Abstract
cing 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
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:surges; sprints; anaerobic power reserve; extreme intensity domain; cycling; triathlon; mountain biking; cross-country skiing 1. Introduction The distribution of effort throughout a race is termed pacing, pacing strategy, pacing profile, or pacing pattern [1,2] and is a key factor for optimal endurance exercise perfor- mance [3]. When high-level athletes are able to pace themselves in short- (approximately 4 min) to long- (up to 2 h) distance events, the distribution of power output usually follows a J-shaped pattern [4]. The initial section of the race is performed at a higher intensity than the average race pace and represents the fast start [5]. Once this phase is completed, the athletes reduce their intensity and maintain an even pace for most of the race. This phase allows the athletes to recover from the intense effort of the fast start, maintaining an intensity that is sustainable during the race and that allows energy to be conserved for the finishing sprint [5]. This sprint, called the end-spurt, is considered a key race-defining moment [6] where multiple events are won [4,7–9]. In many endurance events, however, an even-paced phase does not occur. In these events, the athletes alternate between efforts above and below the average race intensity throughout the race, characterizing a variable pacing profile [1]. These variations in pacing can be so frequent that some endurance events resemble what occurs in team sports [10] and have been referred to as “intermittent endurance events”. The term has been utilized to describe events in cross-country skiing [11], mountain biking [10,12,13], road cycling [14,15], Sports2024,12, 164.
pacing can be so frequent that some endurance events resemble what occurs in team sports [10] and have been referred to as “intermittent endurance events”. The term has been utilized to describe events in cross-country skiing [11], mountain biking [10,12,13], road cycling [14,15], Sports2024,12, 164.
Sports2024,12, 164 2 of 22 and the cycling leg of different triathlon events [16,17]. Changes in topography, course characteristics, and race dynamics and tactics are some of the factors that ensure that athletes will have to perform several variations in intensity during the race, with the characteristics of these surges unique to each sport. These surges are performed at intensities that are not sustainable [18], occurring above the maximal metabolic steady state (MMSS) (the intensity associated with the athlete’s critical power (CP) or the 2nd ventilatory threshold (VT2)) or at supramaximal intensities (above the intensity associated with the achievement of maximal oxygen uptake (VO2max)) during a graded exercise test, also known as maximal aerobic power (MAP) or speed (MAS). Surges at intensities equivalent to 120 to 160% of the athlete’s MAP are common [10,16,19–21], with even higher values (200% to 300% MAP) reported in the literature [10]. A period of low- intensity work (approximately 40% to 60% MAP) [21,22] allows the athletes to recover from the strenuous effort and to cope with the demands of producing frequent bursts of power throughout a race. Given the frequency, duration, and intensity of these surges, this intermittent profile can have important implications for performance. Compared to performing the same amount of work at a constant intensity, a variable profile leads to greater physiological stress and faster fatigue development and negatively influences subsequent performance [23,24]. A change in the pacing profile might also influence the determinants of performance [3,25], with success in these events related to more than just the traditional factors related to endurance performance (namely, VO2max, the intensity associated with the athlete’s lactate threshold (LT) and movement economy) [3]. The ability to perform repeated efforts at a high intensity [8,10,22] and greater anaerobic capacity and power [10,26–28] have been hypothesized to be the key to success in these events. The importance of a higher MAP and VO2max [11,29–31] to performance has also been highlighted. Understanding the specific demands of these races may open new avenues to influence performance in these events [22]. The aim of this review is to characterize the variable
anaerobic capacity and power [10,26–28] have been hypothesized to be the key to success in these events. The importance of a higher MAP and VO2max [11,29–31] to performance has also been highlighted. Understanding the specific demands of these races may open new avenues to influence performance in these events [22]. The aim of this review is to characterize the variable pacing profile seen in endurance events and its implications to performance. This review will (1) elucidate the factors that contribute to a variable pacing profile, (2) describe the characteristics (intensity, duration, work-to-rest ratio) of the surges in intensity that occur in these events, and (3) address the consequences of these surges in intensity to endurance exercise performance. 2. Methods This is a narrative review focused on describing the variable pacing profile that occurs in endurance events. A literature review was performed with the following search terms: “variable pacing”, “intermittent pacing”, “pacing pattern”, “pacing strategies”, “power output distribution”, “power profile”, and “power demands”. These terms were combined with “cycling”, “triathlon”, “cross-country skiing”, and “mountain biking”, as events in these sports have been previously described as intermittent endurance events [10,11,13,15,17]. Further, papers on the “physiological demands”, “physical demands”, and “physiological requirements” of these sports were analyzed. Papers were included in the analysis of variable pacing profile if they provided sufficient information to describe the surges in intensity that occur during the races. Subsequently, a manual search within each identified paper was done to find further papers that provided information about the characteristics of the variable pacing profile in these events. 3. Factors That Contribute to a Variable Pacing Profile in Endurance Events Several factors are implicated in the variable pacing profile that is seen in endurance events. While the course’s characteristics provide the most obvious reason for changes in intensity to occur, race dynamics, tactics, and even the influence of governing bodies can contribute to a variable pacing profile.
Sports2024,12, 164 3 of 22 3.1. Out with Old, in with the New—New Race Formats and Changes in Regulations Influenced the Races’ Pacing Profiles Numerous endurance events have recently been created or modified across different sports to make races more spectacular and spectator friendly [10,17]. Cross-country skiing, for example, had eight out of 12 Olympic events in Sochi 2014 that were different from the 1994 Winter Olympics. Shorter events, such as sprint skiing, and an increase in the number of races with a mass start (10 of the 12 Olympic races now involve mass starts) [32] have increased the demands of surges in intensity and the requirement of sprinting ability in the sport [9,27]. Mountain biking and triathlon have also evolved in their race formats. In Olympic XC MTB (XCO), race duration and lap length were reduced, while the requirement for technical sections in the course increased. Current regulations require races to last between 80 and 100 min, with a lap length of 4–6 km, over a variety of terrains [10,21]. Short track XC MTB (XCC), a new race format introduced in 2018, is performed in loops of no more than 2 km and maximum race times of 20 min [33]. The cycling leg of Olympic and sprint distance triathlons is also performed in shorter loops (3.5 to 5 km) [30], and new race formats, such as super sprints and the team mixed-relay event [34], can be performed in even shorter courses. The shorter courses have increased the number of tight turns and sharp corners in these events, increasing the number of repetitive, high-intensity accelerations that are performed [10,17,20]. In sprint and Olympics distance triathlon, for example, the number of dangerous curves performed per kilometer has a strong correlation with the variability index (a measure of the variations in power output during a race) and to the number of supramaximal efforts performed [30]. These changes to race formats ensure that several variations in intensity will occur during a race, regardless of the influence of other factors on the races’ pacing profile. 3.2. Uphill, Downhill, and Technical Demands—How the Course’s Characteristics
the variability index (a measure of the variations in power output during a race) and to the number of supramaximal efforts performed [30]. These changes to race formats ensure that several variations in intensity will occur during a race, regardless of the influence of other factors on the races’ pacing profile. 3.2. Uphill, Downhill, and Technical Demands—How the Course’s Characteristics Influence Pacing Profile The technical demands of sports, such as MTB, also contribute to the number of surges that are performed. MTB courses present the athletes with numerous jumps, climbs, descents, and other technical features [13,21]. Navigating these challenges requires the performance of multiple short (8 to 15 s) efforts during the race [12,35]. The fact that the number of surges performed per lap in MTB is not significantly reduced when athletes break into smaller packs corroborates that many of these surges occur as a product of the course’s characteristics [13]. Similar influence of the terrain and technical features have also been reported in cyclocross [36] and off-road triathlon [37]. Further, changes in elevation provide their own challenge in different sports. In cross-country skiing, for example, races must have an equal distribution of flat, uphill, and downhill terrain [32]. The time spent in uphill sections, thus, varies based on the event, with shorter efforts (20 to 40 s) reported in sprint skiing [28,38] and longer efforts (up to 4 min) during longer distance races [39,40]. Likewise, in road cycling, mountainous stages require longer efforts (6 to 10 min) at intensities just above that associated with the maximal metabolic steady state (MMSS), while semi-mountainous stages require shorter (30 s to 2 min), more intense efforts [15]. 3.3. Breaking Away—The Influence of Race Dynamics to a Variable Pacing Profile The number and characteristics of the surges might also vary according to the race’s dynamics. Riding in a group leads to a higher number of surges performed as the athletes try to stay within or break away from the pack [14,20]. For example, the four athletes competing as a team in the mixed-relay triathlon performed 17, 11, 8, and 12 surges (>600 W)
characteristics of the surges might also vary according to the race’s dynamics. Riding in a group leads to a higher number of surges performed as the athletes try to stay within or break away from the pack [14,20]. For example, the four athletes competing as a team in the mixed-relay triathlon performed 17, 11, 8, and 12 surges (>600 W) in intensity during the cycling leg of the race (approximately 11 min) [34]. The athlete who only performed 8 surges was described as chasing a pack, while the others were riding within a group.
Sports2024,12, 164 4 of 22 The tactics of the chase group might also influence the surges in intensity. In road cycling, it is possible that the group will allow the breakaway to occur earlier in the race, leading to a surge that is less intense [14]. Later in the race, the power output of the surge is higher, and the intensity remains elevated for a further 30 s to 5 min to try to ensure the success of the action [7,14]. As the race nears its end, multiple 5 to 15 s sprints are performed in the 20 min prior to the end-spurt, as the competitors gradually attempt to break away from the pack or position themselves for a successful sprint to the finish line [7,8,41]. Race tactics and dynamics also play an important role in races where position within the packs is important (for example, single-track races where opportunities to pass a competitor are limited), such as MTB [21] and mass-start cross-country skiing [9]. In these events, a longer sprint (around 20 to 30 s) is performed at the beginning of the race as the athletes try to position themselves for the subsequent laps. Athletes might also perform more surges (skiing) or surges that are more intense (MTB) during the initial lap [9,21] to ensure optimal tactical positioning for the remainder of the race. Despite the negative influence that these intense efforts can have on performance, the benefits of competing within the front pack offset the greater metabolic demands of the increased intensity [9,12]. A summary of the factors contributing to surges in intensity and their consequences on the characteristics of the surges is presented in Table. A brief analysis of these factors shows that these are intrinsic to the sport (e.g., course characteristics), reflect changes made by governing bodies to make races more spectator friendly, or cannot be predicted (e.g., race dynamics, competitors’ tactics). Even increased media exposure can lead an athlete to attempt a breakaway from the group [14]. As such, athletes must be prepared to engage in a highly stochastic race, with the characteristics of these
the sport (e.g., course characteristics), reflect changes made by governing bodies to make races more spectator friendly, or cannot be predicted (e.g., race dynamics, competitors’ tactics). Even increased media exposure can lead an athlete to attempt a breakaway from the group [14]. As such, athletes must be prepared to engage in a highly stochastic race, with the characteristics of these efforts and their importance for overall performance varying according to the sport and the event. Table 1.Summary of factors that contribute to a variable pacing pattern in intermittent endurance events and how it affects the characteristics of the surges. Factors Contributing to Surges Effect on Variable Pacing Pattern Influence on Characteristics of Surges Sports Influenced by It Changes in elevation/topography Variations in intensity according to the duration and length of the climb Performance of short- (<15 s) (MTB), moderate- (30 s to 2 min), and long- (>2 min) (XC skiing, road cycling) efforts during the race MTB, XC skiing, Road cycling Course’s characteristics Repetitive accelerations, tight turns, dangerous curves, technical sections Performance of multiple short (<15 s) efforts Triathlon, MTB Race format Mass start races, competing in shorter loops Performance of multiple short (<15 s) efforts, end-spurt determines winner MTB, XC skiing, Road cycling Race tactics/dynamics Tactical positioning, breakaways, pack riding Longer and more intense surges in first lap (tactical positioning), less intense and shorter surges earlier in the race (breakaway), higher number of surges prior to finishing sprint, need to sustain higher intensity following surge later in the race MTB, XC skiing, Road Cycling, Triathlon 4. Characteristics of Surges in Intensity in Variable Pacing Endurance Events The characteristics of the surges in intensity that occur during a race vary depending on the sport. The variable pacing profile of events in XC skiing, MTB, road cycling, and the cycling leg of different triathlon races, events referred to as “intermittent endurance events” is described below. An overview of the characteristics of the surges in intensity in these sports is presented in Table.
in XC skiing, MTB, road cycling, and the cycling leg of different triathlon races, events referred to as “intermittent endurance events” is described below. An overview of the characteristics of the surges in intensity in these sports is presented in Table.
Sports2024,12, 164 5 of 22 Table 2.Characteristics of variable pacing profile in different sports. Study Participants and Competition Level Race Characteristics Characteristics of Surges Time Spent/Work Done in Each Intensity Zone Distance/Average Duration Average Intensity Number Duration Intensity Recovery Duration/Work to Rest Ratio Triathlon Mixed Relay (MR) Sharma & Périard [34] 4 elite (2 males, 2 females) World Championships Males: 10.5 min Females: 11.5 min NR 11 and 12 (males) 17 and 8 (females) NR >650 W >400 W (8 W/kg) NR 48% and 62% above 85% 4MMAP (males) 58% and 64% above 85% 4MMAP (females) Sprint (SD) and Olympic Distance (OD) Bernard et al. [16] 10 Elite triathletes (5 males, 5 females) World Cup 40 km 72 min females 63 min males 66.0±7.1% MAP L1-L2 60.7±9.1% MAP L3-L4 52.7±7.5% MAP L5-L6 44 13 13 7 s 15 s 7 s >100% MAP >100% MAP >60% MAnP Z1: 51±9% Z2: 17±6% Z3: 15±3% Z4: 17±6% Etxebarria et al. [20] 5 elite male triathletes (12 race profiles from 7 ITU international races) 40 km 252±33 W (3.9±0.5 W/kg) 34±14 * NR >600 W NR NR Cejuela et al. [30] 4 male triathletes 13 WTS races (6 SD, 8OD) Tokyo 2021 Olympic Games (OD) Approx. 40 km (average of 8.86 laps per race) for OD Approx. 20 km (average of 5.4 laps per race) for SD 58.3% MAP (mean power) 65% MAP (normalized power) Athlete’s mean MAP across study: 450 W Average of 13.9±3.6 peaks (surges) per km NR Peaks reported as efforts above MAP Power profile during races— 5 s MMP: 795±102 W (approx. 176% MAP) 30 s MMP: 499±62 W (approx. 110% MAP) 60 s MMP: 411±48 W (approx. 91% MAP) NR Time Z1: 51.9±6.5% Z2: 17.3±3.9% Z3: 13.3±2.6% Z4: 17.4±5.0 Work done Z1: 22.0±5.8% Z2: 20.4±4.0% Z3: 20.0±3.5% Z4: 37.5±10%
Description
This review characterizes variable pacing profiles in endurance events and discusses implications for athlete performance.