The Measurement and Application of Critical Speed and D' in Running: A Scoping Review

Critical speed (CS) represents the maximal metabolic steady state in running, and D' represents the finite distance capacity above CS. However, there is currently no consensus on the optimal measurement and modelling methods to obtain CS and D' estimates, how CS and D' influence running performance, or how CS and D' have been applied within a training environment. The aims of this scoping review were to determine the specific protocols and modelling methods that have been implemented to quantify CS and D' in running; the deterministic potential of CS and D' for running race performance; and the application of CS and D' in individualising running training prescription. The PRISMA guidelines for scoping reviews were followed. PubMed, Scopus, Embase and SPORTDiscus were systematically searched, and studies were screened for eligibility. A total of 124 studies were included in the review, of which 23 investigated CS as the maximal metabolic steady state, 68 investigated different measurement or modelling methods on CS and D', 16 examined different measurement methods on CS only, six investigated D' reconstitution, 26 studies explored the relationship between CS or D' and running performance, and 16 applied CS and D' modelling to individualise training prescription. CS has been validated as the boundary between the heavy- and severe-intensity domains while there is a far smaller body of research investigating D' reconstitution; however, variations in testing protocols may influence CS and D' estimation. Of importance to coaches and athletes is that CS and D' balance are particularly strong determinants of middle- and long-distance running performance (mile to marathon, and 5000 and 10,000 m, for CS and D' balance, respectively), and modelling of CS and D' provides an avenue to individualise training prescription.Open Science Framework (OSF) registration: https://osf.io/rq2h3 .