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Effects of Unilateral Leg Training Using Elastic and Inelastic Barbells on Dynamic Balance and Muscle Activation: A
Jihwan Jeong1, Jayeon Lee2, Chaekwan Lee2
1Department of Convergence Sports Instruction, Hwashin Cyber University, Busan 47558, Republic of Korea.
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.
