psychosocial
(e.g., self-efficacy, resiliency) [13], and biological factors
(e.g., genetic, inflammatory, hormonal) [1417].
Skeletal muscle and bone are closely interconnected
via mechanical and endocrine functions, which are highly
sensitive to physical activity [18, 19]. During physical
activity, external (gravitational and inertial) and internal
(skeletal muscle contraction) mechanical loads stimu-
late dose-dependent changes in bone formation [2022],
and skeletal muscle releases various growth factors and
myokines known to influence muscle protein synthesis and
bone turnover rate (e.g., insulin-like growth factor-1, inter-
leukin-6) [23]. As such, long-term physical exercise train-
ing is a cost-effective and non-pharmacological approach
to limit the health and economic burden of sarcopenia and
osteoporosis in older adults.
Previous meta-analyses have reported beneficial effects
of progressive resistance training for increasing muscle
strength [2427] and BMD [2831] in older adults, with
complementary benefits such as increased muscle mass [24,
27], improved functional capacity [32, 33], and a reduced
fall and fracture risk [34]. However, previous meta-analy-
ses have only focused on muscle strength or BMD inde-
pendently, with only a recent systematic review reporting
a potential benefit of progressive resistance training for
improving muscle strength and BMD in older adults with
low muscle and bone mass [35]. As such, it remains unclear
if progressive resistance training may be used to concomi-
tantly reverse/slow the age-related decline in muscle strength
and BMD in older adults. Moreover, it remains unknown
how dual changes in muscle strength and BMD may be influ-
enced by training characteristics such as mode (resistance-
only training using weighted machines/pulleys and/or free
weights vs. combined resistance training and weight-bear-
ing/impact-loading exercises such as jumping, agility and/
or balance), frequency (sessions per week), volume (sets and
repetitions), load (% one repetition maximum [1RM]), and
program length (total weeks of training). This information
may elucidate optimal progressive resistance training guide-
lines for the concurrent treatment of sarcopenia and osteo-
porosis in older adults, which is of significant clinical value.
The purpose of this systematic review and meta-analysis
is to examine randomized controlled trials that investigated
the effects of progressive resistance training programs on
concomitant changes in lower-body muscle strength and
BMD in older adults over the age of 65years. Furthermore,
a sub-group meta-regression aimed to determine how dual
changes in muscle strength and BMD are affected by train-
ing mode, frequency, volume, load, and program length, so
that exercise prescription guidelines for dual benefits could
be provided.
2 Methods
2.1 Protocol andRegistration
The protocol of this systematic review and meta-analysis
was registered in the Prospero database (https:// www. crd.
york. ac. uk/ prosp ero/, registration number: 220210) and
prepared in accordance with Preferred Reporting Items for
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1941
Resistance Training for Muscle and Bone Strength in Older Adults
Systematic Reviews and Meta-Analyses (PRISMA) guide-
lines [36].
2.2 Eligibility Criteria
Eligibility criteria were based on the PICO approach: (i)
male and female participants with a mean age ≥ 65years; (ii)
randomized controlled trials examining the effect of progres-
sive resistance training only or resistance plus weight-bear-
ing/impact-loading training of 4weeks duration against a
non-training prescribed control group; (iii) changes in BMD
for hip, lumbar spine and/or femur (no limitations on assess-
ment method); and (iv) changes in muscle strength of the
lower limbs assessed via leg press/knee extension 1RM or
isometric/isokinetic knee extension strength. Studies were
excluded if participants had cancer, were rehabilitating
from acute orthopedic surgery (within 6months), were
administered hormone replacement therapy as part of the
study intervention, were actively losing weight during the
study period, or were judged as having a high risk of bias.
Only peer-reviewed journal articles published in English and
matching the eligibility criteria were considered for analysis.
2.3 Information Sources andSearch Strategy
A literature search in electronic databases PubMed/MED-
LINE via EBSCOhost and Embase via Ovid retrieved arti-
cles published in English before 1 June, 2021. The reference
lists of all included studies were also screened for eligibil-
ity. A combination of MeSH/Emtree and free-text terms
were included in our Boolean search syntax: (geriatrics OR
aged OR older adults OR elderly) AND (resistance training
OR resistance exercise OR strength training) AND (mus-
cle strength OR sarcopenia OR muscle mass OR muscle
power) AND (bone mineral density OR osteoporosis OR
bone strength OR osteopenia).
2.4 Study Selection
All records retrieved from the literature search were com-
piled into an Endnote library and imported into COVI-
DENCE software for screening (https:// www. covid ence.
org/). Titles and abstracts of potential articles for inclusion
were screened against the eligibility criteria by two inde-
pendent reviewers (SO and CG or MW). When title and
abstract screening implied inclusion, the full-text article was
then screened by two independent reviewers (SO and CG
or MW). If it was unclear whether an article met the inclu-
sion criteria during the full-text screening process, study
authors were contacted for clarification via e-mail. Any
disagreements on inclusion were resolved when consensus
was reached through discussions with a third reviewer (IL).
2.5 Data Collection
The following information was manually extracted from each
individual study included in the analysis and entered into
a Microsoft Excel spreadsheet by the first author (SO): (i)
full article reference; (ii) participant characteristics includ-
ing sex, age (years), body mass (kg), height (cm), and body
mass index [BMI] (kg/m2); (iii) general training description
including exercises performed (upper and/or lower body),
equipment used (resistance machines, free weights, weighted
vests, resistance bands), whether training sessions were
supervised and training attendance; (iv) training specifics
including mode (resistance only or resistance plus weight-
bearing/impact-loading), frequency (# per week), volume
(sets and repetitions per exercise), load (% 1RM), and pro-
gram length (weeks), and; (v) pre-exercise and post-exercise
intervention mean ± standard deviation (SD) measures for
the primary outcomes including muscle strength (leg press
1RM, knee extension 1RM, or maximal isometric/isokinetic
knee extension force) and BMD (femoral neck, total hip,
thigh, inter-trochanteric region, trochanter, Ward’s triangle,
or lumbar spine); and (vi) statistical significance for changes
in secondary outcomes including body composition, func-
tional performance, falls, and self-efficacy.
A second reviewer (CG) validated the extracted data
in-person with the first author (SO) by cross-referencing
the spreadsheet against printed hard-copy versions of the
included studies. If a study reported multiple outcome meas-
ures for muscle strength, leg press 1RM was chosen as the
preferred outcome for analysis because of its superior rep-
resentation of overall lower-limb muscle strength (n = 5); if
leg press 1RM was not reported, then maximal isometric/
isokinetic knee extension force was used (n = 7). If a study
reported BMD for multiple sites on the femur, the femoral
neck was chosen as the preferred outcome for analysis as
it was the most reported across articles (n = 8); if femoral
neck BMD was not reported, total hip (n = 2) or proximal
one-third thigh (n = 1) BMD was used. Where standard
errors (SEs) were reported, the SD was calculated using
the equation
SD = SE × n
. The mean changes in muscle
strength and BMD were calculated by subtracting the post-
intervention mean score from the pre-intervention mean
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1942 S.J.O’Bryan et al.
score, whereas the SD of the change was calculated using a
correlation coefficient (Corr = 0.52 for muscle strength [37]
and 0.97 for BMD [38]) and the equation:
Data were pooled together [39] if there was more than
one training intervention group [4042], if data on male and
female individuals were reported separately [43], if non-
exercise groups were supplemented with placebo or vitamin
D/calcium [44, 45], and if data were reported for the left and
right leg separately [46].
2.6 Risk‑of‑Bias andQuality Assessment
Two assessors (SO and MW) independently assessed the
risk of bias for each outcome measure using the Cochrane
risk-of-bias tool (version 2.0) [47]. Where any differences
between assessors were observed, discussions between the
authors were conducted to arrive at agreement. In addition to
a risk of bias, inconsistency, indirectness, imprecision, and
publication bias were assessed using the Grading of Rec-
ommendation, Assessment, Development, and Evaluation
(GRADE) approach [48] to evaluate the overall quality of
the evidence.
2.7 Statistical Analysis
Statistical analyses were performed using Stata software
(version 16.1; Stata Corporation, College Station, TX,
USA) and RStudio (version 1.2.5042, 2020; RStudio, Inc.,
Boston, MA, USA). Effect size was expressed as Hedges’
g standardized mean difference (SMD) between interven-
tion and control for muscle strength, and as the mean differ-
ence (MD) between intervention and control for BMD. A
random-effects multi-variate meta-analysis using restricted
maximum likelihood was performed on percent change (∆%)
in muscle strength and BMD. Because of unknown within-
study correlations, Riley’s model was used to estimate an
overall correlation between concomitant changes in the out-
comes [49]. A univariate meta-analysis was also performed
separately for each primary outcome. A random-effects
meta-regression was performed using restricted maximum
likelihood estimation to determine how muscle strength and
BMD were affected by resistance training characteristics
(mode, frequency, volume, load, and program length) and
population characteristics (when differences were identi-
fied between studies). Heterogeneity (quantified as I2 meas-
ure) larger than 60% was considered substantial [48], and
p < 0.05 was regarded as statistically significant. A small
study effect was evaluated using funnel plots and Egger’s
SDchange =
SDpre
2
+ SDpost
2
−(
2
× Corr × SDpre × SDpost)[
39
]
.
test. When a small study effect was observed, a sensitivity
analysis trim-and-fill method was performed.
3 Results
3.1 Study Selection
A flow diagram of the study selection process is presented
in Fig.1. Overall, 780 studies were identified in the initial
database search. Following removal of duplicates (n = 350),
430 titles and abstracts were screened against the inclusion
criteria, and 389 studies were irrelevant. A full-text review
of the remaining 41 studies excluded a further 26 studies
because of a wrong patient population (n = 7), a wrong com-
parator (n = 8), wrong outcomes (n = 7), or a wrong inter-
vention (n = 4). Fifteen studies were included following a
full-text review. Screening of reference lists identified 30
potential articles; however, none of these met the inclusion
criteria. Of the 15 included studies, one study was excluded
because of a high risk of bias (Electronic Supplementary
Material [ESM]). A total of 14 studies were included in the
final meta-analysis.
Several studies appeared to meet the inclusion criteria but
were excluded. This included two non-progressive resist-
ance training studies [50, 51], two studies that prescribed
low-intensity supervised exercise programs to the control
group (e.g., stretching, walking) [52, 53], three studies that
prescribed different doses of whey protein to the control and
intervention groups [5456], and one study that reported
three repetition maximum strength outcomes [57].
3.2 Study Characteristics
The training and participant characteristics of included stud-
ies are detailed in Table1. A total of 1130 participants across
the fourteen studies were included. Of the twelve studies
that reported sex [40, 41, 4346, 5863], 944/1022 (92%)
were female. The mean age across studies was 70 ± 6.1years
(range 65–77years). Most studies described participants as
being apparently healthy, not engaged in regular physical
activity, and having no/limited previous resistance train-
ing experience, although one study classified participants
as being mild to moderately frail [63] and another study
only included participants who had experienced a fall in the
previous twelvemonths [45]. Of the nine studies reporting
BMI, according to World Health Organization classifica-
tion ranges [64], three included participants with normal
BMI [40, 41, 65], five included participants who were over-
weight [44, 46, 6062], and one included participants who
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1943
Resistance Training for Muscle and Bone Strength in Older Adults
were obese [63]. Five studies supplemented participants with
varying doses of calcium (range 500–1500mg per day) and
vitamin D (range 200–1000IU per day) [40, 44, 45, 59,
63]; in this instance, control and exercise groups were sup-
plemented equally [46, 6062].
Training programs were supervised by members of
the research team or physical therapists in thirteen stud-
ies [4046, 5963, 65], whereas one study supervised
participants during the initial threemonths of a twelve-
month program [58]. Mean training attendance was 77%
(range 53–98%). Eight studies [4043, 58, 61, 62, 65] uti-
lized exclusively resistance training-only exercises using
weighted/pulley machines and/or free weights (i.e., push,
pull), five studies [4446, 59, 63] utilized combined resist-
ance training plus weight-bearing/impact-loading exercises
such as jumping, agility (e.g., change of direction, sideways
movements), balance (e.g., heel-to-toe), or aerobic (e.g.,
step-ups, squats, stair climbing), and one study [60] com-
pared resistance training-only and combined resistance plus
weight-bearing/impact-loading programs. Mean program
length was 43 ± 17weeks (range 24–84weeks). Training fre-
quency was three sessions per week for nine studies [4042,
5863], two sessions per week for four studies [4346],
and one study examined the effect of one vs. two vs. three
780studies identified through database searching350 duplicates removed
430title and abstracts screened 389 irrelevant
41 full-text articles assessed for eligibility 26 excluded
Wrong patient population (n = 7)
Wrong comparator (n = 8)
Wrong outcomes (n = 7)
Wrong intervention (n = 4)
15 studies included following full-text review 30 articles identified from
reference lists
15 studies assessed for quality
14 studies included in final analysis
30 irrelevant
1 excluded due to high risk of
bias
Identification
ScreeningEligibility
Included
Fig. 1 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram of the study selection process
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1944 S.J.O’Bryan et al.
Table 1 Individual studies examining the combined effect of resistance training on lower-body muscle strength and bone mineral density in older adults
References Sex (M/F) Age (years) Mass (kg) Sup; Att Mode Length
(weeks)
Freq.
(week−1)
Load (%
1RM)
Sets (#) Reps (#) Strength out-
come
BMD outcome
Pruitt etal.
[40]
C: 0/11
G1: 0/7
G2: 0/8
C: 69.6 ± 4.2
G1: 67.6 ± 1.4
G2: 67.0 ± 0.5
C: 63.8 ± 9.1
G1: 61.5 ± 4.6
G2: 64.5 ± 9.2
Y; 65% RES 52 3 G1: 40%
G2: 80%
G1: 3
G2: 2
G1: 14
G2: 7
G1: LP, KE
G2: LP, KE
G1: FN, LS,
Hip, WT
G2: FN, LS,
Hip, WT
Taaffe etal.
[41]
C: 0/7
G1: 0/7
G2: 0/7
C: 69.6 ± 3.4
G1: 67.6 ± 1.3
G2: 67.0 ± 0.5
C: 63.8 ± 7.1
G1: 61.5 ± 4.5
G2: 63.4 ± 9.3
Y; 79% RES 52 3 G1: 40%
G2: 80%
G1: 3
G2: 2
G1: 14
G2: 7
G1: LP, KE
G2: LP, KE
G1: TH
G2: TH
McCartney
etal. [43]
C: 21/35
G1: 29/28
Ca: 68.2 ± 5.3
G1a: 68.1 ± 4.5
Ca: 70.4 ± 13.2
G1a: 72.2 ± 11.1
Y; 85% RES 84 2 80% 3 12 LP LSb
Taaffe etal.
[65]
C: 12
G1: 11
G2: 12
G3: 11
(sex not
reported)
C: 68.9 ± 3.6
G1: 68.5 ± 3.6
G2: 69.4 ± 3.0
G3: 71.0 ± 4.1
C: 80.4 ± 10.3
G1: 70.2 ± 14.4
G2: 70.3 ± 8.9
G3: 72.4 ± 13.0
Y; 98% RES 24 G1: 1
G2: 2
G3: 3
80% 3 8 G1: LP, KE
G2: LP, KE
G3: LP, KE
G1: LS, Hip
G2: LS, Hip
G3: LS, Hip
Rhodes etal.
[58]
C: 0/22
G1: 0/22
C: 68.2 ± 3.5
G1: 68.8 ± 3.2
C: 61.7 ± 12.9
G1: 68.4 ± 12.0
MN; 85% RES 52 3 75% 3 8 LP, KE FN, LS, T,
WT
Vincent and
Braith [42]
C: 16
G1: 24
G2: 22
(sex not
reported)
C: 71.0 ± 5
G1: 67.6 ± 6
G2: 66.6 ± 7
C: 71.0 ± 14
G1: 74.4 ± 16
G2: 74.8 ± 15
Y; ≥ 85% RES 26 3 G1: 50%
G2: 80%
1 G1: 13
G2: 8
G1: LP;
KE
G2: LP, KE
G1: FN, LS,
WT
G2:
FN; LS,
WT
Jessup etal.
[59]
C: 0/9
G1: 0/9
C: 69.4 ± 4.2
G1: 69.1 ± 2.8
C: 84.2 ± 17.7
G1: 78.0 ± 9.2
Y; N/A RES + WB 32 3 75% 1 8—10 LP, KEc FN; LS
Bunout etal.
[44]
C: 5/43
G1: 4/44
C: 77.0 ± 4.5
G1: 77.0 ± 4.1
C: 65.0 ± 11.2
G1: 66.3 ± 10.7
Y; 53% RES + WB 39 2 Elastic bands 3 10 KE FN, LS
Karinkanta
etal. [60]
C: 0/37
G1: 0/37
G2: 0/36
C: 72.0 ± 2.1
G1: 72.7 ± 2.5
G2: 72.9 ± 2.2
C: 74.3 ± 10.8
G1: 74.3 ± 11.0
G2: 69.4 ± 10.6
G1:
Y; 74%
G2:
Y; 67%
G1: RES
G2:
RES + WB
52 3 75 – 80% 3 8—10 G1: KE
G2: KE
G1: FN
G2: FN
Bocalini etal.
[61]
C: 0/12
G1: 0/13
C: 64 ± 8
G1: 66 ± 9
C: 69.1 ± 2.2
G1: 67.9 ± 1.3
Y; N/A RES 24 3 60 – 70% 3 10—12 KE FN, LS
Marques etal.
[62]
C: 0/24
G1: 0/23
C: 67.9 ± 5.9
G1: 67.3 ± 5.2
not reported Y; 78% RES 32 3 75 – 80% 2 6—8 KE T, Hip; FN,
IT
Marques etal.
[46]
C: 0/30
G1: 0/30
C: 68.2 ± 5.7
G1: 70.1 ± 5.4
not reported Y; 72% RES + WB 32 2 Elastic bands 1—3 8—15 KE FN
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1945
Resistance Training for Muscle and Bone Strength in Older Adults
Supsupervised, Att attendance rate, Freq. frequency, C control group, G1 intervention group 1, G2 intervention group 2, G3 intervention group 3, RES resistance training only, RES + WB
resistance plus weight-bearing/impact-loading, statistical improvement post-training compared to control group (p ≤ 0.05), statistical decrement post-training compared to control group
(p ≤ 0.05), no statistical difference post-training compared to the control group (p > 0.05), LP leg press, KE knee extension, FN femoral neck, LS lumbar spine, WT Ward's triangle, TH proxi-
mal 1/3rd thigh, T trochanter, IT inter-trochanteric region, Y yes, MN mostly no—participants supervised during initial three months of twelve-month program
a Estimated from McCartney etal. [53]
b BMD assessed via dual photon absorptiometry rather than dual energy x-ray
c Sum of multiple exercises includingLP and KE
Table 1 (continued)
References Sex (M/F) Age (years) Mass (kg) Sup; Att Mode Length
(weeks)
Freq.
(week−1)
Load (%
1RM)
Sets (#) Reps (#) Strength out-
come
BMD outcome
Villareal etal.
[63]
C: 9/18
G1: 10/16
C: 69 ± 4
G1: 70 ± 4
C: 101 ± 16.3
G1: 99.2 ± 17.4
Y; 88% RES + WB 52 3 65 – 80% 1—2 8—12 LP, KE Hip; LS
Uusi-Rasi
etal. [45]
C: 0/204
G1: 0/205
C: 74.0 ± 3.0
G1: 74.5 ± 2.9
C: 72.5 ± 12.7
G1: 72.0 ± 10.6
Y; 73% RES + WB 52 2 60 – 75% 2 8—12 KE FN, LS
Vincent and
Braith [42]
C: 16
G1: 24
G2: 22
(sex not
reported)
C: 71.0 ± 5
G1: 67.6 ± 6
G2: 66.6 ± 7
C: 71.0 ± 14
G1: 74.4 ± 16
G2: 74.8 ± 15
Y; ≥ 85% RES 26 3 G1: 50%
G2: 80%
1 G1: 13
G2: 8
G1: LP;
KE
G2: LP, KE
G1: FN, LS,
WT
G2:
FN; LS,
WT
Jessup etal.
[59]
C: 0/9
G1: 0/9
C: 69.4 ± 4.2
G1: 69.1 ± 2.8
C: 84.2 ± 17.7
G1: 78.0 ± 9.2
Y; N/A RES + WB 32 3 75% 1 8—10 LP, KEc FN; LS
Bunout etal.
[44]
C: 5/43
G1: 4/44
C: 77.0 ± 4.5
G1: 77.0 ± 4.1
C: 65.0 ± 11.2
G1: 66.3 ± 10.7
Y; 53% RES + WB 39 2 Elastic bands 3 10 KE FN, LS
Karinkanta
etal. [60]
C: 0/37
G1: 0/37
G2: 0/36
C: 72.0 ± 2.1
G1: 72.7 ± 2.5
G2: 72.9 ± 2.2
C: 74.3 ± 10.8
G1: 74.3 ± 11.0
G2: 69.4 ± 10.6
G1:
Y; 74%
G2:
Y; 67%
G1: RES
G2:
RES + WB
52 3 75 – 80% 3 8—10 G1: KE
G2: KE
G1: FN
G2: FN
Bocalini etal.
[61]
C: 0/12
G1: 0/13
C: 64 ± 8
G1: 66 ± 9
C: 69.1 ± 2.2
G1: 67.9 ± 1.3
Y; N/A RES 24 3 60 – 70% 3 10—12 KE FN, LS
Marques etal.
[62]
C: 0/24
G1: 0/23
C: 67.9 ± 5.9
G1: 67.3 ± 5.2
not reported Y; 78% RES 32 3 75 – 80% 2 6—8 KE T, Hip; FN,
IT
Marques etal.
[46]
C: 0/30
G1: 0/30
C: 68.2 ± 5.7
G1: 70.1 ± 5.4
not reported Y; 72% RES + WB 32 2 Elastic bands 1—3 8—15 KE FN
Villareal etal.
[63]
C: 9/18
G1: 10/16
C: 69 ± 4
G1: 70 ± 4
C: 101 ± 16.3
G1: 99.2 ± 17.4
Y; 88% RES + WB 52 3 65 – 80% 1—2 8—12 LP, KE Hip; LS
Uusi-Rasi
etal. [45]
C: 0/204
G1: 0/205
C: 74.0 ± 3.0
G1: 74.5 ± 2.9
C: 72.5 ± 12.7
G1: 72.0 ± 10.6
Y; 73% RES + WB 52 2 60 – 75% 2 8—12 KE FN, LS
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1946 S.J.O’Bryan et al.
sessions per week [65]. In one study [45], training frequency
was reduced from twice per week to once per week in year
two of a two-year program, and hence data after only the
first year were examined. Resistance training intensity was
a load between 60 and 80% of 1RM for nine studies [43, 45,
5863, 65], and three studies examined the effect of 40%
1RM [40, 41] or 50% 1RM [42] vs. 80% 1RM. Two studies
used elastic resistance bands and, therefore, load could not
be quantified [44, 46]. The number of completed sets per
exercise was three for six studies [43, 44, 58, 60, 61, 65],
two for two studies [45, 62], one for two studies [42, 59] and
ranged between one and three sets for four studies [40, 41,
46, 63]. Repetitions ranged from six to fifteen per exercise
for seven studies [45, 46, 5963] whereas others completed
twelve [43], ten [44], or eight repetitions [58, 65]; two stud-
ies performed seven or fourteen repetitions depending on
the load [40, 41].
Three studies met the eligibility criteria but did not report
both outcome measures in sufficient detail, and information
could not be retrieved via e-mail correspondence with study
authors [43, 44, 59]. As such, these three studies were omit-
ted from the meta-analysis.
3.3 Risk‑of‑Bias andQuality Assessment
A detailed risk-of-bias analysis is provided in the ESM.
Thirteen studies had an overall low risk of bias, one study
had some concerns [42], and one study had a high risk of
bias [66] and was excluded from the quantitative analysis.
The overall quality of the evidence was high for muscle
strength, moderate for femur/hip BMD, and very low for
lumbar spine BMD (Table2).
3.4 Concomitant Changes inMuscle Strength
andBMD Following Resistance Training
Eleven studies [4042, 45, 46, 58, 6063, 65] were included
in the multi-variate meta-analysis of combined changes in
muscle strength (control n = 406; intervention n = 498) and
femur/hip BMD (control n = 402; intervention n = 501).
Progressive resistance training programs concomitantly
increased muscle strength (∆ SMD = 1.1%; 95% confidence
interval [CI] 0.73, 1.47; p ≤ 0.001) and femur/hip BMD (∆
MD = 2.77%; 95% CI 0.44, 5.10; p = 0.02) with a Riley’s
correlation of r = 0.28 (Fig. 2). When muscle strength
was reported as changes in leg press 1RM [41, 42, 58, 63,
65], the pooled MD was 25.06% (95% CI 16.87, 33.25;
p 0.001). The likelihood for positive change in muscle
strength was more certain than femur/hip BMD, evidenced
by lower heterogeneity (I2 = 78.1% vs 98.6%), a higher
lower limit of the prediction interval (> ∆ 0% vs ~ 5%)
−10 −5 0510 15 20
0.00.5 1.01.5 2.0 2.5 3.0
Femur/hip BMD (mean difference in % change)
)
egnahc%niecnereffiddezidradnats(htgnertsbmilrewoL
Fig. 2 Correlation between changes in lower-limb muscle strength
and femur/bone mineral density (BMD) for each individual study
(black dots) and their 95% confidence intervals (dashed ellipses). The
green diamonds show the estimated pooled change for each outcome
separately, while the blue diamond shows the overall combined effect
of the two outcomes. The red ellipse represents the 95% confidence
interval of the combined effect, whereas the black ellipse represents
the prediction interval for future studies
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1947
Resistance Training for Muscle and Bone Strength in Older Adults
Table 2 GRADE analysis of the overall quality of the evidence
DXA dual X-ray absorptiometry, SMD standardized mean difference
a Although substantial overall heterogeneity reported, this was downgraded to moderate when considering training mode
b Considerable heterogeneity that could not be explained by individual training characteristics
c Large differences in beneficial effects
d The lower limit of the 95% confidence interval contradicts the benefit of the intervention
Certainty assessment № of patients Main Effects Overall Certainty
№ of studies Study design Risk of bias Inconsistency Indirectness Imprecision Publication bias Progressive
resistance
training
Non-
exercise
control
Absolute
(95% CI)
Muscle Strength (follow-up: range 24weeks to 52weeks; assessed with: leg press or knee extension 1RMAX)
11 Randomised trials Not serious Not seriousaNot serious Not serious Undetected 498 406 Mean 1.1% SMD higher
(0.73 higher to 1.47 higher)
⨁⨁⨁⨁
High
Femur/hip bone mineral density (follow-up: range 24weeks to 52weeks; assessed with: DXA)
11 Randomised trials Not serious SeriousbNot serious Not serious Undetected 501 402 Mean 2.77% g/cm3 higher
(0.44 higher to 5.1 higher)
⨁⨁⨁◯
Moderate
Lumbar spine bone mineral density (follow-up: range 24weeks to 52weeks; assessed with: DXA)
10 Randomised trials Not serious Very seriousb,c Not serious Serious dUndetected 447 390 Mean 1.6% g/cm3 higher
(1.44 lower to 4.63 higher)
⨁◯◯◯
Very low
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1948 S.J.O’Bryan et al.
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Rhodes et al. [58]
Vincent and Braith [42]
Bocalini et al. [61]
Marques et al. [62]
Marques et al. [46]
Villareal et al. [63]
Bunout et al. [44]
Karinkanta et al. [60]
Uusi-Rasi et al. [45]
Mean age 65 - 70 years
Mean age >70 years
Overall
Heterogeneity: 2 = 0.26, I 2 = 69.35%, H 2 = 3.26
Heterogeneity: 2 = 0.07, I 2 = 70.55%, H 2 = 3.40
Heterogeneity: 2 = 0.23, I 2 = 78.09%, H 2 = 4.57
Test of i = j: Q(8) = 25.43, p = 0.00
Test of i = j: Q(2) = 6.71, p = 0.03
Test of group differences: Q b(1) = 3.93, p = 0.05
Study
Favours control Favours intervention
0 1 2 3
Lower limb strength
(standardized difference in % change)
with 95% CI
Hedges’ g
1.76 [
2.01 [
1.16 [
1.94 [
1.07 [
2.03 [
0.79 [
0.38 [
0.73 [
1.08 [
0.61 [
0.47 [
1.24 [
0.69 [
1.07 [
0.82,
1.07,
0.47,
1.24,
0.48,
1.09,
0.20,
-0.13,
0.18,
0.66,
0.21,
0.27,
0.83,
0.33,
0.74,
2.70]
2.96]
1.85]
2.65]
1.66]
2.98]
1.37]
0.88]
1.28]
1.51]
1.01]
0.66]
1.65]
1.04]
1.39]
5.97
5.93
7.76
7.61
8.54
5.93
8.61
9.27
8.91
9.91
10.10
11.45
(%)
Weight
a
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Rhodes et al. [58]
Vincent and Braith [42]
Bocalini et al. [61]
Villareal et al. [63]
Marques et al. [62]
Marques et al. [46]
Karinkanta et al. [60]
Uusi-Rasi et al. [45]
Mean age 65 - 70 years
Mean age >70 years
Overall
Heterogeneity: 2 = 5.40, I 2 = 95.79%, H 2 = 23.78
Heterogeneity: 2 = 0.00, I 2 = 0.00%, H 2 = 1.00
Heterogeneity: 2 = 4.37, I 2 = 95.70%, H 2 = 23.27
Test of i = j: Q(8) = 53.11, p = 0.00
Test of i = j: Q(1) = 0.02, p = 0.90
Test of group differences: Q b(1) = 2.87, p = 0.09
Study
Favours controlFavours intervention
-10 -5 0 5 10
Femur/hip BMD
(mean difference in % change)
with 95% CI
Mean Diff.
-0.51 [
1.20 [
1.49 [
7.63 [
2.88 [
1.76 [
2.08 [
-0.87 [
3.61 [
0.73 [
0.63 [
2.22 [
0.66 [
1.90 [
-3.86,
0.53,
-7.62,
5.59,
0.21,
1.61,
1.15,
-2.55,
2.16,
-0.58,
-0.08,
0.52,
0.03,
0.52,
2.85]
1.87]
10.60]
9.67]
5.56]
1.91]
3.02]
0.80]
5.06]
2.04]
1.34]
3.93]
1.28]
3.28]
7.84
9.28
3.86
8.73
8.33
9.34
9.21
8.92
9.02
9.08
9.27
(%)
Weight
b
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1949
Resistance Training for Muscle and Bone Strength in Older Adults
(Fig.2]), and higher overall quality of the evidence (high vs
moderate) (Table2). From ten studies [40, 42, 43, 45, 46,
58, 59, 61, 63, 65] that included lumbar spine BMD (control
n = 390; intervention n = 447), no change in this outcome
was detected following the resistance training intervention
(∆ MD = 1.60%; 95% CI − 1.44, 4.63; p = 0.30).
3.5 Effect ofParticipant Characteristics
onConcomitant Changes inMuscle Strength
andBMD Following Resistance Training
From the differences in participant characteristics identi-
fied in Sect.3.2, a sub-group meta-regression determined
the effects of age (mean age 65–70years vs. > 70years)
and BMI (normal BMI vs. overweight BMI) on strength
and BMD outcomes. Age had no significant effect on the
positivechange in strength or femur/hip BMD following the
resistance training intervention (both p ≥ 0.05), although the
magnitude of the increase tended to be greater for the 65- to
70-year-old group (Fig.3a, b). Participants with a normal
BMI demonstrated greater improvements in muscle strength
(∆ SMD = 1.05%; 95% CI 0.7, 1.41; p = 0.02) but no differ-
ence in BMD compared to the overweight group (Fig.4a,
b, c).
3.6 Effect ofResistance Training Characteristics
onConcomitant Changes inMuscle Strength
andBMD
None of the individual training characteristics showed a
significant combined effect on both muscle strength and
BMD, presumably because of significant heterogeneity and
noticeably large 95% CIs for BMD (Fig.5 and Table3).
However, similar positive main effects on muscle strength
and femur/hip BMD were observed with higher training fre-
quencies, whereas differences in the magnitude and direc-
tion of the main effect for muscle strength and femur/hip
BMD were observed for mode, volume (sets and repetitions),
and load. For example, strength improvements were signifi-
cantly better following resistance training only (Fig.6a) and
enhanced with a higher number of sets, whereas improve-
ments in femur/hip BMD were enhanced following resist-
ance plus weight-bearing/impact-loading training, lower
volumes, and higher loads. Program length had a minimal
effect on both outcomes.
3.7 Secondary Outcomes
Changes in secondary outcomes following the exercise
intervention are detailed in the ESM. Briefly, the following
changes were reported for the intervention group compared
with the control group: (i) lean body mass increased for 3/5
studies [62, 63, 65], (ii) muscle hypertrophy increased for
2/2 studies [41, 43], (iii) functional performance increased
for 10/11 studies [4346, 5963, 65], (iv) number of injuri-
ous falls decreased for 1/1 study [45], and (v) self-efficacy
increased for 2/3 studies [60, 63].
3.8 Small Study Effect
A small study effect was observed for the strength outcome
(Egger’s test p < 0.001) [ESM]. The trim-and-fill method
imputed three additional studies, and pooled Hedges’ g was
slightly smaller than initial results ( SMD = 0.84%; 95%
CI 0.45, 1.23 vs SMD = 1.07; 95% CI 0.74, 1.39) [ESM].
While there was some asymmetry in funnel plots for both
femur/hip and lumbar spine BMD outcomes, Egger’s test
was not significant (ESM).
Fig. 3 Sub-group meta-regression for the effect of age on changes in
muscle strength (a) and femur/hip bone mineral density (b). Lumbar
spine bone mineral density was omitted because there was only one
study in the > 70-year-old age group [45]. CI confidence interval, Diff
difference
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1950 S.J.O’Bryan et al.
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Bunout et al. [44]
Karinkanta et al. [60]
Bocalini et al. [61]
Marques et al. [62]
Marques et al. [46]
Villareal et al. [63]
Normal BMI
Overweight BMI
Overall
Heterogeneity: 2 = 0.05, I 2 = 21.78%, H 2 = 1.28
Heterogeneity: 2 = 0.08, I 2 = 54.52%, H 2 = 2.20
Heterogeneity: 2 = 0.19, I 2 = 67.88%, H 2 = 3.11
Test of i = j: Q(2) = 2.35, p = 0.31
Test of i = j: Q(5) = 11.84, p = 0.04
Test of group differences: Q b(1) = 5.03, p = 0.02
Study
Favours control Favours intervention
0 1 2 3
Lower limb strength
(standardized difference in % change)
with 95% CI
Hedges' g
1.76 [
2.01 [
1.16 [
1.08 [
0.61 [
2.03 [
0.79 [
0.38 [
0.73 [
1.56 [
0.83 [
1.05 [
0.82,
1.07,
0.47,
0.66,
0.21,
1.09,
0.20,
-0.13,
0.18,
1.01,
0.51,
0.70,
2.70]
2.96]
1.85]
1.51]
1.01]
2.98]
1.37]
0.88]
1.28]
2.11]
1.16]
1.41]
5.97
5.93
7.76
9.91
10.10
5.93
8.61
9.27
8.91
(%)
Weight
a
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Karinkanta et al. [60]
Bocalini et al. [61]
Villareal et al. [63]
Marques et al. [62]
Marques et al. [46]
Normal BMI
Overweight BMI
Overall
Heterogeneity: 2 = 0.00, I 2 = 0.00%, H 2 = 1.00
Heterogeneity: 2 = 1.89, I 2 = 89.89%, H 2 = 9.90
Heterogeneity: 2 = 1.26, I 2 = 86.33%, H 2 = 7.32
Test of i = j: Q(2) = 0.96, p = 0.62
Test of i = j: Q(4) = 18.50, p = 0.00
Test of group differences: Q b(1) = 0.26, p = 0.61
Study
Favours controlFavours intervention
-10 -5 0 5 10
Femur/hip BMD
(mean difference in % change)
with 95% CI
Mean Diff.
-0.51 [
1.20 [
1.49 [
0.73 [
1.76 [
2.08 [
-0.87 [
3.61 [
1.14 [
1.52 [
1.36 [
-3.86,
0.53,
-7.62,
-0.58,
1.61,
1.15,
-2.55,
2.16,
0.48,
0.21,
0.39,
2.85]
1.87]
10.60]
2.04]
1.91]
3.02]
0.80]
5.06]
1.79]
2.84]
2.33]
7.84
9.28
3.86
9.08
9.34
9.21
8.92
9.02
(%)
Weight
b
Fig. 4 Sub-group meta-regression for the effect of body mass index
(BMI) on changes in muscle strength (a), femur/hip bone mineral
density (b), and lumbar spine bone mineral density (c). Body mass
index was classified according to World Health Organization classifi-
cation ranges [64]. CI confidence interval, Diff difference
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1951
Resistance Training for Muscle and Bone Strength in Older Adults
Pruitt et al. [40]
Taaffe et al. [65]
Bocalini et al. [61]
Marques et al. [46]
Villareal et al. [63]
Normal BMI
Overweight BMI
Overall
Heterogeneity: 2 = 0.00, I 2 = 0.00%, H 2 = 1.00
Heterogeneity: 2 = 0.00, I 2 = 0.00%, H 2 = 1.00
Heterogeneity: 2 = 0.00, I 2 = 0.00%, H 2 = 1.00
Test of i = j: Q(1) = 0.02, p = 0.88
Test of i = j: Q(2) = 1.93, p = 0.38
Test of group differences: Q b(1) = 0.09, p = 0.76
Study
Favours controlFavours intervention
-10 0 10
Lumbar spine BMD
(mean difference in % change)
with 95% CI
Mean Diff.
0.60 [
-0.36 [
1.02 [
1.86 [
0.47 [
0.54 [
1.03 [
1.02 [
-2.69,
-12.77,
0.83,
0.49,
-1.05,
-2.64,
0.84,
0.84,
3.89]
12.05]
1.21]
3.23]
1.99]
3.72]
1.21]
1.21]
10.52
4.00
12.00
11.72
11.66
(%)
Weight
c
Fig. 4 (continued)
-6 -4 -2 02468
Repetitions
Sets
Load
Frequency
Program length
Mode
∆% Main effects
Femur/hip BMD
Muscle strength
Favours shorter durationFavourslonger duration
Favours lower frequenciesFavourshigher frequencies
Favours lighter load Favoursheavier load
Favours less sets Favoursmore sets
Favours less repetitionsFavours more repetitions
Favours RES FavoursRES + WB
*
Fig. 5 Effect of the different training characteristics on the combined
changes in muscle strength (∆% standardized mean difference) and
bone mineral density [BMD] (∆% mean difference) with 95% con-
fidence intervals when entered into the multi-variate model one at a
time. *Significant main effect (p < 0.05). RES resistance training only,
RES + WB combined resistance training plus weight-bearing/impact-
loading exercises. The confidence interval for program length and
load effect on muscle strength is hidden behind the main effect sym-
bol
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1952 S.J.O’Bryan et al.
Fig. 6 Sub-group meta-regres-
sion for the effect of exercise
mode on changes in muscle
strength (a), femur/hip bone
mineral density [BMD] (b),
and lumbar spine BMD (c)
following training interven-
tions. CI confidence interval,
Diff difference, RES resistance
training only, RES + WB com-
bined resistance training plus
weight-bearing/impact-loading
exercises
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Rhodes et al. [58]
Vincent and Braith [42]
Bocalini et al. [61]
Marques et al. [62]
Bunout et al. [44]
Marques et al. [46]
Villareal et al. [63]
Uusi-Rasi et al. [45]
RES
RES + WB
Overall
Heterogeneity: 2 = 0.15, I2 = 50.80%, H2 = 2.03
Heterogeneity: 2 = 0.06, I2 = 60.28%, H2 = 2.52
Heterogeneity: 2 = 0.25, I2 = 78.07%, H2 = 4.56
Test of i = j: Q(6) = 12.00, p = 0.06
Test of i = j: Q(3) = 7.56, p = 0.06
Test of group differences: Qb(1) = 9.69, p = 0.00
Study
Favours controlFavours intervention
−2 −1 0 1 2 3
Lower limb strength
(standardized difference in % change)
with 95% CI
Hedges’ g
1.76 [
2.01 [
1.16 [
1.94 [
1.07 [
2.03 [
0.79 [
1.08 [
0.38 [
0.73 [
0.47 [
1.46 [
0.65 [
1.12 [
0.82,
1.07,
0.47,
1.24,
0.48,
1.09,
0.20,
0.66,
−0.13,
0.18,
0.27,
1.05,
0.33,
0.77,
2.70]
2.96]
1.85]
2.65]
1.66]
2.98]
1.37]
1.51]
0.88]
1.28]
0.66]
1.86]
0.96]
1.47]
5.97
5.93
7.76
7.61
8.54
5.93
8.61
9.91
9.27
8.91
11.45
(%)
Weight
a
Pruitt et al. [40]
Taaffe et al. [41]
Taaffe et al. [65]
Rhodes et al. [58]
Vincent and Braith [42]
Bocalini et al. [61]
Marques et al. [62]
Jessup et al. [59]
Marques et al. [46]
Villareal et al. [63]
Uusi-Rasi et al. [45]
RES
RES + WB
Overall
Heterogeneity: 2 = 7.59, I2 = 96.60%, H2 = 29.41
Heterogeneity: 2 = 41.09, I2 = 99.12%, H2 = 114.26
Heterogeneity: 2 = 16.87, I2 = 98.76%, H2 = 80.97
Test of i = j: Q(6) = 46.42, p = 0.00
Test of i = j: Q(3) = 56.47, p = 0.00
Test of group differences: Qb(1) = 0.86, p = 0.35
Study
Favours controlFavours intervention
−10 0 10 20
Femur/hip BMD
(mean difference in % change)
with 95% CI
Mean Diff.
−0.51 [
1.20 [
1.49 [
7.63 [
2.88 [
1.76 [
−0.87 [
15.58 [
3.61 [
2.08 [
0.63 [
2.01 [
5.22 [
3.10 [
−3.86,
0.53,
−7.62,
5.59,
0.21,
1.61,
−2.55,
11.30,
2.16,
1.15,
−0.08,
−0.28,
−1.16,
0.53,
2.85]
1.87]
10.60]
9.67]
5.56]
1.91]
0.80]
19.85]
5.06]
3.02]
1.34]
4.30]
11.60]
5.67]
7.84
9.28
3.86
8.73
8.33
9.34
8.92
7.13
9.02
9.21
9.27
(%)
Weight
b
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1953
Resistance Training for Muscle and Bone Strength in Older Adults
Table 3 Output statistics from the univariate sub-group meta-regression for the effect of the different training characteristics on changes in mus-
cle strength, femur/hip BMD, and lumbar spine BMD
Significant values are in bold. RES resistance training only, RES + WB resistance plus weight-bearing/impact-loading exercises
Outcome Training characteristic Studies (#) Coefficient (95% CI) I2 (%) R2 (%) Z score p value
Muscle
strength
Mode (RES vs RES + WB) 12 −0.786 (− 1.236, − 0.335) 50.6 70.1 − 3.42 0.001
Training frequency (3 vs 2) 12 0.513 (− 0.119, 1.145) 72.9 13.5 1.59 0.111
Duration 12 − 0.0004 (− 0.03, 0.03) 79.1 0 − 0.03 0.978
Load 10 − 0.043 (− 0.097, 0.012) 76.3 12.4 − 1.54 0.124
Volume
Sets 12 0.347 (− 0.132, 0.827) 76.0 7.4 1.42 0.156
Reps 12 − 0.043 (− 0.315, 0.229) 80.0 0 − 0.31 0.757
Femur/hip
BMD
Mode (RES vs RES + WB) 12 2.052 (− 2.846, 6.951) 98.2 0 0.82 0.411
Training frequency (3 vs 2) 12 1.158 (− 4.776, 7.093) 98.5 0 0.38 0.702
Duration 12 − 0.059 (− 0.264, 0.146) 97.6 0 − 0.57 0.570
Load 11 0.171 (− 0.230, 0.572) 98.8 0 0.83 0.404
Volume
Sets 12 − 2.065 (− 5.404, 1.273) 97.8 0 − 1.21 0.225
Reps 12 − 0.793 (− 2.637, 1.051) 98 0 − 0.84 0.399
Lumbar spine
BMD
Mode (RES vs RES + WB) 10 3.578 (− 2.564, 9.721) 98.7 0 1.14 0.254
Training frequency (3 vs 2) 12 4.149 (− 1.755, 10.054) 97.2 10.6 1.38 0.168
Duration 10 − 0.127 (− 0.272, 0.018) 96.3 27.0 − 1.72 0.086
Load 9 0.025 (− 0.564, 0.615) 97.9 0 0.08 0.934
Volume
Sets 10 − 3.44 (− 7.104, 0.222) 98.2 25.6 − 1.84 0.066
Reps 10 − 0.759 (− 3.269, 1.751) 97.9 0 − 0.59 0.553
Pruitt et al. [40]
McCartney et al. [43]
Taaffe et al. [65]
Rhodes et al. [58]
Vincent and Braith [42]
Bocalini et al. [61]
Jessup et al. [59]
Marques et al. [46]
Villareal et al. [63]
Uusi-Rasi et al. [45]
RES
RES + WB
Overall
Heterogeneity: 2 = 7.46, I2 = 97.31%, H2 = 37.18
Heterogeneity: 2 = 46.32, I2 = 98.76%, H2 = 80.54
Heterogeneity: 2 = 19.99, I2 = 98.86%, H2 = 87.50
Test of i = j: Q(5) = 305.14, p = 0.00
Test of i = j: Q(3) = 43.50, p = 0.00
Test of group differences: Qb(1) = 1.15, p = 0.28
Study
Favours controlFavours intervention
−10 0 10 20
Lumbar spine BMD
(mean difference in % change)
with 95% CI
Mean Diff.
0.60 [
−4.19 [
−0.36 [
2.73 [
0.50 [
1.02 [
15.16 [
1.86 [
0.47 [
−0.57 [
−0.08 [
3.92 [
1.60 [
−2.69,
−4.74,
−12.77,
0.33,
−8.35,
0.83,
10.25,
0.49,
−1.05,
−1.48,
−2.77,
−2.88,
−1.44,
3.89]
−3.63]
12.05]
5.13]
9.35]
1.21]
20.06]
3.23]
1.99]
0.33]
2.60]
10.71]
4.63]
10.52
11.96
4.00
11.17
5.95
12.00
9.15
11.72
11.66
11.88
(%)
Weight
c
Fig. 6 (continued)
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1954 S.J.O’Bryan et al.
4 Discussion
We investigated the effect of progressive resistance train-
ing programs on concomitant changes in muscle strength
and BMD in older adults and report that: (i) progressive
resistance training concomitantly increased muscle strength
and femur/hip BMD, but not lumbar spine BMD, (ii) larger
heterogeneity and uncertainty for positive adaptation was
reported for femur/hip BMD over muscle strength, (iii) the
strongest determinant for concomitant increases in muscle
strength and femur/hip BMD was a higher training fre-
quency, and (iv) opposite main effects on muscle strength
and femur/hip BMD were observed for resistance training
mode, load, and volume.
4.1 Progressive Resistance Training
andConcomitant Changes inMuscle Strength
andBMD
The loss of muscle and bone is an inevitable part of the
aging process. As such, effective interventions that can miti-
gate both muscle and bone loss have an important clinical
relevance. We report that progressive resistance training
improved muscle strength in 13/14 studies (∆ SMD = 1.12%
or MD 25.06% when measured via leg press 1RM) [4045,
5863, 65], while femur/hip BMD was improved in 6/12
studies (∆ MD = 2.77%) [42, 46, 59, 6163]. The magnitude
of the increase is clinically relevant considering the positive
association between muscle strength and functional capacity
[67] and the inverse relationship between BMD and fracture
risk [68] in older adults, and was greater than reported by a
previous meta-analysis evaluating the effects of other non-
pharmacological interventions on muscle and bone strength
including whole-body vibration [69], Tai Chi [50], and aer-
obic training [31]. The reduced likelihood for significant
increases in BMD compared to muscle strength is perhaps
due to the slower physiological response of bone to mechani-
cal loading [70] and/or that bone requires more time and
more novel loading as well as higher dynamic strain rates
to maximize positive adaptation [2022]. However, despite
the reduced likelihood for significant increases in BMD of
the femur/hip, some suggest that maintenance in BMD could
be clinically relevant [71]. Indeed, some studies that failed
to identify changes in BMD following resistance training
reported significant improvements in mobility (e.g., timed
up and go, chair stand, figure of 8 running) [44, 60, 65],
enhanced endurance [43], and a reduced risk of injurious
falls [45] (ESM).
Nine out of ten studies showed that the exercise training
protocols did not improve BMD of the lumbar spine [40,
4245, 58, 59, 63, 65]. In fact, one study reported a signifi-
cant decrease in BMD at this site compared with a control
group; although, the authors could not physiologically
explain this response [43]. The lack of change in lumbar
spine BMD was somewhat surprising considering that five
of the studies that reported no change had included specific
back strengthening exercises (e.g., lumbar extension, seated
row, latissimus pull-down) [40, 42, 45, 59, 65]. However,
these exercises were completed in a seated or prone posi-
tion, which would considerably offset external load and
strain placed through the lumbar spine, which is essential
for triggering an osteogenic response. As such, it is pos-
sible that more extensive compound exercises performed in
the standing position and that promote gravitational loading
through the lumbar spine may be necessary for improving
BMD at this site [72].
The magnitude of the increase in muscle strength and
BMD following resistance training was not significantly
affected by age (65–70years vs. > 70years), although
the 65- to 70-year-old group tended to exhibit a greater
improvement compared with the > 70-year-old group. The
somewhat reduced capacity for the resistance training inter-
vention to stimulate muscle and bone strength adaptation
in the > 70-year-old group may stem from the accelerated
decline in neuromuscular structure and quality with advanc-
ing age [73], which would subsequently reduce internal bone
stress required to stimulate bone formation [2022]. How-
ever, it is important to acknowledge that progressive resist-
ance training remains an effective strategy for increasing
muscle strength [24] and bone formation [74] into very old
age (> 75years).
Participants in the normal BMI range exhibited greater
improvements in muscle strength compared with their over-
weight counterparts, whereas the change in BMD was not
different between the groups. This result supports the blunt-
ing effect of excess adipose tissue on strength adaptations
to resistance training [75], which evolve from impairments
in muscle protein metabolism and reduced muscle quality
[76, 77]. Thus, we support the recommendation of combin-
ing progressive resistance training with a weight manage-
ment program (including ~ 1g of high-quality protein per
kilogram of body weight per day) and moderate-to-high-
intensity aerobic weight-bearing exercises (e.g., walking,
stair climbing) to maximize concomitant improvements in
muscle strength and BMD in overweight individuals [63].
4.2 Effect ofIndividual Training Characteristics
onConcomitant Changes inStrength andBMD
The sub-group meta-regression did not detect significant
effects of the individual training characteristics on concomi-
tant changes in muscle strength and femur/hip BMD, likely
because of considerable heterogeneity in the outcomes. As
such, it is difficult to make clear recommendations in terms
of the effect of training mode, frequency, volume, load, and
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1955
Resistance Training for Muscle and Bone Strength in Older Adults
program length on concomitant changes in muscle strength
and BMD. However, as muscle strength increased irrespec-
tive of differences within the common training characteris-
tics, whereas positive adaptation for femur/hip BMD was
more heterogeneous and uncertain, we recommend that pro-
grams adopt characteristics more likely to improve femur/
hip BMD. Despite a lack of statistical significance and wide
CIs for the effects of the individual training characteristics
on femur/hip BMD, the direction of the main effects may
indicate that higher training frequencies enhance both out-
comes, whereas mode, volume, and load may differentially
affect strength and BMD.
Resistance training frequencies of three times per week
seemed to enhance concomitant improvements in muscle
strength and femur/hip BMD compared with two times per
week. Previous reviews and original studies have reported
that higher training frequencies increase muscle cross-sec-
tional area [78] and strength [7981], although these effects
are minimized when equated for weekly training volume
[79, 80]. In terms of the bone response, higher training fre-
quencies seem to facilitate BMD improvements following
completion of weight-bearing/impact-loading programs [82,
83], but have less effect following resistance training pro-
grams [65, 84], likely contributing to the wide CIs reported
for the frequency effect on femur/hip BMD. As such, fre-
quency effects on muscle may depend on volume, whereas
frequency effects on BMD may be more dependent on mode.
Of all the individual training characteristics, training
mode had the largest effect on strength and bone adapta-
tions. Traditional resistance training programs were signifi-
cantly better for improving muscle strength, whereas add-
ing a weight-bearing impact-loading component appeared
to be better for improving femur/hip BMD. High-volume
resistance training has been advocated as the most impor-
tant factor for facilitating improvements in muscle strength
and size [85]. In contrast, resistance plus weight-bearing/
impact-loading protocols have been suggested to be superior
for BMD improvements [86]. Altogether, the evidence sug-
gests that to maximize combined gains in muscle strength
and BMD, it seems necessary to maintain resistance training
volume while incorporating weight-bearing impact-loading
exercises into the program. However, adding weight-bear-
ing exercises to a resistance training session would (in most
cases) reduce training volume and limit strength adapta-
tions [25, 87]. As such, one potential approach would be
to perform resistance and weight-bearing/impact-loading
activities on alternate days to mitigate a reduction in within-
session resistance training volume. Indeed, 4/6 resistance
plus weight-bearing/impact-loading studies included in this
review combined these activities into a single session [46,
59, 61, 63], which likely decreased total resistance training
volume and exacerbated differences in the strength response
between the training modes. Conversely, Karinkanta etal.
[60] reported no statistical difference in strength and BMD
between resistance-only and resistance plus weight-bearing/
impact-loading training when modes were performed on
alternating days [60].
Increasing the number of completed sets seemed to
improve muscle strength, whereas fewer sets may be better
for improving femur/hip BMD. The expression of signaling
pathways known to promote myofibrillar protein synthesis
(e.g., insulin-like growth factor 1, Akt/mTOR) is highly sen-
sitive to changes in resistance training volume [88], which
likely explains increased strength with an increased number
of completed sets. Moreover, it is possible that higher train-
ing volumes stimulate positive neuromuscular adaptations
such as motor unit remodeling and a type IIa fiber type shift
[89]. However, the mechanosensitivity of bone declines soon
after a stimulus is initiated, meaning that if the load is ade-
quate, increasing volume provides no additional osteogenic
benefit [90, 91]. In support of this, Taaffe etal. [65] reported
no additional benefit to BMD when resistance training at
80%1RM was completed once, twice, or three times per
week. Moreover, Cunha etal. [87] reported that three sets of
resistance training increased muscle strength compared with
one set, but had no additional benefit to BMD in osteosarco-
penic women [87]. Despite this, of the eight studies included
in this review that evaluated the effect of one or two sets per
exercise on strength and BMD outcomes [4042, 45, 46, 59,
62, 63], all (but one that used elastic bands [46]) reported
increased muscle strength and six reported increased femur/
hip BMD [41, 42, 46, 59, 62, 63]. This is in contrast to
the eight studies that evaluated the effect of three sets per
exercise [40, 41, 43, 44, 58, 60, 61, 65], which all reported
increased muscle strength but only one reported an increase
in femur/hip BMD [61]. Indeed, meta-regression showed
that training volume had the second largest main effect on
femur/hip BMD behind training mode and, therefore, is an
important variable to consider when targeting bone forma-
tion with progressive resistance training. Although a physio-
logical explanation for the observed favorable effect of lower
training volumes on femur/hip BMD is unclear, a higher
volume of resistance training may induce fatigue and require
a reduction in the external load, subsequently reducing bone
strain and the osteogenic response [18, 92]. Unfortunately,
none of the included studies specified if the load remained
constant within a session or if repetitions were completed to
failure, which could provide insight into participant fatigue
development during training sessions.
The external load (%1RM) had minimal effect on muscle
strength, whereas external loads of 75–80% 1RM seemed
better for improving the BMD response. Previous meta-anal-
yses have advocated higher external loads for facilitating
strength adaptations in older men and women [25]. Rea-
sons for discrepancy may evolve from a higher percentage
of female individuals in our study (92% vs ~ 50/50 split).
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1956 S.J.O’Bryan et al.
Higher intensity loads tend to favor older male individuals
compared with female individuals [27], potentially because
women display a failure to downregulate myostatin after
resistance loading compared with age-matched men [93],
and older men exhibit greater anti-inflammatory benefits in
response to external loads compared with women [94]. In
terms of BMD, heightened mechanical loads stimulate bone
modeling and remodeling to increase bone mass and bone
stiffness [92, 95], and the higher loads advocated here are
in agreeance with current recommendations for optimizing
BMD in older adults [96]. However, a recent meta-analysis
by Souza etal. [97] reported similar effects of high (≥ 70%
1RM) and low (< 70% 1RM) load resistance training on
BMD in male and female adults aged 45years. Taken
together, it is possible that the effects of the external load
on BMD may be influenced by hormonal changes with age
(i.e., middle-aged vs old age) and/or if resistance training
is performed in conjunction with weight-bearing exercises.
4.3 Limitations
Limitations of the evidence include a lack of specific
details pertaining to the rate of mechanical loading/move-
ment velocity [98], time under tension [25], contraction
type [99], and whether repetitions were completed to fail-
ure [100], some of which may explain some of the reported
heterogeneity and lack of significant effects for the indi-
vidual training characteristics. Moreover, seven studies
reported range values for load, sets, and/or repetitions [45,
46, 5963] and two studies utilized elastic bands during
resistance training [44, 46], likely increasing inter-individ-
ual variability in the strength and BMD responses. Last,
the underrepresentation of older male participants (8% of
the total sample) makes it difficult to determine whether
similar concomitant changes in muscle strength and BMD
following progressive resistance training exist between
the sexes. A sub-group meta-regression to determine sex
differences was not conducted as sufficient data were not
available for male and female individuals separately.
The PRISMA guidelines [36] were adhered to in
preparation of this review, although some limitations of
the processes should be acknowledged. For example, the
omission of gray literature, conference abstracts, and peer-
reviewed articles not published in English poses some risk
of publication bias. Moreover, if a single study included
multiple intervention groups with different training char-
acteristics (e.g., control vs. varying loads or frequencies)
[4042, 65], it was necessary to pool these data into a sin-
gle intervention group, potentially influencing sub-group
meta-regression. However, the results of the sub-group
analysis were in line with the overall conclusions from
each of these studies.
4.4 Future Directions
Future research needs to carefully consider and report
specific details pertaining to exercise training principles
beyond mode, frequency, volume, load, and program
length, so that the actual effects of these variables on
concomitant changes in muscle strength and BMD can
be clearly defined. Although maximal strength is a pri-
mary indicator of skeletal muscle health and function in
older adults, the ability to produce high forces at fast con-
traction velocities (i.e., power) may be a better predictor
of function [101] and fatigue [102]. Moreover, although
BMD may explain 60–70% of total bone strength [103],
bone architecture [104] and matrix components [105] are
also crucial for bone strength and may better predict frac-
ture risk [106]. Future research may consider combining
techniques such as force–velocity profiling and quantita-
tive computed tomography [107] or magnetic resonance
imaging [108] to concurrently assess changes in muscle
strength, contraction velocity, and power production as
well as trabecular architecture and matrix components
such as mineral, collagen, water, and non-collagenous
proteins. An increase in the representation of male par-
ticipants in future research is also warranted.
5 Conclusions
Progressive resistance training programs concomitantly
increase lower-limb muscle strength and femur/hip BMD
in older adults. However, whereas improvements in muscle
strength occur regardless of manipulation to well-known
training characteristics, positive adaptations in femur/hip
BMD are less certain. As such, to promote concomitant
increases in muscle strength and BMD, we recommend
adopting training characteristics more likely to facilitate
improvements in BMD, which may include resistance train-
ing with a weight-bearing/impact-loading component, train-
ing frequency three times weekly, training volume of one or
two sets per exercise, and an external load of 75–80% 1RM.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s40279- 022- 01675-2.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1957
Resistance Training for Muscle and Bone Strength in Older Adults
Acknowledgements None.
Declarations
Funding Open Access funding enabled and organized by CAUL and
its Member Institutions. No sources of funding were used to assist in
the preparation of this article.
Conflict of interest Steven O'Bryan, Catherine Giuliano, Mary Woess-
ner, Sara Vogrin, Cassandra Smith, Gustavo Duque and Itamar Leving-
er declare that they have no conflicts of interest relevant to the content
of this review.
Author contributions GD, SO, CG, MW and IL conceived the idea for
the review. SO, CG and MW conducted study selection. SO and MW
conducted quality assessment. SO and CG conducted data extraction.
SV performed statistical analysis. SO drafted the initial manuscript.
All authors contributed to data interpretation and reviewing the manu-
script. All authors read and approved the final manuscript.
Availability of data and material Datasets for this review can be made
available from the corresponding author on reasonable request.
Open Access This article is licensed under a Creative Commons Attri-
bution-NonCommercial 4.0 International License, which permits any
non-commercial use, sharing, adaptation, distribution and reproduction
in any medium or format, as long as you give appropriate credit to the
original author(s) and the source, provide a link to the Creative Com-
mons licence, and indicate if changes were made. The images or other
third party material in this article are included in the article's Creative
Commons licence, unless indicated otherwise in a credit line to the
material. If material is not included in the article's Creative Commons
licence and your intended use is not permitted by statutory regula-
tion or exceeds the permitted use, you will need to obtain permission
directly from the copyright holder. To view a copy of this licence, visit
http:// creat iveco mmons. org/ licen ses/ by- nc/4. 0/.
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... Again, we know that exercise programmes that are perceived as being 'too easy' act as a deterrent to strength training adherence (49,55,57). Moreover, other benefits of resistance training (for example, increasing bone mineral density and functional capacity), likely require even higher intensities than the intensities known to build muscular strength (58)(59)(60). Taken together, this evidence supports incorporating 'moderate or higher' intensity guidance into resistance training programmes, as this has been shown to lead to more efficient results, greater satisfaction, and better long-term adherence in our older adult population (34,49,53,61). ...
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In this sub-analysis of a comprehensive meta-analysis, we aimed to determine the effect of different types of exercise on (areal) bone mineral density (BMD) in postmenopausal women. A systematic review of the literature according to the PRISMA statement included (a) controlled trials, (b) with at least one exercise and one control group, (c) intervention ≥ 6 months, (d) BMD assessments at lumbar spine (LS), femoral neck (FN) or total hip (TH), (e) in postmenopausal women. Eight electronic databases were scanned without language restrictions up to March 2019. The present subgroup analysis was conducted as a mixed-effect meta-analysis with “type of exercise” as the moderator. The 84 eligible exercise groups were classified into (a) weight bearing (WB, n = 30) exercise, (b) (dynamic) resistance exercise (DRT, n = 18), (c) mixed WB&DRT interventions (n = 36). Outcome measures were standardized mean differences (SMD) for BMD-changes at LS, FN and TH. All types of exercise significantly affect BMD at LS, FN and TH. SMD for LS average 0.40 (95% CI 0.15–0.65) for DRT, SMD 0.26 (0.03–0.49) for WB and SMD 0.42 (0.23–0.61) for WB&DRT. SMD for FN were 0.27 (0.09–0.45) for DRT, 0.37 (0.12–0.62) for WB and 0.35 (0.19–0.51) for WB&DRT. Lastly, SMD for TH changes were 0.51 (0.28–0.74) for DRT, 0.40 (0.21–0.58) for WB and 0.34 (0.14–0.53) for WB&DRT. In summary, we provided further evidence for the favorable effect of exercise on BMD largely independent of the type of exercise. However, in order to generate dedicated exercise recommendations or exercise guideline, meta-analyses might be a too rough tool.
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Background Older adults display wide individual variability (heterogeneity) in the effects of resistance exercise training on muscle strength. The mechanisms driving this heterogeneity are poorly understood. Understanding of these mechanisms could permit development of more targeted interventions and/or improved identification of individuals likely to respond to resistance training interventions. Thus, this study assessed potential physiological factors that may contribute to strength response heterogeneity in older adults: neural activation, muscle hypertrophy, and muscle contractility. Methods In 24 older adults (72.3 ± 6.8 years), we measured the following parameters before and after 12 weeks of progressive resistance exercise training: i) isometric leg extensor strength; ii) isokinetic (60°/sec) leg extensor strength; iii) voluntary (neural) activation by comparing voluntary and electrically-stimulated muscle forces (i.e., superimposed doublet technique); iv) muscle hypertrophy via dual-energy x-ray absorptiometry (DXA) estimates of regional lean tissue mass; and v) intrinsic contractility by electrically-elicited twitch and doublet torques. We examined associations between physiological factors (baseline values and relative change) and the relative change in isometric and isokinetic muscle strength. Results Notably, changes in quadriceps contractility were positively associated with the relative improvement in isokinetic (r = 0.37–0.46, p ≤ 0.05), but not isometric strength (r = 0.09–0.21). Change in voluntary activation did not exhibit a significant association with the relative improvements in either isometric or isokinetic strength (r = 0.35 and 0.33, respectively; p > 0.05). Additionally, change in thigh lean mass was not significantly associated with relative improvement in isometric or isokinetic strength (r = 0.09 and −0.02, respectively; p > 0.05). Somewhat surprising was the lack of association between exercise-induced changes in isometric and isokinetic strength (r = 0.07). Conclusions The strength response to resistance exercise in older adults appears to be contraction-type dependent. Therefore, future investigations should consider obtaining multiple measures of muscle strength to ensure that strength adaptations are comprehensively assessed. Changes in lean mass did not explain the heterogeneity in strength response for either contraction type, and the data regarding the influence of voluntary activation was inconclusive. For isokinetic contraction, the strength response was moderately explained by between-subject variance in the resistance-exercise induced changes in muscle contractility.