Skeletal muscle adiposity is associated with physical activity,

Skeletal muscle adiposity is associated with physical activity,
exercise capacity and fibre shift in COPD
Matthew Maddocks1*, Dinesh Shrikrishna2*, Simone Vitoriano1, Samantha A
Natanek2, Rebecca J Tanner2, Nicholas Hart3, Paul R Kemp2, John Moxham1,
Michael I Polkey2, Nicholas S Hopkinson2
*Authors contributed equally
1. King’s College London, Departments of Palliative Care, Policy & Rehabilitation
and Asthma, Allergy and Lung Biology, London, UK.
2. National Heart and Lung Institute, NIHR Respiratory Biomedical Research Unit,
Royal Brompton and Harefield NHS Foundation Trust and Imperial College,
London, UK.
3. Guy’s and St Thomas’ NHS Foundation Trust and King’s College London, NIHR
Comprehensive Biomedical Research Centre, London, UK.
Correspondence: Dr Nicholas Hopkinson MA FRCP PhD, Senior Lecturer and
Honorary Consultant Chest Physician National Heart and Lung Institute Royal
Brompton Hospital,
Fulham Road, London, SW3 6NP, United Kingdom. Email:
[email protected] Tel: +44 (0)20 73497775 Fax:+44 (0)20 73497778
ONLINE SUPPLEMENT
METHODS
Physical activity monitoring
Daily step count and physical activity level (PAL) were recorded over 6 consecutive
days incorporating one weekend and four weekdays using a multisensory biaxial
armband accelerometer (SenseWear, Bodymedia; Pittsburgh, US) as described
previously.[1] The monitor incorporates physiological sensors that quantify galvanic
skin response, heat flux and skin temperature to estimate energy expenditure, which
has been validated against indirect calorimetry in patients with COPD [2 3] and
doubly labelled water technique in healthy subjects.[4] Physical activity level (PAL)
was calculated as total energy expenditure (TEE) over sleep energy expenditure,
used as a surrogate for resting energy expenditure (REE). Data were downloaded
and processed using Sensewear professional software (version 6.1) and a valid
physical activity assessment was defined as ≥21.5 hours (90%) wearing time a day
on at least 5 days.
Quadriceps strength and fibre type
Quadriceps maximum voluntary contraction (QMVC) was assessed using the
technique described by Edwards.[5] Subjects sat on a modified chair with their knee
fixed at 90° and with vigorous encouragement performed sustained maximal
isometric quadriceps contractions until 3 consistent traces within 5% of the maximum
were obtained. The force signal from the strain gauge was amplified and displayed
using Labchart software (version 7.1, AD instruments, UK), with QMVC taken as the
highest tension maintained over 1 second. Unpotentiated twitch tension (TwQ) was
measured using the method of Polkey et al.;[6] briefly twitches were obtained
following 20 min rest using supramaximal femoral nerve magnetic stimulation with a
70 mm figure-of-eight coil (Magstim, UK). A measure of voluntary quadriceps
activation (twitch interpolation) was derived by superimposing twitches during the
QMVC.[7]
Percutaneous biopsy of the vastus lateralis of the leg used for strength assessment
was performed using the Bergstrom technique [8] after subjects had rested for 20
min, on a day without strenuous physical activity. Samples for histology and were
frozen in melting isopentane and liquid nitrogen, respectively, prior to storing at 80°C (online supplement). Immunohistochemistry using antibodies against type I and
IIa myosin and laminin was performed on transverse muscle sections to calculate
type I, IIa (both pure IIa and hybrid IIa/IIx fibres, which could not be differentiated)
and IIx fibre proportions from ≥100 fibres.[9] Fibre shift (FS) was defined by type I
fibre proportions falling below and/or type IIx fibre proportions falling above the cutoff taken from healthy 60–70 year olds.[10]
Additional measurements
Body mass index (BMI) was calculated from height and weight measured
prospectively. Spirometry, plethysmographic lung volumes, carbon monoxide
diffusing capacity (TLco) (CompactLab system; Jaeger, Wurzburg, Germany) and
arterial blood gases were determined in accordance with European Respiratory
Society (ERS) /American Thoracic Society (ATS) recommendations.[11 12] Exercise
capacity was measured using the 6 minute walk (6MW) or incremental shuttle walk
(ISW) incorporating a practice walk performed at least 30 minutes prior to testing.[13
14] Fat mass and fat free mass index (FFMI) were determined by bioelectrical
impedance analysis at 50kHz (BodyStat QuadScan 4000; BodyStat, Douglas, United
Kingdom) and a disease specific regression equation.[15] Health-related quality of
life was determined using the St. George’s Respiratory Questionnaire (SGRQ).
RESULTS
Table S1a: Intra-observer reliability for two assessments of thigh composition
using a standardised mid-thigh CT image (n=10)
2
Lean tissue CSA (cm )
Skeletal muscle attenuation
(HU)
2
Intramuscular fat CSA (cm )
% intramuscular fat
2
MTCSA (cm )
Mean value
for both
assessors
Mean difference
between
assessors
198.21
43.52
0.148
0.02
SD of the
difference
between
assessors
0.239
0.01
110.81
5.74
211.52
0.042
0.01
0.129
0.467
0.21
0.352
Inter-class
correlation coefficient
[95% CI]
1.000 [1.000, 1.000]
1.000 [1.000, 1.000]
0.996 [0.986, 0.999]
0.996 [0.984, 0.999]
1.000 [1.000, 1.000]
Table S1b: Inter-observer reliability for two consecutive assessments of thigh
composition using a standardised mid-thigh CT image (n=10)
2
Lean tissue CSA (cm )
Skeletal muscle attenuation
(HU)
2
Intramuscular fat CSA (cm )
% intramuscular fat
2
MTCSA (cm )
Mean value
for both
assessments
Mean difference
between
assessments
198.21
43.52
0.176
0.01
SD of the
difference
between
assessments
0.220
<0.01
11.87
5.74
211.58
0.101
0.12
0.099
0.003
0.31
0.003
Intra-class correlation
coefficient [95% CI]
1.000 [1.000, 1.000]
1.000 [1.000, 1.000]
0.997 [0.988, 0.999]
0.991 [0.965, 0.998]
0.990 [0.960, 0.997]
Table S1c: Inter-occasion reliability for two consecutive assessments of thigh
composition using mid-thigh CT images three months apart in patients with
stable COPD (n=29) receiving a placebo intervention
2
Lean tissue CSA (cm )
Skeletal muscle attenuation
(HU)
2
Intramuscular fat CSA (cm )
% intramuscular fat
2
MTCSA (cm )
Mean value
for both
assessments
Mean difference
between
assessments
183.57
42.69
0.469
0.02
SD of the
difference
between
assessments
0.798
0.02
12.45
6.449
0.203
0.93
0.002
0.84
0.933 [0.856, 0.958]
0.950 [0.893, 0.976]
196.03
0.068
0.078
0.986 [0.970, 0.993]
Intra-class correlation
coefficient [95% CI]
0.988 [0.975, 0.994]
0.863 [0.708, 0.936]
Abbreviations: CSA – cross-sectional area; HU – Hounsfield Unit; SD – standard
deviation; CI – confidence interval
Table S2: Relationships between mid-thigh CSA, lean tissue CSA and
quadriceps strength with physical inactivity, exercise capacity and fibre shift.
BMI
FM
Step count
PAL
ISW
6MW
Type I %
r=0.28
r=-0.13
r=0.05
r=0.32
r=0.16
p=0.02
p=0.29
p=0.70
p=0.06
p=0.23
r=0.17
r=-0.13
r=0.07
r=0.21
r=0.12
FFMI
mid-thigh CSA
Lean CSA
QMVC
p=0.18
p=-0.23
p=0.56
p=0.37
p=0.37
r=0.31
r=-0.06
r=0.11
r=0.18
r=0.11
p=0.01
p=0.76
p=0.39
p=0.26
p=0.42
r=0.24
r=-0.17
r=0.10
r=0.45
r=0.16
p=0.05
p=0.17
p=0.41
p=0.003
p=0.24
r=0.26
r=-0.14
r=0.15
r=0.47
r=0.18
p=0.04
p=0.26
p=0.23
p=0.002
p=0.19
r=0.19
r=-0.14
r=0.11
r=0.28
r=0.17
p=0.13
p=0.25
p=0.35
p=0.08
p=0.22
Abbreviations: BMI – body mass index; FM – Fat mass; FFMI – fat free mass index;
CSA – cross-sectional area; QMVC – quadriceps maximum voluntary contraction,
PAL – physical activity level, ISWT – incremental shuttle walk test, 6MW – six minute
walk text
Figure S1: Relationship between mid-thigh (a) % intramuscular fat and (b)
skeletal
muscle attenuation and proportion of type I muscle fibres in the Vastus
lateralis
muscle.
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