The LTAD model proposed by Balyi & Hamilton (2004) outlines a framework for the development of motor-skills and physical skills which run parallel to a chronological age profile of an athlete. It is an ambitious project that attempts to explain the physiological development of a young athlete all the way to adulthood. It has been ubiquitously implemented as a standard framework by national sporting bodies around the world. However the problem with the LTAD model is that it is based on almost no longitudinal research in humans, and has rarely been analyzed/understood by professional coaches who implement it.
The key concept in the LTAD model is “windows of opportunity“. A window of opportunity is proposed to present at a particular stage in human development corresponding to chronological age i.e. at age X, a window of opportunity presents to train X skill, and therefore all athletes at that age should train that skill to maximise their trainability of it. Two factors are proposed as markers of human development: peak height velocity (PHV) & peak weight velocity (PWV). However, what we know is that kids get taller and heavier across a wide variety of ages; some kids are big from a young age, others aren’t. Some experience their significant growth spurt late in their teens, others much earlier. Individual differences in height & weight growth rates (probably related to genetics) are always at play. So while LTAD is an interesting model, it doesn’t account for individual differences in physical development or retention of motor and physical skills. Its’ generalisation is its weakness, and the window of opportunity concept that needs to be treated with caution by professional coaches. One final introductory point, a window of opportunity implies that the maximal potential enhancement of a skill occurs at that point in time. When that time point passes, then the window of opportunity is diminished or at worst closed forever.
Basic locomotor skills (walking, running, jumping) are fundamental to sports performance and form the basis from which more complex skills are acquired, through development of strength, balance, co-ordination and speed (Cratty 1986). However, given that these qualities develop at different rates in each child, and interact in a complex way, the best we can probably say is that the ages of 6-12 seem to be a good time for basic motor and physical skills to develop, with considerable variability in the expression of skills from one child to the next. It should also hold that rather than a specific window of opportunity opening up at a point in time, that the principles of training applied to that concept will dictate the a skill is trainable and de-trainable at any point in time, with variations in the absolute trainability varying from one individual to the next. This is exactly what the research shows:
1. A study by Ingle et al. (2006) demonstrated that complex training (combined plyometric & resistance training) in boys aged 12 had positive effects on dynamic strength (24-71% increase v 0-4% in control group) and induced small improvements in 40m sprint time, vertical jump & throwing performance. However, once the training period had ceased and detraining occurred, all training gains had been lost. In other words, speed and strength are both trainable but de-training occurs back to baseline upon cessation.
The findings here are in conflict with the LTAD model window of opportunity age 12. The LTAD model purports this age as the ideal age for trainability of peak speed velocity 2 and peak strength velocity 1 & 2. This coincides with the onset of PHV which LTAD uses as it’s key indicator of readiness to develop a particular skill. The inability of the boys to retain the skills gained following 12 weeks of training questions the LTAD claim that speed & strength are preferentially developed at this age. Perhaps speed & strength are just trainable and de-trainable at any age, and might be related to PHV and PWV? And if increased sensitivity is sensed at this age, shouldn’t we observe some retention of the skill following training? What is needed is longitudinal data over a period of 6-8 years where the same group of boys are studied, put through a controlled strength & speed training programme, where height and weight are measured at each step? This way, some sort of relationship between PHV & PWV and speed & strength could be determined. Anthropometric and kinanthropometric measures would also be necessary, to see if measures of speed & strength are related to bone density, hand or foot size, and kinematics. The logistics of this kind of study however are next to impossible to implement, and as a result the window of opportunity model is questionable.
2. Age 6-9 is proposed in LTAD as the ideal window peak motor-skill co-ordination training. Research by Graf et al. (2005) demonstrated that a long-term school based motor-skill programme can improve motor-skills in the 6-9 years age group, as would be expected with motor-skill training. However a study by Barnett et al. (2009) demonstrated no significant long-term retention or motor-skills following one year of specific training in 6-9 year olds. Once again, the claim that a specific window for motor-skill training and retention is not supported by the research.
The LTAD model proposes age 12-16 as the ideal time for aerobic fitness development. However the research is less conclusive. For example, studies Armstrong et al. (1994), Bouchard et al. (1997) and Viru et al. (1999) have all documented increased in peak oxygen uptake from infancy to adulthood. Individual differences in aerobic capacity have been reported by many authors including those just mentioned, supporting the notion that aerobic fitness development does not occur at one specific age. More likely, aerobic fitness development is related to both central cardio-respiratory development and muscular metabolic development. Closely linked to aerobic fitness is biomechanics and the ability to move economically i.e. to run at a given velocity with minimal energy cost. In this regard, Cavagna et al. (1983) have shown that both children and adolescents are less economical at any given speed than adults. Two factors are probably at play here: 1) children and adolescents consume more energy per unit of body mass compared with adults 2) adults through years of training and experience in pacing are more likely to have better movement biomechanics than their younger counterparts. Therefore there is good physiological and biomechanics data contradicting the LTAD model for aerobic fitness development.
One final point: The Heritage Study by Bouchard has demonstrated that there are both high and low responders to cardio-respiratory training. So it is likely that two kids of any age will respond very differently to the same training. However, both should continue to train aerobically throughout their lives as the health related benefits have been demonstrated across almost all ages. Any adult can start to run or cycle, and will experience physiological adaptations. After many years of training in adulthood, biomechanics will improve and further enhancements in aerobic performance can occur.
Speed seems to increase linearly up to the age of 12 in both boys and girls, after which speed development slows down in girls compared to boys (Whitall, 2003). Malina et al. (1988) suggest that the differences in speed development in boys and girls is due to growth and maturation differences between the sexes that occurs after puberty i.e. boys gain more muscle mass, their limbs grow longer, and they are generally taller than girls. On the surface it seems to make sense that bigger and stronger boys are faster.
However, speed is also influenced by muscle enzyme and and musculo-tendinuous composition, biomechanics and co-ordination. Therefore one factor outweighing the other in terms if influencing speed is difficult to quantify. Elite level sprinters are normally not very tall or heavy, with the average male Olympic sprinter coming in at 70-75kg. An interesting study by Butterworth et al. (2004) examined the effect of growth rates on speed and power in boys and girls ages 11-13. 76 boys and girls were tested for speed and power over nine months. A positive relationship between height and speed & power was shown, but no relationship was demonstrated between weight and speed & power. The boys rate of development in jumping was faster than in girls, however this was not repeated for speed. While LTAD suggests that speed develops side by side with PHV and PWV, this is not supported by the research.
Similarly, the LTAD model does not account for muscle metabolic or musculo-tendinous changes, both of which probably influence speed (Erikson, 1980). What we know is that muscles and tendons develop continuously throughout childhood and adolescence. Furthermore, Lin et al. (1997) have shown that muscle-tendon stiffness develops over a period of at least 20 years. We also know that muscle-tendon stiffness is highly related to sprint ability.
There is a paucity of data in paediatric exercise physiology on strength development. Strength increases due to a complex mix of muscular, neural and biomechanics factors, which make it difficult to pin down one of them as the key contributor to strength development. Another confounding factor is that general claims about strength development in youth athletes are difficult to make, given that improvements in strength seem to be specific to muscle groups and are joint specific (De Ste Croix, 2008).
A recurring problem with the LTAD model is that fitness components are said to occur at specific points in time according to chronological age. However, numerous studies have demonstrated that this is not the case for strength. For example, at least four authors have shown that stature and body mass exert significant effects on strength development independent of age. Studies by Round et al. (1999) and Wood et al. (2004) attest to the complex interactions between these factors, each of whom highlighting that growth and maturation do not exert an independent effect on strength development in children.
In terms of LTAD, it proposes that strength is ideally trained 12-18 months following peak height velocity (PHV), however little or no evidence exists to affirm the position. Faigenbaum et al. (2001) demonstrated strength gains in 5 year olds, but these same authors have demonstrated gains in strength in untrained athletes ranging from 5.3 – 87%. Furthermore, Lillegard et al. (1997) and Pfeiffer & Francis (1986) have shown no in differences in the percentage increase in strength gain following a training programme, when subjects of different maturation levels were used. Once again, the key concept of individual difference in response to a training stimulus is evidenced for strength, where both high and low responders have been identified. It seems that strength can be trained at any time, and its trainability is highly variable from one athlete to the next!
The “windows of opportunity” concept for motor and physical skill development requires a lot more research in each fitness component. Similarly, there is no evidence to demonstrate the reverse position: that intensive training outside of the “window of opportunity” does not enhance the trained skill. Finally, using the term “window” suggests period where that the opportunity opens and closes, when in fact it may stay open from childhood into adulthood. The LTAD while comprehensive, should be considered a work in progress where research could help to substantiate its’ claims.
Ford et al. (2011) The Long-Term Athlete Development model: Physiological evidence and application
Journal of Sports Sciences, February 15 2011; 29 (4) 389-402