Purpose: This study investigated the effect of conditioned pain modulation (CPM) on passive knee exten-sion range of motion (PROM) after acute stretching, and assessed the reliability and validity of smartphone based accelerometer by comparing the measurements with that of the Biodex systems 4 pro isokinetic dynamometer.
Method: 3 measurements of knee extension (PROM) were conducted in a fixed position using a dynamic passive protocol for knee extension at 5°/sec. 17 participants were randomized into 2 equal groups. Both groups received 2 repetitions of 30 sec. Constant Angle stretching of the knee flexors with a one minute interval performed by the tester. Cold Pressure Test was carried out in the CPM group while the control group rested passively. The Biodex system 4 isokinetic dynamometer was used to detect resistance to passive stretch and surface electromyografi (SEMG) was used for detecting the muscle activity during PROM.
Results: A very strong correlation with the Biodex system 4 pro r = 0,807 (Spearman rho) and 0,965 (ICC) SEM = 0.84 was found for the smartphone accelerometer. Agreements showed a width of 21,02° (LOA = -10,14°- +10,88°). A significant difference in muscle activity for M. Biceps Femoris in the 4th quarter of PROM was detected between groups (p = 0,024) but not for other measures (p ≥ 0,074). No difference in PROM (p = 0,209) or resistance to passive stretch (p = 0,374) was found between groups.
Conclusion: Smartphone based accelerometer seems to be a valid and reliable method of detecting dy-namic changes in knee joint range of motion. No significant differences in PROM was detected between groups, although the effect size shoved that such a difference might occur, suggesting that central de-scending inhibitory pain mechanisms (CPM) might affect stretch tolerance.