Do you really need warm-up sets before lifting?

Short answer

When testing your max, yes. In sets to failure at 80% of max, rep counts were the same with or without a warm-up, but max lifts were 8.4% higher when easy cycling was added to warm-up sets than with warm-up sets alone.

Do you really need warm-up sets before lifting?
'Skip the warm-up → less strength, more injuries' — does this formula hold?
Warm-up sets, adding weight bit by bit from the empty bar, take real time. People say skipping them costs strength and invites injury. Is jumping straight into working sets actually a loss? We checked the research step by step.
For high-rep sets, there was no difference
Same reps with or without a warm-up
15 people did bench press, squats and arm curls at 80% of their max, 4 sets each to failure. Across four conditions — no warm-up, warm-up sets, cardio, or both — total reps did not differ, and fatigue from set to set was the same.
But for a max lift, it was different
Adding easy cycling lifted 8.4% more
13 people tested their max leg press. Compared with doing only 2 warm-up sets (8 reps at about 50%, 3 reps at 70%), the day they first cycled easily for 20 minutes, their max was 8.4% higher on average.
A long, hard warm-up backfired
15 minutes of harder cycling cut the max by 4%
In a 16-person study, cycling easily for 15 minutes before the warm-up sets raised the max by about 3%. Cycling 15 minutes at moderate intensity instead lowered it by about 4%. Cycling for just 5 minutes was the same as not cycling.
Warm-up sets: heavy and few beats light and many
5 reps at 80% of the working weight worked best
15 people warmed up with 15 reps at 40%, 10 at 60%, or 5 at 80% of their working weight. The 80% x 5 day produced the most total work. In a 14-person squat study, 3 reps at 90% of max did not add reps over a usual warm-up.
What about injuries?
No trial saw more injuries, and 3 of 5 saw fewer
In 5 trials across various sports that looked at warming up and injury, warming up never increased injuries, and 3 of them found significantly fewer injuries. An analysis of 32 studies found performance improved after a warm-up in 79% of measures, with almost no sign of harm.
Bottom line: warm up for max lifts, short and focused
A few reps at 50-80% of the working weight is enough
For sets to failure at 80% of max, warming up did not change rep counts. For max lifts, easy cardio plus warm-up sets raised the max, while a long, hard warm-up hurt. 1-2 sets of a few reps at 50-80% of your working weight is enough.