AIM: To compare trunk muscle volume, muscle activity and lumbar spine posture in young and mature participants without low back pain.
METHODS: Twenty-four participants were allocated to a young group (YG: age 18-25yrs, n=12) or mature group (MG: age 45-60yrs, n=12). Muscle volume of lumbar spine erector spinae (ES), multifidus (M), rectus abdominis (RA) and psoas (PS) was determined bilaterally using T1-weighted axial MRI. Flexor volume (FV) was obtained by summing RA and PS volumes and extensor volume (EV) by summing M and ES volumes. Muscle volume ratio (MVR) was defined as FV/EV. Trunk muscle activity and lumbar spine posture were evaluated from synchronously collected kinematic and EMG data at stance using 10 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) sampled at 1200Hz. Reflective markers were attached to the skin overlying the spinous processes of the 11th thoracic (T11), 2nd lumbar (L2), 5th lumbar (L5) vertebra and sacrum, and sagittal angles were calculated at L2 and L5. sEMG electrodes were placed over ES and RA bilaterally, data full-wave rectified and integrated EMG (iEMG) calculated. Muscle activity ratio (MAR) was defined as RA/ES. Differences between the YG and MG for all parameters were determined using an independent t-test or Mann Whitney test and Pearson’s or Spearman’s correlations were calculated.
RESULTS: There was a significant between-group difference for MAR (YG=1.13, MG=0.82, p=0.045). In the YG, there were significant correlations between ES activity and MAR (r=-0.689, p=0.013) and FV and EV (r=0.851, p=0.000). In the MG, there were significant correlations between FV and MVR (r=0.688, p=0.013), FV and EV (r=0.807, p=0.002), RA activity and MAR (r=0.592, p=0.043), ES activity and MAR (r=-0.736, p=0.006), and L2 and L5 angle (r=-0.579, p=0.049).
CONCLUSION: Adequate lumbar posture at natural stance does not preclude the necessity of additional abdominal training in mature people.
Valentin, S., Elliott, J., & Licka, T. (2014, July). Rectus abdominis activity decreases relative to erector spinae with maturity despite similar muscle volumes and lumbar posture at stance. Paper presented at XX Congress of the International Society of Electrophysiology and Kinesiology (ISEK 2014), Rome, Italy