Performance of a lateral pelvic cluster technical system in evaluating running kinematics

Alternative Models for Pelvic Marker Occlusion in Cycling

Bike fitting aims to optimize riders' positions to improve their performance and reduce the risk of injury. To calculate joint angles, the location of the joint centers of the lower limbs needs to be identified. However, one of the greatest difficulties is the location of the hip joint center due to the frequent occlusion of the anterior superior iliac spine markers. Therefore, the objective of this study was to validate a biomechanical model adapted to cycling (modified pelvic model, MPM), based on the traditional pelvic model (TPM) with an additional lateral technical marker placed on the iliac crests. MPM was also compared with a widely used model in cycling, trochanter model (TM). Thirty-one recreational cyclists pedaled on a roller bike while the movement was captured with a 7-camera VICON system. The position of the hip joint center and knee angle were calculated and compared with the TPM continuously (along 10 pedaling cycles) and discreetly at 90° and 180° crank positions. No significant differences were found in the position of the hip joint center or in the knee flexion/extension angle between the TPM and the MPM. However, there are differences between TPM and TM (variations between 4.1° and 6.9° in favor of the TM at 90° and 180°; P < .001). Bland-Altman graphs comparing the models show an average difference or bias close to 0° (limits of agreement [0.2 to -8.5]) between TPM and MPM in both lower limbs and a mean difference of between -4° and -7° (limits of agreement [-0.6 to -13.2]) when comparing TPM and TM. Given the results, the new cycling pelvic model has proven to be valid compared with the TPM when performing bike fitting studies, with the advantage that the occluded markers are avoided. Despite its simplicity, the TM presents measurement errors that may be relevant when making diagnoses, which makes its usefulness questionable.

Not all brawn, but some brain. Strength gains after training alters kinematic motor abundance in hopping

Background

The effects of resistance training on a muscle’s neural, architectural, and mechanical properties are well established. However, whether resistance training can positively change the coordination of multiple motor elements in the control of a well-defined lower limb motor performance objective remains unclear. Such knowledge is critical given that resistance training is an essential and ubiquitous component in gait rehabilitation. This study aimed to investigate if strength gains of the ankle and knee extensors after resistance training increases kinematic motor abundance in hopping.

Methods

The data presented in this study represents the pooled group results of a sub-study from a larger project investigating the effects of resistance training on load carriage running energetics. Thirty healthy adults performed self-paced unilateral hopping, and strength testing before and after six weeks of lower limb resistance training. Motion capture was used to derive the elemental variables of planar segment angles of the foot, shank, thigh, and pelvis, and the performance variable of leg length. Uncontrolled manifold analysis (UCM) was used to provide an index of motor abundance (IMA) in the synergistic coordination of segment angles in the stabilization of leg length. Bayesian Functional Data Analysis was used for statistical inference, with a non-zero crossing of the 95% Credible Interval (CrI) used as a test of significance.

Results

Depending on the phase of hop stance, there were significant main effects of ankle and knee strength on IMA, and a significant ankle by knee interaction effect. For example at 10% hop stance, a 1 Nm/kg increase in ankle extensor strength increased IMA by 0.37 (95% CrI [0.14–0.59]), a 1 Nm/kg increase in knee extensor strength decreased IMA by 0.29 (95% CrI [0.08–0.51]), but increased the effect of ankle strength on IMA by 0.71 (95% CrI [0.10–1.33]). At 55% hop stance, a 1 Nm/kg increase in knee extensor strength increase IMA by 0.24 (95% CrI [0.001–0.48]), but reduced the effect of ankle strength on IMA by 0.71 (95% CrI [0.13–1.32]).

Discussion

Resistance training not only improves strength, but also the structure of coordination in the control of a well-defined motor objective. The role of resistance training on motor abundance in gait should be investigated in patient cohorts, other gait patterns, and its translation into functional improvements.

An alternative whole-body marker set to accurately and reliably quantify joint kinematics during load carriage

Body armor covers anatomical landmarks that would otherwise be used to track trunk and pelvis movement in motion analysis. This study developed and evaluated a new marker set, and compared it to placing markers on the skin and over-top of body armor. In our method, pelvis and trunk motions were measured using a custom-built sacral and upper-back marker cluster, respectively. Joint angles and ranges of motion were determined while participants walked without and with body armor. Angles were obtained from the new marker set and compared against conventional marker sets placed on the skin or over-top the body armor. Bland-Altman analyses compared the agreement of kinematic parameters between marker sets, while joint angle waveforms were compared using inter-protocol coefficient of multiple correlations (CMCs). The intra- and inter-session similarities of joint angle waveforms from each marker set were also assessed using CMCs. There was a strong agreement between joint angles from the new marker set and markers placed directly on the skin at key anatomical landmarks. The agreement worsened with markers placed on top of body armor. Inter-protocol CMCs comparing markers on body armor to the new marker set were poor compared to CMCs between skin-mounted markers and the new marker set. Intra- and inter-session repeatability were higher for the new marker set compared to placing markers over-top of body armor. The new marker set provides a viable alternative for researchers to reliably measure trunk and pelvis motion when equipment, such as body armor, obscures marker placement.