There are two communication systems in the body, one wired, the nervous system, and the other non-wired, the endocrine system. Communication systems are used to decode the meaning of the environment that the organism finds itself in, and to communicate the environmental messages to the individual cells and DNA of the organism. Hormones do not make the cells do anything differently than what the cells normally do. Instead, hormones change the rate and the magnitude of physiological expression of cellular behavior. Hormones are released from a source cell and make their way to a target cell where they exert their effect. Some hormones are released a great distance from their target cell, others are released from a neighboring cell, while others still are released in the same cell that ultimately is the target cell. The endocrine system utilizes glands, ducts, and the circulatory system to send its messages throughout the body. To exert its effects on the body, a hormone must bind to its receptor at the target cell. Hormone receptors are located either at the plasma membrane, the nuclear envelope, or inside the nucleus. Generally, peptide hormones have membrane-bound receptors, steroid hormones have nuclear envelope receptors, and thyroid hormones have nuclear receptors.
For all the types of hormones, the receptors are always proteins. Protein receptors are shaped in a way that makes them optimal for a specific class of hormones. When the hormone binds to the receptor, the receptor’s charge will be affected by the presence of the new hormone molecule, and the receptor will seek to change shape to find the shape associated with the next most stable charge. This changing of shape of the receptor protein will set off an intracellular/intranuclear physiological cascade effect that will ultimately affect one of the two phases of protein synthesis, transcription or translation.
Transcription is the copying of the genotype for a specific sequence of the genome, while translation is the construction of a protein from the genomic information at the ribosome. The post-translation folded protein is the ultimate phenotypic representation of the cascade effect featuring the cyclic effects of, environmental signal leading to organismal recognition, leading to secretion of a hormone, leading to migration of hormone to target cell, leading to binding of hormone to receptor, leading to intracellular messaging cascade, leading to change in the rate and/or magnitude of expression of DNA or ribosomal protein synthesis activity, leading to new proteins driving cellular behavior, leading to changes in organism behavior, leading to new interactions with the environment…and the cycle repeats again and again.
Due to the complexity of having a multitude of hormones being released from various source cells and reaching target cells simultaneously for a variable message that leads to an enormous number of concurrent intracellular effects, we need a working model to make sense of any of this concept, and to have a sense of what to do with it as a topic for exercise program design. In this article, we will focus on, what makes a specific cell a target cell, and what sort of internal environment is optimal for a robust anabolic hormone response. As with all models, they simplify complex topics to the point where there are occasions of inaccuracy. So the nit-picking evidence-based troll may find several problems with this particular article; however, this article will generally serve as a strong guide for what conditions are appropriate to create on specific training days in a well-crafted training program.
A target cell is one that has the protein receptor for a specific kind of hormone. The attractiveness of a target cell to a circulating hormone becomes greater when the sensitivity and number of the receptors to that hormone is increased (upregulation). We are primarily interested in muscle cells in this article. Skeletal muscle cells are target cells for all of the major types of anabolic hormones. The sensitivity of receptors varies greatly depending upon the state of that particular skeletal muscle cell. The sensitivity of skeletal muscle cell hormone receptors is changed primarily by whether that cell has been recruited and fatigued. The greater the degree of recruitment and fatigue of that particular cell, the greater the upregulation of hormone receptors, and the more that cell becomes a highly attractive target cell for hormones. The next logical question is, how does one recruit and fatigue particular muscle cells.
The Henneman Size Principle is the guiding phenomenon regarding the recruitment of skeletal muscle cells. The Size Principle states that at the lowest levels of force production, the slowest twitch muscle cells will be recruited to perform the task and that as force increases within the task, faster and faster twitch cells will be recruited. At the highest levels of force production, the fastest twitch muscle cells will be recruited.
Fatigue of muscle cells is based on repeatedly using the same cell for a task, and ultimately witnessing a drop off in performance from that cell. The greater the drop off in performance, the greater the overall fatigue. Not all of the mechanisms of what drives performance drop off are known, but some examples include substrate depletion and accumulation of metabolic byproducts. As a general rule of thumb, we can say that slow-twitch cells are easy to recruit and difficult to fatigue, while fast-twitch cells are difficult to recruit and easy to fatigue. The juxtaposition of responses between slow twitch and fast twitch cells to recruitment and fatigue creates an adaptable organism but does present challenges to the exercise program design specialist. The program designer must determine what sorts of cells are necessary for modifying as target cells and devise training schemes that maximize the receptor sensitivity for those cells to drive adaptive changes into them.
In his tour de force, Science and Practice of Strength Training, Zatsiorsky presents his fiber corridor concept. The corridor demonstrates methods that will lead to specificity of twitch type adaptations. Athletes who need to keep body weight low, and still display the highest levels of force production within their sport tend to employ training methods that systematically recruit and fatigue just the fast-twitch cells. Athletes who are looking to put on as much mass as possible without caring too much for what cell type they are targeting can use methods that will recruit and fatigue slow, moderate, and fast-twitch cells.
If you want to target just the fast-twitch fibers for adaptation, you are generally going to choose resistance training methods involving the maximum effort method (repetitions using 90% or greater of 1RM), or the dynamic effort method (sub-maximal loaded repetitions performed at the greatest velocity possible stopping well short of failure). If you want to target moderate twitch fibers, you can start using the repeated effort method (loads under 90% with sets going to failure). Finally, if you want to target slow-twitch cells, you can start using approaches like the stato-dynamic method (explained in greater depth later), which is low force, but high in duration for sets. There are many more methods, particularly when opening the playbook into realms such as plyometrics, change of direction, speed and agility related drills, and conditioning, but for simplicity sake in this article, we will stick to resistance training drills only.
All of the methods described in the previous paragraph, perhaps with the exception of the dynamic effort method, have the ability to create dramatic hormonal responses to training through various pathways. The repeated effort method is the approach most commonly thought of for hormonal effects. Most classical research in the area of hormonal responses to exercise have focused on repeated effort method approaches, and have shown that multiple sets of approximately 10RM efforts with short rest periods seems to be the gold standard for highest possible endocrine responses to exercise. Performing 3 to 5 sets of 10RM with 60 to 90 seconds of rest between sets with compound exercises like the squat is one of the most stressful stimuli that you can impart on an organism. Such a protocol will stress every system in the human body to near maximal.
As was mentioned earlier in the article, the endocrine system is a communication system. What was not mentioned earlier is that the messages that the endocrine system primarily relays have to do with the maintenance of homeostasis. Homeostasis involves a select set of variables that cannot leave an acceptable range of values or the organism will likely die. Some variables considered homeostatic include temperature, blood pH, oxygen tension, and blood glucose. A protocol like 5 sets of short rest 10RM squats will threaten all of the homeostatic variables. In response to this, the body will mobilize defense strategies that will protect homeostasis. Activation of the endocrine system is one such response the body uses to ensure that homeostasis is not lost.
The primary purpose of the endocrine system is to return the body to optimal conditions that provide for the greatest safe haven wherein homeostatic variables remain unchallenged. Ultimately, with training approaches aimed at hormones, we can say that the best way to grow muscle tissue would be to recruit and fatigue the maximal number of muscle cells (now target cells), and threaten homeostatic variables to the greatest possible degree to magnify the absolute hormonal response to the highest possible level. Multiple repeated effort method sets are like a shotgun blast to the systematic steps of maximal protein synthesis. A huge number of cells within the Zatsiorsky fiber corridor are recruited and fatigued, a tidal wave of multiple organ systems stress is unfurled within the organism, and the enormous threat to a variety of homeostatic variables forces the creature’s hand to mobilize massive endocrine responses.
The hormonal response to the multiple bouts of repeated effort method work described previously is a mixed bag. This protocol will cause the highest cortisol and growth hormone responses to any regular training method. Catecholamines will also be powerfully elevated due to the massive sympathetic response to this protocol. The elevation of the catecholamines seems to be related to a downstream testosterone response. The growth hormone response will trigger an increase in insulin-like growth factor (IGF) through downstream mechanisms. In short, you see all of the hormones involved with cellular remodeling all at once in massive amounts. For some athletes, this mixed bag is not optimal. Greater specificity of hormonal responses can be achieved with some of the other methods.
Repeated bouts of short rest between sets maximal effort method training are very effective approaches for driving a significant testosterone response. Loads generally have to be at or above 85% of the 1RM in order to witness this testosterone response. In the past, I have devised blocks that have been testosterone specific blocks. One such block featured a 3-week build-up. I would pair compound exercises, such as front squat and bench press (A day), and deadlift and incline bench press (B day). 60 seconds of rest would exist between the two exercises. Week 1 would feature 6 sets of 3 reps performed at 85% 1RM. Week 2 would feature 8 sets of 2 at 88% 1RM. Week 3 would feature 12 sets of 1 at 92% 1RM. Structuring the training week could be variable, but generally speaking, you want to get at least 3 training sessions in per week, and preferably 4.
This seems aggressive, but I’ve personally done it and witnessed many individuals perform it with extremely impressive responses. I caution participants to avoid getting fired up for sets. Remain neutral emotionally as much as possible. Such a testosterone specific block generally targets fast-twitch cells. I recommend not doing more than 2 of these testosterone specific blocks in an annual training cycle. I believe that this is primarily a neural oriented testosterone specific block. In short, this is because neural cell bodies contain an abundance of androgen receptors, and testosterone exerts profound effects on neural cellular remodeling physiology. The three week build up is a good timing element. Synaptic neuroplastic changes will take place within this time period. Neural cell bodies generally take approximately one month to remodel, but a full month of this protocol borders on what I would consider dangerous, and my hope is that the hormonal surge speeds up the remodeling process at the neural cell body.
The stato-dynamic effort method uses loads of approximately 50% or less, and witnesses the participant moving the load at slow velocities. 2 to 4 second eccentric and concentric motions are typically used for this method. The low load and slow tempo makes this approach target the slow-twitch fibers due to the very low forces. While the force variable is low, the duration of the set should be large. Slow-twitch fibers are easy to recruit but difficult to fatigue, and the longer duration sets are ideal for setting the stage to turn these slow-twitch fibers into target cells. Sets are typically performed for 40 to 60 seconds, and participants can build up to performing multiple rounds of 3 to 5 sets. Typically the rest period is kept in a 1 to 1 ratio with the work duration.
The stato-dynamic effort method fits into the broader category of occlusion based training approaches. Occlusion techniques were made popular by the Japanese, Katso approach, also called Blood Flow Restricted Training (BFR). The overall findings from the various protocols that have been used in BFR approaches is that a substantial increase in growth hormone is typically seen, even when loads of approximately 30% 1RM are used. The thought behind this approach is that occlusion of venous vessels prevents the removal of metabolic byproducts from the local tissue area for an extended period of time, creating a larger than normal level of waste products and heat trapped in the blood that cannot escape until the occlusion is released. Once the occlusion is released, the blood that is loaded with waste products ultimately is circulated back to central regions, such as the heart and neck. Chemoreceptors in the carotid body and arch of the aorta register the high concentrations of metabolic byproducts in the blood, send an afferent signal to the nucleus tractus solitarius, which relays the message to the hypothalamus. The hypothalamus perceives the internal environment of the body to be one that would threaten homeostasis. The hypothalamus then begins a signaling cascade to the anterior pituitary that unleashes a potent growth hormone pulse.
The stato-dynamic effort method asks the participant to never completely lock out the joints during performance of the tempo based exercise. Such an approach keeps the muscle tissue actively creating tension throughout the time period that the exercise is being performed. When muscle tissue is actively creating tension, it mechanically compresses the blood vessels that supply and drain the tissue, thus creating an occlusal effect. Eventually the set ends, and the occluded blood is sent back into circulation, leading to the mechanism of hormonal signaling described in the previous paragraph. Since only the slow twitch muscle was recruited and fatigued with this approach, only the slow twitch tissue is the target cell for the hormonal cascade.
Creating appropriate training templates for athletes of various types could easily be considered an act of cellular remodeling specificity. The wise coach is the one who determines the fiber type that primarily needs to be developed, the rate at which that fiber type needs to be developed, and how much of a hormonal driver for increasing rate and magnitude of adaptations needs to be imparted on the athlete at any point in time. All of the approaches listed in this article are considered to be advanced methods. Such methods may not be necessary for young athletes; however, once athletes are reaching advanced years in college or have been involved with professional sports and intensive training for several annual cycles, these approaches need to be considered. When sport specific skill and technical and tactical knowledge have reached their highest levels in advanced athletes, those with more specific fitness for the physiological demands of the game will have an advantage over their peers. At the highest levels, differences are measured with the edge of the razor. The thought that goes into the focus of training blocks should be just as exacting. If alterations in body composition need to be accomplished, we ultimately come to the concept that the morphology of the organism is largely a hormonally driven phenomenon. Those with the knowledge of specific hormones, and the techniques to create specific target cells will be better suited to help individuals with that need.
About the Author: Dr. Pat Davidson
-Director of Training Methodology and Continuing Education at Peak Performance, NYC.
-Assistant Professor at Brooklyn College, 2009-2011
-Assistant Professor, Springfield College 2011-2014
-Head Coach Springfield College Team Ironsports 2011-2013
-175 pound Strongman competitor. Two time qualifier for world championships at Arnold Classic
-Renaissance Meat Head