COVID-19 has been a unique challenge for the medical and performance staffs of professional and elite sports teams. Players went from mid-season form to a total shutdown within days and left many amateur and pros without access to ice for extended periods of time. Now in a time when the NHL Draft Combine is typically being held, NHL returning to playoffs, and some youth leagues getting the go ahead to return in the fall, we thought this would be an opportune time to discuss how off-ice athleticism relates to on-ice skating performance. To do so, we’re going to lead you through a three part series that i) outlines analytic and human performance concepts, ii) examines how effective the NHL Draft Combine tests actually are at relating to on-ice performance and identifying top talent, and iii) our recommendations to players and coaches on how best to benchmark player fitness for try-outs or specialized strength and conditioning programming.
Part i) The Science: An introduction to analytic and performance concepts and terms
Before we can dig into the research, we need to brush up on or maybe introduce a number of concepts and terms that are commonly used by researchers. We’ve split them up into analytic and performance groupings as an understanding of these two domains will be crucial in dissecting the information in parts ii &iii.
Accuracy: As a hockey mind, we all know this one. A player is accurate if they can snipe that top corner and no matter how many shots they take, they’re always honing in on their intended target. The same goes for darts (Figure 1). A dart thrower is accurate if they consistently hit the bullseye that they’re aiming for and is inaccurate if they’re way off to a side.
Reliability: Another familiar term in that someone or something is dependable or consistent. Regardless of the situation, you can expect a similar result time after time. One thing to note here is that reliability doesn’t necessarily mean it’s good (Figure 1). You could be off your mark by a wide margin but as long as you’re consistently off, you’re demonstrating reliability.
Validity: Validity is actually a broad term that could be referring to a wide range of concepts (internal vs external validity, congruence validity, face validity, etc.). To simplify it in our case though, something is valid if it is both accurate and reliable (Figure 1). If a test is reliable but inaccurate (e.g. your known fastest skater is consistently showing up with the slowest times), your test is not valid.
In Figure 1 below, the far-left dartboard is an example of something that is both unreliable (wide spread of darts) and inaccurate (not around the bullseye). Second from left, we have reliability (consistently in the same position) but inaccuracy (not near the bullseye). Third from left, we have accuracy (throws centred around the bullseye) but unreliability (throws not consistent). Finally, on the far right, we have the only example here of validity in that both accuracy (throws are at the bullseye) and reliability (throws are consistent) are achieved.
Figure 1. A dart throwing example demonstrating accuracy, reliability, and validity.
Correlation: Once again we’re going to simplify this term a bit and say that a correlation is a measure of how much two phenomena are related to each other. Correlations are represented by the letter r and range from -1 (perfect negative correlation – as one measure increases, the other decreases proportionally) to +1 (perfect positive correlation – both measures increase proportionally). A key thing to remember with correlations is that correlation does not equal causation, meaning that just because two phenomena are related to each other, it does not mean one is causing the other. To put this into hockey terms, ice time for forwards typically has a positive relationship to point totals (your top scorers will generally play more), whereas ice time and penalty minutes usually has a negative correlation (if you spend a lot of time in the box, you can’t be racking up minutes on the ice and your coach is likely going to bench you). Remember, you can put a not-so-great player on the ice for the entire game and they still may not score (correlation != causation).
Figure 2. A visual depiction of the range of correlations. In our example, ice time would be on the y-axis and points/PIM would be on the x-axis.
Aerobic fatigue: Aerobic means with oxygen so aerobic fatigue is what you traditionally think of when it comes to endurance sports like running, cross-country skiing, etc. Aerobic fatigue has a basis in hockey performance due to games being 60 minutes in length. Defencemen that lug 25-30 mins per game, have strong aerobic endurance because even though they’re taking rests between shifts and during intermissions, their aerobic system is constantly trying to produce energy to keep up with the demand. As a hockey player, aerobic fitness tests are likely the ones you hated the most in gym class (e.g. the 12-minute run and beep test).
Anaerobic fatigue: Given that aerobic means oxygen, anaerobic indicates the lack of oxygen. As you know, our body can only operate for short periods of time for oxygen so the anaerobic energy systems get used up pretty quickly. Ever wonder why your coach always preached that your shifts should be 30-45s and no longer than a minute? It’s not a coincidence that this is the time point where anaerobic systems start to become depleted and shift the burden to aerobic energy systems. Anaerobic fitness tests are also not typically a delight as they include the 30s Wingate test, shuttle runs, and up to 800 metre runs.
Strength: Everyone knows the definition of being strong – it’s the ability to move weight. In the sports science realm though, it’s important to note that strength has no time component, meaning someone who struggles to bench press 200 lbs over 1.5 seconds is technically just as strong as someone who can bench 200 lbs quickly in 0.5 seconds. This is crucial in sports because players often need to apply forces fast so being able to move weight quickly is often more important to a player’s success. Ps. Old man strength has yet to be scientifically proven but we all know it’s a thing…
Power: Defined as the amount of work divided by time, power is a metric that complements strength in that it describes how fast a person can move weight. Power can also be divided into anaerobic and aerobic domains with them both impacting hockey performance. Anaerobic power, which can be measured through vertical jump or the Margaria Kalamen stair test, is crucial for hockey players because it outlines who can get to that loose puck quicker or lay the big hit. Aerobic power is arguably not as important for hockey players as it’s focussed on the amount of power produced in longer amounts of time. This can be measured through VO2 max tests or a 1200m shuttle test.
Now that we’ve covered the main scientific components related to performance testing, the next installment of this series will examine how the NHL measures athletic performance and if it means anything.