When deciding on strength and conditioning programs there are several elements to consider. Overload, progression, specificity, variation, individuality, diminishing return, reversibility. There are many programs that hit the mark, but there are far more that don’t. Exercise selection is only one factor involved in creating an optimal program. Randomly generated workouts certainly can make a you tired, but unfortunately often fail at providing continuous muscular adaptation.
Principle of Overload
Essentially if you want to get stronger or make the muscle grow, you need to provide enough stimulus to that muscle to cause micro tears as well as central nervous system adaptations. When this happens the bodies, natural response is to repair, and reinforce that muscle, thus making you get bigger and stronger.
Basically, if your putting minimal effort into your workout you can expect little progress.
Progression
Essentially, as you get stronger lifting the same weight day in and day out will stop generating progress. It is necessary to lift heavier weight, or add more repetitions each session, week or training cycle (depending upon your level of experience).
We need to build upon every workout in order to progress
Specificity
Training with specificity refers to when you want to improve your performance in a certain skill, you must train that that skill.
In other words, if you want to squat alot, you have to squat alot.
Variation
minor changes in training can results in greater adaptations. Variations in intensity, volume, as well as exercise should be used throughout your macro cycle (monthly or yearly training plan). This will produce greater and more well-rounded adaptations/gains over time.
Not to be confused with "muscle confusion" where workouts are constantly changing.
Variation and specificity go hand in hand. It is best to change things up every few months, or in some instances every few weeks
Try a back-squat routine for 3 months, then switch it to front squats to ensure continuous progress.
Individually
people train at different rates. This can be a result of age, sex, race, nutrition, genetics, as well as sleep.
It is important to train at your experience level.
The training plans top athletes use today are not the plans that got them to that level.
Create a strong foundation and build upon it
Diminishing Returns
As you become fitter and stronger you will ultimately need to train harder for smaller increases in muscular size and strength.
A beginner lifter who is overweight can easily lose fat, build muscle and acquire loads of strength and endurance. However, as they become more advanced fat loss slows, muscle building slows, and setting personal records begins to take a lot more time.
It is easy to become discouraged at this time, but when this happens it is the perfect time to change up training. Either by adding periodization, or swapping out exercise selection to work on weak points.
There is no real plateau, just reality. Size and strength take time.
Embrace training
Reversibility
"Use it or lose it'
Your body will always adapt to its needs. If you no longer need to be fit and strong your body will not maintain that level, and you will begin to regress.
Generally, 10% of cardiovascular performance will reduce per week, strength begins to reduces after about 2-3 weeks, as well as muscle mass.
Fortunately, it is easier to build back fitness than it is to acquire new levels of fitness