There is a lack of evidence if SWE is sensitive to tissue changes of the lower limb after a single training session in professional athletes. The aim of this study was therefore to examine the impact of an acute exercise on muscles and tendons, measured by SWE. While the median shear wave velocity did not differ between pre- and post-exercise, we detected an increase in stiffness for lower pre-exercise values and decreasing stiffness for higher pre-exercise values in professional female athletes.
For assessing SWE measurement, it is necessary to stick to a standardized measurement protocol, joints, tendons and muscles needed to be in a relaxed position and transducer positioning should be performed without pressure, thus joint position, contraction and pressure do have an impact on SWS (14). Regarding these influences, SWE is a reliable technique in assessing muscle and tendon stiffness (15).
However, exercise activity prior to the measurement can affect the results as indicated by an increase in stiffness for lower pre-exercise shear wave velocity values and decreasing stiffness for higher pre-exercise values in healthy tendons. This implies an individual response of healthy tendons and muscles to a mean optimal stiffness after a short training session in professional athletes. These individual changes post exercise should be considered when diagnosing tendon injuries. Transient changes in stiffness after heel drop exercises have been reported, however in non-professional participants (16). Decreased tendon stiffness was detected after long distance running (17). Risch et al. reported a higher intratendinous bloodflow in AT shortly after a treadmill running exercise in recreational and semiprofessional athletes in some participants, while other ATs were unaffected (18). In this study, especially stiffer ATs showed decreased stiffness values after acute exercise, which could be a sign of higher intratendinous bloodflow. The missing change of tendon stiffness in our cohort may be driven by a professional sports collective with a general high amount of training hours and ongoing stretching exercises combined with physiotherapy care. This study did not detect a stiffness difference between volleyball and handball players. This may be due to the similar training load and similar kinds of exercise activities such as running and jumping.
Professional female athletes seem to have a common AT stiffness after acute exercise between 11 m/s and 12 m/s. Although cut-off values are only useful for one ultrasound system, the general knowledge of changes in tendon stiffness regarding professional athletes is highly important for future research and potential prospective studies. Reference values and stiffness changes shortly after exercise needed to be considered while using SWE in preventive and rehabilitation medicine.
Overall, studies show that SWE is a suitable diagnostic tool for assessing the stiffness of tendons and muscles with potential applicationin rehabilitation and preventive medicine (19-21). Individual regular assessment of tissue health by SWE in professional sports could detect decreasing stiffness of achilles tendon, which may be associated with increased risk of injury. At once, in patellar tendon, with significant lower baseline SWS in comparison to AT, increasing stiffness was reported to correlate with tendinopathy (22). Thus, intra-individual changes of tendon stiffness measured by SWE provides additional information and could be implemented as a screening tool during long-term training plans or high-volume training camps to prevent injuries.
Dirrichs et al. examined that SWE provided good results for differentiating between subjects with painful tendinopathies and asymptomatic, healthy control subjects (10). The results were consistent with the VISA-A Score in subjects with achilles tendinopathy (23). SWE can be used to detect differences in sportive active and non-active individuals (12). When assessing stiffness values measured by SWE effects of gender needed to be considered (24, 25). While the effect of age on tendon stiffness, measured by SWE, is currently inconclusive (25-28).
Standardized SWE measurement protocols with precisely localized transducer positions and exactly defined positions of the test subjects during the measurement would further increase comparability of SWE data in MSK-studies (29). More precise and comparable research protocols in MSK-SWE could allow a great benefit in sports medicine but also in rehabilitation and preventive medicine (6, 10, 30-32).