Grit Determines Success, Unilateral vs Bilateral Training

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I’m about half way through a book that I have been recommending like crazy: Grit, by Angela Duckworth. Angela is the founder/CEO of The Character Lab as well as a psychology professor at The University of Pennsylvania. I have a great appreciation for her deep curiosity, displayed in the book as well as my once personal conversation with her. In her book, she spent some time speaking about a particular study I was surprisingly unfamiliar with but became more intrigued to research further.

The Grant Study was named after William T. Grant, who owned a chain of nation-wide 25 cent stores which ultimately funded the initial methods of the experiment. The longitudinal social science study began in the early 1940’s, and actually continues today. In 1966, the study was taken over by a new principle investigator, George Vaillant, for many decades to come. 268 male Harvard sophomores were the chosen subjects. The measured criteria included: vitals, athletic aptitude, somatotype, masculine features, intelligence, perseverance on a treadmill, and more subjective questionnaires. Given my background, I am quickly intrigued by the treadmill of course. The procedure was to put the participants on a treadmill at a given intensity, instructing the men to maintain pace for five minutes. Some lasted for less than two minutes, others for four minutes. The researchers then tried to normalize conditions for a second bout to adjust for individual variability in aerobic capacity. The second bout was aimed to better measure who was able to persevere through the discomfort, retain mental strength, and hold pace.

The objective of the study was to follow the men for many years to come (still occurring almost 80 years later), and correlate certain measurements to health and happiness. Funny enough, the men who were able to last longer on the treadmill reported enhanced levels of well-being numerous decades later. These participants reported higher self-satisfaction professionally and, in their marriage, fewer sick days, and also greater career growth and income.

The running test at age 20 was found to be a strong predictor of health throughout life. It seems physical health may later predict psychological health, as the second (normalized) trial on the treadmill didn’t show any greater influence than the first trial. These results show that fitness levels, and maybe more so relentless effort, could be key indicators for happiness later in life. Researchers knew the running would show if “a subject is willing to push themselves or has a tendency to quit before the punishment becomes too severe.” How hard you push yourself today may decide your success and happiness tomorrow.

The remaining participants are still being studied and interviewed today. “Some men came to Cambridge to be interviewed, but in most cases I went to them—to Hawaii, Canada, London, New Zealand,” wrote the now 82 year-old George Vaillant in Triumphs of Experience: The Men of the Harvard Grant Study. The Grant Study is now the longest running longitudinal study in the history of social sciences, now being head by Dr. Robert J. Waldinger of Massachusetts General Hospital. The study has included some very accomplished men, including four members who ran for the U.S. Senate, one who served in a presidential Cabinet, and former President John F. Kennedy.



The NSCA has been doing a nice Point/Counterpoint Column moderated by Dr. Andy Galpin. Last month the topic was the effectiveness of unilateral vs bilateral movements. Here are 5 key points from each of the authors.

Unilateral Training, by Kurt Mullican of Barbell Shrugged and IMA Crossfit

  • “Many coaches and researchers now recognize the existence of the bilateral force deficit (BLFD), a phenomenon in which force production per limb, when added together, is greater than the total force generated when both limbs contract simultaneously.” Higher BLFD has been demonstrated in untrained populations.
  • In this case, performing BIL movements would be limiting strength adaptations since “…force production during UNI movements can account for more than 50% of the total force produced during an equivalent BIL exercise. For example, an individual may be able to perform a single-leg press with 60 lbs, yet only able to perform a 2-leg press with 100 lbs.”
  • A recent piece of literature cited the importance of mitigating BLFD as higher BLFD was “…inversely related to sprint start performance, total impulse of force, and velocity on the starting blocks.”
  • One study observing academy rugby players showed that BIL training was no more effective than UNI when observing 40m time, change of direction, and lower body strength. Despite this, UNI training proved to increase vertical jumping more than BIL training.
  • One advantage of UNI training may be the increased activity of secondary movers while still having high demands on the primary mover. An example provided was a split squat placing an increased demand on the adductors compared to BIL squatting patterns. Along with this, it is reasonable to assume UNI movements require higher neuromuscular coordination as well.

Bilateral Training by Ramsey Nijem of the Sacramento Kings

  • Certain literature has shown BIL facilitation, in which the force produced BIL is greater than the sum of forces produced UNI. This would be essentially the opposite phenomena as the previously defined BLFD.
  • Data appears strong that the BLFD is present in untrained populations, which may show that this is only a concern for untrained populations. It may be reasonable to infer that trained athletes mend the BLFD in most periodized programs, whether emphasizing BIL or UNI movements.
  • There is some early evidence to suggest that UNI training may increase the BLFD, whereas BIL training shows to decrease this deficit. This should be studied more abundantly before drawing strict conclusions. From a specificity standpoint, it would make sense that BIL training may diminish the BLFD and possibly increase BIL facilitation.
  • UNI training has shown to increase UNI endurance, but not BIL; where BIL training increased both BIL and UNI endurance. Again, specificity is key here.
  • There is some information which may “…tentatively indicate UNI provides more rapid, yet shorter lasting effect, while BIL offers a slower, more sustainable improvement” in the adaption of various training programs. Therefore, more immediate adaptions may be seen from a UNI training phase when compared to a BIL phase. 

Both points were nicely articulated, showing that there is a place for both UNI and BIL training phases within a well periodized program.


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