At the beginning of an HST cycle you will be using a weight you can do 15 reps with. After proper deconditioning this will induce “some” hypertrophy, but after about 2 weeks the load will be insufficient to induce any further growth. At this time the load must be increased in order to get further growth. Due to the inverse relationship between load and reps/volume (i.e. the heavier it is, the fewer times you can lift it) you have to reduce the volume as the weight gets progressively heavier. As you reduce the volume, the metabolic demands on the muscle tissue drop as well. This reduces the activity of a signaling protein called ERK 1/2 which is known to facilitate hypertrophy. Some very interesting research has evolved in the last 2 years that demonstrate the value of hypoxic stress during muscular work with respect to hypertrophy. So the question becomes, how do I continue to increase the weight over time, and not decrease the activity of ERK ½? Well, you can either put on a tourniquet before each set, or you can do a drop set. Now a drop set doesn’t mean 1 set of reps. It means “repping-out” with lighter weight after your work-set. But in order to be a true drop set, you don’t rest after the work set. You perform your desired number of reps, in this case lets say 5. Then you immediately strip some weight from the bar and keep going without resting. Normally, you will strip the weight twice before “calling it good”. All the reps performed, including the work reps, should reach about 15-20 to create a real metabolic environment inside the cell sufficient to activate ERK1/2 and related signaling proteins. Now, in case I totally misunderstood your question and you meant, why not reduce the weight once, allowing 15 additional reps? Well, the answer is that sometimes if you reduce the weight too much, you can actually rest to an extent which ends up prolonging the set unduly. You will be able to tell if you've created the correct environment, not by how many reps you can perform with a given weight, but because your muscle will be burning tremendously. It will burn/ache like crazy! Drop sets are done by "feel", you don't really have to plan it. So, if you want to only want to strip the weight once and rep-out...go ahead. CNS fatigue in and of itself is not a problem. The problem arises when you begin to overtrain (general term). CNS fatigue all by itself will not hamper your gains. Your gaisn will only be hampered if you can't lift the amount of weight you were supposed to, or if you begin to delay training all together. Here's what I would suggest. If you would like to incorporate drops into your 5s, just do it once the first week. So, I the first day of 5s, do a drop set for the last exercise for each muscle group. Then, see how you feel on Wed (or next workout). The next week, do some drop sets on the first workout that week, and on the alst workout that week. Then, see how you feel. If you feel fine, then you can try doing them more often on your next cycle. It all depends on how well you regain your strength from workout to workout. Usually, when people say "metabolism" they are refering to your basal matabolic rate or BMR. That's how many calories you burn in a day at rest. I was refering to metabolism that occurs inside the muscle cell as it works or contracts. This involves rapid breakdown of fuel substrates like glycogen and rapid recycling of ATP and ADP. Your BMR does not produce lactic acid, but high metabolic rates (fuel burning rates during work) inside muscle cells does. So, cardio on the off days won't necessarily produce the flushing of lactic acid in the muscle accept the one you are working...usually your legs. Even then most people can't carry on an activity that produces intense burning for more than a minute or two. To summarize, I wasn't refering to your body's metabolic rate, I was refering to the build up of metabolic by products such as lactic acid and oxygen radicals in active working muscles. The latter effects are local and have little systemic effect (except for a creating nausea in some people). Static contractions would be fine as "part" of the high rep sets. I would suggest you add a hold at the finish of the last rep. Or, you could do static contraction for the first set, and then do normal reps for the second set. The actual contraction of the muscle is important, even during the higher burning reps. 1) If you are doing multiple sets per exercise, only do a drop set on the last set of that exercise. You don’t want the drop set to prevent you from accomplishing a successful second set at your target weight. It is reasonable to do drop sets on multiple exercises for the same body part though. 2) I think it’s difficult to speak in terms of % when doing drop sets. Drop sets are utilized for a very specific purpose if using HST. Unlike traditional applications of drop sets, which are designed to “increase intensity”, in HST they are designed to alter the metabolic environment inside the muscle cell itself. As such, we don’t think in terms of Load, we think in term of performance. This may be one of the only times you’ll think in terms of performance during HST. So when determining how much weight to tear off the bar, just take some off and keep going. It isn’t important just how much you drop in weight, just so long as it allows about 5 more reps. 3) A drop set should let you achieve 15-20 reps total for the entire set. So, if you are doing sets of 5, you should try to knock out 10 more reps after the first 5. This volume of reps is designed to ensure sufficient metabolic strain. 4) Drop sets are valuable for hypertrophy, as long as they don’t take priority over progressive load and frequency. As mentioned in several other threads, drops sets produce the desired metabolic stimulus to facilitate the hypertrophy induced by the loading regimen of HST. However, they must be utilized properly, and unless you understand their purpose, based on the physiological role they play in hypertrophy, you won’t know how to use them. This is what you see in the articles in the muscle mags. They will write about how “intense” they are and how they’ll put an inch or two on your guns. They’ll show some pro, sprayed down with a water bottle, grimacing as he pretends to “break through the pain barrier”. The high rep work during the 5s is beneficial because of the lack of metabolic demand (activation of MAPKerk1/2) of doing short 5 rep sets. Negatives require even less metabolic energy, so the benefit applies to negatives as well. Of course, the benefit also depends on how many weeks you spend doing 5s and negatives. If you finish your cycle only doing 2 weeks of 5s and then start SD, you probably won't get a whole lot out of high rep dropsets. But if oyu do 4 weeks of 5s then try some negatives, you will get a boost in the hypertrophic signal by flushing the tissue with lactic acid and oxygen radicals. One last suggestion, I would suggest a full 2 weeks of SD if you do 4 weeks of 5s and then negatives with added drop sets. It will simply take a little longer to unadapt after that. Don't sacrifice the usefulness of SD as well as the 15s in order to "train heavy" all the time. It's an easy trap to fall into, and adding dropsets won't protect you from the inevitable plateau.