The Importance Of Load During Resistance Training: Part 1

April 17, 2018


What is the appropriate load to lift during an exercise, or exercises, to achieve your goals? Answering this question intelligently should depend on the aim of the overarching training process, be based on recently executed training sessions, and influenced by training sessions to follow in the near future. As always, it depends! Selection of the appropriate load is contingent on the desired training outcome. To make this discussion more concise, defining exactly what is meant by load is helpful. In this post, load refers to the magnitude of resistance against which a specific movement pattern is intentionally attempted for the purpose of improving a certain fitness characteristic. In other words, load insinuates a certain level of resistance to the contraction of a certain muscle, or muscles, during a movement completed for the purpose of exercise. Since various loading methods can be used to improve a variety of fitness characteristics other than increasing muscle size (i.e., hypertrophy) and maximum strength (i.e., ability to produce force), it’s important to point out that the primary focus of this writing will be on loading for the purpose of hypertrophy or strength, while a discussion of loading methods for improving other fitness attributes is reserved for future writing. However, it is also important to note that these two pursuits of the training process (i.e., muscle size and strength) can improve other aspects of fitness as well (e.g., power). Regardless, the intention of many trainees’ programs is to build or preserve muscle size, improve strength, or both. Therefore, load selection for these pursuits deserves special attention.

Load selection for any individual exercise should fit within the puzzle of the overall training process; where some pieces are larger or smaller than others, but the right pieces fit together to form the picture of a successful training outcome. Practically, this means neither heavy loads nor light loads are always the best option for either hypertrophy or strength. Planning periods of training to address this concept is known as periodization. Periodization can be simply defined as planned variation in training to reduce injury potential, prevent stagnation, and realize performance or aesthetic peaks at desired time points. In my opinion, this is why periodized programs tend to work better than non-periodized programs. Invoking the load descriptors “heavy” and “light” may seem confusing since these seem rather subjective. Fortunately, or maybe not depending upon your perspective, planet Earth’s natural laws (e.g., gravity) have allowed consistent calculation of resistance magnitudes during resistance exercises and an analysis of physiological responses thereof in humans. Further, since we’re all humans (I think) with consistent anatomical and physiological features, adaptive responses to loading paradigms of resistance exercise for hypertrophy and strength are fairly well characterized. Although perfectly personalized resistance exercise programs remain elusive, both anecdotal and scientific evidence have clarified some consistent relationships. However, it would be untrue to say that this topic is entirely clear-cut and deserves no future research. Certainly, there is much left to discover in dosing resistance exercise at certain intensites and volumes to elicit an entirely predictable adaptive response.

Notwithstanding, very consistent observations have been made that can help us program training for hypertrophy and strength purposes. Importantly, the type of resistance discussed herein is referred to on a more relative basis (i.e., percent of one rep max [% 1RM]) rather than in an absolute sense (e.g., peak force in Newtons) to better ensure the information provided is practically meaningful. An entire separate article, or book for that matter, could be dedicated to the biomechanical concepts influencing encountered resistances during exercise and how specific parameters can influence adaptive responses on an individual basis. For those interested in these aspects pertaining to the bench press, deadlift, and squat, my good friend Greg Nuckols has made detailed guides freely available on his site StrongerByScience. Furthermore, a future discovery revealing a genetic relationship predictive of more favorable responses to heavier or lighter lifting on a regular basis seems likely. With that said, I continue on with the following points in mind: 1) resistance during an exercise in the weight room is primarily a product of the force of gravity and the mass being lifted, 2) the use of a barbell, dumbbell, or machine influences the specific calculation of an encountered resistance, 3) limb length, torso length, muscle attachment points, and other individual factors also influence the resistance experienced by a muscle or muscles during a movement in the weight room, and 4) individuals with certain genotypes may respond better to more regular light or heavy lifting. With some of the nuances addressed, let’s segue into some helpful content aiding your direction of load selection for growing muscle or improving strength.

In context of resistance exercise, muscular contraction is preceded by the central nervous system (i.e., brain and spinal cord) sending an electrochemical signal to pertinent musculature to contract. The resulting muscular contraction results in pulling forces on the bones to which the recruited muscles attach via tendons. These pulling forces produce movement. An applied force from an external load, via a loaded barbell for example, can restrict this movement. Considering this, the nomenclature of “resistance” exercise makes more sense. The magnitude of the muscle fibers recruited to overcome the resistance of a load is directly related to the mass of the external load (e.g., size principle). Therefore, the heavier the external load, the more muscle fibers recruited to contract, in general (e.g., size principle). Here’s data from a study we performed demonstrating higher electromyography signals during lifting with heavy loads vs lighter loads as a proxy of this phenomenon.

The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog

Since muscle fiber contraction results in the generation of muscular tension (i.e., pulling forces at the fiber level), and muscular tension is the primary stimulus for increasing muscle protein synthesis (MPS), heavier loads (≥ 60% 1RM) more effectively stimulate muscle growth, from a gross perspective, on a per-repetition basis. Although at least one study has shown lighter loads lifted failure result in a higher MPS response compared to heavy loads lifted to failure, certain practical implications should be considered. First, achieving failure in the lighter condition in Dr. Byrd’s study required participants perform ~5 times the number of reps (i.e., ~5 vs ~25). Second, data from the same study mentioned above in our lab suggests that training to failure with lighter loads results in a longer time to recover, compared to lifting with heavy loads. Here’s a figure showing significantly greater reductions in force production at different velocities of contraction after lifting lighter loads to failure compared to heavy loads.

The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog

Also, over the course of 4 sets, participants had to perform ~120 more reps in the light load condition to achieve concentric repetition failure. Check out the figure below.

The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog

Therefore, it stands to reason that for a similar anabolic response to resistance exercise, lifting with heavy loads is a more efficient practice. Please see two other figures from separate review articles showing positive relationships between acute measurements of MPS and percentages of 1RM, and muscle growth responses from sub-chronic training with heavier loads compared to lighter loads.

The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog

From Poortmans, 2016.

The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog
The Importance of Load During Resistance Training: Part 1 | The Aplyft Blog

From Frye, 2004.

Additionally, regular lifting with relatively heavy loads (≥ 75% 1RM) is clearly more effective for improving maximum strength than regular lifting with lighter loads. This is not to say that lifting heavy is the only way to improve muscle size or strength. Rather, it is a more efficient way, in general, particularly for improving strength. The next post in this series will discuss how both light loads and heavy loads can be included in the same periodized program to attempt to maximize the hypertrophy or strength response desired. One is hard-pressed to find strong evidence for the efficacy of lifting light loads to failure to improve strength, particularly in relatively trained individuals. Furthermore, evidence as far back as the early 2000s suggests that training to failure is not nearly as effective for improving strength as not training to failure, regardless of the load.

With the above in mind, it stands to reason that: a) heavier loads more efficiently stimulate acute MPS, b) heavier loads more effectively improve strength, and c) training to failure doesn’t work as well as not training to failure for improving strength. However, some important considerations remain worthwhile. Although using heavier loads is a more efficient practice for stimulating muscle growth and improving strength, there are practical consequences that must be addressed for effective programming. Heavier loads are more fatiguing on a per-rep basis, but training to failure with lighter loads seems to be more fatiguing than training to failure with heavy loads. If we zoom out for a moment, it becomes practically meaningful to consider the best programming configuration that allows for the greatest stimulation of muscle growth processes over a relatively long period of time. Stated differently, we must consider not only the short-term effectiveness of a programming model, but also the long-term ramifications. In this case, programming for hypertrophy and strength becomes a balance between a stimulus to grow or get stronger, in the form of a training session, the time to recover from this stimulus, and the time required to adapt to this stimulus. Understanding these facets would potentially allow the most frequent presentation of a training stimulus that would result in an improvement in muscle size or strength, without impairing the adaptive response to previous training. So, next time, we will consider how light loads and heavy loads can be used in the same program and planned ahead of time to attempt to maximize the hypertrophy or strength response to training.

Best wishes on your training endeavor and feel free to contact me with any questions.