Tyler Robbins Fitness

B.Sc. Biochemistry, Certified Strength and Conditioning Specialist (CSCS), Certified CrossFit Trainer (CCFT/CF-L3), USA Weightlifting Level 1

Filtering by Tag: Hypertrophy

No need to train until failure

“No pain, no gain!”

“If you’re not puking, you’re not working hard enough!”

“Go until you can’t do one more rep!”

That’s how we should train, right? Well no, at least not in untrained lifters, according to a new study in the Journal of Strength and Conditioning Research.

Effect Of Resistance Training To Muscle Failure Versus Volitional Interruption At High- And Low-Intensities On Muscle Mass And Strength.

Abstract

The purpose of the present study was to investigate the effects of resistance training (RT) at high- and low-intensities performed to muscle failure or volitional interruption on muscle strength, cross-sectional area (CSA), pennation angle (PA) and muscle activation. Thirty-two untrained men participated in the study. Each leg was allocated in one of four unilateral RT protocols: RT to failure at high (HIRT-F) and low (LIRT-F) intensities, and RT to volitional interruption (repetitions performed to the point in which participants voluntarily interrupted the exercise) at high (HIRT-V) and low (LIRT-V) intensities. Muscle strength (1-RM), CSA, PA and muscle activation by amplitude of the electromyography (EMG) signal were assessed before (Pre), after 6 (6W) and 12 (12W) weeks. 1-RM increased similarly after 6W (range: 15.8 - 18.9%, ES: 0.41- 0.58) and 12W (range: 25.6 - 33.6%, ES: 0.64 - 0.98) for all protocols. All protocols were similarly effective in increasing CSA after 6W (range: 3.0 - 4.6%, ES: 0.10 - 0.24) and 12W (range: 6.1 - 7.5%, ES: 0.22 - 0.26). PA increased after 6W (~3.5) and 12W (~9%; main time effect, P < 0.0001), with no differences between protocols. EMG values were significantly higher for the high-intensity protocols at all times (main intensity effect, P < 0.0001). In conclusion, both high- and low-intensity RT performed to volitional interruption are equally effective in increasing muscle mass, strength and PA when compared to RT performed to muscle failure.

Ok, so why is this important? How often do you hear from somebody you know who has recently started a workout program, and all they rave about is how tough it is. “My trainer made me do so many squats that I could barely walk for a week afterwards!”

Although D.O.M.S. (delayed onset muscle soreness) is an inflammatory response to something your body is not used to, it doesn’t always mean that you are necessarily improving. The go beyond that, doing something like squats or push-ups until you can no longer do one more rep shouldn’t necessarily be your end goal either.

What the aforementioned study is telling us, is that in untrained individuals, training to failure isn’t necessarily more effective in improving your strength or muscular size. This is quite important to remember for those just starting out in a workout program because the belief is that you must completely destroy yourself in order to improve.

I would argue that movement mechanics and safety outweigh the importance of how hard you work in the beginning. Take note that I still think intensity and effort need to be high in order to start to develop good habits, however, effective coaching where an athlete or participant is scaled and pushed according to their fitness and skill level should be the primary focus.

I run the CrossFit Orangeville Beginner Bootcamp with this very mentality. Sure, the first few sessions involve soreness (read above: D.O.M.S) and some minimal muscular failure, however, the primary focus is on moving well first, and then we begin to scale up the intensity and effort as the strength and fitness level of the participants begins to climb.

Conclusions

It should be noted that this study was conducted on untrained individuals. We have seen research that shows the vast differences between training intensity and volume in trained individuals. Some people seem to be able to handle more or less overall training volume based on a number of variables and circumstances.

Having said that, for untrained folks, this study tells us that just “getting your feet wet” and ramping up intensity later is probably the best option. Not only that, but I see it time and time again when new trainees start too intense, push their bodies to the limit in the beginning, and end up either injured or too sore to move. The far better option would be to push enough (with proper coaching) and staying consistent over time rather than trying to accomplish everything in a workout or two.





Genetics Series: Muscular Size

Being in the fitness industry, I hear the same goals and aspirations all the time:

Females: "I don't want to get too bulky!"

Males: "I want bigger muscles!"

Obviously this is a generalization, because I am sure there are plenty of women whose goal is to increase the size of their muscles, and plenty of men who wish to stay lean rather than get "bulky." What this blog will hopefully inform you is that regardless of your goals, much of your size and strength is already genetically pre-determined and you won't be able to do much about changing that.

I'll explain.

I'm sure I could write many blogs on the social significance of how we are raised, about what an ideal man or woman looks like. How entertainment, the media, professional athletes, etc. all shape the way we perceive the ideal physique should look like. Truth is, many of the professionals you see - whether they are athletes, actors, or models, are either genetically prone to look the way they look, or have had some *ahem* pharmaceutical help to assist their transformation.

I know, I know, this sounds like a whiny cop-out excuse to success. Don't get me wrong, I know that hard work pays off. I advocate hard work and effort to my clients and followers every single day. That is not what I'm saying here. But just as stretching yourself every single day isn't going to make you any taller, training a certain way because someone told you to isn't necessarily going to get your the big huge muscles you think you want. That is the primary focus of this Genetics Series.

Going beyond the hormonal differences between men and women, and the difficulty for most men, let alone women, to grow any measurable amounts of muscle, there are vast differences in the determination and makeup of our muscles. Case in point:

Genetic determinism of fiber type proportion in human skeletal muscle.

Abstract

Skeletal muscle fiber type distribution is quite heterogeneous, with about 25% of North American Caucasian men and women having either less than 35% or more than 65% of type I fiber in their vastus lateralis muscle. To what extent human skeletal muscle fiber type proportion is under the control of genetic factors is examined in this paper. The results summarized here suggest that about 15% of the total variance in the proportion of type I muscle fibers in human is explained by the error component related to muscle sampling and technical variance, that about 40% of the phenotype variance is influenced by environmental factors, and the remaining variance (about 45%) is associated with inherited factors. These estimates suggest that a difference of about 30% in type I fibers among individuals could be explained exclusively by differences in the local environment and level of muscular contractile activity. However, unidentified genetic factors would have to be invoked to account for the observation that the skeletal muscle of about 25% of the North American Caucasian population have either less than 35% or more than 65% of type I fibers.

This study found a 45% variance in muscle fiber distribution from genetic factors. For those of you unaware, type-I muscle fibers are considered "slow-twitch." They don't generate as much force as type-II fibers, tend to be more "aerobic" in nature, or in other words, they can contract for longer periods of time since they don't generate as much force. Elite marathon runners, for example, tend to have higher ratios of type-I to type-II muscle fibers.

On the other hand, type-II muscle fibers ("fast-twitch") generate more force, but can't contract for as long, or for as many repetitions as type-I muscle fibers. Elite strength and power athletes tend to have a greater ratio of type-II to type-I muscle fibers. Type-II muscle fibers have the greatest affinity for muscular hypertrophy or growth. Type-I fibers can enlarge, but not to the extent of type-II fibers. Strength athletes and bodybuilders have larger muscles for this very reason.

So, as the above study found, genetic variance plays a large role in the ratio of type-I to type-II muscle fibers, and can therefore determine not only the strength and performance of said muscles, but also the size of them too.

This study actually focused on creating and testing workout programs specifically designed for genotypes. What they found is exactly what we would expect - participants who are more well-suited for a specific training stimulus based on their genes saw greater results.

The takeaway? Well, not everyone is able to, or should even worry about a genetic test just to determine their optimal training program. Most of you reading this will probably already have a pretty good understanding of what works for you. Some folks are good runners. Some are not. Some lift weights with ease, while others struggle. Regardless of your current situation, however, focus on improving you and stop comparing yourself to others, regardless of how similar you think you may be to someone else.

Key points to focus on:

  • Size isn't necessarily better - bigger muscles aren't necessarily stronger, so even if you can't build big muscles doesn't mean you can't be strong, relative to your size.
  • Your body frame is a pretty good indicator of the size of your muscles and the strength you can gain. If you have big, broad shoulders, for example, you are more likely to also have large, strong muscles.
  • Despite your genetic advantages or disadvantages, hard work will always improve your current situation.

Summary

A couple key points can be summarized from this type of research. First, we know that certain individuals have a greater affinity for muscular growth due to a number of reasons, including their ratio of type-II to type-I muscle fibers, genetic potential for growth, hormonal response, etc.

Changing gears a bit, however, we can also begin to understand the differences in training stimuli and how they affect hypertrophy. Research that tries to understand optimal hypertrophy training styles are quite variable. If there was a one-size-fits-all approach to training, then research would be far more specific in its findings. For example, lower intensity, higher repetition training may be more beneficial for some individuals whereas higher intensity, lower repetition training may be more beneficial for others. What works well for you may not work well for me.

It is impossible to eliminate all variables when it comes to scientific studies, especially genetic variations. That is why whenever you hear of a health study, the results are presented as percentages or trends. Unfortunately, at times, media outlets like to sensationalize headlines. This results in many jumping to conclusions and taking something as truth, rather than understanding that results need to be generalized and applied to a broad populous.

This is applicable to fitness professionals as well. Just because an individual has large muscles or "looks the part" when it comes to training doesn't necessarily mean they are well-suited to coach another individual on how to duplicate those results. They have found an optimal training style that has helped them personally strive for their goals - be it muscular growth, however that does not mean that what worked well for them would also work well for you. Also, be weary of coaches or fitness professionals who paint a broad stroke, offering fitness plans and/or diet plans that is applicable to the masses. Every individual is different, goals are different, health status is different, genetics are different. A well-rounded coach should be one that is educated and stays up-to-date with current trends and research to offer you the most optimal training and nutritional planning.





Rest longer to get bigger and stronger

The "hypertrophy specialist" Brad Schoenfeld has published yet another fantastic study detailing not only the greater strength gains from longer interset rest periods, but the greater muscular growth adaptations too.

Longer Interset Rest Periods Enhance Muscle Strength and Hypertrophy in Resistance-Trained Men

Abstract

Abstract: Schoenfeld, BJ, Pope, ZK, Benik, FM, Hester, GM, Sellers, J, Nooner, JL, Schnaiter, JA, Bond-Williams, KE, Carter, AS, Ross, CL, Just, BL, Henselmans, M, and Krieger, JW. Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. J Strength Cond Res 30(7): 1805–1812, 2016—The purpose of this study was to investigate the effects of short rest intervals normally associated with hypertrophy-type training versus long rest intervals traditionally used in strength-type training on muscular adaptations in a cohort of young, experienced lifters. Twenty-one young resistance-trained men were randomly assigned to either a group that performed a resistance training (RT) program with 1-minute rest intervals (SHORT) or a group that employed 3-minute rest intervals (LONG). All other RT variables were held constant. The study period lasted 8 weeks with subjects performing 3 total body workouts a week comprised 3 sets of 8–12 repetition maximum (RM) of 7 different exercises per session. Testing was performed prestudy and poststudy for muscle strength (1RM bench press and back squat), muscle endurance (50% 1RM bench press to failure), and muscle thickness of the elbow flexors, triceps brachii, and quadriceps femoris by ultrasound imaging. Maximal strength was significantly greater for both 1RM squat and bench press for LONG compared to SHORT. Muscle thickness was significantly greater for LONG compared to SHORT in the anterior thigh, and a trend for greater increases was noted in the triceps brachii (p = 0.06) as well. Both groups saw significant increases in local upper body muscle endurance with no significant differences noted between groups. This study provides evidence that longer rest periods promote greater increases in muscle strength and hypertrophy in young resistance-trained men.

Research has previously told us that greater rest periods are superior to shorter rest periods when it comes to strength and power adaptations, but there hasn't been nearly as much support and evidence suggesting the same for hypertrophy training.

The belief that shorter rest periods are ideal for training for hypertrophy purposes is challenged with research like this. Not only do we know that longer rest periods are superior for strength and power adaptations, research like this is indicating that longer rest periods illicit greater muscular growth as well. One could postulate that longer rest periods allow for greater recovery and therefore greater force and output on every subsequent set. More force and output on each set allows for greater overall training volume, which would increase the training load.

I also appreciate the fact that this study was conducted on trained individuals. Many strength and hypertrophy studies are conducted on non-trained individuals, who more often than not improve their strength and muscular size simply by being in the study alone (noob gains).

So, how practical is this for you, the reader?

Well, it would appear that rather than slugging through sets with short rest periods, you would be better off resting for longer periods and allowing your muscles to recover more in order to maximize the potential on each subsequent set.

The disadvantage to this training style includes the obvious fact that workouts could potentially take much longer if you are resting for longer periods and one of your primary goals includes getting stronger and increasing muscular size. Rather than waiting around between sets, however, you can get creative with your training and do good old fashioned circuits, training antagonistic movements. For example using an EMOM (every minute on the minute) setup, training bench press on the first minute, barbell row on the second minute, an accessory or core movement on the third minute, rest the 4th minute, and then repeat. This allows the time between exercises to be at least 3 minutes yet keeps you moving the entire time to save on overall workout length.





Your Complete Guide to Sets and Reps

This is an updated guide to reflect the latest science and research surrounding sets and reps and how they relate to muscular strength, endurance, and hypertrophy (muscular growth).

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Focus on the areas in yellow, as these are the "optimal" zones for each training goal. Keep in mind that although you may benefit in various training ranges, there are just rep ranges to focus on based on what your training goal is. For example, you will gain some muscular strength from doing a 20+ rep set of an exercise, however choosing a resistance that keeps you in a 5 or under repetition range is optimal for strength gains.

Strength training is generally most improved in the 1-5/6 repetition range.

Power is generally most improved in the 1-4/5 repetition range.

Endurance is generally most improved in the 12+ repetition range.

Hypertrophy has generally been thought to be most improved in the 6-12 repetition range, although this is the one section that will be most discussed in this guide as some of our current knowledge is being challenged by recent research.

Core vs. Assistance Exercise

You may think a "core" exercise is one that involves the abdominals. The true meaning of a core exercise refers to one that recruits one or more large muscle areas (chest, shoulder, back, hip, thigh), involve two or more primary joints, and receive priority when one is selecting exercises because of their direct application to sport. An example of a core exercise would be a squat because it involves large muscle groups such as the gluteals, quadriceps, hamstrings, etc. and involve more than one primary joint (knees, hips).

"Assistance exercises" on the other hand, usually recruit smaller muscle areas (upper arm, abdonminals, calf, neck, forearm, lower back, or anterior lower leg), involve only one primary joint, and are considered less important to improving sport performance. An example of an assistance exercise would be a leg extension.

I generally don't recommend strength training for assistance exercises. For example, I wouldn't recommend using a weight that keeps you under 6 repetitions for something like a biceps curl.

How muscles contract

We sometimes perceive our muscles as self-controlling structures that abide by an "all or none" mechanism. This is simply not true. Your muscles are made up of muscle fibers, none of which are thicker than a strand of hair. When your muscle contracts, the entire length of the muscle shortens, however only a small percentage of the muscle fibers are doing the work. So, although all of the fibers are shortening in length, only a specific percentage of the fibers are actually completing the work at any given time.

For the purposes of our explanation, let's imagine a toddler biceps curling a 5lb. dumbbell. Because of the amount of overall strength required to lift the 5lb. dumbbell, the toddler will require quite a large percentage of the muscle fibers in their biceps to contract to lift the dumbbell. An average adult, on the other hand, could curl a 5lb. dumbbell with little to no effort at all meaning that a lower percentage of their muscle fibers are actually doing the contracting.

Why is this important? Well, when your muscle fibers fatigue, the fibers that were doing the work stop contracting and other fibers step in to complete the work. There are always at least a small percentage of your muscle fibers resting while others are doing the work. If we think of our dumbbell curl example again, chances are the toddler won't be able to curl the dumbbell as many times as the adult because they are recruiting a higher percentage of muscle fibers for every single repetition, leading to quicker fatigue and failure.

Muscle fiber recruitment is orchestrated by the muscle's neurons. One, often overlooked, positive adaptation to resistance training is the improvements in your mind to muscle connection. Basically, your neurons greatly improve their efficiency at "recruiting" muscle fibers.

So not unlike learning a skill, where your brain must train a synchronized orchestration of your muscles to act in a specific order of events, to say - throw a baseball, the brain must also learn how to actively recruit more muscle fibers in order to generate more force.

It should be noted that during the first 8 weeks of a resistance training program for beginners, nearly all of the "gains" achieved from resistance training can be attributed to neural adaptations. So, even though one may be experiencing strength gains, this is not due to an increase in muscle size or any measurable improvement in the strength of the muscle itself, instead, it is an improvement in the efficiency of the mind to muscle connection!

Repetition Goals

Use the following table to help yourself better estimate the loads you can lift at various repetition goals.

%1RM
Repetitions
100
1
95
2
93
3
90
4
87
5
85
6
83
7
80
8
77
9
75
10
70
11
67
12
65
15

Strength/Power

With our quick lesson on neural adaptations and muscle fiber motor units out of the way, let's discuss how this pertains to strength gains. In the most basic terms, strength is the ability for your muscles to generate as much force as possible. Power, on the other hand, is the ability for your muscles to generate a lot of force quickly. Strength is extremely beneficial for those looking to be able to lift or move heavy objects, but not necessarily within a specific amount of time.

Power, which is closely related, is about generating a lot of force (strength) in as short amount of time as possible. Power has very direct correlations to sport and athleticism. It should be noted that increasing your strength will also help to improve your overall power as strength and power are so closely related.

Keep a mindset that strength and power gains are primarily a "learned" skill. Like we discussed above, by training for strength, our muscles are getting stronger by training our brain how to activate high threshold muscle motor units more effectively. There is a limit to the amount of strength any given muscle in your body can produce, limited by a number of factors including limb length, joint angle, skill, technique, genetics, ratio of type 1 to type 2 muscle fibers, etc. Many of these topics will have to be covered in future blogs.

A definitive stance is proven time and time again with resistance training, strength and power output is most improved in individuals training in the 5 or fewer repetition range. Although endurance and hypertrophy training can be adjusted and benefited from varying repetition ranges (more on that later), we know that strength and power is most greatly improved with higher intensities (high weight).

Strength Repetition Goal:
1-6
Primary Energy System:
ATP-CP
Ideal Rest Periods:
2-5 minutes

Endurance

Like strength and power training, I would consider endurance training to also be a "learned" skill set for your muscle cells. Although strength and power can be considered a "learned" skill, considering the brain is becoming more effective at activating muscle fiber motor units, endurance training can be considered a skill on more of a cellular level as your muscle cells are learning how to become much more aerobically efficient.

Endurance training is highly beneficial for athletes that compete at longer-duration events such as distance running, swimming, etc. It should be noted that sports like hockey or even soccer, although they may be considered sports that requires a higher level of aerobic efficiency, are actually a series of highly intense intervals that would benefit greater from training plans intended for the work duration of such sport.

Endurance Repetition Goal:
12+
Primary Energy System:
Aerobic or Oxidative
Ideal Rest Periods:
30-60 seconds

Hypertrophy

This is decent video to get most of you up to speed on muscle fiber types and how resistance training can cause muscular damage leading to growth (hypertrophy). I will admit that I was a bit disappointed because the video seemed very rushed and ended abruptly, missing a lot of key points. I was also quite surprised that they even made mention of muscular hyperplasia. Hypertrophy is the actual enlarging of muscle cells (increase in volume) whereas hyperplasia is the division of muscle cells - increase in overall quantity. Although it is certainly possible to increase the overall number of muscle cells, the evidence for this isn't entirely clear and most likely does not apply to the general population.

While strength/power and endurance training could be considered a "skill" as I mentioned previously, hypertrophy should be considered a stimulus. In other words, our training is creating a specific demand within our muscle cells to signal growth. This is one area that not only generates a lot of interest amongst fitness enthusiasts, but researchers as well. For years, many thought that training within a 6-12 rep range was optimal for muscular hypertrophy or growth. Research, although not necessarily refuting that evidence, is trying to explain the greater picture in how or why muscles grow and how varying stimuli can promote muscular growth.

As it turns out, the number of repetitions you do does not entirely matter how much muscular growth is promoted. In other words, rep range does not matter for hypertrophy.

In conclusion, this study showed that both bodybuilding- and powerlifting-type training promote similar increases in muscular size, but powerlifting-type training is superior for enhancing maximal strength.

Ideally, your training should meet your needs, goals, and desires. If you wish to train to improve strength and/or performance, then stick to lower repetition ranges with higher intensity. If you wish to train for more aerobic events, then lower intensities and higher repetitions should be targeted.

This study demonstrates that both intensity and exercise-induced metabolic stress can be manipulated to affect muscle anabolic signaling.

What about our previously-thought belief that rest periods determine the growth of muscles? Well, apparently not.

In conclusion, the literature does not support the hypothesis that training for muscle hypertrophy requires shorter rest intervals than training for strength development or that predetermined rest intervals are preferable to auto-regulated rest periods in this regard.

One more variable we can throw into the mix is research that has looked at oxygen restriction and how it affects hypertrophy signalling. One study used tourniquets to restrict blood flow to working muscles to discover whether or not this would alter training stimulus or signalling.

Blood flow restriction resulted in significantly greater gains in strength and hypertrophy when performed with resistance training than with walking. In addition, performing LI-BFR 2-3 days per week resulted in the greatest effect size (ES) compared to 4-5 days per week.

Sarcoplasmic Hypertrophy

Source: http://slidingfilament.webnode.com/skeletal-muscle/

Many coaches or gym bros may want to talk your ear off about how much physiology they know and spout off a very detailed explanation about the two different types of hypertrophy - myofibrillar vs. sarcoplasmic. As the story goes, you can enlarge your muscles either one way or the other. Myofibrillar hypertrophy refers to the enlarging of the structural framework of the muscle fibers whereas sarcoplasmic hypertrophy refers to the increased fluid of the muscle cell sarcomeres.

Anywhere from 70-80% of a muscle cell is made up of structural proteins. If you were to increase the volume of the sarcoplasm and therefore the sarcomere, you would have to increase the overall structural framework of the muscles too. It would be like making the inside your house bigger without actually building any additional walls. In order to increase the size of the sarcoplasm/sarcomere, you have to increase the amount of contractile proteins too. Don't believe me? Check out this study:

The linear distance between myosin filaments (38.7 +/- 0.3 nm before, 38.7 +/- 0.4 nm after training; mean +/- S.E.M.) as well as the ratio of actin to myosin filaments (3.94 +/- 0.03 before, 3.86 +/- 0.06 after training) did not change with training. 3. These results refute the concept that the increases in muscle strength or radiological density during short-term heavy-resistance training are caused by changes in myofilament spacing.

In other words, although the muscles got bigger, the framework didn't simply increase in distance, it had to increase in overall quantity. Both sarcoplasmic and myofibrillar hypertrophy happen at the same time making any discussion about differentiating them total bullshit. There is zero evidence to back up sarcoplasmic hypertrophy. Period.

Hypertrophy Repetition Goal:
Any
Primary Energy System:
Varies
Ideal Rest Periods:
Based on goals/availability

Ok, so for the purposes of hypertrophy training, here is what we can summarize:

  • Lifting heavy things makes you better at lifting heavy things. The heavier you lift (fewer reps), the stronger you will get.
  • Lifting lighter things many times makes you better at, well, lifting lighter things multiple times. In other words, your muscles become more fatigue resistant, also known as endurance training.
  • Volume is the key. You must push your muscles to at least close to failure multiple times to promote growth.
  • Oxygen depletion seems to also promote hypertrophy signalling, so by training at a high rate of metabolism, such during high-intensity interval training (HIIT), you can still promote muscular growth.
  • Forget the term "toned." Nobody should train at higher repetitions to "tone."
  • Stimulating muscle cells to increase in size through resistance training can only take you so far, a proper diet rich in protein and sufficient calories is what makes or breaks most cases of hypertrophy. Oh yeah, hormones count too.
  • There is no such thing as sarcoplasmic hypertrophy so don't let anyone tell you otherwise.

Sets, Repetitions, and Training Goals Summary

Strength - High-load, low-repetition training to improve overall strength of the muscle(s) being trained. Should mainly be targeted by "core exercises." Long periods of rest between sets to allow full recovery of muscle fibers in order to produce maximum amount of force every subsequent set. Remember that many of the strength gains achieved come from improved neuromuscular patterns.

Power - High-load, low-repetition training similar to strength training but designed to increase the overall explosiveness of the muscles. Also designed to be targeted by "core exercises" only. Also intended to have long periods of rest between sets to promote full recovery. Like strength, many power gains are achieved by improving neuromuscular patterns.

Hypertrophy - Enough volume to challenge your muscles to fatigue as many of your overall muscle fibers as possible in order to elicit growth. There is also a potential for growth simply by working until extreme fatigue to create a lack of oxygen and energy replenishment to the muscles such as HIIT training.

Muscular Endurance - Low rest periods, higher rep goals, lower loads. Ideally used to improve the aerobic efficiency of the muscle fibers. Should be used by endurance athletes to improve muscular efficiency. Not intended to improve overall strength or power, however.