Abstract
The purpose of the study was to compare the force outputs achieved during a squat exercise using a rotational inertia device in stable versus unstable conditions with different loads and in concentric and eccentric phases. Thirteen male athletes (mean ± SD: age 23.7 ± 3.0 years, height 1.80 ± 0.08 m, body mass 77.4 ± 7.9 kg) were assessed while squatting, performing one set of three repetitions with four different loads under stable and unstable conditions at maximum concentric effort. Overall, there were no significant differences between the stable and unstable conditions at each of the loads for any of the dependent variables. Mean force showed significant differences between some of the loads in stable and unstable conditions (P < 0.010) and peak force output differed between all loads for each condition (P < 0.045). Mean force outputs were greater in the concentric than in the eccentric phase under both conditions and with all loads (P < 0.001). There were no significant differences in peak force between concentric and eccentric phases at any load in either stable or unstable conditions. In conclusion, squatting with a rotational inertia device allowed the generation of similar force outputs under stable and unstable conditions at each of the four loads. The study also provides empirical evidence of the different force outputs achieved by adjusting load conditions on the rotational inertia device when performing squats, especially in the case of peak force. Concentric force outputs were significantly higher than eccentric outputs, except for peak force under both conditions. These findings support the use of the rotational inertia device to train the squatting exercise under unstable conditions for strength and conditioning trainers. The device could also be included in injury prevention programs for muscle lesions and ankle and knee joint injuries.
Highlights
Traditional free-weight exercise is the most common form of resistance training, utilizing resistance provided by gravitational force
No statistically significant differences were found between the stable conditions (SC) and unstable conditions (UC) for any of the loads in terms of mean and peak force (Fig 3) and displacement
Because there were no significant differences between force outputs under SC versus UC for any of the loads, nor any interaction between condition and load, the data were
Summary
Traditional free-weight exercise is the most common form of resistance training, utilizing resistance provided by gravitational force. The system differs from traditional free-weight forms of resistance exercise in that it generates resistance as a function of the mass, the distribution of the mass and the angular acceleration of the flywheel [2] during coupled concentric and eccentric actions [7]. This means that it offers gravity-independent resistance [2]. The use of the flywheel resistance method suggests that training elicits early, robust neuromuscular adaptations [7]
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