THE EFFECT OF RELATIVE AGE ON THE IDENTIFICATION AND DEVELOPMENT OF SPORTS TALENT
The effect of relative age refers to the difference in skills between people who have been grouped for a particular purpose or function based on age.
Training load control (TL) has become a cornerstone on which to optimise performance and avoid the risk of injury. TL has been widely studied in recent years, among other reasons, due to its close relationship with the incidence of injuries.1 For many years, it has been believed that a high TL increased the risk of injury, this being the main limitation of performance. On the contrary, in order to achieve high sports performance, it is important to make a correct progression in the TL. Consequently, monitoring the TL is currently one of the main interests of coaches and those responsible for physical training, with the objective of finding the necessary balance between TLs that will optimise sports performance while minimising the risk of injury. This has meant an increase in evidence to reduce injuries associated with the TL, however, it has brought the emergence of myths or misconceptions around the relationship between TL, injuries, and performance.
Tim Gabbett, an expert in applied sports science with an extensive career working with athletes and coaches from a wide range of sports, has reproduced in a recent scientific article published in the prestigious British Journal of Sports Medicine the myths or misconceptions associated with the relationship between the TL, injuries and performance that he previously published in 2018.2
Injuries mainly occur when the TL exceeds the adaptive capacity of the tissue (that is, when the TL is greater than the capacity of the tissue to tolerate that TL). High TLs have generally been associated with better performance, while the application of an inappropriate TL is an important risk factor for injury.3–5 Although there is a balance between those TLs that will maximise performance improvements while minimising the risk of injury, it would be very simplistic to think that the risk of injury will be conditioned only by the TL. In fact, biomechanical or emotional factors and “lifestyle” influence the risk of injury in athletes, regardless of the TL. In short, the relationship between training, sports performance and the risk of injury is complex and multifactorial.
There is a popular myth that the increase in the TL should not exceed 10% per week. The “10% rule” has its origin in the 2000s, when this method was used to minimise the risk of injury by prescribing gradual increases in TL of 10%.6,7 Nevertheless, although huge weekly changes in TL increase the risk of injury,8,9 there is no “10% rule” to prevent injuries. Thus, in some cases it has been seen that certain athletes can tolerate TLs between 20% and 25%, at least for short periods of time.10 However, changes greater than 30% do show an increase in the risk of injury.10
Although there seems to be a general consensus that big weekly changes in TL increase the risk of injury, these changes in TL should be interpreted in relation to a previous training background. For instance, a huge change in TL after coming from a stage of low loads would increase the risk of injury, while a weekly increase (> 10%) in high TL after a period with high chronic TL is better tolerated.
Among the methods for developing TL (e.g., 10% increases in TL from week to week as we have just seen), a method of TL control based on analysis of the acute and chronic load ratio (ACWR) has recently gained great popularity,8 where the acute load refers to the TL of the week itself and the chronic load would be in relation to the TL in the longer term, the mean TL of a 4-week period. In this case, when the acute load is higher than the chronic one, it reflects that the fatigue tolerated is higher than the athlete’s fitness, increasing their risk of injury. Besides, physical fitness plays a prominent role in injury prevention, having been observed that athletes with a high chronic load and a moderate acute load tend to suffer fewer injuries than athletes with a lower chronic load.11
Research in a wide variety of sports4,12–15 has shown that “peaks” in TL (a low chronic load compared to acute) significantly increase the risk of injury. When the increase in TL is too fast – peak in TL -, the ability of the tissue to tolerate this stress is exceeded, causing damage. In contrast, “off-peaks” in TL (small increase in acute load in relation to chronic load) result in a lower risk of injury. It is important to note that, although high “peaks” in TL increase the probability of injury, “off-peaks” are also likely to increase it. That is, not only overtraining, but also undertraining which could mean a risk factor for injury.
When considering the ACWR (that is, when considering how high a TL is compared to the TL from previous weeks), if it is between 0.8 and 1.3 (the acute load is approximately equal to the chronic one) we can say that the risk of injury is relatively low due to factors related to TL. However, when the ACWR is ≥1.5 (the acute load is much higher than the chronic load), the risk of injury is greatly increased. Thus, the risk of injury seems to rocket when athletes are subjected to an ACWR between 1.5–2, that is, when the TL of one week (acute load) is 50–100% higher than the average load of the last 4 weeks (chronic load).11
Although the probability of injury seems to increase with an ACWR of ≥1.5, it must be considered that in sports science 1 + 1 is seldom 2. In this case, the value of 1.5 is not a “magic number” below which there is no risk of injury. This would be partly explained by the multifactorial nature of injuries and while some athletes may suffer an injury with an ACWR much lower than 1.5, others will tolerate an ACWR well above 1.5.
While “peaks” in TL that result in high ACWR increase the risk of injury, the importance of chronic load and its role in keeping athletes protected from injuries must not be forgotten. Thus, although Hulin et al. observed that “peaks” in TL increased the risk of injury, players with higher chronic loads were five times less likely to get injured than those with low chronic workloads.12 There are two possible explanations for this protective effect of training: 1) exposure to “load” allows the body to tolerate that “load”; and, 2) training develops physical qualities (e.g., strength or cardiorespiratory capacity), which are associated with a lower probability of injury.
TL control is a cornerstone where both performance optimization and injury prevention revolve around. Nevertheless, we see how some myths or misconceptions about the relationship that is established between training, sports performance and injuries still exist. In this article we have tried to address them and provide evidence that allows the reader to draw their own conclusions.
Javier S. Morales
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