It has been a while since the last time I wrote something here. It is extremely time consuming to write something with quality for the website, and due the growth of social media over the last few years, people’s attention span (including mine!) got reduced and blog posts are not so attractive as they used to be.

However, I do think today’s topic deserve a longer rant due to its practical importance for any training or rehabilitation practitioner who trains athletes. Let’s dive deep!

VELOCITY BASED TRAINING

Barbell velocity and power output are commonly utilised external feedback and monitoring metrics during strength training sessions. Despite not being a new thing, – in fact it has been utilised for decades, as you can confirm in this video – it can be an extraordinary tool for any coach and athlete, especially at the high performance and elite level.

Also known as Velocity Based Training (VBT), I must stress that measuring barbell velocity is not a training method – it is simply a tool that (1) monitor an athlete’s training response, (2) provides intra/inter-set external feedback to the athlete and (3) enhances training prescription.

Velocity Based Training (VBT) is not a training method – it is simply a monitoring tool

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Although the goal of this article is not to explore the pros and cons of VBT, there is one main reason why athletes experience significant improvements when they start using VBT devices. Regardless the type of device and its reliability (whether linear position transducers, accelerometers or video analysis softwares), the athlete is encouraged to have maximal intent during every repetition due to real-time feedback from these devices. Moving external loads with maximal intent is the primary training variable that maximises neural adaptations (mainly intramuscular coordination), resulting in larger improvements for both maximal and explosive strength. This has been repeatedly shown by research (as in this paper).

Most commercial devices provide several metrics, being average/peak velocity and average/peak power output the most widely utilised metrics by practitioners and athletes. Without going in further details about when to use one or the other, or even both, we normally assume that greater velocity or power output means stronger and more powerful athletes.

But is it telling the whole story? Before I try to answer this question, it is important to review some fundamental physics and biomechanics concepts.

NEWTON GAVE US THE ANSWER

Isaac Newton’s laws of motion are some of the most remarkable findings for sports science and sports training. More than 300 years ago, Newton gave us the answer on how to jump higher, throw further and run faster. Although obviously more complex than this, no single being on the planet can escape or avoid these physics “truths”.

Vertical jump height (defined as the displacement of the body’s center of mass) is predetermined by center of mass velocity at the instant of take-off. Although highly correlated, peak velocity during a vertical jump and take-off velocity (TOV) are not the same.

According to Newton’s 2^nd law of motion, a change in velocity of the center of mass is the result of a certain force being applied over a certain period of time (impulse). This is also known as the impulse-momentum relationship.

The impulse corresponds to the area under the force-time curve and the same impulse may be the result of different force and time combinations, as we can see in figure 2. As stated before, vertical jump height is determined by TOV, which in turn is determined by the applied net impulse. It means that for a certain athlete, different strategies (combination of force and time) may result in same vertical jump height, as long as the impulse is the same. This can be clearly stated by rewriting Newton’s 2^nd law of motion:

Now it is pretty clear that in order to increase velocity of the center of mass we can either (1) increase force applied into the ground or (2) apply that force during a longer period of time. Both strategies would result in an increase in take-off velocity, hence resulting in an improvement in vertical jump, as we may see in figure 4.

WHAT ABOUT PEAK VELOCITY AND PEAK POWER?

As you may now realise, peak velocity or power only represent an output, which can be the result of different force-time characteristics according to Newton’s 2^nd law of motion. This does not represent a significant issue or limitation if the goal is to simply maximise the output. However, if an athlete is involved in a sport where time to produce force is a constraint and he/she is using the weight room as a mean to improve an end (ie, training transfer), then peak velocity or power do not tell the whole story. Indeed, an increase in peak velocity or peak power may actually be associated with a negative adaptation to training.

Faster does not always mean better! As shown before in figures 3 and 4, we know that an increase in velocity is the result of larger impulse. If larger impulse comes at the cost of more time to produce force (also associated with larger ranges of motion), then in that particular context higher peak velocity or power wouldn’t represent a positive adaptation for most sports.

In addition to those output measures, practitioners need to start monitoring different metrics that are good descriptors of the strategy utilised. This is where acceleration metrics start to unveil a whole new world for strength training.

Faster does not always mean better! If larger impulse comes at the cost of more time to produce force, then in that particular context higher peak velocity or power wouldn’t represent a positive adaptation for most sports.

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ACCELERATION AS A PROXY FOR POSITIVE TRAINING ADAPTATION

In most sports, time available to produce force is limited (figure 5).

Hence, although different technical models can allow for more time to produce force accounting for individual characteristics of the athlete, creating larger impulse (which results in greater change in velocity) through increased time to produce force is normally not a valid option and it does not represent a positive adaptation, especially if training aims to improve sprinting, jumping and throwing.

Given that most common output metrics (velocity or power) do not account for the utilised strategy, we end up with a gap in our understanding. Acceleration can be one of the solutions for this limitation. Nevertheless, the vast majority of commercialised devices that measure barbell velocity and power do not provide any time or acceleration feedback. It is understandable that most devices are designed for the regular gym user with a particular focus on powerlifting performance, where this limitation is not an issue. Additionally, acceleration metrics are more prone to hardware reliability issues. However, assuming hardware reliability can be ensured to an acceptable level, with a simple tweak on software using basic calculations it is possible to get acceleration feedback since these devices also provide velocity and power output through time and displacement.

At this moment, I’m only aware of 3 commercialised devices that provide barbell acceleration feedback: MUSCLELAB, Enode Pro, Chronojump and GYMAWARE (cloud version). I hope that in a near future more hardware and software developers can solve this limitation.

Given that most common output metrics (velocity or power) do not account for the utilised strategy, we end up with a gap in our understanding. Acceleration can be one of the solutions for this limitation.

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TIME TO PEAK VELOCITY, ACCELERATION INDEX AND DYNAMIC ISOMETRIC STRENGTH

Track & Field coaches Randy Huntington and Rolf Ohman have been utilising acceleration as a key strength training feedback metric for several years. None of this stuff was invented by me, so I elegantly stole them these concepts while reading and listening to their published content.

Acceleration is defined as a change in velocity over time and it is one of the key performance indicators for elite performance in sprinting, jumping and throwing.

In order to complement the information provided by velocity and power output, 3 important metrics are suggested: (1) Time to Peak Velocity (tpV), (2) Acceleration Index (EA-pV) and (3) Dynamic Isometric Strength (EA-DIS).

1. Time to Peak Velocity (tpV)

As the name states, it refers to the elapsed time from the onset of concentric phase to the moment of peak concentric velocity. Sprinting, jumping and throwing are associated with very short time to produce force, hence training exercises with low tpV have greater potential to transfer for those activities, following the concept of Dynamic Correspondence of Yuri Verkhoshansky. As we can see in Figure 6, exercises with short range of motion are normally associated with lower tpV when compared to larger range of motion. Interestingly, there is an inverse correlation between power output and tpV for a variety of exercises – exercises that normally result in high power outputs are also associated with higher tpV.

2. Acceleration Index (EA-pV)

The Elasticity Acceleration Index is simply a ratio between Peak Concentric Velocity and Time to Peak Concentric Velocity. It can also work as a proxy to stretch shortening cycle efficiency. Once again, exercises that maximise EA-pV do not always maximise peak velocity or peak power output (figure 7). Additionally, if an athlete increases peak velocity or power at the cost of a decrease in EA-pV, then it may be a negative training adaptation. EA-pV is more indicative about the utilised strategy than peak velocity/power or tpV alone.

3. Dynamic Isometric Strength (EA-DIS)

Dynamic Isometric Strength is a term coined by Randy Huntington and Rolf Ohman and it is simply a descriptor of what is happening during the transition or coupling between the last few degrees of the eccentric phase and the beginning of the concentric phase. During fast actions such as sprinting and jumping the duration of this coupling is extremely short and it is what separates elite athletes from their non-elite counterparts. Given that it happens extremely fast, muscles “lock” in an isometric or “quasi-isometric” state while elastic structures (such as tendons) store elastic energy, hence the term Dynamic Isometric Strength. It is calculated as the ratio between average or peak eccentric velocity and time to peak concentric velocity. The higher the EA-DIS, the higher the eccentric peak force and RFD demands, as well as the higher the stretch shortening cycle efficiency. Normally, EA-pV and EA-DIS are highly correlated.

As stated previously, an athlete may increase peak velocity or peak power output and show a decrease in tpV, EA-pV and EA-DIS, with that being a negative adaptation to training if the goal is to improve physical capacities that are more relevant to sprinting, jumping and throwing. An example can be seen in Figure 8 and Figure 9.

PEAK VELOCITY AND PEAK POWER DROP-OFF TO ADJUST VOLUME WITHIN A SET OR SESSION

Together with other advantages already mentioned earlier in this article, VBT brought the concept of flexible training prescription. By using velocity or power output coaches and athletes can adjust training volume and intensity in loco, accounting for the readiness of the athlete in that particular session. Additionally, coaches also use Velocity or Power % Drop thresholds within and between sets to decide how many repetitions per set or how many sets should be performed during a training session. Larger drop in velocity or power are associated with more fatigue hence more time needed to recover from the session (Figure 10).

When training goal is maximal power development, 5-10% peak velocity/power % drop threshold is traditionally suggested. However, as stated throughout this article, peak velocity and peak power do not tell the whole story. It is possible to keep velocity and power output stable while changing strategy. Acceleration metrics are way more sensitive to fatigue than peak velocity or peak power output.

To confirm this, I performed a set of Jump Squats @40kg (Video 1). Number of repetitions were dependent on peak velocity drop. A threshold of 10% was prescribed. In other words, as soon as I dropped ~10% in peak velocity, the set was stopped.

The actual set peak velocity and peak power data can be seen in Figure 11 and Figure 12.

I performed 11 repetitions within the peak velocity 10% drop threshold. When looking at peak power output, 7 repetitions were performed within that same threshold, while during the 11^th repetition there was 18% drop in peak power output.

Things change dramatically when analysing tpV, EA-pV and EA-DIS (Figure 13, 14 and 15).

After 4-5 repetitions, tpV, EA-pV and EA-DIS dropped ~15%, while during the 11^th repetition there was a ~30% drop! This is a massive difference when compared to peak velocity and peak power, and it confirms that the strategy is negatively affected by fatigue way earlier than the output.

The same happens during daily readiness monitoring – tpV, EA-pV and EA-DIS are more sensitive to fatigue than peak velocity and peak power output, hence they should be preferred over traditional output metrics.

During daily readiness monitoring – tpV, EA-pV and EA-DIS are more sensitive to fatigue than peak velocity and peak power output, hence they should be preferred over traditional output metrics.

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CONCLUSION

I do not intend to criticise the way coaches or athletes are utilising VBT in their training programs. Velocity and power output feedback have their place and time, especially if the athlete simply wants to simply improve outputs (eg: moving heavy loads, increasing countermovement jump height, etc) or during general phases of the preparation.

However, if the main goal of the training phase is to improve the ability to produce force explosively when time is limited, then acceleration or other strategy-dependent metrics should be preferred. Even if we do not have the technology that provides these metrics, it is important to be aware that higher peak velocity/power do not always mean better and faster.

Few repetitions per set (3 to 5) and emphasising fast eccentric actions with very brief coupling should be general heuristics to be followed when the primary goal is to improve the ability to produce high force in a short amount of time.

Again, I am not saying training should be always centred around low tpV exercises. Heavy and slow efforts are still important from a structural adaptations and health point of view. The main point is that this should be strategically planned over an athlete’s developmental path and over the course of a season. Earlier in the career or during general preparation phase of the season, general and traditional weight room work (longer ROMs, larger tpV, concentric emphasis, etc) should be the primary focus, given that it sets the foundation for later stages of development of preparation. Later in the career or during specific preparation phase of the season, more specific and relevant work should be come the primary focus – specific ROM, lower tpV and emphasising Dynamic Isometric Strength.

ABOUT THE AUTHOR

Luís Mesquita is a physiotherapist and strength & conditioning coach. He has professional experience in training and rehabilitation of high-performance athletes in a variety of sports. He is the founder of THE PEAK.