Effect of two different exercise regimens on trunk muscle morphometry and endurance in soldiers in training.

Background: Limited evidence exists on how strength and endurance exercises commonly used to prevent low back pain affect muscle morphometry and endurance.

Objective: The purpose of this study was to analyze the effects of 2 exercise regimens on the morphometry and endurance of key trunk musculature in a healthy population.

Design: The study was designed as a randomized controlled trial.

Setting: The study was conducted in a military training setting.

Participants: A random subsample (n=340; 72% men, 28% women; mean [±SD] age=21.9±4.2 years; mean [±SD] body mass index=24.8±2.8 kg/m2) from the larger Prevention of Low Back Pain in the Military trial (N=4,325) was included.

Intervention: The core stabilization exercise program (CSEP) included low-load/low-repetition motor control exercises, whereas the traditional exercise program (TEP) included exercises conducted at a fast pace, with the use of high-load, high-repetition trunk strengthening exercises.

Measurements: Baseline and follow-up examinations included ultrasound imaging of the trunk muscles and endurance tests. Linear mixed models were fitted to study the group and time effect and their interactions, accounting for the clustering effect.

Results: Symmetry generally improved in the rest and contracted states, but there were no differences suggestive of muscle hypertrophy or improved ability to contract the trunk muscles between soldiers receiving the CSEP or the TEP. Total trunk endurance time decreased over the 12-week period, but endurance performance favored soldiers in the CSEP group. Endurance time was not associated with future episodes of low back pain.

Limitations: The lack of morphological changes may not be detectable in an already-active cohort, or a more intensive dose was needed.

Conclusions: Although improved symmetry was noted, neither the CSEP nor the TEP resulted in muscle hypertrophy. Longer endurance times were noted in individuals who completed the CSEP but were not strongly predictive of future low back pain episodes.