The proportional distribution of training by elite endurance athletes at different intensities during different phases of the season

Abstract

The present review examines retrospective analyses of training intensity distribution (TID), i.e., the proportion of training at moderate (Zone 1, Z1), heavy (Z2) and severe (Z3) intensity by elite-to-world-class endurance athletes during different phases of the season. In addition, we discuss potential implications of our findings for research in this field, as well as for training by these athletes. Altogether, we included 175 TIDs, of which 120 quantified exercise intensity on the basis of heart rate and measured time-in-zone or employed variations of the session goal approach, with demarcation of zones of exercise intensity based on physiological parameters. Notably, 49% of the TIDs were single-case studies, predominantly concerning cross-country skiing and/or the biathlon. Eighty-nine TIDs were pyramidal (Z1 > Z2 > Z3), 65 polarized (Z1 > Z3 > Z2) and 8 "threshold" (Z2 > Z1 = Z3). However, these relative numbers varied between sports and the particular phases of the season. In 91% (n = 160) of the TIDs >60% of the endurance exercise was of low intensity. Regardless of the approach to quantification or phase of the season, cyclists and swimmers were found to perform a lower proportion of exercise in Z1 (<72%) and higher proportion in Z2 (>16%) than athletes involved in the triathlon, speed skating, rowing, running, cross-country skiing or biathlon (>80% in Z1 and <12% in Z2 in all these cases). For most of the athletes their proportion of heavy-to-severe exercise was higher during the period of competition than during the preparatory phase, although with considerable variability between sports. In conclusion, the existing literature in this area does not allow general conclusions to be drawn. The methods utilized for quantification vary widely and, moreover, contextual information concerning the mode of exercise, environmental conditions, and biomechanical aspects of the exercise is often lacking. Therefore, we recommend a more comprehensive approach in connection with future investigations on the TIDs of athletes involved in different endurance sports.

Keywords: HIIT (High intensity interval training); elite athlete; endurance; endurance training; exercise intensity; training intensity distribution.

Figure 1

The classification of zones and associated physiological adaptations associated with a model that distinguishes between moderate, heavy, and severe exercise intensity (–48). LT₁, first lactate threshold; LT₂, second lactate threshold; VT₁, first ventilatory threshold; VT₂, second ventilatory threshold; OBLA, Onset of Blood Lactate Accumulation; VO_2peak, peak oxygen consumption; MLSS, maximal lactate steady-state; FTP, functional threshold power; Borg, perceived extent of exertion on the Borg 1−10 and 6−20 scales.

Figure 4

The distributions of training intensity categorized on the basis of the method of quantification and further sorted by (1) the phase of the season, (2) the sport, and (3) the proportion of time spent in zone 1. SG-Time, heart rate session goal—total time/session; sRPE, session rating of perceived exertion; RPE-TiZ, RPE time-in-zone; AltTC, altitude training camp; CP, entire competition phase; preCP, pre competition phase; mCP, main competition phase; GPP, General Preparatory Phase; SPP, specific preparatory phase; PP, entire preparatory phase; ♀, female; ♂, male; *, polarized training intensity distribution.

Figure 2

(A) The sporting disciplines and numbers of participants involved in the studies retrieved. (B) The number of investigations on and TIDs reported for each individual sport. (C) The sizes of the study populations involved in the studies retrieved.

Figure 3

The different methods employed to quantify TID in the studies analyzed here. HR-TiZ, heart rate time-in-zone; V-TiZ, velocity time-in-zone; HR-TiZ/SG, heart rate session goal/time-in-zone; SG-Session, heart rate session goal—number of sessions; RP-TiZ, race pace time-in-zone; PO-TiZ, power time-in-zone; SG-Time, heart rate session goal—total time/session; n.s., not specified; sRPE, session rating of perceived exertion; RPE-TiZ, RPE time-in-zone.