Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time.

Year: 1997  Country: Finland   Study Population: N=10 healthy volunteers

Kankaanpää M, Taimela S, Webber C, Airaksinen O, Hänninen O. Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time. European Journal of Applied Physiology 1997;76(3):236-242.

Objective

To develop a submaximal isoinertial repetitive paraspinal muscle endurance test by defining the relationship between objective measures (EMG spectral indices), endurance time and subjective measures (Borg scale). 

Methods

Subjects performed repetitive upper trunk extensions (25° extension and 5° extension, 30 repetitions per min) in David lumbar/thoracic back extension device (110). The tests continued for as long as the subjects were able to maintain the required repetition rate (endurance time). Bilateral surface EMG recordings were obtained. 

Median (MF) and mean power frequency (MPF) slope correlations with endurance time/Borg scale were measured for the first 60 s, the first 90 s, the first 120 s and the whole repetitive run.

Outcome

The decreases in spectral indices that were calculated for up to 90 s correlated highly with Borg scale indicating a relationship between submaximal objective and subjective estimates of fatigue. In addition, high correlations were observed between 90 s MF and endurance time. The test showed high reproducibility on a day-to-day basis.

Hence 90-s submaximal isoinertial repetitive test incorporating EMG spectral indices seems to serve as a valid indicator of low back (L3-S1) muscle fatigue.