Access to this full-text is provided by Frontiers.
Content available from Frontiers in Physiology
This content is subject to copyright.
ORIGINAL RESEARCH ARTICLE
published: 04 February 2014
doi: 10.3389/fphys.2014.00033
Polarized training has greater impact on key endurance
variables than threshold, high intensity, or high volume
training
Thomas Stöggl1,2*and Billy Sperlich3
1Department of Sport Science and Kinesiology, University of Salzburg, Salzburg, Austria
2Department of Health Sciences, Swedish Winter Sports Research Centre, Mid Sweden University, Östersund, Sweden
3Institute of Sport Science, University of Würzburg, Würzburg, Germany
Edited by:
Niels H. Secher, University of
Copenhagen, Denmark
Reviewed by:
Niels H. Secher, University of
Copenhagen, Denmark
Stefanos Volianitis, Aalborg
University, Denmark
*Correspondence:
Thomas Stöggl, Department of
Sport Science and Kinesiology,
University of Salzburg, Schlossallee
49, 5400 Hallein/Rif, Salzburg,
Austria
e-mail: thomas.stoeggl@sbg.ac.at
Endurance athletes integrate four conditioning concepts in their training programs:
high-volume training (HVT), “threshold-training” (THR), high-intensity interval training
(HIIT) and a combination of these aforementioned concepts known as polarized training
(POL). The purpose of this study was to explore which of these four training concepts
provides the greatest response on key components of endurance performance in
well-trained endurance athletes.
Methods: Forty eight runners, cyclists, triathletes, and cross-country skiers (peak oxygen
uptake: (VO2peak): 62.6±7.1mL·min−1·kg−1) were randomly assigned to one of four
groups performing over 9 weeks. An incremental test, work economy and a VO2peak tests
were performed. Training intensity was heart rate controlled.
Results: POL demonstrated the greatest increase in VO2peak (+6.8 ml·min·kg−1or 11.7%,
P<0.001), time to exhaustion during the ramp protocol (+17.4%, P<0.001) and peak
velocity/power (+5.1%, P<0.01). Velocity/power at 4 mmol·L−1increased after POL
(+8.1%, P<0.01) a n d H IIT (+5.6%, P<0.05). No differences in pre- to post-changes
of work economy were found between the groups. Body mass was reduced by 3.7%
(P<0.001) following HIIT, with no changes in the other groups. With the exception of
slight improvements in work economy in THR, both HVT and THR had no further effects
on measured variables of endurance performance (P>0.05).
Conclusion: POL resulted in the greatest improvements in most key variables of
endurance performance in well-trained endurance athletes. THR or HVT did not lead to
further improvements in performance related variables.
Keywords: lactate threshold, peak power, peak oxygen uptake, time to exhaustion, work economy
INTRODUCTION
Athletes participating in endurance sports such as running,
cycling, and cross-country skiing integrate four conditioning
concepts into their training program to maximize athletic perfor-
mance. The first conditioning concept is prolonged high-volume
low-intensity exercise (HVT). The second is training at or near the
lactate threshold (THR); third is low-volume high-intensity inter-
val training (HIIT) and the fourth concept is a combination of the
aforementioned concepts known as “polarized” training (POL).
There is a debate as to which of these training concepts may be
superior in maximizing adaptations and performance.
HVT executed with low (LOW) intensity [approximately
65–75% of peak oxygen uptake (VO2peak)<80% of peak heart
rate (HRpeak)or<2 mmol·L−1blood lactate (Laursen and
Jenkins, 2002; Seiler and Kjerland, 2006)] and prolonged dura-
tion is thought to be a fundamental training concept in preparing
for endurance events. This type of exercise improves VO2peak
by increasing stroke and plasma volume and induces molecular
adaptations for capillary and mitochondrial biogenesis, thereby
improving the efficiency of metabolic key components for energy
fueling (Romijn et al., 1993; Midgley et al., 2006).
HIIT has revealed great improvements in athletic performance
and related key variables of endurance (e.g., time to exhaustion,
time trial performance, VO2peak, maximal and submaximal run-
ning speed, running economy) in both trained and untrained
individuals (Laursen and Jenkins, 2002). These improvements
were largely due to increases in O2availability, extraction and
utilization and the increases in VO2peak (Daussin et al., 2007;
Helgerud et al., 2007). A condensed 2 week block of 10–13 ses-
sions of HIIT led to a 7% increase in VO2peak (Stølen et al.,
2005).
Training at or close to the lactate threshold (LT) (Faude et al.,
2009), referred to as “threshold training,” improves endurance
performance, particularly in untrained participants (Denis et al.,
1984; Londeree, 1997). However, Norwegian world-class sprint
cross-country skiers demonstrated greater training volume close
to the LT when compared to national-level skiers (Sandbakk
et al., 2011). Furthermore, in elite cross-country skiers greater
www.frontiersin.org February 2014 | Volume 5 | Article 33 |1
Stöggl and Sperlich Endurance training concepts
improvements in running speed at lactate threshold and perfor-
mance in a 20-min run when exercising at an intensity elicit-
ing 3–4 mmol·L−1lactate compared with low intensity training
(<3–4 mmol·L−1)werefound(Evertsen et al., 2001). In contrast,
experimental and correlational data from well-trained athletes
suggest that training time close to LT may be ineffective, or even
counterproductive (Esteve-Lanao et al., 2007; Guellich and Seiler,
2010).
Retrospective analysis of the intensity, duration and fre-
quency of the training load of international-level cross-country
skiers (Seiler and Kjerland, 2006), rowers (Steinacker et al.,
1998), cyclists (Schumacher and Mueller, 2002), and runners
(Billat et al., 2001; Esteve-Lanao et al., 2005) revealed that elite
endurance athletes completed most of their yearly training ses-
sions at either intensities below (∼75% of total training volume)
or well above (∼15–20% of total training volume) their LT. Six
weeks of cycling using POL resulted in greater systemic adap-
tation in already well-trained athletes when compared to THR
(Neal et al., 2013). However, no study has investigated the POL
concept in well-trained endurance athletes to determine whether
this concept may be superior to the aforementioned training
strategies.
Inmanyendurancesports,fivekeyvariableshavebeenused
as a benchmark to compare athletic performance in and between
endurance athletes: (i) VO2peak (Bassett and Howley, 2000); (ii)
velocity/power output at the lactate threshold (V/PLT )(Bassett
and Howley, 2000; Midgley et al., 2007; Faude et al., 2009); (iii)
work economy (Di Prampero et al., 1986; Helgerud et al., 2001);
(iv) peak running velocity or power output (V/Ppeak)(Midgley
et al., 2007); and (v) time to exhaustion (TTE) (Laursen and
Jenkins, 2002). The aim of this study was to compare the effects
of four training concepts (HVT vs. THR vs. HIIT vs. POL) on the
aforementioned key variables of endurance performance in well-
trained athletes. We hypothesized that the POL and HIIT group
would lead to superior improvements compared with HVT and
THR.
MATERIALS AND METHODS
PARTICIPANTS
Forty eight healthy competitive endurance athletes who partici-
pated in either cross-country skiing, cycling, triathlon, middle—
or long-distance running volunteered to take part in this study
(mean ±SD:age:31±6 years, body mass: 73.8 ±9kg,
height: 180 ±8 cm). All participants were well-trained [62.6
±7.1 mL·min−1·kg−1(range: 52–75 mL·min−1·kg−1)] athletes,
accustomed to a workload of more than five sessions per week
(10–20 h·wk−1)andhadfrequentlybeeninvolvedinendurance
competitions for at least 8–20 years. Participants were members
of the Austrian cross-country skiing national team (n=8), run-
ning (n=21), triathlon (n=4) or cycling (n=15) teams during
or since the year before the current study. Retrospective analysis
of training protocols over 6 months prior to the study revealed
that none of the participants had regularly executed HIIT. All had
followed a HVT training protocol with a maximum of two THR
training sessions per week.
Based on the participants’ baseline VO2peak and training mode
(running or cycling), all athletes were randomized into HIIT,
HVT, THR or POL. At baseline, the four groups were not sta-
tistically different with regard to age, height, body mass or
VO2peak . During an initial visit, study details and participation
requirements were explained, and written informed consent was
obtained. The study received approval from the University of
Salzburg Austria Ethics Committee and was conducted in accor-
dance with the Declaration of Helsinki.
DESIGN
The intervention lasted 9 weeks plus 2 days of pre- and post-
testing. All athletes (n=15 cyclists; n=3 triathletes) engaging
in cycling training trained with their own bike and completed
all tests on a bicycle ergometer (Ergoline, Ergoselect 100P; Bitz,
Germany) using their own cycling shoes and pedal system.
Other athletes (n=16 runners, n=6 triathletes, n=8 cross-
country skiers) ran during the study and completed their pre-
and post-testing on a motorized treadmill (HP Cosmos, Saturn,
Traunstein, Germany). All participants were instructed not to
change their diet throughout the training period and to main-
tain strength training, if it was part of their training program.
Participants’ nutritional intake was not standardized or con-
trolled during the study, but for the 3h prior to all testing in which
food intake was not permitted. The training intensity was con-
trolled by HR based on the baseline incremental test: (i) LOW
(HR at blood lactate value <2 mmol·L−1); (ii) LT (HR corre-
sponding to a blood lactate of 3–5 mmol·L−1); (iii) HIGH (>90%
HRpeak)]. The HR was measured during each training session and
athletes documented training mode, exercise duration, and inten-
sity in a diary. As a control and for detailed analysis, HR for all
training sessions was stored digitally and analyzed retrospectively.
HVT INTERVENTION
The HVT included three blocks each lasting 3 weeks: 2 weeks of
high-volume training followed by 1 week of recovery (Figure 1A).
The two high volume weeks each included six training sessions
with three 90 min LOW sessions, two 150–240 min LOW sessions
(according to the training mode: running, cycling, or roller ski-
ing) and one 60 min LT session using different types of interval
training (e.g., 5 ×7 min with 2 min recovery, 3 ×15 min with
3 min recovery). The recovery week included three training ses-
sions with two 90 min LOW sessions and one 150–180 min LOW
session.
THR INTERVENTION
The THR included three blocks, each lasting 3 weeks: 2 weeks
of high volume and intensity training followed by 1 week of
recovery (Figure 1B). The two high volume and intensity weeks
each included six training sessions with two 60 min interval ses-
sions at the LT (5 ×6 min and 2min recovery in the first block,
6×7mininthesecondblockand6×8 min in the last block),
one 90 min LT session with longer intervals (3 ×15 min with
3 min active recovery in the first block and 3 ×20 min for the
remaining two blocks), one 75 min session with varying changes
in intensity (“fartlek”) (intensities resulting in a blood lactate
of 1.5–5 mmol·L−1) and two 90 min LOW sessions. The recov-
ery week included one 60 min LOW session and two 60min LT
interval sessions (5 ×6 min with 2 min of active recovery).
Frontiers in Physiology | Exercise Physiology February 2014 | Volume 5 | Article 33 |2
Stöggl and Sperlich Endurance training concepts
FIGURE 1 | Training program for 3-weeks of (A) high volume (HVT), (B)
threshold (THR), (C) polarized (POL) training, and (D) the training
program for the first block of high intensity interval training (HIIT),
excluding the recovery week. LOW, low training intensity (<2 mmol·L−1);
LT, training intensity around the lactate threshold (3–5 mmol·L−1); FL, fartlek;
HIIT, high intensity interval training (>90% HRpeak); R, recovery day.
HIIT INTERVENTION
The HIIT included two interval blocks of 16 days with one adap-
tation week prior to and one recovery week after each block.
The adaptation week included two 60 min HIIT sessions, three
90 min LOW sessions, one 120min LOW session and 1 day of
recovery. The condensed 16 day interval block included 12 HIIT
sessions within 15 days, integrating four blocks of three HIIT
sessions for three consecutive days followed by 1 day of recov-
ery. The recovery week contained four LOW sessions of 90 min
and 3 days without any training (not presented in Figure 1D).
All of the HIIT sessions included a 20 min warm-up at 75%
of HRpeak,4×4 min at 90–95% of HRpeak with 3 min active
recovery and a 15 min cool-down at 75% HRpeak based on the
protocol proposed earlier (Helgerud et al., 2007). The LOW
sessions lasted 90–150 min depending on the training mode
(running vs. cycling) at an intensity resulting blood lactate of
<2 mmol·L−1.
POL INTERVENTION
The POL included three blocks, each lasting 3 weeks: 2 weeks of
high volume and intensity training followed by 1 week of recov-
ery (Figure 1C). The high volume and intensity week included six
sessions with two 60 min HIIT sessions, two 150–240 min long
duration LOW sessions (duration according to training mode:
cycling, running or roller skiing), which included six to eight
maximal sprints of 5 s separated by at least 20 min, and two
90 min LOW sessions. The recovery week included one 60 min
HIIT session, one 120–180 min LOW session and one 90min
LOW session.
PRE AND POST-TESTING
All participants were asked to report well-hydrated and to refrain
from consuming alcohol and caffeine for at least 24-h, as well as
from engaging in strenuous exercise at least 48-h prior to testing.
The pre- and post-tests included the determination of body mass,
an incremental test protocol, a work economy and VO2peak ramp
protocol.
On the first day participants performed an incremental test on
a treadmill (7.2 km·h−1; increment: 1.8 km·h−1every 5 min, with
30 s recovery between stages, inclination 1%) or cycle ergome-
ter (80 W; increment: 40 W every 5 min, cadence >80 rpm) until
volitionalexhaustionwasachievedtoassessthepeakveloc-
ity/power output (V/Ppeak), HR, blood lactate, as well as the
velocity, power output and HR at 2 and 4 mmol·L−1blood lac-
tate (V/P2,V/P
4and HR2,HR
4). The participants’ HR was
recorded by telemetry (Suunto t6, Helsinki, Finland) at 2-s inter-
vals. The mean HR over the last 30 s of each increment was used
for statistical analysis. A 20 µl blood sample from the right ear-
lobe was collected immediately after each increment, as well as
3 and 5 min after the completion of the test into a capillary
tube (Eppendorf AG, Hamburg, Germany). All samples were ana-
lyzed amperometric-enzymatically (Biosen 5140, EKF-diagnostic
GmbH, Magdeburg, Germany) in duplicate, and the mean of the
two measures was used for statistical analysis. The lactate sensor
www.frontiersin.org February 2014 | Volume 5 | Article 33 |3
Stöggl and Sperlich Endurance training concepts
was calibrated before each test using a lactate standard sample
of 12 mmol·L−1. Results within a range of ±0.1 mmol·L−1were
accepted.
One day after the incremental tests, all athletes completed a
combined work economy and VO2peak ramp protocol to deter-
mine their submaximal and peak VO2(VO2submax and VO2peak)
and HR (HRsubmax and HRpeak), as well as time to exhaustion
(TTE). First, the intensity for running was set at 8 km·h−1(incli-
nation: 5%) on the treadmill, and for cycling at 200 W with
a cadence of >80 rpm for 10 min to determine VO2submax and
HRsubmax for this intensity. The mean VO2andHRduringthe
last 5 min of these tests were used for statistical purposes. The
intensity was then increased every 30 s by 0.5 km·h−1(inclina-
tion: 10%) on the treadmill or 15 W on the cycle ergometer until
exhaustion. The overall time for the ramp test was defined as time
to exhaustion (TTE). VO2was measured with an open circuit
breath-by-breath spirograph (nSpire, Zan 600 USB, Oberthulba,
Germany), which was calibrated prior to each test using high pre-
cision gas (15.8% O2,5%O
2in N; Praxair, Düsseldorf, Germany)
and a 1L syringe (nSpire, Oberthulba, Germany). All respiratory
data were averaged every 30 s. VO2peak was achieved if three of
the four following criteria were met: (1) plateau in VO2, i.e., an
increase <1.0 mL·min−1·kg−1despite an increase in velocity or
power output; (2) respiratory exchange ratio >1.1; (3) HR ±5%
of age predicted HRpeak; and (4) peak blood lactate (LApeak)>
6 mmol·L−1after exercise. Reliability analysis of The VO2peak test
(n=18) revealed ICC values of 0.96 for VO2peak and 0.98 for
TTE.
STATISTICAL ANALYSES
All data exhibited a Gaussian distribution verified by the Shapiro-
Wilk’s test and, accordingly, the values are presented as means ±
SD.Two-Way2×4 repeated-measures ANOVA (2 times: pre–
post, 4 groups) to test for global differences between pre- and
post-intervention, the four training groups and the interaction
effect between both factors was applied. When a significant
main effect over time was observed, paired t-tests within each
group were conducted. Based on the different units of peak
power/velocity and power/velocity at 2 and 4mmol·L−1blood
lactate in the incremental and VO2peak test, percent changes
between pre- to post-values were calculated, and a One-Way
ANOVA between groups was performed using Tukey’s post-hoc
analysis. Furthermore, within group changes for these variables
were calculated using Wilcoxon tests. An alpha value of <0.05
was considered significant. The Statistical Package for the Social
Sciences (Version 20.0; SPSS Inc., Chicago, IL, USA) and Office
Excel 2010 (Microsoft Corporation, Redmond, WA, USA) were
used for statistical analysis.
RESULTS
Forty-one participants completed the 9 week training protocol,
fulfilling more than 95% of the training program and staying
within the given HR zones. Seven subjects (2 in HIIT, 1 in HVT
and 4 in THR) withdrew from the study due to illness (n=2), or
were excluded due to changes in competition schedule (n=3) or
for not fulfilling the training protocol (n=2). The total training
hours, number of training sessions and their percent distribu-
tion within LOW, LTP, and HIIT are presented in Tab l e 1 .POL
and HVT had higher training volume compared with THR and
HIIT (P<0.05–0.001), while having a similar number of train-
ing sessions (P>0.05). HVT demonstrated the greatest amount
of LOW, THR of LT, and HIIT in HIGH training sessions (all,
P<0.05).
Body mass after HIIT was reduced by 3.7±3.0% (baseline:
73.5±6.8 kg, post: 70.7±6.5kg, P<0.01) with no significant
change in the HVT, THR or POL groups. The reduction in
body mass after HIIT was greater compared to other training
interventions (P<0.001).
Percent changes in variables from pre- to post-training
and between the training concepts during the VO2peak-
ramp, work economy, and incremental tests are presented in
Tab l e 2 . POL demonstrated the greatest increase in VO2peak
Table 1 | The distribution of volume and training intensity within the 9 weeks training intervention (excluding strength training).
POL HIIT THR HVT F-Value P-Value
Total hours 104 ±20‡$66 ±1*84 ±7*102 ±11‡$a
F(3,37)=20 <0.001
Number of sessions 54 ±347±149±358±3aF(3,37)=1.6 n.s.
Amount of training at low
intensity (%)
37 ±9(68±12%)*20 ±1(43±1%)†§23 ±6(46±7%)†§49 ±7(83±6%)*aF(3,37)=41 <0.001
Amount of training at lactate
threshold (%)
3±4(6±8%)*0 (0%)*26 ±2(54±7%)*9±3(16±6%)*aF(3,37)=197 <0.001
Amount of training at high
intensity (%)
14 ±3(26±7%)*27 ±1(57±1%)*0 (0%)†‡ 1±1(1±1%)†‡ aF(3,37)=769 <0.001
The values presented are means ±SD. F- and P-values were obtained by One-Way ANOVA (4 training groups). POL, polarized training group; HIIT, High intensity
interval training group; THR, threshold training group; HVT, high volume training group.
*Different from all other groups.
†Different from training group “POL.”
‡Different from training group “HIIT.”
$Different from training group “THR.”
§Different from training group “HVT.”
aMain effect between groups.n.s., not significant.
Frontiers in Physiology | Exercise Physiology February 2014 | Volume 5 | Article 33 |4
Stöggl and Sperlich Endurance training concepts
Table 2 | Changes in physiological variables from pre- to post-training.
POL HIIT THR HVT F-Value P-Value
Pre Post Pre Post Pre Post Pre Post
VO2peak -test
VO2peak
[L·min−1·kg−1]
60.6±8.367.4±7.7*** 63.7±7.166.6±5.8*63.2±4.660.8±7.160.5±9.462.1±9.8F(1,37)=13.6a<0.001
11.7±8.4% 4.8±5.6% −4.1±6.7%†††‡ 2.6±4.5%†F(3,37)=0.5bNS
F(3,37)=11.9c<0.001
VO2peak
[L·min−1]
4.4±1.04.9±1.1*** 4.6±0.54.7±4.94.4±0.84.3±9.24.8±0.74.9±0.7F(1,37)=6.4a<0.05
10.4±7.9% 1.1±7.6%†−3.7±7.0%††† 2.9±4.5%†F(3,37)=0.6bNS
F(3,37)=8.0c<0.001
HRpeak [bpm] 187 ±7186±7185±9182±11 18 0 ±10 179 ±9183±4183±4F(1,37)=1.9aNS
−0.6±1.9% −1.3±2.3% −0.2±1.9% 0.3±1.9% F(3,37)=1.4bNS
F(3,37)=1.0cNS
LApeak
[mmol·L−1]
10.2±1.710.7±1.79.6±1.710.2±1.79.5±1.69.9±2.210.1±1.79.9±2.0F(1,37)=1.7aNS
7.5±20.4% 6.4±8.3% 5.3±19.1% −1.0±11 .8% F(3,37)=0.4bNS
F(3,37)=0.4cNS
Work economy
VO2submax
[mL·min·−1kg−1]
38.2±5.539.7±5.034.8±6.135.9±6.234.7±5.133.7±4.435.2±4.435.3±4.7F(1,37)=0.5aNS
4.6±10.5% 3.8±12.0% −2.1±7.80.6±9.5% F(3,37)=2.0bNS
F(3,37)=1.0cNS
VO2submax
[%VO2peak]
62.4±12.359.0±9.8*54.8±5.053.2±5.354.9±7.956.0±8.158.9±8.657.7±9.6F(1,37)=2.3aNS
−4.8±7.6% −2.5±10.5% 2.5±11 .3−2.1±7.0% F(3,37)=1.3bNS
F(3,37)=1.4cNS
HRsubmax [bpm] 136 ±10 135 ±13 141 ±13 131 ±6** 143 ±3139±3*136 ±7134±5F(1,37)=11.7a<0.01
−3.3±6.4% −6.7±4.4% −2.7±1.0−1.1±3.4% F(3,37)=0.4bNS
F(3,37)=1.7cNS
HRsubmax
[%HRpeak]
74 .3±5.472.5±6.376.1±4.771.9±2.2*77.8±3.675.8±3.9** 74 .2±2.173.0±1.6F(1,37)=9.3a<0.01
−2.4±6.3% −5.4±4.5% −2.6±0.9−1.6±2.0% F(3,37)=0.7bNS
F(3,37)=1.0cNS
(Continued)
www.frontiersin.org February 2014 | Volume 5 | Article 33 |5
Stöggl and Sperlich Endurance training concepts
Table 2 | Continued
POL HIIT THR HVT F-Value P-Value
Pre Post Pre Post Pre Post Pre Post
Incremental test
HR2[bpm] 139 ±9136±13 138 ±10 141 ±9152±12 151 ±9138±19 138 ±18 F(1,37)=0.1aNS
−2.3±6.1% 2.2±5.9% −0.1±9.5−0.3±6.5% F(3,37)=3.7b<0.05
F(3,37)=0.5cNS
HR4[bpm] 157 ±14 157 ±13 163 ±12 162 ±11 1 7 1 ±9169±9160±12 162 ±12 F(1,37)=0.2aNS
−0.1±3.9% −0.3±3.8% −1.2±3.81.1±4.8% F(3,37)=2.6bNS
F(3,37)=0.5cNS
HRpeak [bpm] 186 ±6184±5*191 ±10 19 1 ±10 187 ±9184±9187±7184±4F(1,37)=5.5a<0.05
−0.9±1.3% −0.02 ±2.3% −1.2±2.7−1.4±2.9% F(3,37)=1.2bNS
F(3,37)=0.6cNS
LApeak
[mmol·L−1]
10.6±1.511.1±1.611.1±1.811.9±2.39.9±1.810.2±2.510.8±1.49.8±1.3F(1,37)=0.2aNS
4.7±13.4% 7.7±21.1% 4.0±20.0% −7.2±21.0% F(3,37)=1.6bNS
F(3,37)=1.1cNS
The values presented are means ±SD. F and P values were obtained by Two-Way ANOVA (2 ×4: time ×training group) with repeated measures. POL, polarized training group; HIIT, High intensity interval training
group; THR, threshold training group; HVT, high volume training group; VO2, oxygen uptake; HR, heart rate; LApeak, peak blood lactate concentration; *p<0.05; ** p<0.01; ***p<0.001 significant difference
within groups from pre- to post-training. †p<0.05; †††p<0.001 significant different from POL training group.‡p<0.05 significant different from HIIT training group. aMain effect between pre- and post-test.
bMain effect between training groups. ctime ×training group interactive effect.
with an 11.7±8.4%, (60.6±8.3–67.4±7.7ml·min−1·kg−1;
P<0.001), followed by HIIT with a 4.8±5.6% increase (P<
0.05). The change in VO2peak in POL was higher compared to
THR and HVT (P<0.001 and P<0.05). Absolute VO2peak
increased in POL by 10.4±7.9% (P<0.001), which was greater
compared with the other training concepts (HIIT and HVT P<
0.05, THR P<0.001). No changes from pre to post and no dif-
ferences between training groups with respect to HRpeak,LA
peak,
and HR2&4 were detected (P>0.05). Work economy increased
following HIIT (−6.7±4.4% decrease in HR, P<0.01) and
THR (−2.7±1.0% decrease in HR, P<0.05) with no signif-
icant differences between the other concepts. Work economy
expressed as percent of VO2peak was only improved after POL
(−4.8±7.6%, P<0.05) with no significant differences between
the other training groups.
The changes in TTE, V/Ppeak and V/P2&4 from pre- to post-
training and between the single training groups are presented in
Tab l e 3 . The largest percentage increase in TTE, assessed using the
VO2peak ramp test, was observed in response to POL (+17.4%,
P<0.001) followed by HIIT (+8.8%, P<0.01); however, no
statistical differences were found between the four training con-
cepts. V/Ppeak in the incremental test increased in response to
POL and HIIT (5.1±3.0% and 4.4±2.8%, both P<0.01) with
both groups demonstrating greater changes than HVT (P<0.01
and P<0.05). V/P4increased after POL (8.1±4.6%, P<0.01)
and HIIT (5.6±4.8%, P<0.01) demonstrating greater changes
after POL compared to THR and HVT (both P<0.05).
DISCUSSION
The purpose was to determine whether HIIT, HVT, THR, or POL
provides the greatest impact on key variables of endurance per-
formance in well-trained athletes. The main findings were that
(1) POL led to the greatest improvement in VO2peak,TTEand
V/Ppeak;(2)V/P
4increased after POL and HIIT; (3) no significant
differences in work economy were observed pre to post between
any of the groups; and finally (4) body mass decreased by 3.7% in
response to HIIT.
There are several challenges associated with conducting an
exercise training intervention such as the one presented here.
Firstly, the compliance of all athletes is paramount to the success-
ful completion of the study and for the subsequent examination
of the intervention. The athletes attended more than 95% of all
training sessions and all completed their predetermined train-
ing load (intensity based on HR zones, duration, and frequency),
which was confirmed by logging the daily training dose in a diary
and retrospective analysis of HR data. Secondly, an experimen-
tal study is difficult to conduct in elite athletes because typically
neither the athletes nor their coaches like to have the athletes’
training intensity, duration or frequency altered. However, we
successfully managed to conduct the current study in well-trained
male and female athletes (VO2peak: 52–75 mL·min−1·kg−1)overa
9weekperiod.
Of the four training concepts, POL resulted in the greatest
increase in VO2peak,TTE,V/P
peak and, together with HIIT, in
V/P4.Asmentioned,POLwasconfirmedbyretro-perspective
analysis of the intensity, duration and frequency distribution of
the training load in highly trained athletes (Steinacker et al.,
Frontiers in Physiology | Exercise Physiology February 2014 | Volume 5 | Article 33 |6
Stöggl and Sperlich Endurance training concepts
Table 3 | Per cent changes in velocity (V) and power (P) and at various lactate thresholds as well as peak velocity and power.
POL HIIT THR HVT F-Value P-Value
TTE 17.4±16.1*** 8.8±8.6** 6.2±9.08.0±10.3aF(3,37)=2.0NS
V/P29.3±12.412.1±8.8** 2.0±13.80.8±13.3aF(3,37)=1.9NS
V/P48.1±4.6** 5.6±4.8*1.4±4.3†1.2±6.6†aF(3,37)=4.5<0.01
V/Ppeak 5.1±3.0** 4.4±2.8** 1.8±4.8−1.5±4.9††‡ aF(3,37)=4.6<0.01
The values presented are means ±SD. F and P values were obtained by One-Way ANOVA (4 training groups) calculated over the per cent differences between pre-
to post-training. POL, polarized training group; HIIT, High intensity interval training group; THR, threshold training group; HVT, high volume training group; TTE, time
to exhaustion during the ramp test; V/P2, velocity or power at 2mmol·L−1; V/P4, velocity or power at 4 mmol·L−1; V/Ppeak, peak velocity or power in the incremental
test; *p<0.05; **p<0.01; ***p<0.001 significant difference within groups from pre- to post-training.
†p<0.05; ††p<0.01 significant different from POL training group.
‡p<0.05significant different from HIIT training group.
aMain effect between groups.
1998; Billat et al., 2001; Schumacher and Mueller, 2002; Seiler
and Kjerland, 2006; Esteve-Lanao et al., 2007). In these studies,
it was demonstrated that endurance athletes perform approxi-
mately 75% of their yearly training program either below or well
above (∼15–20%) the LT, but little at the LT. In the current study,
POL mimicked this distribution (LOW =68%, LTP =6%, HIGH
=26%). Only the study of Neal et al. (2013) demonstrated that
6 weeks of POL resulted in greater systemic adaptation in trained
cyclists when compared to THR, hence supporting our findings.
In moderately trained persons, HVT improves metabolic and
hemodynamic adaptations over 3 days (Green et al., 1987, 1990;
Coyle, 1999). However, a greater volume of training (∼3–5 weeks
with 3–5 sessions·wk−1) is needed to improve VO2peak (Laursen
and Jenkins, 2002). One reason due to why athletes may choose a
high amount of HVT may be due to that HVT leads to improved
fat and glucose utilization (Romijn et al., 1993), which is ben-
eficial for long lasting endurance events. Therefore, it might be
reasonable to implement HVT in the training programs of elite
endurance athletes for improving oxidative flux, which is impor-
tant for converting energy aerobically and recovery after and
during HIIT sessions with large anaerobic portions. When HVT
becomes the major component of a training program and HIIT
sessions are neglected, no further improvement in VO2peak and
performance in already well-trained athletes occur (Costill et al.,
1988; Laursen and Jenkins, 2002); in line with the findings of
the present study. Further improvements of well-trained ath-
letes require adding high intensity training sessions to HVT, as
demonstrated in POL. However, due to that the participants of
this study mainly used HVT prior to this experiment, the HVT
model might not have provided an adequate stimulus for further
adaptations.
The advantage of HIIT compared to HVT lies in a shorter
period of training time for similar muscular adaptations (Gibala
et al., 2006; Burgomaster et al., 2008). In response to HIIT, sev-
eral central and peripheral adaptations including increased stroke
(Helgerud et al., 2007) and blood volume (Shepley et al., 1992),
O2extraction (Daussin et al., 2007), and improvements in aero-
bic and anaerobic metabolism (Macdougall et al., 1998), such as
increased mitochondrial biogenesis and oxidative capacity, have
been reported (Gibala et al., 2006; Daussin et al., 2007, 2008;
Burgomaster et al., 2008). The aforementioned adaptations in
response to HIIT explain the often documented increases in TTE,
time trial performance (Lindsay et al., 1996), lactate and ventila-
tory threshold (Acevedo and Goldfarb, 1989; Edge et al., 2005)
and VO2peak (Laursen and Jenkins, 2002; Gibala et al., 2006;
Midgley et al., 2006; Daussin et al., 2007, 2008; Burgomaster et al.,
2008).
The present study, as well as that of Helgerud et al. (2007),
demonstrated that training at or near VO2peak maybemoreeffec-
tive in enhancing VO2peak when compared to HVT or THR.
However, POL, a combination of HVT and HIIT, may be supe-
rior for enhancing VO2peak and performance. Numerous studies
using “blocked” or “condensed” HIIT (i.e., several HIIT session
in 1 or 2 weeks) aim to increase VO2peak (Stølen et al., 2005).
Furthermore, in HIIT intervention studies (2–3 HIIT sessions per
week), VO2peak increased approximately 9% over a 10 week train-
ing intervention (McMillan et al., 2005) and 11% over a 6 week
training intervention (Helgerud et al., 2001) in youth and junior
soccer players, suggesting a 0.5% increase in VO2peak per HIIT
training session. In the current study, the increase in VO2peak
following 9 weeks of HIIT (27 HIIT sessions) was 4.8% (0.18%
increase per training session), while POL resulted in an 11.7%
increase in VO2peak with fewer HIIT sessions (14 HIIT) (0.84%
increase per training session). This result may be explained by:
(1) peak adaptation might have been reached following the first
HIIT block, and therefore, repeated HIIT bouts did not pro-
duce any further improvements in VO2peak or performance, or
(2) the combination of HVT and HIIT, much like in POL, leads
to greater long-term adaptations in endurance performance than
with exclusively HIIT or HVT.
THR improves VO2peak, lactate or ventilatory thresholds and
endurance performance in untrained persons (Denis et al., 1984;
Londeree, 1997; Gaskill et al., 2001). These findings contrast those
of the current study, as we did not observe improvements in
VO2peak ,V/P
4,TTEorV/P
peak in our elite athletes in response to
THR. Additionally, it is possible that in well-trained endurance
athletes, repeated training bouts at LT might generate unwar-
ranted sympathetic stress (Chwalbinska-Moneta et al., 1998),
while offering no further stimulus for performance enhance-
ment (Londeree, 1997). In this context, especially within the THR
group, significant variability in the individual changes in VO2peak
from pre- to post-intervention were observed (range: −20 to
www.frontiersin.org February 2014 | Volume 5 | Article 33 |7
Stöggl and Sperlich Endurance training concepts
+4%). However, some THR training might be beneficial to
well-trained athletes since world-class sprint cross-country skiers
demonstrated greater training volume in the low and moderate
intensity zones compared with national-level skiers (Sandbakk
et al., 2011).
The body mass of the well-trained athletes decreased by 3.7%
(approximately 3 kg) after HIIT, but not in response to the other
training concepts. HIIT favors lipid oxidation and promotes adi-
pose tissue loss (Perry et al., 2008; Boutcher, 2011). Depending
on the athlete’s baseline value, reduction in body mass may neg-
atively impact immune function and overall health, as well as
induce a catabolic state. Training blocks with increased volume
and/or exercise intensity might induce symptoms of “overreach-
ing,” reduced physical capacity, burnout symptoms including
tiredness, and lack of energy (Angeli et al., 2004). However,
despite the large differences in the individual responses in some
of the training groups, none of the athletes demonstrated reduced
TTE or V/Ppeak after the study, nor did they report any of the
aforementioned symptoms during and after the 9 week interven-
tion. Based on the observed changes in body mass and smaller
increases in VO2peak in the HIIT group compared with previ-
ously published data (McMillan et al., 2005; Stølen et al., 2005;
Helgerud et al., 2007), longer blocks of training periods with high
intensities could provoke these symptoms.
Except for significant decreases in %VO2peak in the POL group
and HRsubmax/%HRpeak in the HIIT and THR groups (with no
group differences), no improvements in work economy were
found in the current study. Helgerud et al. (2007) reported a ∼5%
improvement in running economy after THR, HIIT, and HVT
with no differences between groups. These improvements were
mainly attributed to an increased amount of running training.
Therefore, the applied training regimes were largely responsi-
ble for the changes in V/Ppeakand VO2peak, while work economy
remained fairly constant. V/P4was only improved in POL (8.1%)
and HIIT (5.6%). This is consistent with findings demonstrating
that running velocity at lactate threshold follows the improve-
ments in VO2peak (Helgerud et al., 2001; McMillan et al., 2005).
LIMITATIONS AND PERSPECTIVES
Standardized methodology of performance diagnostics (incre-
mental test and VO2peak ramp protocol) was utilized to evaluate
the effects of the four endurance training interventions on key
variables of endurance performance. However, a direct transfer to
specific competition situation (e.g., time trial) need to be estab-
lished in future research. Furthermore, the increase of about 11%
in VO2peak with POL within 9 weeks is large for well-trained
endurance and has to be put in perspective within the annual
training periodization. Long-term training studies are warranted
to evaluate these aspects.
CONCLUSION
In this study of elite athletes performing HIIT, HVT, THR or
POL training, POL results in the greatest improvements in key
variables of endurance performance (VO2peak,TTE,V/P
peak,and
V/P4). HIIT led to a decrease in body mass and less pronounced
increases in VO2peak compared with previous findings using short
term (1–2 weeks) HIIT, suggesting that a 9 week HIIT should be
applied with care. Exclusive training with THR or HVT did not
lead to further improvements in endurance performance related
variables in well-trained athletes.
DISCLOSURE OF FUNDING
No funding was received for this work from the National
Institutes of Health, the Welcome Trust, the Howard Hughes
Medical Institute, or other funding agencies to PubMed Central.
None of the authors had any professional relationships with com-
panies or manufacturers who will benefit from the results of the
present study. The authors declare no conflict of interest.
AUTHOR CONTRIBUTIONS
Conception and design of the experiments: Thomas Stöggl,
Billy Sperlich. Performance of the experiments: Thomas Stöggl.
Data analysis: Thomas Stöggl, Billy Sperlich. Preparation of the
manuscript: Thomas Stöggl and Billy Sperlich. Both authors read
and approved the final manuscript.
ACKNOWLEDGMENTS
The authors would like to thank the athletes, coaches, and
research assistants involved in this study for their participation,
enthusiasm, and cooperation. The authors would like to express
appreciation for the support of Donna Kennedy. Special thanks
to Julia Stöggl, Andreas Hochwimmer and Thomas Damisch for
their great assistance in recruitment, care and control of the ath-
letes during the training intervention and pre- and post-testing.
REFERENCES
Acevedo, E. O., and Goldfarb, A. H. (1989). Increased training intensity effects on
plasma lactate, ventilatory threshold, and endurance. Med. Sci. Sports Exerc. 21,
563–568. doi: 10.1249/00005768-198910000-00011
Angeli, A., Minetto, M., Dovio, A., and Paccotti, P. (2004). The overtraining
syndrome in athletes: a stress-related disorder. J. Endocrinol. Invest. 27, 603–612.
Bassett, D. R. Jr., and Howley, E. T. (2000). Limiting factors for maximum oxygen
uptake and determinants of endurance performance. Med. Sci. Sports Exerc. 32,
70–84. doi: 10.1097/00005768-200001000-00012
Billat, V. L., Demarle, A., Slawinski, J., Paiva, M., and Koralsztein, J. P. (2001).
Physical and training characteristics of top-class marathon runners. Med. Sci.
Sports Exerc. 33, 2089–2097. doi: 10.1097/00005768-200112000-00018
Boutcher, S. H. (2011). High-intensity intermittent exercise and fat loss. J. Obes.
2011, 868305. doi: 10.1155/2011/868305
Burgomaster, K. A., Howarth, K. R., Phillips, S. M., Rakobowchuk, M., Macdonald,
M. J., McGee, S. L., et al. (2008). Similar metabolic adaptations during exercise
after low volume sprint interval and traditional endurance training in humans.
J. Physiol. 586, 151–160. doi: 10.1113/jphysiol.2007.142109
Chwalbinska-Moneta, J., Kaciuba-Uscilko, H., Krysztofiak, H., Ziemba, A.,
Krzeminski, K., Kruk, B., et al. (1998). Relationship between EMG, blood
lactate, and plasma catecholamine tresholds during graded exercise in men.
J. Physiol. Phyrmacol. 49, 433–441.
Costill, D. L., Flynn, M. G., Kirwan, J. P., Houmard, J. A., Mitchell, J. B., Thomas,
R., et al. (1988). Effects of repeated days of intensified training on muscle
glycogen and swimming performance. Med. Sci. Sports Exerc. 20, 249–254. doi:
10.1249/00005768-198806000-00006
Coyle, E. F. (1999). Physiological determinants of endurance exercise performance.
J. Sci. Med. Sport 2, 181–189. doi: 10.1016/S1440-2440(99)80172-8
Daussin, F. N., Ponsot, E., Dufour, S. P., Lonsdorfer-Wolf, E., Doutreleau, S., Geny,
B., et al. (2007). Improvement of VO2max by cardiac output and oxygen extrac-
tion adaptation during intermittent versus continuous endurance training. Eur.
J. Appl. Physiol. 101, 377–383. doi: 10.1007/s00421-007-0499-3
Daussin, F. N., Zoll, J., Ponsot, E., Dufour, S. P., Doutreleau, S., Lonsdorfer, E.,
et al. (2008). Training at high exercise intensity promotes qualitative adapta-
tions of mitochondrial function in human skeletal muscle. J. Appl. Physiol. 104,
1436–1441. doi: 10.1152/japplphysiol.01135.2007
Frontiers in Physiology | Exercise Physiology February 2014 | Volume 5 | Article 33 |8
Stöggl and Sperlich Endurance training concepts
Denis, C., Dormois, D., and Lacour, J. R. (1984). Endurance training, VO2 max,
and OBLA: a longitudinal study of two different age groups. Int. J. Sports Med.
5, 167–173. doi: 10.1055/s-2008-1025899
Di Prampero, P. E., Atchou, G., Bruckner, J. C., and Moia, C. (1986). The energetics
of endurance running. Eur. J. Appl. Physiol. Occup. Physiol. 55, 259–266. doi:
10.1007/BF02343797
Edge, J., Bishop, D., Goodman, C., and Dawson, B. (2005). Effects of high- and
moderate-intensity training on metabolism and repeated sprints. Med. Sci.
Sports Exerc. 37, 1975–1982. doi: 10.1249/01.mss.0000175855.35403.4c
Esteve-Lanao, J., Foster, C., Seiler, S., and Lucia, A. (2007). Impact of training inten-
sity distribution on performance in endurance athletes. J. Strength Cond. Res. 21,
943–949. doi: 10.1519/00124278-200708000-00048
Esteve-Lanao, J., San Juan, A. F., Earnest, C. P., Foster, C., and Lucia, A.
(2005). How do endurance runners actually train? Relationship with
competition performance. Med. Sci. Sports Exerc. 37, 496–504. doi:
10.1249/01.MSS.0000155393.78744.86
Evertsen, F., Medbo, J. I., and Bonen, A. (2001). Effect of training intensity on
muscle lactate transporters and lactate threshold of cross-country skiers. Acta
Physiol. Scand. 173, 195–205. doi: 10.1046/j.1365-201X.2001.00871.x
Faude, O., Kindermann, W., and Meyer, T. (2009). Lactate threshold concepts: how
valid are they? Sports Med. 39, 469–490. doi: 10.2165/00007256-200939060-
00003
Gaskill, S. E., Walker, A. J., Serfass, R. A., Bouchard, C., Gagnon, J., Rao, D. C., et al.
(2001). Changes in ventilatory threshold with exercise training in a sedentary
population: the HERITAGE family study. Int. J. Sports Med. 22, 586–592. doi:
10.1055/s-2001-18522
Gibala, M. J., Little, J. P., van Essen, M., Wilkin,G. P., Burgomaster, K. A., Safdar, A.,
et al. (2006). Short-term sprint interval versus traditional endurance training:
similar initial adaptations in human skeletal muscle and exercise performance.
J. Physiol. 575, 901–911. doi: 10.1113/jphysiol.2006.112094
Green, H. J., Jones, L. L., Hughson, R. L., Painter, D. C., and Farrance, B. W. (1987).
Training-induced hypervolemia: lack of an effect on oxygen utilization during
exercise. Med. Sci. Sports Exerc. 19, 202–206. doi: 10.1249/00005768-198706000-
00003
Green, H. J., Jones, L. L., and Painter, D. C. (1990). Effects of short-term training on
cardiac function during prolonged exercise. Med. Sci. Sports Exerc. 22, 488–493.
doi: 10.1249/00005768-199008000-00012
Guellich, A., and Seiler, S. (2010). Lactate profile changes in relation to training
characteristics in junior elite cyclists. Int. J. Sports Physiol. Perform. 5, 316–327.
Helgerud, J., Engen, L. C., Wisloff, U., and Hoff, J. (2001). Aerobic endurance train-
ing improves soccer performance. Med. Sci. Sports Exerc. 33, 1925–1931. doi:
10.1097/00005768-200111000-00019
Helgerud, J., Hoydal, K., Wang, E., Karlsen, T., Berg, P., Bjerkaas, M., et al.
(2007). Aerobic high-intensity intervals improve VO2max more than moder-
ate training. Med. Sci. Sports Exerc. 39, 665–671. doi: 10.1249/mss.0b013e31803
04570
Laursen, P. B., and Jenkins, D. G. (2002). The scientific basis for high-intensity
interval training: optimising training programmes and maximising perfor-
mance in highly trained endurance athletes. Sports Med. 32, 53–73. doi:
10.2165/00007256-200232010-00003
Lindsay, F. H., Hawley, J. A., Myburgh, K. H., Schomer, H. H., Noakes, T. D.,
and Dennis, S. C. (1996). Improved athletic performance in highly trained
cyclists after interval training. Med. Sci. Sports Exerc. 28, 1427–1434. doi:
10.1097/00005768-199611000-00013
Londeree, B. R. (1997). Effect of training on lactate/ventilatory thresholds: a meta-
analysis. Med. Sci. Sports Exerc. 29, 837–843. doi: 10.1097/00005768-199706000-
00016
Macdougall,J.D.,Hicks,A.L.,Macdonald,J.R.,McKelvie,R.S.,Green,H.J.,and
Smith, K. M. (1998). Muscle performance and enzymatic adaptations to sprint
interval training. J. Appl. Physiol. 84, 2138–2142.
McMillan, K., Helgerud, J., Grant, S. J., Newell, J., Wilson, J., Macdonald, R., et al.
(2005). Lactate threshold responses to a season of professional British youth
soccer. Br.J.SportsMed.39, 432–436. doi: 10.1136/bjsm.2004.012260
Midgley, A. W., McNaughton, L. R., and Jones, A. M. (2007). Training to enhance
the physiological determinants of long-distance running performance: can
valid recommendations be given to runners and coaches based on current
scientific knowledge? Sports Med. 37, 857–880. doi: 10.2165/00007256-2007
37100-00003
Midgley, A. W., McNaughton, L. R., and Wilkinson, M. (2006). Is there an optimal
training intensity for enhancing the maximal oxygen uptake of distance run-
ners?: empirical research findings, current opinions, physiological rationale and
practical recommendations. Sports Med. 36, 117–132. doi: 10.2165/00007256-
200636020-00003
Neal, C. M., Hunter, A. M., Brennan, L., O’Sullivan, A., Hamilton, D. L., De
Vito, G., et al. (2013). Six weeks of a polarized training-intensity distribution
leads to greater physiological and performance adaptations than a threshold
model in trained cyclists. J. Appl. Physiol. 114, 461–471. doi: 10.1152/japplphys-
iol.00652.2012
Perry, C. G., Heigenhauser, G. J., Bonen, A., and Spriet, L. L. (2008). High-intensity
aerobic interval training increases fat and carbohydrate metabolic capacities
in human skeletal muscle. Appl.Physiol.Nutr.Metab.33, 1112–1123. doi:
10.1139/H08-097
Romijn, J. A., Coyle, E. F., Sidossis, L. S., Gastaldelli, A., Horowitz, J. F., Endert,
E., et al. (1993). Regulation of endogenous fat and carbohydrate metabolism in
relation to exercise intensity and duration. Am.J.Physiol.265, E380–E391.
Sandbakk, O., Holmberg, H. C., Leirdal, S., and Ettema, G. (2011). The physi-
ologyofworld-classsprintskiers.Scand. J. Med. Sci. Sports 21, e9–e16. doi:
10.1111/j.1600-0838.2010.01117.x
Schumacher, Y. O., and Mueller, P. (2002). The 4000-m team pursuit cycling world
record: theoretical and practical aspects. Med. Sci. Sports Exerc. 34, 1029–1036.
doi: 10.1097/00005768-200206000-00020
Seiler, K. S., and Kjerland, G. O. (2006). Quantifying training intensity distribu-
tion in elite endurance athletes: is there evidence for an “optimal” distribution?
Scand. J. Med. Sci. Sports 16, 49–56. doi: 10.1111/j.1600-0838.2004.00418.x
Shepley, B., Macdougall, J. D., Cipriano, N., Sutton, J. R., Tarnopolsky, M. A., and
Coates, G. (1992). Physiological effects of tapering in highly trained athletes.
J. Appl. Physiol. 72, 706–711.
Steinacker, J. M., Lormes, W., Lehmann, M., and Altenburg, D. (1998). Training of
rowers before world championships. Med. Sci. Sports Exerc. 30, 1158–1163. doi:
10.1097/00005768-199807000-00022
Stølen, T., Chamari, K., Castagna, C., and Wisloff, U. (2005). Physiology of soccer:
an update. Sports Med. 35, 501–536. doi: 10.2165/00007256-200535060-00004
Conflict of Interest Statement: The authors declare that the research was con-
ducted in the absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.
Received: 02 October 2013; accepted: 16 January 2014; published online: 04 February
2014.
Citation: Stöggl T and Sperlich B (2014) Polarized training has greater impact on key
endurance variables than threshold, high intensity, or high volume training. Front.
Physiol. 5:33. doi: 10.3389/fphys.2014.00033
This article was submitted to Exercise Physiology, a section of the journal Frontiers in
Physiology.
Copyright © 2014 Stög gl and Sperlich. This is an open-access article distributed under
the terms of the Creative Commons Attribution License (CC BY). The use, distribut ion
or reproduction in other forums is permitted, provided the original author(s) or licen-
sor are credited and that the original publication in this journal is cited, in accordance
with accepted academic practice. No use, distribution or reproduction is permitted
which does not comply with these terms.
www.frontiersin.org February 2014 | Volume 5 | Article 33 |9
Content uploaded by Thomas Stöggl
Author content
All content in this area was uploaded by Thomas Stöggl on Feb 21, 2014
Content may be subject to copyright.