Boost Endurance with Zone 2 Training

Effort is central to every step you take on a run and every thought you push aside to finish a work project. Yet, scientists across psychology, physiology, and neuroscience have never agreed on a single definition for this fundamental experience. A new guide published in *Sports Medicine* provides a map through this complex research territory. The authors, Lukas Hack, Israel Halperin, and Wanja Wolff, systematically review the three main ways effort is understood and the four types of measurements used to study it.

### Three Competing Definitions of Effort

The researchers categorize the long-standing debate around effort into three conceptual camps. The first is the **force-based account**. This is the most intuitive definition for athletes: effort is the voluntary generation of physical force against resistance. In this view, pushing harder on the bike pedals directly equals more effort.

The second is the **resource-based account**, which comes from cognitive psychology. It views effort as the allocation of limited mental resources, like attention and working memory. Finishing a complex workout plan while tired requires more of this type of effort than a routine jog.

The third is the **mediation-based account**. This perspective sees effort as the subjective sense of cost or difficulty that mediates our decisions. It asks, “How much do I *feel* this task is costing me?” This feeling determines whether you choose to sustain a Zone 2 pace or back off.

### How Scientists Measure Effort in the Lab and Field

Because effort cannot be observed directly, scientists rely on proxies—measurable changes that reflect the underlying construct. Hack and colleagues group these into four systems.

**Neurophysiological proxies** include tools like EEG and fMRI to measure brain activity. Increased activity in specific brain regions, such as the anterior cingulate cortex, often correlates with higher perceived effort.

**Metabolic proxies** are highly relevant to endurance athletes. This includes measurements like oxygen consumption (VO2), heart rate, and lactate production. For example, the metabolic cost of maintaining a given power output serves as a physiological effort indicator. This connects directly to the principles of Zone 2 training for metabolic efficiency, where the effort is regulated to optimize fuel use.

**Psychological proxies** are self-reports, like rating your perceived exertion on the Borg Scale from 6 to 20. While subjective, these ratings are powerful predictors of behavior and tolerance.

**Behavioral output proxies** are observable choices, such as the reduction in force output over time (velocity loss) or the decision to quit a task. Research like our article on optimizing velocity loss in strength training uses this type of measure to gauge effort and fatigue.

### Practical Implications for Training and Performance

This framework has direct applications for anyone involved in endurance sports. First, it clarifies why a coach, a physiologist, and a sports psychologist might assess an athlete’s “hard” session differently. They could be looking at lactate levels (metabolic), power output (force-based), or the athlete’s motivation to repeat the session (mediation-based).

Second, it highlights the importance of using multiple measures. Relying solely on heart rate might miss cognitive effort during a technically complex trail run. Similarly, a perceived exertion score might feel low during an emotionally draining workout, even if power is high. The gut-brain connection, explored in research on how exercise shapes the gut to fight fatigue, adds another layer to how effort is sensed and regulated.

Finally, understanding the resource-based account of effort can improve training design. Scheduling cognitively demanding technique work or race-planning sessions after easy physical training days may lead to better outcomes. It respects that mental resources are finite and need management, much like physical energy systems.

### A Unified Framework for Future Research

The core contribution of Hack, Halperin, and Wolff’s guide is not declaring a winner among these definitions. Instead, they provide a shared framework so researchers from different fields can communicate. A neuroscientist and an exercise physiologist can now specify whether they are discussing effort as a brain signal, a lactate threshold, or a subjective rating.

For the endurance community, this interdisciplinary approach promises better tools. Future fitness trackers might integrate heart rate variability (a neurophysiological proxy) with movement efficiency and subjective mood to give a holistic picture of daily readiness and effort capacity. This integrated view supports broader health goals, such as how cardiorespiratory fitness predicts longevity, by considering the full effort required to build and maintain that fitness.

The study, “A Hitchhiker’s Guide to Physical and Cognitive Effort” (DOI: 10.1007/s40279-026-02510-8; PMID: 42568028), does not simplify effort. It acknowledges its complexity. For athletes and coaches, this means recognizing that a single number on a watch rarely tells the whole story. True performance understanding comes from layering the physical, the metabolic, and the psychological views of effort together.