Investigating the Anabolic Response to Resistance Exercise During Critical Illness: The ARTIST-1 Randomized Controlled Trial
Phase: NA
Conditions: Critical Illness, Muscle Loss
Sponsor: Karolinska University Hospital

Study Protocol (2021-12-08)
Investigating the Anabolic Response To resISTance exercise during critical
illness: The ARTIST-1 Randomized Controlled Trial.
Primary investigator: Martin Sundström Rehal
Co-primary investigators: Arabella Fischer, Olav Rooyackers
Background
The debilitating impact of critical illness has been recognized for several decades. Disability
related to intensive care is now described as a syndrome called ICU-acquired weakness
(ICUAW). ICUAW affects up to 70% of ICU patients and is most common with higher illness
severity. The pathophysiology is heterogenous, and involves muscle protein breakdown, altered
bioenergetics, axonal injury and impaired excitation-contraction coupling. Patients that develop
ICUAW require longer hospitalization and have a higher risk of death [1].
Weakness also has significant long-term consequences. In a landmark study, Herridge et al
observed that predominantly young and previously healthy survivors of acute respiratory failure
had reduced exercise capacity up to five years after ICU stay [2]. Physical function was
unrelated to residual pulmonary dysfunction. Long-term disability was associated with significant
health care costs, delayed return to work, and overall poor quality of life.
Preventing muscle atrophy is a potential way to counteract weakness. Critical illness is
associated with a rapid loss of skeletal muscle, which may exceed 10% of lean body mass in
the first week of intensive care [3,4]. Dos Santos et al found that a majority of ICU survivors had
not recovered their muscle volume up to six months after hospital discharge [5].
During critical illness there is a dramatic increase in muscle protein breakdown, while synthesis
is unaltered [6]. The result is a net loss of total body protein. Aging and comorbid conditions also
contribute toward a resistance to anabolic signals, which may be exacerbated by immobilization
and systemic inflammation [7]. Our research group has previously found that nutritional
interventions such as amino acid supplementation can improve whole-body protein balance in
ICU patients [8,9], but the effect on muscle metabolism is still unknown. Studies in exercise
physiology have demonstrated that resistance training and amino acid ingestion have
synergistic effects on muscle protein synthesis in healthy subjects [10]. It is therefore an

appealing therapy to counteract muscle wasting in ICU, and to regain muscle mass during
convalescence.
Despite several clinical trials, there remains equipoise regarding the efficacy of exercise in
improving physical function in-ICU or after discharge [11,12]. These mixed signals are
unsurprising given the heterogeneous causes of ICUAW. Only a few studies in this field assess
muscle architecture or cellular signaling in response to training [13,14]. However, the gold
standard in determining the anabolic response to exercise is to directly measure the effect on
protein synthesis and breakdown. To our knowledge there is still no published research using
this methodology in critically ill patients.
Aim and hypothesis
The overall aim of this project is to determine the anabolic response to resistance exercise
during and after critical illness.
The investigators hypothesize that resistance exercise, in addition to amino acid
supplementation and routine physiotherapy, results in an improved muscle protein balance in
ICU patients compared to amino acid supplementation and routine physiotherapy alone (primary
outcome). The effect of the intervention on other parameters of muscle protein kinetics and
within-group differences in protein kinetics before and after physiotherapy will be assessed as
secondary outcome measures.
Methods
Study design
Single-center randomized controlled assessor-blind clinical trial.
Population
Inclusion criteria
1.
Adult (≥18 years) patient admitted to the ICU of the study site.
2.
Patient deemed suitable for active mobilization by the attending physician and
physiotherapist.

3.
Not expected to be discharged or transferred from the unit within 24 h.
4.
Functioning arterial catheter in situ.
Exclusion criteria
1.
Not able to provide informed consent.
2.
Systemic anticoagulation with LMWH/UFH/DOAC in therapeutic dose range for deep
vein thrombosis or pulmonary embolism, or dual antiplatelet therapy. If LMWH is
administered twice daily, the patient is eligible for participation provided that vascular
access is performed at nadir prior to the first daily dose.
3.
Clinically significant inherited or acquired disorder of hemostasis.
4.
Morbid obesity that interferes with femoral cannulation or doppler measurements.
5.
Hemodynamic instability requiring ongoing volume resuscitation with crystalloid solutions
or blood products.
6.
Lower-limb amputee.
7.
Lower-limb artheriosclerotic disease with critical ischemia.
8.
Metastatic cancer or active hematological malignancy.
9.
Inherited disorder of amino acid metabolism.
10. Chronic muscle, neuromuscular och neurologic disease with prior documentation of
clinically significant lower-limb involvement.
11. Pregnancy.
12. CAM-ICU screening positive for delirium.
13. Single organ failure not requiring invasive mechanical ventilation prior to enrollment.
Intervention and comparator
All research subjects enrolled in the study will perform a physiotherapist-led session of
standardized active mobilization, while receiving an intravenous infusion of mixed amino acids
(active comparator). Patients randomized to the intervention group will in addition perform a
resisted knee extension exercise as a part of their physiotherapy session.
Outcomes
Primary outcome
The difference between the experimental and active comparator group in change in lower limb
protein balance (nmol Phenylalanine/min) from baseline to post-physiotherapy.

Secondary outcomes
1.
The difference between the experimental and active comparator group in change in
lower limb protein synthesis and breakdown (nmol Phenylalanine/min) from baseline to
post-physiotherapy.
2.
The difference between the experimental and active comparator group in change in
lower limb 3-methylhistidine rate of appearance (nmol/min) from baseline to
post-physiotherapy.
3.
The change in lower limb protein balance, synthesis and breakdown (nmol
Phenylalanine/min) in the experimental group, from baseline to post-physiotherapy.
4.
The change in lower limb lower limb 3-methylhistidine rate of appearance (nmol/min) in
the experimental group, from baseline to post-physiotherapy.
5.
The change in lower limb protein balance, synthesis and breakdown (nmol
Phenylalanine/min) in the active comparator group, from baseline to post-physiotherapy.
6.
The change in lower limb lower limb 3-methylhistidine rate of appearance (nmol/min) in
the active comparator group, from baseline to post-physiotherapy.
Investigation protocol
At the beginning of the protocol, a primed intravenous infusion of labeled ring-2H5-phenylalanine
(bolus 2.94 µmol/kg, infusion rate 2.94 µmol/kg/h) and 2H3-methylhistidine (bolus 0.06 µmol/kg,
infusion rate 0.06 µmol/kg/h) is started to achieve a steady state of tracer dilution in arterial
blood and continued until the end of the protocol. A femoral venous catheter is then sited under
local anesthesia for lower limb blood sampling. The physician placing the catheter is free to
determine the side of placement depending on the vascular anatomy on ultrasound
investigation. A standardized measurement of upper and lower limb muscle thickness is also
performed to quantify the baseline muscle mass of study subjects [15].
After 165 minutes of tracer infusion, four 2 ml samples from arterial and lower limb venous blood
and femoral artery blood flow measurements on the side of the catheterized leg are performed
at five minute intervals. Doppler blood flow measurements will be performed using a
high-frequency linear probe with a fixed probe angulation at a level cranial to the branching of
the deep femoral artery. The vessel diameter is determined at the same level. Immediately after
the baseline measurements, an intravenous infusion of mixed amino acids (Glavamin,
Fresenius Kabi) is administered at a rate of 0.1 g/kg/h.

The study subjects will then participate in a physiotherapy session of protocolized active
mobilization. While sitting on the side of the bed, patients in the intervention group will be
encouraged to perform knee extensions with the leg catheterized for blood sampling, targeting
8-12 repetitions to failure in three sets. Resistance is adjusted using ankle weights. The
physiotherapist in charge will document the number of repetitions and other items of the
mobilization protocol performed.
After returning to bed rest, new blood samples and blood flow measurements as described
above are performed to determine the change in lower limb protein balance every 30 minutes
up to 90 minutes post-intervention. At the completion of the protocol the infusions of labeled and
unlabeled amino acids are stopped and the femoral vein catheter is removed. The protocol is
illustrated in Figure 1.
Figure 1. A schematic illustration of the investigation protocol (not to scale).
All other aspects of treatment will be determined by the attending physician and care team, with
a request that the rate of enteral and parenteral nutrition remains unchanged from 06:00 in the
morning until the end of the protocol.
Calculations
Lower limb protein balance will be determined using a two-pool model [6]. Net balance (NB) of
phenylalanine is derived using the Fick principle:

NB = (CA - CV)*PF
where CA = arterial content  (nmol/ml); CV = venous content (nmol/ml); and PF = plasma flow
(ml/min).
The rate of appearance (Ra) approximates protein breakdown and is calculated as:
Ra = CV*[1-(EV/EA)]*PF
Where EA and EV are the arterial and venous enrichments of tracer expressed as molar
percentage excess and calculated as an average of the four blood samples in each
measurement series.
The rate of disappearance (Rd) approximates protein synthesis and is calculated as:
Rd = NB + Ra
Statistical considerations
Randomization
Randomization will be performed using a computer-generated sequence in permuted blocks of
four. Treatment allocation is concealed in opaque envelopes prepared by a research associate
not involved in the study. The envelope is opened by the physiotherapist supervising the
exercise session just before the intervention. Research staff in charge of outcome assessment
are blinded to allocation until all data analysis is complete.
Sample size
As variation in muscle protein balance between ICU patients is very large [16], only paired
comparisons will allow for studies of small-moderate size to find an effect. Unfortunately, there is
no published data that describes the variation in repeated measures of muscle protein balance
in ICU patients to support a formal power calculation. The best available estimate of effect size
comes from pooled results on changes in whole-body protein balance during nutritional
interventions. Using this data, we determine that 10 patients in each treatment arm are required
to observe a mean change from negative to neutral lower limb muscle protein balance. To
account for potential dropouts we aim to enroll a total of 24 patients.

Statistics
Between-group differences of continuous outcomes will be analyzed using two-way repeated
measures ANOVA. Within-group differences will be analyzed using one-way repeated measures
ANOVA. A normal distribution of within-subject change in protein kinetics is assumed from
previous observations. The predetermined level of significance is p ≤ 0.05. Correction for
multiple comparisons will not be applied and p-values for secondary outcomes should be
considered as exploratory.
References
1. Batt J, Herridge MS, Dos Santos CC. From skeletal muscle weakness to functional outcomes
following critical illness: a translational biology perspective. Thorax. Nov
2019;74(11):1091-1098. doi:10.1136/thoraxjnl-2016-208312
2. Herridge MS, Tansey CM, Matté A, et al. Functional disability 5 years after acute respiratory
distress syndrome. N Engl J Med. Apr 2011;364(14):1293-304. doi:10.1056/NEJMoa1011802
3. Plank LD, Connolly AB, Hill GL. Sequential changes in the metabolic response in severely
septic patients during the first 23 days after the onset of peritonitis. Ann Surg. Aug
1998;228(2):146-58. doi:10.1097/00000658-199808000-00002
4. Puthucheary ZA, Rawal J, McPhail M, et al. Acute skeletal muscle wasting in critical illness.
JAMA. Oct 2013;310(15):1591-600. doi:10.1001/jama.2013.278481
5. Dos Santos C, Hussain SN, Mathur S, et al. Mechanisms of Chronic Muscle Wasting and
Dysfunction after an Intensive Care Unit Stay. A Pilot Study. Am J Respir Crit Care Med. Oct
2016;194(7):821-830. doi:10.1164/rccm.201512-2344OC
6. Klaude M, Mori M, Tjäder I, Gustafsson T, Wernerman J, Rooyackers O. Protein metabolism
and gene expression in skeletal muscle of critically ill patients with sepsis. Clin Sci (Lond). Feb
2012;122(3):133-42. doi:10.1042/CS20110233
7. Morton RW, Traylor DA, Weijs PJM, Phillips SM. Defining anabolic resistance: implications for
delivery of clinical care nutrition. Curr Opin Crit Care. 2018 Apr;24(2):124-130. doi:
10.1097/MCC.0000000000000488.
8. Sundström Rehal M, Liebau F, Tjäder I, Norberg Å, Rooyackers O, Wernerman J. A
supplemental intravenous amino acid infusion sustains a positive protein balance for 24 hours in
critically ill patients. Crit Care. 2017 Dec 6;21(1):298. doi: 10.1186/s13054-017-1892-x.

9. Sundström Rehal M, Liebau F, Wernerman J, Rooyackers O. Whole-body protein kinetics in
critically ill patients during 50 or 100% energy provision by enteral nutrition: A randomized
cross-over study. PLoS One. 2020 Oct 5;15(10):e0240045. doi: 10.1371/journal.pone.0240045.
10. Wolfe RR. Skeletal muscle protein metabolism and resistance exercise. J Nutr. 2006
Feb;136(2):525S-528S. doi: 10.1093/jn/136.2.525S.
11. Doiron KA, Hoffmann TC, Beller EM. Early intervention (mobilization or active exercise) for
critically ill adults in the intensive care unit. Cochrane Database Syst Rev. 2018 Mar
27;3(3):CD010754. doi: 10.1002/14651858.CD010754.pub2.
12. Connolly B, Salisbury L, O'Neill B, Geneen L, Douiri A, Grocott MP, Hart N, Walsh TS,
Blackwood B; ERACIP Group. Exercise rehabilitation following intensive care unit discharge for
recovery from critical illness. Cochrane Database Syst Rev. 2015 Jun 22;2015(6):CD008632.
doi: 10.1002/14651858.CD008632.pub2.
13. Fossat G, Baudin F, Courtes L, Bobet S, Dupont A, Bretagnol A, Benzekri-Lefèvre D, Kamel
T, Muller G, Bercault N, Barbier F, Runge I, Nay MA, Skarzynski M, Mathonnet A, Boulain T.
Effect of In-Bed Leg Cycling and Electrical Stimulation of the Quadriceps on Global Muscle
Strength in Critically Ill Adults: A Randomized Clinical Trial. JAMA. 2018 Jul 24;320(4):368-378.
doi: 10.1001/jama.2018.9592.
14. Hickmann CE, Castanares-Zapatero D, Deldicque L, Van den Bergh P, Caty G, Robert A,
Roeseler J, Francaux M, Laterre PF. Impact of Very Early Physical Therapy During Septic Shock
on Skeletal Muscle: A Randomized Controlled Trial. Crit Care Med. 2018 Sep;46(9):1436-1443.
doi: 10.1097/CCM.0000000000003263.
15. Fischer A, Anwar M, Hertwig A, Hahn R, Pesta M, Timmermann I, Siebenrock T, Liebau K,
Hiesmayer M. Ultrasound method of the USVALID study to measure subcutaneous adipose
tissue and muscle thickness on the thigh and upper arm: An illustrated step-by-step guide.
Clinical Nutrition Experimental. 2020 Aug 1;32:38-73. doi: 10.1016/j.yclnex.2020.06.003
16. Gamrin-Gripenberg L, Sundström-Rehal M, Olsson D, Grip J, Wernerman J, Rooyackers O.
An attenuated rate of leg muscle protein depletion and leg free amino acid efflux over time is
seen in ICU long-stayers. Crit Care. 2018 Jan 23;22(1):13. doi: 10.1186/s13054-017-1932-6.