How do you measure a training session? By the hours you put in? Maybe the distances racked up? Or asking an athlete for verbal feedback?
These are useful guides, but how much does this information really tell you about how each athlete’s body reacts to the training schedule it is being put through?
In this article, we’ll examine how to measure internal load in professional sports, why it matters, and how you can use internal load to:
- Provide a clearer picture of an athlete’s response to training
- Help prevent overtraining and manage injury risk
- Enable better periodization and workload management
- Support more precise decision-making for performance optimization
What is Internal Load?
Internal load is the relative biological stressors imposed on an athlete during training and competition. Simply put, it is how the body reacts physiologically to the workload of a certain session.
Where external load (distance covered, sprints made, etc., typically measured using GPS) measures the work performed, internal load describes the impact of this workload.
The training process (Impellizzeri et al. 2005)
Every athlete will respond differently to any given training session, and each athlete will respond differently to the same stimulus from day to day. Therefore, we need to measure internal load every session to keep a running check on those responses.
The internal state of the body will always play a larger role than the external load imposed upon the body. No matter how perfect a training program may appear, if an athlete is not able to deal with such external loads, there is no way the desired internal adaptations will take place.
Why Measuring Internal Load Matters in Elite Sports
Understanding internal load is essential for S&C coaches looking to optimize athlete performance and manage injury risk. While external load, including metrics like distance covered, sprints performed, or weight lifted, provides valuable data, it doesn’t tell the full story. Two athletes performing the same session may experience drastically different physiological responses.
Combined with external load information, internal load data provides an overview of training load to give coaches a more in-depth understanding of the physiological stress placed on athletes during a training session, whilst providing quantitative data on whether a session is having the desired effect.
Although monitoring external load may be easier to understand, it is the internal training load that drives adaptation in the body, so it’s vital we monitor this aspect of training above all others.
Think of internal and external load like cooking:
Your ingredients (external training load) are thrown into the pot, you put the lid on for 30 minutes, and see what happens at the end. It could be good, it could be bad, but you don’t know until it’s on the plate (competition day).
But take the lid off during cooking, taste the food on the way, make sure the ingredients are doing what they’re supposed to, and make adjustments as required. This is like monitoring the internal load to make sure the resultant meal turns out just as you wanted it.
Methods to Measure Internal Load
Subjective Measures
Teams without an internal load monitoring system like Firstbeat are limited to using subjective methods to measure internal load. This can include RPE questionnaires where athletes self-report their perceived effort.
The trouble with this approach is that the results are subject to bias and inconsistency, as the performance staff at AFL team Sydney Swans found before they started working with Firstbeat. In our joint webinar on optimizing training and recovery in the AFL, they highlighted some of the key challenges, including:
- Timing matters: When RPE is collected, right after a session or hours later, it can influence responses. Plus, what’s happening next (e.g., a light drill vs. a tough conditioning block) impacts how athletes feel.
- Learning curve: Athletes might not be familiar with RPE scales, leading to inconsistent ratings.
- The copycat effect: Sometimes, athletes just echo what teammates say about a session, reducing accuracy.
Objective Measures (The Firstbeat Approach)
The Firstbeat Sports method for tracking internal training loads and recovery is built on an advanced analysis of heart rate and heart rate variability data.
With Firstbeat Sports, coaches can get a precise understanding of:
- Session Load (TRIMP): Quantifying the internal load of each session. Firstbeat uses beat-to-beat heart rate data to calculate TRIMP scores, ensuring more accurate training load assessment in interval type training.
- TRAINING EFFECT (Aerobic/Anaerobic): Understand the physiological impact of an individual session. An interpretation of EPOC describing the impacts of the training session on 0.0 to 5.0 scale.
- Acute & Chronic Load: Balancing training stress over time. Ensuring there is a balance between short and long-term training load helps to manage injury risk and maintain and improve fitness and performance.
- Heart Rate Recovery (HRR): An additional tool for coaches to assess the status of their athletes, giving further insights into conditioning and recovery status. Identifies the best HRR identifies from a specific time (e.g. a session or drill) for 30s, 60s, and 120s.
- Time Spent in Heart Rate Zones (Z1-Z5): Understanding the distribution of effort. By tailoring training to the specific demands of their sport, coaches can better prepare their athletes for the physiological challenges they will face in competition.
What Sets Firstbeat Apart from Other Internal Load Monitoring Systems?
Data accuracy
Data is only useful if it’s accurate, but how do you know that you can trust the data you’re being given? Coaches rely on accurate and reliable data to make informed decisions. Here at Firstbeat, we are proud to be the only internal load monitoring system for teams that communicates the quality of data openly with our users.
The Firstbeat sensor is worn with a chest strap because it provides the most accurate data collection. Scientific studies have shown that chest straps outperform vests in capturing HR data and HR-derived physiological metrics when compared to clinical-grade HR monitoring. Unlike chest straps, vests are not specifically designed for precise heart rate measurement, making them less reliable for internal load monitoring.
Data contextualization
Firstbeat goes beyond basic internal load monitoring by adding contextual layers that help coaches make informed decisions.
Coaches can identify trends, prevent overtraining, and fine-tune preparation strategies for peak performance at the right time by providing:
- Historical Comparisons: Compare similar sessions over time (e.g., “Matchday -3” training loads), track progress and identify patterns to optimize preparation.
- Team, Positional, and Individual Insights: Examine the physiological responses of individual players or positional groups and tailor training plans accordingly.
- Sport-Specific and Customized Comparisons: Ensure training aligns with the unique demands of each sport.
Conclusion
Measuring internal load is a game-changer in strength and conditioning. It moves training from a one-size-fits-all approach to a data-driven, athlete-specific strategy.
Firstbeat’s cutting-edge technology provides deep insights into internal load, allowing coaches to optimize training, manage the risk of injuries, and drive peak performance.
Learn more about Firstbeat’s internal load metrics by downloading our free training load guide here.
