Optimum displacement of muscle in relation to thickness for biceps brachii hardness measurement using a push-in meter

Changes in biceps brachii muscle hardness assessed by a push-in meter and strain elastography after eccentric versus concentric contractions

Changes in biceps brachii muscle hardness assessed by a push-in meter (PM) and strain elastography (SE) were compared between eccentric (ECC) and concentric contractions (CON) of the elbow flexors to test the hypothesis that muscle hardness would increase greater after ECC. Ten men performed 5 sets of 10 ECC with their non-dominant arms and 5 sets of 10 CON with their dominant arms using a dumbbell corresponding to 50% of maximum voluntary isometric contraction (MVIC) force at 90º elbow flexion. Before and 1–4 days after the exercise, MVIC force, elbow joint angles, upper-arm circumference, and muscle soreness as muscle damage makers, and biceps brachii muscle hardness at maximally extended elbow joint by PM and SE were measured. Changes in these measures over time were compared between ECC and CON. All muscle damage markers showed greater changes after ECC than CON (p < 0.001). Muscle hardness assessed by PM and SE increased (p < 0.05) and peaked at 4 days post-ECC with 154.4 ± 90.0% (PM) and 156.2 ± 64.2% (SE) increases from the baseline, but did not change significantly after CON. The changes in muscle hardness post-ECC were correlated between PM and SE (r = 0.752, p < 0.001). A correlation (p < 0.001) between the normalized changes in resting elbow joint angle and changes in muscle hardness assessed by PM (r = − 0.772) or SE (r = − 0.745) was also found. These results supported the hypothesis and suggest that the increases in muscle hardness after ECC were associated with muscle damage (increased muscle stiffness), and PM and SE detected muscle hardness changes similarly.

Biceps brachii muscle hardness assessed by a push-in meter in comparison to ultrasound strain elastography

This study investigated the relationship between push-in meter (PM) and ultrasound strain elastography (USE) for biceps brachii (BB) muscle hardness. BB hardness of 21 young men was assessed by PM and USE during rest and isometric contractions of six different intensities (15, 30, 45, 60, 75, 90% of maximal voluntary contraction: MVC) at 30°, 60° and 90° elbow flexion. Muscle hardness (E) was calculated from the force-displacement relationship in PM, and strain ratio (SR) between an acoustic coupler (elastic modulus: 22.6 kPa) and different regions of interest (ROIs) in BB was calculated and converted to Young's modulus (YM) in USE. In resting muscle, E was 26.1 ± 6.4 kPa, and SR and YM for the whole BB was 0.88 ± 0.4 and 30.8 ± 12.8 kPa, respectively. A significant (p < 0.01) correlation was evident between E and logarithmical transformed SR (LTSR) for the ROI of whole BB (r = - 0.626), and E and converted YM (r = 0.615). E increased approximately ninefold from resting to 90% MVC, and E and LTSR (r = - 0.732 to - 0.880), and E and converted YM for the SR above 0.1 were correlated (r = 0.599-0.768, p < 0.01). These results suggest that muscle hardness values obtained by PM and USE are comparable.