The Characteristics of Endurance Events with a Variable Pacing Profile-Time to Embrace the Concept of "Intermittent Endurance Events"?

Abstract

A variable pacing profile is common in different endurance events. In these races, several factors, such as changes in elevation or race dynamics, lead participants to perform numerous surges in intensity. These surges are so frequent that certain events, such as cross-country (XC) skiing, mountain biking (MTB), triathlon, and road cycling, have been termed "intermittent endurance events". The characteristics of these surges vary depending on the sport: MTB and triathlon require athletes to perform numerous short (<10 s) bouts; XC skiing require periods of short- and moderate-(30 s to 2 min) duration efforts, while road cycling is comprised of a mix of short-, moderate-, and long-duration (>2 min) bouts. These bouts occur at intensities above the maximal metabolic steady state (MMSS), with many efforts performed at intensities above the athletes' maximal aerobic power or speed (MAP/MAS) (i.e., supramaximal intensities). Given the factors that influence the requirement to perform surges in these events, athletes must be prepared to always engage in a race with a highly stochastic pace. The aim of this review is to characterize the variable pacing profile seen in endurance events and to discuss how the performance of multiple maximal and supramaximal surges in intensity can affect how athletes fatigue during a race and influence training strategies that can lead to success in these races.

Keywords: anaerobic power reserve; cross-country skiing; cycling; extreme intensity domain; mountain biking; sprints; surges; triathlon.

Figure 1

The range of intensities of the surges reported in the literature and their relation to intensity domains and the athletes’ anaerobic power reserve (APR). The image illustrates the numerous surges in the severe and extreme intensity domains and how classifying these as a single intensity zone (green bar) does not accurately represent their physiological demands. NP: no power, MMSS: maximal metabolic steady state, MAP: maximal aerobic power, MAS: maximal aerobic speed, MPP: maximal peak power.

Figure 2

Time spent at different intensity zones during intermittent endurance events in triathlon (top) and mountain biking (bottom). Data for triathlon from Bernard et al. [16] and Cejuela et al. [30]; data for mountain biking from Granier et al. [10] and Hays et al. [21]. Training zones in triathlon correspond to: Z1: below VT1, Z2: between VT1 and VT2, Z3: between VT2 and MAP, Z4: above MAP. In MTB: Z1: no power or 10% below MAP, Z2: 10% MAP to below VT1, Z3: VT1 to VT2, Z4: VT2 to MAP, Z5: above MAP.

Figure 3

Blood lactate concentrations during a repeated sprint protocol performed, consisting of fifteen 10 s sprints at three different intensities. MAP: maximal aerobic power, 25APR: intensity associated with 25% of the participant’s APR; 50APR: intensity associated with 25% of the participant’s APR.

Figure 4

Performance during a 30 s Wingate, following the completion of the repeated sprint protocol. Each circle represents a data point. (Top panel) maximal peak power (MPP); (bottom panel) mean power during the 30 s effort. * p < 0.05, ** p < 0.01, **** p < 0.001, ns = non significant.