A Randomized Controlled Trial on the Effect of Early Progressive Strength Exercise for Treatment of Acute Achilles Tendon Rupture. The Achilles Tendon Back-On-Track Study.
Phase: NA
Conditions: Achilles Tendon Rupture
Sponsor: Aalborg University Hospital

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Protocol 
Administrative information 
1.Title 
A randomized controlled trial on the effect of Early progressive strength exercise for treatment of 
acute Achilles tendon rupture. The Achilles tendon Back-On-Track study. 
 
2.Trial registration 
2a Trial registration 
The study will be registered at ClinicalTrials.gov: nr and date 
2b WHO Trial Registration Data Set 
Data category 
Information 
Primary registry and trial identifying 
number 
Clinical Trials 
Date of registration in primary registry 
23 January 2021 
Secondary identifying numbers 
Ethics Committee N-20200041 
Source(s) of monetary or material support 
Physiotherapy and Occupational therapy, 
Aalborg University Hospital 
Primary sponsor 
Physiotherapy and Occupational therapy, 
Aalborg University Hospital 
Secondary sponsor(s) 
Orthopaedic department, Aalborg University 
Hospital 
Contact for public queries 
mc@rn.dk 
Contact for scientific queries 
mc@rn.dk  
Public title 
The Achilles tendon Back-On-Track study. A 
randomised controlled trial on the effect of 
Early progressive strength exercise for 
treatment of acute Achilles tendon rupture. 
Scientific title 
A randomised controlled trial on the effect of 
Early progressive strength exercise for 
treatment of acute Achilles tendon rupture. 
Countries of recruitment 
Denmark 
Health condition(s) or problem(s) studied 
Achilles tendon rupture 
Intervention(s) 
Early progressive strength exercise programme 
Key inclusion and exclusion criteria 
Inclusion criteria: Patients with acute Achilles 
tendon rupture treated non-surgically. 
Diagnosed and treatment initiated within 3 days 
(of their injury). Age 18 – 65, able and willing 
to participate in the intervention. Able to speak 
and understand Danish 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
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Exclusion criteria: Achilles tendon rupture 
close to insertion on calcaneus or in the 
musculotendinous junction of the triceps surae. 
Previous Achilles tendon rupture or other 
conditions in either leg causing lower leg 
disability (pain, deficits in strength or range of 
movement). Treated with Fluoroquinolons or 
Corticosteroids within the last 6 months. 
Diabetes or rheumatic diseases. Severe medical 
illness: ASA score higher than or equal to 3 
(ASA: American Society of Anesthesiologists 
physical status classification system) 
Study type 
Randomized controlled trial 
Date of first enrollment 
January 2021 
Target sample size 
82 
Recruitment status 
Not yet recruiting 
Primary outcome(s) 
Achilles Tendon total Rupture Score ATRS 
Key secondary outcomes 
ATRS, IPAQ short form, ATRA, Achilles 
tendon length, fear of re-rupture, adverse 
events, isometric strength and endurance, 
compliance, cost-effectiveness outcomes 
 
3. Protocol version 
Version 1.0 23Jan2021 
 
4. Funding 
The Physiotherapy and Occupational therapy department and Orthopaedic Surgery department at 
Aalborg University Hospital has guaranteed for the funding of the PhD study. This work was also 
supported by the Danish Physiotherapist Research Foundation, North Denmark Region Research 
foundation, AP Møller Lægefonden, Toyotafonden, Praksisfonden for fysioterapi, Danish Society 
of Sports Physical Therapy 
 
5. Roles and responsibilities 
5a Names, affiliations, and roles of protocol contributors 
• Marianne Christensen (MC) 
• Physiotherapy and Occupational Therapy, Aalborg University Hospital, Hobrovej 18-22, 
9000 Aalborg, Denmark, mc@rn.dk , Phone: +45 97662530 
• Interdisciplinary Orthopaedics, Aalborg University Hospital, Aalborg, Denmark 
• Department of Clinical Medicine, Aalborg University, Aalborg, Denmark 
• Inge Lunding Kjær (ILK), Orthopeadic Department, Aalborg University Hospital, Hobrovej 18-
22, 9000 Aalborg, Denmark. i.kjaer@rn.dk 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
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• Karin Grävare Silbernagel (KGS), Department of Physical Therapy, University of Delaware, 
DE USA, kgs@udel.edu 
• Jennifer A. Zellers (JAZ), Program in Physical Therapy, Washington University School of 
Medicine in St. Louis, USA, jzellers@wustl.edu 
• Michael Skovdal Rathleff (MSR), Physiotherapy and Occupational Therapy, Aalborg 
University Hospital, Hobrovej 18-22, 9000 Aalborg, Denmark, misr@hst.aau.dk 
This study is initiated by Marianne Christensen physiotherapist MHSc PhD student and she is the 
project manager. The project will be conducted with MC as primary investigator as part of her 
Ph.D.-studies. MC and MSR wrote the first draft of the protocol. ILK, JAZ and KGS all made 
valuable scientific additions to the draft. ILK is chief orthopaedic foot surgeon and has the clinical 
responsibility for the study. MSR, ILK, JAZ and KGS provided contribution to the study design, 
contents of the intervention and the evaluation methods. 
 
5b Name and contact information for the trial sponsor 
Physiotherapy and Occupational Therapy department, Orthopaedic department, 
Clinic Head- and Orto, 
Aalborg University Hospital 
Hobrovej 18-22 
9000 Aalborg 
Denmark 
 
5c Role of study sponsor and funders  
Sponsor is a part of the study, but is not involved in design, planning and analysis of the study. 
Sponsor will collaborate to ensure the right conditions for planning and conduct of the study and the 
publication of the results. Sponsor is non-commercial and declares no conflict of interest. 
The funding sources will have no influence in the design of this study and will not have any role 
during the study execution, interpretation of the data or dissemination of results. 
 
5d Composition, roles, and responsibilities of the coordinating centre, steering committee, 
endpoint adjudication committee, data management team, and other individuals or groups 
overseeing the trial, if applicable (see Item 21a for data monitoring committee) 
N/A 
 
Introduction 
6. Background and rationale 
6a Description of research question  

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Acute Achilles tendon rupture is a common injury and in Denmark the incidence has increased in 
recent years from 18.2/100.000 in 1984 and up to 31.17/100.000 in 2013.(1,2) Rupture usually 
occurs at age 30-50 with a male to female ratio 3-5:1.(1–3) The Achilles tendon is the largest and 
strongest tendon in the human body and is crucial for normal gait and running.(4) Historically 
surgical treatment has been favoured mainly because the re-rupture rates are lower compared to 
non-surgical treatment (3 vs 13%, respectively).(5,6) However, there is a risk of wound infection in 
surgical treatment compared to non-surgical and the results after a deep infection are often 
devastating.(7,8)  
Regardless of choice of either surgical or non-surgical treatment, long-term muscular deficits and a 
decreased function after Achilles tendon rupture is found up to 7 and 10 years later.(9–11) The 
majority of the patients are of working age and a deficit in physical performance will have impact 
on returning to work and sports.(12–14) The risk of not being able to return to work or sport has 
potential influence on patients quality of life, risk of lifestyle diseases and healthcare economics. 
There have been promising results in treatments using early functional rehabilitation (EFR) during 
the first eight weeks of treatment after both surgical and non-surgical treatment. The re-rupture rate 
with non-surgical treatment combined with EFR is reported similar to the rates with surgical 
treatment, which is an improvement compared to the former non-surgical treatment with 
immobilization.(7,15–18) The intention with early functional rehabilitation is to minimize the loss 
of muscle strength that is inevitable in the immobilizing period. Laboratory studies have also 
indicated that early loading of the ruptured tendon will improve the tendon healing in 
animals(19,20) and clinical studies have confirmed this.(21) 
 
Several studies have reported use of controlled ankle/foot exercises, but few studies examined the 
effect of the exercises on its own and even fewer combined with non-surgical treatment.(22–25) We 
conducted a systematic review investigating the EFR used in the first 8 weeks of treatment and it 
showed very heterogeneus intervention protocols.(26) The components used in the EFR ranged 
from early weight-bearing and controlled range of motion ankle/foot exercises to strength exercises. 
The resistance exercises used in the early phase were most often isometrics, seated heel-rises or 
resistance exercises with an elastic band, but many studies did not describe the exercises and lacked 
information of exercise descriptors (eg. load, repetitions, sets) needed for a replication.(27) 
Based on the results from this systematic review and our clinical expertise we designed a new, well-
defined treatment protocol with exercises that were initiated earlier and with more progression than 
standard care today. We recently tested the feasibility of this new treatment protocol (N-20180072) 
which showed that the early initiation of exercises was highly feasible and patient acceptability was 
high. Based on our findings from 1) the systematic review and 2) our recently completed feasibility 
study, we now wish to test and compare this intervention to the current standard care that is 
delivered today. Such an intervention has the potential to negate the negative long-term functional 
consequences of Achilles tendon ruptures. By enhancing the physical function in the early stage, 
patients will have less sick leave and be able to return to work earlier. We expect that restoring 
early function could also positively benefit long-term outcome.  

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6b Explanation for choice of comparators 
The standard care exercise program is the standard treatment in the hospitals in the North Denmark 
Region. It is considered a safe treatment and well accepted in Denmark and in international 
literature. This program will be included in both study arms and the early progressive exercises will 
be an add-on to the standard treatment. 
 
7. Objectives 
The purpose of this trial is to investigate the efficacy of standard care versus standard care 
combined with an early exercise program in improving the Achilles tendon Total Rupture Score 
ATRS(28) score 13 weeks after non-surgical treated Achilles tendon rupture. 
We hypothesize that individuals with Achilles Tendon rupture randomized to standard care and 
early exercises will have a significantly higher ATRS score (primary outcome) after 13 weeks 
(primary endpoint) compared to individuals receiving standard care only. 
 
8. Description of trial design including type of trial  
The trial is designed as a randomized, superiority trial with a 2-group parallel design with two 
centers. Reporting of the protocol follows the SPIRIT(29) statement and TIDieR(30) and CERT(31) 
for intervention description. The preparation of the trial, including publishing this trial protocol, was 
done in accordance with the PREPARE Trial guide. Before the inclusion of the first participant, the 
trial will be registered on clinicaltrials.gov.  
Potential participants who are excluded during the physical examination and eligible participants 
who decide to withdraw before randomization will be asked to be part of a concurrent observational 
cohort. 
 
Methods: Participants, Interventions, and Outcomes 
9. Study setting 
Participants will be recruited from the outpatient clinics at Orthopaedic department in Aalborg and 
Hjørring. Participants will attend baseline and complete the intervention at these two locations. The 
intervention will take place at the hospital and as home exercise. The physical follow-up will be 
done at Aalborg University Hospital after 9, 13 and 52 weeks. Links to the questionnaires used will 
be sent by REDCap (Vanderbilt University, Nashville, TN, USA)(32) to participants’ e-mail 
address for 9, 13, 26 and 52 week follow-ups. 
 
 
 

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10. Eligibility criteria 
Inclusion criteria: 
- 
Patients with acute total Achilles tendon rupture treated non-surgically (Standard care of 
treatment in North Denmark Region) 
- 
Diagnosed within 3 days (of their injury) 
- 
Age 18 - 65, able and willing to participate in the intervention 
- 
Able to speak and understand Danish 
Exclusion criteria:  
- 
Achilles tendon rupture close to insertion on calcaneus or in the musculo-tendinous junction 
of the triceps surae 
- 
Previous Achilles tendon rupture or other conditions in either leg causing lower leg 
disability (pain, deficits in strength or range of movement) 
- 
Treated with Fluorquinolons or Corticosteroids within the last 6 months 
- 
Diabetes or rheumatic diseases 
- 
Severe medical illness: ASA score higher than or equal to 3.(33)  
Excluded patients and patients not willing to participate will follow the usual program of 
rehabilitation for non-surgical treatment at the hospitals. 
 
11. Interventions 
11a Interventions for each group with sufficient detail to allow replication 
The exercise intervention take place while the participant is still in the immobilizing period with an 
orthosis. The exercises are designed as a daily home training program.  
General information for both groups: 
All participants receive general information about Achilles tendon rupture, tendon healing, choice 
of treatment and risks. The long-term prognosis of the Achilles tendon rupture is associated with 
lack of muscle strength and physical function and therefore forms the rationale for performing the 
exercise therapy. This information will be delivered both verbally and in a written leaflet. 
 
A: Standard exercise program. Initiated at the 2-week (14 days) appointment in the outpatient clinic 
and a booster visit in the sixth week in the physiotherapy. The exercises are performed 5 times daily 
and with 25 repetitions: 
- 
Range of motion. In the third week the participant is instructed to take the orthosis off and 
begin range of motion. The exercises are dorsal/plantar flexion and pronation/supination.  
For both exercises it is emphasized that dorsiflexion is restricted beyond neutral position of 
the foot. Position: seated with the foot hanging free from the chair and not resting on the 
floor. They carefully perform active dorsiflexion towards neutral and a passive 
plantarflexion. After one week gradually active plantarflexion is allowed.  

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- 
Resistance strength exercise with elastic band. In the sixth week the participant is 
instructed to do plantarflexion from neutral position with the resistance from an elastic band 
(low resistance). They are not allowed to pull the foot in dorsiflexion beyond neutral foot 
position. Position: seated with straight knee. 
 
B: Standard exercise program plus add-on exercises. There will be an introduction to the exercises 
in week 2 (from day 7) and booster visits after 1 and 3 weeks. The sessions will be approx. 45 min.:  
- 
Range of motion (identical to standard care). In the third week the participant is 
instructed to take the orthosis off and begin range of motion. The exercises are 
dorsal/plantar flexion and pronation/supination.  For both exercises it is emphasized that 
dorsiflexion is restricted beyond neutral position of the foot. Position: seated with the foot 
hanging free from the chair and not resting on the floor. They carefully perform active 
dorsiflexion towards neutral and a passive plantarflexion. After one week gradually active 
plantarflexion is allowed. 
- 
Resistance strength exercise with elastic band (identical to standard care). As in the 
standard treatment, plus Add-on that starts one week earlier and contains progression. In the 
fifth week the participant is instructed to do plantarflexion from neutral position with the 
resistance from an elastic band. They are not allowed to pull the foot in dorsiflexion beyond 
neutral foot position. They are instructed to progress by pulling the elastic band tighter or to 
change to a stronger elastic band. Position: seated with straight knee. 
- 
Isometric contraction. In the second week while still immobilized in the orthosis the 
participant is instructed to do isometric contractions of the leg muscles/triceps surae. In the 
beginning it will be short time under tension (TUT) and low load and then progression as 
the participant feels comfortable. Progression of load will be a) allowing to push the forefoot 
against the bottom of the walker with more pressure, b) performing isometric contractions 
while standing. Position: can be seated, standing or lying down with bent or straight knee.  
- 
Seated heel-rise. In the third week the participant is instructed to do a seated heel-rise while 
in the orthosis with the heel on the wedges and with open straps to allow movement. The 
wedges under the heel of the foot prevents excessive dorsiflexion of the foot. Progression is 
done with external weight on the knee. As the wedges are removed during the treatment the 
range of motion is increased. A book or a rolled towel is placed under the front of the 
orthosis to stabilize. Position: seated with bent knee in 90 degrees and possibly a cushion on 
the chair to compensate for the height of the orthosis with wedges. Alternative in the last 
three weeks is a supine pelvic lift combined with heelrise. 
- 
Progression: The participant is instructed to progress the resistance exercises when they 
can. It is emphasised that the exercises must not cause sudden or severe pain in the tendon, 
but muscle soreness is to be expected. The exercise exertion should be within 2-5 on the 
Borg Scale. 
 
Schedule of the exercise program and Exercise descriptors is presented in appendix. 
 

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Rehabilitation after the intervention period: 
All participants are referred to rehabilitation in group sessions led by a physiotherapist from week 9 
to 17. The program follows a standard protocol with exercises for strength and function progressing 
over time and there is advice for home exercise. 
 
11b Criteria for discontinuing or modifying allocated interventions  
Exercise sessions begin with assessing the progression of the tendon healing. In the first weeks with 
immobilization and physical examination is not possible, the participant is asked if there has been 
any constant or sudden pain or swelling and if there has been any excessive load to the tendon. At 
the 2-week appointment in the outpatient clinic the standard procedure is to examine any reported 
symptoms and perform a physical examination of the tendon and muscle structure.  
In case of deviation from the protocol or adverse events, the Data and Safety Monitoring Board (see 
21.a) will decide to either continue with modifications or to withdraw the participant from the 
study. 
 
11c Strategies to improve adherence  
During the first visits, the participants are informed about the importance of adherence to the 
exercise intervention. At the sessions the physiotherapists will use verbal encouragement to 
motivate the patients to perform the exercises. To promote adherence to the home exercise program 
there will be a pamphlet with detailed description of the exercises and a training journal.  
Each appointment will be registered in the hospital booking system and this features a possibility of 
having text messages prior to the appointments. If the participant fails to attend an appointment, the 
physiotherapist will arrange another appointment. If the participant decides to leave the study, the 
reason for leaving will be registered. 
 
11d Relevant concomitant care and interventions that are permitted or prohibited  
During the first nine weeks of treatment the patients are advised to avoid activities with high load 
on the foot, and to focus on oedema prophylaxis and training for a better overall result. Most 
activities of daily living will be possible, but it is advisable to take sick leave from work in the first 
two to nine weeks or longer depending on the workload. 
 
12. Outcomes 
During the initial clinical examination, we will collect the following descriptive data: age, height, 
body mass, educational level, work and sports activity status, trauma cause and smoking. 
Primary outcome: 
The primary outcome is Achilles tendon Total Rupture Score (ATRS), which is a validated self-
reported questionnaire for acute Achilles tendon rupture.(28)  It consists of 10 items concerning 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
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limitations related to symptoms and physical function. Each item is rated from 0 (very limited 
function) to 10 (not at all limited).  Items: strength, fatigue, stiffness, pain, activities of daily living, 
walking on uneven surfaces, walking quickly upstairs or uphill, running, jumping and hard physical 
labour. The ATRS is validated in a Danish population and is used in the Danish Achilles Database 
DADB.(12,34) The primary endpoint is 13 weeks. The questionnaire will also be filled out at 
baseline to re-call a pre-rupture level and at the 26- and 52-weeks follow-up. 
Secondary outcomes: 
International Physical Activity Questionnaire (IPAQ) short form Danish version. It consists of 7 
items concerning physical activity as time spent performing vigorous and moderate activities, the 
time spent walking and sitting during the past week. The IPAQ gives an estimate of the total weekly 
physical activity measured in MET-minutes per week and total minutes spent sitting.(35) The 
questionnaire will be filled out at baseline (to re-call a pre-rupture level) and at the 13, 26 and 52 
weeks follow-up.  
Achilles tendon resting angle (ATRA) is validated as an indirect measure of the Achilles tendon 
length.(36–38) The ATRA will be measured at 13 and 52 weeks. 
Ability to perform a standing Heel-rise. The participants will be classified as being able to 
perform a single-leg heel-rise if they are able to lift the heel at least 2 cm while keeping the knee 
straight. Position is standing with ankle in a neutral position and fingertips on the wall for balance 
support.(39,40) Measured at 13 and 52 weeks. 
Achilles tendon properties - length measured by ultrasound using Copenhagen Achilles length 
measure (CALM) for tendon length(41) will be performed at 9, 13 weeks and 52weeks. 
Isometric muscle strength – is measured as maximal isometric plantar flexor muscle strength 
using a Fysiometer.(42) The leg is placed on a Wii platform and secured with a belt around the knee 
and the Wii platform. When the isometric contraction is performed, the Wii is calculating the 
maximum peak force and the rate of force. Position: seated with 90 degrees flexion in hip and knee. 
Measured at 9, 13, 52 weeks. 
Muscle endurance is measured with the MuscleLab measurement system (Ergotest Technology, 
Oslo, Norway).(39) External weight load on the knee is calculated to 50% of the bodyweight. A 
linear encoder is attached to the heel of the shoe. When heel-rise is performed, the string is pulled, 
and the sensor measures the muscle endurance. Measured seated at 13 weeks and standing at 52 
weeks. 
The fear of re-rupture. When asked, patients often mention the fear of re-rupture and feeling the 
“pop” of the tendon as the worst thing that could happen again. This could influence the willingness 
to participate in the early exercises and how much they will load during the exercises.  
The Tampa scale of Kinesiophobia (TSK) is used and validated for backpain, but has previously 
been used for Achilles tendon rupture evaluation as the questions about kinesiophobia could have 
associations to how patients with Achilles tendon rupture manage rehabilitation and return to 
sports.(40) The questionnaire consists of 17 items concerning pain and kinesiophobia and has 4 
answers from “Strongly disagree” to “Strongly agree”. Measured at baseline, 9, 13 and 52 weeks. 

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Question: Were you afraid to do the prescribed load when performing the exercises? If  yes why? 
Measured at 9 weeks 
 
Compliance with the intervention: The participants will register the number of exercise sessions 
they perform each day in a training journal. The timeframe will be from the day they start the 
exercises to the end of week 9. 
 
Safety and Adverse events. The number of serious and minor adverse events is registered in a pre-
defined list based on Common Terminology Criteria for Adverse Events(43) and the participants 
will be asked open questions at each session. Serious adverse events are re-rupture, non-union of 
the tendon or symptomatic deep vein thrombosis (DVT). Muscle soreness or mild pain is 
considered inevitable and normal when initiating exercises after a period of immobilization. 
Cost-effectiveness outcomes. To evaluate the cost-effectiveness of the intervention, we will use 
self-reported health state as measured by the EQ-5D-5L.(44) Work productivity outcomes are 
measured using the Work Productivity and Activity Impairment Questionnaire WPAI:GH and 
condition-related expenses as measured by a self-developed questionnaire. The EQ-5D provides a 
simple descriptive profile and a single index value for health status and has been used extensively in 
research to measure QALYs gained and thereby perform health economic evaluations. The 
questionnaires will be filled out during all follow-ups. 
 
13. Participant timeline 
Baseline data will be collected at the first appointment in the outpatient clinic. During the 
intervention the participants will be followed closely and monitored on progression of tendon 
healing and adverse events. Assessment of outcome takes place at 9, 13, 26 and 52 weeks and will 
include patient reported questionnaires and physical measurements. 
RCT 
STUDY PERIOD 
 
Enrolment 
Post-allocation 
Follow-up 
Close-
out 
TIMEPOINT 
Day 1-7 
1 
week 
2 
weeks 
4-8 
weeks 
9 
weeks 
13 
weeks 
26 
weeks 
52 
weeks 
ENROLMENT: 
 
 
 
 
 
 
 
 
Eligibility screen 
X  
 
 
 
 
 
 
 
Informed consent  
X 
 
 
 
 
 
 
 
Allocation 
X  
 
 
 
 
 
 
 
INTERVENTIONS: 
 
 
 
 
 
 
 
 
Intervention A 
 
 
 
 
 
 
 
 
Intervention B 
 
 
 
 
 
 
 
 
Concurrent observational cohort 
 
 
 
 
 
 
 
 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
11 
 
BASELINE ASSESSMENTS: 
 
 
 
 
 
 
 
 
Pre-score ATRS, IPAQ 
X 
 
 
 
 
 
 
 
Demographics 
X 
 
 
 
 
 
  
 
ASSESSMENTS questionnaires: 
 
 
 
 
 
 
 
 
ATRS 
 
  
 
 
 
 X  
X   
X   
IPAQ 
 
 
 
 
 
X  
X  
X  
EQ5D-5L 
X  
 
 
 
X 
X  
X  
X  
Tampa scale of Kinesiophobia TSK 
X  
 
 
  
 
X   
  
 X  
General health V2.0 (WPAI:GH) 
 
 
 
 
X 
X  
X  
X  
ASSESSMENTS physical: 
 
 
 
 
 
 
 
 
ATRA 
 
 
    
  
X  
   X  
  
X   
Achilles tendon length 
( by ultrasound) 
 
 
 
 
X  
   X  
 
X  
Achilles tendon cross-sectional area 
( by ultrasound) 
 
 
 
 
X  
X  
 
X  
Ability to perform single Heel-rise 
 
 
 
  
 
X  
 
X   
Isometric muscle strength 
 
  
 
  
X 
X  
 
X   
Ability to do single leg heelrise 
 
 
 
 
 
X  
 
 
Muscle endurance 
 
 
 
 
 
X  
  
X   
Compliance with the intervention 
 
 
 
 
X  
 
 
 
Complications  
 
 
 
 
 
 
  
 
 
14. Sample size  
Sample size calculations are based on the primary endpoint ATRS with a clinically relevant 
difference at 10 point and estimated standard deviation 15 point. With a two-sided 5% significance 
level and a power of 80%, the sample size will be 37 in each group and a total of 82 participants 
when allowing for potential dropouts. 
 
15. Recruitment 
The participants are recruited in the Orthopaedic outpatient clinics at Aalborg and Hjørring. All 
relevant subjects will pass through these departments. All medical and administrative staff involved 
in treating the patients in the Emergency departments and the outpatient clinics will be informed of 
the study and notified of the inclusion/exclusion criteria. There will be written information for staff 
and information handouts for patients. Daily, the referral lists in the outpatient clinics will be 
searched to retrieve all incoming referrals of acute Achilles tendon ruptures. Patients potentially 
eligible for the study will be contacted by telephone and screened by the Primary Investigator (MC) 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
12 
 
or a project physiotherapist. If the patient is interested in participating and is eligible, an early 
appointment in the outpatient clinic or a telephone meeting is arranged, where the patient receive 
the oral information about the project. Final inclusion will take place at this meeting if the eligibility 
is confirmed. After the telephone contact the written information is also send by email (in e-Boks). 
It will be ensured that the participants have at least 24 hours to read the document before the oral 
information. Patients will be given the possibility of contacting the project manager by phone or 
Email, if they have questions. 
 
Methods: Assignment of Interventions (for controlled trials) 
Allocation 
16a Sequence generation 
Randomization of participants is performed using a random number generator on 
www.sealedenvelope.com and it will be stratified by sex, as female sex is less present and is 
associated with lower outcome in the ATRS. Block randomized in random concealed block sizes of 
2-4 (1:1) into two parallel groups is used to avoid imbalance in the randomization between the 
intervention groups.  
 
16b Allocation concealment mechanism 
A researcher not involved in the trial will generate the allocation sequence and is the only person 
who knows the block sizes. The randomization results are kept in opaque sealed envelopes and 
stored in a locked cabinet where only the project personnel performing the randomization has 
access. 
 
16c. Implementation 
In practice, after a participant has been enrolled, has filled out baseline questionnaires and received 
initial information regarding the practicalities of participation, the Primary investigator will inform 
the project secretary of the new participant. The project secretary will open the envelope and assign 
the participant to the allocated treatment based on randomization. The notes in the envelopes state 
group allocation number and the intervention. The secretary will inform the participant and the 
physiotherapy department regarding the randomization results. The randomization is coded so that 
the Primary investigator does not know which intervention is linked to which group number (Group 
1 or 2). 
 
17a Blinding(masking) 
The Primary investigator (MC) will be responsible for performing the statistical analyses and will 
remain blinded to the coding until after the analyses have been performed. The analyses will be 

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13 
 
performed after the examination that includes the primary endpoint (the 13-week follow-up) of the 
last participant. All follow-up examinations will be blinded for the group allocation. 
It is not possible to blind the participants to the content of the allocated exercise program, but we 
will minimize the information regarding the differences of the two treatment arms. In the participant 
information sheet and the oral information, participants will be informed that the study compares 
two different courses of exercise treatment, which both include the treatment services that are 
normally offered. The specifics of the differences between the exercises will not be shared with the 
participants. The reasons for not informing participants about the specific content of the 
intervention are two-fold. First, given the simplicity of the intervention, knowledge about the actual 
content would increase the likelihood that participant would, to some degree, implement these 
strategies in their rehabilitation, for instance by increasing their exercise dose. This would lead to 
contamination of the control condition of this trial, leading to possible underestimation of the 
effectiveness of the intervention in question. Secondly, by keeping participants blind to treatment 
allocation, the negative effects (such as disappointment) of not receiving the intervention in 
question, could be avoided. This is important as these effects could negatively affect the outcomes, 
with a risk of an overestimation of the effect of the intervention in question. 
 
17b If blinded, circumstances under which unblinding is permissible, and procedure for 
revealing a participant’s allocated intervention during the trial 
In case of adverse events that are considered associated with the intervention, the treatment 
allocation will be revealed to the patient and the treating clinician in the outpatient clinic. 
 
Methods: Data collection, management, and analysis 
18 Data collection methods 
18a Plans for assessment and collection of outcome, baseline, and other trial data  
Baseline data will be collected at the first appointment in the outpatient clinic or online via link in 
an email after the oral information has taken place. The Informed consent is filled out in Redcap 
before baseline information. During the intervention the participants will be followed closely and 
monitored on progression of tendon healing and adverse events. Assessment of outcome takes place 
at 9, 13, 26 and 52 weeks and will include patient reported questionnaires and physical 
measurements. Participant data will be stored in REDCap hosted at Aalborg University Hospital. 
The personnel providing the randomization, exercise interventions and follow-up will follow 
standardized protocols for the intervention and receive training before initiation of the study. During 
the study there will be quality control regarding adherence to the protocols. 
 
18b Plans to promote participant retention and complete follow-up 
During the first visits, the participants are informed about the importance of adherence to the 
exercise intervention. They will follow the usual plan for clinical follow-up in the outpatient clinic, 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
14 
 
where the staff can assist in solving any problems with attaining the study follow-ups. In case of 
adverse events or deviation from the treatment plan, the follow-up sessions will be executed if 
possible. For example, if physical examinations are not possible due to re-rupture, then only the 
patient questionnaires will be completed. 
 
19. Data management 
All data will be stored electronically and are handled according to the General Data Protection 
Regulation. Participant data will be stored in REDCap hosted at Aalborg University Hospital. It is a 
secure web application for building and managing online surveys and databases and has secure 
logged entry. Data processor agreements and protocols will be stored on a secure server at Aalborg 
University Hospital. Any paper forms will be kept in a locked room in the outpatient clinics at the 
study sites. To prevent data entry errors, data collection instruments have been developed in 
REDCap so that required data must be included or an error will be displayed, and validation of each 
field has been chosen (e.g. if the format of the data does not appear to be a date in the field ‘Date’, 
an error is displayed). All data will be kept for 10 years after completion of the trial in accordance 
with The European Code of Conduct for Research Integrity. 
 
20. Statistical methods 
20a Statistical methods for analysing primary and secondary outcomes 
The primary intention-to-treat analysis will investigate the between-group difference in ATRS. We 
will use a linear mixed effects regression model with the participant as random effect and time 13, 
26 and 52 weeks, group allocation (standard care vs standard care plus add-on) and baseline value 
as fixed effects. Conclusions will only be drawn based on the primary endpoint (13 weeks). 
All statistical analyses will be performed by a blinded data analyst according to a pre-established 
analysis plan. This plan is written in consultation with a statistician and will be published on the 
Aalborg University website before the inclusion of the last participant. STATA will be used as 
statistical software. We will use Q-Q plots and histograms to assess data normality. 
 
20b. Methods for any additional analyses (eg, subgroup and adjusted analyses) 
N/A 
 
20c Definition of analysis population relating to protocol non-adherence (eg, as randomised 
analysis), and any statistical methods to handle missing data (eg, multiple imputation) 
The intention-to-treat principle is used for analyses and all participants are included in the analyses 
regardless of the compliance to the intervention. 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
15 
 
Methods: Monitoring 
21. Data monitoring 
21a Composition of data monitoring committee (DMC) 
Safety of the tendon healing has great importance in this study. There will be a Data and Safety 
Monitoring Board with the principal purpose of monitoring data and safety. The study setup will 
aim at preventing adverse events by monitoring the tendon healing and setting threshold values for 
initiation and progressing the exercises in the intervention. The data monitoring committee will be 
composed of the primary investigator, the project physiotherapists, the chief orthopaedic foot 
surgeon (ILK) and an orthopaedic surgeon not otherwise involved in the study. They will assess all 
matters regarding data and safety and will grade all adverse events and decide whether to delay the 
proceeding of the intervention or the participant should be withdrawn from the study due to the 
adverse event. Presentation of each item on the agenda will be blinded for the primary investigator. 
The adverse events will be graded 1 to 5 according to the Common Terminology Criteria for 
Adverse Events v4.03.(43)  
Action and treatment of adverse events will start immediately following the usual treatment 
protocols. The assessment of the adverse event in the DMC will be done within 7 days for serious 
adverse events. Serious Achilles tendon injury adverse events are re-rupture, non-union of the 
tendon or deep vein thrombosis (DVT). Muscle soreness or mild pain is considered inevitable and 
normal when initiating exercises after a period of immobilization and will not be considered an 
adverse event. 
 
21b Description of any interim analyses and stopping guidelines 
If the rate of re-rupture or other serious adverse events is noted to be exceptionally high or increases 
rapidly after the intervention has been implemented, the DMC can recommend terminating the trial. 
 
22. Harms 
All participants receive information about possible adverse events relative to the Achilles tendon 
rupture in general and to the specific intervention. In case of serious adverse events they are 
encouraged to seek immediate medical attention and for minor adverse events to contact the project 
physiotherapist by phone. At each session the participants will answer questions of possible adverse 
events during and between the sessions. During and after completion of the study the included 
participants will also be followed in the outpatient clinic and in The Danish Achilles tendon 
Database (DADB). 
 
23. Auditing 
N/A 
 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
16 
 
Ethics and Dissemination 
24. Research ethics approval 
Before initiation of the study, approval of the study protocol, informed consent and participant 
information will be approved by: 
• The Physiotherapy and Occupational therapy department and the Orthopaedic Department at 
Aalborg University Hospital  
• 
The Ethics committee of North Denmark Region. Project identification number: N-20200041  
As this is designed as an add-on intervention to standard of care, all participants will receive an 
evidence-based treatment that is at least equal to standard care today.  
 
25. Protocol amendments.  
Important protocol modifications are registered and approved by The Ethics committee of North 
Denmark Region. 
 
26ab. Consent or assent 
The primary investigator will obtain informed consent from the participants. 
 
27. Confidentiality 
All personal data collected on potential and enrolled participants is collected by telephone 
screening, at baseline appointment or at study sessions. Data will be kept secure and for 10 years. 
The GDPR – General Data Protection Regulation is followed. The study is registered at The Danish 
Data Protection Agency at Aalborg University Hospital. 
 
28. Declaration of interests 
All authors have no competing interests. 
 
29. Access to data 
All authors will have access to the full dataset before publication. The dataset will be stored at the 
sponsor site, Aalborg University hospital. 
 
30. Ancillary and posttrial care 
During and after completion of the study the included patients will be followed in the outpatient 
clinic and in The Danish Achilles tendon Database (DADB). Any serious adverse event occurrence 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
17 
 
will be reported and consulted with the Chief foot surgeon (ILK) within three days for re-ruptures 
or DVT and within 7 days for minor adverse events. Participation in the study will be covered under 
the Patient Compensation Association (Patienterstatningen). 
 
31a. Dissemination policy 
The results of the study will be submitted for publication regardless of the result being positive, 
negative or inconclusive. Publication will be aimed at an international peer-reviewed journal. The 
preliminary title is: “A randomised controlled trial on the effect of Early progressive strength 
exercise for treatment of acute Achilles tendon rupture. The Achilles tendon Back-On-Track study”. 
The results will also be presented at relevant physiotherapy and orthopaedic conferences. 
Guidelines and the exercise protocol will be made available for online download, to ensure 
translation of the research results into useful information for clinical practice. 
 
31b. Authorship eligibility guidelines and any intended use of professional writers 
All co-authors are expected to make substantial scientific contributions that will qualify them as co-
authors according to the International Committee of Medical Journal Editors (ICMJE) 
recommendations for authorship(45): 
• 
Substantial contributions to the conception or design of the work; or the acquisition, analysis, or 
interpretation of data for the work; AND 
• 
Drafting the work or revising it critically for important intellectual content; AND 
• 
Final approval of the version to be published; AND 
• 
Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy 
or integrity of any part of the work are appropriately investigated and resolved. 
MC will draft the manuscript with input from all the authors. MSR, ILK, JAZ and KGS will all 
participate with valuable scientific contributions to the manuscript. All authors have no competing 
interests. 
 
31c. Plans, if any, for granting public access to the full protocol, participant-level dataset, and 
statistical code 
Data will be available upon reasonable request. 
 
Appendixes 
32. Informed consent materials 
33. Biological speciments 
None  
 

SPIRIT Protocol_RCT_ver1.0_23.jan2021 
18 
 
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Samtykke_RCT_ver1.0_27042020 
 
Side 1 af 1 
 
 
 
Informeret samtykke til deltagelse i et sundhedsvidenskabeligt forskningsprojekt. 
 
Forskningsprojektets titel:   
Akillessenen på banen igen. Et randomiseret kontrolleret studie af effekten af tidlig progressive 
styrketræning til akut Akillessene ruptur. 
 
Erklæring fra forsøgspersonen: 
Jeg har fået skriftlig og mundtlig information og jeg ved nok om formål, metode, fordele og  
ulemper til at sige ja til at deltage.  
Jeg ved, at det er frivilligt at deltage, og at jeg altid kan trække mit samtykke tilbage uden at  
miste mine nuværende eller fremtidige rettigheder til behandling.   
Jeg giver samtykke til, at deltage i forskningsprojektet, og har fået en kopi af dette samtykkeark samt en 
kopi af den skriftlige information om projektet til eget brug. 
 
Forsøgspersonens navn: ________________________________________________________ 
 
Dato: _______________   Underskrift: ____________________________________________ 
 
 
Ønsker du at blive informeret om forskningsprojektets resultat samt eventuelle konsekvenser for dig?: 
 
Ja _____ (sæt x)         Nej _____ (sæt x) 
 
Erklæring fra den, der afgiver information: 
Jeg erklærer, at forsøgspersonen har modtaget mundtlig og skriftlig information om forsøget. 
 
Efter min overbevisning er der givet tilstrækkelig information til, at der kan træffes beslutning om 
deltagelse i forsøget.   
Navnet på den, der har afgivet information:        
 
Dato: _______________   Underskrift: ____________________________________________ 
 
 
 
 
 
 
Projektidentifikation:  
Videnskabsetisk Komité for Region Nordjylland projektnr N-20200041 
 

Schedule of the new exercises vs the usual treatment_ClinicalTrials 
RCT study. Schedule of exercise program. 
Exercises 
  
  
 
  
  
  
  
  
  
  
  
  
  
  
  
  
Elastic 2 
Elastic 2 
Elastic 2 
Elastic 1 
Heelrise 
Heelrise 
Heelrise 
Heelrise 
Heelrise  
Heelrise 
Heelrise 
Iso stand Iso stand Iso stand Iso stand 
Iso 
Iso 
Iso 
Elastic 1 
Elastic 1 
Elastic 1 
Elastic 1 
Iso 
ROM 
ROM 
ROM 
ROM 
ROM 
ROM 
ROM 
Weeks 
1 
2 
3 
4 
5 
6 
7 
8 
9 
Immobilizing Walker, 3 wedges 
Walker, 2 wedges 
Walker, 1 wedge 
Walker, no wedge 
Weight 
bearing 
Non WB 
P- WB, 2 crutches 
P-WB, 1-2 crutches 
Full WB, crutches for long walk 
Rationale 
 
 
 
A.  
Facilitation 
 
B.  
Initiation of load 
 
C. 
Progression to more load 
 
Total 
exercise 
dose (time 
under 
tension) 
 
 
Facilitation of 
muscle activity by 
isometric 
contraction without 
ROM 
Slow controlled movement to 
avoid peak forces on tendon 
while prioritizing long TUT to 
maintain/increase strength 
 
Improve strength (go to failure 
IF THEY ARE comfortable with it) 
 
 
 
Progression 
 
 
 
 
 
 
Progress from A to 
B: 
If patient feel 
comfortable doing 
facilitating exercises 
If clinical screening 
is OK at “2-week 
follow-up” (no 
tendon gap, equal 
ATRS, no pain 
during exercises). 
Progress from B to C: 
If patient feel comfortable doing 
“initiation of load” exercises. 
If exercises are managed well 
- with regards to Toigo 
descriptors, 
- without persistent pain or 
discomfort during and after 
exercises,  
- no compensating movements 
while performing exercises. 
Progress from C to exercise and 
mobilize without walker boot: 
The decision to discontinue the 
walkerboot is done at the 
Outpatient clinic. 
The exercises should provide the 
foundation for the patient to be 
confident in future decisions of 
choosing sufficient amount of 
load to improve the muscle 
performance while still avoiding 
too much strain on the healing 
tendon (i.e. avoid strenuous 
load, avoid stretching in 
dorsiflexion with load)  
 
Blue: Standard exercise program. Orange: Add-on exercises. Iso: Isometric contractions. Elastic 1: Light load (yellow-
red). Elastic 2: Progression of load to stronger elastic band (red, blue, green). WB: Weight bearing. P-WB: Partial 
weight bearing. Heelrise is seated. ROM is unloaded range of movement. 
 
 
 

Exercise descriptors table_ClinicalTrials 
 
Appendix 
Toigo & Boutellier 
exercise descriptors 
 
Isometric contraction 
Seated heel-rise 
Elastic band 
X1 Load magnitude 
15-20 RM 
 
15-20 RM 
Progress to 15RM week 
6/7 
 
15-20 RM 
Progress to 15RM week 
6/7 
 
X2 number of 
repetitions 
 
5 
10-15 
10-15 
X3 number of sets 
 
5 
3 
3 
X4 rest btw sets 
 
5 sec 
10 sec 
10 sec 
X5 number of 
exercise 
interventions 
Every hour (approx 12 
hours per day) for week 
2-3,  
then change to 5 times 
per day in week 4-9  
 
5 per day 
5 per day 
X6 duration of the 
experimental period 
 
Week 2 to 9 
Week 3 to 9 
From week 5 to 9 
 
X7 Fractional and 
temporal 
distribution of the 
contraction modes 
per repetition and 
duration (s) of one 
repetition 
 
5 sec 
3s shortening 
3s isometric 
3s lengthening 
3s-3s-3s 
(Focus is on the 
concentric phase. 
Important not to push 
beyond the neutral 
position in the eccentric 
phase) 
X8 Rest in-between 
repetitions 
 
2 
2 
2 
X9 Time under 
tension  
125s per session 
1625s per day (hourly)  
 
625s per day (5 times) 
 
270-405s per session 
1350-2025s per day 
270-405s per session 
1350-2025s per day 
X10 Volitional 
muscular failure 
 
No 
No 
No 
X11 Range of motion 
No range of motion. The 
foot is immobilized in 
equinus according to 
the number of wedges. 
From plantarflexed foot 
position on the wedges to 
more plantarflexed, when 
performing the heel-rise 
Dorsiflexion above 
neutral is not allowed. 
Full plantarflexion 
allowed. 
 
X12 Recovery time 
in-between exercise 
sessions 
 
1 hour 
3 hours 
3 hours 

Exercise descriptors table_ClinicalTrials 
 
X13 Anatomical 
definition of the 
exercise (exercise 
form) 
Isometric contraction is 
performed inside the 
walkerboot with the 
foot in equinus 
according to the week-
plan.  
 
Push the forefoot 
against the bottom of 
the walker and feel the 
contraction of the leg 
muscles as if you are 
going to make a heel-
rise, but the walker 
boot restricts your 
motions. Extend the big 
toe to minimize the 
activity of the muscles 
for the big toe and 
increase activity of the 
leg muscles. 
From week 6 the 
exercise can be 
performed in standing. 
 
Seated heel-rise with leg 
in walker with “the 
wedges of the week”. 
Open straps and liner of 
walker. Knee in 90 
degrees position. Hold 
one hand at the back of 
the walker to stabilize.  
 
Lift the heel from the 
walker/wedges. Make 
sure that you are using 
the leg muscles and not 
pulling up the leg with 
your thigh muscles. 
Extend the big toe to 
minimize the activity of 
the muscles for the big 
toe and increase activity 
of the leg muscles. Rest 
the foot on the forefoot 
pad rather than on the 
toes alone. 
Progression: add weight 
on knee (either water 
bottle, upper body, 
weights -
sandbag/kettlebell) 
 
Performed seated with 
straight knee. Wrap the 
elastic band around the 
forefoot and hold both 
ends in the hand. Tighten 
the band, but make sure 
that the foot is not pulled 
beyond 90 degrees. 
 
Press the foot down 
against the tightened 
elastic band as far as you 
can move the foot. Hold 
the position and then 
slowly pull up the foot 
again, but still with a 
tightened band. 
Progression: Tighten the 
band or change the band 
to other color (more 
strength) 
Level of load 
Borgs scale – Perceived exertion during exercise (/10) is used to guide the 
patients to progress or regress the load in each exercise. The recommended level 
being “easy” to “hard” (2-5/10). It is emphasized that the exercises must not 
cause sudden or severe pain in the tendon, but muscle soreness is to be 
expected. 
 
Progression 
Progression of the exercises will be a continuous process. There are three main 
phases: facilitating, initiation of load, progression to more load. When 
progressing to the next phase or new type of exercise the following criteria must 
be observed: 
The load magnitude of the present exercise should be accomplished with the 
patient feeling comfortable doing the exercises and without persistent pain or 
discomfort during and after exercises.