An EMG Optimization Model of the Kinetic Demands on the Lower Back During Asymmetrical Gait and Load Carriage

Gait asymmetries are associated with a high incidence of lower back pain (LBP). Although there are several causes of gait asymmetry (i.e. amputation, injury, or deformities), lower back kinetic demands have not been quantified and suitably compared due to experimental limitations in these clinical populations. Further, the impact of gait asymmetry on lower back demands during carrying tasks has not been established. This dissertation addressed these issues by artificially and safely inducing gait asymmetry in healthy able-bodied participants during walking and carrying tasks. LBP risk was assessed by L5/S1 vertebral joint force levels estimated with an OpenSim musculoskeletal model of the lower back adapted to incorporate participant-specific responses using an EMG optimization approach. The model was evaluated systematically for force estimate efficacy and sensitivity to input parameters prior to gait asymmetry assessments.

Twelve participants performed walking and carrying tasks on a treadmill at individually scaled speeds while kinematics, external kinetics, and muscle activities (EMG) were recorded. Walking conditions consisted of unperturbed symmetrical gait, and asymmetrical gait induced by perturbing the right leg with a 2.54 cm shoe leveler, ~1 kg ankle weight, combined weight and shoe leveler, or a clinical walking boot that restricted ankle joint motion and added mass. Load carrying was performed while holding 7.5% and 15% bodyweight dumbbells in one or two hands during symmetric gait and asymmetric gait induced by the walking boot.

The perturbations were successful in producing different degrees of gait asymmetry. However, L5/S1 joint forces were not significantly different between conditions despite unique spatiotemporal asymmetries. This indicates that LBP in those with gait asymmetry may not be due solely to level planar walking. During carrying tasks, gait asymmetry induced by the walking boot increased some metrics of lower back loading. Further, carrying a load in the hand contralateral to the walking boot produced larger forces than when carried on the same side. These results emphasize the importance of evaluating specific sources of gait asymmetry during daily activities other than walking when assessing LBP risk and would encourage more inclusive ergonomic carrying guidelines.

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Year

Entry

2007

Anderson AE, Ellis BJ, Weiss JA. Verification, validation and sensitivity studies in computational biomechanics. Comput Methods Biomech Biomed Eng. June 2007;10(3):171-184.

1998

Novacheck TF. The biomechanics of running. Gait Post. January 1998;7(1):77-95.

1992

Panjabi MM. The stabilizing system of the spine, II: neutral zone and instability hypothesis. J Spinal Disord. December 1992;5(4):390-396.

1999

Andersson GBJ. Epidemiological features of chronic low-back pain. Lancet. August 14, 1999;354(9178):581-585.

1990

Gracovetsky S. Musculoskeletal function of the spine. In: Winters JM, Woo SL-Y, eds. Multiple Muscle Systems: Biomechanics and Movement Organization. New York, NY: Springer-Verlag; 1990:410-437.