ECSS Paris 2023: OP-BM12
INTRODUCTION: Previous studies have clarified the dynamics of the muscle-tendon unit (MTU) during normal walking (NW) and running. During walking, muscle fascicles of the medial gastrocnemius contract almost isometrically, while the tendon undergoes stretch-shortening cycles. In contrast, running is characterized by larger changes in muscle fascicle length, which contribute to higher locomotion speeds and distinct MTU behavior compared with walking. Race walking is characterized by unique kinematic constraints imposed by the rules, particularly the requirement to maintain knee extension from foot contact to mid-stance. However, the behavior of the MTU during race walking has not been clarified. Therefore, the purpose of this study was to investigate differences in the MTU behavior of the medial gastrocnemius between NW and race walking at matched locomotion speeds. METHODS: Seven race walkers (4 males and 3 females) performed NW and RW at 8 km/h for 30 s each on a treadmill. The fascicle length and pennation angle of the medial gastrocnemius were measured using ultrasonography, whereas the lower limb joint angles and ground reaction forces (GRF) were simultaneously recorded using a three-dimensional motion capture system and force plates. Electromyography (EMG) was used to record the muscle activity of the medial gastrocnemius. MTU lengths were estimated using a previously reported equation [4], and series elastic element (SEE) lengths were calculated as the difference between MTU and fascicle lengths. RESULTS: RW showed a significantly shorter step length and significantly higher step frequency compared to NW. Changes in MTU and fascicle lengths throughout the stance phase were significantly smaller during RW, whereas no significant difference was observed in SEE lengths change. During the first half of the stance phase, fascicle lengthening and SEE shortening occurred simultaneously during NW, whereas both the fascicles and the SEE maintained nearly constant lengths during RW, likely reflecting the kinematic constraint of maintaining knee extension. Additionally, the timing of MTU and SEE shortening during the latter half of the stance phase differed between NW & RW. Regarding EMG activity patterns, RW exhibited an earlier peak in muscle activity than NW. CONCLUSION: These findings demonstrate distinct MTU dynamics between NW and RW, suggesting different muscle contraction modes: eccentric-concentric transition in NW versus predominantly isometric contraction in RW. References 1. Fukunaga et al., Proc Biol Sci, 2001 2. Ishikawa et al., J Appl Physiol, 2005 3. Ishikawa et al., Gait Posture, 2007 4. Hawkins and Hull., J Biomech, 1990
Read CV Keiji MIYAMOTOECSS Paris 2023: OP-BM12
INTRODUCTION: Monitoring the biomechanics of military personnel during locomotion and physically demanding tasks is essential for understanding movement strategies, injury risk, and the effects of load carriage in operational environments. Wearable inertial measurement units (IMUs) are a candidate approach for field-based biomechanical sensing, with demonstrated validity during steady-state gait in controlled laboratory conditions[1]. However, their performance across varied gait conditions and highly dynamic military tasks remains unclear. Establishing confidence in IMU-derived kinematics under these conditions is critical for biomechanical monitoring in military contexts and downstream applications, including adaptive assistive systems[2]. This work therefore assessed the criterion validity of IMU-derived lower-limb kinematics in the laboratory and evaluated their feasibility during simulated military activities. METHODS: Two experimental studies were conducted. 1) 20 healthy adults performed treadmill walking and running in 30 s bouts across multiple speeds (1.1–3.0 m·s⁻¹) and inclines (−10%-+15%), with and without an additional 20 kg load. IMU and optical motion capture-derived lower-limb joint kinematics were determined using OpenSim and compared via root mean squared difference (RMSD) and correlation coefficients. 2) A field-based feasibility study involving 18 actively serving military personnel completing a standardised obstacle course replicating dismounted military tasks. IMUs were worn throughout. Sensor disruptions were recorded and full-body kinematics were compared during standardised functional movements performed pre- and post-course completion. RESULTS: 1) Hip and knee flexion-extension displayed strongest IMU-motion capture agreement during walking (RMSD = ~10° [~3-13° IQR]; Hip: r=0.91; Knee: r=0.92) irrespective of gradient or load. Differences increased during jogging and running (~20°), while sagittal hip and knee correlations remained high (r = 0.79-0.96). Frontal- and transverse-plane kinematics exhibited largest errors (~30°) and weakest correlations. Removing systematic model pose offsets substantially reduced RMSD values, indicating calibration-related bias. 2) 17 participants (94%) completed post-task assessments with usable IMU data. 26 sensor disruptions were recorded, predominantly affecting lower-limb sensors during prone and crawling tasks. Pre- and post- lower-limb joint range of motion RMSD ranged from 4-16° (r = 0.6-0.9). Post-task walking kinematics generally remained within the pre-task mean ± 2 standard deviations. CONCLUSION: While using IMUs for monitoring the biomechanics of military personnel during dynamic tasks seems feasible, our work identifies several key issues that need addressing for successful application. This includes optimising sensor attachment and data-processing strategies that avoid the need for input from other systems. References: 1) Al Borno M, et al. J NeuroEngin Rehabil. 2022;19:22; 2) Slade P, et al. Nature. 2022;610:277–82.
Read CV Samuel WisdishECSS Paris 2023: OP-BM12
INTRODUCTION: Resisted sprinting (RS) suppresses increases in running speed by applying an external load from behind the runner. When a high load is imposed, the movement can be constrained to resemble the initial acceleration phase of unresisted sprinting (US), whereas a lower load can be adjusted to approximate the near maximal speed phase. Similar to US, RS also comprises an acceleration phase and reaches a plateau once a certain running speed is attained (plateau phase). A recent study has reported that, at the same running speed, there are no differences in kinematics or kinetics between US and RS. In contrast, other research has shown that near the plateau phase of RS, horizontal ground reaction forces (GRFs) decrease and vertical GRFs increase, even at matches speeds. The discrepancy may be attributable to differences in running phase (acceleration vs. plateau) during RS. Therefore, this study aimed to clarify how differences in running phase during RS affect sprint kinematics and kinetics. METHODS: Seventeen male collegiate soccer players performed maximal 15 m sprints in four conditions: US and RS with the loads corresponding to 5%, 10%, and 15% of body mass (1080Sprint). GRFs were recorded on a 50 m force-plate form (TF-90100), and 3D kinematics were captured with an optical system (Mac3D). Spatiotemporal variables, GRF variables, center of mass (CoM) height, scissor angle, and lower-limb joint kinematics/kinetics were calculated. For each load, the two steps immediately preceding the 15-m mark were defined as representative of the plateau phase. Two steps from unresisted sprinting (US) and other RS conditions matched for running speed were then extracted and compared with the plateau-phase variables at each load. To identify the running phases in US and RS, a saturated exponential model was fitted to the speed–distance relationship to estimate maximal running speed and the distance at which it occurred for each trial, and these values were subsequently used for normalization. RESULTS: During the plateau phase, RS exhibited a lower step frequency and a longer step length compared with US. This difference was attributable to an increased vertical impulse. In addition, hip and knee joint angles during stance were more extended, and the scissor angle was greater in RS than in US. The COM was also positioned higher, suggesting a more upright trunk posture in RS relative to US. In contrast, during the acceleration phase, RS showed no significant differences from US in most variables. CONCLUSION: RS exhibited sprint mechanics similar to US during the acceleration phase but differed from US during the plateau phase.
Read CV Taiyo KuritaECSS Paris 2023: OP-BM12