What improved my strength more than anything was Bulgarian style lifting, maximums everyday, I litterally increased my squat by 25kg in 4 weeks after a 2 year plateu, as soon as I went back to traditional methods, plateu again.
Now obviously this type of training is not suitable for use with sprinting, so a compromise must be made. What I found incredibly effective was two exercises per training session for 8 sets of 2 reps. When capable of completeing 8 sets of 3 then increase the weight. This was the system of training used by the legendary strongman Doug Hepburn. Example:
Monday: Squat: 90-95% x 2reps x 8sets
Bench: 90-95% x 2reps x 8sets
Chin ups: max reps x 1-3 sets
Wednesday: Deadlift or rack pull and bench press.
Friday: Squat: 90-95% x 2reps x 8sets
Bench: 90-95% x 2reps x 8sets
Hyperextension: 1 set x 5reps
Reverse hyper: 1 set x 5reps
Hyper complex: 1 set x 5reps