Influence of static lumbar flexion on the trunk muscles' response to sudden arm movements

BACKGROUND Viscoelastic creep of lumbar ligaments (prolonged forward bend) has been shown to negatively influence the spine's muscular reflexive behaviour and spinal stability. No studies to date have investigated the influence of spinal viscoelastic creep on the feedforward response of the trunk muscles to sudden arm raises. METHODS Surface myoelectric activity was collected from the transversus abdominis/internal oblique, the lower erector spinae and the deltoid muscle during sudden ballistic arm raising before and after 10 minutes of prolonged forward bend in 11 healthy participants free of low back injury. The timing of trunk muscle activity relative to the deltoid muscle was calculated for 5 trials before and 5 trials after the creep procedure. RESULTS Viscoelastic creep had no influence on the feedforward response of the trunk muscles during sudden arm raises. A feedforward response of the trunk muscles was not seen in every study participant and during every trial. CONCLUSION Passive trunk muscle fatigue does not appear to influence the timing of the stabilizing role of the investigated trunk muscles to sudden arm flexion.