Acute effect of running exercise on physiological Achilles tendon blood flow

Multispectral Optoacoustic Tomography Enables In Vivo Anatomical and Functional Assessment of Human Tendons

Tendon injuries resulting from accidents and aging are increasing globally. However, key tendon functional parameters such as microvascularity and oxygen perfusion remain inaccessible via the currently available clinical diagnostic tools, resulting in disagreements on optimal treatment options. Here, a new noninvasive method for anatomical and functional characterization of human tendons based on multispectral optoacoustic tomography (MSOT) is reported. Healthy subjects are investigated using a hand-held scanner delivering real-time volumetric images. Tendons in the wrist, ankle, and lower leg are imaged in the near-infrared optical spectrum to utilize endogenous contrast from Type I collagen. Morphology of the flexor carpi ulnaris, carpi radialis, palmaris longus, and Achilles tendons are reconstructed in full. The functional roles of the flexor digitorium longus, hallicus longus, and the tibialis posterior tendons have been visualized by dynamic tracking during toe extension-flexion motion. Furthermore, major vessels and microvasculature near the Achilles tendon are localized, and the global increase in oxygen saturation in response to targeted exercise is confirmed by perfusion studies. MSOT is shown to be a versatile tool capable of anatomical and functional tendon assessments. Future studies including abnormal subjects can validate the method as a viable noninvasive clinical tool for tendinopathy management and healing monitoring.

Intraindividual Doppler Flow Response to Exercise Differs Between Symptomatic and Asymptomatic Achilles Tendons

Objective

This study investigated intraindividual differences of intratendinous blood flow (IBF) in response to running exercise in participants with Achilles tendinopathy.

Design

This is a cross-sectional study.

Setting

The study was conducted at the University Outpatient Clinic.

Participants

Sonographic detectable intratendinous blood flow was examined in symptomatic and contralateral asymptomatic Achilles tendons of 19 participants (42 ± 13 years, 178 ± 10 cm, 76 ± 12 kg, VISA-A 75 ± 16) with clinically diagnosed unilateral Achilles tendinopathy and sonographic evident tendinosis.

Intervention

IBF was assessed using Doppler ultrasound “Advanced Dynamic Flow” before (Upre) and 5, 30, 60, and 120 min (U5–U120) after a standardized submaximal constant load run.

Main Outcome Measure

IBF was quantified by counting the number (n) of vessels in each tendon.

Results

At Upre, IBF was higher in symptomatic compared with asymptomatic tendons [mean 6.3 (95% CI: 2.8–9.9) and 1.7 (0.4–2.9), p < 0.01]. Overall, 63% of symptomatic and 47% of asymptomatic Achilles tendons responded to exercise, whereas 16 and 11% showed persisting IBF and 21 and 42% remained avascular throughout the investigation. At U5, IBF increased in both symptomatic and asymptomatic tendons [difference to baseline: 2.4 (0.3–4.5) and 0.9 (0.5–1.4), p = 0.05]. At U30 to U120, IBF was still increased in symptomatic but not in asymptomatic tendons [mean difference to baseline: 1.9 (0.8–2.9) and 0.1 (-0.9 to 1.2), p < 0.01].

Conclusion

Irrespective of pathology, 47–63% of Achilles tendons responded to exercise with an immediate acute physiological IBF increase by an average of one to two vessels (“responders”). A higher amount of baseline IBF (approximately five vessels) and a prolonged exercise-induced IBF response found in symptomatic ATs indicate a pain-associated altered intratendinous “neovascularization.”

Doppler Flow Response Following Running Exercise Differs Between Healthy and Tendinopathic Achilles Tendons

Background

The relationship between exercise-induced intratendinous blood flow (IBF) and tendon pathology or training exposure is unclear.

Objective

This study investigates the acute effect of running exercise on sonographic detectable IBF in healthy and tendinopathic Achilles tendons (ATs) of runners and recreational participants.

Methods

48 participants (43 ± 13 years, 176 ± 9 cm, 75 ± 11 kg) performed a standardized submaximal 30-min constant load treadmill run with Doppler ultrasound “Advanced dynamic flow” examinations before (U_pre) and 5, 30, 60, and 120 min (U₅-U₁₂₀) afterward. Included were runners (>30 km/week) and recreational participants (<10 km/week) with healthy (H_run, n = 10; H_rec, n = 15) or tendinopathic (T_run, n = 13; T_rec, n = 10) ATs. IBF was assessed by counting number [n] of intratendinous vessels. IBF data are presented descriptively (%, median [minimum to maximum range] for baseline-IBF and IBF-difference post-exercise). Statistical differences for group and time point IBF and IBF changes were analyzed with Friedman and Kruskal-Wallis ANOVA (α = 0.05).

Results

At baseline, IBF was detected in 40% (3 [1–6]) of H_run, in 53% (4 [1–5]) of H_rec, in 85% (3 [1–25]) of T_run, and 70% (10 [2–30]) of T_rec. At U₅ IBF responded to exercise in 30% (3 [−1–9]) of H_run, in 53% (4 [−2–6]) of H_rec, in 70% (4 [−10–10]) of T_run, and in 80% (5 [1–10]) of T_rec. While IBF in 80% of healthy responding ATs returned to baseline at U₃₀, IBF remained elevated until U₁₂₀ in 60% of tendinopathic ATs. Within groups, IBF changes from U_pre-U₁₂₀ were significant for H_rec (p < 0.01), T_run (p = 0.05), and T_rec (p < 0.01). Between groups, IBF changes in consecutive examinations were not significantly different (p > 0.05) but IBF-level was significantly higher at all measurement time points in tendinopathic versus healthy ATs (p < 0.05).

Conclusion

Irrespective of training status and tendon pathology, running leads to an immediate increase of IBF in responding tendons. This increase occurs shortly in healthy and prolonged in tendinopathic ATs. Training exposure does not alter IBF occurrence, but IBF level is elevated in tendon pathology. While an immediate exercise-induced IBF increase is a physiological response, prolonged IBF is considered a pathological finding associated with Achilles tendinopathy.

The Role of the Vascular and Structural Response to Activity in the Development of Achilles Tendinopathy: A Prospective Study

BACKGROUND

Several risk factors have been suggested in the development of Achilles tendinopathy, but large-scale prospective studies are limited.

PURPOSE

To investigate the role of the vascular response to activity of the Achilles tendon, tendon thickness, ultrasound tissue characterization (UTC) of tendon structure, and foot posture as possible risk factors in the development of Achilles tendinopathy.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

The study began with 351 first-year students at Ghent University. After 51 students were excluded, 300 were tested in the academic years 2013-2014 and 2014-2015 and were followed prospectively for 2 consecutive years by use of a multilevel registration method. Of those, 250 students were included in the statistical analysis. At baseline, foot posture index and UTC were investigated bilaterally. Blood flow and tendon thickness were measured before and after a running activity. Cox regression analyses were performed to identify significant contributors to the development of Achilles tendinopathy.

RESULTS

During the 2-year follow-up, 27 of the included 250 participants developed Achilles tendinopathy (11%). Significant predictive effects were found for female sex and blood flow response after running ( P = .022 and P = .019, respectively). The risk of developing Achilles tendinopathy increased if the blood flow increase after running was reduced, regardless of sex, foot pronation, and timing of flow measurements. The model had a predictive accuracy of 81.5% regarding the development of Achilles tendinopathy, with a specificity of 85.0% and a sensitivity of 50.0%.

CONCLUSION

This prospective study identified both female sex and the diminished blood flow response after running as significant risk factors for the development of Achilles tendinopathy. UTC of tendon structure, Achilles tendon thickness, and foot posture did not significantly contribute to the prediction of Achilles tendinopathy. A general evaluation of tendon structure by UTC, measurement of tendon thickness, or determination of the foot posture index will not allow clinicians to identify patients at risk for developing Achilles tendinopathy. Furthermore, it may be possible to improve blood flow after activity by using noninvasive techniques (such as prostaglandins, compression stockings, heat, massage, and vibration techniques). These techniques may be useful in the prevention and management of Achilles tendinopathy, but further research is needed.