Crashing Your Nervous System
No other lift is as devastating on the nervous system as the deadlift. Maxing out on the deadlift, or doing a high volume of heavy work, can negatively impact your subsequent workouts for an entire week. For that reason, training the deadlift hard every week might not be a good idea unless your nervous system is formidably resilient.
That's one of the reasons why guys at Westside Barbell rarely do a deadlift on max effort day (they mostly do squats or good morning variations). That's also why for traditional powerlifting peaking a lot of guys do their last heavy deadlift 10 days before a competition, while the last heavy squat can be done 7 days before, and the last heavy bench 5 days before the meet.
Trashing yourself on the deadlift, while satisfying, can drastically decrease your performance on your next few sessions. Remember, the key to maximum gains is how many good workouts you have. If you get two or three less solid workouts per week just to get one that's at a higher level, you won't benefit in the long run.
Why is the deadlift more demanding on the nervous system than a squat? After all, both use a similar amount of muscle mass. There are a few possible explanations and the truth is likely a combination of them:
1 The deadlift challenges your grip strength.
The first sign of a fatigued CNS is a drop in grip strength. So it's logical that everything that pushes your grip to its limit would also dramatically increase the neural demands of an exercise. On a side note, using straps when deadlifting does decrease the neural demands of the exercise and allow you to do more volume of heavy work or more frequency.
2 The deadlift provides greater axial loading.
There's more loading of the spine (axial loading), than even a low-bar squat. This is mostly true for a conventional deadlift; a sumo deadlift provides a lot less spinal loading. The spine being the key area for neural transmission, when it's "threatened" there's a much more important stress response and the nervous and hormonal systems are pushed much harder to resist to that stress.
3 The deadlift starts from a dead start.
Doing an exercise from a dead start instead of benefiting from a preparatory eccentric phase makes the beginning of the movement much harder. The nervous system has to activate the muscles more since you can't take advantage of the stretch reflex to get the weight moving.
4 Most people deadlift more weight than they can squat.
We're talking about 10-30% more in most cases. I'm talking about raw lifting, not using a squat suit and knee wraps, which help the squat a lot more than the deadlift and can give you false ratios. Of course, you lift more weight in the deadlift than in the squat because of leverage reasons, but also because more muscles are involved. More weight equals more neurological demands. It also means more stress on the skeletal and hormonal systems. All of these to make the deadlift more systemically demanding.
5 It's easy to have a successful deadlift with horrible technique.
In a squat, if you start to get out of the groove, you won't be able to make that lift. On a deadlift, if the bar moves forward or if you lose your lower back tightness, for example, you'll often be able to make the lift by grinding the bar up from sheer willpower. These reps are killers for the nervous system. Maxing out often like this will only hurt your training. And unless you're a world class powerlifter, nobody cares.
The deadlift is better trained with submaximal weights (75-85%) with a strong focus on using optimal technique and maintaining muscle tension and perfect position on every rep... and using assistance work to get the back, glutes, and legs stronger.
If you work on your deadlifting technique and get the involved muscles stronger via less traumatizing exercises, your deadlift will still get a lot stronger without negatively affecting the rest of your training week.