Introduction: Although delayed onsets of trunk muscle activations were present in response to external perturbations, there is currently no convincing evidence for the altered ankle muscle activations in regards to tray usage and limb dominance between subjects with and without low back pain (LBP) following a perturbation. The aim of this study was to compare the functional mobility and reaction times of the ankle muscles in regards to tray usage between subjects with and without chronic LBP following a treadmill-induced slip perturbation.

Methods: Thirty-seven right limb dominant subjects with LBP and 37 subjects without LBP participated in the study. Functional mobility was compared based on the duration of the Timed Up and Go test (TUG). Each subject was introduced to slip perturbations (1.37 m/sec velocity for 8.22 cm) with and without a handheld tray in random order (Figure 1). This treadmill-induced slip allowed subjects to recover by stepping forward for a 0.12 second duration while bilateral tibialis anterior (TA) and gastrocnemius (GA) muscle reaction times were measured by electromyography (Figure 2).

Results: Functional mobility was significantly different between groups (t = -2.33, p = 0.02). The groups demonstrated significant interactions on the lower limb sides and muscles (F = 4.86, p = 0.03). The dominant TA reaction time was significantly faster in the LBP group (t = 2.14, p = 0.03) while holding a tray.

Discussion: Although functional mobility decreased in the LBP group, their reaction time on the dominant TA was faster with tray usage in order to enhance step propulsion and control. Clinicians need to consider dominance-dependent compensatory ankle strategies in LBP patients to help them avoid potential fall risks and to enhance dynamic balance.

Key words: kinematics; perturbations; low back pain; motor learning; compensatory motion.