Resistance training: should athletes be exposed to resistance exercise at a younger age?

The implications of young athletes performing resistance training

Mention the words 'resistance training' and 'children' in the same sentence and most people will start giving you funny looks. To say the subject is controversial is an understatement(5, 16). This is hardly surprising when you consider that until recently the benefits of resistance training to athletic performance have largely been dismissed in the UK. Only now are coaches, athletes and the general public beginning to realise that 'pumping iron' can not only transform your physical appearance but can also improve your health and sporting performance (1,7, 9,14).

As the UK wakes up to the fact that adult athletes can seriously enhance their performance if they adopt a structured resistance training programme a new question arises: is it too little too late? At what age can we start to introduce our young Beckhams and Henmans to resistance training? For the purposes of this article I am talking about children from the age of 11 and up and it is precisely this age group which many of the world's most successful sporting nations are introducing to resistance training during school training programmes.

So what do we mean by the term 'resistance training'? For some the phrase will conjure up images of muscle-bound ironmen pumping iron (and much else besides), posing in front of the mirror. In fact resistance training is simply a programme of exercise, which uses one or more types of training system(1). Methods include exercises using bodyweight, such as sit-ups, press-ups and dips. Resistive tubing, free weights and machines may also feature in resistance work. Even many of the traditional Olympic lifts, if taught with correct technique and light implements, can substantially improve a child's balance, proprioception, strength and power. What we should not do, however, is confuse resistance training with maximal-type exercises performed during competitive Olympic and power lifting competitions. The key is not to perform maximal lifts with young performers(13).

First, though, why the bad press for resistance training?
The popular myth that resistance training was not only potentially harmful to young performers but was also of little use for improving strength and power was first fostered in the research community. One of the earliest papers came from Eastern Europe back in the early 1960s. A study investigating the trainability of lower back muscles following a course of isometric resistance training failed to demonstrate any significant improvements in strength. Further studies looking at leg and arm strength also failed to find any substantial strength gains(18). During the next couple of decades a groundswell of support backed the notion that resistance training methods failed to provide significant increases in strength in young performers. As is often the case, subsequent research built upon the limitations of earlier investigations.

So why did earlier studies fail to provide evidence of strength gains? The 1960s investigators used only modest training loads, resulting in a lack of progressive overloading (possibly one of the most important training principles, irrespective of the training method being used). When combined with relatively short monitoring periods, it is hardly surprising that little or no improvement was seen. Modern training theory now confirms that, in order to achieve significant strength gains in young athletes, training mode, intensity, volume and duration must all be manipulated to provide the optimal combination. Researchers and coaches alike are now confident that if a suitable resistance training programme is employed, significant strength and power gains in young performers are possible (5, 10,11).

In recent years research has started to provide compelling evidence of the benefits of resistance training. Training programmes incorporating progressive overloading of the muscles have provided evidence that strength gains in young athletes is possible (even if they have not gone through puberty). In 1986 a group of boys aged between nine and 10 embarked on a period of resistance training. At the end of the training period significant increases in elbow and knee flexion and extension were recorded(11). Further studies found that over a period of 20 weeks, progressive overloading of the elbow flexor and knee extensor muscle groups, using isotonic training techniques, produced significant increases in strength(12). 1RM double leg press (22%), maximal voluntary isokinetic elbow flexion (26%) and knee extension (21%) were achieved.

Yet again, it has a lot to do with neurological systems
So recent evidence has shown that resistance training could be a useful tool in the coaches' 'toolbox' of training ideas. But you may find yourself asking: how can a boy who has yet to go through puberty (and has therefore yet to have testosterone coursing though his body) possibly experience gains in strength. Surely, gains in strength are related to muscle hypertrophy, which is influenced, by the amount of testosterone in the body? Early research showed that the young athletes were not experiencing significant gains in muscle size (as would be expected with adults) and, when coupled with the lack of strength improvement, it seemed sensible to conclude that resistance training was of little benefit. However, more recent studies have shown that strength can be improved even in the absence of muscle hypertrophy. The question is: how?
What the early studies failed to recognise was that children are not just miniature adults and that the mechanisms which bring about an increase in strength in adults may differ for children. So how can children improve strength if testosterone is not responsible? Testosterone does not start to increase until mid to late puberty, effectively ruling out the male hormone's contribution to strength gains in young performers(16).

And, given that girls (who, of course, don't produce testosterone) can also improve their strength, that very fact points us in the direction of a different explanation.

Theorists have pointed to the possible contribution of neurological systems(10). Evidence suggests that strength increases in line with the development of the nervous system, which is of primary importance in the exertion and development of muscular strength(16). Research has indicated that there are three likely determinants of strength gains: improved motor skill coordination; increased motor unit activation; and undetermined neurological adaptations(16,13). Early theories were based largely on indirect supposition and so direct assessment of these neurological adaptations was needed. Using ground-breaking techniques, researchers investigated the changes in motor unit activation (MUA) following a period of resistance training in pre-adolescent boys(12). Results indicated that after the first 10 weeks of training, MUA of the elbow flexors increase by 9% and MUA of the knee extensors increased by 12%. Slower increases in MUA were recorded during the second 10 weeks. The results confirmed current thinking that the nervous system has many roles to play in improving athletic performance, as demonstrated in many recent PP articles.
Subsequent research confirmed that strength gains in young performers could be attributed in part to increased neuromuscular activation. Both MUA and motor coordination increase still further when multi-joint complex lifting activities are used rather than isolated movements. Specificity is important for improved motor coordination: researchers have demonstrated that more significant improvements in strength occur in the specific exercises performed during training than with non-specific exercises such as isometric elbow flexion and knee extension(1).

Can you really swim faster, jump higher and hit harder?
While you may be prepared to accept the body of laboratory evidence which shows that resistance training can improve strength in young performers and that the dominant underlying mechanism is neural in origin, it is legitimate to ask whether this can be translated to the sporting arena. It has been said that the stronger an individual is, the higher he will jump, the faster he will run or swim and the harder he will hit a ball. Sports such as netball, rugby, athletics, tennis and cricket all require strength and power in order to perform complex multi-joint movements. It's not unreasonable, based on the research, to suggest that the results seen in controlled laboratory studies could be transferred to the sporting arena. Although there is limited direct research in this area, studies have shown that intensive resistance training can improve both strength and swim speed in pre-adolescent boys and girls(2). Indirect evidence has shown that an increase in strength can improve specific activities, such as vertical jump, swim speed and running speed(15) and, if you look at the investment most high-performance teams are now making in strength training for their performers, I would suggest that resistance training is an extremely effective tool for improving athletic performance.

If you are still not convinced about the impact resistance training can have on performance, just look at leading sports performers from a decade ago and compare them with those competing now: today's competitors are bigger, stronger and faster than ever before. While the cynical may refer to illegal aids, the more astute will recognise that sports performers are increasingly using resistance training to help improve their performance. Although there is limited research on youngsters, it is reasonable to suggest that younger athletes could also enjoy the same type of improvements in athletic performance seen in adults following a period of resistance training.

But what about injuries? Surely, all that training can't be good for young bodies? In 1987 the US Consumer Product Safety Commission reported that resistance training was a harmful activity for children(1). The report highlighted the disturbingly large number of injuries associated with resistance type exercises; 8,543 injuries were incurred by 0-14 year olds and ranged in severity from sprains and strains to fractures. Approximately 40% of the injuries occurred during unsupervised sessions in the home. A subsequent study investigating sport-related injuries in school children taking part in 22 sports found that resistance training produced just seven injuries from a total 637, placing it 17th on the injurious list(17). The message is clear and obvious: if young athletes play around with weights at home or during unsupervised sessions they could well end up in their local A&E department. However, if you closely supervise your young athletes during resistance training sessions, ensuring they follow a structured training programme, they should be at no greater risk of injury than when they are taking part in their chosen sport.

But what about the immature musculoskeletal system?
Another area of concern is the potential damage resistance training can cause to the immature skeleton: increased physical activity in children is often associated with musculoskeletal damage(4). The skeletal system is in its formative stages during pre-adolescence and does not fully mature until early adulthood (6,8). It is commonly thought that the use of resistance training could contribute to damage of cartilage, bones, joint surfaces and tendons. It has even been suggested that damage to growth cartilage can result in stunted growth. Other structures, such as the spine, have also been highlighted as an area of potential injury. Although these issues are a serious cause for concern, some experts feel that the case may be somewhat overstated. Research has shown that sport-related musculoskeletal damage occurs very rarely. The majority of cases have been linked with maximal overhead lifts of the sort associated with power lifting, and no evidence has been found of skeletal damage in relation to resistance training (1).
So, based on sound research, it would be safe to say that a good-quality resistance training programme is an effective training method to complement the existing training regime of young performers. If you are a coach looking to introduce your young athletes to the benefits of resistance training, here are some guidelines to take into consideration.

The young performer:

should complete a medical examination by doctor before starting the training programme;
should be mature enough to accept instruction;
should want to participate in the programme;
must possess the basic motor skills of their primary sport;
must maintain correct form during lifting;
must avoid competition during training.

For his or her part, the coach should:
ensure the young performer is closely supervised during training sessions;
ensure the training offers variety;
pay particular attention to the strengthening of the back and abdominal muscles;
ensure that in the event of any pain, training is discontinued;
ensure that the resistance training programme forms part of a comprehensive programme designed to increase motor skills and fitness levels;
ensure that all exercises are carried out though a full range of motion;
Prohibit any attempts at maximal lifts.

If resistance training is a new area to you, here are some of the basic guidelines you should think of when putting together a training programme:
1. Begin and end each session with 5-10 minutes of warm-up and stretching.
2. Balance the workout by altering pairs of muscle groups, ie perform a 'pull' exercise after each 'push' exercise. (Examples of pull exercises are barbell or dumbbell bent over row, cable lat pulldown, seated row; push exercises may include barbell, dumbbell or machine bench press, squats and shoulder press.)
3. Exercise the larger muscle groups (pectoralis major - chest; latissimus dorsi - back; quadriceps) first, and the smaller muscle groups (biceps and triceps - arms; deltoids - shoulder; gastrocnemius/soleus - calves) at the end.
4. Perform 1-3 sets of 6-15 repetitions. Younger children may use fewer sets and more repetitions.
5. Allow 48 hours of recovery after each strength training session.
6. Work on the schedule 2-3 times per week while maintaining other sporting activities.
7. Younger children can spend 20-30 minutes per session while older children can increase the duration of each session.
Nick Grantham

References

1. Sports Medicine 15, 389-407, 1993

2. Australian Journal of Sport Science 1, 3-6 1981

3. Effects of Physical Activity On Children, Broekhoff J, Human Kinetics, 78-87, 1986

4. Child Health, Nutrition and Physical Activity, Cheung & Richmond. Human Kinetics, 1995

5. Designing Resistance Training Programmes, Fleck SJ & Kraemer WJ, Human Kinetics, 1987

6. Strength Training For Sport, Hazeldine R, The Crowood Press, 1990

7. Sports Medicine in Primary Care, August S.5-S.8, 1995

8. Exercise Physiology Energy, Nutrition and Human Performance (3rd Ed), McArdle WD, Katch, FI, Katch VL, Lea & Febiger, 1991

9. Sports Med 16, 57-63, 1993

10. Medicine and Science in Sports and Exercise 26, 510-514, 1993

11. Physician and Sportsmedicine, 14, 134-139; 142-143, 1986
12. Strength Training Effects In Prepubescent Boys, 22, 605-614

13. National Strength and Conditioning Association Journal 13, 39-46, 1991

14. Physician and Sportsmedicine, 21, 105-116. 1993

15. Medicine and Science in Sports and Exercise 6, 629-638, 1986

16. Wilmore JH & Costill DL, Physiology of Sport and Exercise, Human Kinetics, 1994

17. American Journal of Sports Medicine 8, 318-323, 1980

18. Medicine and Sport, 11, 152-158, 1978

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