I would assume that this is a combination of mental and physical issues.
9/10 recreational lifters completely alter their lifestyle for weeks that they do not train, without really knowing what they are doing to themselves. It is as if they subconsciously say to themselves "If I am not working out..., then there is no reason for me to be on my normal structured schedule." So they alter their lifestyle to something that barely resembles what is required to support physical progress. Common mistakes are as follows:
1 - You eat less. This is a combination of your appetite decreasing (due to a decrease in daily/weekly caloric expenditure), and the fear of "getting fat if I eat all that food when not working out." A HUGE, HUGE, HUGE, mistake.
2 - You drink less fluids. Since you are not as active, you inadvertently decrease your daily/weekly net water loss (less sweating), therefore you don't "feel thirsty." Again..., this is a huge mistake.
3 - You sleep less. Most treat their week(s) off as a bit of a "vacation" so to speak, so they go out with friends, stay up playing video games, or watch TV until the wee hours of the morning. Some just can't sleep because they have too much energy due to lack of caloric output. Disrupting your Circadian Rhythm is a huge bodybuilding no no.
The combination of these common mistakes cause a complete reversal of three important aspects of your lifestyle. So..., your body panics, and tries to adjust to the new environment. When you go back to the gym, your body will be in a quite lower state of hydration (not exactly dehydrated, your body just has a new homeostatic level of hydration lower than when you were training regularly.) Since hydration and glycogen stores have a directly proportional relationship, your will be training with depleted glycogen stores. The alteration to eating habits also lead to this physical adaptation.
Inadvertently forcing your body to adapt in the opposite direction like this is quite common for "normal weight lifters" and will no doubt make you "weaker" in your lifts. HOWEVER..., this sudden weakness is more likely due to lowered metabolic reserves, as I described above, than musculoskeletal atrophy. It would take longer than 7 days to cause substantial atrophy of skeletal muscle unless you went to the extreme, as one bro mentioned already.
When you go back to the gym, you will have the attitude that "this always happens to me after a layoff," so subconsciously you have already convinced yourself that you will be weaker before you even walk in the door. So forget about any fight or flight response, because you will be mentally passive and insecure.
So if you were my client, your caloric intake would remain the same during your off week, but I would manipulate your macros a bit to control the release of insulin. I would also increase your water intake to support formation of new glycogen stores. Extra vitamin C, E, B-complex, and Beta Carotene should be taken to lower free radicals, which will encourage faster healing. And an additional 1-2 hours of sleep per night.
The bottom line in ALL bodybuilding endeavors is placing the body in the PROPER ENVIRONMENT to allow favorable adaptation to take place. If you are not sure of what that entails, you might want to get someone to help you along. We all started at the bottom, so we all had to learn this craft from someone or somewhere. I hope this helps. Good luck to you bro.
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