Do Functional Tests Estimate Physical Activity in COPD?

The association between physical activity in daily life (PADL) and simple functional tests is not yet clearly understood in subjects with chronic obstructive pulmonary disease (COPD). Therefore, the aim of this study was to investigate the association of two functional tests (Sit-to-Stand test [STS] and the 4-Metre Gait Speed test [4MGS]) with PADL, as well as to identify whether these tests can discriminate those subjects who are physically inactive. In this cross-sectional study, 28 subjects with COPD performed the five repetitions Sit-to-Stand (STS5r), the 4MGS and used the DynaPort activity monitor for 7 days in order to assess PADL. Walking time, movement intensity while walking (MI) and Physical Activity Level index (PAL) were considered as PADL outcomes. STS5r and 4MGS, respectively, were significantly associated with walking time (R² = 0.16; p = 0.024 and R² = 0.25; p = 0.006) and PAL index (R² = 0.17; p = 0.002 and R² = 0.30; p = 0.003), whereas movement intensity was associated only with the 4MGS (R² = 0.23; p = 0.009). Additionally, both tests were able to discriminate physically inactive subjects (cutoffs: STS5r = 11.48s [AUC = 0.73]; 4MGS = 1.09m/s [AUC = 0.88]). In conclusion, STS5r and 4MGS can predict up to 30% of PADL in subjects with COPD. Both tests are related to PADL duration (e.g. time spent walking), while only the 4MGS reflects movement intensity. Both tests presented discriminative capacity to identify subjects with worse PADL pattern.