Do people with unilateral mid-portion Achilles tendinopathy who participate in running-related physical activity exhibit a meaningful conditioned pain modulation (CPM) effect: a pilot study

Objectives: Our primary objective was to report the presence of a conditioned pain modulation (CPM) effect in people with localised mid-portion Achilles tendinopathy and whether changes occur over a 12-week period. Our secondary objectives were to quantify the proportion of participants who present for tendinopathy research with previous interventions or co-morbidities, which may impact the CPM-effect and investigate modulating factors.

Design: Prospective, observational cohort pilot study.

Method: 215 participants presented for this Achilles tendinopathy research and were screened for inclusion with nine being included. Included participants had the CPM-effect (cold-pressor test) assessed using pressure pain thresholds at the Achilles tendon and quantified as absolute, relative and meaningful change at baseline and 12-week follow-up.

Results: The most common reasons for exclusion were failure to meet a load-related diagnosis for Achilles tendinopathy (15.5%), presence of confounding other injury (14.1%) and previous injection therapy (13.6%). All participants had a meaningful CPM-effect at baseline and 12-week follow-up. The mean (SD, n) baseline relative CPM effect (reduction in PPTs) was -40.5 (32.7, 9) percent. Moderators of the CPM-effect as well as follow-up changes were not statistically analysed due to a small sample size.

Conclusion: Based on these data, we would suggest that a homogenous population of patients with chronic, unilateral mid-portion Achilles tendinopathy and no other co-morbidities are likely to exhibit a meaningful CPM-effect. Impairments to endogenous analgesic mechanisms seen in people presenting with mid-portion Achilles tendinopathy may be due to other confounding variables.