Maximal power of trunk flexor and extensor muscles as a quantitative factor of low back pain

Torque-velocity and power-velocity relationships, which determine the different indicators of muscle function, have some practical application during rehabilitation program. These relationships for trunk flexor and extensor muscles during isokinetic conditions have yet to be studied in chronic lower back pain patients in order to demonstrate that maximal power could be used as a quantitative factor for this population. Ten healthy male subjects and eleven chronic lower back pain male patients performed series of isokinetic trunk flexions and extensions at six different velocities, ranging from 45 degrees/s to 120 degrees/s, on a Biodex dynamometer. The torque-velocity and power-velocity relationships of trunk muscles were described by linear (P < 0.01; r = 0.9-0.99) and parabolic (P < 0.05; r = 0.9-0.99) relationships, respectively. Maximal power was the only parameter which showed a significant difference (P < 0.01) between the two populations for both flexor and extensor muscles. It was concluded that the lower back pain did not influence the shape of trunk muscles' torque- and power-velocity relationships. The different maximal power observed between the two groups suggests that rehabilitation program should focus on strength training for the extensor muscles whereas the flexor group would follow velocity exercise session.