I suggest you do 2 sets per exercise during the 15s. Then do 2 sets during the first week of 10s, and 1 set during the second week of 10s. Then do 2 sets during the first week of 5s, and finish doing one set (after warm ups of course) during the last week of 5s. Always warm up first regardless of how many work sets you are doing. The volume isn't necessarily supposed to decrease each minicycle. It often does, simply as a result of the increasing poundages and cumulative damage. If you are doing HST properly you won't be able to just increase your volume at will. If you are doing HST properly you should already be using as much volume as you can reasonably handle and still feel healthy (no injuries etc). HST builds strength sure enough, however, the actual manifestation of that strength depends on the recovery of the CNS (and other neuromuscular factors) from workout to workout. Sometimes a person will gain a little ground on their CNS recovery and their strength output will go up. Those who zigzag are more likely to experience significant "strength" gains mid cycle. The size gains are dependant on what's happening to the tissue. This of course is dependant on the absolute load as well as the relative condition of the tissue at the time. So, should you increase, maintain or decrease "volume" as the cycle progresses? It depends! I know how many people hate to hear that...but its true. Here is how you decide. Keep in mind that these factors are to considered “collectively”, meaning each factor must be weighted, not taken as an absolute indicator. Increase volume if: You are never sore You are never tired You are not growing Maintain volume if: You are slightly sore most of the time You are tired enough to sleep well, but not so tired you lose motivation to train. You are noticeably “fuller” Decrease volume if: You are experiencing over use pain, and strain symptoms in joints and/or muscles. You are tired and irritable all the time, yet don’t sleep well. Strength levels are significantly decreasing. I said, “The number of Sets is determined by the minimum effective volume (this changes over time according to current load and Conditioning.)" You said, “I thought … that the expression of the hypertrophic genes was increased in proportion to time under tension, i.e. 'more is better' up to a rational point.” If I understand correctly, you are concerned about the “minimum” effective volume part. Why should a person adjust the # of sets according to the minimum effective volume if “more is better”? Answer, because other factors such as Training Load and Training Frequency are inversely related to training volume. In other words, the higher the volume of exercise, the lower the Load and Frequency that can be effectively maintained over time. Likewise, the lower the training volume, the higher the Training Load and Training Frequency that can be effectively maintained. It is just a matter of defining “minimum”. In this case, “minimum” means as many sets as you can do without having to reduce the Load from set to set and the without having to reduce the frequency beyond 48 hours. Keep in mind that some signaling proteins are turned on by the combination of time and tension, sometimes referred to as the “time-tension integral”, and others are turned on primarily by the magnitude of tension without regard to time. Nevertheless, both signal-types will respond with a flattened out bell curve. There is a point where the signaling response to the stressor is at maximum. Further load and/or volume will not elicit a greater response. So yes, there is "a point of growth/no growth". That point is determined by the Load, the Volume, and the level of Conditioning of the tissue. To understand this we have to look at what has to happen to the muscle during a workout in order to get it to grow. In order of importance: 1) Satellite cells must be activated, differentiated, and fuse with existing fibers, donating their nuclei. 2) Mechanical stress must be transmitted to the sarcolemma (mechanotransduction) and contractile protein structures within the sarcomeres. This will trigger focal adhesion kinases (FAK) that in turn initiate the downstream signaling events leading to an increase the contractile and cytoskeletal protein expression/synthesis. 3) pH and oxidative stress must be acutely increased within the muscle fiber. Focusing just on the workout, this pretty much sums it up. If #1 doesn’t happen, you will not grow…ever. If number two doesn’t happen, you will grow a little, but you will soon reach the limits of the sarcoplasmic/nuclear ratio and growth will stop. If #3 doesn’t happen, you will still grow quite significantly, but the rate of growth might be enhanced or facilitated if #3 is achieved. #1 is achieved when a certain level of microtrauma is experienced by the fibers. This is brought about by load, eccentric contractions, and to a much lesser extent, hypoxia (A.K.A. #3) When load, eccentric contractions and #3 occur, each fiber will produce and release muscle specific-IGF-1 (sometimes called mechano-growth factor) The IGF-1 in turn seeps out of leaky sarcolemmas and acts on nescient satellite cells to initiate #1. Microtrauma is rapidly reduced from workout to workout (Repeated bout effect) thereby limiting the effectiveness of any given load to induce further hypertrophy. #2 is achieved by loading a muscle that is actively contracting. #3 is achieved by contracting a muscle (doing reps) until you create an oxygen deficit and subsequent hypoxic byproducts (e.g. lactate and oxygen radicals). The afore mentioned physiological principles of muscle growth are what we follow in order to ensure that 1,2 and 3 happen. 1 set is not necessarily "better" than 3 sets. As far as muscle hypertrophy is concerned, high duration of load is best. The cellular signals that are initiated by strain on the structural and contractile proteins of the cell are increased as time under load increases. If it weren't for the involvement of fatigue in performing the actual reps and sets, you would be better off doing tons of sets and reps. HST uses lower numbers of sets because the muscle is trained much more often. So, the muscle isn't actually loaded for less time, its just that the loading is more evenly spread out over time to keep the signal more constant. If there are any factors that allow a person to do more sets per workout, he/she should do them. From what other research there is on the time course of genetic expression in response to overload, it is clear that we don’t even come close the amount of time needed to elicit the greatest hypertrophic effect. But what are you going to do? We have to lift the weight a lower it over and over in order to overload the muscle. From the overload research, I personally feel longer time under tension is better. But you have to balance that with CNS fatigue, and absolute load. More sets with heavier weight is better than fewer sets with less weight. But there is a limit to our exercise tolerance. So you have to figure out a way to get as much loading of the muscle as you can, as often as you can, and still be able to constantly increase the load over time, without burning out or getting injured. Keep in mind that HST does not dictate that the total volume (i.e. number of sets per body part) over the course of the week should be lower than what a person is accustomed to using with traditional routines. HST only advises that the volume be evenly distributed over more workouts in the same time period. So if you are used to doing 9 sets for back on "back day" using a traditional routine (e.g. training each body part once per week), HST would have you do 3 sets at a time for 3 different workouts. Obviously, a guy who is used to doing something like 12 sets for back once per week, is not going to gain much by dropping to doing only 1 set for back even if it is 3 times per week. He went from 12 sets to 3 sets per week. Not only that, but HST would have him use submax weights most of the time where he is obviously plateaued and used to doing 100% max weights (Not true 100%, but 100% with the fatigue that inevitably accumulates by the 3rd set). This is just too great a reduction in training to provide him with significant gains. The key here of course is Strategic Deconditioning, that would then allow him to begin growing again, with less "average" weight and volume, but higher frequency. Well, for me, 2 sets is enough on most bopdyparts. But then again, with body parts like back, I will usually do 3 sets at different angles of pull and grip widths. But the amount of volume each person is used to varies. I am not saying that you have to train to your volume limit. I'm just saying that if 1 set isn't enough, do another. Do too much and you'll begin to get progressively weaker, and/or injured and you will lose your desire to train. At first, you won't know how much is too much and how much is too little. So, start with 1 work set per body part per exercise, and work up from there. Sometimes, you will find that you need to do more during the lighter workouts, and fewer sets during the heavier workouts. I hate to say this, but play it by ear, while you stick to the principles. You have to learn what it feels like. You have to actually experience growth from a series of workouts to be able to associate the specific feeling of "enough" work with subsequent growth. But just a hint, you will feel whether the set is a good one or not before you finish the set. You will literally feel the strain of the weight on the muscle itself. You have to look past the effort required to lift it, and try to feel the mechanical strain on the muscle. "Off the record" it is a type of pain, kind of like the pain you feel when you stretch a muscle. Its mild, but it is in the "belly" of the muscle. When your done with the set, the muscle will pump, and in the morning you will be a little stiff in that bodypart. I hate to talk in such subjective terms like this but this is where experience actually means a hill of beans. Yes, you can damage a muscle to such a degree that it doesn't work properly 36-48 hours. The thing is, this type of damage isn't necessary to get it to grow. In fact, you can get necrotic fibers (dying fibers) if the damage is too severe. So too much of a good thing is a bad thing. It isn't absolutely necessary to be able to "feel" this in the muscle. It is just a way of judging something that is inherently hid from view. Trial and error is just as good as "feeling it". If you get so sore that you can't move, you've obviously overdone it. You will recover, but it isn't necessary to cause that much damage. The serious damage is usually the result of too much too soon after a layoff. Too much burn won't cause it. It is usually the result of super high volume when one is not accustomed to the weight nor volume.