• By: Pedro Candeias
  • Date: 01/03/2017

DESTROY THE MYTH: “Strength Training is Bad for Children and Young Karateka”



What kind of Karate Instructor are you?


  1. The “Young-Karateka-are-Fragile” Instructor that thinks that Strength Training for kids is DANGEROUS?


  1. The “Anti-Muscle” Instructor that thinks Strength Training is a waste of time and believes that will make his or her students “Slow-Motion Karateka”. Believes that all of his/her students have to do are thousands of repetitions of Kihon or Kata. Because that’s all they need to get stronger and faster’



  1. The “Be-Strong-or-Die” Instructor that looks to his/her young Karate students and all he/she can see are small adults. And this “small adults” have to train hard like their Japanese ancestors did 100 years ago?!?


I bet you know some Senseis that look exactly like these ones, right? But they are all wrong!!!







  1. Strength Trainability
  2. Risk Factors
  3. Bone Adaptations
  4. Motor Skills and Performance in Karate (sports)
  5. Body Composition
  6. Recommendations



  1. STRENGTH TRAINABILITY IN YOUTH (children and adolescents)


The most recent scientific research clearly shows 30% to 50% of strength gains in untrained children and adolescents, in programs of only 8-12 weeks. The relative gains are similar in children and adults.


So, there is no doubt that children and adolescents really get stronger with strength training programs!


There are two types of adaptations to Strength Training: morphological and neurological. And these contributions are different between children, adolescents, and adults:


  1. In CHILDREN, the main factors to strength gains are neurological factors, as muscle firing activation and motor-unit recruitment. In a practical way, strength in children is associated, mostly, with coordination improvements and learning. One explanation for this is the reduced circulation of androgens in pre-pubertal kids – the primary and most well-known androgen is testosterone. This factor reduces the capacity of the muscles to grow (hypertrophy)


  1. During and after ADOLESCENCE, testosterone growth leads to a quicker gain of muscle size and strength.


Strength gains in CHILDREN are, therefore, mainly explained by neural adaptations as motor-unit activation, intermuscular coordination and the development of neuromuscular learning.


The training programs should focus, preferably, on multi-joint exercises, because allow a wider intermuscular coordination and less overload in one isolated muscle and joint.


When we talk about adolescence (after the growth spurt) the strength gains are similar to adults and occur by this order:


  1. Intermuscular Coordination
  2. Intramuscular Coordination / Factors
  3. Hypertrophy (the magnitude of muscle growth depends on the type of training method and the athlete’s or participant’s goal)




Risk Factor Number 1 – one of the major concerns in most trainers and parents is the possible injury in the growth plate located in bone’s extremities (epiphyseal region), during strength training. These areas are more susceptible to acute and chronic injuries than ligaments or tendons. But those kind of injuries are unusual and can be easily prevented with correct training: proper technique, good supervision and not use maximal leads.


Risk Factor Number 2 – another risk factor is the possible occurrence of injuries in the lumbar region (at the long term). This type of injury is common only if young Karateca that don’t use proper technique or if strength training sessions are wrongly periodized with unbalanced volume vs intensity. It’s also very important that Karate trainers progressively improve the strength of body areas like the abdomen, lumbar region or hips.


Faigenbaum et al. (2002) didn’t find any kind of injury in children, after strength training, because they were well supervised during the program. Many studies show that weight lifting, for example, is less propitious for injuries than sports like rugby or soccer. Most of the injuries occur due to bad execution or lack of supervision.


(DESTROY THE MYTH: As you can see, scientific evidence knows the benefits of strength training in youth for many years)




The fear of that strength training is bad for children and adolescents bone system is completely put away by most recent scientific findings.


In fact, childhood and adolescence are the most appropriate periods for the modeling and remodeling process of bone strengthening – this is due to the tension caused by load sustenance (it can be body weight, a medicine ball, dumbells or an elastic band, for example).


The problem is not the strength training, but the excessive loads, wrong technique execution, unbalanced and incorrect effort/rest ratio.




A proper program of strength training for kids and adolescents is essential for bone’s strong foundation, more resistant bones over the years and healthier growth.


Nichols et al.(2001) demonstrated increases of 4% in all-body bone density in adolescents, after 15 months of strength training.


(DESTROY THE MYTH: As you can see, scientific evidence knows the benefits of strength training in youth for many years)


Kara & Snow (2000) related increases in bone density on the humerus of 3,1% – in 14 years old girls and after 9 months of high-intensity plyometric training.


And the increments of bone density are correlated with the gains of muscular strength and muscle growth. Conroy et al (1993) observed that bone density was higher in young weightlifters than adults without training experience (these adults were between 20 and 29 years old).


(DESTROY THE MYTH: As you can see, scientific evidence knows the benefits of strength training in youth for many years)


This happens because as the intensity increases, there are proportional stimulus to new formations in the periostium surface of the bones. These are powerful osteogenic stimulus for bone adaptations.


Specifically, in children, strength training is responsible for helping bone density increasing, without negative effects on the maturation process.


Besides that, bone mass enhancement during and immediately after the growth phase seems to be an important strategy for osteoporosis in adulthood – but the maintenance of that bone density level may need a long term strength program.





Margaritopoulos et al (2015) show us that there is a significant correlation between Mawashi Geri force and jumping performance, for example; and jumping performance depends a lot on muscle strength – neural and muscle factors.


And Davaran et al (2014) conducted a research where they compared the levels of several physical qualities between two Iranian Karateka groups (age 14-18 years old): 1) Group 1 executed a combined plyometric-speed training along with their regular Karate training; 2) Group 2 only trained their Karate specific training.


Group 1 had the following results (compared with Group 2): Power (15,5% more power); Change of Direction Speed (2,3% faster).


No one doubts that Power and Change of Direction Speed are fundamental physical qualities to any Karate athlete/participant!!





Scientific Studies are demonstrating that the inclusion in strength training results in positive improvements of body composition.


This is mainly due to a so, so important factor: muscle development, that allows children and adolescents to perform more complex motor tasks (and these motor tasks lead to bigger energy consumption).


Our kids become more active if they have more strength.


Scientific evidence and clinical observations demonstrate that overweight children and adolescents enjoy strength training (in contrast, for example, with aerobic activities) because they present a reduced aerobic rate and allow them to experience success and motivation on their performance.


After that, they can easier go through a more aerobic training.


And think about it!!


Is this right only for overweighted kids?


Of course not!


This is fully true to every student that enters for the first time in your Dojo and haven’t trained background or don’t train for years.


No matter if they are 6, 15, 35 or 50 years old.


First of all, make them STRONG!!


Their self-esteem will rise and strength training brings quicker results than aerobic training.


Forget the traditional model of training endurance first – it’s boring, harder and the results are much slower.


START WITH STRENGTH TRAINING and they will support endurance training much easier (in a more advanced phase).






Dynamic exercises/activities for 5-10 minutes. Warm-up for kids can and should include some games.


Training Methods

Strength training programs for children and adolescents should include, besides traditional machines, elastic bands, medicine balls, free weights, and body weight.


Besides that, the use of bars without additional disks or wood sticks are great tools to teach the correct technique before increasing the loads.


Exercises Choice

Jump Training or Plyometrics are great and practical methods to use in your Dojo and daily sessions. And kids love it!! You can train both lower body and upper body with this methods. You just have to use cheap equipment like hurdles, steps and medicine balls.


Multi-joint exercises should appear before single-joint exercises.


This sequence allows your students’ body to execute the more challenging exercises at the beginning of the training session, where the neuromuscular system is less fatigued.



After each strength training for children and adolescents – like every kind of training – it’s essential to promote a cool-down for about 5-10 minutes, with stretches and relaxation exercises.



In resume, THE PROBLEM with strength training for children and adolescents is not the training itself or the biological or chronological age of your Karate students…




Become a real professional Karate Instructor with Science…Give your students and athletes only the best, proven and healthier training methods!! They deserve it, don’t they?!?



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P.S. – Did you know that the best and most practical way of training strength with your younger Karate students is Plyometrics? And do you really know how Plyometrics work and the proper way to use it in your several classes? Karate Science Academy has the mission to give you all of this knowledge. Keep following our Blog articles and Facebook posts (LINKS PARA AS NOSSAS PÁGINAS)