The Effect of Flywheel Inertia on Peak Power and Its Inter-session Reliability During Two Unilateral Hamstring Exercises: Leg Curl and Hip Extension

Abstract

This study investigated the effect of flywheel moment of inertia (0.029, 0.061, and 0.089 kg·m2) on concentric and eccentric peak power and eccentric:concentric peak power ratio during unilateral flywheel leg curl and hip extension exercises. Moreover, the inter-session reliability of peak power was analyzed during both exercises. Twenty amateur male soccer athletes attended five visits—performing three sets of eight repetitions of either unilateral leg curl or hip extension (all three moments of inertias) during each visit. For the unilateral leg curl, there were no differences in any measure between moments of inertia (p = 0.479) but a higher eccentric than concentric peak power for all moments of inertia (p < 0.001). For the unilateral hip extension, differences between moments of inertia were reported for all measures (p < 0.05). Specifically, the lowest moment of inertia elicited the greatest concentric peak power (p = 0.022), there were no differences with the medium inertia (p = 0.391), and the greatest moment of inertia obtained the greatest eccentric peak power (p = 0.036). Peak power measures obtained acceptable to excellent reliability while the eccentric:concentric ratio reported unacceptable to good reliability for both exercises. A variety of moments of inertia can elicit high eccentric knee flexor demands during unilateral leg curls, whereas higher moments of inertia are needed to achieve an eccentric-overload in peak power during hip extensions. Different exercises may have different inertia-power relationships. Concentric and eccentric peak power measures should continue to inform training, while the eccentric:concentric ratio should not be used.

Concentric Phase Assistance Enhances Eccentric Peak Power During Flywheel Squats: Intersession Reliability and the Linear Relationship Between Concentric and Eccentric Phases

“…The eccentric:concentic ratio reliability ranged lower (ICC = 0.54-0.66) relative to concentric and eccentric peak power outputs (ICC = 0.70-0.89) using moments of inertia that are typically prescribed in practice (0.025 -0.075 kg•m 2 ) 17 . A similar trend was reported with unilateral hamstring exercises 24 . It remains unknown how incorporating the upper limbs during the flywheel squat would impact reliability of mechanical outputs, and if the eccentric:concentic ratio can be reliably utilised, particularly given the increased movement complexity during the assisted squat.…”

“…Although this study reports acceptable to good reliability estimates for assisted and unassisted eccentric:concentic ratios (albeit with relatively greater uncertainty), the use of ratios remains a debated topic 29 . Previous studies report that the E:C ratio are not as reliable as its peak power components 17,24 . Specifically, in the present investigation, the use of the E:C ratio remains questionable due to its lower reliability in comparison to peak power values and its inability to discern higher and lower peak power outputs 24 .…”

“…Previous studies report that the E:C ratio are not as reliable as its peak power components 17,24 . Specifically, in the present investigation, the use of the E:C ratio remains questionable due to its lower reliability in comparison to peak power values and its inability to discern higher and lower peak power outputs 24 . A bias towards smaller values may deceive practitioners when using the E:C ratio.…”

“…The reliability of flywheel training measures can also affect the ability to monitor and prescribe training, and so must be investigated. The effects of altering moment of inertia on reliability of open 23,24 and closed 17,25 kinetic chain exercises have recently been investigated. For the flywheel squat, the reliability of concentric and eccentric peak power has previously been rated acceptable to excellent 15,26 , while the eccentric:concentric (E:C) ratio has been rated poor to questionable 17 .…”

Perception and use of flywheel resistance training amongst therapists in sport

“…In contrast to the theory that a greater evidence base guides exercise selection, a great deal of therapists would prescribe the Romanian deadlift, unilateral leg curl, and upper body rotational exercises ( Figures 4 , 5 ). Therapists would utilise such exercises even though very limited evidence is available regarding such lower body flywheel exercises ( 33 – 35 ). The present study is the first to investigate the use of upper body flywheel exercises amongst therapists, reporting that almost all therapists would use rotational exercises while fewer would consider unilateral pull and push exercises ( Figure 4 ).…”