If you looking for that explosive start, leg drive, knee lift, top end speed and stride frequency out of the starting block then resistant training is your best choice. At practice I use SpeedSac Sled weights training to help build explosiveness out of the starting block, leg drive and stride frequency.
The SpeedSac comes with three sand bags that hold about 10LB of sand each. You can use the weight that is best for the sprinter’s needs or what he looking to achieve.
I’m using a 10LB sand bag in the sac for the past two to three weeks and I’m seeing some serious improvements with speed with one of my sprinter. I’m seeing some aggressiveness at start and mid-way in the race.