I wrote this the elite fitness training board, both in response to and to try and feed a recent HST buzz that's started there. I figured it was appropriate to repost it here.
There have been a lot of questions and potential confusion surrounding HST (hypertrophy-specific training) recently. What I'm going to attempt to do is give a very non-technical explanation of the program itself as well as the physiology behind it. The purpose is to clearly present the program as an effective means of achieving hypertrophy.
Bryan Haycock, the guy behind HST, has already done this before: http://www.hypertrophy-specific.com/hst_index.html. The website is somewhat technical, and I remember feeling just as confused after reading it. What I'm going to try to do is fill in the gaps try to clarify, practically, why the program works.
Most training programs were conceived based on practical experience and modified based on medical knowledge. What makes HST special is that it is the opposite: it was formulated based on the way muscle grows in the lab, and then modified based on practical experience.
What is hypertrophy?
hypertrophy - n - A nontumorous enlargement of an organ or a tissue as a result of an increase in the size rather than the number of constituent cells
In other words, muscle hypertrophy is the enlarging of the muscle fibers as opposed to an increase in the number of muscle fibers (hyperplasia).
The principles behind HST:
1) Mechanical Load:
Tension upon muscle cells is necessary to induce hypertrophy. When cells experience tension, the delicate sarcomeres are disrupted. Given adequate nutrients, the muscle is then repaired to a greater size than it originally possessed.
Side note: It is commonly misunderstood that muscle failure is the stimulus for muscle growth. Intuitively, it makes sense. How can someone not sustain growth if they are working to the very limits of their capacity? Unfortunately, this is not true! The tension on the muscle is what actually causes growth.(1)
2) Frequency Potentially the most controversial, so I'll be spending a lot of time on it.
The various growth factors initiated by training all peak at around 24 hours post-workout, and than fall back to baseline by 48 hours. (2, 3, 4, and especially 6, 7) Typically, programs will sacrifice training frequency for the ability to add volume. This is counterproductive if your goal is to have bigger muscles. Given the average split of once/week, this means one will spend two days growing and five days maintaining muscle size without adding to it. This has been confirmed in the lab. One study compared the effects of a volume of weight training performed all on one day of the week to the same volume spread across three days of the week. The thrice-per-week group saw greater muscle gains as well as strength gains over 40% greater than the once-per-week group.(5)
This can also seem counterintuitive, as muscle soreness and strength often do not recover after a mere two days. In actuality, neither of those factors (soreness or voluntary strength) is related to muscle growth.
The ability to recover one's strength is directly related to muscle failure. Training to failure directly inhibits voluntary strength. Basically, training to failure fries your nerves (not the technical term ) and prevents them from being able to contract the muscles for long periods of time. So when one trains to failure and then waits until strength is recovered to train a muscle again, oftentimes the muscle has long recovered and is waiting for the nervous system to catch up.
This means that sometimes, with HST, you will be training through soreness. This is totally okay! Soreness is not harmful, and people generally find that training a sore muscle will cause the soreness to stop.
3) Progressive Load
Anywhere one goes, one hears "Changing one's routine is a way to prevent stagnation. If you're not growing, change things."
We're all in the business of growing muscle. Unfortunately, the body doesn't like to do that. It's rather expensive for the body to repair and produce new muscle tissue. It requires both lots of protein and lots of energy (sort of like the "parts" and the "labor). So, when an exercise is performed that damages the muscle tissue, in addition to the growth response the muscle also becomes resistant to further damage from that load. This is called the Repeated Bout Effect. (4) This is why routines fail to cause further progress. It is also why HST incorporates progressive load.
Side note: strength programs and growth
As anyone who's done WSB will tell you, strength programs can induce a good deal of hypertrophy. As a result, many bodybuilders adopt strength-training programs as a means of causing growth. By isolating and understanding WHY they cause growth, you can just skip straight to the growth-causing elements without wasting time with all of the neural tricks that strength training uses to increase your 1RM.
Strength programs typically have people work with very low reps, often to failure. Both of those have been shown to increase the nervous system's efficiency at performing a movement, thus increasing strength. So, when someone starts a strength training program, initially he/she sees a lot of growth. His/her muscles are not that resistant to damage, and at high tension levels the Repeated Bout Effect takes a little while to kick in. As long as he/she also continues making strength gains, he/she will experience progressive load, and will see muscle growth as long as he/she is overeating. Unfortunately, after a time the strength gains will slow to a crawl, and at that point the muscles are very resistant to damage and will simply not grow.
At this point, conventional wisdom would have our trainee change up his/her routine. This advice is somewhat sound, as new exercises can put new levels of tension on muscle fibers and thus elicit more growth. Also, a rep change can stimulate new growth as well, but ONLY if the new rep range is lower and allows more weight to be used, thus loading the tissue at new levels.
Instead of changing the routine, HST advocates...
4) Strategic Deconditioning
Before each cycle, in order to make the muscles responsive to the light weights in the beginning, a period of 9-14 days is taken off from all training. This reverses some of the effects of the RBE. It allows HST-users to experience rapid and sustainable progress.
This is one of the reasons why newbies experience such great initial gains. They have had such long deconditioning periods. Trained individuals also notice this; when coming off of a planned or unplanned layoff they often experience a renewal of gains.
1) Warren GL, Hayes DA, Lowe DA, Armstrong RB. Mechanical factors in the initiation of eccentric contraction-induced injury in rat soleus muscle. J Physiol. 1993 May;464:457-75
2) Nosaka K, Clarkson P.M. Muscle damage following repeated bouts of high force eccentric exercise. Med. Sci. Sports Exrc., 27(9):1263-1269,1995
3) Smith LL., Fuylmer MG., Holbert D., McCammon MR., Houmard JA., Frazer DD., Nsien E., Isreal RG. The impact of repeated bout of eccentric exercise on muscular strength, muscle soreness and creatine kinase. Br J Sp Med 28(4):267-271, 1994
4) T.C. Chen, Taipei Physical Education College, and S.S. Hsieh, FACSM,. The effects of a seven-day repeated eccentric training on recovery from muscle damage. Med. Sci. Sports Exrc. 31(5 Supp) pp. S71, 1999
5) McLester JR., Bishop P., & Guilliams M. Comparison of 1 and 3 day per week of equal volume resistance training in experienced subjects. Med. Sci. Sports Exrc. 31(5 Supp) pp.S117 1999
6)MacDougall JD, Gibala MJ, Tarnopolsky MA, MacDonald JR, Interisano SA, Yarasheski KE. The time course for elevated muscle protein synthesis following heavy resistance exercise.
Can J Appl Physiol. 1995 Dec;20(4):480-6.
7)Phillips, S. M., K. D. Tipton, A. Aarsland, S. E. Wolf, and R. R. Wolfe. Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am. J. Physiol. 273 (Endocrinol. Metab. 36): E99-E107, 1997
Edit: 5/16: Added studies 6 and 7, other minor editing