Edinburgh Napier University

  AIM: To investigate erector spinae muscle activity in healthy young and mature females relative to trunk movement in forward flexion at stance
METHODS: In ten female participants (young 18-25yrs, n=5; mature 45-60yrs, n=5) left and right erector spinae (ES) muscle activity and thoracolumbar spine motion were evaluated from synchronously collected kinematic and EMG data during forward flexion and return to neutral. Ten high speed cameras (Eagle Digital Real Time System, Motion Analysis Corp, USA) recording at 120Hz using kinematic software (Cortex 3.6) and surface electromyography (sEMG) (Delsys Trigno, Boston, USA) sampling at 1200Hz were used. A reflective marker attached to the skin over the 11th thoracic (T11) vertebra was used to determine craniocaudal trunk motion. sEMG electrodes were placed over ES bilaterally at the thoracolumbar junction and data were full-wave rectified and a 6Hz low pass Butterworth filter was applied to obtain a linear envelope. Range of T11 displacement, maximal concentric activity (MCA) and minimal activity during the flexion relaxation phenomenon (minFRP), as well as maximal eccentric activity (MEA) were further analysed. Also, the time delay between the occurrence of maximal T11 displacement (MDispl) and minFRP (MDispl - FRP) was noted. Parameters were compared between age groups (using the independent t-test), as well as between left and right sided values (using the paired t-test), resulting in no differences. Pearson’s correlation between the MEA peak (difference of MEA and min FRP) and the remaining MCA peak (difference of MCA and MEA) was calculated of the combined data set.
RESULTS: Both groups showed a similar range of MDispl (young: 305.56 ± 85.79 mm; mature: 333.25 ± 45.37mm; p=0.547), also a clear minFRP was identified in all participants, and in the majority of participants minFRP occurred just after maximal T11 displacement was reached. Standard deviation of muscle activity values was larger in the young, whereas standard deviation of the timing delay was larger in the mature. There was no correlation between the MEA and MCA peaks (r=0.112; p=0.758), even though MEA was smaller than MCA in all participants.
CONCLUSION: In females with no clinical signs or symptoms of back pain, FRP is clearly identifiable in a continuous flexion/extension movement independent of age. However, in such healthy females the magnitudes of concentric and eccentric erector spinae activity appear to be independent, raising the question whether these different activities should both be evaluated in clinical studies.