Recurrence quantification analysis of sustained sub-maximal grip contractions in patients with various metabolic muscle disorders

Recurrence quantification analysis (RQA) was used to analyse force signals during sustained sub-maximal grip contraction (SSGC) of three types of patients suffering from a metabolic muscle disorder (glycogen storage disease type III (GSD III), glycogen storage disease type V (GSD V) and mitochondrial myopathies (MITO)) compared to control subjects. Recurrence plots (RP) of patients showed clear non-uniformity, in comparison to control subjects who displayed quasi-periodic patterns. Quantitative analysis of the RP showed significant differences between patients with metabolic disorders and the control group for four RQA parameters. The results showed that the SSGC signals of patients had decreased Lmax, which indicated more chaotic patterns. In addition the deterministic component of the signals was less complex for patients than for controls. The differences of SSGC signal observed using RP and RQA were possibly related to the underlying changes in metabolism of muscle fibres due to the disease. Results of this study illustrate that the RQA technique is well suited to analyse sustained grip-force signals.