Wearable Technology for Hockey Players

Zack Leddon - November 30, 2020

Wearable tracking technology is the logical next step in an industry obsessed with objective data and quantifying information.

Technological progress has enabled coaches and training staff to detect and measure internal and external player workloads utilizing wearable sensors. (1) The ability to apply numerical values to player activities on the ice is a drastic improvement over the subjective evaluations of yesteryear. Specific numbers can now replace vague definitions of easy, medium, and hard days. Research has shown us that, “In sporting scenarios where wearable tracking devices are employed, it is both possible and feasible to accurately classify team sport-related activities.” (2) This gives us a much deeper insight into what truly occurs during on-ice sessions by using wearable trackers. This insight in turn allows us to answer questions that we only had educated guesses at before.

The Two Types of Wearable Tracking Devices

These tracking devices can be placed into two categories, physiological sensors and movement sensors. While there are multiple different physiological sensors, when talking about on-ice performance generally only heart rate monitors are used. Movement sensors on the other hand can be either an accelerometer and gyroscope system or varying different global positioning satellite (GPS) devices (3). However, most systems now utilize a combination of all the aforementioned devices to get a more complete picture of internal and external loading. While different styles of devices utilize varying methods, their purpose is the same; to track volume, intensity, and individual player's performance and recovery during on-ice sessions to reduce injury risk and optimize performance.

Devices & Measurements

GPS

GPS systems have been regularly used in professional sports since its introduction to physical activity monitoring in 1997. (4) In fact, GPS technology has been utilized significantly to calculate the movement demands of many sports. (5,6) GPS units can log velocity, acceleration/deceleration, change of direction, and distance. These measurements can be used to create multiple different volume and intensity metrics. Total distance is the most common volume metric used in GPS systems. Relative distance is the intensity metric paired with it and is simply the average distance an athlete travels per minute. The number and distance of high-speed “sprints” is also used to determine an amount of “high-intensity efforts”. Certain speeds are broken into different zones for this metric and generally strength coaches will look at the distance or time an athlete spent in their highest zone. Recently, more focus has been drawn to another measurement of “high-intensity efforts”, the number of accelerations and decelerations in a session. The energy demands, disruptive effects on tissue, and greater frequency of acceleration/deceleration over high-speed sprints has led to greater usage of this metric recently. (7,8,9) GPS systems can have issues tracking short, explosive change of direction moves that are sport specific). Data accuracy is generally reduced with these types of moves compared to slower longer distance events. (10,11,12)

Accelerometer & Gyroscope

These issues with the purely GPS system led to the inclusion of an accelerometer and gyroscope device. This change was with the purpose of increasing the measurement accuracy of collisions, explosive change of direction, and sport specific movements. (13) The accelerometer functions by measuring acceleration in meters per second squared in three directions: x, y, and z. The gyroscope measures angular acceleration, otherwise known as rotation. (14,15) This combination has increased the accuracy of classifying explosive movements and sport specific movements by up to 14% and given us a variety of new metrics to evaluate. (16) 

The accelerometer/gyroscope device is used to calculate the “player load” metric, which is a measurement of the stress, or “load” a player goes through during a session. Player Load is specifically the summation of all accelerations divided by 100. It can also be used to determine intensity when divided by time, giving player load per minute. (17) Player load has been shown as an accurate way to monitor loads over periods of time. (18) This allows a strength coach to monitor loading throughout a season and notice trends within different time frames, positions, and individual players. Another load metric that has been created through the device is specific to ice hockey and is skating load. Skating load is the summation of all peak accelerations during the skating stride, multiplied by an athlete's mass, and divided by 100. This is a way to look purely at the amount of load a player accrues through just skating as all other movements are not registered. (19) 

With the use of acceleration data, two new avenues for evaluating intensity have emerged. The first is another form of high-intensity effort known as explosive efforts which measure the frequency of how many explosive movements were performed. This includes acceleration/deceleration, hard skating strides, change of direction, and high effort shots. If any explosive effort occurred at a rate greater than 2 meters per second it is registered. We can then analyze the amount of these explosive efforts for an overall intensity of the session. The second is through measuring the force output of each individual skating stride. Enough data must be collected to create player specific ranges for their individualized skating strides and that data can be then used to set high, medium, and low force bands. From there it is possible to look at the strides a player took and see what percentages of them were highly intense thus giving a clearer picture of intensity of the practice. Percentage high force stride is the percent of total strides that fell in the high force band. (19)

Heart Rate Monitors

Heart rate monitors are generally used in conjunction with external measurement tools to see the internal loading and response to external loads. It allows us to not only see the loading a player accrued during a session, but also how they internally responded to it. The most common metrics utilized are time spent above 90% max HR and one-minute recovery from a high HR peak. Time above 90% functions as a measure of intensity showing us how hard the players body had to work to perform a certain level of effort in the session. A one-minute recovery is a measure of a player's fitness and their ability to recover from high intensity efforts. It should be noted that HR metrics are very individual specific, and players should be compared to themselves more significantly than against others. (20) Although heart rate is generally used in conjunction with other devices it can also be used as a standalone.   

Heart Rate monitors generally use Training Impulse (TRIMP) to measure the volume of a session. TRIMP is not a singular measurement method, but a multitude of ways of combining relative effort and a time component into a single number. There is research to back the usage of TRIMP to measure load throughout a sports season (21), but different TRIMP formulas are better suited to certain sports over others. For example, Banisters TRIMP is not as effective for intermittent sports such as ice hockey because mean heart rate does not reflect the fluctuations in heart rate that occur during the sprint and recovery nature of shifts in games or drills in practice. Other limiting factors can be generic ordinal categories or exponential weighting factors which are needed to prevent high scores from long, easy bouts of exercise. (22)     Intensity using heart rate can be determined by using TRIMP/min which is simply the TRIMP score divided by the duration of the exercise. (23) These metrics allow teams that only have access to a heart rate monitoring system to have measures of volume and intensity to evaluate players.

Practical Application of Metrics

With the progress of wearable technology, we have significantly more data at our fingertips to make decisions than ever before. With this massive amount of data, it is very easy to become too focused on collecting as much as possible that not enough time is put towards evaluating the data and making decisions based off it. The true value of the data is in that it allows us to answer questions and gain a clearer picture of what is really going on. We now have a greater understanding of loading that occurs daily, weekly, and throughout the season. This in turn enables us to monitor trends within individual players, positionally, and team wide. (24)

Short-Term

On a daily level teams can now design and implement practices with a greater understanding of what they are trying to accomplish that day and what is the best way to go about doing it. When enough data has been collected it is possible to group a team's drills by the area of focus and by volume and intensity. This allows a team to know which prescribed drills involving the desired aspects of the game match the volume/intensity that is warranted during that session. It also allows a team to know how drills impact positions differently. This enables a staff to zero in on what they want to accomplish during a session/practice. Want less intense drills that focus on zone entries and breakouts? Or maybe more intense d zone drills? The strength coach can provide a list of drills based upon previous monitoring that meet those needs.    

Intelligent monitoring of daily loads leads to being able to manipulate weekly loads. This is of vital importance because recent research has shown that very high volume or intensity over three a three-week period and rapid increases in acute workload are the greatest associations with increased injury risk. However, progressive increases in chronic workloads help develop a tolerance to increased acute loads and help develop some injury resilience. (25,26) Injuries due to workload most often occur with the highest minute players on a team and the lowest minute players on a team. High minute players generally accrue a workload throughout a season that can be two to three times greater than the lowest minute players. It is often beneficial to manipulate practices giving these players a lower workload or limiting them to off ice work to allow ample recovery, especially during a span of dense game frequency. With low minute players workload injuries often happen when they are bumped up in the lineup and subsequently have significantly greater playing time. This causes a drastic increase in their acute workload compared to their chronic. Extra drills during full practices and having them perform on-ice work when higher minute players may be off are two effective ways of having them increase their chronic workload to be prepared in the instance they are called upon.    

Long-Term

The ability to manipulate short term workloads and intensities allows a team to look ahead and plan out acute and chronic stressors for months and the entire season. This is just one aspect of what goes into the scheduling and planning of a team but used in conjunction with all other tools in a staffs' toolbox allows for more effective and comprehensive planning. This in turn allows for chronic workloads to be kept relatively stable. Over time, evaluation of the team's performance with different approaches to differing situations will allow strength coaches to perceive trends. These trends can enable teams to make more informed decisions in certain regards to scheduling. How to approach back-to-backs, days off, morning skates, and optional days can be examined through performance in previous decisions.

Injury & Rehabilitation

Through the usage of wearable technology teams are now able to have a more educated approach to injury reduction outside of the implications of volume and load. Specifically, to hockey is the ability to measure and evaluate an individual's skating stride force. This allows for discrepancies in strides and force between legs and for change over time within an individual's stride to be measured. This can hopefully allow for a training staff to notice a developing issue before it becomes a serious injury or strain. Between this knowledge, physiological testing, and conversations with players staff can have greater knowledge of players bodies and problems that may arise.

Once a player has been injured wearable technology can also be utilized in the rehabilitation process. Off-Ice, force plates have been recently used to monitor a player's progress in returning to pre-injury levels of performance in varying jump protocols. Utilizing high force stride, it is now possible to use the same principle during the on-ice portion of a player's rehab. Their post-injury force production progress can be compared to pre-injury levels to see how rehab is going. This, along with comparing a player's pre- and post-injury heart rate response and recovery, can be used to evaluate when a player is ready to return to play.     

Closing Thoughts on Wearable Technology in Hockey

When embarking on the possible use of on-ice player monitoring, it's important to research the myriad of devices on the market because currently there are no industry-wide standards, and each brand is subject to its own validity and reliability. Some concerns have been raised due to the results of some research into wearable technology. (27,28) It should also be noted that very minimal research has been done evaluating the reliability and validity of wearable technology usage in ice hockey. The skating movement is unique and very different than the running stride in field sports where most of the research has been done on. Because of this, careful research should be done into what teams are looking to gain by implementing wearable technology and what measurements/metrics they choose to use. Since these measurements are relatively new to the hockey field, there are no sport or industry standards set, therefor, teams should be intelligently evaluating their own data to create standards and norms that work for them. 

Players concerns must also be considered when utilizing wearable technology. The most common issue that players have is if it will be used against them in any way. The fact that it could be used to effect roster decisions, playing time, and contract negotiations leaves many nervous of its usage. In fact, this has been repeatedly brought up by the players association and in the collective bargaining agreement meetings. It is of the upmost importance that wearable technology be used only for the players benefit, to help them perform at their best. If it is used against them in any way the players' trust will be lost and the effectiveness of the technology lost with it. 

Even with some of the concerns, wearable technology is an incredible advancement in how to perceive and quantify loading and intensity during on-ice practices. Coupled with heart rate data, off-ice testing, and other metrics, it can be utilized to vastly improve our understanding of what stressors players' bodies are going through and how they are responding to them. With more research into wearable technology and its usage in ice hockey, the training staff's ability to care for players will only improve allowing for better performance during games and reduction in injuries.

Zack Leddon, M.S., C.S.C.S., Assistant Strength & Conditioning Coach Washington Capitals

References

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