Measures of paraspinal muscle performance do not predict initial trunk kinematics after tripping

The ability to limit the trunk flexion associated with an anteriorly directed trip is a determinant of successful recovery of recovering postural stability and is subservient to rapidly detecting and correcting the imposed trunk flexion in the available time. This experiment tested the hypothesis that subjects demonstrating greater eccentric trunk/hip extension strength, faster voluntary reaction times, shorter automatic response latencies, and larger automatic activation amplitudes of the paraspinal muscles, would demonstrate less trunk flexion following a trip. An isokinetic protocol was used to obtain measures of trunk extension strength, response latencies, and activation amplitudes. Motion analysis methods were used to quantify trunk kinematics during the positioning phase of recovery following an induced trip. Statistically significant and functionally meaningful relationships between eccentric strength of the trunk/hip extensors, voluntary-reaction time, automatic reaction time, activation amplitudes and trunk kinematics failed to emerge. Thus, although automatic and voluntary paraspinal muscle responses have the potential to limit trunk flexion during the positioning phase of recovery, the task may be achieved through intersegmental factors or other muscular sources such as the gluteus maximus and hamstrings.