Unique training for unique athletes (that’s you!)

Humans are all genetically unique, so what does this mean for the way training programs should be constructed? SPB looks at recent research

As a student of biochemistry many moons ago, I was well aware that each human is unique. However, it wasn’t until a read a revolutionary book titled ‘Biochemical Individuality’ written by an insightful scientist called Roger J. Williams that I realized just how different we all are. As Williams’ book explains (supported with studies from the literature), even identical twins are not identical biochemically. Even closely related people have varying sizes and shapes of different organs, such as hearts and livers, different enzymatic, endocrine and excretion patterns, different reactions to drugs, and different needs as to the amount of various vitamins and minerals they require and more.

Individuality and athletes

Even though the evidence on biochemical and physiological individuality is overwhelming, it’s surprising just how often this self-evident truth can be forgotten when designing training programs for athletes. It’s not just variations in the way that different athletes perceive or enjoy the same training program. Research has established that our physiological responses to the same training stimulus can vary greatly.

As an example of this athletic biochemical individuality, a pioneering study on ten sets of identical twins in 1984 found considerable individual differences in the training response to a short-term endurance training program(1). At the time, this greatly surprised the scientific community because genetically, identical twins are extremely similar, with only tiny differences arising in their genotypes during the nurturing process. Since innate muscle biochemistry is largely determined by genotype, you would have expected responses to an identical training program to be nearly identical!

Later studies confirmed that large differences do indeed exist in the way athletes respond to a training stimulus. For example, several studies found that athletes attained very similar adaptations in performance and physiological parameters after training schedules involving markedly different exercise volumes and intensities(2,3). More recently, other studies in which athletes have undertaken the same moderate-intensity continuous training and high intensity interval training (HIIT) programs have shown that the training responses between individuals are hugely variable(4,5).

Individuality in runners

In a 2020 study, Portuguese scientists investigated the individual training responses of 20 female recreational runners(6) who undertook either moderate-intensity continuous or high-intensity interval training (HIIT) for a period of 12 weeks, then competed in the same half marathon race. In the moderate-intensity group, the range of responses to the continuous training were highly variable; three subjects were high responders with a mean time reduction of 15 minutes, four subjects were normal responders achieving a mean decrease in their finishing time of 2 minutes 26 seconds and three subjects were non-responders, increasing their mean previous finishing time by 5 minutes and 31 seconds! The responses in the HIIT group were even more variable; five subjects were responders, with an average time reductions of 7 minutes 54 seconds compared to the mean of their previous finishing times, while the other five were non-responders, increasing their mean previous finishing time by 3 minutes 37 seconds (see figure 1).

Figure 1: Individual percentage changes before and after the training program(6)

(A) – percentage changes in time comparing previous (before) finishing times and the finishing times. (B) – percentage changes in VO2max before and after the training programs. (C) – percentage changes in time to exhaustion (TTE) obtained in a field maximal incremental test before and after the training programs.

In practice, this research demonstrated that there’s no way of knowing for sure whether an athlete will likely be a good or poor responder to a particular mode of training such as HIIT. This suggests that athlete will need to constantly monitor their progress when embarking on a new training program; rather than slogging on endlessly with a program and hoping for the best on race/competition day, monthly performance testing should be considered (eg a flat out time trial over a set distance). No gains or even a performance decline will likely indicate that the athlete is a poor responder due to their biochemical individuality.

Individual recovery

As all older athletes will be well aware, the capacity to recover is one of the main changes that take place as a result of the aging process. As athletes get older, full recovery from an equivalent bout of exercise takes longer, especially after a period of immobilization through injury or break from training (eg a holiday)(7). Also, research shows that the training adaptation in older people following very vigorous exercise is less extensive than in younger people, making consecutive bouts of the same exercise more difficult as aging progresses(8).

However, due to biochemical and physiological individuality, the recovery capacity between athletes of the same age is also highly variable (something that most likely explains the findings in the Portuguese study above). Now a brand new study in recreational runners suggests that the rate of recovery is not only highly individualized, but also impacts (or should impact) the progression of a training program – ie training program progression should be individualized based on the unique training and recovery responses to that program(9).

In this study, researchers examined whether individually-adjusted endurance training based on recovery and training status would lead to greater adaptations compared to a predefined program where athletes simply followed a structured progression. Thirty recreational runners were divided into one of two groups:

  • Predefined – where the program progressed in a pre-prescribed fashion (ie the kind of conventional approach used by many athletes when adopting a training program).
  • Individualized – where the training load was decreased, maintained or increased twice a week based on nocturnal heart rate variability, the athletes’ perceived recovery, and heart rate-running speed index (the measured heart rate measured at a predetermined speed – a lower heart rate at that speed indicates better recovery).

Both groups followed the same overall training structure, which consisted of a three-week preparatory phase (low volume, low intensity), six-week volume phase (where volumes were increased) and a six-week interval phase (where the main focus was on interval training). The difference was that in the predefined group, athletes increased volume and intensity according to the schedule. In the individualized group however, athletes used their measures of recovery between workouts to determine whether to increase intensity/volume in the next session or maintain/back off. Incremental treadmill tests (using increasing speed to determine maximum sustainable speed) and 10km running time trials were performed before the preparatory period (T0) and after the preparatory (T1), volume (T2), and interval (T3) periods.

What they found

Both groups improved their maximal treadmill speed (vMax) and 10km time-trial times from T1 to T3. What was really significant however was that the improvement in 10km time trial times was substantially greater in the athletes who used the individualized approach (6.2% faster) than in those who used the predefined approach (2.9% faster). Just as significant was the fact that athletes in the individual group had more excellent responders compared to the predefined group (50% individualized vs. 29% predefined). Even better, none of the athletes in the individualized group showed a poor response (zero improvement or even negative improvement). However, in the predetermined group, one in five athletes were poor responders, meaning that a fifth of them either showed no improvement or got worse following the training program!

Implications for athletes and coaches

Experienced and successful coaches will already understand and appreciate the need for tailoring training programs to each athlete, and these recent studies merely confirm what many already knew. For self-trained athletes however, these findings should serve as a warning: a training program is only a starting point. For that program to bring success, the training load and intensity MUST be adapted to suit each athlete. And the only person who can do that is you!

In practice, this means two things: firstly, athletes should use both subjective (eg perceived fatigue) and objective measures of recovery (eg heart rate variability or early morning resting heart rate) to determine the precise intensity and load of the next training session. If recovery seems poor or incomplete, it is wise to back off during the next training session, or even take an extra day’s rest completely. In the longer term (perhaps every couple of months), athletes should perform time trials or other fitness tests to check they are making steady progress. If performance remains static, or even worse declines, it’s time to bin that training program and try another approach – one that is better suited to your individual and unique body!


  1. Sci. Sports Exerc. 1984; 16, 489–493
  2. Physiol. 2008; 586, 151–160. doi: 10.1113/jphysiol.2007.142109
  3. PLoS One 2014; 9:e98119. doi: 10.1371/journal.pone.0098119
  4. Physiol. Nutr. Metab. 2016; 41, 229–234.
  5. Aging Phys. Act. 2018; 26, 655–670
  6. Physiol. 2020;11:579835. doi: 10.3389/fphys.2020.579835. eCollection 2020
  7. Appl. Physiol. 2010;109:1628–1634
  8. Eur J Appl Physiol. 2006 Jul;97(5):619-26
  9. Med Sci Sports Exerc. 2022 Aug 13. doi: 10.1249/MSS.0000000000002968. Online ahead of print

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