Postural control measured as the center of pressure excursion in young female gymnasts with low back pain or lower extremity injury

Gymnasts are known to practice and compete although suffering from injuries and pain. Pain may change strategies for postural control. The primary aim of the present study was to investigate how center of pressure (COP) measurements are influenced by low back pain and lower extremity injury in top-level female gymnasts. A secondary aim was to study the reliability of these measurements using a test–retest design, and how this depends on the duration of the test. Fifty-seven top-level gymnasts were included in four groups: non-injured (NI, n = 18), low back pain (LBP, n = 11), lower extremity injury (LEI, n = 17) and a multiple injury group (MI, n = 11). COP excursion during quiet stance was measured on a force platform, during 120 s: (1) hard surface/eyes open, (2) hard surface/eyes closed, (3) foam surface/eyes open and (4) foam surface/eyes closed. The COP excursion increased, for all groups, during the foam surface/eyes closed measurement compared to the other three tests. Furthermore, the LBP group showed a 49% (p = 0.01) larger COP area compared to the LEI group in the foam surface/eyes closed condition. Measurements on foam surface were in general more reliable than tests on hard surface and tests with eyes closed were more reliable than tests with eyes open. Tests during 120 s were in most cases more reliable than tests during 60 s. In conclusion the COP excursion is influenced by injury location. Quiet stance measurements on foam surface with eyes closed seems to be reliable and sensitive in young female gymnasts.