Neuromuscular Fatigue Aetiology Comparison Between Prepubertal Boys and Adults (LENGTH-FATIG)

The study of neuromuscular fatigue in children is a recently topic in the field of sport sciences. Such knowledge could improve the efficiency and security of training and rehabilitation in healthy children and children with diseases like obesity.

The LENGTH-FATIG study will provide knowledge about the peripheral and central mechanisms of the neuromuscular fatigue in children and adults. Fatigue will test for different muscle groups (knee extensors and ankle plantar flexors) at different muscle lengths (short, optimal and long).

During high-intensity exercise, prepubertal children are more resistant to fatigue than adults. Contributions of the central and peripheral components to the development of neuromuscular fatigue are also different between both populations. The reduced children's fatigue coud be particularly related to a lower peripheral (i.e. muscular) fatigue. This might be attributed to the fact that prepubertal children rely more on oxidative than anaerobic metabolism than adults during fatiguing exercise. On the other hand, nervous factors could also explain differences in fatigue between children and adults. However, this topic is scarcely documented and still controversial. To our knowledge, no study has still compared the aetiology of central fatigue (supra-spinal vs. spinal) between children and adults. Only the voluntary activation level had been studied in children, conventionally used to assess central fatigue. But this factor doesn't differentiate spinal and supra-spinal contributions to neuromuscular fatigue development.

The LENGTH-FATIG research project is a physiological and observational study comparing two age groups (adults and children). Subjects will have to perform three randomized fatigue protocols at three muscle lengths (short, optimal and long) with the knee extensors and the ankle plantar flexors.

Data will be analyzed using LabChart 7.3 Pro software (ADInstrument, New South Wales, Australia) and Statistica 8.0 software (StatSoft, Inc.) and significance will be accepted at a two-sided alpha level of p<.05. The normality and homogeneity of the variables will be checked respectively from a Shapiro-Wilk test and a Barlett test.

If normality and homogeneity of the variables are verified, absolute values of variables (Force, EMG, NIRS, etc.) will be compared using three factors (age x muscle length x muscle group) analyses of variance (ANOVA) with repeated measures. If analyses reveal a significant effect of any factor or interaction of factors, post-hoc Newman-Keuls tests will be performed to determine differences between the different conditions.

If, on the contrary, normality and homogeneity of the variables are not verified, the effects of muscle length, muscle group and age will be evaluated using a Friedman test. If the tests show significant effects, comparisons of the different conditions will be performed using Mann-Whitney and Wilcoxon tests.