In this post we are going to look at the impact that the load we choose to use whilst performing an exercise has on our results. This is the second in a series of blog posts inspired by and featuring recent conversations with James Fisher, Senior Lecturer Sports Conditioning and Fitness at Southampton Solent University, and James Steele, Principal Investigator at UK Active Research Institute; Associate Professor Sport and Exercise Science at Southampton Solent University. Read the first one on perception of effort and its impact on achieving true muscular failure.
In research, the load used for an exercise is often referred to as a % of 1 rep max (%1RM) for that exercise. We also see and hear the terms “heavy load”, “light load” and “heavier load” and “lighter load” used a lot too, but what do these descriptors actually mean? There may be no exact agreed upon measure or definition for these terms, however, below is a suggested practical template of load categories and their predicted time under loads (TUL) to reach momentary failure (MF):
When exercising with strength and hypertrophy adaptations in mind we need to recruit all the motor units in a target muscle group.
In a heavy load set (as defined above), full motor unit recruitment occurs from the start of the set. With moderately heavy and moderately light loads, motor unit recruitment is increased as the set progresses and fatigue builds resulting in full recruitment in the reps just prior to MF. Therefore heavy, moderately heavy and moderately light loads all have the potential to optimize strength and hypertrophy.
With light loads there is a probably a load threshold below which full motor recruitment may not occur meaning that strength and hypertrophy adaptations are not fully realized.
– James Steele
A recent research paper (1) has suggested that very light loads- 20% 1RM, stimulate less hypertrophy than loads of 40% 1RM and above. I covered this research in some detail in another article, titled The Long Read on Muscle Fibers: Types, Strength, Hypertrophy and Training Optimization. Fisher and Steele have also referred to this possibility that there may be a threshold load below which hypertrophic adaptation suffers too, in an opinion piece (2).
Lesser hypertrophy seen with using light loads may be influenced by another factor too: a level of discomfort that blurs the ability of subjects to go to true MF (2). Fisher and Steele both state that the longer it takes to get to MF the higher the level of discomfort the trainee will experience (3, 4).
Light load sets lasting longer than 2 minutes to MF may be effective, but only with a highly motivated individual who can tolerate discomfort well. James Steele has himself been known to knock out a 3+ minute wall-sit, and as a pre-exhaust to body weight squats no less! However, it is probably prudent to consider sets longer than 2 minutes to be less than ideal in most circumstances, due to discomfort and other factors we will look in to below. James Steele highlights practical application, “if someone dislikes the discomfort then use a heavier load, especially if the discomfort prevents them from reaching failure.”
At the other end of the spectrum training with heavy loads (>80% 1RM) can certainly stimulate hypertrophy effectively however it is very likely that using these loads will require a multiple-set approach to do so, due to the brevity of each individual set (5-25 seconds).
The Sweet Spot?
– James Fisher
This leaves moderately heavy and moderately light loads as practical for use in a single set to MF approach, for most people. This means selecting a load that can be used to bring about MF somewhere between 30-120 seconds, in other words a load in the range of 40-80% 1RM.
30-120 seconds still represents a broad window, are there advantages to gravitating toward one end of this spectrum or the other? James Fisher reiterates that a moderately heavy load and shorter TUL “makes it easier to reach true muscular failure.” And that with a load of 40% 1RM or less “discomfort is a lot higher and likely prevents people reaching true muscular failure.” He elaborates, “The physiological sensation of pain and discomfort is so great that psychologically I tell my body I can’t carry on.” In real world terms a 90-120 second set to MF is going to be a more uncomfortable experience than a 30-60 seconds set to MF.
This is a valuable insight for personal trainers working with a wide variety of clients, particularly when training those who are not as motivated to really go at a set and achieve MF. Some individuals will be more likely to end a set prior to MF due to the aforementioned discomfort with a longer set. As a trainer why put clients through more pain and discomfort than necessary, you do after all want them to come back! See the previous post in this series for more detail on discomfort during exercise.
But Lighter Loads Are Safer Right?
Seems intuitive to think so, indeed there is often an assumption that heavier loads are inherently riskier or more dangerous than lighter loads, but is this really the case? Research is beginning to reveal that this seemingly intuitive line of thinking may be inaccurate.
Both James Fisher and James Steele were involved in a recent paper that showed it preferable to use a 6RM load (~30 seconds TUL) compared to a 15RM load (~75 seconds TUL) when training hypertensive postmenopausal women (5).
The lighter load group showed increased markers related to cardiovascular stress. James Steele explains how the different loads used impacted on Heart Rate Variability. The subjects who used the lighter load saw increases in sympathetic nervous system activity (SNS) after the workout whereas those who used the high loads did not. Increased SNS activity represents fight or flight mode and a catabolic environment: a stress on the physiology. Steele points out that hypertensive individuals already tend to have a predominance of SNS activity and it is preferred that an exercise protocol doesn’t exacerbate this. Higher load exercise where MF occurs closer to the 30 second mark may well be prove to be safer for hypertensive individuals.
James Fisher recalls that after writing a letter to the editor of Sports Medicince in 2013 (6) critiquing a review article by Schoenfeld (7) he has often been assumed to be in the “lighter load” camp. He emphasises this is simply not the case and if anything, he is “finding more and more reason to lift heavier loads.” He offers the example of a paper by researchers Genner and Weston (8) that showed lighter sets (55% 1RM) resulted in “clear substantial increases” in blood lactate and salivary cortisol when compared to heavier sets (70 and 85% 1RM). This again suggests that lighter loads are more physiologically stressful than heavier loads, when both are performed with the same degree of effort (i.e. both to MF). As Fisher points out lighter load training is certainly not easier, not only are levels of experiential discomfort higher, metabolic stress is greater, and recovery takes longer too: physical function may be impaired for successive days due to greater muscle damage.
Whilst moderately light loads taken to MF provide as good a hypertrophic stimulus as moderately heavy loads to MF, moderately light loads appear to have potential downsides. Again, the question arises why put yourself or your clients through more discomfort and stress than necessary to stimulate the benefits of exercise?
What about Bone
James Fisher raises an important, often overlooked point amongst individuals focused on muscle hypertrophy, what about bone? He notes that most research on strength training for bone mineral density suggests a load of 80% 1RM or greater is required and “a set lasting 3 minutes might be fine for strength and hypertrophic adaptation but not for bone mineral density.” Indeed if bone strength is a primary concern it is then possible that MF may need to be achieved at the lower end of our TUL spectrum, perhaps in the 30-50 second range with a load equating to around 80% 1RM.
A Practical Approach
James Fisher suggests using a load that brings about MF within 30-90 seconds may be optimal when using single sets per exercise: short enough so that discomfort doesn’t significantly impede on the effort/ability to reach MF. This would equate to a load of about 50-80% 1RM. James Steele adds: “in an initial session stick with a moderate load and then experiment from there.”
For those that either struggle with discomfort during training, feel wiped out after workouts or fatigued for several days it may prove helpful to use moderately heavy loads closer to 80% 1RM levels that bring about MF within 30-60 seconds. Remember loads at around 80% 1RM are also shown to be less stressful on the cardiovascular system, cause less metabolic stress, less fatigue and are more likely to enhance bone mineral density.
Other individuals may not face the issues above at all, perhaps even enjoying the challenge of enduring the discomfort of longer sets. If this is you, you can at least periodically use moderately light load sets seeing TULs gravitate upwards towards 2 minutes.
Ultimately because the effective loading range and TUL span for stimulating strength and hypertrophy adaptations when training to MF, are relatively broad, personal preference can be allowed to influence loading and TUL choice. As James Steele notes this can have a very practical impact on long term adherence: beneficial for your own training, and for personal trainers: for your clients and business too.