Testing biomechanical models of human lumbar lordosis variability

Using inertial measurement units to estimate spine joint kinematics and kinetics during walking and running

Optical motion capture (OMC) is considered the best available method for measuring spine kinematics, yet inertial measurement units (IMU) have the potential to collect data outside the laboratory. When combined with musculoskeletal modeling, IMU technology may be used to estimate spinal loads in real-world settings. To date, IMUs have not been validated for estimates of spinal movement and loading during both walking and running. Using OpenSim Thoracolumbar Spine and Ribcage models, we compare IMU and OMC estimates of lumbosacral (L5/S1) and thoracolumbar (T12/L1) joint angles, moments, and reaction forces during gait across six speeds for five participants. For comparisons, time series are ensemble averaged over strides. Comparisons between IMU and OMC ensemble averages have low normalized root mean squared errors (< 0.3 for 81% of comparisons) and high, positive cross-correlations (> 0.5 for 91% of comparisons), suggesting signals are similar in magnitude and trend. As expected, joint moments and reaction forces are higher during running than walking for IMU and OMC. Relative to OMC, IMU overestimates joint moments and underestimates joint reaction forces by 20.9% and 15.7%, respectively. The results suggest using a combination of IMU technology and musculoskeletal modeling is a valid means for estimating spinal movement and loading.

Variation in human 3D trunk shape and its functional implications in hominin evolution

This study investigates the contribution of external trunk morphology and posture to running performance in an evolutionary framework. It has been proposed that the evolution from primitive to derived features of torso shape involved changes from a mediolaterally wider into a narrower, and antero-posteriorly deeper into a shallower, more lightly built external trunk configuration, possibly in relation to habitat-related changes in locomotor and running behaviour. In this context we produced experimental data to address the hypothesis that medio-laterally narrow and antero-posteriorly shallow torso morphologies favour endurance running capacities. We used 3D geometric morphometrics to relate external 3D trunk shape of trained, young male volunteers (N = 27) to variation in running velocities during different workloads determined at 45–50%, 70% and 85% of heart rate reserve (HRR) and maximum velocity. Below 85% HRR no relationship existed between torso shape and running velocity. However, at 85% HRR and, more clearly, at maximum velocity, we found highly statistically significant relations between external torso shape and running performance. Among all trained subjects those with a relatively narrow, flat torso, a small thoracic kyphosis and a more pronounced lumbar lordosis achieved significantly higher running velocities. These results support the hypothesis that external trunk morphology relates to running performance. Low thoracic kyphosis with a flatter ribcage may affect positively respiratory biomechanics, while increased lordosis affects trunk posture and may be beneficial for lower limb biomechanics related to leg return. Assuming that running workload at 45–50% HRR occurs within aerobic metabolism, our results may imply that external torso shape is unrelated to the evolution of endurance running performance.

Trunk muscle endurance, strength and flexibility in rural subsistence farmers and urban industrialized adults in western Kenya

OBJECTIVES

High trunk muscle endurance, strength, and moderate flexibility reportedly help maintain musculoskeletal health, but there is evidence for tradeoffs among these variables as well as sex differences in trunk muscle endurance and strength. To test if these observations extend similarly to both men and women in nonindustrial and industrial environments, we investigated intra-individual associations and group and sex differences in trunk muscle endurance, strength, and flexibility among 74 (35 F, 39 M; age range: 18-61 years) adults from the same Kalenjin-speaking population in western Kenya. We specifically compared men and women from an urban community with professions that do not involve manual labor with rural subsistence farmers, including women who frequently carry heavy loads.

METHODS

Trunk muscle endurance, strength, and flexibility were measured with exercise tests and electromyography (EMG).

RESULTS

We found a positive correlation between trunk extensor strength and endurance (R = .271, p ≤ .05) and no associations between strength or endurance and flexibility. Rural women had higher trunk extensor and flexor endurance, EMG-determined longissimus lumborum endurance, and trunk extensor strength than urban women (all p ≤ .05). Rural women had higher trunk extensor and flexor endurance than rural men (both p ≤ .05). Urban women had lower trunk flexor and extensor endurance than urban men (both p ≤ .01).

CONCLUSIONS

High levels of physical activity among nonindustrial subsistence farmers, particularly head carrying among women, appear to be associated with high trunk muscle endurance and strength, which may have important benefits for helping maintain musculoskeletal health.

Shock attenuation in the human lumbar spine during walking and running

During locomotion, each step generates a shock wave that travels through the body toward the head. Without mechanisms for attenuation, repeated shocks can lead to pathology. Shock attenuation (SA) in the lower limb has been well studied, but little is known about how posture affects SA in the spine. To test the hypothesis that lumbar lordosis (LL) contributes to SA, 27 adults (14 male, 13 female) walked and ran on a treadmill. Two lightweight, tri-axial accelerometers were affixed to the skin overlying T12/L1 and L5/S1. Sagittal plane accelerations were analyzed using power spectral density analysis, and lumbar SA was assessed within the impact-related frequency range. 3D kinematics quantified dynamic and resting LL. To examine the effects of intervertebral discs on spinal SA, supine MRI scans were used to measure disc morphology. The results showed no association between LL and SA during walking, but LL correlated with SA during running (P<0.01, R²=0.30), resulting in as much as 64% reduction in shock signal power among individuals with the highest LL. Patterns of lumbar spinal motion partially explain differences in SA: larger amplitudes of LL angular displacement and slower angular displacement velocity during running were associated with greater lumbar SA (P=0.008, R²=0.41). Intervertebral discs were associated with greater SA during running (P=0.02, R²=0.22) but, after controlling for disc thickness, LL remained strongly associated with SA (P=0.001, R²=0.44). These findings support the hypothesis that LL plays an important role in attenuating impact shocks transmitted through the human spine during high-impact, dynamic activities such as running.