Tyler Robbins Fitness

Tyler Robbins has his B.Sc. in Biochemistry: Pre-Medical, is a Certified Strength and Conditioning Specialist (CSCS) through the National Strength and Conditioning Association (NSCA), is certified through USA Weightlifting, and a CrossFit Level 2 Trainer.

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.