An investigation into the relevance of the pattern of temporal activation with respect to erector spinae muscle endurance.

The aim of the present study was to evaluate the viability of a relationship between the temporal activation pattern of parts of the erector spinae muscle and endurance. Seven subjects performed intermittent isometric contractions [4s at 70% maximal voluntary contraction (MVC), 2 s rest] until exhaustion, during which the electromyographical (EMG) activity of the multifidus, iliocostalis thoracis and longissimus muscle segments was recorded. Endurance was defined as the time until exhaustion. Subjects were divided into a high and a low endurance group. The high endurance group showed significantly more variability of EMG amplitude over succeeding contractions. This group demonstrated significantly more alternations of EMG activity between parts of the muscle also. Variability of the EMG amplitude within the contractions did not differ between the groups, nor did MVC. The results indicated that alternating activity between different parts of the erector spinae muscle may function to postpone exhaustion of this muscle as a whole.