Author(s): BAKICI, D., CROSS, M.R.1, BRUGHELLI, M.1, JUKIC, I.1,2, Institution: AUCKLAND UNIVERSITY OF TECHNOLOGY, Country: NEW ZEALAND, Abstract-ID: 937

INTRODUCTION:
Flywheel resistance training is commonly used to enhance muscle strength, power, and the performance of athletic tasks. Where the extent of eccentric overload (EO) provided by traditional flywheel systems is variable and often difficult to induce, recently developed motorised flywheel systems may provide a more consistent stimulus. Therefore, this study aimed to quantify how inertial load and motorised versus non-motorised modes influence concentric and eccentric mechanical outputs in flywheel squats.
METHODS:
Twelve resistance-trained males (age 26.5 ± 5.40 years; one-repetition maximum back squat 1.70 ± 0.29 kg/body-mass) completed multiple sets of half-squats on a flywheel device under motorised (20% eccentric boost) and non-motorised modes across six inertial loads (0.025–0.15 kg·m²), following a randomised, within-subject, counterbalanced crossover design. Mean and peak power were recorded during concentric and eccentric phases using a linear position transducer and a strain gauge. For each variable, the eccentric-concentric ratio was calculated to characterise EO. Data were analysed using linear mixed-effects models, with differences between flywheel modes, across phases and inertias, quantified via comparisons of estimated marginal means (in raw units) supplemented with standardised effect sizes (Hedges’ g calculated with raw data).
RESULTS:
Compared to the non-motorised mode, the motorised mode produced significantly higher eccentric mean and peak power across all inertial loads (p < 0.001, mean power = 279 to 713 W vs 199 to 525 W; peak power = 833 to 2195 W vs 746 to 1552 W), except for peak power at lower inertial load (0.025 kg·m², p > 0.05), with differences between modes tending to increase in tandem to inertia in both mean and peak power (g = 0.29 to 2.40). The non-motorised mode elicited significantly greater concentric mean and peak power at higher inertial load ranges than the motorised mode (0.10-0.15 kg·m², p < 0.01, g= 0.55 to 0.90, mean power= 355 to 632 W vs 394 to 568 W; peak power = 925 to 1569 W vs 969 to 1340 W). Notably, while concentric power peaked within the measured range, eccentric power in the motorised mode tended to increase continuously across the range of inertias. Regarding EO, motorised mode elicited stepwise increases in ratios for both mean and peak power (p < 0.001, mean power EO ratio = 0.79-1.46; peak power EO ratio = 0.98-1.85), whereas the non-motorised mode showed significant increases in eccentric-concentric ratios only for mean power (p < 0.05, EO ratio = 0.65-0.89).
CONCLUSION:
Motorised flywheel systems provide a superior eccentric stimulus compared to traditional non-motorised flywheels, substantially increasing EO across a range of inertial loads. These findings have important implications for eccentric-focused training prescription, although the translation of these acute mechanical advantages into long-term performance adaptations requires further investigation.