My entire lifting career which spans 43 years or more, and with 27 year of competition I have only taken days off when I absolutely had to. I got my best all time results doing a more Conjugate style training where intensity was >90% and exercises were rotated. If you eat properly, train properly and rest adequately there is no need for a deload. If your CNS is burning out, you are doing something wrong with your training, rest and/or diet.
If you have to take a week off it is not going to kill you. It can be much harder on cardiovascular training though. When I was a strength coach my athletes also lifted all year round and kept the intensity >90, even through the season. We got stronger as the season instead of weaker. We even trained through all holidays. After the season ended we went through a General Physical Preparation (GPP) phase except for those going straight to powerlifting, but the intensity of the exercise was still very high in order to get the body prepared for the next phase which was off season. Only those who were injured did not participate until they were released by the doctor/trainer.
Gaining more from doing less? The effects of a one-week deload period during supervised resistance training on muscular adaptations
Background Based on emerging evidence that brief periods of cessation from resistance training (RT) may re-sensitize muscle to anabolic stimuli, we aimed to investigate the effects of a 1-week deload interval at the midpoint of a 9-week RT program on muscular adaptations in resistance-trained...
peerj.com
Conclusion
In conclusion, our findings suggest that a 1-week deload period at the midpoint of a 9-week RT program appears to
negatively influence measures of lower body muscle strength but has
no effect on lower body hypertrophy, power or local muscular endurance.
So a week off is not going to cause any significant muscle loss but may cause a loss in strength.
Most powerlifters took off a week before a contest from all heavy lifts and two weeks off for deadlift. I never took off a week and treated the contest as just another day in the gym. My second attempt was my last gym max and depending on how I got that I went up 5-10lbs over on the 3rd attempt. Again, with proper rest, and diet the body will adapt. Bulgarian lifters trained .
I remember Dr. Fred Hatfield telling me about how the Bulgarian team trained for a meet. The lifter trains up to a max each day; this could be a true max or it could be the max weight that can be lifted on that day. The lifter then may back off and work back up or drop down for some doubles with sub-maximum weights. This basic workout would be done several times a day in small increments. First would be squats followed by a break, then snatches followed by a break and finally clean and jerks. The afternoon would start with snatches, break, clean and jerks, break, and more squats. A third session later in the evening could be added if more work is needed. When lifters begin the training year, they may only reach 85%-90% of their best, but gradually as the year progresses they begin to lift closer to their true max more often. Also, at the beginning of the year they may only train once a day and then twice a day and then finally during the heaviest periods of training three times a day. As the major competition draws near (i.e. the World Championships) they begin to reduce the amount of training,
but continue to lift maximum weights. The total training time during the lighter periods would be approximately 3-4 hours a day and the training time during the heavy periods would be around 6-8 hours a day. This would include the breaks.
I remember asking Dr. Squat if it was truly possible to train heavy year round and up to three times a day. He said of course as long as you have plenty of rest and plenty of food, the body will adjust. Coaches like the late Louie Simmons have been claiming this for years with his Conjugate style training which can be accommodated for almost any style of resistance training.
With cardiovascular training, plasma volume can decrease by around 5% within the
first 48 hours of stopping training. VO2 max declines is due to reductions in blood and plasma volumes, which decrease by as much as
12% in the first four weeks after a person stops training. VO2 max falls sharply, back to pre-training levels, in
less than eight weeks.