Strength testing and training: Understanding which strength quality to focus on

Over the last 20 years there has been en exponential increase in availability of strength testing options. So when it comes to assessing the different classifications of strength, how should coaches see the wood for the trees? Lachlan James and a number of other authors recently published an update to their classic paper, Strength classification and diagnosis: not all strength is created equal. So we asked Lachlan six questions to pull out the key points.

Are there any strength testing or training methods that you feel have become commonplace but are overhyped for whatever reason?

The relevance of strength testing methods to a given situation should be objectively defined through a thorough needs analysis. This process will tell you what tests and metrics to focus on and, therefore, what training interventions are needed. Often, we researchers (and consequently practitioners) miss this step, getting lost in the minutia of examining a single test. In other words, it’s a case of missing the forest for the trees. The result is some tests getting far more exposure than others.

So how do we undertake an objective needs analysis to avoid the hype?

Liaising with the sport scientist to establish the key performance indicators of your sport is an important first step. Those indicators themselves must be empirically linked to competition outcome (e.g., wins vs. losses, ladder position). Performance can also be expressed as higher vs. lower level competitors in a sport: pro vs. amateur, elite vs. subelite.

Once practitioners determine these performance factors they can establish the connection between them and testing metrics. Those unique metrics with the strongest associations can take priority in the strength assessment system. Then, we can implement those training interventions that have the biggest impact on the most important strength measures.

By applying this process (Figure 1), practitioners can be confident that they’ve selected the most suitable strength metrics and associated training for their context while avoiding any hype that might have come their way.

What are the five strength and speed strength qualities that you feel should be tested, and how?

There is a huge number of lower body strength and power tests available to the practitioner. It gets even more overwhelming when we consider that many variables can be derived from a single test. However, when we analyse them statistically these variables form only a few independent domains, and each variable within a domain contains very similar information. So, when we put all the multi-joint, lower body strength-power tests in the mix, five unique, independent strength qualities (domains) appear to emerge.

Maximal isometric strength: The greatest amount of force applied to an immovable object, regardless of the rate or ability to sustain the effort. Practitioners can assess this via the isometric mid-thigh pull (IMTP) or isometric squat.

Explosive strength: In research settings, this is typically referred to as the rate of force development (RFD) or fast/rapid force production. It describes the slope of the initial portion of the force-time curve generated by the IMTP or isometric squat.

Fast dynamic strength: Force expressed maximally against no or little external load over relatively long movement times (>300 ms). Common assessments are the countermovement jump (CMJ) or squat jump.

Heavy dynamic strength: Force expressed against heavy loads, most often via a 1- or 3RM primary lift like a squat or deadlift. We can also assess heavy dynamic strength via the repetition velocity of a heavy but submaximal load (80-90% 1-RM) of a primary lift. It is important to note that heavy dynamic strength is distinct from maximal isometric strength, except in competitive weightlifters.

Reactive strength: The ability to tolerate and produce force in a fast (<250 ms) stretch shortening cycle action. The standard assessments are the drop jump or rebound jump with the cue to minimise contact time and maximise jump height.  

The needs analysis process outlined above dictates the decision on which strength qualities to include in a testing battery.

When testing with equipment like force plates, we can collect countless metrics. However, what metrics within these tests should we focus on?

Any end user of strength assessment reports (e.g., the high performance manager, the sport scientist, the lead strength & conditioning coach) can only take in so much information at once, so a key principle in data reporting is to present as much information as possible in the lowest number of metrics.

Like the process of comparing results between tests, we can reduce the metrics within a test to only a few independent domains. The decision on which of the many interrelated variables within a domain to choose is up to the practitioner based on their context.

Maximal isometric strength is an easy one. The metric of interest is peak force, which may or may not be scaled to body mass depending on the context.

Explosive strength is quantified by the force, impulse or rate of force development (if reliable) at 150 ms or less in the IMTP or isometric squat. Durations greater than this threshold produces strength outputs that are too similar to maximal isometric strength to be considered a unique strength quality. My rule of thumb is to select the earliest time point that’s reliable, which in our experience seems to be force at 100 ms.

It’s well documented that the CMJ assessment of fast dynamic strength can produce dozens of metrics. Data reduction procedures can reduce them to one primary and one secondary domain. The primary domain includes measures such as jump height or peak velocity, while the secondary domain seems to be represented by a timing metric such as time to take-off.

Heavy dynamic strength is well known to practitioners via RM and velocity testing. Eccentric and concentric-only variations of RM testing are available, but they don’t tell you anything different from a conventional RM test.

The reactive strength index derived from the drop jump or rebound jump is the key takeaway for reactive strength. Divide the jump height by the contact time, and give feedback after each trial to make sure the contact time is <250 ms.

For each of these qualities, are you able to give us any recommendations as to how to train each of them?

Based on the principle of specificity, the training most similar to the testing task will have the greatest transfer. However, we have to consider other factors such as proper periodisation, the athlete’s existing capabilities and the constraints of the training environment. With this in mind, here is a general framework.

Is there space for very sport specific tests within a battery? How can we ensure that these tests are reliable and valid, and that we understand what constitutes real change within them? 

There is definitely a space for them, depending on the situation. Such tests are often forms of jump tests, like a running vertical jump off one or two legs in sports where jumping is a key technical aspect of performance.

However, it’s important for practitioners to understand that they can’t simply make up a test or metric!

We must first establish that the new metric or test generates unique information that pre-existing measures do not. Then, as discussed in the first point of this article, we need to draw the association to performance in the sport, and that association should ideally be stronger than what already exists in other metrics. Then practitioners must confirm that the test or metric is reliable within and between individuals, and is sensitive to change across time. Finally, they must be able to conduct the test and analysis within the training environment.  

What are the biggest mistakes you see young practitioners make and what advice would you give them to help?

Presenting a ton of data which could easily be captured in just a couple of variables

If you’re doing a test using instrumentation, choose just two variables from that test and make sure they each contain unique information (i.e., have a very low correlation).

Getting distracted by the instrumentation and not coaching, cueing and providing feedback to the athlete.

Familiarise yourself extremely well with all the equipment and the testing protocols. Pilot, pilot, pilot! This will leave you with extra attention during testing to focus on the athletes themselves.

The ability to manage large groups, think on the fly and quickly adjust training sessions based on situational constraints (e.g., limited time/equipment).

Have plan A, B, C and D in your toolbox. How do you acquire the knowledge to have multiple plans? Shadow experienced coaches, practitioners and applied sport scientists for as long as possible and see how they handle it. The more situations and challenges you get exposed to in a low risk environment, the more prepared you will be once you’re solo in the wild.