Purpose: Drop sets are a great way to promote muscle growth, bust through plateaus and to enhance your training by stimulating your muscle fibers to adapt. Pretty much for a muscle to change and grow you have got to challenge it to the point that it has to change or it will die. That is what drop sets do.
Drop sets are just one of the options for this, and there is a reason why many bodybuilders swear by it: it works, it is safe (safer than most failure ideas) and it also allows for you to not sacrifice form (and hence isolation) in the acquisition of another rep.
Definition: Drop sets involve performing an exercise with a specific amount of weight at the start, then dropping the weight when you can no longer do reps with that weight (momentary failure). The process is repeated until absolute fatigue is reached in the muscle.
Why they work:
The pump from the high volume of work (enhanced swelling of the muscle for a transitory period) increases blood flow: which can assist with the trigger of the repair and re-boot process.
Increased use of the muscle causes it to remain slightly “pumped” and contracted for hours after the session has finished.
The extra volume fatigues the metabolism (depletion of glycogen and hence increase acidosis in the bloodstream: the result is the triggering of a repair response) as well as mechanical fatigue which promotes muscle growth. As you deplete more glycogen, you increase the muscles' ability to store more glycogen and hence you can increase the muscle volume.
The structural damage to muscle fibers from mechanical failure signals a repair process by increasing the production of satellite cells. When repaired the fibers can be greater in diameter: thicker fiber means more force, and you get stronger for the next session (given adequate rest and nutrition between sessions).
NOT SO FAST!
How to use drop sets: The preference for a drop set is on a machine (which is safer and controlled) and a close chain movement. When you are taking things purposefully to failure, it is time to ensure that the failure doesn't result in an X-ray! Furthermore, it allows for easy dropping in the weight by pulling the pin (and not literally dropping the weight: do each movement with proper control and form to maximize your training time).
Fixed bar weights, dumbbells, and weights plates are also useful and can be changed easily. Choose drop sets on isolation exercises (such as push downs) rather than compound moves (such as deadlifts), again for safety and prevention of injury.
The best time to use drop-sets is at the end of your workout as a “finisher”. The overload initiates the physiological change in the muscle. One or two of your exercises at the end of the session (potentially in the lagging body parts) should be enough to do this without overexertion.
Not to mention that the last part of something is the easiest to remember, so nailing your tricep dips to an absolute shaking point allows you (and me) to walk out of that room with the athlete feeling of total annihilation. Winning!
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