Jakob Lorentzen

Post-activation depression of Soleus stretch reflexes in healthy and spastic humans

Reduced depression of transmitter release from Ia afferents following previous activation (post-activation depression) has been suggested to be involved in the pathophysiology of spasticity. However, the effect of this mechanism on the myotatic reflex and its possible contribution to increased reflex excitability in spastic participants has not been tested. To investigate these effects, we examined post-activation depression in Soleus H-reflex responses and in mechanically evoked Soleus stretch reflex responses. Stretch reflex responses were evoked with consecutive dorsiflexion perturbations delivered at different intervals. The magnitude of the stretch reflex and ankle torque response was assessed as a function of the time between perturbations. Soleus stretch reflexes were evoked with constant velocity (175°/s) and amplitude (6°) plantar flexion perturbations. Soleus H-reflexes were evoked by electrical stimulation of the tibial nerve in the popliteal fossa. The stretch reflex and H-reflex responses of 30 spastic participants (with multiple sclerosis or spinal cord injury) were compared with those of 15 healthy participants. In the healthy participants, the magnitude of the soleus stretch reflex and H-reflex decreased as the interval between the stimulus/perturbation was decreased. Similarly, the stretch-evoked torque decreased. In the spastic participants, the post-activation depression of both reflexes and the stretch-evoked torque was significantly smaller than in healthy participants. These findings demonstrate that post-activation depression is an important factor in the evaluation of stretch reflex excitability and muscle stiffness in spasticity, and they strengthen the hypothesis that reduced post-activation depression plays a role in the pathophysiology of spasticity.

Distinguishing active from passive components of ankle plantar flexor stiffness in stroke, spinal cord injury and multiple sclerosis

OBJECTIVE Spasticity is a common manifestation of lesion of central motor pathways. It is essential for correct anti-spastic treatment that passive and active contributions to increased muscle stiffness are distinguished. Here, we combined biomechanical and electrophysiological evaluation to distinguish the contribution of active reflex mechanisms from passive muscle properties to ankle joint stiffness in 31 healthy, 10 stroke, 30 multiple sclerosis and 16 spinal cord injured participants. The results were compared to routine clinical evaluation of spasticity. METHODS A computer-controlled robotic device applied stretches to the ankle plantar flexor muscles at different velocities (8-200deg/s; amplitude 6°). The reflex threshold was determined by soleus EMG. Torque and EMG data were normalized to the maximal torque and EMG evoked by supramaximal stimulation of the tibial nerve. Passive resistance (the torque response to stretches) was confirmed to be a good representation of the passive stiffness also at higher velocities when transmission in the tibial nerve was blocked by ischemia. RESULTS Passive torque tended to be larger in the neurological than in the healthy participants, but it did not reach statistical significance, except in the stroke group (p<0.05). Following normalization to the maximal stimulus-evoked torque, the passive torque was found to be significantly larger in neurological participants identified with spasticity than in non-spastic participants (p<0.01). There was no significant difference in the reflex threshold between the healthy and the neurological participants. The reflex evoked torque and EMG were significantly larger in all neurological groups than in the healthy group (p<0.001). Twenty three participants with evidence of hypertonia in the plantar flexors (Ashworth score⩾1) showed normal reflex torque without normalization. With normalization this was only the case in 11 participants. Increased reflex mediated stiffness was detected in only 64% participants during clinical examination. CONCLUSION The findings confirm that the clinical diagnosis of spasticity includes changes in both active and passive muscle properties and the two can hardly be distinguished based on routine clinical examination. SIGNIFICANCE The data suggest that evaluation techniques which are more efficient in distinguishing active and passive contributions to muscle stiffness than routine clinical examination should be considered before anti-spastic treatment is initiated.

Passive muscle properties are altered in children with cerebral palsy before the age of 3 years and are difficult to distinguish clinically from spasticity

Clinical determination of spasticity is confounded by the difficulty in distinguishing reflex from passive contributions to muscle stiffness. There is, therefore, a risk that children with cerebral palsy (CP) receive antispasticity treatment unnecessarily. To investigate this, we aimed to determine the contribution of reflex mechanisms to changes in the passive elastic properties of muscles and tendons in children with CP.

Muscle growth is reduced in 15‐month‐old children with cerebral palsy

Lack of muscle growth relative to bone growth may be responsible for development of contractures in children with cerebral palsy (CP). Here, we used ultrasonography to compare growth of the medial gastrocnemius muscle in children with and without CP.

Science-Based Neurorehabilitation: Recommendations for Neurorehabilitation From Basic Science

ABSTRACT Neuroscience has fundamentally changed the understanding of learning and memory within recent years. Here, the authors discuss a number of specific areas where they believe new understanding of the CNS from basic science is having a fundamental impact on neurorehabilitation and is leading to new therapeutic approaches. These areas have constituted a basis for development of some basic principles for neurorehabilitation: Optimal rehabilitation should involve (a) active (patient) participation in the training, (b) training that does not only involve many repetitions, but also continues to challenge the skill of the training person, (c) motivation and reward, (d) intensive training and practice over a long time, (e) careful organization of the training in relation to other activities, and (f) incorporation of other potentially beneficial parameters such as sleep and diet. It should in this relation also be pointed out that albeit neurorehabilitation may be predicted to have the most optimal effect early in life and as soon after injury as possible, there is no reason to believe that beneficial effects of training may not be obtained late in life or several years after injury.

Gait training reduces ankle joint stiffness and facilitates heel strike in children with Cerebral Palsy

BACKGROUND Foot drop and toe walking are frequent concerns in children with cerebral palsy (CP). Increased stiffness of the ankle joint muscles may contribute to these problems. OBJECTIVE Does four weeks of daily home based treadmill training with incline reduce ankle joint stiffness and facilitate heel strike in children with CP? METHODS Seventeen children with CP (4-14 years) were recruited. Muscle stiffness and gait ability were measured twice before and twice after training with an interval of one month. Passive and reflex-mediated stiffness were measured by a dynamometer which applied stretches below and above reflex threshold. Gait kinematics were recorded by 3-D video-analysis during treadmill walking. Foot pressure was measured by force-sensitive foot soles during treadmill and over-ground walking. RESULTS Children with increased passive stiffness showed a significant reduction in stiffness following training (P = 0.01). Toe lift in the swing phase (P = 0.014) and heel impact (P = 0.003) increased significantly following the training during both treadmill and over-ground walking. CONCLUSIONS Daily intensive gait training may influence the elastic properties of ankle joint muscles and facilitate toe lift and heel strike in children with CP. Intensive gait training may be beneficial in preventing contractures and maintain gait ability in children with CP.

Impaired gait function in adults with cerebral palsy is associated with reduced rapid force generation and increased passive stiffness

OBJECTIVE It is still not clarified whether spasticity contributes to impairments of gait function. Here we compared biomechanical measures of muscle weakness and stiffness of ankle muscles to impairments of gait function in adults with cerebral palsy (CP). METHODS Twenty-four adults with CP (mean age 34.3, range 18-57 years) and fifteen healthy age-matched controls were biomechanically measured for passive and reflex-mediated stiffness of the ankle plantarflexors at rest, maximal voluntary plantarflexion and dorsiflexion effort (MVCpf,df) and rate of force development (RFDpf,df). Kinematic analysis of the ankle joint during treadmill walking was obtained by 3-D motion analysis. RESULTS Passive stiffness was significantly increased in adults with CP compared to controls. Passive stiffness and RFDdf were correlated to reduced toe lift. RFDpf provided the best correlation to push-off velocity, range of movement in the ankle joint and gait speed. Reflex-mediated stiffness was not correlated to any parameters of impaired gait. CONCLUSIONS Impaired gait function in adults with CP is associated with reduced RFD and increased passive stiffness of ankle muscles. SIGNIFICANCE These findings suggest that reduced rapid force generation and increased passive stiffness of ankle muscles rather than increased reflex-mediated stiffness (spasticity) likely contributes to impaired gait function in adults with CP.

Assessment of a portable device for the quantitative measurement of ankle joint stiffness in spastic individuals

OBJECTIVE Spasticity is a common complication with neurological diseases and CNS lesions. Instrumented systems to evaluate spasticity often cannot provide an immediate result, thus limiting their clinical usefulness. In this study we investigated the accuracy and reliability of the portable Neurokinetics RA1 Ridgidity Analyzer to measure stiffness of the ankle joint in 46 controls, 14 spinal cord injured (SCI) and 23 multiple sclerosis (MS) participants. METHODS Ankle stiffness measures were made twice by two raters, at speeds above and below the expected stretch reflex threshold. Ankle torque was measured with the portable device and a stationary torque motor. Inter- and intra-rater reliability was assessed with the intra-class correlation coefficient (ICC). RESULTS Stiffness measures with the portable and stationary devices were significantly correlated for controls and MS participants (p < 0.01). Intra-rater reliability for the portable device ranged from 0.60-0.89 (SCI) and 0.63-0.67 (control) and inter-rater reliability ranged from 0.70-0.73 (SCI) and 0.61-0.77 (control). Ankle stiffness measures in SCI and MS participants were significantly larger than in controls for both slow (p < 0.05) and fast movements (p < 0.01), with stiffness being larger for fast compared to slow movements in SCI and MS participants (p < 0.05), but not in controls (p = 0.5). CONCLUSION The portable device correlated well with measures obtained by a torque motor in both controls and MS participants, showed high intra- and inter-rater reliability for the SCI participants, and could easily distinguish between stiff and control ankle joints. However, the device, in its current form, may be less accurate during rapid movements when inertia contributes to stiffness and the shape of the air-filled pads did not provide a good interface with the foot. SIGNIFICANCE This study demonstrates that a portable device can potentially be a useful diagnostic tool to obtain reliable information of stiffness for the ankle joint.

Twenty weeks of home-based interactive training of children with cerebral palsy improves functional abilities

BackgroundHome-based training is becoming ever more important with increasing demands on the public health systems. We investigated whether individualized and supervised interactive home-based training delivered through the internet improves functional abilities in children with cerebral palsy (CP).MethodsThirty four children with CP (aged 9–16; mean age 10.9 ± 2.4 years) (GMFCS I-II; MACS I-II) were included in this non-randomized controlled clinical training study. 12 children (aged 7–16; mean age: 11.3+/−0.9 years) were allocated to a control group in which measurements were performed with 20 weeks interval without any intervening training. Daily activities, functional abilities of upper- and lower limbs, and balance were evaluated before, immediately after training and 12 weeks after training. The training consisted of 30 min daily home-based training for 20 weeks delivered through the internet.ResultsThe training group on average completed 17 min daily training for the 20 week period (total of 40 h of training). The training group showed significant improvements of daily activities (AMPS), upper limb function (AHA) and functional tests of lower limbs (sit to stand, lateral step up, half knee to standing) after 20 weeks of training. No difference was found between the test after 20 weeks of training and the test 12 weeks after training. No significance was reached for balance after training. No difference was found for any parameter for the control group.ConclusionsInteractive home training of children with CP is an efficient way to deliver training, which can enable functional motor improvements and increased activity to perform daily activities.Trial registrationISRCTN13188513. Date of registration: 04/12/2014

A pilot study on early home-based intervention through an intelligent baby gym (CareToy) in preterm infants

BACKGROUND CareToy is an intelligent system, inspired by baby gyms, aimed to provide an intensive, individualized, home-based and family-centred early intervention (EI) program. AIMS A pilot study was carried out to explore the feasibility of CareToy intervention in preterm infants, aged 3-9 months of corrected age. METHODS Twenty low-risk preterm infants, without brain lesion or other clinical complications (14 allocated to CareToy intervention and 6 to Standard Care) were recruited. The Infant Motor Profile (IMP) was predefined as the primary outcome measure and Alberta Infant Motor Scale and Teller Acuity Cards as secondary measures. Moreover, 202 pre-programmed training scenarios were developed and instructions for the management of CareToy intervention were defined as general guidelines. OUTCOMES AND RESULTS All infants received 4 weeks of their allocated intervention and were evaluated with the selected tests before and immediately after the 4 weeks. The mean difference changes in IMP total score and Teller Acuity Cards over the intervention period were higher in the CareToy group than in the Standard Care group. CONCLUSIONS AND IMPLICATIONS CareToy seems a feasible device for providing EI. An adequately powered randomized clinical trial is warranted.