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Trial registered on ANZCTR


Registration number
ACTRN12623001165673
Ethics application status
Approved
Date submitted
30/08/2023
Date registered
9/11/2023
Date last updated
9/11/2023
Date data sharing statement initially provided
9/11/2023
Type of registration
Retrospectively registered

Titles & IDs
Public title
The impact of hamstring muscle length during isometric strengthening exercise on muscle structure and function adaptations
Scientific title
The impact of hamstring length during isometric knee flexion training on muscle architecture and function in healthy, recreationally active participants
Secondary ID [1] 310469 0
Nil known
Universal Trial Number (UTN)
Nil
Trial acronym
Linked study record
Nil

Health condition
Health condition(s) or problem(s) studied:
Hamstring strain injuries 331271 0
Sport injuries 331274 0
Condition category
Condition code
Musculoskeletal 328025 328025 0 0
Other muscular and skeletal disorders
Injuries and Accidents 328032 328032 0 0
Other injuries and accidents

Intervention/exposure
Study type
Interventional
Description of intervention(s) / exposure
1. Name:
i) Short-muscle-length (70° knee flexion) intervention group (SML)during isometric strengthening exercise and;
ii)Long-muscle-length (20° knee flexion) group intervention (LML) during isometric strengthening exercise

2. Why:
In running-based sports, hamstring strain injuries (HSIs) are one of the leading causes of time lost from competition for athletes. HSI also has a high reoccurrence rate, with the risk of sustaining a HSI only increasing with a history of previous HSIs. Training interventions that load the hamstrings while they lengthen, known as eccentric strengthening exercises, have demonstrated the ability to reduce HSI incidence by modifying the hamstring internal structure (known as muscle architecture) and strength of the hamstring muscle. Eccentric strengthening exercises are believed to be effective as they occur where the muscle is being stretched, mimicking the hamstring position where most HSI occur. As such, hamstring eccentric strengthening protocols have been recommended and attempted to be adopted by many professional sporting organisations.

However, a common adverse side effect of eccentric strengthening exercise is muscle soreness, stiffness and tenderness, which often persists for 24-72 hours post-training. As a result, compliance with eccentric strengthening exercise programs can be poor. Isometric strengthening exercises, where the muscle is loaded but does not change in length, is associated with less muscle soreness and has been proposed as a possible alternative to eccentric strengthening exercise due to the ability to still train the hamstrings in lengthened muscle positions. However, there is minimal evidence surrounding the impact of isometric strengthening exercises on hamstring muscle structure and strength. Thus, the effect of isometric strengthening exercises at lengthened muscle positions on markers of HSI risk is unknown.

This proposed project will determine if an isometric strengthening exercise intervention can lead to favourable adaptations in the structure and function of the hamstrings.

3. What/ Procedures:

Experimental Protocol: Longitudinal cohort training study. Participants will complete a 6-week intervention, comprised of either a short-length (70° knee flexion; 0° being full knee extension) or long-length (20° knee flexion) isometric strengthening exercise. Participants will be familiarised with all testing/training methodologies included in the project. After a minimum of seven days, lower limb strength and ultrasound-derived measures will then be assessed in a separate session (“pre-intervention testing”). Three to five days after these assessments, participants will commence their isometric training intervention. At the halfway point of the intervention, biceps femoris long head (BFlh) fascicle length will be re-assessed to track the rate of change across the two intervention groups. All measures will be re-assessed following the completion of the training intervention (“post-intervention testing”) and after a subsequent 28-day detraining period (“de-training testing”).

Intervention: 30 participants will undertake a six-week intervention comprised of either a short-length (70° knee flexion) or long-length (20° knee flexion) isometric strengthening exercise using an isokinetic dynamometer (n = 15/ group). Each participant will train one leg only, with the other leg serving as a within-participant control leg. The training leg will be randomised, allowing for the contralateral leg to act as a control comparison as it will not receive any training stimulus but will be tested alongside the trained limb at pre-, post- and mid-intervention and de-training time points.

Data collection techniques:
Hamstring strength: Isokinetic dynamometry will be used to assess the lower limb strength of both legs (training and control) at all time points (pre-, post- and mid-intervention and de-training).
BFlh architecture: A passive 2D ultrasound scan of the participants’ BFlh will provide a measurement of fascicle length.
BFlh stiffness: Passive shear wave ultrasound scans of participant’s BFlh will provide a measurement of muscle stiffness.
Muscle soreness: Approximately 24 hours following each training session, participants will be contacted by the research team to rate their perceived posterior thigh soreness from 0-10 using a Visual Analogue Scale (VAS), where 0 = no soreness whatsoever, and 10 = unbearable soreness.

4. WHO

The investigation will be conducted by Miss Abigail Paduch (Bachelor of High-Performance Sport), who is undertaking her Honour’s research project in sports science and injury prevention. The project will be supervised by A/Prof David Opar, Dr Robert Crowther and Mr Declan Carmichael from the School of Behavioural and Health Sciences at the Australian Catholic University (Melbourne Campus).

A/Prof David Opar is the Director of ACU’s Sports Performance, Recovery, Injury and New Technologies (SPRINT) Research Centre. As the lead for SPRINT’s Injury Research Program, A/Prof Opar has led the way in hamstring injury research. Professional sporting teams and rehabilitation protocols around the world have adopted findings from his research.

Dr Robert Crowther is a Senior Lecturer in ACU’s Exercise Science department. Dr Crowther is a well-published human movement specialist, completing his Doctor of Philosophy in exercise therapy, biomechanics, and motor control.

Mr Declan Carmichael is a research assistant within the SPRINT Research Centre. Mr
Carmichael brings experience from his own research in hamstring isometric and eccentric training interventions and has experience in using ultrasound to non-invasively assess muscle structure and function.

An internal reliability study on the ultrasound device will be carried out by Miss Abigail Paduch and Mr Declan Carmichael to ensure valid and reliable data collection.

How/ Mode of Delivery:
Individual, face-to-face

5. WHERE:
All sessions will be conducted on-site at Australian Catholic University, Melbourne Campus (115 Victoria Parade, Fitzroy VIC 3065) in the laboratory on Lv 4 of building 420. This is to ensure we have access to the isokinetic dynamometer and ultrasound machine.

6. WHEN & HOW MUCH:

Wk 1: 1 session. 2 sets of 5 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.
Wk 2: 2 sessions. 2 sets of 4 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.
Wk 3: 2 sessions. 2 sets of 6 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.
Wk 4: 2 sessions. 3 sets of 5 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.
Wk 5: 2 sessions. 2 sets of 5 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.
Wk 6: 2 sessions. 3 sets of 6 repetitions, 5s isometric maximal efforts with 1.5 min rest between sets.

Session compliance will be reported as a percentage of overall sessions completed and/or participant drop out.

Tailoring/ Modifiation & How Well: N/A
Intervention code [1] 326874 0
Prevention
Intervention code [2] 327335 0
Rehabilitation
Comparator / control treatment
Each participant will train one leg only, with the other leg serving as a within-participant control comparison leg. This means that the control limb will not receive the intervention stimulus and only the training leg will undergo the 6-week training intervention. Participants are instructed to continue their daily activities and exercise but avoid any unilateral hamstring strengthening execrises. This allows minimal distribution to the participant's life and maintains baseline strength of the control limb, while allowing the training limb to undergo the 6-week intervention. The training leg will be randomised, allowing for the contralateral leg to act as a control comparison as it will not receive any training stimulus but will be tested alongside the trained limb at pre-, post- and mid-intervention and de-training time points.
Control group
Active

Outcomes
Primary outcome [1] 335898 0
1. Unilateral isometric knee flexor strength assessed by an isokinetic dynamometer
Timepoint [1] 335898 0
Pre-intervention (~1 week after randomisation - primary timepoint), mid-intervention (after wk 3/ beginning week 4 of training), post-intervention (~5-7 days after last training session - primary timepoint) and de-training (~4 weeks post-intervention).
Primary outcome [2] 335899 0
2. Biceps femoris long head fascicle length assessed by 2D ultrasound extended field of view images as well as small field of view images.
Timepoint [2] 335899 0
Pre-intervention (~1 week after randomisation- primary timepoint), mid-intervention (after wk 3/ beginning week 4 of training), post-intervention (~5-7 days after last training session - primary timepoint) and de-training (~4 weeks post-intervention).
Primary outcome [3] 335900 0
3. Biceps femoris long head pennation angle assessed by 2D ultrasound extended field of view images as well as small field of view images.
Timepoint [3] 335900 0
Pre-intervention (~1 week after randomisation - primary timepoint), mid-intervention (after wk 3/ beginning week 4 of training), post-intervention (~5-7 days after last training session - primary timepoint) and de-training (~4 weeks post-intervention).
Secondary outcome [1] 426067 0
Biceps Femoris long head stiffness assessed by shear wave ultrasound taken at rest.
Timepoint [1] 426067 0
Pre-intervention (~1 week after randomisation), post-intervention (~5-7 days after last training session) and de-training (~4 weeks post-intervention).
Secondary outcome [2] 426068 0
Muscle soreness: from 0-10 using a Visual Analogue Scale (VAS), where 0 = no soreness whatsoever, and 10 = unbearable soreness.
Timepoint [2] 426068 0
~24 hours following each training session

Eligibility
Key inclusion criteria
Either male or female sex who are:
- Recreationally active
- 18-35 years old
- non-clinical population
- Free from lower limb injury at the time of participation that would impede the ability to complete the requirements of the study safely
Minimum age
18 Years
Maximum age
35 Years
Sex
Both males and females
Can healthy volunteers participate?
Yes
Key exclusion criteria
- history of hamstring injury in the previous 12 months
- major knee injury or major knee surgery (i.e., ACL rupture, ACL reconstruction)
- clinical population or acute condition/injury that impacts the ability to complete testing and training sessions

Study design
Purpose of the study
Treatment
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Allocation is not concealed.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using coin-tossing.
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?



The people analysing the results/data
Intervention assignment
Other
Other design features
Each participant will have a training limb and a control limb. This will allow within-group comparisons (training vs control) and between-group comparisons (training vs training; control vs control etc). Both the limb and group will be randomised.
Phase
Not Applicable
Type of endpoint/s
Efficacy
Statistical methods / analysis
Power analysis has been undertaken using G*Power to determine a sample of ~15 per group is required to provide sufficient power.

Where appropriate, data will be screened for normal distribution using the Shapiro–Wilk test and homoscedasticity using Levene_s test. A split-plot design ANOVA, with the within-participant variables being limb (trained or untrained) and time point (pre-, mid- and post-intervention and de-training) and the between-subject variable being SML or LML groups, will be used to compare changes in biceps femoris long head architecture throughout the training study.

Other outcome variables will use a similar split-plot design ANOVA, however, with different time point variables (pre-, mid- and post-intervention and de-training). Where significant limb–time–group interactions are detected, post hoc t tests will be used to identify which comparisons differed. Significance will be set at a P=0.05. Cohen’s d will also be reported for the comparison effect sizes, with the levels of effect being deemed small (d = 0.20), medium (d = 0.50), or large (d = 0.80).

Recruitment
Recruitment status
Recruiting
Date of first participant enrolment
Anticipated
Actual
16/08/2023
Date of last participant enrolment
Anticipated
2/08/2024
Actual
Date of last data collection
Anticipated
1/10/2024
Actual
Sample size
Target
30
Accrual to date
10
Final
Recruitment in Australia
Recruitment state(s)
VIC
Recruitment postcode(s) [1] 41252 0
3065 - Fitzroy

Funding & Sponsors
Funding source category [1] 314673 0
University
Name [1] 314673 0
Australian Catholic Univerity
Country [1] 314673 0
Australia
Primary sponsor type
University
Name
Australian Catholic University
Address
115 Victoria Parade, Fitzroy VIC 3065
Country
Australia
Secondary sponsor category [1] 316641 0
None
Name [1] 316641 0
Address [1] 316641 0
Country [1] 316641 0

Ethics approval
Ethics application status
Approved
Ethics committee name [1] 313692 0
Australian Catholic University Human Research Ethics Committee
Ethics committee address [1] 313692 0
Australian Catholic University
North Sydney Campus
PO Box 968
NORTH SYDNEY, NSW 2059
Ethics committee country [1] 313692 0
Australia
Date submitted for ethics approval [1] 313692 0
22/05/2023
Approval date [1] 313692 0
07/07/2023
Ethics approval number [1] 313692 0
2023-3183H

Summary
Brief summary
In running-based sports, hamstring strain injuries (HSIs) are one of the leading causes of time lost from competition for athletes. HSI also has a high reoccurrence rate, with the risk of sustaining a HSI only increasing with a history of previous HSIs. Training interventions that load the hamstrings while they lengthen, known as eccentric strengthening exercises, have demonstrated the ability to reduce HSI incidence by modifying the hamstring internal structure (known as muscle architecture) and strength of the hamstring muscle. Eccentric strengthening exercises are believed to be effective as they occur where the muscle is being stretched, mimicking the hamstring position where most HSI occur. As such, hamstring eccentric strengthening protocols have been recommended and attempted to be adopted by many professional sporting organisations.

However, a common adverse side effect of eccentric strengthening exercise is muscle soreness, stiffness and tenderness, which often persists for 24-72 hours post-training. As a result, compliance with eccentric strengthening exercise programs can be poor. Isometric strengthening exercises, where the muscle is loaded but does not change in length, is associated with less muscle soreness and has been proposed as a possible alternative to eccentric strengthening exercise due to the ability to still train the hamstrings in a lengthened muscle positions. However, there is minimal evidence surrounding the impact of isometric strengthening exercises on hamstring muscle structure and strength. Thus, the effect of isometric strengthening exercises at lengthened muscle positions on markers of HSI risk is unknown.

This proposed project will determine if an isometric strengthening exercise intervention can lead to favourable adaptations in the structure and function of the hamstrings.
Trial website
N/A
Trial related presentations / publications
N/A
Public notes

Contacts
Principal investigator
Name 129034 0
A/Prof David Opar
Address 129034 0
Australian Catholic University (Melbourne), 115 Victoria Parade, Fitzroy VIC 3065
Country 129034 0
Australia
Phone 129034 0
+613 9953 3742
Fax 129034 0
Email 129034 0
david.opar@acu.edu.au
Contact person for public queries
Name 129035 0
A/Prof David Opar
Address 129035 0
Australian Catholic University (Melbourne), 115 Victoria Parade, Fitzroy VIC 3065
Country 129035 0
Australia
Phone 129035 0
+613 9953 3742
Fax 129035 0
Email 129035 0
david.opar@acu.edu.au
Contact person for scientific queries
Name 129036 0
A/Prof David Opar
Address 129036 0
Australian Catholic University (Melbourne), 115 Victoria Parade, Fitzroy VIC 3065
Country 129036 0
Australia
Phone 129036 0
+613 9953 3742
Fax 129036 0
Email 129036 0
david.opar@acu.edu.au

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No
No/undecided IPD sharing reason/comment
Not approved by the ethics committee.


What supporting documents are/will be available?

No Supporting Document Provided



Results publications and other study-related documents

Documents added manually
No documents have been uploaded by study researchers.

Documents added automatically
No additional documents have been identified.