It is known that children with NF1 can have weak muscles and suffer from tiredness. It is also known that in similar conditions affecting children's muscles, standing on a vibration device for a few minutes each day can strengthen muscles and improve their ability to perform day-to-day activities. The investigators believe this vibrating platform can be used to strengthen the muscles of children with NF1 also, beyond standard exercises, and therefore allow them to perform day-to-day activities better, do more activity and feel less tired.

If families are keen to take part in this study, the investigators will first need to check they are suitable for the trial. This will be based on the participant's age (6-16 years), their other medical problems that would affect use of the vibration device or tests to assess how effective it is, and their level of muscle weakness.

Once families have agreed to take part, participants will be randomised either to receive a muscle-strengthening exercise session delivered by a physiotherapist that children with weak muscles should continue to perform daily for the next 6 months; or to receive a vibration device to take home and use for a few minutes 5 days a week for 6 months as well as the exercises.

All participants will be invited to attend for a variety of activities and tests, just before starting the trial and 6 months later at the end of the trial to see if there is any benefit from the vibration device. The investigators will repeat these tests again 3 months later, to see if any benefits observed remain, even after the device is removed. They will involve jumping, hopping and balancing on a board, gripping a machine as hard and as long as possible, being fitted with a device that measures activity for 7 days, walking as far as possible for 6 minutes, scanning muscles using MRI, completing a tiredness and general well-being questionnaires, and parents completing a questionnaire of the participant's attention and intellect. The jumping will also be performed 3 months into the study, to see if there is any early improvement in this key test.

All participants will be given full details of what the trial involves before taking part. As with any other trial, participants and their families are free to stop taking part at any time. Although the investigators do not anticipate any safety issues, if any do arise, the families will be asked to contact the trial team.

Children with neurofibromatosis type 1 (NF1) have been shown in many studies to have reduced muscle mass, strength and function. This could potentially contribute to the fatigue and low quality of life reported in these children. However, to date interventions to improve muscle mass, strength and function in these children have not been established. Whole body vibration (WBV) has been demonstrated to improve walking speed and distance, muscle mass and strength, spasticity and balance in children with other neuromuscular conditions.

In this proposed preliminary matched-pairs interventional trial, the investigators aim to identify whether a home-based WBV therapy programme (9 minutes twice daily for 5 days per week) in addition to standard daily muscle-strengthening exercises improves muscle mass, strength and function over a six month period in children with NF1 aged 6-16 years, compared to daily muscle-strengthening exercises alone. Participants must have evidence of poor muscle strength, with grip force used to assess for this. Key exclusion criteria include significant learning difficulty or autistic spectrum disorder which would create difficulty in use of the WBV device, focal skeletal abnormalities and contraindications to WBV therapy.

The primary outcome measure will be dynamic muscle function using mechanography to measure peak power per kilogram on single two-legged jump.

Secondary/exploratory outcome measures include the 6-minute walk test (to assess lower limb muscle function and mobility), accelerometer data (as a surrogate marker of type and duration of physical activity), hand-held dynamometry (to assess upper limb grip force and endurance), measures on mechanography other than jumping power (to further assess dynamic muscle function), MRI for muscle cross-sectional area and signal intensity, fatigue and general well-being questionnaires and parental reports of attention and cognition.

These measures will be undertaken at baseline, on completion of intervention at 6 months, and again 3 months after to identify whether there is any sustained effect of the intervention following removal. Halfway through the intervention period (3 months), participants will also be invited just to complete the primary outcome of single two-legged jump on ground reaction force plate, as an interim measure.

The investigators hypothesise that WBV therapy will result in increased muscle mass and passive muscle strengthening of the lower limbs, which will translate into better muscle function in the lower limbs compared to baseline data and control group. As it is hypothesised that muscle weakness contributes to the fatigue demonstrated in children with NF1, the investigators would expect to see an improvement in their fatigue scores, which, combined with greater muscle strength, will translate into greater physical activity. The investigators hypothesise that WBV may also have an impact on muscle function in the upper limbs through central sensory stimulation and neuronal rewiring. Many children with NF1 have evidence of attention problems, and the investigators hypothesise that this may improve with WBV, again through central neuronal rewiring.

The trial will be conducted in compliance with this protocol, Good Clinical Practice (GCP) and applicable regulatory requirements.

Inclusion Criteria:

• Neurofibromatosis Type 1 (confirmed by NIH consensus criteria)
• Grip force less than -1 SDS according to age- and gender-matched normative data

Exclusion Criteria:

• Focal skeletal abnormalities (pseudoarthrosis, kyphoscoliosis likely to require surgery, known spondylolisthesis)
• Significant autistic spectrum disorder or learning difficulties (neurodevelopmental age less than 6 years)
• Inability to adequately weight-bear or balance on vibrating platform
• Lower limb plexiform causing limb length discrepancy
• Contraindications to use of whole-body vibration device (acute thrombosis, implants in activated regions of the body, acute inflammation of the locomotor system, herniae, propensity to fragility fractures or fracture within the past 3 months, history of renal calculi, epilepsy)