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Is there any evidence that humans suffer muscle loss or inferior muscle growth when working out 7 days out of 7?

Or is the idea based on the evidence suggesting that growth happens during rest, thus common logic would assume not resting impairs muscle loss?

So, has it been tested?

  • What does working out mean? For some it's active recovery, for others it would be the most intense workout of their life. Why do you ask? – Raditz_35 May 18 at 22:13
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Yes. Biochemical changes that occur following the application of an exercise stimulus were originally investigated by Nikolai N. Yakovlev, his first paper on the subject being published in 1955. His discoveries led to the modern theory of super-compensation, which describes the process of stimulus, fatigue, recovery, and advancement (illustrated below).

The super-compensation cycle

Following a training stimulus, capacity is temporarily reduced at (1) before recovery begins at (2). Recovery is complete at the line between (2) and (3), then super-compensation begins at (3). During (3) and (4), capacity is greater than it was before the application of a training stimulus, and therefore the period during which want to train again. This is, of course, a conceptual model, but the biochemical processes associated with these stages is now well understood.

However, this does not answer your question directly, since the amount of muscle fibre damage resulting from any bout of exercise is so heavily dependent upon the volume, load, and focus on contraction.

Yes, it is theoretically possible to work out every day and still grow. Indeed, this is what physical labourers have always done, albeit with a statistically high rate of overuse and injury. However, this depends on the bouts of exercise being minor enough so as to allow us to fatigue, recover, and super-compensate within a space of less than 24 hours. Thus, our notion of what comprises an exercise bout has to reflect the low volume, limited eccentric contraction regimen that would make that possible.

I hope that makes sense.

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Great answer by POD, but I would like to throw in my two cents as well.

I would more lean to yes and no, and there is a reason. When working out, most people target specific muscle groups on certain days and have a cyclic routine throughout the week. If this is the case, in theory you won't be working out the same parts of your body everyday. So if your routine was like something below, you could target certain muscle groups while resting others.

Monday: Push, Tuesday: Pull, Wednesday: Legs, Thursday: Push, Friday: Pull, Saturday: Cardio and core, Sunday: Legs

However, I do suggest that you give yourself recovery time and do a 4-5 day-a-week routine. Your body builds better on a consistent plan, and staying consistent 4 or 5 days a week is a lot easier than 7 days a week.

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  • You are, of course, entirely correct. There are well-established norms as to the way most of us train, and what that training looks like (how much/many, how heavy, how often)—and those norms have already accounted for our need for recovery. But I interpreted the question as a hypothetical: Could we theoretically train every day? And that is possible if we bring the training volume down low enough, and avoid training regimen (in particular, excessive eccentric contraction) that has a high cost on our system. – POD May 19 at 0:41
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There is a program called Easy strength by Dan John and Pavel Tsatsouline that have you doing each exercise 2 sets x 5 repetitions 5 days a week. The important part here is to go really easy on each set (hence the name) in order to not accumulate much fatigue.

This program probably works slightly better than a 3 sets x 5 repetitions 3 days a week program. The reason is probably that frequent practice causes more of some not yet understood neural adaptation.

For most people training 3 x a week is more practical than 5 x a week. However for some people such as firefighters, police officers and military personell, high frequency training may be better. The reason is that with this style of training you are never really badly fatigued in case you eg have to run after a criminal. The same thing may be harder to do the day after 3 or 5 sets of 5 reps almost to failure squats.

Also there is a other model of stimulus and recovery named the fitness-fatigue model: enter image description here

In this model you are getting stronger from immediately after your workout. However the increase in fitness is masked by fatigue so that the performance is worse until you have recovered from the fatigue.

From the link above: "Without the fitness-fatigue model, we could easily fall into the trap of believing that the fitness adaptations to a workout only occur after a couple of days, because of the reduction in performance. In fact, adaptations probably occur very soon after the workout itself. For example, in strength-trained lifters, a large proportion of the adaptations in the central nervous system after a strength training workout occur on the same day as the workout. Also, muscle growth is stimulated by a transitory increase in the rate of muscle protein synthesis that is already falling before 24 hours have passed." This tells us that the fitness-fatigue model is slightly more correct but still a gross oversimplification.

I think both super-compensation and fitness-fatigue are just conceptual models made to fit what has been observed in practice. From what I understand Yakovlevs experiments were on glucose concentration in muscle cells. The jump from supercompensation of glucose to a general theory of training and recovery is so big that I would say that neither model really have any experimental basis or mechanism behind it.

In practice I think the super-compensation model is generally more useful. It visually illustrates what an athlete must know: you must allow for sufficient time to recover after training. On the other hand you must repeat training sufficiently soon before the super-compensation fades.

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  • Never met anyone who gets tired from 5 sets of 5 reps up to the next day and I always trained in public gyms... – user33290 May 20 at 20:24
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    Yes, Yakovlev's study on glycogen was where the term was coined. However, he subsequently did a huge amount of research on the biochemical mechanisms of stimulus, fatigue, and recovery, encouraged largely by the early work of Hans Selye. The general model of super-compensation was essentially based on Selye's General Adaptation Syndrome (GAS) model, and on the general principles of stimulus, fatigue, and recovery described by Georgy Vladimirovich Folbort. (We could arguably accredit the model to Selye or Folbort, too.) – POD May 21 at 0:15
  • But the history of the model of super-compensation is just that, and it is now used as a general description of the observable phenomena associated with stimulus and recovery. It is important to understand that yes, it is conceptual, but yes, so is the fitness-fatigue model. And it is important to understand, also, that the fitness-fatigue and super-compensation models are not mutually exclusive; indeed, the former is just a modern adaptation of the latter. Both are useful if they are interpreted correctly, and both can be deleterious or dangerous if they are not. – POD May 21 at 0:21
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    Yes, the fitness-fatigue model is more complex, but the question I have is whether it really adds anything to our understanding. It is a matter of personal judgement, of course, but I find it rather contrived—you are fitter, but your fitness is masked by fatigue? Well, yes, but are you really fitter then? In the way that most people would understand fitness, I would argue not. All of this said, neither model is wrong; if they help us plan and balance our training to improve, they are useful. – POD May 21 at 0:40
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    @POD: Yes I agree. The super-compensation model is generally more useful. It visually illustrates what an athlete must know: you must allow for sufficient time to recover after training. On the other hand you must repeat training sufficiently soon before the super-compensation fades. The fitness-fatigue model is probably best suited for a really curious person or a research scientist. The problem with this model is that it still is not complex enough. It seems like but a stepping stone on the way to an even more complex model. – Andy May 21 at 5:52

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