Ja Yeon Lee

Hip Lock, a coaching construct for single-leg actions, comprises stance-side hip co-contraction for pelvic stabilization and free-side pelvic elevation, but how task strategies influence these components remains unclear. This study examined which combination of foot-contact and upper-limb strategies strengthens both components. Thirty healthy young men performed a single-leg extension task under four conditions combining foot-contact strategy (flat-foot vs. heel-raised contact) and upper-limb strategy (arm restriction vs. free arm use). Three-dimensional kinematics, surface electromyography, and ground reaction force were recorded, and 25 variables were analyzed using two-way repeated-measures analysis of variance with false discovery rate correction. Frontal-plane hip co-contraction was higher with flat-foot contact (η²p = 0.31) and extensor–flexor hip co-contraction was higher with free arm use (η²p = 0.31), whereas free-side pelvic elevation was greater with heel-raised contact (η²p = 0.52) and was not reduced by arm use. No interaction remained significant after correction. Pelvic elevation was greatest under heel-raised contact with free arm use (17.4 ± 4.9°). Thus, foot-contact strategy shifted the emphasis between stabilization and elevation, whereas arm use increased co-contraction without compromising elevation. These preliminary findings suggest that heel-raised contact with free arm use may serve as a candidate condition for future Hip Lock training studies.

Background: Elastic barbells generate continuous, unpredictable perturbations through elastic deformation of the bar, delivering a top-down instability stimulus that transfers from the upper to the lower limbs. Whether repeated exposure produces training-related changes in muscle activation, and whether any postural control gains transfer to an untrained movement condition, remains unknown. Methods: Twenty-eight resistance-trained men (mean age 22.8 ± 1.6 years; experimental group (EG) 23.4 ± 1.4, control group (CG) 22.3 ± 1.7) were randomly assigned to train with an elastic barbell (EG, n = 14) or an inelastic barbell (CG, n = 14). Both completed an identical progressive unilateral leg training program twice weekly for 12 weeks (20–40% of one-repetition maximum). Pre- and post-intervention measures were the Y-Balance Test (YBT), centre of pressure (COP) displacement during single-leg deadlift (SLDL), and surface electromyography (%RVC) of seven trunk and lower-limb muscles across three lifting speeds. Data were analyzed with mixed-design ANOVA (α = 0.05). Results: The EG showed greater gains in dynamic balance; the post-intervention YBT composite score was significantly higher in the EG (102.55 ± 6.22%) than in the CG (90.65 ± 12.95%; Group × Time F(1, 26) = 7.25, p = 0.012). A significant Group × Time interaction for COP under the untrained inelastic barbell task (anterior–posterior F(1, 26) = 8.86, p = 0.006; medial–lateral F(1, 26) = 5.61, p = 0.026) indicated task-specific transfer of postural control. The semitendinosus was the only muscle with a significant Group × Time interaction in both barbell tasks, with activation decreasing in the EG and increasing in the CG. Conclusions: Elastic barbell training improved dynamic balance and altered lower-limb muscle activation more than inelastic barbell training, and the postural control benefit transferred to the same task performed with an untrained barbell. Because injury outcomes and motor-unit behaviour were not assessed, injury outcomes were not assessed; any application to injury prevention remains a hypothesis for future investigation.

Background: Achilles tendon viscoelasticity and ankle neuromuscular co-contraction are functionally linked, yet how they jointly adapt during brief high-speed repetitive loading remains unclear. We simultaneously quantified Achilles tendon viscoelasticity (MyotonPRO) and ankle agonist–antagonist co-contraction (surface electromyography, sEMG) under two stance conditions and three repetition counts. Methods: Twenty-seven active male collegiate American football players (23.19 ± 2.63 years) performed rapid heel-raise/landing cycles in a bilateral ground stance (BGS) and a unilateral box stance (UBS) at 1, 5, and 10 repetitions. Tendon decrement (D), stiffness (S), and tone (F), the co-activation index (CoAct), and the co-contraction index (CCI) were analyzed using two-way (2 × 3) repeated-measures ANOVA. Results: D decreased significantly as repetitions increased (pooled across stance conditions: 1 rep 0.973 → 10 reps 0.937; F (2, 52) = 4.68, p = 0.014, ηp² = 0.153), indicating improved elastic-recovery efficiency, whereas S and F remained stable. CoAct was maintained constantly at ≈72% regardless of stance or repetition (all p > 0.05), and the medial gastrocnemius was consistently activated first (agonist-led feedforward priming). Tissue-level elastic adaptation thus occurred without a concurrent change in neuromuscular co-contraction—a tissue–neural dissociation confirmed in both change scores and correlation structure. Conclusions: Acute enhancement of Achilles tendon elasticity during high-speed repetition appears to be a peripheral, tissue-level mechanical phenomenon expressed independently of neuromuscular co-contraction. Combined myotonometric–sEMG assessment reveals functional information not captured by imaging alone.

Maintaining lower-limb joint stability is essential for safe and efficient performance during landing and directional changes. This pilot study examined the effects of a 10-week perturbation-based Dynamic Stability Training (DST) program using an inertial water load on lower-limb joint moments during single-leg landing and a 3-s stabilization phase following a 90° cutting maneuver. Fifteen healthy young men completed DST twice weekly. Three-dimensional motion capture and force-plate data were collected at pre-, mid-, and post-training to compute hip, knee, and ankle joint moments. During landing, hip flexion and abduction moments increased, whereas knee abduction moment decreased. During the stabilization phase, hip flexion, hip rotation, and ankle abduction moments decreased, while knee abduction moment increased. These joint-specific changes suggest potential adaptations in frontal- and transverse-plane control when training with unstable inertial water loads; however, interpretations should remain cautious given the exploratory design and absence of a control group. Larger randomized controlled trials are needed to confirm these preliminary findings.

Objective: Head-to-head evidence comparing closed-kinetic-chain (CKC) and open-kinetic-chain (OKC) training on balance in middle-aged women with knee osteoarthritis (KOA) is limited. Purpose: To compare 10-week hip abduction/external rotation-focused CKC versus OKC on static and dynamic balance. Methods: Twenty-two women with KOA were randomized to CKC (n = 11) or OKC (n = 11) and trained twice weekly for 10 weeks. The primary outcome was the center of pressure (COP) during single-leg stance (AP/ML range, excursion, velocity, and RMS); the secondary outcome was the Y-Balance Test (YBT) composite score. Results: CKC produced significant within-group reductions across all COP variables and significant YBT increases for both affected and unaffected limbs (p < 0.05). OKC showed only small changes in select COP indices and no meaningful change in YBT. Post-intervention between-group comparisons consistently favored CKC for AP/ML and total COP excursion/velocity and for the YBT composite score (p < 0.05). Conclusions: Under weight-bearing conditions, a hip-focused CKC program that promotes multi-joint coordination and co-contraction yields broader and more consistent improvements in postural stability and dynamic balance than OKC in middle-aged women with KOA. These findings support prioritizing CKC when rehabilitation aims include gait and functional stability.

Background/Objectives: This study investigated the effects of dynamic stability train-ing using inertial water load on lower limb joint moments and postural control during landing and directional changes. Given the high biomechanical demands of transition-ing from the non-dominant to dominant leg, we examined whether perturbation-based training could enhance neuromuscular control and movement efficiency. Methods: Twenty-six healthy males in their 20s were randomly assigned to an experimental group (n = 13), performing water-filled bag training for 10 weeks, or a control group (n = 13) with no training. Participants completed a landing followed by a 90° cutting maneuver, with joint moments measured via a 3D motion capture system. Analyses were con-ducted for the landing and change-of-direction phases. Results: In the landing phase, group differences were observed in hip, knee, and ankle moments, particularly in the frontal and transverse planes (p < 0.05), but none remained significant after Bonferroni adjustment. The experimental group generally showed lower hip flexion/extension (Hip Moment X) and greater knee and ankle internal/external rotation moments (Knee, Ankle Moment Z). In the cutting phase, only knee abduction/adduction (Knee Moment Y) showed a significant time effect (p = 0.007), not surviving adjustment, with a trend to-ward improved frontal plane control. Conclusions: Ten weeks of water-filled inertial load training improved neuromuscular coordination, shock absorption, and postural control patterns, especially in frontal and transverse planes. Perturbation-based training may be a sport-specific strategy to enhance movement efficiency and reduce lower-limb injury risk during rapid directional changes.