You can actually train for increased explosiveness using those machines. Just do light weight, high reps. And make your reps quick (but still controlled). Twice as long retracting as contracting because that's where you build most of your muscle.
But as far as my knowledge goes, you're fine, as long as you train them right. Look into "fast-twitch" muscle fiber. Find some good exercises under that umbrella, and you'll be good to go.