By: Cody Haun, PhD, MA, CSCS
In part 1 of this blog post series, I laid the foundation for this post. I encourage you to read part 1 if you haven’t so we’re on the same page as I shift the focus a bit in this post from foundational to more applied. For those of you whom choose not to read part 1 [ :**( ], a brief summary follows.
When heavy (e.g., > ~60 % 1RM) and light loads (e.g., < ~40 % 1RM) are compared on a per-repetition basis, the following points can be made:
b) lifting heavier loads results in greater strength improvement
Two other important points related to the training process in general were made:
c) training to momentary muscular failure does not seem to improve strength as much as not training to failure
It seems clear that heavier loads are generally more effective for improving muscle size and strength on a per-repetition basis. However, this post will briefly describe some important caveats and considerations pertaining to the above in hopes of providing you with some practical implications. In my opinion, it is critical to a successful training process to appreciate the concept that there is a time to “go heavy” and a time to “go light”. Understanding when lifting heavy or light is appropriate and why can provide powerful fatigue management capabilities and result in more successful training outcomes. First, I’ll provide some background physiological information that will help clarify some of the key, practical differences between light RT and heavy RT. Next, I’ll discuss training load manipulation for muscle growth (i.e., hypertrophy) outcomes, specifically. I’ll conclude with some take-home points that I hope you’ll find helpful. In the next blog post (part 3 of this series), I’ll be discussing load manipulation for strength improvement. In a future blog post, load manipulation for power and endurance performance will be discussed. Although this post is by no means a comprehensive discussion of the topic, I’m confident you’ll be able to glean some meaningful information you can apply to your own training or to the programming of your clients or athletes for hypertrophy purposes.
Before discussing practical application of heavy or light load programming, it’s worthwhile to appreciate some of the neuromuscular physiology underlying recruitment of muscle fibers to contract. As described in part 1, signaling for muscle contraction during RT starts in the brain. An electrochemical signal is sent from the primary motor cortex of the brain to alpha motor neurons exiting the spinal cord (i.e., nerves innervating skeletal muscle). These nerves conduct this signal toward the membranes of innervated muscle fibers and this results in muscle fiber contraction. Motor nerves exhibit different sizes and their size and physiology can change in response to RT. Detailed discussion of motor nerve adaptation to RT exceeds the length of this blog. However, pertaining to their size, larger motor nerves tend to innervate larger muscle fibers and smaller motor nerves tend to innervate smaller muscle fibers. In other words, from a continuum perspective, the size of a motor nerve tends to be strongly related to the size and number of fibers innervated. Nerve innervation to fiber ratios cover a wide range in the human body and largely depend on the level of fine motor control common to the muscle innervated. For example, innervation ratios range from ~1:10, in the case of muscles requiring fine motor control (e.g., select muscles of the hand), to ~1:2000 in the case of muscles involved in gross movement patterns (e.g., gastrocnemius of the calf).
It is helpful to view skeletal muscle as a set of individual fibers innervated by motor nerve branches rather than a blob of whole tissue connected to one nerve for this process to make more sense (as shown above). Which motor nerves are recruited and the rates at which motor nerves are recruited and conduct the signals described above depends on the loading task at hand and the fatigue status of an individual. To simplify, motor nerves and the fibers they innervate (i.e., motor units) are recruited primarily based on their size. This is known as the size principle. In general, relatively high force requirements of a task (e.g., the heavier the load being lifted) result in both more and larger motor units being recruited. Since recruitment and firing of these nerves causes muscle contraction, and contraction results in tensile forces produced by the muscle fibers innervated, it makes sense that heavier loads tend to result in greater hypertrophic responses given that mechanical tension is the primary stimulus for increasing MPS. Practically speaking, heavier loads recruit a greater number of fibers earlier in a set of resistance exercise given that a larger number of fibers are required to overcome the relatively high resistance. However, physiological processes resulting in fatigue of select motor units (i.e., reduced capacity to produce force) during light RT can also affect motor unit recruitment patterns. During high-repetition sets, various metabolites (e.g., H+ ions) can accumulate in skeletal muscle cells and in the interstitial space between the end of the motor nerve and the muscle membrane interfering with effective contraction of muscle. This can result in other motor units being called into action while fatigued motor units recover, although the absolute load being lifted remains relatively light. A visual representation from Dankel et al. in a manuscript published in the European Journal of Applied Physiology highlights this point nicely.
With the above in mind, the underlying mechanisms of hypertrophy-related signaling seem largely the same in the case of light and heavy RT to volitional failure at the muscle fiber level (e.g., mechanical tension-driven). Fatigue during light RT can result in recruitment of larger motor units innervating larger muscle fibers which are recruited comparatively earlier in a set of resistance exercise involving heavier loads. This can result in similar signaling phenomena in recruited fibers eventually resulting in an increase MPS. However, light RT to failure will likely require more time and may take longer to recover from.
It is now clear that muscle hypertrophy can occur from a variety of loading paradigms in both trained and untrained individuals. After completion of ≥ 6 weeks of resistance training (RT), significant hypertrophy has been shown to occur from average training loads ranging from ~30 % 1RM – ~90 % 1RM. Notably, although effect sizes tend to favor higher loads for hypertrophy, as stated above, it stands to reason that light loads can invoke hypertrophic adaptations. Although intriguing, some important considerations are worthwhile before regular employment of light loads for hypertrophic outcomes.
Almost all studies showing favorable hypertrophic outcomes from light loads involve training to failure. As discussed in part 1, training to failure is suboptimal for strength outcomes, light RT (e.g., 30 % 1RM) to failure seems to result in longer force-recovery times than heavy RT to failure (e.g., 80 % 1RM), and, regardless of load, training to failure likely results in longer times to recover compared to not training to failure. So, before you start taking your 30 RM to failure on the back squat dreaming of the consequent quad growth while rejoicing in not having to go heavy to get jacked, consider that this may result in a longer time to recover than completing your 8-12 RM a few reps shy of failure, and note that each scenario is likely to result in similar growth outcomes. Additionally, if training to failure with light loads impedes subsequent RT sessions that could have involved the presentation of an additional overloading stimulus, the effects of this practice can quickly become a net negative. In light of this, a clear dose-response relationship between training volume (e.g., sets per muscle per week) and hypertrophy outcomes has emerged from the literature, as clearly revealed through meta-analytical data from Schoenfeld et al. Briefly, sets per week per muscle totaling to ~10 sets results in comparatively greater hypertrophic outcomes than lower set values ≤ 5 sets per week. So, if any training practice negatively influences the ability to present ≥ 10 sets per muscle week, when hypertrophy is the goal of the RT program, strong consideration of its removal or absence altogether is warranted. For example, light RT to failure on a regular basis.
Stated differently, if maximal hypertrophy is the primary goal of an RT program, the design and execution of the program should result in the most frequent, maximum MPS response to RT over time. Hence, sessions should not be viewed as standalone but rather viewed in context of a larger-scale process resulting in the greatest muscle growth over time. This concept was highlighted by Dankel et al. recently in the Journal of Sports Medicine where the authors promote the consideration of increasing the frequency of training sessions as a method of overloading beyond overloading through the addition of sets, reps, load, or some combination of each as sole overloading techniques. If light RT to failure or training to failure in general significantly impedes this process, the design of the RT program is suboptimal.
Although the pictured model is certainly intriguing, it stands to reason that a practically effective training cycle for hypertrophy would involve the addition of training volume over time since a clear dose-response relationship exists between training volume and hypertrophy, at least up to a point. Interestingly, it remains to be clearly determined at what point RT volume is excessive and results in no additional hypertrophy from an increase in dose in a variety of human populations (e.g., young, old, etc). Theoretically, the figure below shows an expected response.
The point at which hypertrophy plateaus with a continued increase in RT dose is not yet clear. I just finished collecting and writing up data for my Doctoral Dissertation (hopefully published soon!) and it seems that completion of far more than 10 sets per muscle per week are effective for stimulating hypertrophy, at least in resistance-trained young men. Look out for more writing on this in the near future! Consequently, ensuring an increase in the number of working sets emphasizing a muscle each week over the course of a training cycle provides insurance for hypertrophic outcomes, at least up to 10 sets per muscle per week. And, for most people, I’m confident recommending working up to anywhere between 20-25 sets per muscle per week at an average of ~70 % 1RM for selected exercises toward the end of a training cycle to elicit maximal growth responses. Doses beyond this warrant caution, and a “deload” (i.e., reduction in training stress to recover and adapt) week is likely a good idea subsequent to doses of RT this high. To be clear, when mapping out a hypertrophy program, attention should first be paid to total weekly volume per muscle. The RT program to maximize hypertrophy on an individual basis should consider the manner in which the greatest volume can be achieved over the course of a training cycle whilst avoiding injury and fiber size regression. This is likely to occur from implementing the following guidelines:
1.) Train each muscle each week with mostly loads between 60-85 % 1RM no less than 2 times per week but potentially up to 6 times per week (depending on the muscle).
2.) Aim for ~10 total sets per muscle during week 1 of a hypertrophy training cycle.
3.) Complete a number of reps per set using the load magnitudes above stopping sets ~2-3 reps shy of failure for each movement during week 1, ~1-2 reps shy during week 2, ~1 rep shy thereafter per week, until indication of time to deload (see below). This will likely result in the performance of between 5-20 reps per set.
3.) Increase the number of sets for each muscle each week by 3-5 sets, and consider slightly increasing the load.
a) Since total weekly volume seems more important, absolute loads on a per-set basis could actually be decreased slightly to achieve greater per-session and total weekly volumes, since the absolute load itself is less important than total volume load, in general. For example, if 3 x 10 at 100 kg was completed for a session during week 1, 5 x 10 at 90 kg would still be technically overloading, but with a lower weight per set to achieve a higher volume load.
b) One could even increase the dose of RT during a training cycle until it became practical to divide RT into two separate sessions per day, if time allows, given egregious session durations (e.g., >2 hours, AM and PM) when total sets per session approach ~40. In other words, with the addition of weekly volume during a cycle, it becomes difficult to complete programmed volumes beyond ~40 sets per session in less than ~2 hours at which point glycogen reduction, tissue microdamage, and neuroendocrine factors can reduce acute training capabilities.
4.) Continue increasing the dose using the guidelines above until……….not certain about this. My good friend Chris Vann, MS, CSCS is writing up a manuscript and blog right now on deloading which will clarify some practical indications of when it’s likely time to reduce training stress for a period of time (i.e., deload or active rest). We are actively researching this in our laboratory, mentored by the amazing Dr. Michael Roberts. However, I generally agree with Dr. Michael Israetel of Renaissance Periodization on identifying time to deload in context of hypertrophy training. Dr. Israetel suggests that when performance capability markedly decreases during the subsequent week of training, this likely indicates a dose of training representative of the upper limit of a trainee’s recoverability (i.e., maximum recoverable volume [MRV]). Practically, this presents as a need to decrease the per-set load relative to the previous week’s performance during the added sets, or an inability to maintain similar per-set repetition totals with a slight increase in load or the same load. For example, let’s say you squatted 6 x 10 at 100 kg the previous week with 1-2 reps left during your lower push session. During this week’s lower push session, the following occurs:
Set 1: 105 kg x 10 with 2 technically-proficient reps left
Set 2: 105 kg x 10 with 1 rep left
Set 3: 105 kg x 10 with 0 reps left
Set 4: 105 kg x 9 with 0 reps left
Set 5: 100 kg x 9 with 0 reps left
Set 6: 100 kg x 6 with 0 reps left
Set 7: 95 kg x 4 with 0 reps left
Set 8: 95 kg x 4 with 0 reps left
Hypothetically, this dose of RT indicates a current upper limit of short-term recoverability.
I hope you found this post helpful. If you find any of this confusing, or have any questions, comments, or suggestions, please feel free to email me at: email@example.com
Further, consider hiring a qualified professional to program your training if you’re unaccustomed to this process or want to better ensure these concepts are appropriately applied to your own training. Thanks for reading, and best wishes!
Until next time,
“I am a scientist first and a coach second. I have a passion for positively impacting the lives of people through providing critically thought-out, data-driven, scientifically-sound nutrition and training programming services that equip individuals to successfully achieve their performance and/or physique goals. I seek to offer the best service within my power and I am confident, given my background, education, experience, and relentless pursuit of knowledge pertaining to human physiology and the training process, that I can provide you with programming to realize great results. Feel free to contact me with any questions.”
Cody Haun, PhD(c), MA, CSCS
-APLYFT Science Consultant