Recent analysis of the training intensity distribution (TID) in different endurance sports (1) revealed that athletes invest approximately 75% of their training time in long sessions with low-intensity (LOW) in “Zone 1” (i.e., <2 mmol·L−1 blood lactate; <1st ventilatory threshold (VT1); perception < “somewhat hard” equivalent to <13 on Borg’s scale (2)), with a decreasing proportion of training time in “Zone 2” (also referred to as “threshold intensity” at 2 to 4 mmol·L−1 blood lactate, >VT1 and < VT2, perception “hard” equivalent to 14 to 16 on Borg’s scale) and at high-intensity (HIGH) in “Zone 3” (i.e., >4 mmol·L−1 blood lactate, >VT2, perception > “very hard” equivalent to >17 on Borg’s scale). However, the retrospective TID analysis of very successful elite endurance athletes revealed a “polarized” (POL) distribution, incorporating a significant amount of time at low-intensity (approximately 75% of training time) in “zone 1,” 5% to 10% in “zone 2,” and 15% to 20% in “zone 3” (3–5).
One of the recent experimental prospective training studies dealing with TID confirmed that mesocycles with POL TID combining HIGH (>90% of peak HR) and LOW exercise (<2 mmol·L−1 blood lactate) in already well-trained athletes (peak oxygen uptake [V˙O2peak], 62.6 ± 7.1 mL·min−1·kg−1) improved V˙O2peak (+11.7% ± 8.4%) when compared to HIGH or LOW TID (6). However, the latter study did not measure actual performance outcomes (e.g., time trial performance or 5000-m running time).
In contrast to elite athletes, far less is known about the physiological responses of subelite individuals executing POL, especially in running. Munoz et al. (7) randomly assigned 30 recreational runners (V˙O2peak of the group performing POL TID: 61 ± 8 mL·min−1·kg−1; V˙O2peak of the group performing threshold TID: 64 ± 7 mL·min−1·kg−1) to five to six sessions per week for 10 wk emphasizing either POL (Zone 1: 77%; Zone 2: 3%; Zone 3: 20%) or a threshold TID (46/35/19%) with equal volume in Zone 3 (i.e., two sessions per week at ≥85% V˙O2peak) and equal training loads (as measured by training impulse [TRIMP] (8)). Both groups with different TID increased their 10.000-m performance by 3.5% to 5%. However, the study did not provide mechanistic evidence on how the increase in performance may have physiologically occurred.
Success in most running events has been, although not exclusively, related to three major physiological components including V˙O2peak, velocity at lactate threshold (vLT) and work economy (9). Although V˙O2peak is recognized as an important component of running performance, evidence suggests that the velocity at lactate threshold (vLT) may be more closely correlated to endurance performance than V˙O2peak (9–12). Finally, the running economy (RE), expressed as the steady-state oxygen uptake during constant submaximal running (13,14) also substantially contributes to endurance performance (14,15).
Because POL seems superior to LOW and HIGH in improving key variables of endurance performance in elite endurance athletes, and because no comprehensive data for subelite runners exist, the questions remain i) whether a mesocycle comprising of POL may also be superior in recreational runners compared to LOW and HIGH TID to improve 5000-m running performance and ii) which factors (V˙O2peak, vLT or running economy) may explain changes in performance.
Forty-two (n = 19 male, n = 23 female) healthy noncompetitive runners volunteered to take part in this study (V˙O2peak, 45.2 ± 5.8 mL·min−1·kg−1 [range, 34.9–59.0 mL·min−1·kg−1], 27 ± 6 yr, body mass, 70.3 ± 12.4 kg; height, 173 ± 10 cm). All participants were accustomed to less than two sessions per week (1–2 h·wk−1) involving low-intensity exercise (running, cycling and swimming) for no more than 60 min and had not been frequently involved in any type of competitive endurance events. All participants gave their written consent to participate in the study which was conducted in accordance with the Declaration of Helsinki, and all protocols were preapproved by the institute's ethical committee.
The overall study design is illustrated in Figure 1.
The experiment lasted 8 wk including four visits for testing procedures at baseline (T0), after four (T1), seven (T2) and 8 wk (T3). During the first 4 wk (wash-in mesocycle), the TID was identical for all participants. During the wash-in mesocycle all participants performed two to four sessions per week of running depending on their common exercise routine. Based on their baseline V˙O2peak the participants were systematically parallelized into three groups performing a 3-wk mesocycle involving sessions with either high-intensity low-volume (HIGH) or high-volume low-intensity (LOW) running, or a combination of HIGH and LOW (referred to as polarized TID (POL). After the 3-wk mesocycle with either HIGH, LOW, or POL all participants performed a 1-wk taper microcycle involving two low intensity training sessions. At T0, T1, T2, T3 all participants performed a 5000-m all-out run and an incremental treadmill test to assess their V˙O2peak, lactate threshold and running economy. The training intensity was controlled by HR based on the peak HR obtained during the incremental tests.
Testing Procedures at T0, T1, T2, T3
All participants were asked to remain 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 before all testings. All testings included the determination of basic and anthropometric data (age, body mass, fat, and fat-free mass), an outdoor 5000-m all-out run and an incremental test protocol in the laboratory.
Height was measured using a folding rule with the subjects standing barefoot. Body mass, fat and fat-free mass were assessed with a four-electrode bio-impedance scale (Model 1609N; Tanita Corp, Tokyo, Japan) to the nearest 0.1 kg and body mass index (kg·m−2) was then calculated. All performed an incremental treadmill (mercury, h/p/cosmos sports and medical GmbH, Nussdorf-Traunstein, Germany) test (5 min running at 7 km·h−1 (for women) and 8 km·h−1 (for men); increment, 1 km·h−1 every 3 min, with 15-s recovery between stages for blood sampling; inclination of the treadmill was kept at 1% throughout the test) until volitional exhaustion. During the test, HR and oxygen uptake were obtained continuously with an open breath-by-breath gas analyzer (Cortex Metamax 3B, Leipzig, Germany), which was calibrated before each test using high precision gas (15.8% O2, 5% O2 in N; Praxair, Düsseldorf, Germany) and a 3-L syringe.
Before and immediately after the treadmill test, as well as during the 15-s recovery period between each increment, 20 μL of blood from the right earlobe was collected into a capillary tube (Eppendorf AG, Hamburg, Germany) and analyzed amperometric-enzymatically (Biosen C-Line; EKF-diagnostic GmbH, Magdeburg, Germany) in duplicate, and the mean of the two measures was used for statistical analysis. The lactate sensor was calibrated before each test using a standard sample of 12 mmol·L−1.
Peak oxygen uptake and HR
All gas analysis data was averaged every 30 s, and the peak value was considered as V˙O2peak if three of the four following criteria were met: 1) plateau in V˙O2, that is, an increase < 1.0 mL·min−1·kg−1 despite an increase in velocity; 2) respiratory exchange ratio >1.1; 3) HR ± 5% of age predicted HRpeak; and 4) peak blood lactate (peak lactate) > 6 mmol·L−1 after exercise. The highest HR values were considered to be HRpeak.
Velocity at lactate threshold
The velocity at lactate threshold was identified as the first significant elevation of blood lactate above resting levels as described previously (16). A two-phase linear regression model estimated the inflection point of the lactate curve. A log transformation to the running velocity and blood lactate concentration was applied (17).
Running economy was calculated using the average oxygen uptake of the last 60 s at 9 km·h−1. This speed was chosen because it corresponds to be below 85% of V˙O2peak which is required to assess RE (18).
Performance in 5000-m run
The 5000-m all-out test took place on a flat 400-m track. After a warm-up of 400 to 600 m each participant began to run at will, simultaneously starting the Polar V800 GPS sports watch (Polar V800, Polar Electro Oy, Kempele, Finland) and stopping it after 5000 m. Simultaneously, a researcher measured the time for the 5000 m using a second Polar V800 watch. The mean value of both 5000-m times was used for statistical analysis.
Training Load Monitoring
All runners measured their HR during each training session (Polar V800; Polar Electro Oy, Kempele, Finland) and stored the data online (Polar Flow software; Polar Electro Oy). According to previous recommendations and studies (7,19) the individual HR zones were defined by the corresponding HR at 2 and 4 mmol·L−1 blood lactate. From the data provided by the online version of the HR monitor (Polar Flow software), the total time spent in each HR zone for each training session was calculated.
The participants controlled running intensity by their own HR prescription and session RPE (6–20) (2). The estimated total TRIMP was calculated by using an approach described previously (20). Briefly, each of the three zones has a weighting factor which is multiplied by the duration in this zone. Total TRIMP is then obtained by adding the three zone scores.
During a 4-wk preintervention mesocycle all participants performed two to four sessions per week of running. The primary aim of the wash-in cycle was to observe the amount of training (i.e., frequency, intensity, and duration of training) of each participant to allow the calculation of weekly TRIMP for each individual to increase the weekly TRIMP by 50% during the subsequent 3-wk mesocycle.
The weekly TRIMP during the 3-wk mesocycle was supposed to be 50% greater compared to the mean weekly TRIMP for each runner as measured during the wash-in mesocycle. The increase in TRIMP with LOW was mainly achieved by increasing the duration per session. With HIGH the TRIMP increase was implemented by increasing intensity during the sessions.
Based on earlier findings (21) each session in HIGH consisted of a 10-min low-intensity (running at an intensity of HR <2 mmol·L−1 blood lactate) warm-up followed by 4 × 4 min high-intensity running (running at an intensity of HR >4 mmol·L−1 blood lactate) interspersed with 3-min walking and 10-min cool-down running. HIGH performed three to five sessions per week depending on the number of sessions per week performed during the wash-in mesocycle.
High-volume Low-intensity Training
Depending on the number of sessions per week during the wash-in mesocycle, the LOW group performed three to five sessions per week of high-volume low-intensity running. All sessions lasted 60 to 90 min and were performed at an intensity corresponding to <2 mmol·L−1 blood lactate.
Polarized Training-intensity Distribution
The POL group performed three to five sessions per week, depending on the participants’ individual number of sessions per week during the wash-in mesocycle. POL comprised of a mix of 4 × 4-min interval sessions (see HIGH) and 60- to 90-min sessions at an HR intensity of HR <2 mmol·L−1 blood lactate. As a rule, one HIGH session followed two LOW sessions.
As shown earlier (22) a 1-wk taper microcycle with reduced training load (volume, frequency, and intensity (23)) is common to maximize physiological adaptations and minimize accumulated fatigue (24). The taper microcycle in this study consisted of two 20- to 30-min sessions running at an intensity of HR < 2 mmol·L−1 blood lactate.
Data for each variable at T0, T1, T2, and T3 are presented as mean ± SD and 95% confidence interval (CI). Similar to previous analysis and recommendations the statistical analysis comprised of between-group and univariate between-time point analysis, effect size calculations, and individual response magnitude (25,26). The individual response magnitude for each variable for changes from T0 to T3 (%) were summarized in three categories, namely, “nonresponse” defined as <3% change, “moderate response” as 3% to 9% change and “large response” as >9% change. These cutoff values were adapted from previous research (25).
The summary of the individual response magnitude of all groups from T0 to T3 was categorized into “+” when more than 30% of the runners displayed moderate or large responses, and “++” when more than 60% of them demonstrated moderate or large responses.
An adaptation index for each participant was calculated as the mean of the percent-change in V˙O2peak, running economy, velocity at lactate threshold, and 5000-m performance from T0 to T3.
T0 and T1 values for each parameter were compared using a one-way between-groups ANOVA (with post hoc analysis). The same analysis was performed for comparing the number of sessions per week, session-goal/time in-zone, average RPE per session, mean duration per week and TRIMP per week between LOW, HIGH, and POL. A repeated-measures model (ANOVA) was used to compare differences between T0, T1, T2, and T3 in each group. An alpha level of 0.05 was considered to be significant and all analyses were carried out using the Statistica software package for Windows® (version 7.1; StatSoft Inc., Tulsa, OK).
The main training characteristics of all three groups are summarized in Table 1.
During the 4-wk wash-in mesocycle and based on the time spent in HR zone as well as RPE analysis all groups displayed similar TID with an average of 2.6 to 2.8 sessions per week. The TRIMP during the wash-in cycle was higher in POL compared with the other two groups (P < 0.05).
During the 3-wk intervention mesocycle HIGH group spent more time in zone 3 compared to LOW and POL. HIGH showed significantly lower TRIMP compared to LOW and POL (P < 0.05).
During the 1-wk taper microcycle all groups displayed identical TID and TRIMP (P > 0.05).
Body mass, body fat, and muscle mass were not different between the groups at T0. Body mass, body fat, and muscle mass were unaltered between T0 and T2 and T3. Solely, body mass decreased with HIGH by 1.4% (P = 0.01) from 72.5 ± 14.2 kg at T1 to 71.5 ± 13.9 kg at T2. Both, the percentage of body fat and the muscle mass, were unaltered between all time points of measurement.
LOW, HIGH, and POL improved their 5000-m time from baseline to after the 3-wk intervention mesocycle (from T0 to T2) significantly (all P < 0.05). The mean (95% CI) improvement in 5000-m performance from T0 to T2 was 7% (2–12), 10% (5–16), and 8% (3–14) in the HIGH, LOW, and POL groups, respectively. 5000-m time improved from T0 to T3 in all groups (all P < 0.05) (Table 2). The 5000-m performance in all groups did not improve from beginning (T2) to end (T3) of the 1-wk tapering microcycle.
V˙O2peak increased from T0 to T2 by 5% (P = 0.03) and from T0 to T3 by 8% (P < 0.001) with HIGH. V˙O2peak improved from T0 to T2 with LOW (4%, P = 0.02) and from T0 to T3 with POL (6%, P = 0.006).
The running economy improved from T1 to T3 (P = 0.04) and from T2 to T3 (P = 0.03) only in LOW with no changes in HIGH and POL (all P > 0.05). The velocity at lactate threshold did not alter between any time point (all P > 0.05).
Individual response magnitude
Figure 2 illustrates the individual response magnitude for each variable. Figure 3 shows the adaptation index for each participant in HIGH, LOW, and POL.
Altogether, LOW showed the greatest individual response magnitude in 5000-m running performance, with 71% of the runners improving their 5000-m time by 9% or more. In POL 27% and in HIGH 23% of the participants improved their performance by >9%. The percentage of participants with improvements in V˙O2peak by >3% and >9% were 60% and 33% in POL, 69% and 31% in HIGH, and 50% and 21% in LOW. The percentage of participants improving running economy by >3% and >9% were 40% and 13% in POL, 8% and 0% in HIGH, and 50% and 7% LOW. Finally, in POL 53% and 13%, in HIGH 38% and 23% and in LOW 43% and 29% of the participants improved their velocity at lactate threshold by >3% and >9%, respectively.
The intention of this study was to apply two mesocycles: one 4-wk wash-in mesocycle with identical TID and one 3-wk intervention mesocycle with different TID but similar TRIMP (i.e., 50% increase of the weekly TRIMP during the wash-in mesocycle), ending with a 1-wk taper microcycle to identify the strategy that provides the greatest improvements in 5000-m performance and in key variables of running performance in recreational runners.
The main findings of the present randomized study were as follows:
- (i) 5000-m performance increased in all groups from T0 to T2 and T3;
- (ii) V˙O2peak increased from T0 to T2 and T3 with HIGH, from T0 to T2 with LOW, from T0 to T3 with POL;
- (iii) Running economy improved from T1 to T3 and from T2 to T3 only in LOW.
Based on individual response magnitude:
- (i) showed the highest individual response magnitude in 5000-m running performance;
- (ii) HIGH and the POL showed similar individual response magnitudes for changes in V˙ O2peak with “lower” responses in LOW;
- (iii) LOW and POL showed high individual responses to changes in running economy with no improvements in HIGH;
- (iv) All groups stimulated low individual responses to changes in velocity at lactate threshold;
- (v) The individual mean response analysis indicated a high number of responders (n = 13 out of 16) in LOW, with less in HIGH (n = 6/13) and POL (n = 8/16).
Based on the group analysis, the 5000-m times improved in all groups from T0 to T2 and T3 at a magnitude of 5% to 13%. This response magnitude in performance is comparable with previous studies investigating the effect of HIGH and LOW with a similar mesocycle duration in well-trained runners (27).
Contrary to recent experimental prospective training studies involving elite (6) and recreational runners (7), we cannot confirm that POL is a superior TID when compared with LOW or HIGH. In fact, based on the individual response magnitude, LOW showed the greatest responses in 5000-m running performance. As pointed out earlier, the success in most running events has been, although not exclusively, related to three major physiological components including V˙O2peak, vLT and work economy (9).
Although changes in V˙O2peak have been associated with high-intensity exercises rather than continuous low-intensity running (21), our study showed that some individuals may improve their V˙O2peak by applying a 3-wk mesocycle of either HIGH, LOW, or POL at a magnitude of >20%. Because the baseline V˙O2peak of our runners was clearly below those of elite athletes (52–75 mL·min−1·kg−1) (6) and recreational runners (61 ± 8 to 64 ± 7 mL·min−1·kg−1) (7), we may conclude that, at least for a mesocycle of 3 wk in previously nonexperienced runners and at a group level, V˙O2peak increased by 8% with HIGH, by 4% with LOW, and by 6% with POL. 5000-m running time improved from T0 to T2 by 7%, 10%, and 8% with HIGH, LOW, and POL, respectively. The similar percent-differences from T0 to T2 show that on a group level all three TID are (equal) potent strategies to improve both 5000-m performance and V˙O2peak in previously nonexperienced runners.
We found no changes in the velocity at lactate threshold between the groups and time points. The overall insignificant changes in this variable are probably due to short mesocycles of approximately nine LOW sessions being too short to elicit evident changes. Training adaptations associated with improvements in lactate threshold seem mainly to be related to skeletal muscle adaptations (9), which may need a longer duration than in our study. Furthermore, training at intensities slightly above the lactate threshold appears to be an optimal training strategy for improving the lactate threshold for sedentary people (28).
Although the group analysis revealed that all TID improved the 5000-m performance, the individual mean response analysis showed the highest individual response magnitude with LOW. The adaptation index in Figure 3 confirms that most of the individuals performing LOW displayed positive adaptation.
The intention of this study was to compare mesocycles with progressively increasing workloads (+50% TRIMP) and varied TID. Based on our data, all groups improved TRIMP by >20% (LOW: +55% in TRIMP; HIGH +30%; POL +21%). However, only LOW achieved the targeted 50% increase in TRIMP (from wash-in phase to intervention phase), and the groups differed in the percent-increase in TRIMP as well as absolute TRIMP values. The targeted 50% increase in TRIMP was not achieved by the runners with HIGH and POL, because this would have meant to incorporate either longer or more training sessions. The sudden extension of HIGH (i.e., longer duration per session) or more HIGH sessions per week might lead to high physical and mental strain as well as time constraints in recreational runners. The high physical demands associated with a sudden 50% elevation of TRIMP in HIGH and POL is therefore not feasible in a real-life training scenario. Thus, the interpretation of the present results in our recreational runners is blunted by the matter “just training more” versus “training using a different intensity distribution” when explaining the physiological and performance outcomes. Therefore, the effect of training distribution as a training variable cannot be entirely isolated, because of the variation in TRIMP between the groups.
However, the adaptation index in Figure 3 provides very informative insights into the individual responses to LOW, HIGH and POL. Compared with the wash-in mesocycle, LOW decreased the intensity of training, but nearly doubled the mean training duration per week. In contrast, HIGH slightly decreased the total weekly duration, but increased the duration in zone 3 by approximately 500% with 3 of 15 runners improving >5% and 7 runners not responding (adaptation index, <3%). In contrast, 6 of 16 runners in LOW responded by 6%, with 3 of 16 nonresponding. From this perspective, the relative risk of nonresponding is quite different between these two groups. Based on the overall adaption index over half of the recreational runners in HIGH and POL were essentially nonresponders (adaption index, <3%) and 13 of 16 runners responded well to LOW. The high number of responders in LOW (i.e., the doubling of mean training duration) is in line with previous findings investigating the dose of training (i.e., one session vs two sessions vs three sessions vs four sessions vs five sessions of 60 min cycling at an average exercise intensity of 65% per week for 6 wk) in n = 78 adults (V˙O2peak: approximately 37–44 mL·kg−1·min−1). All initial nonresponders became responders when the amount of training increased (29).
Taper microcycles are commonly applied in training plans to undergo a period of reduced training before competition with the aim of maximizing physiological adaptations, and additionally reducing fatigue to enhance performance (24). In the present study, running economy with LOW improved after the taper microcycle. Because optimization in performance seems to be achieved with 2 wk of tapering (30), potentially the duration of 1 wk in this study was not sufficient for the HIGH and POL group to further improve running performance related variables, such as running economy.
The present study applied two mesocycles, one 4-wk mesocycle with identical TID and one 3-wk mesocycle with differing TID (HIGH vs LOW vs POL), to recreational runners. We conclude that, on a group level, HIGH, LOW and POL are similarly potent in improving a recreational runner’s 5000-m time, with similar improvements in peak oxygen uptake. Changes in running economy occurred only with LOW and body mass reduction occurred only with HIGH (from T1 to T2), with no changes in all groups from T0 to T2. Based on the individual response of recreational runners, the relative risk of nonresponding is greater with HIGH and POL compared with LOW
None of the authors has any conflicts of interest. Polar Electro Oy provided funding for this study. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.
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Keywords:© 2018 American College of Sports Medicine
ENDURANCE PERFORMANCE; LACTATE THRESHOLD; MAXIMAL OXYGEN CONSUMPTION; TRAINING LOAD