Decoding Fatigue: Can We Measure It Live in Team Sports? – Part 1
Introduction
“Mladen, can you tell me which player is fatigued so I can adjust the tactics or possibly make a substitution?” This is a question that many sports scientists and strength & conditioning coaches have likely heard from a head coach during practice or a match. But can we truly determine which athlete is fatigued in real time using live data—such as heart rate, GPS metrics, or other monitoring tools—during a session or competition?
To address this, we first need to ask: what exactly is fatigue? Even within this simple example, we can observe a potential clash between two perspectives: the “Place of Things” approach (reductionism) and the “Forum for Action” perspective (phenomenology), as discussed by Jordan Peterson (Note 1). Let me explain these concepts and how they relate to the issue at hand.
In Maps of Meaning, Jordan Peterson introduces two fundamental ways of interpreting the world:
Place of Things: This perspective views the world as a collection of objective, material entities. It aligns with the scientific approach, emphasizing empirical observation and the measurable properties of objects. Through this lens, reality is understood in terms of “what there is,” focusing on the tangible aspects of existence.
Forum for Action: This perspective interprets the world as a stage for human action, meaning, and value. It is expressed through narratives found in arts, humanities, rituals, drama, literature, and mythology. Here, the emphasis is on “what should be,” considering the implications for behavior and the moral significance of events and objects.
Peterson argues that a comprehensive understanding of reality requires integrating both perspectives, acknowledging both the objective properties of things and their significance within human experience
From the “Place of Things” perspective, fatigue is typically understood through biomechanical and physiological lenses. Roger M. Enoka, in Neuromechanics of Human Movement, defines fatigue as a decline in a muscle’s ability to generate force or power due to sustained activity. This decline can stem from peripheral factors, such as metabolic changes within the muscle, or central factors, such as reduced neural drive from the central nervous system.
Fatigue can be categorized into two forms: manifested and latent (hidden).
-
Manifested fatigue refers to the observable inability to perform a task at the required intensity (e.g., force, power, speed, or height).
-
Latent fatigue, on the other hand, involves internal compensatory changes that allow the maintenance of intensity. These changes may include recruiting additional muscle fibers or altering movement strategies. For instance, the body might increase circulation and respiration to deliver oxygen or remove metabolic waste—factors that can either cause fatigue or interfere with force and power generation. This process also heightens the perception of effort, exhaustion, and tiredness. (For a more detailed exploration, refer to my Strength Training Manual).
When evaluating fatigue, it’s important to balance external demand with internal effort. For example, a decrease in running intensity during a match doesn’t necessarily indicate fatigue—it might simply reflect a reduced demand in that phase of play. Conversely, even if an athlete is not fatigued, excessively high demands may exceed their capacity to perform, resulting in task failure.
The mechanisms of fatigue vary depending on the activity and intensity domain (e.g., moderate, heavy, severe, or extreme endurance domains) (Table 1). In team sports, players rarely operate within a single domain, making fatigue highly dynamic and context-dependent. For instance, an athlete may experience manifested fatigue that impairs their ability to sprint but still retain the capacity to jog or stride, enabling them to fulfill tactical responsibilities without relying on high-speed efforts.
Moreover, as fatigue progresses, the athlete’s skill and their interactions with teammates can shift the demands placed upon them. This interplay further complicates the assessment of fatigue in team sports, where performance depends on a delicate balance of individual capacity, team strategy, and fluctuating game demands.
| Intensity Domain | Thresholds | Maximal Duration | Fatigue Mechanisms | Limiting Factors (“Bottlenecks”) |
|---|---|---|---|---|
| Moderate | Below the lactate threshold (LT1) | Hours (e.g., >2 hours) | – Depletion of muscle glycogen and fatty acid oxidation capability. – Central fatigue due to prolonged exertion. |
– Availability of energy substrates (fat and glycogen). – Thermoregulation. – Central nervous system (CNS) regulation. |
| Heavy | Between LT1 and critical power (CP) or lactate turn-point (LT2) | 30 minutes to 2 hours | – Accumulation of lactate and H⁺ ions causing metabolic acidosis. – Increased recruitment of type II fibers. |
– Muscle buffering capacity. – Oxygen delivery and utilization efficiency. – Central fatigue. – Ventilation rate. |
| Severe | Above CP or LT2, below VO₂max | 5 to 30 minutes | – Rapid depletion of glycogen. – Accumulation of metabolites (e.g., lactate, H⁺, Pi). – Reduced pH levels. |
– VO₂max capacity. – Cardiac output. – Peripheral muscle oxygen extraction efficiency. – Local muscular endurance. |
| Extreme | Beyond VO₂max | Seconds to ~5 minutes | – Rapid ATP depletion. – PCr (phosphocreatine) depletion. – Severe acidosis. – Neuromuscular fatigue. |
– Immediate energy system capacity (ATP-PCr). – Intracellular buffering capacity. – Maximal neuromuscular drive. |
Table 1: Endurance intensity-domains and limiting factors
In cycling endurance sports, “durability” refers to an athlete’s ability to sustain physiological performance over prolonged periods. This concept highlights the relationship between external workload (e.g., power output) and internal workload (e.g., heart rate response). During extended exercise, even when external workload remains consistent, internal responses like heart rate tend to drift upwards—a phenomenon known as cardiovascular drift. By monitoring the ratio of external to internal workload, coaches can assess how an athlete’s physiological state deteriorates under sustained effort. A smaller deviation in this ratio indicates greater durability, reflecting better resilience to fatigue. Enhancing durability can improve training design and pacing strategies for endurance athletes.
Responses