SENSITIVE PERIODS IN YOUNG PLAYERS GROWTH

The new season for the return to the playing fields is fast approaching. For many, it may have already commenced, or for some they will be transferring from one sport and or adding on another one. The issue to be considered by coaches and parents is the onset of Peak Height Velocity (PHV) in their players. Managing this and allowing for possible “unusual or unexpected” changes in the player’s performance may be as a result of this sensitive period in a player’s maturation.

What is Peak Height Velocity?

Peak height velocity (PHV) is simply the period of time in which an adolescent experiences the fastest upward growth in their stature (i.e. the time when they grow the fastest during their adolescent growth). It is also known as the “growth spurt.”

It indicates hormonal, physiological and anatomical changes in the body bringing a child into adolescence.

PHV is determined by simply measuring standing height at regular intervals (e.g. every month, Gore, 2000). Once several measurements have been obtained, velocity curves (i.e. how fast a child is growing) can be charted.

The time when the annual height increase is maximized is called the peak height velocity (PHV); it usually occurs around 13–15 years of age for boys and 11–12 years of age for girls. This is the primary period of growth but there can be a few minor growth spurts later, continuing until usually 15.5 to 16 in girls and 18 in boys, but in some cases until approximately 21 (in boys).

The age at which the process commences is highly variable and sex-dependent. The average age in children growing at an average rate is approximately 11 years in boys and 9 years in girls, and peak height velocity occurs at a mean age of 13.5 years and 11.5 years, respectively, in these children. Peak growth can last from a few weeks to a few months. The following graph depicts the norm PHV in girls and boys.

What actually happens during PHV?

• During PHV significant changes occur in the body. In summary these include: Hormonal: The release of Oestrogen (girls) and Testosterone (boys)).
• Sexual Characteristics: As a result of hormonal change, girls will experience breast enlargement and a widening of the pelvis. Boys will have a change in voice tenor, body and facial hair growth and increased muscle mass and strength.
• Growth: The are approximately 48 long bones in a child’s body. Most long bones in children have at least two growth plates, and there are roughly 48 long bones in a child's body. Therefore, many children have around 96 growth plates.
• Physical Characteristics: The physical capabilities of boys and girls rapidly change, with increases in strength, speed, agility and endurance. Boys generally have more dramatic increases in strength due to higher testosterone levels, but often remain less flexible than girls.

Why is peak weight velocity important for athletic performance?

Physical performance is commonly measured as the outcome of motor tasks requiring speed, agility, strength, and power . However, the rapid increases in body dimensions and muscle hypertrophy during adolescence suggest that movement proficiency may be affected as athletes negotiate with fluctuating levels of coordination (i.e. the sudden increase in body size nearly always affects coordination.

As a result of the physical changes that accompany adolescence, both males and females may struggle to perform simple motor tasks such as balancing, running, and change of direction tasks. Coaches must be mindful of this and allow athletes to develop new strategies and solutions in essentially a ‘new’ body.

Without muscle hypertrophy, high-force activities such as landing, change of direction tasks or heavy strength training could predispose children to poor force-attenuating capabilities, limit physical performance, and increase the relative risk of injury. However, alterations in bone mineral content, muscle size and tendon strength will occur as a result of Peak Weight Velocity, which inevitably leads to an increase in muscle strength, power, reactive strength index and stretch-shortening cycle function over time.

Why is PHV important?

From a coach’s perspective, ensuring that appropriate training, game frequency, intensity of impact and allowances for body coordination and emotional shifts as a result of the impact of PHV must be a factor in the training and preparation of their team / players.

During puberty there can be significant differences between chronological age (birthdays) compared to biological age (the level of biological maturity of the body). The Skeletal age can range from 9 to 16 in a group of 13 – 14-year-olds. Consequently, the size of the players can vary hugely and the potential for injury from overuse or impacts must be factored into the team and player preparation. Negative comments, questioning of their commitment and emotional stress from these changes or even the lack of growth yet, are important elements for a coach to consider.

Of course this is very challenging for a coach who has 20 +/- players who are all in this PHV category, but at different stages of the category. Then there is the desire to win and the pressure this may have on all concerned. Not to mention the player who is sought by an older age group to make that team and the pressure that has on him/her.

Generally with the rapid rates of change occurring, the adolescent body may now respond differently to exercise with higher energy requirements. These demands are in the form of;

Increased energy demands – high calorie intake of quality nutritious foods.

Increased Risk of injury During growth the bones lengthen but the muscles, ligaments, sinews and tendons take time to catch up. The result can be breaks, tears, pulls, chronic overuse or acute injury, or a combination of the above. Examples of growth plate injuries include Osgood-Schlatter’s (knee) and Sever’s pain (heel). Reducing excessive high impact loading (e.g. jumping, running, aggressive tackling) during PHV can help prevent this.

Opportunity to enhance physical development Rest and recovery are important elements during PHV but it is also the opportunity to maximise the hormonal change to introduce or increase strength, endurance and flexibility of muscles and tendons by employing the correct kind of S &C training exercises.

What do I do once I know the age of PHV?

With the above information you need to think about their lifestyle and activity. Question to consider would be some of the following;

Is there excessive high impact training during PHV?

Are they doing enough Strength and Conditioning training?

Do they have enough variety in their exercise and training?

Do they have enough rest days in their diary?

Do they eat enough of the right foods? Do they sleep enough?

Helpful tool on how to calculate age of PHV

To calculate your PHV, you will need to know your player / child’s.

• Gender
• Date of Birth
• Date of Measurement
• Standing Height (cm)
• Sitting Height (cm)
• Weight (with minimal clothing) (kg)

Once you have recorded the above, put the figures into the online calculator created by the University of Saskatchewan to calculate your child’s PHV.