Resistance Training for Youth: Part IV

In part four of the Resistance Training for Youth series, we’ll discuss the role of different training elements (or modalities) in athletic development. We recommend reading  Part I, Part II, and Part III for some necessary background information before moving on to this one. As always, thanks for reading!

A variety of training modalities are included in the Long Term Athletic Development (LTAD) model, including “core”, balance, plyometric, and resistance training (see Fig. 1). Aside from sport-specific skills, these form the base upon which athletic potential is built. This section will serve as a review of the role of each of these modalities within the design of a training program.

Figure 1: Different training modalities contributing to development of the athlete. 

Different activities involve these components to different degrees. There is not a “minimal effective dose” needed for each training modality, and some, such as “core” training likely need better definitions before any specific training parameters can be laid out. For example, a child developing balance skills is also likely improving trunk control or their “core,” and resistance training involving odd-shaped objects likely involves balance work as well. Arbitrary delineation of what constitutes balance, plyometric, and even resistance training leads to arbitrary prescriptions for those modalities. While involving components of each is recommended, approaching athletic development as a spectrum of skills is a better operational framework for improving overall athletic performance

Core Training

Before we can discuss a particular training modality, we must first define what that type of training it involves. In the case of “core training” this tends to be highly variable between practitioners due to different definitions of what the “core” actually is. There is little consensus in the research literature regarding whether the core includes only the muscles surrounding the spine, all the muscles between the shoulders and pelvis, or some other subset thereof.

A study by Clark et al surveyed athletes, coaches, sports scientists, and sports medicine practitioners on their perception of what influences their decisions when it comes to “core” training. When the 241 subjects were asked how to measure the “core”, 22% reported that there is no effective way to measure core stability, while almost half (43%) proposed a subjective assessment determined by the provider. If a subjective assessment of the provider is chosen, there is risk of the practitioner fitting the athlete to their rigid, arbitrary definition of “normal” instead of the athlete finding their own normal.

These discussions often involve nebulous phrases such as “proximal stability before distal mobility”, which lack any real substance or supporting evidence. In this way, “core training” is often in the eye of the prescriber, as well as the perceived ability to identify deficits in core strength. This often leads to haphazard prescription of exercises and the assigning of a weak core as a contributor to symptoms or difficulty with performing a given task.

There is also a movement to prioritize correction of asymmetries; however, this fails to recognize the adaptive asymmetries observed in numerous sports including baseball, rowing, and cricket. Furthermore, Niemelainen et al observed an asymmetry of greater than 10% in lumbar paraspinal muscle size among the healthy asymptomatic adult population. Core training is advocated by the LTAD for three of the four stages — but if we cannot properly define what constitutes the “core”, it is likely impossible to impart the principle of specificity for training it.

A review by Wirth et al in 2017 took a critical approach to the application of core training, finding no advantage of core training over classic resistance training with respect to athletic performance. There is no good evidence for direct core isolation training being more effective than a more global approach to strength training in youth athletes. While there is some evidence for neuromuscular training being advantageous for reducing the risk of lower extremity injuries such as ACL injuries, this is more directly related to landing mechanics than specific “core” work.

Balance Training

In reviews by Hrysomallis in 2011 and Kiers et al in 2013, improved balance was correlated with increased athletic performance and reduced overall injury risk. But while balance training is an important prerequisite for learning complex motor skills, it requires a similar discussion on specificity of training and its defining parameters. 

In 2017 Kummel et al conducted a systematic review and meta-analysis on the role of balance training in healthy individuals and found that while balance training can have a positive effect on trained tasks (i.e., specificity), there is little carryover to untrained tasks. Said another way, athletes improve at balance tasks they are exposed to, but there does not appear to be a “global effect” that carries over to novel tasks. This argues for exposure to a wide variety of tasks when developing youth balance skills.

There is also a movement to integrate training on unstable surfaces, theoretically to increase balance and proprioception in different populations. Specific to youth, Behm et al in 2015 reviewed the role of unstable surfaces, stating that unstable training showed small effects for improving muscle strength, power, and balance in youth. They did note that these results disappeared when the effects were compared to training on stable surfaces. Overall, training on different surfaces did not appear to show any differences in outcomes. Again, specificity and variability must be considered in the integration of balance training.

It is likely that during the “FUNdamentals” and “Learning To Train” periods of development that athletes should be exposed to as many different activities involving balance as possible. Developing athletic ability is an “open system”, and sport is often predicated on being able to interact and react with opponents and/or the environment. If an athlete only learns a limited means of reacting to their opponent and environment, they only have limited solutions with which to react. Too much time is often spent on teaching a narrow view of a “right way” to move or to accomplish a task without acknowledging that much of being an athlete is based on being able to accomplish a task in a manner that your opponent cannot.

There is utility in implementing balance training, especially in the early phases of youth development, in order for athletes to improve static and dynamic balance. As with many training modalities, the duration of training seems to have the largest effect on overall improvements. A meta-analysis by Gebel et al advocated for at least 12 weeks of training in order to benefit from a particular modality. This likely has to do with the reversibility principle where, if a stimulus is removed from training, there is regression to the mean of the skill practiced. The authors of this meta-analysis go on to state that balance training:

• Has moderate effects on standing balance and large effects on dynamic balance
• Is a highly effective method to improve balance performance irrespective of age, sex, training status, setting and testing methods
• Was not moderated by training frequency or period.

Overall, balance training should serve a role in a well developed program but it does not require special surfaces or devices. The development of skill in balance is task-specific and therefore should likely include a variety of tasks. The sum of these tasks, and the environment within which they are performed (i.e. turf, dry field, wet field) will help to develop a broad base of balance skills and a well-rounded athlete.

Plyometric Training

In contrast to the ambiguity of what constitutes core or balance training, there is a clear history of the origins of plyometrics. It was originally used by Russian and Eastern European track athletes in the 1960s by Verkhoshansky before officially being coined as a term in 1975 by Fred Wilt, a track coach at Purdue University. Even with the clear history, the implementation of what constitutes plyometric training in its current form is much more broad. Plyometrics are a broad category of exercises predicated on rapid stretching or contracting of muscles. This is inclusive of jump training and rebounding exercises where there is an intention of fast movement. Exercises such as squat jumps, bounding, single leg hops, and depth jumps would all fall under the plyometric umbrella.

The most-referenced article on plyometric training in youth is Johnson et al’s meta-analysis on best-scenario dosing. “Best-scenario” would be dosing with which results are maximized with the lowest risk of injury. They advocate for blocks of training being the most effective, with an ideal around 8-10 weeks. The primary focus of sessions should be on rate of force development (RFD), a measurement of explosive strength where force is generated as quickly as possible. This is why much of plyometric training is geared towards increasing jumping outcomes (vertical or horizontal) and sprinting. The authors recommend only 10-25 minutes of a session devoted to this skill set with short bouts of training (10 seconds) followed by longer bouts of rest (90 seconds). Rest is a common theme with many training modalities and the shortest typically advocated for being 90 seconds. The shorter bouts (less than half an hour) would seem to call into question the movement towards speed camps early in childhood development. Speed camps often promise that youth athletes will jump higher and run faster than their peers. The camps often run 4-12 weeks and promise results in terms of either increased vertical jump height or decreased 40 yard dash time. As with all training, the principle of reversibility still applies and once this stimulus has been removed, athletes should not be expected to maintain the benefit. A better approach likely being consistent work on the basics in which some plyometric work is dosed in. 

There is also the systematic review by Behm et al on the role of strength and power development in youth athletes. Unsurprisingly, there was a contribution here from the training history of the athletes. In trained youth athletes, power training was able to improve jump outcomes with strength training having a lesser effect. In untrained youth both strength and power training had large effects on jump and sprint outcomes. Unsurprisingly, most training modalities have an effect on untrained individuals.

This is not to undermine what often falls under the umbrella of “speed work” entirely. Even with the recommendation of less than a half hour of work devoted to actual plyometric work, there is still room to incorporate technique work. Plyometric training focused on running and jumping technique would not occur at the same intensity as repeated bouts of jumping or sprinting. This technique work can further develop an athlete’s ability to run and jump in a way to better meet sport demands. And just as we do not recommend repeatedly attempting a 1RM with resistance training, repeatedly jumping or sprinting at max effort as a part of training is also not advised. Instead, it is the accumulation of sub-maximal work that tends to reap the largest gains in terms of athletic performance.

Agility Training

The last modality advocated for in the LTAD is agility training, which constitutes the ability to stop, start, and change direction. Quick changes in direction have been correlated with injuries in lower extremities across a variety of sports. Here, there is a surprising paucity of literature specific to “change of direction” training. This could be because it is typically grouped with neuromuscular training (which we will cover below) or because a good amount of change of direction is predicated on eccentric components (which will be covered in the resistance training section).

The ability to change direction quickly is a fundamental skill in most sports, but especially those which involve cutting. If a player can decelerate more efficiently, they are effectively absorbing eccentric forces. Some of this skill is predicated upon coordinated movements which can be taught via technique, and others through having sufficient capacity in the tissues.

Once again, environment plays a role in the determination of change of direction or deceleration training. Simple drills such as running to a cone, planting on one foot and performing a cut at an angle are the basic fundamentals. The most typical example in sport being route running as a wide receiver in football. Here, there is a technical component and the fundamentals of change of direction can be implemented. The complexity of the drill changes with the addition of a defender. Now, change of direction and deceleration are dictated partially by an opponent. Space can also be used as a means of improving agility. Performing drills in a small space forces athletes to be able to operate within those parameters and not rely on top end speed to perform a task. If athletes play tag in a 100 ft by 100 ft space there is much more emphasis on quick movements and changes of direction than in a 200 ft by 200 ft space where linear speed can contribute to success in the game.

While agility training is one of the least studied, it is one of the easiest to turn into simple games as a paradigm for training. This can be especially useful in the earlier phases of the LTAD where skills can be developed within the constructs of different games. Another simple drill would be to have two athletes facing each other within a certain space, each with a ball that they will toss back and forth. The goal of the game is to toss and catch within the predetermined space without dropping. Here, simple hand eye coordination tasks are drawn in as well as planting and changing direction. These types of drills turn the focus towards a more global athletic development as balance and agility are both honed. In such instances we may be better served by referring to the drills as neuromuscular training.

Neuromuscular Training

With the emphasis we typically place on language and semantics at Barbell Medicine, we would propose a movement towards the use of neuromuscular training (NMT) as a better alternative to either core or balance training. The astute reader may now quip that “all physical exercise is neuromuscular” — and of course they are correct. However, the peer-reviewed literature has adopted this term to describe a series of activities that typically incorporate exercises coaches would consider “core” and “balance” work. The most well known of these is the FIFA 11+ program utilized for risk reduction of ACL injuries in soccer athletes. The program includes exercises that emphasize single-leg stance, change of direction, plyometrics, plank variations, and eccentrics without significant external load. Systematic reviews have demonstrated a reduction of injury risk of approximately 35% for teams that adhere to the program.

Neuromuscular training is not “free play”, but rather structured movement training in which athletes address the technique of landing, running, jumping, cutting. Here, as with many other modalities of training, compliance appears to play a large role in the benefit. A cluster RCT by Slauterbeck et al demonstrated no benefit for risk reduction in teams completing the FIFA 11+, however only two-thirds of coaches had their teams complete the program 1x/week and only one-third the recommended 2x/week. This was corroborated by an earlier study by Steffen et al that demonstrated no effect of neuromuscular training but only a 60% adherence rate.

What is interesting from an athletic development standpoint is that while much of programming is focused on increasing athletic performance, neuromuscular training seems to focus on reducing the risk of injury. The most talented athlete cannot compete while they are injured, and it would seem that this type of training can be especially effective for keeping athletes on the field, court, or platform. It is quite possible that while much of the focus is on creating programs to develop the best athlete, including components of NMT may help develop more resilient athletes. However, the issue here is achieving coach and parent buy-in. Steffen et al in a separate study increased the adherence rate of participation in the FIFA 11+ by presenting it as a means of both increasing performance and decreasing the risk of injury.

There are multiple systematic reviews on the role of neuromuscular training in youth athletes and risk reduction of injury (the authors use the term “prevention” but injuries cannot be prevented, only reduced in risk). The first of which by Emery et al included a meta-analysis demonstrating a 36% reduction in lower extremity injuries with neuromuscular training. The authors advocate for programs that include components of strength, balance, and plyometrics as these demonstrated the largest effects. Still, most programs included qualify strength as bodyweight training.

The next systematic review by Faude et al, also found that neuromuscular training can reduce the risk of injury by as much as 40%. The authors conducted an analysis to determine different variables that influenced this effect. The main themes being that longer programs (>23 training sessions) had a greater effect on outcomes and that players >15 years old seemed to respond to the program at a higher degree on all performance outcome measures than athletes <15 years old. This holds with much of performance adaptation occurring after the onset of puberty and continues to make the case that younger athletes should be participating in a variety of activities.

But what, really, is the sum of neuromuscular training? Despite a preference for this term in the literature, perhaps a better way to frame this discussion is skills training. Much of what constitutes balance training is actually developing specific skills in certain positions. “Balance” as a whole is about developing those skills through a wide array of positions and activities. The ability to sprint, jump, and change direction are all skills, with technical components fundamental to athletic development. While there are certainly means with which strength can improve each of these skills, technical prowess allows that baseline strength to be expressed as athletic ability.

Skills Training

Hopefully by this juncture we have waded through the minutiae of training modalities in favor of a broader approach to athletic development. Now, to make it actionable.

Athletes should devote a substantial portion of their training time, especially in the early and late childhood phases (~ 6-13 years old) to skill development. At a young age it should be much more about developing athletic skill over winning an arbitrary game. Taking the time to develop these skills may come at a cost of not winning immediately. There are tricks to quickly improve variables such as jump height and speed, but the goal is to elicit long-term adaptation, which takes time.

While coaches often develop and teach skills, it is often conducted in a sterile environment. It is one thing to be able to perform a drop vertical jump and another to be able to get a rebound while being contacted by three other players. A study by Leukel et al demonstrated that something as simple as cueing the purpose of a drop jump changed how an athlete landed. The uncertainty of the task changed how it was performed. Similarly, it is one thing to be able to perform a 45 degree cut in front of an orange cone and another entirely to be able to do it when being checked at the 5 yard line by a cornerback. Most of what is conducted under the guise of skill training would be closer to training for a dance in terms of specificity. Being able to run a ladder drill may be impressive on social media, but the skill there is likely more related to being able to perform a pattern than break down a defender.

In school we begin by teaching the alphabet, followed by grammar, and then evolving into full prose or poetry. Skills training is the diagramming of sentences on the field or court. It allows athletes to learn the component pieces of athleticism to develop their own movement patterns. If the emphasis is placed on learning plays and constantly scrimmaging during practice, athletes learn those patterns, but they do not learn the fundamentals of movement. What’s more, the athletes who learn those plays may be more successful early on, but they are not learning to be an athlete. They are merely learning to follow rigid instructions, not be to expressive (see Fig. 2).

Figure 2: Model of Long Term Athletic Developmental Model (LTAD)

An honest question is where should the peak occur? If performance is pushed too early at the expense of skill, there is also likely increased risk incurred. There is ample discussion regarding technical proficiency and its correlation with risk of injury. When an athlete is at practice, there should be an understanding that they can be self-governing, and dial back intensity if they are fatigued or not feeling well. In competition, the goal is to win, and that can come at the cost of pushing beyond the capable limits of an athlete. 

It is impossible to ascertain how many athletes who were elite at a young age missed out on the opportunity to compete at a higher level due to injury. However, we do have evidence such as from Webster et al that 12 months after ACL reconstruction 15% of athletes had given up on their sport. From the same cohort, at 12 months after surgery, only 1 in 4 had returned to their prior level of participation. According to Arden et al only 55% of normal athletes return to their prior level of function after reconstruction. This is approximately the same percentage that return to prior level after hip arthroscopy as well. We are likely better off prolonging events that incur an increased risk of injury in favor of developing an athlete first.

We should likely emphasize neuromuscular/skills training early on as part of overall athletic development and practice. If an athlete can learn the fundamentals of movement, when the time comes to express those fundamentals, they will be more prepared than their peers. In early and late childhood it is likely that up to half of practice time for sport is best spent working on skills training, and not necessarily with the focus on maximizing performance. It is important to train to jump higher and run faster, but it is more important to train youth in a manner that allows them to develop the skills needed for sport while keeping them in those sports for as long as possible.

A sample training program under this paradigm may resemble:

• High Knees 2 sets of 10-15 m
• Butt Kicks 2 sets of 10-15 m
• Cariocas 2 sets of 10-15 m
• Single leg alternating hops where an athlete bounds from one foot to another 2 sets 10-15 m
• Frog hops 2 sets of 10-15 m
• Lateral side to side hops 2 sets of 10
• Double leg lands from a plyo box 2 sets of 10
• Single leg lands from a plyo box 2 sets of 10

The above components can serve as both an introduction to neuromuscular training and a warm-up for more advanced athletes. Once the athletes are warm, they can move into more reaction-based drills such as:

• Drop lands with a lateral hop where the coach calls the direction
• Single leg lateral hops with coach calling change of direction
• 4 corner drills
• Tag in a confined space
• Spikeball

The possibilities are endless here, but there should be drills in place in which the coach or another athlete is dictating changes in direction. That can also be performed by running drills where two athletes have to go for a ball and contact is initiated. This mimics the normal physical contact dictated in sport and allows work on landing and cutting in a more game-like scenario. 

Of course, there are different subsets of drills and positions specific to each sport. For sports like basketball and soccer, skill training involves ball-handling drills, and these can be performed with the same environmental considerations discussed in the agility section. Having a basketball player dribble only in the paint against a defender restricts the space in which they can move. For a soccer player, cones can be utilized to force ball handling and change of direction in a much smaller space. For a volleyball player, playing toss over the net with a light medicine ball forces lateral movement but also works deceleration when catching the ball. The volleyball and basketball players would benefit from increased work on landing mechanics either through activities like single-leg landing drills or more plyometric-based training like bounding over hurdles. 

It bears repeating here that this is not a case for young athletes needing “perfect form”. An emphasis on perfection has proven detrimental to an athlete’s risk of injury as well as psychological burnout. Applying only one solution to an athlete’s ability to run, jump, or throw reduces variability in an athlete’s ability to adapt to the different scenarios presented in sport. Constraints such as the difficulty of the task, the environment in which it is performed, and the equipment used will all increase or decrease the difficulty of the task depending on how each is modified. The key is to modify each of these constraints in a manner that continually facilitates learning and development. 

Running a drill against no opponents, one opponent, or multiple opponents all increase the difficulty of the task. This can also be accomplished by using a heavier weight, throwing a ball further, or making a goal smaller, each of which emphasizes a different component of task demands. The goal here should be to prepare individuals for the variable demands of sport.

When new tasks or skills are introduced, there will be a high amount of variability in an athlete’s performance. This variability often is advantageous as it promotes motor learning, and remains present to an extent all the way to elite levels of performance. Coaches should not dichotomize movements into good or bad or seek to eliminate all variability, but rather push towards optimal performance for the individual.

The take-home point for this section is that we likely over-complicate skills training by creating silos for small subsets of skills. The fundamentals of running, jumping / landing, cutting, and being able to stand on one leg are pillars of a broad range of athletic tasks and should be developed as such. At a young age, athletes should be exposed to a wide range of skills and while drills are best taught in a sterile environment, sport is typically a “dirtier” place. Being able to turn drills into games can make the process much more enjoyable and increase individual buy-in. Have athletes perform in small spaces. If you want, have them play games on unstable surfaces. Above all else, the training should be fun and encompass a wide skill set for overall athletic development.

Edited by Austin Baraki, MD, Jordan Feigenbaum, MD, MS, and Michael Ray, MS, DC