Pilot Study Looking at the Effect of Thermodynamics on Achilles Tendon using Elastography.

Shear wave elastography (SWE) was first introduced in the 1990s and has recently been used to investigate muscle and tendon stiffness. While studies have demonstrated that SWE is an effective method of determining muscle stiffness, limited data exist on how SWE measurements of the Achilles change with passive heat and stretching. PURPOSE: to determine Achilles tendon stiffness measured in two different ankle positions, and to assess whether the application of passive heat independently alters Achilles tendon stiffness. METHODS: 13 subjects participated in this study (4 men and 9 women). Mean age 21.5 ± 2.5 yrs for men and 23.2 ±4.2 (range = 19-48). Mean height (cm) is 175.9 ± 6.99 for men and 165.1 ±12.7 for women. Mean weight (kg) is 73.4 ± 8.96 for men and 62.9 ± 9.68 for women. Participants lay prone with their ankles resting off surface in relaxed position. Baseline SWE of right and left Achilles tendons were measured at relaxed and neutral positions. The left ankle was fixed in a dorsiflexed position at the point of stretch-tolerance for 10 minutes with SWE assessed at one-minute intervals. SWE was then assessed in both the relaxed and neutral ankle positions two minutes post stretch. For the right leg, a clinical moist hot pack was applied to the right calf/Achilles for 10 minutes and the SWE was assessed again. The right ankle was then stretched in the same manner as the left with subsequent SWE measurements. RESULTS: Achilles stiffness at baseline was significantly greater in the relaxed position as compared to ankle neutral (t=70.92, p=0.0073). 10 minutes of heat application resulted in increased Achilles stiffness in the neutral position (p<.05 from SNK post hoc analysis). Changes in stiffness were lower for females (p=0.0462). Stiffness of the Achilles was significantly different (p=0.0338) between heat and no heat over the 10 minute duration. CONCLUSION: Stiffness of the Achilles tendon appears to increase with passive heating. This characteristic has been noted in active warm-up or running studies. SWE appears to be a viable way to track stiffness changes in the tendon. Results also suggest that stiffness of the Achilles does not decrease over the course of a stretch load like the muscle response. Further studies are needed to look at this muscle/tendon response relationship and the influence of gender.