ST works by creating microscopic tears in the muscle fibers, which then grow back stronger. But it takes time for this to happen, and most experts recommend resting 48-72 hours between ST sessions, which implies 2-3 times per week.
The key to strength training is genuinely challenging your muscles at close to their maximum potential. This means lifting heavy, and increasing the weight over time. Once you can do 12+ reps of an exercise, it is time to move up to a heavier weight/more challenging exercise. It is likely that you will have to shift up several times to maintain the degree of challenge.
In addition, it is a good idea to switch to a different routine every 4-6 weeks or so, to work a slightly different set of muscles. Some folks rotate exercises more frequently than this (eg. every workout), which is fine too.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.
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