Jeremy – I found a significant relationship between total horizontal impulse (i.e. front and back) and block POWER (I used block power as the outcome variable, as opposed to block velocity), with an r value of 0.87, and and r squared value of .76 (i.e. horizontal impulse accounted for 76% of horizontal block power). This allowed me to conclude that horizontal impulse was a strong predictor of block power. I could then determine the correlations between rear foot and front foot peak force values and horizontal block power. The correlations here were 0.55 for front foot (insignificant) and 0.77 (significant to p<0.001). I hope that answers your question, but I am happy to answer more!
Brooke – I speculated in my discussion as to the reasons elite sprinters utilised to back block more. My possible ideas were:
* They had stronger hip extensor muscles, and so could produce more force
* They had received better coaching, and so their block positioning allowed greater use of the back block (studies have looked at the distance between the bloc pads and the effect on start velocity – better athletes may have had better block spaces)
* Better athletes have better neuromuscular control and/or type IIb fibre type percentage, and so can produce force much quicker than poorer athletes (this would be important as the back foot leaves to block pad relatively quickly, whereas the front food is in contact for a lot longer!)
If anyone else has any questions I will try to answer them, but I did this study two years ago, so it isnt completely in the front of my mind!