Resistance ExerciseKidRExNCT06698055
Muscle Adaptations in Children and Adults Following Twelve Weeks of Flywheel or Weight Stack Resistance Exercise
A study testing Flywheel Resistance Exercise and Weight Stack Resistance Exercise in people with Resistance Exercise and Muscle Hypertrophy, run by Björn Alkner at 1 site in Sweden.
Trial summary
The goal of this trial is to compare resistance exercise using traditional techniques and flywheel training to controls in healthy children ages nine to 13 and adults ages 18 to 50. Read more about this study
- Who is it for?
- Ages 9 to 50 yearsHealthy volunteers can take part
- Conditions the study is for
- Resistance Exercise, Muscle Hypertrophy, Skeletal Muscle
- What is being tested?
- Flywheel Resistance Exercise and Weight Stack Resistance Exercise
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 91 participants
- Where
- 1 siteSweden
- Study dates
- 28 Aug 2022to 12 Feb 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 9 to 50 years
- All sexes
- Healthy volunteers accepted
- Child, Adult
Who may be able to join
- Adults at the age of 18 to 50 at time of inclusion.
- Children at the age of nine to 13 (attending Swedish middle school) at time of inclusion
Who cannot join
- Neuromuscular disease.
- Previous or current musculoskeletal injury, primarily of the lower limb, preventing resistance exercise.
- Heavy resistance training of the lower limb at inclusion (i.e., more than one session per week of weight training of the lower limb or other equivalent activity)
Trial locations and contacts
1 site in 1 country.
Sweden1 site
Department of Orthopaedic Surgery, Höglandssjukhuset District Hospital Eksjö
Eksjö, Region Jönköping County, 57581
About this study
Official title: KidREx - Muscle Adaptations in Children and Adults Following a Twelve-week of Resistance Exercise Period Using Either Flywheel or Traditional Weight Stack Devices - a Randomized Controlled Study
The goal of this trial is to compare resistance exercise using traditional techniques and flywheel training to controls in healthy children ages nine to 13 and adults ages 18 to 50. The main questions it aims to answer are:
- The degree of response to resistance exercise in children compared to adults regarding muscle hypertrophy and strength?
- Is there a negative impact on the physis of children due to resistance exercise?
Participants will be randomized to one of three groups, control, traditional resistance exercise, or flywheel. Following a baseline battery of tests, they will enter a 12-week training period, using leg press and leg extension. Additionally, post-training tests are conducted, and an eight-week detraining period commences followed by new tests. Researchers will compare children and adults and each intervention arm to see if children can achieve muscle hypertrophy, the degree and rate of changes in strength, and the potential impact on the physis.
Read the detailed description
The KidREx-study is an intervention study aiming to investigate the effects of two alternative forms of resistance exercise on adults and children. Exercise forms include leg press and leg extension, in either traditional weight stack machines or flywheel training machines. It has been proposed and discussed that resistance exercise would cause injury to the growth plate and even premature closure of the physis in children. Multiple studies have shown that this is not the case regarding growth height and radiography of the physis. However, the direct effects of resistance exercise on physis using magnetic resonance imaging are yet to be investigated.
This study is a randomized, controlled, prospective intervention study. Two separate groups (children and adults) are included, children ages 9 to 13 and adults ages 18-50. Participants are randomly assigned to one of six arms for the twelve-week intervention period. Arms include two control groups "living as usual" (children and adults), two flywheel training groups (children and adults), and two weight stack training groups (children and adults). Throughout the intervention period, the training groups conduct a total of 30 sessions (alternating between two or three sessions per week). Following the intervention period, all participants enter an 8-week detraining phase, where no organized resistance training is conducted.
At baseline, all participants conduct a test battery including vertical jump height, horizontal jump length, balance tests, and tests of muscle activity in the specific training machines and in an isokinetic dynamometer. In conjunction with the first exercise bout, venous blood samples are obtained from both adults and children, and skeletal muscle biopsies from m. vastus lateralis are obtained from the adults. This procedure is repeated after 12 weeks of training and following the 8-week detraining period. Outcomes related to this, blood samples and muscle tissue, beyond the fiber-specific hypertrophy, will be subject to ancillary studies.
The investigators hypothesize that weight stack training and flywheel training will result in muscle adaptation in both adults and children, where the rate of adaptation is faster for the flywheel training group. Expected muscle adaptation includes an increase in muscle hypertrophy, strength, and functional strength-related outcomes (balance, vertical jump height, and standing long jump). Additionally, the investigators hypothesize that the growth plate of pre- and intra-pubertal children will not be affected negatively by resistance exercise.
- Conditions
- Resistance Exercise, Muscle Hypertrophy, Skeletal Muscle, EMG, Magnetic Resonance Imaging, Growth Plate Early Closing
- Being tested
- Flywheel Resistance Exercise, Weight Stack Resistance Exercise
- Keywords
- Skeletal Muscle, Resistance Exercise, Magnetic Resonance Imaging, EMG, Muscle Hypertrophy, Flywheel Training, Strength Training in Children and Adolescents, Growth Plate, Muscle Adaptation, Muscle Memory, Histology, Immunohistochemistry, Transcriptomics, Methylomics, Proteomics, Functional Outcomes, Physical Activity Monitoring, Physical Self Esteem
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Flywheel Resistance ExerciseOther
FW is conducted in a leg extension machine (LegExx, Exxentric, Stockholm, Sweden) and leg press machine (YoYo™ Leg Press, nHANCE, Sweden).
Weight Stack Resistance ExerciseOther
WS is conducted in a leg extension machine (Seated leg press, Nordic Gym, Bollnäs, Sweden) and a leg press machine (Seated leg extension, Nordic Gym, Bollnäs, Sweden)
| Study group | Role | What they receive |
|---|---|---|
| aFW = Flywheel resistance exercise intervention group adults | Active comparator | FW undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. Receives: Other: Flywheel Resistance Exercise |
| aWS = Weight stack resistance exercise intervention group adults | Active comparator | WS undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. Receives: Other: Weight Stack Resistance Exercise |
| aCON = Control group adults | No intervention | The CON group will continue living as normally with the aim of remaining at a constant activity level like that at baseline. All groups undergo a baseline test battery witch is repeated following the end of the training period. After the training period all groups enter in to a detraining period were no weight training of the lower limb will be conducted for eight weeks. Following the detraining period the test battery will once more be repeated. |
| cFW = Flywheel resistance exercise intervention group children | Active comparator | FW undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. Receives: Other: Flywheel Resistance Exercise |
| cWS = Weight stack resistance exercise intervention group children | Active comparator | WS undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. Receives: Other: Weight Stack Resistance Exercise |
| cCON = Control group children | No intervention | The CON group will continue living as normally with the aim of remaining at a constant activity level like that at baseline. All groups undergo a baseline test battery witch is repeated following the end of the training period. After the training period all groups enter in to a detraining period were no weight training of the lower limb will be conducted for eight weeks. Following the detraining period the test battery will once more be repeated. |
What is being measured
The primary outcome is the main question the study is designed to answer.
Change from Baseline Muscle Volume Following 12 Weeks of Resistance Exercies
The groups of children and adults will undergo magnetic resonance imaging of the anterior thigh in a standardized fashion. Subsequently, the muscle volume is calculated by contouring cross-sectional area of muscle. Primary analysis is muscle growth of the m. quadriceps femoris in the two active comparator groups compared to the control group.
Measured: Time Frame: Before intervention start (0 weeks) and following twelve weeks of training (12 weeks)
Secondary outcomes (22)
Changes in muscle thickness
The group of adults and children undergo ultrasound scans of the anterior thigh in a standardized fashion. The scans will encompass all four heads of the m. quadriceps femoris.
Measured: Time Frame: Prior to intervention start, biweekly during the intervention period (i.e., after two, four, six and eight weeks). Additional scans will be performed following the end of intervention (12 weeks) and the end of detraining (20 weeks).
Change from baseline in rate of physeal closure following resistance exercise
The children will undergo magnetic resonance imaging of the physis of the knee in the non-dominant limb. The degree of closure of the growth plates of the distal femur and proximal tibia will be graded.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Change in muscle volume at 20 weeks
The groups of children and adults will undergo magnetic resonance imaging of the anterior thigh in a standardized fashion. Subsequently, the muscle volume (cm3) is calculated by contouring cross-sectional area of muscle. Primary analysis is muscle growth of the m. quadriceps femoris in the two active comparator groups compared to the control group.
Measured: Time Frame: Before intervention start (0 weeks) and end of intervention (12 weeks) compared to volume following the detraining period (20 weeks)]
Changes in peak torque during isokinetic concentric and eccentric knee extension and flexion
Concentric and eccentric peak torque (Nm) of the knee extensors and flexors are measured in an Isokinetic dynamometer. Peak torque is measured at 60,120,180 and 300 deg/ sec during concentric actions and 60 deg/sec during eccentric.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during isokinetic concentric and eccentric knee extension and flexion
Concentric and eccentric power (W) of the knee extensors and flexors are measured in an Isokinetic dynamometer. Power is measured at 60,120,180 and 300 deg/ sec during concentric actions and 60 deg/sec during eccentric.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in work during isokinetic concentric and eccentric knee extension and flexion
Concentric and eccentric work (J) of the knee extensors and flexors are measured in an Isokinetic dynamometer. Work is measured at 60,120,180 and 300 deg/ sec during concentric actions and 60 deg/sec during eccentric.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activity during isokinetic concentric and eccentric knee extension and flexion measured using sEMG
Concentric and excentric actions of the knee extensors and flexors are measured in an isokinetic dynamometer using surface electromyography (sEMG) to capture muscle activity from the quadriceps and hamstring musculature. Muscle activity is measured in volts and following post-processing presented in absolute numbers or relative percentages of maximal voluntary contraction (MVC). MVC is acquired during maximal isometric concentric contraction at 60 degrees.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during flywheel resistance exercise
All participants perform test sessions in a flywheel leg press and leg extension where power (W) during the concentric and eccentric face is measured using a rotational encoder.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activation with flywheel resistance exercise measured using sEMG
All participants perform test sessions in a flywheel leg press and leg extension where muscle activity of the knee extensors and knee flexors are recorded during two sets and seven repetitions in each machine. Muscle activity (mV) will be adjusted to maximal voluntary contractions (MVC) measured at 90 degrees of knee flexion and extension. Concurrently the joint angel is measured using a goniometer during the entire range of motion.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during weight stack resistance exercise
All participants perform test sessions in a weight stack leg press and leg extension where power (W) during the concentric and eccentric face is measured using a linear encoder.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activation during weight stack resistance exercise measured using sEMG
All participants perform test sessions in a weight stack leg press and leg extension where muscle activity of the knee extensors and knee flexors are recorded using electromyography. During two sets and seven repetitions in each machine. Muscle activity (mV) will be adjusted to maximal voluntary contractions (MVC) measured at 90 degrees of knee flexion and extension. Concurrently the joint angel is measured using a goniometer during the entire range of motion.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power output during training
Power (W) is measured during all training sessions in both training groups. In the flywheel resistance exercise groups using a rotational encoder and in the flywheel stack machine using a linear encoder. Training is performed alternating two to three times weekly during the intervention period.
Measured: Time Frame: Continuous power measurements during all training sessions, weeks 1 through 12 weeks
Changes in Balance
The participants will perform two standardized sets of tests aimed to quantify their balance, including a series of perturbations and modified-SOT.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in vertical jump height
The participants will perform two bouts of vertical countermovement jumps, with arms locked upon the hips and with free arms respectively. This will be performed on a force plate and using a motion tracking system.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in isometric maximum strength
All participants will perform an isometric maximal contraction of the knee extensors with a 90° knee angle using a force sensor connected in serie with the foot pad in the knee extension weight stack device
Measured: Time Frame: Baseline (0 weeks), 2 weeks of intervention, 4 weeks of intervention, 6 weeks of intervention, 8 weeks of intervention and post intervention (12 weeks) and post detraining (20 weeks)
Changes in standing long jump
The participants will perform three trials of standing long jump. If there is an continues upwards trend, the participants are allowed further trials until a plateau is reached.
Measured: Time Frame: Baseline (0 weeks), 2 weeks of intervention, 4 weeks of intervention, 6 weeks of intervention, 8 weeks of intervention and post intervention (12 weeks) and post detraining (20 weeks)
Change in type I-fiber cross-sectional area.
Resting muscle biopsies are acquired from the m. vastus laterals muscle of the adults. Fiber-specific staining is performed and cross-sectional area is calculated
Measured: Time Frame: Baseline (0 weeks), two weeks of training, six weeks of training, post training (12 weeks) and post detraining (20 weeks).
Change in type II-fiber cross-sectional area.
Resting muscle biopsies are acquired from the m. vastus laterals muscle of the adults. Fiber-specific staining is performed, and cross-sectional area is calculated
Measured: Time Frame: Baseline (0 weeks), two weeks of training, six weeks of training, post training (12 weeks) and post detraining (20 weeks).
Changes in testosterone levels in children during the intervention
All child participants will donate blood at baseline, post training and post detraining to assess changes in testosterone (nmol/L) levels.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in estradiol levels in children during the intervention
All child participants will donate blood at baseline, post training and post detraining to assess changes in estradiol (pmol/L) levels.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in IGF-1 levels in children during the intervention
All child participants will donate blood at baseline, post training and post detraining to assess changes in insulin-like growth factor 1 (ug/L) levels.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Questionnaire based assessment of physical self-esteem (children)
Physical self-esteem will be assessed using a translated version (Swedish) of the questionnaire The Children and Youth Physical Self-Perception Profile (CY-PSPP). Total score from 36 to 144 where 144 is the best result.
Measured: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted20 Nov 2024
- Study start28 Aug 2022
- Primary completion2 Feb 2025
- Study completion12 Feb 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Resistance ExerciseStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Randomized controlled resistance exercise intervention study
- Masking
- Single blind
- Who is masked
- Outcomes assessor
- Enrolment
- 91 participants (actual)
Sponsor and investigators
- Lead sponsor
- Björn Alkner
- Sponsor type
- Other government
- Collaborators
- Karolinska Institutet, Umeå University, Medical Research Council of Southeast Sweden, Swedish Research Council for Sport Science, Linkoeping University, The Swedish Research Council
- Responsible party
- Sponsor-investigator, Björn Alkner, Region Jönköping County
- Investigators
- Björn A Alkner, MD, PhD, Principal investigator, Department of Orthopaedic Surgery, Eksjö, Region Jönköping County and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06698055
- Sponsor's protocol ID
- RJonkopingC KidREx
- Acronym
- KidREx
- Status last verified
- Apr 2025
- First submitted
- 29 May 2023
- Last updated
- 16 Dec 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: All data will be shared upon reasonable request when the data set is is complete
Study at a glance
From the registry record, last updated by the sponsor on 16 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- KidREx - Muscle Adaptations in Children and Adults Following a Twelve-week of Resistance Exercise Period Using Either Flywheel or Traditional Weight Stack Devices - a Randomized Controlled Study
- ClinicalTrials.gov ID
- NCT06698055
- Acronym / sponsor ID
- KidREx / RJonkopingC KidREx
- Conditions
- Resistance Exercise, Muscle Hypertrophy, Skeletal Muscle, EMG, Magnetic Resonance Imaging, Growth Plate Early Closing
- Keywords
- Skeletal Muscle, Resistance Exercise, Magnetic Resonance Imaging, EMG, Muscle Hypertrophy, Flywheel Training, Strength Training in Children and Adolescents, Growth Plate
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 91 participants (actual)
- Lead sponsor
- Björn AlknerOther government
- Collaborators
- Karolinska Institutet, Umeå University, Medical Research Council of Southeast Sweden, Swedish Research Council for Sport Science, Linkoeping University, The Swedish Research Council
- Study start
- 28 Aug 2022 (actual)
- Primary completion
- 2 Feb 2025 (actual)
- Study completion
- 12 Feb 2025 (actual)
- First posted
- 20 Nov 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The goal of this trial is to compare resistance exercise using traditional techniques and flywheel training to controls in healthy children ages nine to 13 and adults ages 18 to 50. The main questions it aims to answer are:
- The degree of response to resistance exercise in children compared to adults regarding muscle hypertrophy and strength?
- Is there a negative impact on the physis of children due to resistance exercise?
Participants will be randomized to one of three groups, control, traditional resistance exercise, or flywheel. Following a baseline battery of tests, they will enter a 12-week training period, using leg press and leg extension. Additionally, post-training tests are conducted, and an eight-week detraining period commences followed by new tests. Researchers will compare children and adults and each intervention arm to see if children can achieve muscle hypertrophy, the degree and rate of changes in strength, and the potential impact on the physis.
Detailed description
The KidREx-study is an intervention study aiming to investigate the effects of two alternative forms of resistance exercise on adults and children. Exercise forms include leg press and leg extension, in either traditional weight stack machines or flywheel training machines. It has been proposed and discussed that resistance exercise would cause injury to the growth plate and even premature closure of the physis in children. Multiple studies have shown that this is not the case regarding growth height and radiography of the physis. However, the direct effects of resistance exercise on physis using magnetic resonance imaging are yet to be investigated.
This study is a randomized, controlled, prospective intervention study. Two separate groups (children and adults) are included, children ages 9 to 13 and adults ages 18-50. Participants are randomly assigned to one of six arms for the twelve-week intervention period. Arms include two control groups "living as usual" (children and adults), two flywheel training groups (children and adults), and two weight stack training groups (children and adults). Throughout the intervention period, the training groups conduct a total of 30 sessions (alternating between two or three sessions per week). Following the intervention period, all participants enter an 8-week detraining phase, where no organized resistance training is conducted.
At baseline, all participants conduct a test battery including vertical jump height, horizontal jump length, balance tests, and tests of muscle activity in the specific training machines and in an isokinetic dynamometer. In conjunction with the first exercise bout, venous blood samples are obtained from both adults and children, and skeletal muscle biopsies from m. vastus lateralis are obtained from the adults. This procedure is repeated after 12 weeks of training and following the 8-week detraining period. Outcomes related to this, blood samples and muscle tissue, beyond the fiber-specific hypertrophy, will be subject to ancillary studies.
The investigators hypothesize that weight stack training and flywheel training will result in muscle adaptation in both adults and children, where the rate of adaptation is faster for the flywheel training group. Expected muscle adaptation includes an increase in muscle hypertrophy, strength, and functional strength-related outcomes (balance, vertical jump height, and standing long jump). Additionally, the investigators hypothesize that the growth plate of pre- and intra-pubertal children will not be affected negatively by resistance exercise.
Study design
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Single blind (outcomes assessor)
- Number of arms
- 6
- Model description
- Randomized controlled resistance exercise intervention study
| Arm | Type | Receives |
|---|---|---|
| aFW = Flywheel resistance exercise intervention group adults | Active comparator | Other: Flywheel Resistance ExerciseFW undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. |
| aWS = Weight stack resistance exercise intervention group adults | Active comparator | Other: Weight Stack Resistance ExerciseWS undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. |
| aCON = Control group adults | No intervention | –The CON group will continue living as normally with the aim of remaining at a constant activity level like that at baseline. All groups undergo a baseline test battery witch is repeated following the end of the training period. After the training period all groups enter in to a detraining period were no weight training of the lower limb will be conducted for eight weeks. Following the detraining period the test battery will once more be repeated. |
| cFW = Flywheel resistance exercise intervention group children | Active comparator | Other: Flywheel Resistance ExerciseFW undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. |
| cWS = Weight stack resistance exercise intervention group children | Active comparator | Other: Weight Stack Resistance ExerciseWS undergo a twelve-week training intervention with alternating two to three sessions per week. At each training session the participant will perform four sets of leg press and a leg extension with seven repetitions per set in each machine were resistance is provided by a flywheel and a weight stack respectively. |
| cCON = Control group children | No intervention | –The CON group will continue living as normally with the aim of remaining at a constant activity level like that at baseline. All groups undergo a baseline test battery witch is repeated following the end of the training period. After the training period all groups enter in to a detraining period were no weight training of the lower limb will be conducted for eight weeks. Following the detraining period the test battery will once more be repeated. |
Who may qualify
- Ages
- 9 to 50 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Child, Adult
Key inclusion criteria (2 listed)
- Adults at the age of 18 to 50 at time of inclusion.
- Children at the age of nine to 13 (attending Swedish middle school) at time of inclusion
Key exclusion criteria (3 listed)
- Neuromuscular disease.
- Previous or current musculoskeletal injury, primarily of the lower limb, preventing resistance exercise.
- Heavy resistance training of the lower limb at inclusion (i.e., more than one session per week of weight training of the lower limb or other equivalent activity)
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Flywheel Resistance ExerciseFW is conducted in a leg extension machine (LegExx, Exxentric, Stockholm, Sweden) and leg press machine (YoYo™ Leg Press, nHANCE, Sweden). | Other | aFW = Flywheel resistance exercise intervention group adults, cFW = Flywheel resistance exercise intervention group children |
| Weight Stack Resistance ExerciseWS is conducted in a leg extension machine (Seated leg press, Nordic Gym, Bollnäs, Sweden) and a leg press machine (Seated leg extension, Nordic Gym, Bollnäs, Sweden) | Other | aWS = Weight stack resistance exercise intervention group adults, cWS = Weight stack resistance exercise intervention group children |
Primary outcome
Change from Baseline Muscle Volume Following 12 Weeks of Resistance Exercies
Time frame: Time Frame: Before intervention start (0 weeks) and following twelve weeks of training (12 weeks)
The groups of children and adults will undergo magnetic resonance imaging of the anterior thigh in a standardized fashion. Subsequently, the muscle volume is calculated by contouring cross-sectional area of muscle. Primary analysis is muscle growth of the m. quadriceps femoris in the two active comparator groups compared to the control group.
22 secondary outcomes
Changes in muscle thickness
Time frame: Time Frame: Prior to intervention start, biweekly during the intervention period (i.e., after two, four, six and eight weeks). Additional scans will be performed following the end of intervention (12 weeks) and the end of detraining (20 weeks).
Change from baseline in rate of physeal closure following resistance exercise
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Change in muscle volume at 20 weeks
Time frame: Time Frame: Before intervention start (0 weeks) and end of intervention (12 weeks) compared to volume following the detraining period (20 weeks)]
Changes in peak torque during isokinetic concentric and eccentric knee extension and flexion
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during isokinetic concentric and eccentric knee extension and flexion
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in work during isokinetic concentric and eccentric knee extension and flexion
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activity during isokinetic concentric and eccentric knee extension and flexion measured using sEMG
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during flywheel resistance exercise
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activation with flywheel resistance exercise measured using sEMG
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power during weight stack resistance exercise
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in muscle activation during weight stack resistance exercise measured using sEMG
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in power output during training
Time frame: Time Frame: Continuous power measurements during all training sessions, weeks 1 through 12 weeks
Changes in Balance
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in vertical jump height
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in isometric maximum strength
Time frame: Time Frame: Baseline (0 weeks), 2 weeks of intervention, 4 weeks of intervention, 6 weeks of intervention, 8 weeks of intervention and post intervention (12 weeks) and post detraining (20 weeks)
Changes in standing long jump
Time frame: Time Frame: Baseline (0 weeks), 2 weeks of intervention, 4 weeks of intervention, 6 weeks of intervention, 8 weeks of intervention and post intervention (12 weeks) and post detraining (20 weeks)
Change in type I-fiber cross-sectional area.
Time frame: Time Frame: Baseline (0 weeks), two weeks of training, six weeks of training, post training (12 weeks) and post detraining (20 weeks).
Change in type II-fiber cross-sectional area.
Time frame: Time Frame: Baseline (0 weeks), two weeks of training, six weeks of training, post training (12 weeks) and post detraining (20 weeks).
Changes in testosterone levels in children during the intervention
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in estradiol levels in children during the intervention
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Changes in IGF-1 levels in children during the intervention
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Questionnaire based assessment of physical self-esteem (children)
Time frame: Time Frame: Baseline (0 weeks), post training (12 weeks) and post detraining (20 weeks)
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 16 Dec 2025.
- Individual participant dataSharing planned: Yes. All data will be shared upon reasonable request when the data set is is complete
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Active, not recruiting
Flexibility, Resistance, Aerobic, Movement Execution Training in Adults With Hereditary Spastic Paraplegia
Hereditary Spastic Paraplegia
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Björn A Alkner, MD, PhD principal investigator
Department of Orthopaedic Surgery, Eksjö, Region Jönköping County and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Flywheel Resistance Exercise and Weight Stack Resistance Exercise in people with Resistance Exercise and Muscle Hypertrophy, run by Björn Alkner at 1 site in Sweden.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 2 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 16 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Sweden. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Change from Baseline Muscle Volume Following 12 Weeks of Resistance Exercies (time frame: Time Frame: Before intervention start (0 weeks) and following twelve weeks of training (12 weeks)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 16 Dec 2025.