An Investigation of Running Kinematics with Recovered Anterior Cruciate Ligament Reconstruction on a Treadmill and In-Field Using Inertial Measurement Units: A Preliminary Study.

Anterior cruciate ligament reconstruction (ACLR) may affect movement even years after surgery. The purpose of this study was to determine possible interlimb asymmetries due to ACLR when running on a treadmill and in field conditions, with the aim of contributing to the establishment of objective movement assessment in real-world settings; moreover, we aimed to gain knowledge on recovered ACLR as a biomechanical risk factor. Eight subjects with a history of unilateral ACLR 5.4 ± 2.8 years after surgery and eight healthy subjects ran 1 km on a treadmill and 1 km on a concrete track. The ground contact time and triaxial peak tibial accelerations were recorded using inertial measurement units. Interlimb differences within subjects were tested and compared between conditions. There were no significant differences between limbs in the ACLR subjects or in healthy runners for any of the chosen parameters on both running surfaces. However, peak tibial accelerations were higher during field running (p-values < 0.01; Cohen's d effect sizes > 0.8), independent of health status. To minimize limb loading due to higher impacts during field running, this should be considered when choosing a running surface, especially in rehabilitation or when running with a minor injury or health issues.

The 'Ride' Feeling during Running under Field Conditions-Objectified with a Single Inertial Measurement Unit.

Foot rollover and the 'ride' feeling that occurs during heel-toe transition during running have been investigated mostly in laboratory settings due to the technical requirements of 'golden standard' measurement devices. Hence, the purpose of the current study was to investigate 'ride' and rollover with a heel cap-mounted inertial measurement unit (IMU) when running under field conditions to get realistic results. Twenty athletes ran on a 1 km outdoor track with five different shoe conditions, only differing in their midsole bending stiffness. The peak angular velocity (PAV) in the sagittal plane of the shoe was analyzed. The subjective evaluation of the 'ride' perception during heel-toe transition was rated on a visual analogue scale. The results revealed that PAV and 'ride' varied for the different shoes. The regression analysis showed that PAV has a significant impact on the 'ride' rating (R2 = 0.952; p = 0.005). The shoe with a medium midsole bending stiffness had the lowest value for PAV (845.6 deg/s) and the best rating of perceived 'ride' on average. Our results show that IMU can be used as a low-cost method to investigate the heel-toe transition during field-running. In addition, we found that midsole bending stiffness influenced PAV and the subjective feeling of 'ride'.

Differences in Mechanical Midsole Characteristics of Running Shoes do not Influence Physiological Variables in Aerobic and Anaerobic Running.

The purpose of this study was to determine the influence of footwear stiffness and energy loss on oxygen uptake and heart rate in athletes running under aerobic and anaerobic conditions. Four footwear conditions with identical outsoles, insoles, upper materials, but different mechanical properties regarding polyurethane midsole materials were investigated. Respective midsole material characteristics were selected to represent a wide range of running shoes. The test procedure for eighteen well-trained male runners was divided into three treadmill testing sessions: an incremental ramp protocol to estimate the individual ventilatory threshold (day 1), a test with 6-minute stages in each shoe at 70% (aerobic, day 2) and 102% (anaerobic, day 3) of the participant's ventilatory threshold. For oxygen uptake and the heart rate, no significant differences between footwear conditions were found for either running condition. Furthermore, no significant relationships between physiological variables and mechanical midsole characteristics were found. The wide range of significant stiffness differences in the rearfoot (52.7 N/mm) and forefoot areas (50.7 N/mm), as well as significant differences of the shoe midsole material energy loss in the rearfoot (18.8%) and forefoot areas (10.7%) were too low to influence physiological variables significantly when running below and slightly above the ventilatory threshold. It seems that shoe mass and shoe comfort can influence physiological variables more than the mechanical midsole characteristics of stiffness and energy loss. These results may have practical implications for shoe manufacturers, coaches, and athletes, alike.

The Effect of the Accelerometer Operating Range on Biomechanical Parameters: Stride Length, Velocity, and Peak Tibial Acceleration during Running.

Previous studies have used accelerometers with various operating ranges (ORs) when measuring biomechanical parameters. However, it is still unclear whether ORs influence the accuracy of running parameters, and whether the different stiffnesses of footwear midsoles influence this accuracy. The purpose of the present study was to systematically investigate the influence of OR on the accuracy of stride length, running velocity, and on peak tibial acceleration. Twenty-one recreational heel strike runners ran on a 15-m indoor track at self-selected running speeds in three footwear conditions (low to high midsole stiffness). Runners were equipped with an inertial measurement unit (IMU) affixed to the heel cup of the right shoe and with a uniaxial accelerometer at the right tibia. Accelerometers (at the tibia and included in the IMU) with a high OR of ±70 g were used as the reference and the data were cut at ±32, ±16, and at ±8 g in post-processing, before calculating parameters. The results show that the OR influenced the outcomes of all investigated parameters, which were not influenced by tested footwear conditions. The lower ORs were associated with an underestimation error for all biomechanical parameters, which increased noticeably with a decreasing OR. It can be concluded that accelerometers with a minimum OR of ±32 g should be used to avoid inaccurate measurements.

The influence of inertial sensor sampling frequency on the accuracy of measurement parameters in rearfoot running.

Increasingly, inertial sensors are being used for running analyses. The aim of this study was to systematically investigate the influence of inertial sensor sampling frequencies (SF) on the accuracy of kinematic, spatio-temporal, and kinetic parameters. We hypothesized that running analyses at lower SF result in less signal information and therefore the inability to sufficiently interpret measurement data. Twenty-one subjects participated in this study. Rearfoot strikers ran on an indoor running track at a velocity of 3.5 ± 0.1 ms-1. A uniaxial accelerometer was attached at the tibia and an inertial measurement unit was mounted at the heel of the right shoe. All sensors were synchronized at the start and data was measured with 1000 Hz (reference SF). Datasets were reduced to 500, 333, 250, 200, and 100 Hz in post-processing. The results of this study showed that a minimum SF of 500 Hz should be used to accurately measure kinetic parameters (e.g. peak heel acceleration). In contrast, stride length showed accurate results even at 333 Hz. 200 Hz were required to calculate parameters accurately for peak tibial acceleration, stride duration, and all kinematic measurements. The information from this study is necessary to correctly interpret measurement data of existing investigations and to plan future studies.