Skeletal muscle loss has a devastating effect on daily lives of people with interstitial lung disease (ILD). Pulmonary rehabilitation (PR) improves muscle strength; however, the lack of cut-off values to define clinical improvement limits the interpretability of the obtained gains.

To estimate the minimal clinically important difference (MCID) for quadriceps maximal voluntary contraction (QMVC) in people with ILD, assessed with hand-held dynamometry as an absolute value in kilogram-force (KgF) and as percentage of the predicted value (% pred), after PR in people with ILD.

A secondary analysis of data from three previous studies was conducted. Participants took part in a 12-week community-based PR programme. The MCIDs were computed using anchor- and distribution-based methods. Anchors explored were the 1-min sit-to-stand (1-min STS) test, the 6-min walking distance, handgrip strength, modified Medical Research Council questionnaire, St. George's Respiratory Questionnaire and Functional Assessment of Chronic Illness Therapy-Fatigue Subscale. The pooled MCIDs were computed using the weighted arithmetic mean (2/3 anchor and 1/3 distribution-based methods).

Fifty-nine people with ILD (61 % female, 66 ± 11years) were included in the analysis. The 1-min STS test was the only anchor fitting the criteria. There were significant improvements after PR in the QMVC (mean difference = 3.9 ± 8.2 KgF and median difference = 10.9 [1.6; 22.0] % pred, p < 0.001) and 1-min STS test (mean difference = 6.6 ± 7.1 repetitions, p < 0.001). The pooled MCIDs were 3.2 KgF and 10.6 % pred.

An increase of at least 3.2 KgF or 10.6 % pred for QMVC in people with ILD after PR represents clinically relevant improvements.