Influence of maximal muscle strength and intrinsic muscle contractile properties on contractile rate of force development.

'Explosive' muscle strength or contractile rate of force development (RFD) is a term to describe the ability to rapidly develop muscular force, and can be measured as the slope of the torque-time curve obtained during isometric conditions. Previously, conflicting results have been reported regarding the relationship between contractile RFD and various physiological parameters. One reason for this discrepancy may be that RFD in various time intervals from the onset of contraction is affected by different physiological parameters. The aim of the present study was to investigate the relationship between voluntary contractile RFD in time intervals of 0-10, 0-20, ..., 0-250 ms from the onset of contraction and two main parameters: (1) voluntary maximal muscle strength and (2) electrically evoked muscle twitch contractile properties. The main finding was that voluntary RFD became increasingly more dependent on MVC and less dependent on muscle twitch contractile properties as time from the onset of contraction increased. At time intervals later than 90 ms from the onset of contraction maximal muscle strength could account for 52-81% of the variance in voluntary RFD. In the very early time interval (<40 ms from the onset of contraction) voluntary RFD was moderately correlated to the twitch contractile properties of the muscle and was to a less extent related to MVC. The present results suggest that explosive movements with different time spans are influenced by different physiological parameters. This may have important practical implications when designing resistance training programs for specific sports.