Reproducibility of Isometric Strength in Children with Cerebral Palsy

Introduction

Cerebral Palsy (CP) is a diagnosis based on an insult to the immature brain and resultant observed movement disorders, the maturation or development central nervous system function is often the focus of intervention [1]. Children with cerebral palsy are very weak compared to their able-bodies match controlled [2, 3]. Additionally, muscle weakness can be a major problem for many young people with spastic hemiplegic CP [2, 3, 4, 5]. The term “hemiplegia” refers to weakness and movement in coordination involving one side of the body [2, 6]. The majority of studies assessing muscle strength in children with CP use only functional measures of muscle strength without endurance time. Although functional measures of muscle strength are important indicators of a child’s motor ability, they do not quantify muscle force, lack the ability to detect small incremental changes in strength, and confounded by motor planning and control issues [5]. For another way, the evidence supporting the case for either inclusion or exclusion of strength training is based on sound scientific results from reproducible studies [3]. In general, further research of sufficient methodological quality is required to increase evidence on trainability after a good reproducibility of all fitness parameters and functional ability in children with cerebral palsy [2, 3]. Then, a better knowledge of the innocuity of sports, if correctly practiced, as well as a precise appreciation of the clinical and physiological parameters, should also help and overprotection and, eventually, to delay as long as possible the course towards cerebral palsy. An increasing number of studies have investigated assessment of strength in children with spastic CP [4, 5, 7, 8, 9]. However, most of the relevant literature consists of one trial of isokinetic and/or isometric contractions without reproducibility for almost. Whereas it is the best strategy of the validation of a test before apply the clinical feasibility of the programs [2, 3]. Quantitative measurement instruments have been shown to reliably assess muscle strength in children with and without neuromuscular disorders [9, 10, 11]. Indeed, an assessment tool may not be reliable in all patient populations and/or with all analysis system [12]. However there is a paucity of studies which use our current methodology to assess the reproducibility of muscle strength which assessed the responses to rehabilitation Accordingly, the objectives of this study are two folds: (i) To determine whether the strength and endurance during sustained isometric contraction of quadriceps femoris is reproducible in spastic hemiplegic CP kids, and (ii) To documented the methodology of the evaluation of the strength in children with CP., in the case of the optimization therapy in children with CP.

Discussion

In this study, reliability of skeletal muscle function measured by Cybex Norm II during isometric contraction was examined in a homogeneous group of right hemiplegic children with CP classified to GMFCS-level I and II. In our study, we tested the affected leg because we wanted to validate the protocol in the altered leg. The population of this study was right hemiplegic cerebral palsy, and we compared the results of their isometric strength with the right leg of their able-bodied match children. However must studies of strength in children with cerebral palsy only use the unaffected leg as controlled but do not get healthy controlled children [21, 22]. Moreover those studies do not do Bland and Altman plot. Where as to be more relevant in clinical practice, a tool of evaluation should compared the results of the research between disability population and typically developing. Additionally, for a clinical reproducibility study, Bland and Altman should be plotted to show a good agreement between the repeated measures for all variables assessed, and to clarify and attest the use of interclass correlation coefficient in the evaluation of the agreement [20, 23]. It is obvious that reproducibility is the hallmark of science. Therefore, given that the population of our study was homogeneity, we used ICC. It was assumed that, it is useful to use also SEM and SDD on sample heterogeneity [22]. In their study, Willemse et al 2013 [22] found that hand-held dynamometry is reliable and can be used to detect changes in isometric muscle strength in children with CP when using the mean of at least 2 trials. They also say that to further improve reliability, taking the average of 2 occasions on separated days is recommended, depending on group size and muscle group. Indeed, although the protocol is not quite the same, we agree closely with Willemse et al. (2013) [22]. We reported a reproducibility of isometric strength and endurance in children with cerebral palsy when participants were tested twice at an interval of 1 week. In support of this view, Ayalon et al. (2000) [21] evaluates the reliability of isokinetic testing of Knee flexors and extensors in children with CP. They concluded that the finding indicate that measuring isokinetic strength in the tested population is highly reliable and should be considered in rehabilitation protocols. Unfortunately, their study does not included endurance test and the participants in their study represent heterogeneity sample of children with CP. Our sampling was larger of the participant's capacity and confirmed the higher reliability that was manifested by the ICC. Molnar et al. (1979) [10] also investigated the reliability of isokinetic testing on a variety of muscle groups of the lower and upper extremities in children aged 7 to 15 years. They confirmed that isokinetic testing is simple to conduct and highly reliable for typically developing children with normal intelligence as well a children with minor learning disability. Similarly, Damiano et al. (1999) [9] argued that manuel muscle testing (MMT) and hand-held dynamometry are the most commonly used methods to assess strength both in clinical practice and in research. Our study confirmed those [9]. Most of these studies on reproducibility of isometric strength in children with CP forsake the endurance time during the sustained force. However, the outcome of the endurance time could be a good index of a relevant reproducibility. We can argue that static endurance time at 50% of individual's maximal voluntary torque is a parameter of the isometric strength. This in turn might suggest that static endurance time could enhance the ability of child with CP to sustain isometric concentrations. One important limitation to the interpretation of correlation coefficients is that they are very sensitive to the range of values studied [23], with higher ICCs if the range of values is wide. Moreover, even a high inter-test correlation does not necessary imply that a measurement is reproducible. Most previous investigators have used arbitrary cut-off values to rate the reproducibility of data [24, 25]. Nadler et al. (2000) [24] accepted an ICC >0.75 as indicative of good reliability and Portney and Watkins defined values <0.75 as having poor to moderate reliability; others have required an ICC of 0.80 for an acceptable test. Adopting the 0.75 cut-off, one would conclude that in children with hemiplegic cerebral palsy, the Cybex Norm dynamometer yields several MVIF and SET measurements that have a satisfactory level of reproducibility over a one-week interval. The coefficient of reproducibility (COR) of Bland and Altman (1986) [20] can be more informative than either the ICC or the CV.

Thus, a COR of 115 Nm for strength in children with cerebral palsy implies that 95% of inter-test differences were less than 115 Nm. This is important practical information for the clinician who must decide whether an apparent improvement in gait cycle is due to measurement variability or a response to treatment. The COR value is also helpful in calculating minimum sample sizes when designing a study of group responses to treatment [23, 26]. Testing of the reproducibility of quadriceps femoris isometric strength may therefore be important for treatment planning or for assessing the effectiveness of treatment.

Conclusion

Results of this repeated sustained isometric contraction of quadriceps support the view that home- based on reproducibility test programmes is a prerequisite to validate the feasibility of a protocol before apply it use. Forward, our study showed good reproducibility of isometric voluntary maximal force and static endurance time in children with spastic hemiplegic CP classified at Gross Motor Function Classification level I and II, suggesting the utility of using the sustained isometric test as a valid tool to measure strength in clinical rehabilitation.

Acknowledgement

We acknowledge the cooperation and expert technical assistance of the medical staff of the cerebral palsy center during data collection and processing, and the generous cooperation of the children and parents participating in this study. The authors disclose any potential conflict of interest.