Author(s): DE BLAS FOIX, X., PADULLÉS, X., IBAÑEZ, M., Institution: FPCEE-BLANQUERNA, UNIVERSITAT RAMON LULL, Country: SPAIN, Abstract-ID: 2607

INTRODUCTION:
Rotational inertia resistance machines or flywheels (IM) have proven to be a highly efficient method for strength training. The resistance of an IM varies according to three parameters: the mass distribution of the flywheel in the inertial machine (determined by the number of counterweights), the multiplier (number of moving pulleys used) and the rope winding diameter (constant in cylindrical machines and variable in conical machines). This versatility poses a problem in exercise prescription because athletes are provided with different IM configurations without often knowing whether one configuration provides more resistance than another. A unified and intuitive parameter is proposed for prescribing the load in physical exercise with inertial machines: equivalent mass (EM) widely used in other contexts as in vehicle mechanics.
METHODS:
The Squat-type IM (NESS Three) was connected to a low-friction pulley (at a height of 2.25 m) using a non-elastic rope with a diameter of 6 mm. Weight discs of 2.5, 5, 10, 15, 20, and 25 kg were dropped for the following counterweight configurations: 0, 2, 4, 6, 8 (n=30). Knowing the material properties and dimensions of the flywheel, the flywheel of this IM was modelled in Solid Works v.2014 to calculate the moment of inertia (0.0580 kg/cm2). After measuring the rope winding diameter (0.04 m), the mass and geometry of the counterweights (0.440 kg) and their distance from the axis of rotation (0.143 m), these values were entered into the Chronojump v.2.6.0 software and the accelerations of the falling discs were measured. A Chronojump rotary encoder was used to measure the rotation of the flywheel with a sampling frequency of 1 kHz. From this capture, spline smoothing (spar: 0.7) was performed and the average acceleration in 0.5 s in the stable central section was extracted. This measured acceleration (MA) was compared with the theoretical acceleration (TA) calculated from the ME using an analogue physical system that transforms the circular motion system of the inertial machine and its moment of inertia into a linear system, whose displaced mass would correspond to said EM. The data were analysed using Pearson's correlation and Bland-Altman's test in R v.4.5.0.
RESULTS:
The correlation between both accelerations MA and TA is high (r=0.9910 p<0.001). The Bland-Altman analysis showed an average bias of 0.0509 (95% CI: 0.0223 to 0.0796), with a lower limit of agreement at 95% between -0.1492 and -0.0500 and an upper limit between 0.1519 and 0.2511.
CONCLUSION:
EM appears to be a valid, unified and potentially applicable indicator for standardising IM training prescriptions. A research line has been initiated that will continue with other studies that will include the remaining parameters: use of mobile pulleys, variation in the diameter where the rope is wound (conical machines), as well as the evaluation of a growing set of machines from different manufacturers.