Assessment and Evaluation of Force–Velocity Variables in Flywheel Squats: Validity and Reliability of Force Plates, a Linear Encoder Sensor, and a Rotary Encoder Sensor

Abstract

Research into flywheel (FW) resistance training and force–velocity–power (F–v–P) profiling has recently gained attention. Ground reaction force (GRF) and velocity (v) during FW squats can be predicted from shaft rotational data. Our study aimed to compare the inter-set reliability of GRF, v, and F–v–P relationship output variables calculated from force plates and linear encoder (presumed gold-standard) and rotary encoder data. Fifty participants performed two sets of FW squats at four inertias. Peak and mean concentric and eccentric GRF, v, and F–v–P outcomes from mean variables during the concentric phase of the squat were calculated. Good to excellent reliability was found for GRF and v (ICC > 0.85), regardless of the measure and the variable type. The F–v–P outcomes showed moderate to good reliability (ICC > 0.74). Inter-measure bias (p < 0.05) was found in the majority of GRF and v variables, as well as for all the calculated F–v–P outcomes (trivial to large TEs) with very large to perfect correlations for v (r 0.797–0.948), GRF (r 0.712–0.959), and, finally, F–v–P outcomes (ICC 0.737–0.943). Rotary encoder overestimated the force plates and linear encoder variables, and the differences were dependent on the level of inertia. Despite high reliability, FW device users should be aware of the discrepancy between the measures.

Differences in Force-Velocity Profiles During Countermovement Jump and Flywheel Squats and Associations With a Different Change of Direction Tests in Elite Karatekas

“…These results opened some questions regarding the direct comparison of the F-v profiles due to the difference in the tempo of the motor task execution. Future studies should be focusing on the determination of the optimal methodology for comparing the F-v outcomes between CMJ and FW squats ( Spudić et al, 2021a ). Moreover, it was shown that previous experience in the use of FW devices influences mechanical squat performance ( Galiano et al, 2021 ; de Keijzer et al, 2022 ).…”

“…By means of an FW device, the method allows for significantly increased eccentric force demands compared to traditional resistance exercises ( Norrbrand et al, 2011 ; Smajla et al, 2021b ). Further, when performing an FW squat with delaying the braking action in the first third of the eccentric phase, greater eccentric than concentric peak force production can be achieved, which is known as an eccentric overload ( Tesch et al, 2017 ; Spudić et al, 2020 ; Spudić et al, 2021a ). It was previously found that, despite the full voluntary effort, neuromuscular activation of the quadriceps femoris muscle appears inhibited during slow and fast eccentric contractions ( Aagaard et al, 2000 ) due to tension-limiting mechanism specific to eccentric action ( Amiridis et al, 1996 ; Alcazar et al, 2019 ).…”

“…Participants performed squats on a custom-made FW device used in previous studies ( Spudić et al, 2020 ; Spudić et al, 2021a ; Smajla et al, 2021b ; Spudić et al, 2021b ). Based on previous findings we used four FW loading conditions for all participants: 0.025, 0.075, 0.225 and 0.25 kgm 2 ( Spudić et al, 2020 ).…”

“…Similarly, FW squat performance depends on the ability of athletes to make a quick transition from the eccentric to the concentric portion of the squat and therefore could be a representative measure of karate-specific movement pattern. This could be mainly due to the use of a harness, where only part of the additional load is applied to the trunk extensors ( Spudić et al, 2021a ) which are commonly a weak point when lifting heavy weights from a barbell squat.…”

“…In general, CMJ and FW squats are very similar in terms of kinematics, thus, higher associations between F-v outcome measurescould be expected than previously observed between jump and sprint or jump and hip thrust tasks. On the other hand, there are some differences between CMJ execution (full leg extension and maximal acceleration during the jump) and FW squats (reduction of acceleration before the full leg extension) in the execution and tempo of the motor tasks ( Spudić et al, 2021a ).…”