Overall, our findings suggest that during isometric fatiguing contractions, CV and FD slopes are reliable variables, with potential application in clinical populations.

Background. The purpose of this study was to determine the correlation between the patellar tendon mechanical properties and oxygenation in healthy men. Methods. In two subsequent sessions, eight (mean age ± SD: 27 ± 4) recreationally active, healthy males performed 4-sec isometric knee extensions of the dominant leg at 20-80% of maximal voluntary contraction (MVC), maintaining a knee joint angle of 90° of flexion. In the first session, B-mode ultrasonography was used to record tendon length, cross-sectional area (CSA), and elongation, parameters needed to calculate stiffness. In the second session, tendon/peritendon hemodynamic parameters, namely total hemoglobin ΔtHb, ΔHHb and tissue oxygenation index (TOI% = O 2 Hb/tHb x 100), as indicators of blood flow and oxygen extraction respectively were measured by near infrared spectroscopy (NIRS). Correlations between blood volume (tHB), tissue oxygenation and tendon mechanical properties were tested using Pearson's correlation coefficient (R). Results. At all % of MVCs, a reduction of tHb and TOI%, and an increase of HHb were observed. At 80% MVC, ΔTOI% was negatively correlated with strain (R =-0.64) and elongation (R =-0.48), whereas a significant positive correlation was found with Young modulus (R = 0.69) and stress (R = 0.62); as regards blood volume, a significant negative correlation was found between elongation and ΔtHb (R =-0.44) and a positive correlation was found between stress and ΔtHb (R = 0.4). Conclusions. Patellar tendon mechanical properties and tendon/peritendon oxygen extraction and blood volume appears to be moderately correlated when studied by ultrasound and NIRS.

Purpose The purpose of the present study was to evaluate the Pearson correlations between hemodynamic parameters obtained with near infrared spectroscopy (NIRS), namely total hemoglobin (tHb) and tissue oxygen index (TOI %), as indicators of blood flow and oxygen extraction, and myoelectric parameters obtained with surface multichannel electromyography (sEMG), namely fractal dimension (FD) and conduction velocity (CV) slopes, as descriptors of central and peripheral fatigue, during sustained high level isometric contractions at 60% maximal voluntary contraction (MVC), in elderly subjects. Methods Ten recreationally healthy elderly subjects (age 67.7 ± 4.6 years), 5 males and 5 females, performed one isometric contraction of the elbow flexors at 120° joint angle at 60% of MVC until exhaustion in two subsequent trials 1 week apart, one for the sEMG and the other one for NIRS recordings from the biceps brachii. Results A negative strong Pearson's correlation between TOI % slope in the functional hyperemic phase (HP) of contraction and a positive correlation between the slope of TOI % recorded during the ischemic phase (IP) and the CV slope were found (r = − 0.76, P < 0.05; r = 0.91, P < 0.01, respectively). A negative strong correlation between tHb IP slope and tHb HP slope and TOI % IP slope and TOI % HP slope (r = − 0.78, P < 0.01; r = − 0.78, P < 0.01, respectively) were also found. No correlation was found between FD slope and hemodynamic parameters (FD slope vs. HP tHb slope, r = − 0.19; FD slope vs. IP tHb slope, r = 0.16; FD slope vs. HP TOI % slope, r = 0.19; FD slope vs. IP TOI % slope, r = 0.27). Conclusion In aged individuals, CV slope correlated with muscle O 2 desaturation (TOI %) rather than reduced muscle blood flow (tHb) in the ischemic phase of isometric contraction to exhaustion. No correlations were found between myoelectric manifestations of central fatigue (FD slope) and data obtained by NIRS.

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Background: COVID-19 may require hospitalization in an intensive care unit (ICU) and is often associated with the onset of critical illness polyneuropathy (CIP) and critical illness myopathy (CIM). Due to the spread of the disease around the world, the identification of new rehabilitation strategies for patients facing this sequence of events is of increasing importance.Case presentation: We report the clinical presentation and the beneficial effects of a prolonged, supervised adapted motor activity (AMA) program in a highly deconditioned 61-year-old male COVID-19 patient discharged from the ICU and complicated by residual CIP and CIM. The program included aerobic, strength, gait, and balance training (1 h, 2 sessions per week).Measures: Pulmonary (spirometry), metabolic (indirect calorimetry and bioimpedance), and neuromuscular functions (electromyography) were evaluated at baseline and after 1 year of training.Results: Relative to baseline, an amelioration of several spirometric parameters such as vital capacity (VC, +40%), total lung capacity (TLC, +25%), and forced expiratory volume in 1 s (FEV1, +28%) was appreciable. Metabolic parameters such as body water (60%–46%), phase angle (3.6°–5.9°), and respiratory quotient (0.92–0.8) returned to the physiological range. Electromyographic parameters were substantially unchanged. The overall amelioration in clinical parameters resulted in a significant improvement of patient autonomy and the quality of life.Conclusion: Our results highlight the importance of AMA for counteracting respiratory, metabolic, and functional but not neuromuscular impairments in COVID-19 patients with residual CIM and CIP.

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