Muscle Adaptations in Children and Adults Following Twelve Weeks of Flywheel or Weight Stack Resistance Exercise
NCT ID: NCT06698055
Last Updated: 2025-12-16
Study Results
The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.
Basic Information
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COMPLETED
NA
91 participants
INTERVENTIONAL
2022-08-28
2025-02-12
Brief Summary
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* 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
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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
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Study Design
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RANDOMIZED
PARALLEL
OTHER
SINGLE
Study Groups
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aWS = Weight stack resistance exercise intervention group adults
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.
Weight Stack Resistance Exercise
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)
aFW = Flywheel resistance exercise intervention group adults
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.
Flywheel Resistance Exercise
FW is conducted in a leg extension machine (LegExx, Exxentric, Stockholm, Sweden) and leg press machine (YoYo™ Leg Press, nHANCE, Sweden).
aCON = Control group adults
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.
No interventions assigned to this group
cFW = Flywheel resistance exercise intervention group children
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.
Flywheel Resistance Exercise
FW is conducted in a leg extension machine (LegExx, Exxentric, Stockholm, Sweden) and leg press machine (YoYo™ Leg Press, nHANCE, Sweden).
cWS = Weight stack resistance exercise intervention group children
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.
Weight Stack Resistance Exercise
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)
cCON = Control group children
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.
No interventions assigned to this group
Interventions
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Flywheel Resistance Exercise
FW is conducted in a leg extension machine (LegExx, Exxentric, Stockholm, Sweden) and leg press machine (YoYo™ Leg Press, nHANCE, Sweden).
Weight Stack Resistance Exercise
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)
Eligibility Criteria
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Inclusion Criteria
* Children at the age of nine to 13 (attending Swedish middle school) at time of inclusion
Exclusion Criteria
* 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)
9 Years
50 Years
ALL
Yes
Sponsors
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Karolinska Institutet
OTHER
Umeå University
OTHER
Medical Research Council of Southeast Sweden
OTHER_GOV
Swedish Research Council for Sport Science
OTHER
Linkoeping University
OTHER_GOV
The Swedish Research Council
OTHER_GOV
Björn Alkner
OTHER_GOV
Responsible Party
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Björn Alkner
Principal Investigator, MD, PhD, Associate professor
Principal Investigators
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Björn A Alkner, MD, PhD
Role: PRINCIPAL_INVESTIGATOR
Department of Orthopaedic Surgery, Eksjö, Region Jönköping County and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
Locations
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Department of Orthopaedic Surgery, Höglandssjukhuset District Hospital Eksjö
Eksjö, Region Jönköping County, Sweden
Countries
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Other Identifiers
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RJonkopingC KidREx
Identifier Type: -
Identifier Source: org_study_id