The effect of repetitive exercise on tensile changes in the infraspinatus muscle evaluated with ultrasound elastography.

Background: The ability to identify muscle strain accurately is a critical aspect in managing exercise-induced muscle damage. Using differences in muscle stiffness as a proxy for muscle damage and recovery can better inform the decision to continue exercise versus pursue recovery.

Hypothesis/purpose: To identify changes in rotator cuff stiffness after a single bout of exercise as measured by ultrasound elastography.

Study design: 10 healthy subjects, average age of 23.7, were enrolled in this prospective interventional trial. Each subject had a baseline scan then completed a standardized exercise program followed by another scan and daily evaluations until the results returned to within 10% of baseline.

Methods: Elastography measurements were collected around the infraspinatus tendon, and the deltoid was used as a baseline standard.

Statistical analysis used: Summary statistics, t-test, and regression analysis were completed for the data.

Results: Average strain was 0.5 at baseline, 0.7 immediately post-exercise, 0.6 on follow-up day 1, and 0.4 on follow-up day 2. There were statically significant differences between every timepoint. baseline-post 0.24, (p < 0.0001), post-day1 (decrease of 0.14, p < 0.0001), day1-day2 (decrease of 0.15, p < 0.0001), and BL-day2 (decrease of 0.05, p < 0.005).

Conclusions: These results demonstrate that the infraspinatus muscle stiffness increases immediately after exercise and takes up to 48 h to return to within 10% of baseline. We also found that at day 2 there continued to be an overcorrection with the infraspinatus remaining softer at this time point.