Can GPS systems monitor a goalkeeper’s training load?

Are GPS systems, even the latest-generation models, truly capable of quantifying a goalkeeper’s training load? Understanding how they work is the best way to be prepared.

What GPS systems are in football

GPS (Global Positioning System) systems used in football are small devices, usually housed in a pocket between the shoulder blades inside a tight-fitting vest. They are essentially receivers that communicate with satellites and reconstruct the athlete’s position over time. From this sequence of positions, all the metrics we are now familiar with can be derived: total distance covered, distance covered within different speed zones, number of sprints, peak speed, accelerations, and decelerations.

What are they used for in practice?

They are used to measure external load, that is, the physical work performed. For an outfield player, much of what matters from a workload perspective is related to locomotion (how much they have run, at what intensity, how often they changed pace, etc.). A winger who constantly runs up and down the flank, a defensive midfielder who repeatedly covers the box and recovers, or a striker making runs in behind the defense—all of their work consists largely of moving through space. By accurately measuring that movement, GPS captures a substantial portion of their workload.

Internal load and external load

Before going any further, however, it is important to distinguish between external load and internal load.

External load is the physical work prescribed or performed. In essence, it is the dose: the stimulus that the fitness coach plans and administers. Internal load, on the other hand, is the psychophysiological response of the body to that dose: heart rate, TRIMP*, sRPE**, heart rate variability, and lactate levels.

The simplest analogy is that of medication. External load is the number of milligrams prescribed; internal load is the effect those milligrams produce in that specific patient, on that specific day. The exact same dose can have very different effects depending on fitness level, accumulated fatigue, heat, sleep quality, and emotional state.

External and internal load complement each other. It is by looking at them together that we understand what actually happened on the field. Compared side by side, they tell us not only what the response was, but also what caused it. In the background remains the ability of the coach and conditioning specialist, with their trained eye, to anticipate what the numbers will eventually reveal.

Why GPS works well for outfield players

For outfield players, GPS captures precisely what carries the greatest workload in those roles—movement through space. And in these athletes, running performance is closely linked to the body’s physiological response.

Simply put, when a midfielder covers large distances and repeatedly changes pace, heart rate rises, perceived fatigue increases, and physiological effort grows in parallel with the work performed. This is why only a little additional information is needed to complete the picture. Alongside GPS metrics, a simple internal measure (such as session RPE collected at the end of training, or heart-rate monitoring) is often enough to provide a reliable assessment of workload.

Goalkeeper performance: another sport within the same field

Goalkeeper performance has unique demands, and GPS alone cannot fully capture them. It misses short positioning movements, explosive multidirectional actions, isometric holds, and the mechanical stresses placed on muscles and tendons during technical actions, all of which involve a strong cognitive component.

Moreover, goalkeepers cover roughly half the distance of an outfield teammate (on average 4–6 km per match). They also cover it differently: mostly by walking or moving at low intensity, rather than through repeated bursts of activity like other players. High-intensity actions account for only about 1% of match time, while sprint volume is minimal—just 11 ± 12 meters per game. Professional clubs will undoubtedly possess their own datasets, with values that may differ somewhat. However, those differences are unlikely to be large enough to alter the overall picture.

Even internal load measures based on heart rate (HR) are difficult to interpret in goalkeepers. The reasons are physiological. Heart rate responds with a certain delay to rapid changes in intensity and struggles to reflect anaerobic alactic work accurately. In these situations, the heart simply does not have enough time to mirror the true intensity of the action.

A second factor further complicates interpretation: heart rate is influenced by emotional responses. It may increase even in the absence of significant locomotor activity, driven solely by tension, anticipation, or psychological stress.

Therefore, both traditional approaches (external load measured through GPS and internal load estimated through heart rate) have a blind spot precisely where greater clarity is needed to properly assess the goalkeeper’s training load.

• Di Salvo et al. (2008) — PMID 18997646
• Kubayi A. (2020) — testo integrale, SA J Sports Med

What IMU systems are and what they add

IMU stands for Inertial Measurement Unit. It is a small sensor, often the same chip already integrated into modern GPS devices. Inside, it combines an accelerometer (which measures linear accelerations along three axes), a gyroscope (which measures angular velocities, i.e., rotations), and usually a magnetometer (which measures orientation). Unlike GPS, an IMU does not rely on satellites and does not measure position. Instead, it directly measures how the body moves in every direction, even while remaining in the same location.

Based on this technology, devices specifically designed for goalkeepers have been developed. They provide metrics such as the number of dives, jumps, recovery time after getting back to the feet, and similar indicators. Alongside these event-based metrics, software platforms often provide a single synthetic accelerometric load value intended to summarize “how much” work the goalkeeper has performed. In essence, these devices primarily provide information about the mechanical component of external load.

This is precisely where the first limitation arises, and it is a conceptual one. That synthetic value is an accelerometric index and can be misleading because it is often interpreted as if it described the goalkeeper’s internal load, whereas it primarily reflects the mechanical component of external load. Mistaking it for a measure of actual exertion may lead coaches either to overload or underload the goalkeeper at the worst possible moment. An IMU does not directly measure physiological stress, let alone the cognitive and emotional stress associated with technical performance, which for goalkeepers probably represents the most demanding component of fatigue.

The second limitation concerns validation. Several goalkeeper-specific metrics available in commercial software have not yet achieved the same level of independent, published, and replicated validation as more traditional GPS-derived metrics. Furthermore, many of these values are generated by proprietary algorithms that researchers cannot access, making it impossible to independently verify their accuracy.

Can GPS and IMU systems monitor goalkeeper training load?

According to a recent review, if the objective is to quantify goalkeeper training load with the same scientific rigor applied to outfield players, the answer appears to be no at least not yet. Currently, there is no validated technology capable of doing so. These devices provide role-specific metrics, but without the level of independent validation available for the metrics commonly used with outfield players.

On one hand, the measured external load remains an imperfect indicator, capturing mainly the mechanical component of performance. On the other hand, internal-load measures such as heart rate and perceived exertion are useful but also imperfect, and are not particularly sensitive to the type of fatigue experienced by goalkeepers. In this population, cognitive, emotional, and technical demands play an especially important role, likely a greater one than the purely physical dimension. Comparing two imperfect measures does not automatically produce an accurate quantification. Consequently, the data must be interpreted with caution, as the margin of error remains substantial.

If, instead, the objective is to obtain feedback that complements one’s own assessment and, through the accumulation of longitudinal data, contribute to the future development and validation of these technologies, then IMU sensors find their most appropriate application. It should also be remembered that goalkeeper coaches already estimate the mechanical component of external load during the planning phase of training sessions, simply by considering how many dives, high ball interventions, double save sequences, and other goalkeeper-specific actions are expected to be performed during the session.

*TRIMP (Training Impulse) is an index that summarizes training load by combining exercise duration and heart-rate intensity. In practical terms, the longer an athlete trains and the higher their heart rate remains, the greater the “dose” of physiological stimulus received by the cardiovascular system.

**RPE stands for Rating of Perceived Exertion, a measure of perceived effort. At the end of a training session, athletes are typically asked, “How hard was this session?”, and they respond using a numerical scale (usually the modified Borg scale ranging from 1 to 10). The “s” in sRPE stands for session: the perceived exertion score is multiplied by the duration of the session, expressed in minutes, to provide an estimate of internal training load. The main limitation of sRPE is its subjective nature. It can be influenced by the athlete’s mood, personality, timing of the assessment, and ability to recall the overall session. For this reason, it should be collected using a standardized procedure (typically 15 to 30 minutes after the end of training) to avoid the response being disproportionately influenced by the final effort performed.