Abstract
Introduction
The evidence of fascia involvement in musculoskeletal pathologies and sport- specific adaptations has increased over the last few years. For example, Tenberg et al. (2021) found a 14–17% fascia increase after eccentric exercise, claiming, this is associated with the severity of muscle soreness. Wilke et al. (2019) reported age-related differences up to 40% might be related to pain causes (e.g. lower back pain) and less flexibility in these areas. Ultrasound is commonly used for fascia thickness diagnostics, but especially measurements of thin structures are prone to errors. Since conventional reliability indices such as the Intraclass Correlation Coefficient (ICC) can mask measurement variance in thin tissue due to their high sample dependence, a comprehensive error analysis is mandatory. Therefore, this study aimed to determine reliability, objectivity, and absolute measurement errors of ultrasound assessments of deep fascia thickness in the gastrocnemius medialis muscle in raters with different experience.
Methods
The sample comprised 65 healthy, physically active participants (30 males, 35 females, 22±4 years, 173±15.8 cm, 75.42±19.43 kg). Ultrasound measurements were taken at the point with the highest thickness in a prone position with feet hanging down the massage bench. To determine intra- and interday reliability (ICC) as well as test-retest systematic and random errors (MAPE), two pictures of the muscle-fascia complex were taken on two test days each. Pictures were analyzed by two blinded assessors with different experience levels (R1=experienced, R2=unexperienced)
Results
Mean fascia thickness was 0.918±0.257mm and mean muscle thickness was 18.88±3.297mm. No Systematic intrarater difference was found. A significant systematic Interrater difference was found fordeep fascia thickness (p=<.001, F=14.93-18.41). Intraday fascia thickness reliability was moderate to good for the first (R1) (95% ICC = 0.0.678–0.883, MAPE of 15.33–16.59%) and moderate to excellent for the second rater (R2) (95% ICC = 0.664–0.915, MAPE of 12.86–13.25%). For muscle thickness, intraday reliability was excellent for both raters (95% ICC=0.991–0.996; MAPE=2.03–2.24%). Intersession fascia thickness reliability was poor to good, depending on the rater (R1: 95% ICC=0.480–0.810, MAPE=16.49% R2: 95% ICC=-0.456–0.798, MAPE=16.64%). Interday muscle thickness measurement reliability was moderate to excellent for both raters (R1: 95% ICC=0.796–0.924, R2: 95% ICC=-0.805–0.927, MAPE=6.99–7.13%). The objectivity between raters was moderate to excellent for fascia thickness (95% ICC=0.744–0.944, MAPE=11.09–16.03%) and excellent for muscle thickness (95% ICC=0.993–0.999, MAPE=0.74–1.087%).
Discussion
Although, muscle and fascia thickness measures agree with current literature (e.g., Schadmy et al., 2024), this was the first study showing that insufficient reliability and measurement errors MAPEs (~13–16.6%) conflate interpretability especially for thin tissues and small absolute intervention induced changes regardless of assessor experience. Since high measurement precision is considered a precondition for internal validity, comparatively small changes of 14–17% from previous studies (e.g. Wilke et al. 2018, Tenberg et al. 2021) should be interpreted cautiously. Importantly, even a 'good' ICC (e.g., R2 intraday fascia ICC 0.813 (0.703-0.883) can still be accompanied by a 16.59% measurement error (MAPE), which can equal or exceed these reported adaptations.
References
Koo, T. K., & Li, M. Y. (2016). A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. Journal of chiropractic medicine, 15(2), 155–163. https://doi.org/10.1016/j.jcm.2016.02.012
Schadmy Levy, S., Weiss, K., & Kalichman, L. (2024). Ultrasound evaluation of deep fascia thickness: Reliability and association with clinically evaluated changes. Journal of bodywork and movement therapies, 40, 350–355. https://doi.org/10.1016/j.jbmt.2024.04.011
Tenberg, S., Nosaka, K., Wilke, J. (2021). Fascia thickness increases following eccentric exercise leading to delayed onset muscle soreness. [PREPRINT].10.21203/rs.3.rs-826566/v176.
Wilke, J., Macchi, V., De Caro, R., & Stecco, C. (2019). Fascia thickness, aging and flexibility: is there an association? Journal of anatomy, 234(1), 43–49. https://doi.org/10.1111/joa.12902