Determining concentric and eccentric force-velocity profiles during squatting.

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.

Fasted Exercise and Increased Dietary Protein Reduces Body Fat and Improves Strength in Jockeys.

The present study assessed the effects of a diet and exercise intervention in jockeys on body composition, metabolism, bone and mental health. 10 jockeys followed an individually prescribed 6-wk diet (Carbohydrate=2.5-3.5 g/kg, Protein=2.5 g/kg, Fat=1.0 g/kg). Body mass (59.2±4.6 vs. 57.6±4.5 kg), fat mass (7.5±3.5 vs. 6.2±2.6) and body fat (13.1±5.9 vs. 11.5±4.9%) all decreased (P<0.05) from pre to post-intervention whilst lean mass (47.1±5.3 vs. 47.0±5.5 kg) was maintained (P=0.80). RMR (1703±329 vs. 1975±313 kcal.d(-1)), VO2max (3.8±0.8 vs. 4.1±0.7 L/min(- 1)) chest strength (65±11 vs. 71±13 kg), leg strength (160±28 vs. 175±29 kg) and jumping height (40±6 vs. 48±5 cm) significantly increased (P<0.05). Bone health (DXA) did not change (P>0.05) at hip (-1.04±1.29 vs. - 0.76±0.71) or lumbar sites (-1.32±0.76 vs. - 1.31±0.77). Psychometrics (GHQ-12 and EAT-26) remained unchanged (10.3±4.3 vs. 8.9±3.8 and 14.8±9.6 vs. 11.0±5.6, P>0.05, respectively). This approach represents a marked difference from jockeys' habitual weight-making that largely involves dehydration and food deprivation.