ECSS Paris 2023: CP-BM07
INTRODUCTION: Unloaded or assisted jumping is used in assessment and training to reduce mechanical loading while maintaining functional movement patterns. However, most approaches focus on countermovement jumps, which are suitable for assessing force and power but do not adequately address repetitive stretch-shortening cycle and stretch-reflex behavior [1]. To target the stretch-shortening cycle in populations unable to safely perform hopping tasks, such as older adults or patients in rehabilitation, unloaded repetitive hopping is required. However, validated protocols for unloaded hopping are lacking. Therefore, this pilot study aimed to develop and biomechanically validate an elastic assisted hopping protocol enabling progressive unloading of up to 40% of body weight (BW) while preserving key stretch-shortening cycle characteristics. METHODS: Five healthy adults (32.8 ± 9.1 years) performed repetitive hopping on a force plate using a custom-built elastic assistance system providing progressive unloading (0, 10, 20, 30 and 40% BW). For each condition, participants completed 60 consecutive hops using a self-selected frequency. Peak force, contact time, flight time and hopping frequency were derived from ground reaction force data. Activity of the soleus and tibialis anterior muscles was recorded and quantified as the integral of the rectified EMG signal within 100 ms after ground contact (SOL EMG and TA EMG, respectively). For soleus, the short-latency reflex (SLR) was derived as the integration of the electromyographic signal between 30 and 60 ms after ground contact and was additionally normalised to SOL EMG (SLR/SOL EMG). Non-parametric repeated-measures statistics were applied using Friedman tests, with effect sizes reported as Kendall’s W. RESULTS: Significant main effects of unloading were observed for peak vertical ground reaction force (p = 0.001, W = 0.90), flight time (p = 0.003, W = 0.79), hopping frequency (p = 0.008, W = 0.70) and SLR (p = 0.048, W = 0.48). Peak vertical ground reaction force decreased progressively with increasing unloading, indicating effective mechanical load reduction. Flight time increased with unloading, whereas hopping frequency showed a systematic decrease with increased unloading. SLR decreased progressively with higher unloading levels. In contrast, contact time, SOL EMG, TA EMG and the SLR/SOL EMG ratio showed no significant main effects (p > 0.18). CONCLUSION: Elastic assisted hopping effectively reduces mechanical loading while preserving essential temporal characteristics of hopping. The reduction in SLR, in the absence of changes in normalised SLR/SOL EMG, indicates diminished stretch velocities with decreased loading rather than a loss of stretch-shortening cycle function per se, supporting feasibility for populations unable to tolerate high mechanical loading. The protocol is sensitive to graded unloading and provides a methodological basis for future studies. References: [1] Tufano JJ et al. J Strength Cond Res, 36(6), 1518–1523, 2022.
Read CV Michael SchwenkECSS Paris 2023: CP-BM07
INTRODUCTION: The purpose of this study was to simulate game-like conditions in which athletes are unable to fully focus on landing tasks by implementing a distracted attention paradigm during repeated single-leg lateral jump-landings. Dynamic taping was applied to examine its effects on dynamic postural stability and neuromuscular control. This experimental design aimed to elicit ankle inversion injury risk and to investigate lower-extremity compensatory strategies and the supportive effects of dynamic taping. METHODS: Nineteen female collegiate Division I athletes participated in this study. Participants performed four consecutive single-leg lateral jump-landings followed by a 5-second balance task under conditions with dynamic ankle taping. During testing, a dual-task (DT) paradigm was introduced in which participants held a wireless handgrip dynamometer with their dominant hand and maintained grip force at 30% of maximal voluntary contraction using real-time visual feedback. A two-way repeated-measures ANOVA was conducted to examine the effects of dual-task condition and dynamic taping. RESULTS: Under dual-task (DT) conditions, mediolateral center-of-pressure excursion and sway area increased significantly, indicating reduced landing stability. During lateral landing with dynamic taping, hip angular velocity increased in the sagittal and transverse planes but decreased in the frontal plane, suggesting greater proximal contribution and rotational shock absorption. Knee transverse-plane external rotation angular velocity increased, potentially enhancing rotational control at initial contact. Ankle range of motion was partially restricted. DT also increased rectus femoris activation during pre-landing and initial contact. The highest rectus femoris and vastus lateralis activation during push-off occurred under combined dynamic taping and DT conditions. CONCLUSION: The findings demonstrate that dual-task conditions significantly impair lateral landing stability, as evidenced by increased mediolateral center-of-pressure sway. This suggests that cognitive load disrupts sensorimotor integration and increases the difficulty of maintaining landing control. Following the dynamic taping intervention, a distinct proximal adjustment strategy was observed. Specifically, the results indicate that dynamic taping may facilitate a redistribution of rotational shock absorption demands toward the hip and knee joints, thereby enhancing rotational control during landing. Electromyographic data further suggest that athletes compensate for attentional distraction by increasing quadriceps pre-activation and push-off output. Notably, dynamic taping appears to augment this neuromuscular response under dual-task conditions. Overall, these findings support the potential role of dynamic taping as an adjunct strategy to promote proximal control and improve landing stability in high cognitive-load sporting contexts.
Read CV JIAN-ZHI LINECSS Paris 2023: CP-BM07
INTRODUCTION: The external attentional focus of attention (e.g, focusing on the rungs of the Vertec to be reached) has been shown to increase jump height by promoting greater forces. However, the current studies primarily targeted bilateral jump performance, and these findings may not necessarily be applicable to unilateral activities. Moreover, the presence of larger inter-limb asymmetry (IA) in single-leg countermovement jumps (SLCMJ) is often linked to decreased sports performance and a higher risk of injury, suggesting the high importance of observing SLCMJ asymmetry. This study investigated the impact of the external focus cue ("reaching for the ceiling") on jump height (JH) and time to take-off (TTT) during SLCMJ in recreationally active young adults, as well as the IA changes. The findings can inform better coaching language to enhance training effects for the SLCMJ exercise with executions directed to external attentional focus. METHODS: Twenty-six healthy participants, aged between 18 and 35 years old, performed multiple akimbo SLCMJs on each leg under two randomised conditions: 1) Control (no cue used) and 2) external cue (head reach for the ceiling). JH and TTT were measured using Hawkin Dynamics wireless dual force plates. Asymmetries were calculated using the Standard Percentage Difference formula. Paired t-tests, effect sizes (Hedges’ g), and intraclass correlation coefficients were computed to compare performance changes. RESULTS: ICC values indicated excellent reliability for JH (0.900–0.901) and good-to-excellent reliability for TTT (0.857–0.888). External cueing significantly improved JH for both legs (effect sizes: left leg g = 0.671, p = 0.002; right leg g = 1.082, p = 0.049). JH asymmetry showed a minimal, non-significant reduction from 10.60% to 9.44% (p > 0.05). Individual-leg TTT increased significantly (left leg: g = 0.237, p = 0.016; right leg: g = 0.280, p = 0.03), despite non-significant changes in TTT asymmetry (p > 0.05). CONCLUSION: Adding external cues when performing unilateral CMJ can increase jump height and time to take-off but it cannot induce significant changes in JH and TTT asymmetry. Therefore, the external attentional focus can be used to maximise unilateral CMJ height during plyometric tasks, but it is not effective in lowering IAs for injury prevention purpose. To further explore the use of external cues for IA reduction, future studies may include the condition of applying the external cue only to the weaker limb. Since the use of external attentional focus can boost the SLCMJ performance, it is speculated that the “asymmetric” application of external focus on the weaker side may potentially minimise the IA.
Read CV Mavis, Nga Ting LaiECSS Paris 2023: CP-BM07