Biomechanical Analysis of Running Foot Strike in Shoes of Different Mass.

Different shoes and strike patterns produce different biomechanical characteristics that can affect injury risk. Running shoes are mainly designed as lightweight, minimal, or traditional cushioned types. Previous research on different shoes utilized shoes of not only different mass but also different shoe structures. However, it is unclear whether biomechanical changes during running in different shoe types with differing mass are the result of the structural design or the mass of the shoe. Thus, the purpose of this study was to investigate the effect of shoes of different mass on running gait biomechanics. Twenty male runners participated in this study. The experimental shoe masses used in this study were 175, 255, 335 and 415 g. The peak vertical ground reaction force increased with shoe mass (p < 0.05), but the strike index, ankle plantarflexion at initial contact, peak moment of the ankle during the stance phase, and initial contact angles of the lower extremity joints did not change. During the pre-activation phase, the integrated EMG data showed that the tibialis anterior muscle was the most activated with the 175 g and 415 g shoes (p < 0.05). During the push-off phase, the semitendinosus, lateral gastrocnemius and soleus muscles displayed higher activation with the heavier shoes (p < 0.05). The center of pressure also moves forward; resulting in mid foot striking. The lightest shoes might increase gastrocnemius muscle fatigue during the braking phase. The heaviest shoes could cause semitendinosus and triceps surae muscle fatigue during the push-off phase. Therefore, runners should consider their lower extremity joints, muscle adaptation and cushioning to remain in their preferred movement path.

A comparison of methods to quantify control of the spine.

Low back pain (LBP) affects many individuals worldwide. The established association between LBP and spine motor control has led to the development of many control assessment techniques. To understand spine control and LBP, it is essential to know the relationship between assessment techniques. Systems identification (SI) and local dynamic stability (LDS) are two methods of quantifying spine control. SI provides a detailed description of control but uses linearity assumptions, whereas LDS provides a "black box" non-linear assessment during dynamic movements. Therefore, the purpose of this project was to compare control outcomes of SI and LDS. 15 participants completed two tasks (SI and LDS) in a random order. For the SI task, participants were seated and ventrally perturbed at the 10th thoracic vertebrae. They were instructed to resist the perturbations (resist condition) or to relax the trunk (relax condition). Admittance was computed, and a neuromuscular control model quantified lumbar stiffness, damping and muscle spindle feedback gains. For the LDS task, participants completed three repetitive movement blocks consisting of flexion/extension, axial rotation, and complex movements. In each block, the maximum finite-time Lyapunov exponent (λmax) was estimated. A stepwise linear regression determined that λmax during the rotation task was best predicted by SI outcomes in the relax condition (adjusted R2 = 0.83). Many conditions demonstrated no relationship between λmax and SI outcomes. These findings outline the importance of a consistent framework for the assessment of spine control. This could clarify research comparisons and the understanding of the cause/effect role of LBP on spine control.

The effect of attentional focus on local dynamic stability during a repetitive spine flexion task.

The association between low back pain and spine movement control suggests that it is important to reliably quantify movement behavior. One method to characterize spine movement behavior is to measure the local dynamic stability (LDS) of spine movement during a repetitive flexion task in which a participant is asked to touch multiple targets repetitively. Within the literature, it has been well established that an individual's focus of attention (FOA) can modulate their neuromuscular control and affect task performance. The goal of this project was to examine the unknown effect of FOA on LDS measurements and timing error during a repetitive spine flexion task that is commonly used to assess movement control. Fourteen healthy adults (7 male) were instructed to touch two targets (shoulder height and knee height) to the beat of a metronome (4 s/cycle) for 35 consecutive cycles. They completed this task under internal (focus on trunk movement) and external (focus on targets) FOA conditions. Motion capture data of the trunk and sacrum were collected at 120 Hz. The lumbar spine angle was defined as the orientation of the trunk relative to the pelvis. The local divergence exponent (λmax) was calculated from the sum of squares of the 3-dimensional spine angle. Timing error was calculated as the time difference between target touches and metronome beats. Changing an individual's FOA had no effect on λmax calculations or timing error. Although clear task instructions are important, it is not essential to control for FOA during this movement assessment protocol.

Assessment of Three-Dimensional Trunk Kinematics and Muscle Activation during Cycling with Independent Cranks.

Independent cranks (IC) are recently introduced bicycle cranks that are decoupled; therefore allowing each leg to pedal independent of the other. Despite this introduction, limited research has been conducted assessing biomechanical changes when cycling with IC. Therefore, the purpose of this study was to evaluate and compare trunk kinematics and surface electromyography (sEMG) during IC and normal crank (NC) cycling during a graded exercise test to volitional fatigue. Ten healthy, physically active men performed two tests (IC and NC) on a cycling ergometer on separate days. 3D motion capture data of the trunk and pelvis and sEMG of the latissimus dorsi, tibialis anterior, gastrocnemius lateral head, rectus femoris, vastus lateralis and the biceps femoris were collected bilaterally. The first 30 seconds (beginning) and the last 30 seconds (end) of each trial were analyzed with respect to external load (beginning vs end), crank type (IC vs NC) side (left vs right), and phase of the pedal cycle (push vs recovery). Mean load at volitional fatigue in NC (351 W) was significantly greater than IC (318 W; p < 0.001). As external load increased, there was a similar increase in spine flexion angle in the sagittal plane for both NC (8.2°) and IC (4.6°). The NC condition demonstrated significantly greater increase in muscle activation from the beginning to the end than the IC condition in the tibialis anterior, rectus femoris and biceps femoris in the push phase, and the rectus femoris and biceps femoris in the recovery phase. As IC demonstrated less increase in activation, they cause less variation in muscular contraction from beginning to end throughout the full pedal range of motion, yet do not alter gross trunk kinematics. Due to altered muscle activation patterns when cycling with IC, they are proposed as a potentially beneficial training tool to increase training diversity.