ECSS Paris 2023: OP-BM07
INTRODUCTION: Along the standardization–ecological-validity continuum, hands-on-hips single-leg countermovement jumps (SL-CMJ) provide repeatable stretch–shortening cycle (SSC) benchmarks but are self-paced and context-poor. Semi-immersive extended reality (XR) can add ball-coupled, externally timed goals (e.g., heading) while retaining laboratory-grade kinetics, potentially revealing soccer-relevant jump–landing strategies (1). We compared XR jump–head–land (XR-JHL) with SL-CMJ and tested moderation by sex and limb dominance. METHODS: Forty-five competitive amateur soccer players (22 males, 23 females; dominance = preferred kicking leg) performed bilateral SL-CMJ and XR-JHL using a semi-immersive XR system (MotumXR). In XR-JHL, athletes used arms freely, timed the jump to head a time-standardized, height-scaled virtual ball at a prescribed contact height, and landed on the same force plate. 3D kinematics (Qualisys; 200 Hz) and ground reaction forces (AMTI; 1000 Hz) were synchronized with MotumXR and displayed on a wall screen (4.85×2.75 m; viewing distance 5.33 m). Valid trials required ball contact, clean force-plate contact, and a stable single-leg landing. Outcomes were jump height, RSI, and discrete sagittal-plane peak trunk/lower-limb kinematics and kinetics (moments, power). Mixed ANOVA tested Condition (XR-JHL vs SL-CMJ) with Sex and Dominance (α=0.05). RESULTS: Compared with SL-CMJ, XR-JHL increased jump performance (height +4.0–6.4 cm; Sex×Condition×Dominance p=.018; RSI +13%, p<.01). XR-JHL induced a more extended jump strategy (lower trunk/hip/knee flexion; ankle dorsiflexion −2°) with higher loading (knee moment +0.33; ankle moment +0.48–0.61; all p≤.007) and a distal shift in positive power (knee +1.41; ankle +2.41 W·kg⁻¹) with lower hip positive power (−0.61 W·kg⁻¹). Dominance effects were present (Dom < NonDom for ankle dorsiflexion, knee moment, and positive knee/ankle power; all p<.01) and XR amplified limb-specific loading (Condition×Dominance for ankle moment; p≤.007). During landing, XR-JHL was more upright with sex/limb moderation, with lower knee moment (−0.12; p<.05) but higher ankle moment (+0.56; p<.01), plus reduced ankle negative power (−8.1 to −9.6 W·kg⁻¹), especially in males. CONCLUSION: Externally timed, ball-coupled XR heading reshaped SSC expression versus SL-CMJ: athletes jumped higher and more reactively, yet adopted a more extended strategy with distally redistributed peak demands toward the knee–ankle complex. Kicking-leg dominance systematically moderated these signatures (dominant limbs: lower dorsiflexion and reduced knee/ankle positive power), and XR magnified limb-specific loading, exposing soccer-relevant asymmetries that self-paced benchmarks may mask. Joint power complemented moments by distinguishing high-moment/low-velocity (“stiffer”) distal landing control under soccer-specific constraints from higher-excursion solutions typical of SL-CMJ. REFERENCES: 1) Pinder et al., J Sport Exerc Psychol, 2011
Read CV Soran AminiAghdamECSS Paris 2023: OP-BM07
INTRODUCTION: In volleyball, the spike and block jump are crucial technical factors that determine competitive performance. These jump heights are a key determinant of performance, with successful spikes requiring greater jump heights than unsuccessful attempts 1) and higher jump heights in blocking are considered to increase the likelihood of stopping an opponent’s attack. In contrast, focusing on the landing phase, the vertical ground reaction forces acting on the foot reach approximately 3.7 times body weight in spike jumps and 2.8 times body weight in blocking 2). Therefore, reducing landing impact in volleyball jumps is an essential issue for the prevention of lower-limb injuries. Generally, volleyball is played on wooden flooring in arenas, but international competitions use Taraflex®, while Japan’s professional league uses Connect Mat®, both of which are synthetic sports surfaces. These synthetic sports surfaces were originally introduced to reduce injury risks associated with the deterioration of wooden flooring and are also considered to provide superior impact attenuation compared with wooden flooring. However, the effects of these surfaces on both jump performance and mechanical load on the body during actual volleyball jumps have not been fully elucidated. Therefore, the purpose of this study was to compare jump height and plantar loading during spike and block jumps on different sports surfaces. METHODS: Twenty-six healthy female collegiate volleyball players participated in this study. Participants performed spike and block jumps on three different surface conditions: wooden flooring and two types of synthetic sports surfaces (Taraflex® [Kuriyama Japan Corp., Japan] and Connect Mat® [TOLI Corp., Japan]). Both jumps were recorded from sagittal plane using a video camera, and jump height was estimated based on flight time. Plantar loading was recorded using sensor insoles, calculating peak plantar loading and impulse during the take-off phase, and peak plantar loading and loading rate during the landing phase. Discrete variables were analyzed using a one-way ANOVA across the surface conditions. RESULTS: In spike jumps, synthetic surfaces showed significantly higher jump height and lower landing peak plantar loading than wooden flooring. Conversely, in block jumps, synthetic surfaces showed significantly lower jump height, with no significant differences in plantar loading. CONCLUSION: The findings of this study suggest that the influence of sports surfaces on jump performance and mechanical loading varies depending on the specific movement characteristics of volleyball jumps. In conclusion, synthetic surfaces enhanced jump height and reduced landing impact in spike jumps, but decreased jump height in block jumps compared to wooden flooring. No significant differences were observed between the two types of synthetic surfaces across all variables. 【References】 1) Sarvestan et al., J Sports Sci, 2020. 2) Garcia et al., BMC Sports Sci Med Rehabil, 2022.
Read CV Yohei YamazakiECSS Paris 2023: OP-BM07
INTRODUCTION: Highly standardized countermovement jumps (CMJ) provide repeatable benchmarks of performance but have low ecological validity in sport-specific scenarios (e.g. soccer) as movements are often unplanned and require rapid adaptation to external stimuli. Introducing sport-relevant timing and goal-directed actions into controlled testing is expected to elicit movement solutions that better reflect sport behavior (1). Semi-immersive extended reality (XR) enables soccer-specific heading movements to be performed using external cues while retaining laboratory-grade biomechanics. Therefore biomechanics of bilateral CMJ landings were compared with a planned XR jump-head-land task (XR-JHL) and an unplanned XR jump-head-land task (upXR-JHL) to identify distinct adaptations in landing mechanics. METHODS: 21 male competitive soccer players performed 3 valid trials of a CMJ, XR-JHL, and upXR-JHL each. Data was recorded using 3D motion capture (Qualisys, 200Hz) and force plates (AMTI, 1000Hz). A customized XR software was used to transfer the participants movements into a interactive soccer scenario for the XR-JHL and tasks. A virtual ball was thrown to the participant’s avatar in both XR conditions. XR-JHL consisted of a pre-planned bilateral landing following the heading task, whereas in the upXR-JHL the bilateral landing was only one of 3 different landing signals displayed with a 400ms delay. Outcome variables were calculated between Initial contact (IC) and the end of the absorption phase (COM zero velocity). Sagittal-plane lower-limb joint kinematics (at IC and peak flexion), peak moments and vertical ground reaction force (vGRF), jump height and vertical stiffness (k_vert) were analyzed. A rANOVA with 3 within-subject variables was used for statistical analysis (p<0.05). RESULTS: In the XR-JHL, athletes landed with reduced hip (IC: 22.3±7.4° vs 34.9±13.1°, p<0.001; peak: 62.0±15.6° vs 88.6±29.4°, p<0.001) and knee flexion (peak: 69.8±10.5° vs 80.6±20.6°, p=0.002) compared to the CMJ, and with the largest ankle plantarflexor moment (1.87±0.38 vs 1.10±0.42 Nm/kg, p<0.001). In the upXR-JHL, the knee extensor moment was lower than in both CMJ (1.96±0.35 vs 2.31±0.43 Nm/kg, p<0.01) and XR-JHL (2.35±0.37 Nm/kg, p<0.001), and the hip flexor moment greater relative to planned landings (1.05±0.60 vs −0.06±0.80 Nm/kg, p<0.001), while joint angles remained similar to CMJ (p>0.05). Peak vGRF and k_vert did not differ between conditions (p>0.05). CONCLUSION: Soccer-specific demands alone as well as additionally introducing unpredicted movements significantly modified landing mechanics compared with CMJ. XR-JHL landings were characterized by a less flexed lower-limb posture and greater ankle joint loading, whereas upXR-JHL landings reduced knee joint loading while increasing hip involvement. These findings indicate that task predictability alters inter-joint load distribution during landing without necessarily increasing external impact forces. REFERENCES: 1) Pinder et al., J Sport Exerc Psychol, 2011
Read CV Julia ScharbertECSS Paris 2023: OP-BM07