a guide to strength development: PART I

When we were young, things were easy.

The young strength coach in the early 90s had a few journals they could read in the library (remember those?), a few good books, and - if they were lucky - some good conversations with experts in the field.

… and that's about it.

The internet was not around yet, DVDs were not available, and S&C Conferences were few and far between. We say it was easy because of the scarcity of information. Most of us had access to the same material - and coming up with a training philosophy was not the potential mess of mass confusion that it is now.

Besides the almost infinite information at our fingertips, today’s coaches have the added (often contradicting) influences of Olympic weightlifting, powerlifting, Crossfit, etc. Where does a young coach start?

We don’t envy these coaches. It’s great that we have so much information at our fingertips - but without context, and background knowledge, if is challenging to know where to begin.

We don’t profess to be all-knowing in this, but with our collective backgrounds, we feel we are in as strong a position as anyone to offer our thoughts. And hopefully provide some context, and some basic information that will help coaches with their program design.

We’d like to start where we always should -- with a single word:

WHY

Why do we lift?

Or - why do we have our athletes lift?

Until we answer this question -- until we have a very clear justification of what is possibly a taken for granted assumption, we are behind the eight ball before we even get started. How can we write an effective strength program, if we don’t truly understand why we are doing it in the first place?

So that's the point of this series -- or at least it's the point of this first post in the series.

We hope you enjoy the following - what we feel is necessary background information.

Digest this - then do some additional reading around the areas that are more interesting - or more confusing - to you, and please come back in a few days for section two, which will offer more information on loading parameters.

PART I:

FIRST PRINCIPLES IN MUSCULAR STRENGTH

Since the times of the Ancient Greeks, maximal muscle strength has been recognized as an important element for athletic performance. However, in recent years, with the advent of the internet and the tendency for new training paradigms to emerge simply for the sake of the newness factor, it seems that in certain circles an assault on maximal muscle strength and its related muscle properties has emerged - ranging from benign questions such as “how much strength is enough” right up to the suggestion that developing maximal muscle strength is really a thing of the past for an athlete. However, the development of maximal muscle strength is often espoused within certain camps as a key - if not the key - to unlocking athletic potential.

So, where does this leave the coach who wants to employ strength training to improve athletic performance?

The challenge for great coaches is not to classify a training element using a binary “yes/no” or “good/bad” system, but instead to understand when and how things fit together into a cohesive training philosophy.

MAXIMAL STRENGTH

In order to evaluate the relevance of any physical fitness parameter for athletic performance it is valuable to begin with a physiological and biomechanical basis for how improving a specific ability might transfer to a seemingly unrelated skill or sport performance environment.

The first fundamental observation regarding maximal muscle strength is that unlike many of the mechanical muscle properties related to explosive muscle force production, maximal muscle strength is highly trainable in nearly every type of athlete. Even more so than the capacity to develop muscle hypertrophy, one could argue that nearly everyone possesses the capacity to gain maximal muscle strength. With its high training potential, maximal muscle strength should not be overlooked and instead should be at the very least optimized for the sport and athlete in question.

Maximal muscle strength is often defined as the maximum force producing capability of a muscle - or muscle groups - in a single maximal voluntary contraction of either a concentric, eccentric or isometric muscle action.

The important element here is not how long force can be sustained or how quickly it can be developed, but instead how much force can be generated. To assess maximal muscle strength, the gold standard laboratory measurement often reported in the scientific literature is the maximal voluntary isometric contraction. Here the athlete is strapped into a dynamometer and asked to push or pull against an immovable object while force is recorded from a force sensor.

The criticism of this approach is that most sport movements are not isometric, and require the application of muscle force to overcome an external load (i.e. concentric muscle action), or yield against an external load (i.e. eccentric muscle action). Alongside consideration for specificity and greater simplicity for assessment, maximal muscle strength is easily assessed in the weight room using repetition maximum (RM) testing that requires the athlete to perform a series of efforts or sets with increasing load until the maximum amount of external load lifted with correct technique for a given number of repetitions is determined. Maximal muscle strength can be estimated virtually every time an athlete enters into the weight room for a training session.

Of course, some limitations of this approach exist - including the possibility for technical variations, which can dramatically affect the outcome measure (load lifted) in the absence of a real change in general maximal muscle strength.

For example, suppose two athletes are assessed using a maximal voluntary contraction of isometric leg extension using an instrumented leg press. Midway through the training phase, Athlete A makes a significant change in his squat stance, which permits him to make a jump from 100kg to 120kg in the external load. Athlete B continues with his existing technique and makes a 10kg improvement. It is conceivable that the 20% improvement in external load for the squat could occur alongside a smaller gain in the technically independent measure of maximal strength obtained from the isometric leg extension. The purpose of this example is not to discount one method over the other, but more to introduce the coach to the element of task specificity and the importance of evaluating changes in weight room performance of maximal muscle strength alongside other potential confounding factors.

MUSCLE ACTION

As discussed above, maximal muscle strength is dependent on the type of muscle action. The unique behaviour of skeletal muscle during different types of muscle actions has existed for more than 80 years. In fact, in the late 1930’s, seminal experiments performed by the great exercise physiologist A.V. Hill demonstrated the production of extra heat for a shortening muscle as the velocity of shortening increased. This experiment changed our understanding of muscle physiology and yielded the characteristic hyperbolic muscle force-velocity relationship (Figure 1).

However, further anomalous observations were made when muscles lengthened against an external load (i.e. performed an eccentric muscle action). Andrew Huxley noted these observations in his 1957 paper that provided a mathematical basis for the sliding filament theory, which we now know as the crossbridge theory. Huxley remarked that while the behaviour of muscle could be relatively accurately explained using his mathematical equations for isometric and concentric muscle actions, the equations could not predict muscle behaviour during eccentric actions.

FORCE-VELOCITY RELATIONSHIP

In practical terms, maximal eccentric strength is predicted to be as much as 40% greater than maximal isometric strength. It also uses less energy, despite the fact it produces greater force. It seems there might be another passive element that contributes to muscle force in an eccentric muscle action. However, we are interested in the human force-velocity relationship, and comparing the force-velocity relationship obtained from a human to a single muscle as in the experiments of A.V. Hill is not possible. The first observation of the force-velocity relationship of the human is that the often hyperbolic concentric portion of the force-velocity relationship is much more linear and the maximal shortening velocity need to be extrapolated as most strength testing equipment is incapable of assessing the maximal velocity of shortening for dynamic single joint human movements. Additionally, the 40% difference between maximal isometric strength and maximal eccentric strength is not found. In fact, this difference is much smaller.

INTRAMUSCULAR COORDINATION

The discrepancy between the maximal eccentric strength of a muscle and a human performing an eccentric movement is attributable to neural factors, which are absolutely critical for the expression of maximal muscle strength. The first category of neural factors effecting the expression of maximal muscle strength is called intramuscular coordination, and includes the rate at which a motor unit fires and the number of motor units that are recruited. Motor unit firing rate or rate coding is important for the early rise of muscle force during explosive movements and is important for increasing muscle force above 85% of maximal muscle force.

Put another way, the orderly recruitment of motor units increases as the external load increases - up until approximately 85% of maximum strength (i.e. more motor units are recruited). After this point, the motor units begin to fire with increasing frequency as muscle force continues to rise. Intramuscular coordination is highly trainable through maximal strength training methods and this is one of the very critical adaptations of interest for athletes. Additionally, maximal muscle strength can be inhibited by the afferent feedback originating from muscle proprioceptors such as Golgi tendon organs. This too is highly trainable and, with respect to improving maximal muscle strength, can be effectively diminished using heavy strength training.

Training against heavy loads enables a greater signal to reach the working muscle both through greater efferent drive (i.e. stronger neural signal coming from the central nervous system) and reduced inhibition from afferent sources.

INTERMUSCULAR COORDINATION

As the name indicates, intermuscular coordination refers to the coordination between muscles, and can be seen as the optimal recruitment of agonist, antagonist and synergist muscles in a complex movement. Of course the precise behaviour of the different muscles and muscle groups in dynamic movements is difficult to ascertain, but for the coach, the observation that increasing the activation of the core and trunk muscles to stiffen the spine during heavy lifting often improves the expression of maximal strength, provides a nice example of intermuscular coordination.

PCSA

Intramuscular coordination and intermuscular coordination are important neural or tuning factors effecting the expression of muscle force - but as with a car, a highly tuned four cylinder engine can’t compete against a less tuned six or eight cylinder engine.

This analogy comes from an article written by Warren Young from Australia and in this case, the size of the engine is comparable to the size of a muscle. In scientific terms, muscle size, or the physiological cross sectional area (PCSA) is directly proportional to the force producing capability. The bigger the muscle, the greater the muscle force. Of course, there is important interplay between improving muscle PCSA and neural coordination as it pertains to the long-term development of maximal muscle strength.

Often, the design of strength training programs has focused on various organizational or periodization structures of training methods designed to uniquely affect either the development of muscle PCSA (hypertrophy) or neural factors.

One of the first suggestions that maximal muscle strength adaptation can be maximized by addressing both muscle hypertrophy and neural factors was made by Dietmar Schmidtbleicher in the 1980’s based on a study that evaluated changes in strength, size and neural drive to three different training programs. His conclusion: training methods that improve muscle hypertrophy and neural factors (i.e. maximal strength training) should be employed in an alternating manner for long-term gains in muscle performance.

Many papers since then have elucidated the different approaches for improving muscle hypertrophy and neural factors through strength training.

FORCE-LENGTH RELATIONSHIP

In addition to muscle PCSA, neural factors, and the force-velocity relationship, muscle length is a key player in the expression of maximal muscle strength. This observation was most notably characterized in an experiment in 1966 performed by Gordon and colleagues that demonstrated the unique effects of changing muscle length on muscle force, which yielded the characteristic force-length or length-tension relationship with its ascending limb, plateau region and descending limb (Figure 2).

In the realm of strength training for athletic performance, the effects of training on the force-length relationship have often been overshadowed by a somewhat myopic focus on the force-velocity and/or power-velocity relationship.

Why exactly the importance of the force-length relationship has been minimized is unclear - as it is a trainable and influential factor of muscle performance. In fact, in the mid 1990s, Walter Herzog from the University of Calgary, demonstrated that elite cyclists and runners operated on completely different regions of the rectus femoris force-length relationship, and indicated the highly specific trainability of the force-length relationship. Force-length relationship shifts are also seen in other contexts such as after eccentric training.

In practical terms, coaches are aware of the importance of the force-length relationship when athletes with force deficits at specific joint angles or sticking points are encountered. These sticking points arise in sport performance as well - especially in sports like speed skating or alpine ski racing in which specific, and sub-optimal, knee joint angles are inherent to the sport skill. For these athletes, developing range of motion specific strength is essential. There are many pragmatic approaches to influencing the force-length relationship such as performing isometric training at specific joint angles or performing accentuated lifting with the use of bands, chains or other barbell attachments.

However, assessing the force-length relationship in the context of developing maximal muscle strength seems to be less prioritized both in practice and in the scientific literature compared to the emphasis on the force-velocity relationship.

ADDITIONAL BENEFITS OF MAXIMAL STRENGTH

Until now, the focus of this first section has been on the muscular and neural factors influencing maximal muscle strength in the context of establishing a physiological basis for why a coach might want to employ maximal strength training to improve athletic performance. Of course, the effects of maximal strength training on enhancing neural drive is of great benefit to an athlete both in sports requiring maximal muscle strength and explosive muscle strength. This latter point is of great interest - as many sports require the expression of explosive muscle force or explosive strength.

An important side effect of improving maximal muscle strength through heavy strength training is a marked increase in explosive muscle strength - especially in less developed athletes. A recent meta-analysis by Seitz et al. (2015) in Sports Medicine provides an excellent review of the transfer of maximal strength improvements in the back squat to sprint running performance. The results are unequivocal. Clearly, making an athlete stronger is often a gateway to making an athlete faster.

Additionally, the ability to perform high rates of muscle work or mechanical muscle power is critical for many sports, and as with the concomitant improvement in explosive strength observed following heavy strength training, the expression of maximal mechanical muscle power and the ability to sustain mechanical power are positively influenced by maximal strength training.

The benefits of maximal strength training can be extended to other tissues - including the skeletal and connective tissue. Heavy strength training imposes important loads on tendons and other connective tissue. Similar to muscle, heavy strength training increases the cross sectional area of tendons and the mechanical load helps to align the collagen fibres that are critical for bearing load. These adaptations increase tendon stiffness, which leads to better force transfer between joints in multi-joint movement.

Additionally, by increasing cross sectional area, the strain capacity of tendons is increased, which has important considerations for injury prevention - especially in sports such as long distance running where repetitive and cyclical movements often lead to tendon injury. Interestingly, slow heavy strength training is as effective as surgery for dealing with chronic tendonitis.

For the endurance athlete, the improvement in tendon stiffness is a potential mechanism underlying the transfer of improved maximal muscle strength to improved endurance performance as summarized by Per Aagaard in his 2010 article in the Scandinavian Journal of Medicine and Science in Sports.

Improving maximal muscle strength is also associated with enhanced economy of movement - which is a key factor for endurance performance. Contrary to intuition that often leads coaches to erroneously conclude that high repetition schemes should be employed with endurance athletes, it is in fact the heavy strength training schemes that have the greatest positive impact on endurance performance.

PRECAUTIONS

With all the scientific and practical evidence in support of using heavy strength training to improve athletic performance, it might seem as though we have identified a panacea for physical preparation. However, there are other considerations.

First, while short-term training studies demonstrate improvement in explosive strength following heavy strength training especially in less trained subjects, the long-term (i.e. several years) effects of chronic heavy strength training on sport performance and sport skill are less understood. In the medium-term (i.e. several weeks to months), chronic heavy strength training results in a muscle fibre type shift from the fast Type IIx fibre to the more oxidative Type IIa fibre.

The primary difference between fibre types is the maximal shortening velocity, and it is possible that while on the one the hand, benefits for explosive sport movements are obtained from heavy strength training, the overall slowing of the contractile properties of a muscle could potentially blunt performance particularly when very high movement velocities are required.

This suggestion is not scientifically supported and is highly speculative. However, in order to present a balanced viewpoint on the how-why-when should maximal strength training be incorporated into the training program of an athlete, this remains an important consideration.

It is also clear that while many sports skills require maximal strength, there are lots of examples of sporting movements that are dominated by other mechanical muscle properties.

Anecdotally, great coaches often refer to athletes in speed-power and technical sports who uniquely solve motor tasks like sprinting using other strategies that rely far less on maximal strength. Of course, it is tempting to suggest that in these situations, improving maximal strength would only benefit the athlete and not harm performance - but this has never been shown scientifically. Furthermore, through personal conversation with many high level coaches, it is clear that enough examples examples exist of athletes who avoided heavy strength training, yet managed to attain incredibly high levels of explosive athletic performance to warrant careful consideration of when, and with who, heavy strength training methods are employed.

NEEDS ANALYSIS

In order to navigate this complicated process of answering the how-why-when questions, coaches are advised to perform a careful analysis of the sport in question to identify key performance indicators (KPIs). Using these indicators, it is then possible to objectively determine the success or failure of a particular strength training intervention.

As maximal muscle strength determined through either RM testing or using isometric dynamometry is often unrelated to many sport skills, coaches should possess the ability to assess other mechanical muscle properties. As discussed above, two properties that are often of interest are explosive strength and maximal mechanical muscle power.

Explosive strength is defined as the rapid rise in force during an explosively performed movement. This can be evaluated by calculating the rate of force development (RFD) in dynamic or isometric movements, although only assessment under isometric conditions is sufficiently reliable to be employed for testing purposes.

Assessing explosive strength through isometric dynamometry fell out of vogue through the mid-1990s, but it remains an important dimension of mechanical muscle performance for three specific reasons:

• As mentioned above, isometric dynamometry has much better reliability when evaluating explosive strength using RFD

• Per Aagaard, a modern day pioneer in revitalising the relevance of isometric dynamometry, has related the contractile impulse or the area under the force-time curve obtained during an isometric contraction to the limb velocity that would have been attained should the limb have been permitted to move freely

• Finally, by calculating the time frame for force application in sport, the contractile impulse can be evaluated over the same time intervals permitting a high degree of specificity to the sport skill all the while using a standardized and repeatable testing method

To make this a bit more salient, suppose a coach was evaluating explosive strength in two sprinters. He is interested in a standardized assessment to evaluate explosive mechanical muscle performance as it would pertain to accelerating and sprinting.

He chooses to compare isometric dynamometry against an evaluation of explosive muscle performance using the vertical jump.

He determines the ground contact time at maximum running velocity to be approximately 90ms, and 150-200ms for the acceleration phase. However, he misses an important aspect of how the two athletes perform the vertical jump.

Athlete A is a slow jumper and he requires 300ms to perform the countermovement jump. To reach maximal jump output, he descends to deeper knee angles that fall outside the joint angles of sprinting to generate maximum vertical propulsion. As such, he consistently outperforms Athlete B in terms of jump output, as Athlete B is a much faster jumper and generates a slightly smaller vertical impulse in a shorter but more sport-specific timeframe.

Using the vertical jump output as the outcome measure, it seems Athlete A is as good - or better - than Athlete B. But the main issue here is that Athlete A will never have 300 ms to perform his sport skill.

At a maximum, the acceleration phase of sprinting involves a ground contact time of 150-200ms. Using isometric dynamometry, the coach then sets a specific joint angle related to the positions of sprinting. He then instructs the athletes to perform rapid and explosive isometric contractions to evaluate the contractile impulse over 90ms time-frames.

Again, because the contractile impulse would relate to the limb velocity that would occur had the limb been permitted to move and as the time-frame for force application are evaluated over a duration that is specific to the sport skill, the performance gaps for Athlete A and Athlete B would be better identified through isometric dynamometry.

At this point, you might be thinking that evaluating the jump output alongside the jump strategy could be very telling. Maybe consideration for the slow jumping strategy of Athlete A would reveal further insight into explosive mechanical muscle performance.

If this is your line of thinking, you are correct.

The vertical jump and its variants (e.g. drop jump, countermovement jump, squat jump, and single-leg jumps) are excellent movements for evaluating explosive mechanical muscle performance in athlete populations.

However, jump performance should be considered alongside jump strategy.

In order to gain insight not only into jump performance but also jump strategy, it is important to have instruments that can measure how the athlete attains a specific jump output.

A limitation with contact mats, optical sensors, and vertical jump ergometers like the Vertec is that only jump output can be evaluated. Instruments such as the force plate provide greater insight into how a jump is performed through analysis of the vertical force time curve. With this approach, the coach can identify fast jumpers, slow jumpers, and vertical impulse attained during specific jump phases such as the eccentric deceleration phase and concentric phase.

Additionally, jump performance can further be evaluated by looking at the take-off velocity, or total work performed. Jump strategy can also be more sophisticatedly evaluated by plotting force-displacement and force-velocity graphs to look at the positional and velocity changes of the body centre mass throughout the jumping movement.

Clearly, the evaluation of explosive muscle performance must be undertaken alongside evaluation of maximal muscle strength - especially for sport skills relying on explosive strength. By identifying KPIs and relevant mechanical muscle properties, the coach is now able to employ creativity in program design and develop new approaches for developing mechanical muscle function as it relates to improving sport skills and athletic performance.

Based on personal communication with many high level sport and strength coaches, the approach to strength training program design must expand to include several different types of strength training methods in addition to heavy strength training. There are, in fact, many ways to positively affect explosive mechanical muscle performance, and the drawbacks/benefits of each method form the basis of answering the how-when-why questions related to incorporating strength training into a cohesive training program.

SUMMARY

The starting point for any coach wanting to employ maximal strength training methods with athletes is to first have good understanding of the physiology and biomechanics of the expression of muscle force. These first principles will provide the best basis for answering the questions of how and when different strength training methods should be used to improve athletic performance.

By no means was this an exhaustive list of the potential benefits of the various strength training methods provided. Instead, a few key points were highlighted to shift the focus from what we believe works for improving sport performance to what the science supports. The benefits of strength training go much beyond this, and include many other factors related to injury prevention and creating athletes with sufficient structural tolerance to support the large training volumes of the modern day athlete. Do not forget as well that for hundreds - and possibly thousands of years - strength training has been an important element of physical training programs for athletes.

Moving beyond tradition - through experience and on to the science - strength training is critical for the athlete.

The transfer from the weight room to sport performance goes far beyond developing an exercise that mimics a sporting movement - and includes the many unique neural and functional adaptations to strength training that are of great interest for the elite athlete.