Determining concentric and eccentric force-velocity profiles during squatting

Abstract

Purpose: The 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.

Methods: Fifteen 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).

Results: The 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.

Conclusions: These 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.

Keywords: Assessment; In vivo; Isovelocity; Multi-joint.

Fig. 1

Kineo Training System; participant is connected to an electric motor via a hip/shoulder harness attached to a cable pulley system. A The start of the eccentric phase/end of concentric phase, B the end of the eccentric phase/start of the concentric phase. Two additional force plates, one under each foot, where added to this experimental setup (not shown) to measure vertical ground reaction forces (N)

Fig. 2

Schematic of concentric isovelocity squatting trials. A Start position, B submaximal eccentric squat to parallel squat depth, and C maximal effort concentric squat. Arrows represents direction of movement, solid-black arrow denotes maximum effort trial that is recorded for data analysis

Fig. 3

Schematic of eccentric isovelocity squatting trials. A Start position, B submaximal eccentric squat to parallel squat depth, C near-maximal concentric squat to full hip/knee extension to preload, and D maximal effort eccentric squat. Arrows represents direction of movement, solid-black arrow denotes maximum effort trial that is recorded for data analysis

Fig. 4

Group mean ± SD force–velocity relationships of isovelocity squatting. A Vertical ground reaction force (N). B Normalised force relative to isometric. Concentric velocities are +ve, eccentric velocities are -ve

Fig. 5

Force–velocity relationship from isovelocity squatting in A sub-group of participants that did not achieve an eccentric force increase (normalised eccentric force ≤ 1.0) (n = 4) and B sub-group of participants that did achieve an eccentric force increase group (normalised eccentric force > 1.0) (n = 11)

Fig. 6

Scatter plots showing A positive linear correlation between concentric force and eccentric force at − 0.75 (P = 0.036), − 0.5 (P = 0.001), & − 0.25 m s⁻¹ (P = 0.002). B No correlation between concentric force and normalised eccentric force (P = 0.19–0.757)