Cerebral palsy (CP) is the most common cause of physical disability in children that presents at birth or in early infancy as a result of non-progressive encephalopathies of varied aetiology (1). Clinical symptoms may include impaired muscle function, reduced bone mineral density (BMD) (2), reduced muscle mass (3), as well as varying degrees of mobility impairments (4) and reduced walking endurance (5). The management of CP involves a multidisciplinary approach that includes therapeutic, pharmaceutical, and surgical interventions aimed at increasing mobility, improving muscle and bone health, thereby promoting overall health and well-being (1, 6).

Over the last two decades, side-alternating vibration therapy (sVT) has been investigated as an additional tool in the management of CP. The impulses produced by a vibration platform are thought to stimulate muscle spindles, inducing cyclic elongation and contraction of the stimulated muscles (7). sVT has been shown to improve BMD, muscle mass, walking endurance, muscle strength, and coordination in children and adults with CP (8–10). Nonetheless, interpretation of research findings is difficult due to differences in protocols, including frequency, duration of individual sessions, and duration of the intervention (8).

Studies in children and adolescents with CP tend to use a 9 min protocol with three 3 min sVT bouts, separated by 3 min breaks, following the manufacturer's recommendations and previous published studies (10–13). To the best of our knowledge, only one study has evaluated a longer 18 min protocol with six 3 min sVT bouts (14). However, in that study, each sVT bout varied in frequency, foot placement, and participant position on the vibration plate, which differed from the more standardized protocols typically used in studies of sVT in children (10–13). While that study may provide valuable insights, it is difficult to compare their findings to studies using standardized 9 min protocols. In addition, the authors did not provide information on safety (i.e., adverse effects) or acceptability (i.e., adherence to the sVT protocol, reasons for missing sessions or withdrawal) (14). Therefore, it is still unknown whether longer sVT sessions are feasible in children and adolescents with CP or would offer additional health benefits similar to those seen with an increased load in strength training (15). We hypothesized that prolonged exposure to sVT may have a more marked impact on mobility, muscle, and bone health due to the increased stress on the musculoskeletal system, resulting from greater training levels due a higher number of repeated cycles of muscle contraction and relaxation. Therefore, this feasibility study aimed to assess the safety, acceptability, and potential effectiveness of a longer sVT protocol (15 min per session) in children and adolescents with CP.

Fifteen participants aged 5.2–17.4 years were recruited, including 6 females and 9 males, all of NZ European ethnicity (Table 1). Of the 15 participants, 8 children (57%) were diagnosed with global developmental delay and 4 (23%) had medically well-controlled seizures.

Mean adherence to the 15 min sVT protocol was relatively high at 83% [quartile 1 = 63.9%; median = 84.7%; quartile 3 = 97.2%). The main reported reason for missing individual sVT sessions was a lack of time. All recruited participants completed the prescribed 20 weeks of sVT, without any study dropouts. Importantly, there were no transient or serious adverse events reported.

After 20 weeks of sVT, participants appeared to have increased the distance covered in the 6MWT by 43 m on average (+10%; p = 0.0018) (Table 2). In addition, following sVT, participants reached most of the individual 6MWT milestones earlier (Figure 1). There was also some evidence that more participants were able to reach the furthest milestones, so that 13 participants (87%) managed to reach the 400 m mark after sVT compared to 8 (53%) at baseline (+33%; p = 0.063) (Figure 1).

There were no observed changes in body composition apart from a small increase in spine BMD (+5%; p = 0.013), even though spine BMD z-score was unchanged after the intervention (Table 3). There were no observed differences in the GRFP assessments, namely the CRT or the STLJT (Table 2).

This study showed the 15 min 20-week sVT protocol is feasible in children and adolescents with CP GMFSC level II. Adherence was high (83% on average), and sVT was well-tolerated with no adverse events reported, and no dropout of participants so that all completed the 20-week intervention period. In addition, the obtained data indicated a likely improvement on mobility after sVT as shown in the 6MWT.

It is important to note that the additional training time (from 9 to 15 min per session) did not adversely affect adherence to the sVT protocol. On average, 83% of prescribed sVT sessions were completed by the study's participants, which is similar to the adherence levels of 77%–85% in previous studies using a 9 min sVT protocol in participants with CP and other musculoskeletal disorders (13, 23, 24).

Our preliminary results suggest a notable 10% improvement in the distance covered by the 6MWT, which is consistent with the results from other studies using variations of the 9 min protocol in children with CP (10, 13) and other musculoskeletal conditions (24). Gusso et al. (10) reported an 11% improvement in the distance covered in the 6MWT among 34 children and adolescents with CP GMFCS level II after 20 weeks of sVT (10), while Vesey et al. (24) reported a 9% improvement among seventeen children and adolescents with musculoskeletal disorders using the same sVT protocol (24). Another large study showed that the improvement in the 6MWT distance after sVT was greater in children with higher degrees of physical impairment (i.e., GMFCS levels III and IV) in comparison to participants with GMFCS level II (23). The specific mechanisms underpinning the beneficial effects of sVT on walking capacity in children and adolescents with CP are not well described. However, proposed mechanisms include the activation of alpha motor neurons (7) and Golgi tendon organs (25), facilitation of the sensory input (26), proprioception stimulation, and the secretion of hormones such as growth hormone and testosterone (7, 27). Further, sVT can stimulate spinal and supraspinal functions, leading to improved nervous control of muscle fiber recruitment (27). These mechanisms may allow for greater activation of the musculoskeletal system in individuals with limited ability to perform weight-bearing activities, providing a potential pathway for increasing mobility (i.e., walking capacity). Irrespective of the underlying mechanisms, improving walking capacity is an important therapeutic goal for children with CP (19), particularly since such improvement could lead to increased participation in other forms of physical activity. By improving activity levels through to adulthood, there could be overall health benefits, such as improvements in bone and muscle function. Thus, the inclusion of sVT in the health management of young people with mild CP could lead to substantial improvements in quality of life in the long term through increased functional mobility.

The tested 15 min sVT protocol also suggested an increase in spine BMD but not the corresponding z-score. Studies on this outcome have described conflicting findings, and a meta-analysis investigating sVT in children with CP reported improvements in femur BMD but not in lumbar spine BMD when compared with controls (28). Further research is needed to reliably ascertain the impact of sVT and protocol length on BMD in young people with CP. Importantly, natural development and growth and its effect on bone density in children and adolescents should be considered while analyzing the study results (29, 30), but our statistical models did adjust for the participant's increase in age over the study period. In addition, sVT interventions for a minimum of 6 months have been suggested as necessary to achieve improvements in bone health (31), which might not be detectable in shorter sVT protocols. While our findings suggest that the 15 min sVT protocol produced similar outcomes to the 9 min protocol used in previous studies (10, 23), it remains unclear whether longer sessions could result in greater improvements to health outcomes.

As a feasibility study, its design had limitations. We only recruited participants with CP of GMFCS level II, so that our findings cannot be extrapolated to children with more severe forms of CP or other disorders. Our exploratory analyses on health outcomes did not account for other concurrent forms of rehabilitation, but no participants started on new forms of rehabilitation during the study.

Nonetheless, our primary focus was to assess the safety and acceptability of a 15 min sVT protocol, and, to our knowledge, this study was the first to show that longer sVT sessions are feasible for children and adolescents with CP. Although our study was not specifically designed to evaluate the efficacy of sVT on physical function and body composition, our preliminary findings suggest potential health benefits associated with a 15 min sVT protocol in this population. These findings warrant further investigation through gold standard randomized controlled trials. In addition, it would be valuable to compare the effects of different sVT protocol lengths, such as 9 min vs. 15 min. Such trials should also investigate the potential effects of sVT on muscle metabolism and other relevant biochemical markers, including growth factors and on sensory deficits seen in children with CP.