An updated conceptual framework on physical performance and training in soccer: a narrative review

Soccer practitioners routinely use external load (EL), internal load (IL) and fitness measures to monitor players; however, the same monitoring variable may be interpreted as training load (TL), performance, or athlete capacity depending on its purpose and reference. The conceptual problem addressed in this review is therefore not the absence of definitions for EL, IL, or fitness status, but rather the lack of an integrated interpretative structure explaining how these established constructs should be differentiated when evaluating soccer physical performance. This conceptually focused narrative review therefore aims to clarify the distinction between TL, physical performance output, physiological response, and athlete fitness capacity, and to integrate these established concepts within an interpretative framework for soccer training and monitoring. The framework does not propose match demands, physiological responses, or fitness status as replacements for the established concepts of EL, IL, and fitness. Rather, it organizes their interpretation according to three related questions: what external output did the athlete produce, what physiological response accompanied that output, and what does the relationship between output and response indicate about the athlete's capacity to perform?. By separating the purpose for which monitoring variables are interpreted, the framework aims to support practitioners in selecting appropriate measures and aligning training prescription with either physiological adaptation targets or the external performance demands that players are required to reproduce in competition.