THE RELATIONSHIP BETWEEN LUMBAR SPINE LOAD AND MUSCLE-ACTIVITY DURINGEXTENSOR EXERCISES

Background and Purpose. There have been no previous studies that quant itatively assessed the load on the spine during extensor exercises. Th e purpose of our study was to investigate the loading of the lumbar sp ine and trunk muscle activity levels while subjects performed typical trunk extensor exercises. Subjects. Thirteen male volunteers (mean age = 21.0 years, SD=1.0, range=l9-23; mean height= 176.0 cm, SD=6.2, rang e=165-188; mean mass=77.0 kg, SD=7.0, range=63-89) participated. Metho ds. The subjects performed four different back exercises. Electromyogr aphic (EMG) activity was recorded from 14 trunk muscles The postures t hat corresponded external moment were identified and quantified using rigid body modeling combined with an EMG-driven model to determine joi nt loading at the L4-5 joint. The exercises were then evaluated based on the lumbar spine loading-and peak muscle activity levels. A referen ce task of lifting 10 kg from midthigh was included for comparison. Re sults. The exercises involving active trunk extension produced the cs and muscle activity levels. Exercises involving leg extension with the spine held isometrically demonstrated asymmetricaI activity of tile t runk muscles, thereby reducing-loads on the spine. Conclusion and Disc ussion, The back extensor exercises examined provided a wide range of joint loading and muscle activity levels. Single-leg extension tasks a ppear to constitute a low-risk exercise for initial extensor strengthe ning, given the low spine load and mild extensor muscle challenge. Whe n combined with contralateral arm extensions, the challenge and demand of the exercise were increased. The compressive loading and extensor muscle activity levels were highest for the trunk extension exercises.