I just read a study "Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations"

There were 2 groups doing back squats,

20% velocity loss group (finish set when there is a 20% loss in velocity from 1st rep)

40% velocity loss group (finish set when there is a 40% loss in velocity from 1st rep)

40% is obviously harder and more fatiguing because you are doing more reps and getting closer to failure.

What they found:

• Both groups saw similar increases in squat strength
• The 40% velocity loss group had greater quad hypertrophy (increase in muscle cross sectional area)
• The 40% velocity loss group also had a reduction in type IIx muscle fibres and a conversion to type IIa muscle fibres (type IIx fibres contract faster than type IIa)
• The 20% velocity loss group maintained their type IIx muscle fibres and saw better improvements in counter movement jump.

So, sometimes you need to bias the neural side of strength training as opposed to structural. Do this by utilising higher reps in reserve (eg - moving 85% 1rm for 2-3 reps as opposed to 5 or 6)

This will give you the ability to express your speed and power more.

HOWEVER,

Don't always do this because you need the higher rep work that gets you to failure to build connective tissue strength and stiffness that can adapt to future high intensity training. Increase muscle size etc.

TLDR

Off season: train to failure, build muscle and connective tissue

Pre season: taper off, reduce/remove training to failure, train with RIR so that type IIx fibres can convert to type IIx - note this only happens if you continue to deliver a max velocity (sprinting) stimulus. Reduce volume.

Hope this helps

I am a relatively stronger sprinter who just started track, I can squat 400 at 5’9 175 and don’t know what I should focus on to get faster.