Shear-Wave Elastography Assessments of Quadriceps Stiffness Changes prior to, during and after Prolonged Exercise: A Longitudinal Study during an Extreme Mountain Ultra-Marathon.

In sports medicine, there is increasing interest in quantifying the elastic properties of skeletal muscle, especially during extreme muscular stimulation, to improve our understanding of the impact of alterations in skeletal muscle stiffness on resulting pain or injuries, as well as the mechanisms underlying the relationships between these parameters. Our main objective was to determine whether real-time shear-wave elastography (SWE) can monitor changes in quadriceps muscle elasticity during an extreme mountain ultra-marathon, a powerful mechanical stress model. Our study involved 50 volunteers participating in an extreme mountain marathon (distance: 330 km, elevation: +24,000 m). Quantitative SWE velocity and shear modulus measurements were performed in most superficial quadriceps muscle heads at the following 4 time points: before the race, halfway through the race, upon finishing the race and after recovery (+48 h). Blood biomarker levels were also measured. A significant decrease in the quadriceps shear modulus was observed upon finishing the race (3.31±0.61 kPa) (p<0.001) compared to baseline (3.56±0.63 kPa), followed by a partial recovery +48 h after the race (3.45±0.6 kPa) (p = 0.002) across all muscle heads, as well as for each of the following three muscle heads: the rectus femoris (p = 0.003), the vastus medialis (p = 0.033) and the vastus lateralis (p = 0.001). Our study is the first to assess changes in muscle stiffness during prolonged extreme physical endurance exercises based on shear modulus measurements using non-invasive SWE. We concluded that decreases in stiffness, which may have resulted from quadriceps overuse in the setting of supra-physiological stress caused by the extreme distance and unique elevation of the race, may have been responsible for the development of inflammation and muscle swelling. SWE may hence represent a promising tool for monitoring physiologic or pathological variations in muscle stiffness and may be useful for diagnosing and monitoring muscle changes

Quantification of capillary blood cell flow using reflectance confocal microscopy

BACKGROUND/PURPOSE: In vivo reflectance confocal microscopy (IVCM) is a new tool for skin microcirculation. However, the measure of quantitative blood cell flow (QBCF) has not been standardized. We studied the inter-investigator and the intra-capillary reproducibility of the manual measure of QBCF on IVCM videos and investigated if a software program might help measure QBCF and be sensitive to vascular occlusion tests. METHODS: The inter-investigator reproducibility of the manual QBCF was evaluated on 107 videos. The intra-capillary reproducibility of QBCF measured manually and by 2 semi-automatic procedures based on Image J software analysis was evaluated on 19 capillaries. One of the semi-automatic methods (peaks of luminous intensity) was also used to measure the QBCF during vascular occlusion tests. RESULTS: The manual measure did not show a good inter-investigator reproducibility (Pearson's coefficient <0.5). The 'peaks of luminous intensity' method was found to have a good intra-capillary reproducibility and to be sensitive to vascular occlusion. CONCLUSION: Differently from the manual count, the count of peaks of luminous intensity by Image J software seems to be promising to measure QBCF. The future is to create software allowing for real-time measure of the QBCF based on the peaks of luminous intensity inside the capillaries recorded by IVCM

Hemolysis induced by an extreme mountain ultra-marathon is not associated with a decrease in total red blood cell volume

Prolonged running is known to induce hemolysis. It has been suggested that hemolysis may lead to a significant loss of red blood cells; however, its actual impact on the erythrocyte pool is unknown. Here, we test the hypothesis that prolonged running with high hemolytic potential decreases total red blood cell volume (RCV). Hemolysis (n = 22) and RCV (n = 19) were quantified in ultra-marathon runners before and after a 166-km long mountain ultra-endurance marathon (RUN) with 9500 m of altitude gain/loss. Assessment of total hemoglobin mass (Hb(mass) ) and RCV was performed using a carbon monoxide rebreathing technique. RUN induced a marked acute-phase response and promoted hemolysis, as shown by a decrease in serum haptoglobin (P < 0.05). Elevated serum erythropoietin concentration and reticulocyte count after RUN were indicative of erythropoietic stimulation. Following RUN, runners experienced hemodilution, mediated by a large plasma volume expansion and associated with a large increase in plasma aldosterone. However, neither Hb(mass) nor RCV were found to be altered after RUN. Our findings indicate that mechanical/physiological stress associated with RUN promotes hemolysis but this has no impact on total erythrocyte volume. We therefore suggest that exercise 'anemia' is entirely due to plasma volume expansion and not to a concomitant decrease in RCV