Motor disability in children is most commonly caused by cerebral palsy, a disorder which results from early-infancy brain damage and is usually discovered only when children have difficulty in standing or walking: “The affected muscles fail to grow along with the bones from babyhood onwards, which is why it would be good to intervene at an early stage. Stretching is used almost daily as a therapy for children with cerebral palsy. However, there haven’t been sufficient investigations yet into whether such regular training can prevent the shortening of muscles and the development of potential deformations,” is how Annika Kruse from the University of Graz describes her research focus. Kruse is a sports scientist who specialises in movement science. With the support of her research colleague Markus Tilp and paediatric orthopaedic surgeon Martin Svehlik, she measures and evaluates the effects of two stretching methods on the calf muscles of young patients in an FWF-funded Hertha Firnberg project. The measured results on the short-term effects of the stretching methods are already available, indicating that such stretching does not reach the shortened muscle at all. Instead the increase in movement is produced by the tendon in the joint, as Kruse explains. However, not all measurements have been evaluated as yet.
A disturbance in the brain and changes in the muscles
Statistically speaking, 1.5 to 2.5 children out of every 1,000 children in Europe are born with spastic cerebral palsy. This neuromuscular disorder has a variety of causes and the symptoms vary in severity. While some children have only moderate limitations, others require a wheelchair or multiple operations. Among other things, cerebral palsy causes an excessive muscle tone (spasticity) and affects the ability to control muscles. Consequently, the patients suffer from muscle weakness and the spastic muscles do not grow along with the bones. Why and how exactly this happens is not yet known. As a result, the entire musculoskeletal system is affected and the adverse effects include bone deformities. If the calf muscles are severely shortened, for instance, the ability to walk normally is impaired. In her doctoral thesis, Annika Kruse already analysed the structure and architecture of the calf muscles of children with cerebral palsy after functional strength training. In this project she examined the effects of a single stretching session as well as those over an eight-week programme.
Is stretching an effective therapy?
In order to be able to assess the effects, the researchers measured several aspects in young patients, including muscle characteristics, muscle strength, joint mobility and gait pattern. “Muscles, strength, gait pattern – it’s all connected,” emphasises Annika Kruse. At the first appointments, the team collected baseline values, the stretching programme was performed just once, and possible short-term effects were measured immediately afterwards. For the study, Kruse recruited children between the ages of 6 and 15 who were able to walk independently or master short distances with walking aids (crutches, for example). The young patients were divided into two groups so as to have a control group. One of the two groups did stretching exercises at home several times a week for eight weeks with the support of their parents, while the others went about their daily lives. In order to find out which stretching method works, how it works and at what level, Kruse employed a combination of methods. The examinations were conducted in several sessions using, among other things, 3D gait analysis with infrared cameras (gait pattern), an isokinetic dynamometer for strength testing, and 2D ultrasound for muscle measurement. Richard Jaspers from the Free University of Amsterdam was also involved to establish a 3D ultrasound technique for measuring muscle volume. Kruse demonstrated the exercises in front of parents and children and followed up with a measurement programme to capture the immediate response of the calf muscles after a single stretching session.
The tendon takes over
Contrary to the common belief that muscles, or more precisely the muscle belly, can be lengthened even by a short stretching session, the initial results show that in the spastic muscle-tendon unit it is rather the tendon that can be stretched. “Consequently, the increased joint mobility that we found is produced by the tendon. This observation is important for further applications,” Kruse notes. In the long term, stretching the tendon could actually have a negative effect on the relationship between muscle and tendon, making spastic muscles even weaker. Currently, the team is evaluating the data from the multiple-week training programme. Annika Kruse hopes that the final results of the study will help to produce new knowledge about spastic cerebral palsy and facilitate the development of targeted and, above all, effective therapy for affected children and adolescents.
Annika Kruse completed her PhD at the Department of Human Movement Science, Sport and Health at the University of Graz in 2018. Her doctoral thesis focused on changes in the morphological and mechanical properties of the muscles of children with spastic cerebral palsy and the effects of strength training in this group. Since September 2018, Kruse has been working on her project on static stretching in children with spastic cerebral palsy in the context of a Hertha Firnberg Fellowship of the Austrian Science Fund FWF, benefitting from her expertise in training, movement analysis, ultrasound diagnostics and in the therapy of children with cerebral palsy.
Kruse A., Rivares C., Weide G., Tilp M., Jaspers RT: Stimuli for Adaptations in Muscle Length and the Length Range of Active Force Exertion – A Narrative Review, in: Frontiers in Physiology, 2021
Kruse A., Habersack A., Tilp M., Svehlik M.: Acute effects of proprioceptive neuromuscular facilitation stretching in children with spastic cerebral palsy – A preliminary analysis, in: Gait & Posture 90, 2021