Eccentric training in Achilles tendinopathy: is it harmful to tendon microcirculation?

Background: Eccentric training has been shown to reduce pain and gain function in patients with chronic Achilles tendinopathy. However, currently no data are available regarding any potential adverse effects of an eccentric training intervention on Achilles tendon microcirculation. Methods: 59 patients (49 (12) years; body mass index 27 (5); 49 mid-portion, 10 chronic insertional tendinopathy) with 64 symptomatic (54 mid-portion, 10 insertional) Achilles tendons were prospectively enrolled. Baseline tendon microcirculation at four distinct tendon positions from the insertion to the proximal mid-portion area was assessed using a laser Doppler system for capillary blood flow, tissue oxygen saturation and postcapillary venous filling pressure. A 12-week daily painful home-based eccentric training regimen was initiated (3 x 15 repetitions per tendon and day). Results: Achilles tendon capillary blood flow was significantly reduced at the insertion (by 35%, p = 0.008) and the distal mid-portion area (by 45%, p = 0.015) at 2 mm and by 22% (p = 0.007) and 13% (p = 0.122) at 8 mm tissue depths, respectively. Achilles tendon oxygen saturation was not decreased after the 12-week eccentric training regimen throughout the insertion to the proximal mid-portion area (insertion 72 (13) vs 73 (10), proximal mid-portion 63 (13) vs 62 (11), both NS). Achilles tendon postcapillary venous filling pressures were significantly reduced at the insertion (51 (16) vs 41 (19), p = 0.001) and the distal mid-portion (36 (13) vs 32 (12), p = 0.037) at 2 mm and at the insertion at 8 mm (63 (19) vs 51 (13), p = 0.0001). Pain was reduced from 5.4 (2.1) to 3.6 (2.4; p = 0.001) in the mid-portion and from 6 (2.5) to 3.2 (2.7; p = 0.002) in the insertional tendinopathy group. No Achilles tendon rupture or any interruption during the eccentric training was noted among the 59 patients. Conclusion: Daily eccentric training for Achilles tendinopathy is a safe and easy measure, with beneficial effects on the microcirculatory tendon levels without any evident adverse effects in both mid-portion and insertional Achilles tendinopathy.