Abstract
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.
Highlights
Measuring muscle mechanical properties in the setting of pathological states, such as neuromuscular diseases, has attracted great interest, as mechanical property measurements can be used to monitor neuromuscular disease courses or potential treatment-elicited improvements in neuromuscular diseases [1,2,3,4]
The present study aims to evaluate the capability of Shearwave elastography (SWE) to track quadriceps muscle stiffness variations before, during and after the world's most challenging extreme mountain ultramarathon
Intra-session reliability varied from good (ICC = 0.88 during the Pre and Mid sessions) to high (ICC = 0.90 and 0.92 at the Finish and Recovery sessions, respectively), and no significant differences in reliability were noted among the times (p = 0.16)
Summary
Measuring muscle mechanical properties in the setting of pathological states, such as neuromuscular diseases, has attracted great interest, as mechanical property measurements can be used to monitor neuromuscular disease courses or potential treatment-elicited improvements in neuromuscular diseases [1,2,3,4]. Ultrasound imaging is a very promising alternative, as it provides muscle damage-related anatomical information and enables the performance of quantitative wave velocity measurements in tissues, which have been shown to be related to muscle stiffness [8,9,10,11]. Shearwave elastography (SWE) is an ultrasound-based technique that characterizes tissue elastic properties based on the propagation of remotely induced shear waves [12,13,14]. SWE calculates tissue stiffness based on tissue shear wave propagation velocity measurements. When performed under well-controlled conditions that ensure reproducibility, SWE has been shown to be a reliable technique for investigating muscle biomechanical properties [16,17,18,19,20]
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