Date of Award
Doctor of Philosophy
Tim R. Derrick
The occurrence of low back pain in society is a widespread and costly problem, while running is an accessible and common form of physical exercise. The intervertebral disc is a commonly studied location of interest within the low back, however limited research has been performed attempting to assess the risks or benefits associated with running on the health of the intervertebral disc, with zero research which estimates in-vivo loading on the intervertebral disc during running. Meanwhile, the available literature is not in agreement on whether running poses more of a risk or a benefit to intervertebral disc health, with some research suggesting that running has the potential to positively affect the intervertebral disc, while additional research suggests that long distance running will increase the likelihood of injury among runners. Thus, it is of interest to determine in-vivo estimates of forces on the L5/S1 intervertebral disc in order to assess changes in pressure within the disc nucleus pulposus during running.
As such, for this dissertation, three studies were completed. The first involved model development in order to estimate L5/S1 joint angles, forces, and moments, followed by further model development to estimate muscular forces crossing the L5/S1 joint and joint compressive forces, and concluding by utilizing a finite element model of the intervertebral disc to estimate joint pressure. Following model validation, two studies were completed using repeated measures study designs in order to compare changes in intervertebral disc pressure due to running at different velocities, using different footstrike patterns, and following fatigue.
Validation of the models used when estimating in-vivo intervertebral disc pressures resulted in estimates for joint moments that were similar to those estimated during a previous research study. The shape of the curves estimating muscular forces were similar to muscular stimulation curves derived via electromyography (EMG), however due to limitations of the data collection process for both muscle modeling and EMG it was impossible to reach a strong agreement when comparing these data sources. Validation of the finite element model resulted in estimated disc compression leading to percent stature loss that was similar in error magnitude to some previously published research comparing in-vivo and simulated data. Comparisons of previously recorded in-vivo disc pressure for a single subject to estimations for the present study resulted in minimum pressures that were similar across the studies, with greater maximum pressure estimated using the current modeling approach.
An increase in velocity resulted in an increase in the average and peak pressures on the intervertebral disc during running, while faster velocities resulted in reaching peak pressure later on in stance than slower velocities. Changing footstrike patterns did not cause any differences in average or peak intervertebral disc pressure, however running with a forefoot strike did cause runners to achieve peak intervertebral disc pressures earlier on during the stance phase than when running with a rearfoot strike pattern. During fatigued running, a moderate-large effect size was observed with higher pressures on the disc during the fatigued state which were not statistically significant (p>0.05), and with no change in the percent stance needed to reach peak pressure.
The models appear to perform adequately when utilized in a repeated measures study design, but are not able to accurately detect specific pressures within the intervertebral disc. The true meaning behind these results is unknown as higher pressures or loading rates during certain conditions may lead to increased risk of injury, or alternatively there might be little effect on injury risk as the higher pressure/loading may increase fluid flow into and out of the disc thus enhancing nutrient absorption. Further research needs to be performed in order to determine the risks associated with increases in pressure due to running at faster velocities, potential increases in the loading rate during forefoot strike running due to reaching peak pressure sooner than rearfoot strike running, and potential risks associated with increased intervertebral disc pressure during fatigued running.
Jeffrey Ray Mcclellan
Mcclellan, Jeffrey Ray, "The effects of running speed, form, and fatigue on intervertebral disc pressures at L5/S1: A developmental musculoskeletal and finite element modeling approach" (2018). Graduate Theses and Dissertations. 16634.