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: Endurance

Long-Term Twins Study

I came across quite a fascinating study published in the Journal of Strength and Conditioning Research.



Variations in physical ability between individuals depend on both training background and genetics. Previous research has investigated the details of this phenomenon by studying monozygous (identical) twins with long-term, moderate differences in physical activity patterns and/or monozygous twins with short-term, but greater differences in physical activity patterns. However, no previous research has used monozy-gous twins with both substantial and long-term differences in physical activity patterns. Purpose: Thus, to enhance our understanding of heritability and adaptability of various performance factors we analyzed the physiological profile of a set of monozygous twins with 35 years of differing exercise habits. Methods: One pair of male monozygous twins (age = 52 years) participated in this study. DNA testing confirmed zygos-ity. The trained twin (TT, ht = 186 cm mass = 94 kg) is a physical education teacher and track coach who began running crosscountry and track in 1981. TT has been training and competing in endurance sports (e.g., running, triathlons, etc.) consistently over the past 35 years. He has ;39,431 running miles recorded from July 1993 to June 2015. In 2005, he qualified for All World Bronze Level in the Ironman. The untrained twin (UT, ht = 183 cm, mass = 104.5 kg) is a delivery truck driver. He was recreationally active in swimming, biking, and team sports early in life, but, has not engaged in regular or structured exercise since then (;35 years). Since 1991 UT recreational physical activity has been limited to ;20–30 min walks, 3–43$wk 21. Both participants performed 4 trials of 6-second maximal isometric contractions of the right leg exten-sors, 5 trials of grip strength testing with both hands (hand grip dynamometer), as well as a maximal aerobic capacity (V _ O 2 max) test (cycle ergometer). Additionally, a dual-energy X-ray ab-sorptiometry scan was used to determine body composition and total bone mineral content (BMC). Results: UT displayed higher absolute peak torque (254 vs. 137 N$m, 59.9% difference) and grip strength (right = 56.5 vs. 44.3 kg, 24.2% difference ; left = 51.7 vs. 43.7 kg, 16.8% difference). When normalized to lean body mass (LBM), UT continued to display higher peak torque (3.40 vs. 1.83 N$m 21 $kg 21 , 60% difference) and grip strength (right = 76 vs. 59% of LBM, 25.2% difference; left = 69 vs. 58% of LBM, 17.3% difference). However , UT had a lower absolute (3.67 vs. 4.66 L$min 21 , 23.9% difference) and relative (35.1 vs. 47.5 ml$kg 21 $m 21 , 30.1% difference) V _ O 2 max. UT also had a higher body fat percentage (BF%) (27.8 vs. 19.2%, 36.6% difference), but nearly identical LBM (74.6 vs. 74.7 kg, 11.0% difference) and BMC (3575.7 vs. 3653.0 g, 2.1% difference). Conclusions: Long-term, mixed mode endurance training positively influenced V_ O2max and BF%, did not alter LBM or BMC, and was associated with lower isometric leg extensor and handgrip strength. The percent difference between the participants also demonstrates a level of “trainability” that exceeds previous research. Practical Applications: Leg strength and V_ O2max are significant and independent predictors of mortality. Training can influence both of these variables. However, adaptations are specific to imposed demands. Therefore, an ideal lifestyle approach should incorporate resistance exercise and endurance training to maximize both leg strength and aerobic capacity. Journal of Strength and Conditioning Research | www.nsca.com VOLUME 30 | SUPPLEMENT 1 | DECEMBER 2016 | S43-44

One of the toughest variables to control for in the world of health and fitness and strength and conditioning is the large variation in genetic differences. Monozygous (identical) twins tend to be "holy grail" subjects to study because they are identical, genetically. Therefore, we can then study how lifestyle habits relate to their overall health without having to factor in the genetic variability.

There have been studies done in the past comparing lifestyles of twins, but this study in particular is so amazing due to its length of time - 35 years. Let's break down the differences between the two twins above:

Trained Twin (TT)

  • Phys. Ed. teacher
  • Track Coach
  • Started running cross country track in 1981
  • Training and competing in endurance sports (e.g. running, triathlons, etc.) consistently for 35 years.
  • 39,431 total running miles logged from July 1993 to June 2015.
  • 2005 All World Bronze Level Ironman qualifier.

Untrained Twin (UT)

  • Delivery truck driver.
  • Active early in life but has not engaged in structured physical activity in 35 years.
  • Activity has been limited to 20-30min walks.


  • UT is stronger.
  • TT is healthier aerobically (VO2 Max).
  • TT has less overall body fat.
  • Both UT and TT have essentially the same amount of muscle (lean body mass).


It is to be expected that the trained twin is "fitter" overall aerobically, after all, he has been running close to 40k miles in the last 24 years alone. Having said that, how much healthier is he? The untrained twin has just as much muscle mass as his the trained twin, and despite the fact that he is heavier due to carrying around more body fat, is actually stronger despite the fact that he doesn't "exercise."

Now, there could be a discussion or argument made towards the activity level of the untrained twin. Sure, he hasn't been following a structured exercise or strength and conditioning program, but being a delivery truck driver, one could assume has its fair share of physicality to it. Not only that, but just the act of carrying around extra body mass requires more physical exertion and strength requirements from the muscles.

Despite all of that, this should be a large eye opener for chronic endurance athletes. As this study points out at the end:

Therefore, an ideal lifestyle approach should incorporate resistance exercise and endurance training to maximize both leg strength and aerobic capacity.

Would I classify or consider the untrained twin to be "healthy?" Not by any stretch of the imagination. However, lower body strength is actually a significant predictor of mortality, and in this case, the untrained twin actually has a lower risk of mortality than the trained twin.

Not only that, but it is not uncommon for runners or endurance athletes to completed avoid lower body training because they "get enough strength work" from running/cycling/swimming. Although endurance exercise may improve your overall aerobic capacity, it does not replace the need for lower body strength and conditioning work. Squats, deadlifts, lunges, etc. are so critical and crucial to not only improve the strength and functionality of the lower body, but to reduce the effects of aging as well.

Many readers to my site know that I have been a bit critical of chronic endurance exercise, despite my fair share of it in the past. Training for, and competing in, a marathon, triathlon, Ironman, etc. is a great life goal and something many put on their bucket list. Having said that, for overall health, performance, body composition, and longevity, a well-rounded strength and conditioning program with a little bit of everything (see: moderate running) is the best approach in my opinion.

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).


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.



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:
Primary Energy System:
Ideal Rest Periods:
2-5 minutes


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:
Primary Energy System:
Aerobic or Oxidative
Ideal Rest Periods:
30-60 seconds


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:
Primary Energy System:
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.