Individualizing Volume & Intensity For Hypertrophy Training

In my last article titled, Hypertrophy Training: Adaptation Mechanisms & Training Guidelines, I discussed the current 'best practices' based on the convergence of evidence in the strength and hypertrophy training literature. However, while this is a step in the right direction, it's not the end goal. There is a crucial error in reading the literature and following those recommendations to the letter. While 'bros' make the mistake of thinking what works for them will work for others, I often see evidence-based coaches make a similar mistake. That is, that they think what works for the average in a study will work for the individual. Afterall, research is not meant to tell us exactly how to train. It's meant to lead us in the right direction and give us some ball park approximations for what the best practices are. As coaches and athletes we need to take that information and contextualize it in our training program. Our past training history, individual genetic factors, physiological predisposition, and even personal taste will all impact what 'optimal' is for us. 

In a way, the applied training literature is like the sonar of a deep sea fishing vessel. The sonar tells you where fish are gathered, but it does not tell you exactly where you need to cast your line to catch a fish. In the same way, the literature can give us some normalized figures for how much volume, intensity, and frequency we may want to train with, but it doesn't tell us exactly what we should do or how to set our program up. In this way, training is just as much an art as it is a science. In this article I want to bridge the gap a little bit and provide some nuanced takes as to how we can go a step further than what the greater body of research provides us with and understand some of the underlying factors that determine what 'optimal' training is for the individual.

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Zoning Resistance Training

If you accept that mechanical tension and local muscular fatigue are the two main drivers of muscle hypertrophy, any choice of training intensity represents a tradeoff between those two mechanisms. The heavier you go, the more tension you develop, but the less local muscular fatigue and subsequently metabolic stress you develop before the point of fatigue and vice versa. However, it seems that there needs to be some balance of both mechanisms to maximize growth.This points to a fundamental question about low-load training for hypertrophy: how low can you go while still eliciting a growth response?

Based on the current body of research it looks like a set performed with thirty percent of an individual's maximum voluntary contraction or one repetition maximum provides the same stimulus for muscle growth as a set performed with ninety percent, assuming both sets are taken to volitional failure. This has been demonstrated by Jenkins and colleagues in their 2015 paper titled, Neuromuscular Adaptations After Two and Four Weeks of 80% Versus 30% 1RM Resistance Training to Failure, as well as by Schoenfeld and colleagues in their 2015 paper titled, Effects of Low vs. High-Load Resistance Training on Muscle Strength and Hypertrophy In Well-Trained Men. Thirty percent on an individual's one repetition maximum is quite light. To put things into perspective, that would mean that an individual who squats five hundred pounds can use a load as light as one hundred fifty pounds and still get muscle hypertrophy assuming they took the set to near failure. When using that low a percentage of one’s one repetition maximum they will be able to tell there’s some load on the bar, but they’ll likely be able to do more than forty reps at a steady cadence before reaching volitional failure. If we can still drive hypertrophy with as little as thirty percent of one’s one repetition maximum, can we do it with ten percent? Where is the low end cut off point? In a study by Lasevicius and colleagues titled, Effects of Different Intensities of Resistance Training With Equatted Volume Load on Muscle Strength and Hypertrophy, the investigators sought to answer this question. Based on their findings we can infer that the low end cut off for muscle hypertrophy occurs between twenty to thirty percent on an individual's one repetition maximum, though I'd wager that it may be higher than thirty percent for select individuals who were underrepresented in this study.  The crux for any athlete wishing to achieve a meaningful degree of muscle hypertrophy is figuring out where their cut off points are so they can train with greater specificity. If the number of hard work sets you can do for a given muscle group per week are limited, as they are for any individual, then it’s crucial that all works sets be performed in an intensity range where an individual is capable of desaturating a tissue, increasing motor unit recruitment, and eliciting hypertrophy.

Despite the fact that NIRS has traditionally been used for endurance training applications, I believe it can be a highly effective, and minimally invasive, means of parsing out effective intensity and loading ranges for hypertrophy training. During quick, short, bursts of high intensity or high load movements, like lifting weights, the muscles are reliant on the supply of the high energy molecule ATP, from phosphocreatine breakdown, which maintains cellular energy balance. It is now well understood that the replenishment of phosphocreatine and ATP relies heavily on energy synthesis from aerobic, oxygen consuming, processes. As a result, muscle oxygen saturation declines instantaneously with the onset of high intensity exercise, indicating that high intensity strength training is intimately linked to oxygen availability in the muscle. Specifically, this represents the near immediate replenishment of ATP via aerobic means. Therefore, measuring oxygen consumption with NIRS can be a very useful tool to aid in strength training. However, it should be noted that NIRS may not be a useful tool when performing work in a very close proximity to an individual's one repetition maximum, where neuromuscular limitations are dominant, but it becomes exponentially more useful as the rep count, and reliance on oxygen consumption, increases. 

When using a NIRS to monitor skeletal muscle microvascular blood volume and oxygen kinetics there are three types of mechanical effects I observe: compression outflow and return, venous occlusion and release, and arterial occlusion and release. For all intents and purposes, we're primarily concerned with these first two. A compression reaction is when muscle tension squeezes blood out of the muscle. This occurs within several seconds of the onset of tension and is diminished upon the release of tension. Typically this reaction occurs at loads below thirty percent of an individual's maximum voluntary contract or one repetition maximum, though this varies from person to person.

Venous occlusion is when muscle tension restricts the outflow of blood from the muscle. This occurs over tens of seconds to minutes and upon the release of tension blood is able to leave the muscle. Subjectively athlete's feel 'a pump' when this occurs since blood is entering the muscle and isn't escaping. As a result, a venous occlusion is often referred to as an outflow restriction or a reduction in venous return. In most instances, this will occur between thirst and seventy percent of an individual's maximum voluntary contraction or one repetition maximum.

I find it interesting that the purported effective intensity range for hypertrophy of thirty to ninety percent of an individual's one repetition maximum largely overlaps with the loading ranges where venous outflow and arterial inflow are restricted. Given the oxygen conforming response, which states that when force output is maintained during exercise muscle activation rapidly increases as blood flow is impaired and muscle oxygen saturation decreases towards a nadir, it’s likely that the low end cut off range for hypertrophy is a product of when an individual transitions from compressing to occlusion the blood vessels in response to loading. In order to parse out when this transition occurs I'll have athletes start with low loads on a local or regional movement and progressively build to a five to ten repetition maximum. After doing so we can back analyze the data and determine what percentages of their one repetition maximum they compress, venous occlude, or arterial occlude, which varies slightly for each muscle group or movement pattern. The utility of this type of assessment lies in its prescriptive qualities for strength and hypertrophy training. Athletes who do not respond well to traditional strength training protocols may not be creating enough intramuscular retention relative to the pumping capacity of their heart, and as a result they occlude at higher percentages of their one repetition maximum than is common. As a result, their strength and hypertrophy training will look much different than an athlete who occludes at lower loads. 

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Maximum Productive Volume

If you want to boil water on the stove you wouldn’t put the flame on the lowest setting — the water would never reach a rolling boil no matter how much time you gave it. Instead, you would set the flame to the appropriate intensity and then lend it the necessary time it needs to work its magic and make the water boil. In training terms for hypertrophy, if you’re not pushing your sets close enough to failure, or training with enough intensity, it doesn’t matter how high your weekly set volume is because it will ultimately be a waste of effort. That being said, assuming intensity is within an effective loading range for a given individual, the total number of work sets taken to near failure for a specific muscle group is likely the greatest determiner for building muscle. However, as volumes get higher, it appears that we need to drive frequency up to see gains or even prevent a backslide from occurring. Based on the current body of evidence, it seems that the most productive sets you can do in a session for a given body part range from eight to fourteen sets on average. The exact optimal volume in a session is likely a product of the proximity to failure for each work set, the specifics of the training plan, the muscle group being trained, and individual factors like recovery, genetics, work capacity, physiological predisposition. For example, if you’re only doing ten sets of bicep training per week, you’re probably fine doing all of your volume in a single session, though splitting it up into two sessions may allow for higher training quality and subsequently greater gains. But, if you’re performing twenty sets of biceps training per week, it is ill-advised to do all of that in one session, and you’d probably fare better spreading that out over two to three sessions.

It makes intuitive sense that you can only stimulate so much muscle growth, or any other adaptation, within a single workout. The body's adaptive capacities are limited, and adaptations are only desirable against repeated stresses over time. However, if we apply these transient stressors with enough volume and frequency for an extended duration they will effectively become environmental stressors which are potent stimuli that will elicit structural adaptations. Which are changes to the muscle, bone, mitochondria, and so forth. Another reason why higher frequency may be desirable as training volume, defined as total work sets per week for a given muscle group, is that there is a limit to the amount of quality training you can do in one session. One of the more obvious reasons for this is that neuromuscular fatigue will accumulate across a workout, which will reduce muscle activation and subsequently mechanical tension. Another reason is that we will accumulate more muscle damage with each set performed. This ties into the concept of repeated bouts, which says that the magnitude of adaptation you get from each subsequent set gets smaller and smaller, so past a given point each additional work set provides such little benefit that it is not worth the cost of being performed. If you keep pushing past that point each set may not only provide little benefit, but may actually be counterproductive as it may result in a negative protein balance, due to muscle protein breakdown, without stimulating more muscle growth or muscle protein synthesis. If this is done frequently enough over time you may end up in a net negative protein balance which can lead to losses in muscle mass.

The presence of a maximum productive training volume per workout would also explain why some studies find benefits of higher training frequencies, but others do not. Most of the studies that find benefits of higher training frequencies are in trained lifters with higher than average weekly training volumes. Conversely, there are many studies where training frequency does not seem to matter independent of training volume and these studies are mainly done with training volumes below ten sets per week for a given muscle group. We already discussed that the evidence points to eight to fourteen sets per muscle group being the maximum productive volume in a single session, but that still leaves us with a pretty big range which doesn’t have a lot of practical value. It also leaves us scratching our heads for answers as to why that is the case. Why would eight sets be the low end maximum productive volume per session on average and fourteen be the top end cut off? And is this a moving target that can be skewed upwards or downwards based on individual factors? Additionally, is there a practical way to know what the optimal intra-session volume is on a given day so we can maximize productive volume across a day, week, micro-cycle, macro-cycle, or training career? If we only have so much time, energy, and ‘adaptation currency’ why waste it on training that won’t bring us closer to our goal? I believe that near-infrared spectroscopy technology, and muscle oxygenation monitoring, can give us a highly effective, and minimally invasive, way of figuring this out.

NIRS is the first hope for coaches who are interested in monitoring stress reactions in real-time, so we can try and figure out how much productive volume an athlete can handle in a given day such that we can maximize it across a week, or cycle. In Patrick Drouin and colleagues 2019 paper titled, Fatigue-Independent Alterations in Muscle Activation and Effort Perception During Forearm Exercise: The Role of Local Oxygen Delivery, the investigators demonstrated that for a given skeletal muscle force output, muscle activation increases as muscular oxygen saturation decreases and that this response is rapidly reversible upon muscle reoxygenation. This is relevant for hypertrophy training because when we utilize oxygen at a faster rate than it can be delivered to the skeletal muscle there will be an impairment in the sensitivity of actin-myosin myofilaments to calcium ions, which appears to drive peripheral fatigue — peripheral fatigue will then cause increases in motor unit recruitment, which will lead to increases in mechanical tension.

When I'm monitoring muscle oxygenation, during hypertrophy training, one of the things I'm looking at is whether or not someone can desaturate the target muscle when we put it under load. If we are using a high enough percentage of the athletes one repetition maximum, and they are pushing a set close to their failure point, I generally see muscle oxygen saturation dropping in a near linear manner across the work set. This is demonstrated in the figure below which depicts an athlete’s response to “10 reps x4 sets” of back squatting at a moderately challenging load.

In each set we can observe a rapid drop in muscle oxygen saturation down to roughly ten percent, which indicates a progressive increase in motor unit recruitment across the set as the athlete approaches failure. It should be noted that this individual was able to desaturate the working muscles to the same nadir on each set and they were able to recover muscle oxygen saturation levels to the same baseline during rest periods, which indicates that they have not yet reaching a point of diminishing return where additional work sets yield a progressively smaller return on investment. However, if we continued to push this athlete and have them perform more set we would not only see a drop in objective performance measures, but also in their ability to desaturate the target tissues, which indicates that they are no longer getting the requisite amount of mechanical tension needed to elicit a meaningful degree of muscle hypertrophy. This inability to desaturate the target tissues after a given volume of work is shown in the figure below where we have NIRS data displayed from an athlete performing a strength workout composed of fifteen sets of back squats at a load greater than eighty percent MVC. For each set the reps are continued until muscle oxygen saturation reaches a nadir. Sets one to three show the low plateau reaching the individual's performance baseline. Sets four to seven show that the low plateaus are a bit above the performance baseline. Sets eight to eleven are after an extended recovery and again show the low plateau reaching the performance baseline. The final four sets show that the athlete cannot get close to the performance baseline, which may indicate that they have crossed the threshold of diminishing returns where these sets are not only no longer effective, but also counter productive.

The key to maximizing volume over an extended duration is all about walking the razors of ‘just enough’ before we start to see detriment, while simultaneously being able to drive progressive overload as a proxy for ensuring we’re getting muscle growth. Additionally, training volume should be optimized with training frequency in mind, not separately. Training volume should also be considered on a per-workout basis, not just on a total weekly basis. Training your chest two times per week with ten sets per session may have worse results than training three times per week with six to seven sets per session or even four sessions per week with five sets per session. That being said, when training with lower volumes, below twelve sets per week per muscle group, manipulating frequency doesn’t appear to be nearly as important as when training with fifteen to thirty sets per week for a given muscle group. The crux then becomes figuring out which of the above options are optimal. Increases in muscle mass are very difficult to measure, and even the rate of strength progression may not be a reliable way to know if we’re managing volume and frequency optimally. My belief is that NIRS and muscle oximetry may prove to be a valid, non-invasive, and practical way to determine how much volume we can handle on a given day.

Later this week i’m going to post the next article of this series titled, Individualizing Resistance Training with Auto-Regulation, where i’ll provide practical takeaways and specific training protocols that you can use to auto-regulate resistance training with or without a NIRS device.

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