K. Kunz1, D. Kirk1, J. Wadner1, N. Martonick2

1University of Washington School of Medicine, Seattle, WA; 2University of Idaho, Moscow, ID;

Instrument-assisted soft tissue mobilization (IASTM) is a commonly used intervention in sports medicine to improve the function of muscles, fascia, and tendons through the application of shearing forces. However, little is known about the influence of different forces on muscle stiffness as measured by shear wave elastography. PURPOSE: To investigate alterations in tissue stiffness at the gastrocnemius and soleus after application of a high and low force IASTM treatment. Additionally, the study explored potential correlations between pre-treatment shear wave measurements and ankle or knee flexion during a single-leg squat. METHODS: Participants (n=10) identified as having functional dorsiflexion restrictions during a double leg squat received both a high and low force IASTM treatment on the randomly allocated lower extremity. Knee and ankle flexion kinematics during the single leg squat (SLS) were collected with inertial measurement units. Stiffness data of the gastrocnemius and soleus muscles were then collected with participants in the prone position using shear wave elastography. Measurements were taken with ankles in a neutral position and with the ankles actively dorsiflexed before and after the IASTM treatment. The IASTM treatment was performed on one leg with a light force (0-5N) and on the contralateral leg with a high force (10-15N). Changes in stiffness data were assessed with separate 2X2 ANOVAs ([pre/post] x [low/high]) in the dorsiflexed and neutral ankle positions at the gastrocnemius and soleus. Correlations between muscle stiffness and kinematics were analyzed with statistical parametric mapping. RESULTS: Significant differences in tissue stiffness were not found after high and low force treatments. Soleus stiffness in the dorsiflexed position was correlated with SLS knee flexion from 0-12% (r2=0.82; p=0.014) and 82-100% (r2=0.87; p=0.004) of the SLS. CONCLUSION: Our findings indicate that tissue stiffness was not affected by the low or high force IASTM treatments. The current findings indicate that practitioners may use forces interchangeably or base forces off of factors such as patient comfort. Researchers assessing tissue stiffness after IASTM interventions should consider taking stiffness measures in weightbearing positions that may better reflect functional demands.

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