Abstract
h-intensity training (HIT) has commonly been the most effective training method for improvement in maximal oxygen uptake (VO 2max) and work economy, alongside a substantial volume of low-intensity training (LIT). The polarized training model combines both low- and high-intensity training into a specific training intensity distribution and has gained attention as a comprehensive approach. The objective of this review was to systematically search the literature in order to identify the effects of polarized training intensity distribution on VO 2max, peak oxygen uptake (VO 2peak), and work economy among endurance athletes. A literature search was performed using PubMed and SPORTDiscus. A total of 1836 articles were identified, and, after the selection process, 14 relevant studies were included in this review. The findings indicate that a polarized training approach seems to be effective for enhancing VO 2max, VO 2peak, and work economy over a short-term period for endurance athletes. Specifically, a training intensity distribution involving a moderate to high volume of HIT (15–20%) combined with a substantial volume of LIT (75–80%) appears to be the most beneficial for these improvements. It was concluded that polarized training is a beneficial approach for enhancing VO 2max, VO 2peak, and work economy in endurance athletes. However, the limited number of studies restricts the generalizability of these
distribution involving a moderate to high volume of HIT (15–20%) combined with a substantial volume of LIT (75–80%) appears to be the most beneficial for these improvements. It was concluded that polarized training is a beneficial approach for enhancing VO 2max, VO 2peak, and work economy in endurance athletes. However, the limited number of studies restricts the generalizability of these findings. Keywords:high-intensity training; low-intensity training; HIT; LIT; VO 2max 1. Introduction Endurance training, which leads to positive results, always involves adjustments of the duration, intensity, and frequency of training sessions [1,2]. Therefore, sports that require endurance always consist of planning and adjustments of endurance training [3–5], aiming to meet the crucial work demands required to perform. Furthermore, the relative effects of various combinations of duration and training intensity distribution have been a subject of study and debate for decades among athletes, coaches, and scientists [2]. To gain deeper insights, three common approaches to training intensity are used in endurance training aiming at enhancing performance [2,6]. Low-intensity training (LIT) is characterized by speeds adjusted for longer durations, often referred to as long slow distance training below the first ventilatory threshold, or <2 mmol·L −1 . Moderate-intensity training (MIT) involves intensities commonly performed continuously or in intervals between the two ventilatory thresholds, typically ranging from 2 to 4 mmol·L −1 . While high-intensity training (HIT), corresponds to speeds above the second ventilatory threshold, or >4 mmol·L −1 , and is primarily conducted as interval training, intermittent intervals, or short, high-intensity sprints [2,7]. High-intensity training has commonly been the most effective training approach for improvements in endurance sports performance [8]. This includes improvements in crucial performance factors such as maximum oxygen uptake (VO2max) and work economy among endurance athletes [3,9]. VO2maxrepresents the highest rate at which an individual can Sports2024,12, 326.
Sports2024,12, 326 2 of 13 consume oxygen (O2) during intense exercise, reflecting aerobic capacity and cardiovascular fitness [10]. Enhanced VO2maxsupports better O2delivery and energy production, making it a key performance indicator in endurance sports [3,5,10]. Work economy, on the other hand, indicates how efficiently an athlete uses O2during at a given intensity [11]. An improved work economy means that less O2is needed to maintain a given intensity, conserving energy and delaying fatigue [12]. This efficiency is crucial for resisting fatigue and enhancing performance, especially in long-distance competitions [3,5,11]. However, an approach consisting of a high volume of HIT can thus lead to undesirable effects that can cause inadequate recovery, which is also related to a decrease in perfor- mance [13,14]. Therefore, substantial volumes of LIT appear to be a crucial component of endurance training, as it may create a foundation for the specific adaptations that result from HIT [6,15]. Additionally, LIT has also shown a great ability to increase recovery from HIT [16], and a combination of both LIT and HIT has, therefore, been mentioned in previous papers as optimal for the improvement of endurance performance [2,6]. At the same time, it is still unclear how the distribution of LIT and HIT should be modeled. Traditionally, endurance athletes follow several common training programs, such as the threshold model, typically emphasizing > 40% MIT, and the pyramidal model, emphasizing a high volume of LIT (>70%), with progressively smaller proportions of MIT and HIT [2,7]. Another widely used approach, the polarized training model, uniquely combines low- and high-intensity into a specific intensity distribution. This model primarily consists of a high volume of LIT, with a smaller but substantial amount of HIT, and a relatively small proportion of MIT. As a result, this leads to an intensity distribution consisting of approximately 70–75% volume LIT, 0–5% MIT, and 15–20% HIT [2,7,17]. Therefore, the polarized training model is characterized by specific high-intensity sessions separated by several low-intensity workouts, with the training intensity being tightly monitored [18]. It has been discussed whether polarized training is optimal or not for endurance athletes [17,19]. Seiler [2] mentioned a
leads to an intensity distribution consisting of approximately 70–75% volume LIT, 0–5% MIT, and 15–20% HIT [2,7,17]. Therefore, the polarized training model is characterized by specific high-intensity sessions separated by several low-intensity workouts, with the training intensity being tightly monitored [18]. It has been discussed whether polarized training is optimal or not for endurance athletes [17,19]. Seiler [2] mentioned a typical training intensity distribution consisting of 80% LIT and 20% high-intensity work of competitive endurance athletes. Additionally, Laursen [6] suggested polarized training where ~75% of the total training volume is performed at low intensities and 10–15% performed at high intensities as an optimal training intensity distribution for elite athletes performing at endurance competitions. This also corresponds well with another study, where a polarized training distribution consisting of ~73% LIT and ~14% HIT significantly improved 10 km running performance among recreational athletes [20]. Therefore, it was concluded that polarized training could stimulate great performance-related effects after a 10-week intervention period. Moreover, a previous review comparing polarized training with threshold training suggested that polarized training resulted in a significantly greater improvement in time-trial performance compared to threshold training [21]. This also underlines the potential benefits of polarized training for performance improvement. Based on this, it can be assumed that similar significant improvements may also impact other parameters related to endurance performance. The previous literature has mentioned VO2maxand work economy as two crucial factors determining the ability to perform in endurance sports [3,5,10]. However, current reviews still lack some knowledge regarding the specific effects of polarized training on VO2maxand work economy across a range of endurance sports [21,22]. Although both systematic reviews and meta-analyses provide research summaries, a systematic review was conducted due to the limited number of stud- ies that directly compare the effects of polarized training. Therefore, this present systematic review aims to examine whether polarized training intensity distribution positively affects maximal oxygen uptake and work economy among endurance athletes.
Sports2024,12, 326 3 of 13 2. Materials and Methods 2.1. Literature Search This systematic review was conducted following the 2020 guidelines and checklists established by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Table S1) [23]. The used keywords in this literature search were combined with Boolean operators (AND, OR) in the research process. No limitations were placed on publication dates due to the relatively limited number of studies published on this subject. A SPORTDiscus and PubMed literature search from inception to 14th of April 2024 was performed. The title, abstract, and keywords were searched using the following search strategy: ((“polarized” OR “POL” AND “training method”) AND (“endurance” OR “aerobic” AND “sports” OR “exercises” OR “activities”)). 2.2. Inclusion Criteria Studies were included in this review if the following inclusion criteria were met: (1) They analyzed the effects of polarized endurance training on VO2maxor VO 2epakand/or measures of work economy. (2) They involved at least a 4-week training intervention, and employed a one-, two, or multiple-group- crossover design. (3) The participants were at least at a recreational level or higher. (4) The studies included were in English and published in a peer-reviewed journal. Due to the limited studies published on the effects of polarized training on endurance sports, gender and training background were not considered as differentiating factors. A flowchart of the literature search strategy and study selection process is presented in Figure.Sports 2024, 12, x FOR PEER REVIEW 3 of 13 2. Materials and Methods 2.1. Literature Search This systematic review was conducted following the 2020 guidelines and checklists established by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Table S1) [23]. The used keywords in this literature search were combined with Boolean operators (AND, OR) in the research process. No limitations were placed on pub- lication dates due to the relatively limited number of studies published on this subject. A SPORTDiscus and PubMed literature search from inception to 14 th of April 2024 was per- formed. The title, abstract, and keywords were searched using the following search strat- egy: ((“polarized OR “POL” AND “training method”)
in the research process. No limitations were placed on pub- lication dates due to the relatively limited number of studies published on this subject. A SPORTDiscus and PubMed literature search from inception to 14 th of April 2024 was per- formed. The title, abstract, and keywords were searched using the following search strat- egy: ((“polarized OR “POL” AND “training method”) AND (“endurance OR “aerobic” AND “sports” OR “exercises” OR “activities”)). 2.2. Inclusion Criteria Studies were included in this review if the following inclusion criteria were met: (1) They analyzed the effects of polarized endurance training on VO2max or VO2epak and/or measures of work economy. (2) They involved at least a 4-week training intervention, and employed a one-, two, or multiple-group- crossover design. (3) The participants were at least at a recreational level or higher. (4) The studies included were in English and pub- lished in a peer-reviewed journal. Due to the limited studies published on the effects of polarized training on endurance sports, gender and training background were not con- sidered as differentiating factors. A flowchart of the literature search strategy and study selection process is presented in Figure 1. Figure 1. Flow chart of the search strategy and study selection. 2.3. Data Extraction The results from the database search were imported into the software for biblio- graphic management (Endnote version 21 for Windows). The abstracts were evaluated in this software, and, if the abstracts exhibited potential, the full texts of the articles were read. The articles were then examined for whether or not they met the inclusion criteria. The studies included had to measure baseline-, post-, and change-values for at least one following variables: work economy during a given submaximal intensity (veloc- ity/power at 4 mmol·L −1 , anaerobic threshold, second lactate threshold, or second ventila- tory threshold), and/or maximal oxygen uptake (ml·min −1 ·kg −1 ), and/or reported as either Figure 1.Flow chart of the search strategy and study selection. 2.3. Data Extraction The results from the database search were imported into the software for bibliographic management (Endnote version 21 for Windows). The abstracts were evaluated in this
threshold, second lactate threshold, or second ventila- tory threshold), and/or maximal oxygen uptake (ml·min −1 ·kg −1 ), and/or reported as either Figure 1.Flow chart of the search strategy and study selection. 2.3. Data Extraction The results from the database search were imported into the software for bibliographic management (Endnote version 21 for Windows). The abstracts were evaluated in this software, and, if the abstracts exhibited potential, the full texts of the articles were read. The articles were then examined for whether or not they met the inclusion criteria.
Sports2024,12, 326 4 of 13 The studies included had to measure baseline-, post-, and change-values for at least one following variables: work economy during a given submaximal intensity (velocity/power at 4 mmol·L −1 , anaerobic threshold, second lactate threshold, or second ventilatory thresh- old), and/or maximal oxygen uptake (ml·min −1 · kg −1 ), and/or reported as either VO2max or VO 2peak. VO2maxrefers to the plateau of O2consumption reached, while VO 2peakindi- cates the highest O2consumption attained during an incremental test [24]. Furthermore, the following characteristics from each study were also extracted: au- thors with publication year, sample size, training status of the participants, the duration of the training interventions, and training intensity distribution. 2.4. Quality Assessment The methodology quality and risk of bias for each study were evaluated by two independent observers using the PEDro scale [25] (Table). The PEDro scale in- cludes 11 items to evaluate scientific rigor. Item 1 assesses external validity (yes/no), while items 2–11 rate internal validity, where each is scored as 0 (absent) or 1 (present), giving a total score out of 10. Due to the impracticality of blinding assessors, and the inability to blind the participants and investigators in supervised exercise interventions, items 5–7 related to blinding were removed from the scale [26], following the approach of previous systematic reviews [25]. Consequently, the highest total score was 7 instead of 10. Studies with quality scores ranging from 6 to 7 were classified as “excellent”, a score of 5 was considered “good”, a score of 4 was rated as “moderate”, and studies that scored 0–3 were considered to be “poor” [25]. Table 1.PEDro ratings of the included studies. Study PEDro Scale: Item Number 1 2 3 4 5 6 7 8 Total Score Rating Pla, et al. [27] Yes 1 0 1 0 0 1 1 4 Moderate Jaime Arroyo-Toledo, et al. [28] Yes 0 0 1 1 0 1 1 4 Moderate Stöggl and Sperlich [29] Yes 1 0 1 1 0 1 1 5 Good Kim, et al. [30] Yes 0 0 1 0 0 1 1 3 Poor Carnes and Mahoney
Pla, et al. [27] Yes 1 0 1 0 0 1 1 4 Moderate Jaime Arroyo-Toledo, et al. [28] Yes 0 0 1 1 0 1 1 4 Moderate Stöggl and Sperlich [29] Yes 1 0 1 1 0 1 1 5 Good Kim, et al. [30] Yes 0 0 1 0 0 1 1 3 Poor Carnes and Mahoney [31] Yes 1 0 1 1 0 1 1 5 Good Festa, et al. [32] Yes 1 0 1 1 0 1 1 5 Good Filipas, et al. [33] Yes 1 0 1 1 0 1 1 5 Good Neal, et al. [34] Yes 1 0 1 1 0 1 1 5 Good Stöggl and Björklund [35] Yes 1 0 1 1 0 1 1 5 Good Selles-Perez, et al. [36] Yes 1 0 1 0 0 1 1 4 Moderate Röhrken, et al. [37] Yes 1 0 1 0 0 1 1 4 Moderate Pérez, et al. [38] Yes 1 0 1 1 0 1 1 5 Good Treff, et al. [39] Yes 1 0 1 1 0 1 1 5 Good Schneeweiss, et al. [40] Yes 1 0 1 0 0 1 1 4 Moderate Items in the PEDro scale: 1 = eligibility criteria were specified; 2 = subjects were randomly allocated to groups; 3 = allocation was concealed; 4 = the groups were similar at baseline regarding the most important prognostic indicators; 5 = measures of 1 key outcome were obtained from 85% of subjects initially allocated to groups; 6 = all subjects for whom outcome measures were available received the treatment or control condition as allocated or, where this was not the case, data for at least 1 key outcome were analyzed by “intention to treat”; 7 = the results of between-group statistical comparison are reported for at least 1 key outcome; 8 = the study provides both point measures and measures of variability for at least 1 key outcome. 3. Results 3.1. Study Selection A literature search on the databases SPORTDiscus and PubMed identified 1836 poten- tially relevant articles (Figure). A total of 7 duplicates
7 = the results of between-group statistical comparison are reported for at least 1 key outcome; 8 = the study provides both point measures and measures of variability for at least 1 key outcome. 3. Results 3.1. Study Selection A literature search on the databases SPORTDiscus and PubMed identified 1836 poten- tially relevant articles (Figure). A total of 7 duplicates were removed, and 20 articles were selected for full-text review after screening of the titles and abstracts. After the screening of the full texts, 6 records were eliminated with the following reasons: (1) the studies did not measure either VO2max, VO 2peak, or work economy (n = 3); (2) the excluded studies did
Sports2024,12, 326 5 of 13 not specify training intensity distribution or did not match a training intensity distribution primarily consisting of LIT and HIT, which characterizes the polarized training method (n = 2); (3) the training intervention period was shorter than 4 weeks (n = 1). After the selection, a total of fourteen studies met the inclusion criteria and were included in this systematic review. 3.2. Quality of Studies Regarding the quality of the selected studies in this review, the mean score on the PEDro scale was 4.5±0.65, with values ranging from 3 to 5 (Table). Eight studies achieved a rating of good quality, five studies were of moderate quality, while the remaining one study was classified as poor quality (Table). 3.3. Characteristics of Participants Four studies performed polarized training interventions on recreational participants, six included well-trained participants, and four studies were conducted on elite athletes (elite junior, national elite, and national team). A total of 163 participants (129 men and 34 women) were included in the selected studies, with an age ranging from 17 to 44 years. 3.4. Characteristics of the Included Studies The characteristics of the selected studies are presented in Table. Of the included studies, four performed polarized training interventions in running [31,32,38,41], two stud- ies were performed on triathletes [36,37], two in swimming [27,28], one on rowers [39], one on mountain bikers [40], and one study in cycling [34]. Three studies also included more than one endurance sport in their study design. Two of these studies included running, cy- cling, triathlon, and cross-country skiing [29,35], while another study performed polarized training intervention on both cross-country skiers and biathletes [30]. Two of the included studies had a four-group-comparison design, one study had a three-group design, ten had a two group-design, and one study had a one-group design. The mean length of the training interventions was 9.1±2.9 weeks, with a duration ranging from 4 to 13 weeks. Of the fourteen studies included, eight measured baseline, post-, and change-values in VO2maxor VO 2peakand work economy, four studies only measured work economy, while two studies measured only VO2maxafter the polarized
a two group-design, and one study had a one-group design. The mean length of the training interventions was 9.1±2.9 weeks, with a duration ranging from 4 to 13 weeks. Of the fourteen studies included, eight measured baseline, post-, and change-values in VO2maxor VO 2peakand work economy, four studies only measured work economy, while two studies measured only VO2maxafter the polarized training intervention. 3.5. Training Intensity Distribution The average training intensity distribution across the eleven included studies was 81.3±8.0% LIT, 3.4±3.2% MIT, and 15.4±6.3% HIT. Treff, et al. [39] and Röhrken, et al. [37] showed the largest volume of LIT (respectively, 92 and 91%), while the lowest percentage of LIT (68%) was observed in two studies [29,35]. Additionally, four studies reported 0% as their total training volume of MIT [28,34,37,40], with the largest volume of MIT (11%) found in Carnes and Mahoney [31]. Lastly, Stöggl and Sperlich [29] and Stöggl and Björklund [35] reported the highest training volume of HIT (26%) among the included studies, while Kim, et al. [30] and Treff, et al. [39] had the smallest HIT volume (7% and 6%, respectively) in their polarized training interventions.
Description
The review examines polarized training's impact on endurance performance metrics.