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August 11, 2014
Internal Load; Judging the Stress of your Sport

The performance industry market is flooded with devices that track and log training volume using GPS and accelerometers. The manufactures of these devices and tracking tools do a good job of selling these devices as “sports science.” Tracking work-out volume is only one part of the training equation, and today we want to discuss a term (and concept) that is a more complete look at an athlete’s training experience, Internal Load.

Internal Load represents an individual athlete’s response to training, and can be quantified by the intensity and duration of the physiological stress imposed on the athlete. To better understand how internal load fits in to the training equation we’re going to use the graphic below.

IMPELLIZZERI, F. M., RAMPININI, E. & MARCORA, S. M. 2005. Physiological assessment of aerobic training in soccer. J Sports Sci, 23, 583-592.
IMPELLIZZERI, F. M., RAMPININI, E. & MARCORA, S. M. 2005. Physiological assessment of aerobic training in soccer. J Sports Sci, 23, 583-592.

Getting a better idea of what Internal Load is requires understanding external load. External load represents all the training modalities imposed on the athlete. External load is what can be measured by GPS and accelerometers. It has also been traditionally measured by sets and reps, duration, distance, etc. When you combine external load with individual characteristics like sleep, nutrition, stress and other factors, you get a full idea of the athlete’s experience, called the Internal Training Load.

How do you measure Internal Load? One way that has been studied and proven is heart rate. An athlete’s heart rate is a great way to assess how the cardiovascular system is coping with the external training load. It has also been shown to to be a good indicator of individual characteristics. For example, if an athlete who normally performs a given training set (3000 meters of swimming) at a given heart rate may have an elevated heart rate (indicating more cardiovascular stress) when performing that set while under sleep deprivation or elevated stress level. Heart rate monitors can be annoying or just plain not available, so what is another way to measure Internal Load?

RPE (Rated Perceived Exertion) is another great way to measure internal load. RPE is a scale used to measure the intensity of exercise. The RPE scale runs from 0 – 10 (nothing at all — very, very heavy). RPE has been strongly correlated with both heart rate (internal load) and GPS (external load) showing that athletes are accurate raters of their own exertion levels. Athletes can use the scale to let you know how hard they felt a session was.

The take-home message here is that with all the new technology out there we can’t get too caught up in measuring training volumes. A training volume that is manageable for an athlete one day, can be complete over-exertion another day under different circumstances. As performance coaches it’s easy to get caught up in improving our athletes’ ability to train. At the end of the day we have to remember that our job is not to turn our athletes into professional exercisers, it is to get them better at their particular sport. GPS and accelerometers are great measurement tools, but they are no substitute for checking in constantly with your athletes; asking them how they’re feeling, how they are sleeping and eating, and how their training is going. Athletes are incredibly attuned to their own bodies and can offer us insight that no single piece of technology can.

The picture below is a view from our Dashboard, including Internal and External Load metrics.

Screen shot 2014-08-11 at 11.05.49 AM
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August 11, 2014
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17 thoughts on “Internal Load; Judging the Stress of your Sport”

  1. Good article Phil. Michael Regan (Catapult’s Head of Sports Science) said in an inteview with an ESPN reporter last spring (it’s on Catapult’s site) that all Catapult measured was external load. He was very blunt about that. Catapult is more than GPS though with their inertial sensors that can detect accelerations, decelerations, etc. It’s not just volume but stress stopping, starting etc. It’s interesting that teams like the Falcons and Jaguars use both Catapult and SpartaTrac while others like the Eagles use Catapult and Omegawave. Dashboards looking at multiple variables with tools like SpartaTrac or Catapult’s OpenField seem to be the wave of the future for forward-thinking pro teams.

    1. Timothy,

      You can record RPE (1-10) and multiply by # of minutes for the effort you are rating. For example, a session of 6 out of 10 for 30 minutes would be an internal load of 180

  2. I actually was on a workshop on deep data analysis with inertial sensors last week with Catapult’s Head of Sports Science in Australia. It’s amazing the data you can get from the accelerometers, magnetometers, and gyroscopes. He even said you almost need a sports scientist telling a computer scientist what to do. I can tell you the majority of teams that will be in the NFL playoffs are Catapult clients along with FSU, Oregon, and Alabama in the Final 4 for the college football playoffs.

    In regard to internal load there are companies like Omegawave that allow you to monitor HRV and also (according to Omegawave – you can read research on their site) CNS fatigue.
    Keep in mind you only want to measure things that are going to benefit you and that are cost-effective and time-efficient. It’s possible to get bogged down in all of this data. Like Phil said, RPE is a good and easy variable to measure.

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