Introduction: Individuals with recurrent low back pain (LBP) exhibit neural changes that underlie dynamic balance deficits, and continuous pain episodes may relate to postural control. The aim of this study was to investigate adaptive changes on the lower limb reaction, swing, and step times, as well as step length changes, following repeated trip perturbations in individuals with and without recurrent LBP.

Methods: There were 30 subjects with LBP and 40 control subjects who participated in the study. The lower limb reaction, swing, and recovery step times (sec) and step lengths (cm) were analyzed following three repeated random trips (velocity: 0.31 m/sec, displacement: 0.62 m) in standing. The treadmill-induced trip caused subjects to walk forward for 4.90 sec (Figure 1).

Results: There was no group interaction on the lower limb reaction (F = 2.15, p = 0.15), swing time (F = 0.79, p = 0.38), or step length changes (F = 0.51, p = 0.48). However, the groups demonstrated a significant interaction on the recovery step times following trips (F = 4.04, p = 0.04). The LBP group demonstrated faster recovery step time (t = 2.68, p = 0.01) only at the first perturbation (Figure 2).

Discussion: The limb reaction, swing time, and step lengths were not sensitively reflected by the trips; however, the novelty of the first perturbation substantially enhanced recovery step times. Although the recovery step times were not significantly correlated with the reaction times, the fast recovery step time suggests the likelihood of a fall prevention strategy to improve dynamic stability from the trip-induced instability in the LBP group.

Key words: reaction time; recovery step time; perturbations; low back pain; compensation.