Biomarkers of Peripheral Fatigue in Subjects with Vascular and Neurological Motor Disabilities During an Incremental Treadmill Test Using Near-Infrared Spectroscopy

Exercise is a recognized tool to improve or maintain physical functioning and quality of life in chronic diseases, particularly in the presence of disability. Patients affected with vascular and neurological motor disabilities, such as people with multiple sclerosis (PwMS) or peripheral arterial disease (PAD), are daily limited by fatigue. This symptom, which can occur in a variety of forms, could interfere with exercise execution and the rate of adherence to rehabilitative programs. The early detection of objective biomarkers of peripheral fatigue and their integration into specific training programs could increase the long-term engagement of these patients in exercise. In this light, the study aims to analyze the association between muscle oxygenation, cardiovascular response and perceived exertion during a treadmill incremental walking test in healthy and chronically ill subjects. After eligibility assessment, a total of 53 subjects were divided into three subgroups: 17 patients diagnosed with PAD (mean age: 71
$\pm 9$
years), 26 with MS (mean age:
$45\pm 12$
years), and 10 healthy subjects (mean age: 23
$\pm 1$
years). Parameters of muscle metabolism at the gastrocnemius were collected by near-infrared spectroscopy (NIRS) during an incremental treadmill test and quantified as area-under curve for oxygenated
$(\mathrm{O}_{2}\text{Hb}_{\text{AUC}})$
and deoxygenated
$(\text{HHb}_{\text{AUC}})$
hemoglobin traces. Heart rate values during the test and the rate of perceived exertion by the Borg scale 0–10 were also collected.
$\mathrm{O}_{2}\text{Hb}_{\text{AUC}}$
was significantly lower in the PAD group with an opposite trend for
$\text{HHb}_{\text{AUC}}$
, whereas MS subjects showed heterogeneous trends in both
$\mathrm{O}_{2}\text{HHb}_{\text{AUC}}$
and
$\text{HHb}_{\text{AUC}}$
, suggesting a different but abnormal pattern associated with the perception of peripheral fatigue in the two diseases. Significant and negative correlations were indeed observed between changes in
$\mathrm{O}_{2}\text{Hb}$
, heart rate and perceived exertion in the whole population. At this stage of the research, the dynamic and objective measurement of oxygenation in the fatiguing muscle enabled the discrimination of different abnormal responses to exercise in different diseases and among subjects. These results in a second phase of the study will be analyzed with the purpose of identifying early objective markers of fatigue that could possibly be integrated into semiautomatic technology-assisted ergo meters to personalize training programs.