Abstract
PurposeThe force–velocity relationship of muscular contraction has been extensively studied. However, previous research has focussed either on isolated muscle or single-joint movements, whereas human movement consists of multi-joint movements (e.g. squatting). Therefore, the purpose of this study was to investigate the force–velocity relationship of isovelocity squatting.MethodsFifteen male participants (24 ± 2 years, 79.8 ± 9.1 kg, 177.5 ± 6 cm) performed isovelocity squats on a novel motorised isovelocity device (Kineo Training System) at three concentric (0.25, 0.5, and 0.75 m s−1) and three eccentric velocities (− 0.25, − 0.5, and − 0.75 m s−1). Peak vertical ground reaction forces, that occurred during the isovelocity phase, were collected using dual force plates (2000 Hz) (Kistler, Switzerland).ResultsThe group mean squat force–velocity profile conformed to the typical in vivo profile, with peak vertical ground reaction forces during eccentric squatting being 9.5 ± 19% greater than isometric (P = 0.037), and occurring between − 0.5 and − 0.75 m s−1. However, large inter-participant variability was identified (0.84–1.62 × isometric force), with some participants being unable to produce eccentric forces greater than isometric. Sub-group analyses could not identify differences between individuals who could/could not produce eccentric forces above isometric, although those who could not tended to be taller.ConclusionsThese finding suggest that variability exists between participants in the ability to generate maximum eccentric forces during squatting, and the magnitude of eccentric increase above isometric cannot be predicted solely based on a concentric assessment. Therefore, an assessment of eccentric capabilities may be required prior to prescribing eccentric-specific resistance training.
Highlights
The force–velocity (F–V) relationship defines an important dynamic property of muscle contraction (Alcazar et al 2019; Fenn and Marsh 1935; Hill 1938)
It is theorised that if it were not for these neural factors, the eccentric joint moment would be ~ 60% greater than typically observed (Pain and Forrester 2009). Due to these neural constraints and the variability of their effect, F–V relationships must be established in vivo so that the complexity of co-ordinating human movement may be considered, rather than relying on ex-vivo measurements, before eccentric loading recommendations for applied training can be made
The group mean force during isovelocity squatting conformed to the expected in vivo F–V profile, with the maximum force 1.095 times greater than isometric, which was recorded during the highest velocity eccentric trial (− 0.75 m s−1) (Fig. 4)
Summary
The force–velocity (F–V) relationship defines an important dynamic property of muscle contraction (Alcazar et al 2019; Fenn and Marsh 1935; Hill 1938). It is theorised that if it were not for these neural factors, the eccentric joint moment would be ~ 60% greater than typically observed (Pain and Forrester 2009). Due to these neural constraints and the variability of their effect, F–V relationships must be established in vivo so that the complexity of co-ordinating human movement may be considered, rather than relying on ex-vivo measurements, before eccentric loading recommendations for applied training can be made
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