No Additional Benefits of Block- Over Evenly-Distributed High-Intensity Interval Training within a Polarized Microcycle

Training Intensity Distribution of a 7-Day HIIT Shock Microcycle: Is Time in the "Red Zone" Crucial for Maximizing Endurance Performance? A Randomized Controlled Trial

BACKGROUND

Various studies have shown that the type of intensity measure affects training intensity distribution (TID) computation. These conclusions arise from studies presenting data from meso- and macrocycles, while microcycles, e.g., high-intensity interval training shock microcycles (HIIT-SM) have been neglected so far. Previous literature has suggested that the time spent in the high-intensity zone, i.e., zone 3 (Z3) or the "red zone", during HIIT may be important to achieve improvements in endurance performance parameters. Therefore, this randomized controlled trial aimed to compare the TID based on running velocity (TIDV), running power (TIDP) and heart rate (TIDHR) during a 7-day HIIT-SM. Twenty-nine endurance-trained participant were allocated to a HIIT-SM consisting of 10 HIIT sessions without (HSM, n = 9) or with (HSM + LIT, n = 9) additional low-intensity training or a control group (n = 11). Moreover, we explored relationships between time spent in Z3 determined by running velocity (Z3V), running power (Z3P), heart rate (Z3HR), oxygen uptake ( Z 3 V ˙ O 2 ) and changes in endurance performance.

RESULTS

Both intervention groups revealed a polarized pattern for TIDV (HSM: Z1: 38 ± 17, Z2: 16 ± 17, Z3: 46 ± 2%; HSM + LIT: Z1: 59 ± 18, Z2: 14 ± 18, Z3: 27 ± 2%) and TIDP (Z1: 50 ± 8, Z2: 14 ± 11, Z3: 36 ± 7%; Z1: 62 ± 15, Z2: 12 ± 16, Z3: 26 ± 2%), while TIDHR (Z1: 48 ± 13, Z2: 26 ± 11, Z3: 26 ± 7%; Z1: 65 ± 17, Z2: 22 ± 18, Z3: 13 ± 4%) showed a pyramidal pattern. Time in Z3HR was significantly less compared to Z3V and Z3P in both intervention groups (all p < 0.01). There was a time x intensity measure interaction for time in Z3 across the 10 HIIT sessions for HSM + LIT (p < 0.001, pη2 = 0.30). Time in Z3V and Z3P within each single HIIT session remained stable over the training period for both intervention groups. Time in Z3HR declined in HSM from the first (47%) to the last (28%) session, which was more pronounced in HSM + LIT (45% to 16%). A moderate dose-response relationship was found for time in Z3V and changes in peak power output (rs = 0.52, p = 0.028) as well as time trial performance (rs = - 0.47, p = 0.049) with no such associations regarding time in Z3P, Z3HR, and Z 3 V ˙ O 2 .

CONCLUSION

The present study reveals that the type of intensity measure strongly affects TID computation during a HIIT-SM. As heart rate tends to underestimate the intensity during HIIT-SM, heart rate-based training decisions should be made cautiously. In addition, time in Z3V was most closely associated with changes in endurance performance. Thus, for evaluating a HIIT-SM, we suggest integrating a comprehensive set of intensity measures. Trial Registration Trial register: Clinicaltrials.gov, registration number: NCT05067426.

Adding LIT to HIIT: Is Low-Intensity Training Vital for Endurance-Trained Athletes during a 7-day HIIT Shock Microcycle?

PURPOSE

This study aimed to investigate the effects of a 7-d high-intensity interval training shock microcycle (HIIT-SM) with or without additional low-intensity training (LIT) on aerobic fitness and endurance performance compared with a control group (CG).

METHODS

Thirty-three endurance-trained athletes (7 women, 26 men, mean ± SD: age, 30.2 ± 6.9 yr; maximal oxygen uptake (V̇O 2max ), 59.8 ± 4.9 mL·min -1 ·kg -1 ) performed exercise testing at T1 and were randomly assigned to one of three groups: i) HSM, 10 running-based HIIT sessions (5 × 4 min at 90%-95% maximal heart rate) over 7 d; ii) HSM + LIT, equal to HSM with additional 30 min of LIT after each HIIT; iii) CG, regular training. Exercise testing was repeated 3 d (T2), 7 d (T3), and 14 d (T4) after the intervention. A 5-km time trial (TT 5km ) was performed 3-4 d before T1 and 10-11 d after the intervention. Data were analyzed by two-way repeated-measures ANOVA.

RESULTS

No interaction effect was found for V̇O 2max ( P = 0.170, pη2 = 0.09), peak power output ( P = 0.734, pη2 = 0.04), and work economy ( P = 0.804, pη2 = 0.03). There was an interaction for velocity at lactate threshold ( P = 0.006, pη2 = 0.18) with increased velocity in HSM at T2 (3.2%, P = 0.030), T3 (4%, P = 0.006), T4 (4%, P = 0.003), as well as in HSM + LIT for T2 (3.2%, P = 0.011), whereas CG showed no change. There was an interaction for TT 5km ( P = 0.044, pη2 = 0.19), with HSM improving 2.7% ( P = 0.003) and HSM + LIT 2.3% ( P = 0.010), whereas CG was, on average, -0.3% ( P = 0.821) slower.

CONCLUSIONS

HIIT-SM with or without additional LIT has negligible effects on V̇O 2max but improves other key endurance variables in endurance-trained athletes. No superiority of either intervention group was demonstrated. Therefore, additional LIT during HIIT-SM is not beneficial.

A 6-day high-intensity interval microcycle improves indicators of endurance performance in elite cross-country skiers

Purpose

The aim of this study was to compare the effects of a 6-day high-intensity interval (HIT) block [BLOCK, n = 12, maximal oxygen uptake (V̇O2max = 69. 6 ± 4.3 mL·min−1·kg−1)] with a time-matched period with usual training (CON, n = 12, V̇O2max = 69.2 ± 4.2 mL·min−1·kg−1) in well-trained cross-country (XC) skiers on physiological determinants and indicators of endurance performance. Furthermore, the study aimed to investigate the acute physiological responses, including time ≥90% of V̇O2max, and its associated reliability during repeated HIT sessions in the HIT microcycle.

Methods

Before the 6-day HIT block and following 5 days of recovery after the HIT block, both groups were tested on indicators of endurance performance. To quantify time ≥90% of V̇O2max during interval sessions in the HIT block, V̇O2 measurements were performed on the 1st, 2nd, and last HIT session in BLOCK.

Results

BLOCK had a larger improvement than CON in maximal 1-min velocity achieved during the V̇O2max test (3.1 ± 3.1% vs. 1.2 ± 1.6%, respectively; p = 0.010) and velocity corresponding to 4 mmol·L−1 blood lactate (3.2 ± 2.9% vs. 0.6 ± 2.1%, respectively; p = 0.024). During submaximal exercise, BLOCK displayed a larger reduction in respiratory exchange ratio, blood lactate concentration, heart rate, and rate of perceived exertion (p &lt; 0.05) and a tendency towards less energy expenditure compared to CON (p = 0.073). The ICC of time ≥90% V̇O2max in the present study was 0.57, which indicates moderate reliability.

Conclusions

In well-trained XC skiers, BLOCK induced superior changes in indicators of endurance performance compared with CON, while time ≥90% of V̇O2max during the HIT sessions in the 6-day block had a moderate reliability.

The Salzburg 10/7 HIIT shock cycle study: the effects of a 7-day high-intensity interval training shock microcycle with or without additional low-intensity training on endurance performance, well-being, stress and recovery in endurance trained athletes-study protocol of a randomized controlled trial

BACKGROUND

Performing multiple high-intensity interval training (HIIT) sessions in a compressed period of time (approximately 7-14 days) is called a HIIT shock microcycle (SM) and promises a rapid increase in endurance performance. However, the efficacy of HIIT-SM, as well as knowledge about optimal training volumes during a SM in the endurance-trained population have not been adequately investigated. This study aims to examine the effects of two different types of HIIT-SM (with or without additional low-intensity training (LIT)) compared to a control group (CG) on key endurance performance variables. Moreover, participants are closely monitored for stress, fatigue, recovery, and sleep before, during and after the intervention using innovative biomarkers, questionnaires, and wearable devices.

METHODS

This is a study protocol of a randomized controlled trial that includes the results of a pilot participant. Thirty-six endurance trained athletes will be recruited and randomly assigned to either a HIIT-SM (HSM) group, HIIT-SM with additional LIT (HSM + LIT) group or a CG. All participants will be monitored before (9 days), during (7 days), and after (14 days) a 7-day intervention, for a total of 30 days. Participants in both intervention groups will complete 10 HIIT sessions over 7 consecutive days, with an additional 30 min of LIT in the HSM + LIT group. HIIT sessions consist of aerobic HIIT, i.e., 5 × 4 min at 90-95% of maximal heart rate interspersed by recovery periods of 2.5 min. To determine the effects of the intervention, physiological exercise testing, and a 5 km time trial will be conducted before and after the intervention.

RESULTS

The feasibility study indicates good adherence and performance improvement of the pilot participant. Load monitoring tools, i.e., biomarkers and questionnaires showed increased values during the intervention period, indicating sensitive variables.

CONCLUSION

This study will be the first to examine the effects of different total training volumes of HIIT-SM, especially the combination of LIT and HIIT in the HSM + LIT group. In addition, different assessments to monitor the athletes' load during such an exhaustive training period will allow the identification of load monitoring tools such as innovative biomarkers, questionnaires, and wearable technology.

TRIAL REGISTRATION

clinicaltrials.gov, NCT05067426. Registered 05 October 2021-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT05067426 . Protocol Version Issue date: 1 Dec 2021. Original protocol. Authors: TLS, NH.

No Differences Between 12 Weeks of Block- vs. Traditional-Periodized Training in Performance Adaptations in Trained Cyclists

The purpose of this study was to compare the effects of 12 weeks load-matched block periodization (BP, n = 14), using weekly concentration of high- (HIT), moderate- (MIT), and low- (LIT) intensity training, with traditional periodization (TP, n = 16) using a weekly, cyclic progressive increase in training load of HIT-, MIT-, and LIT-sessions in trained cyclists (peak oxygen uptake: 58 ± 8 ml·kg⁻¹·min⁻¹). Red blood cell volume increased 10 ± 16% (p = 0.029) more in BP compared to TP, while capillaries around type I fibers increased 20 ± 12% (p = 0.002) more in TP compared to BP from Pre to Post12. No other group differences were found in time-trial (TT) performances or muscular-, or hematological adaptations. However, both groups improved 5 and 40-min TT power by 9 ± 9% (p < 0.001) and 8 ± 9% (p < 0.001), maximal aerobic power (W_max) and power output (PO) at 4 mmol·L⁻¹ blood lactate (W_4mmol), by 6 ± 7 (p = 0.001) and 10 ± 12% (p = 0.001), and gross efficiency (GE) in a semi-fatigued state by 0.5 ± 1.1%-points (p = 0.026). In contrast, GE in fresh state and VO_2peak were unaltered in both groups. The muscle protein content of β-hydroxyacyl (HAD) increased by 55 ± 58% in TP only, while both TP and BP increased the content of cytochrome c oxidase subunit IV (COXIV) by 72 ± 34%. Muscle enzyme activities of citrate synthase (CS) and phosphofructokinase (PFK) were unaltered. TP increased capillary-to-fiber ratio and capillary around fiber (CAF) type I by 36 ± 15% (p < 0.001) and 17 ± 8% (p = 0.025), respectively, while BP increased capillary density (CD) by 28 ± 24% (p = 0.048) from Pre to Post12. The present study shows no difference in performance between BP and “best practice”-TP of endurance training intensities using a cyclic, progressively increasing training load in trained cyclists. However, hematological and muscle capillary adaptations may differ.

Anthropometric, Physiological, and Performance Developments in Cross-country Skiers

PURPOSE

This study aimed to describe changes in laboratory-assessed anthropometric and physiological characteristics, training volumes, and competitive performance in national development-team cross-country skiers over a 25-month period, and to analyze whether changes in competitive performance could be predicted by changes in laboratory-assessed qualities and training volumes.

METHODS

Data collected over 25 months from 30 national development-team cross-country skiers (14 women, 16 men; age, 18-23 yr) were analyzed retrospectively using multivariate statistics. Anthropometric and physiological characteristics were assessed via dual-energy x-ray absorptiometry and incremental roller-ski treadmill tests, respectively. Total training volumes and distributions of low- and high-intensity training were analyzed from online training diaries, and competitive performance was determined by International Ski Federation (FIS) distance and sprint points.

RESULTS

Whole- and upper-body lean mass increased in the full cohort of skiers (n = 30; both P < 0.05), whereas lower-body lean mass, whole-body fat mass, speed and oxygen uptake (V˙O2) at a blood lactate concentration (BLa) of 2 and 4 mmol·L-1, as well as time-trial completion time, power output, and peak V˙O2, improved in the women only (all P < 0.05). Valid predictive models were identified for female skiers' best FIS distance points (R2 = 0.81/Q2 = 0.51) and changes in FIS distance points (R2 = 0.83/Q2 = 0.54), with body mass, fat mass, lean mass, V˙O2peak, and speed at a BLa of 4 mmol·L-1 identified as consistently important variables for projection.

CONCLUSIONS

The valid prediction of competitive performance was achieved for women only in distance events. This study suggests that improvements in body composition and aerobic capacity may be more beneficial for elite female development-level skiers than for their male counterparts. These results have implications for athlete selection and performance development.

Acute and Chronic Effects of Interval Training on the Immune System: A Systematic Review with Meta-Analysis

Simple Summary

Interval training (IT) is a popular training strategy recognized by its positive effects on metabolic and cardiovascular system. However, there seems no consensus regarding the effects of IT on immune system parameters. Therefore, we aimed to summarize the evidence regarding the effects of IT on the immune system. As our many findings, an IT acutely promote a transitory change on immune cell count followed by reduced function. The magnitude of these changes seems to vary in accordance with IT type. On the other hand, the regular practice of IT might contribute to improve immune function without apparent change on immune cell count.

Abstract

Purpose: To summarize the evidence regarding the acute and chronic effects of interval training (IT) in the immune system through a systematic review with meta-analysis. Design: Systematic review with meta-analysis. Data source: English, Portuguese and Spanish languages search of the electronic databases Pubmed/Medline, Scopus, and SciELO. Eligibility criteria: Studies such as clinical trials, randomized cross-over trials and randomized clinical trials, investigating the acute and chronic effects of IT on the immune outcomes in humans. Results: Of the 175 studies retrieved, 35 were included in the qualitative analysis and 18 in a meta-analysis. Within-group analysis detected significant acute decrease after IT on immunoglobulin A (IgA) secretory rate (n = 115; MD = −15.46 µg·min⁻¹; 95%CI, −28.3 to 2.66; p = 0.02), total leucocyte count increase (n = 137; MD = 2.58 × 10³ µL⁻¹; 95%CI, 1.79 to 3.38; p < 0.001), increase in lymphocyte count immediately after exercise (n = 125; MD = 1.3 × 10³ µL⁻¹; 95%CI, 0.86 to 1.75; p < 0.001), and decrease during recovery (30 to 180 min post-exercise) (n = 125; MD = −0.36 × 10³ µL⁻¹;−0.57 to −0.15; p < 0.001). No effect was detected on absolute IgA (n = 127; MD = 47.5 µg·mL⁻¹; 95%CI, −10.6 to 105.6; p = 0.11). Overall, IT might acutely reduce leucocyte function. Regarding chronic effects IT improved immune function without change leucocyte count. Conclusion: IT might provide a transient disturbance on the immune system, followed by reduced immune function. However, regular IT performance induces favorable adaptations on immune function.

Comparison of Aerobic Capacity Changes as a Result of a Polarized or Block Training Program among Trained Mountain Bike Cyclists

This study compared the effectiveness of a block training program and a polarized training program in developing aerobic capacity in twenty trained mountain bike cyclists. The cyclists were divided into two groups: the block training program group (BT) and the polarized training program group (PT). The experiment lasted 8 weeks. During the experiment, the BT group alternated between 17-day blocks consisting of dominant low-intensity training (LIT) and 11-day blocks consisting of sprint interval training (SIT), and high-intensity interval training (HIIT), while the PT group performed SIT, HIIT, and LIT simultaneously. Before and after the experiment, the cyclists performed incremental tests during which maximal oxygen uptake (VO₂max), maximal aerobic power (Pmax), power achieved at the first ventilatory threshold (P_VT1), and at the second ventilatory threshold (P_VT2) were measured. VO₂max increased in BT group (from 3.75 ± 0.67 to 4.00 ± 0.75 L∙min^-1) and PT group (from 3.66 ± 0.73 to 4.20 ± 0.89 L∙min^-1). In addition, Pmax, P_VT1, and P_VT2 increased in both groups to a similar extent. In conclusion, the polarized training program was more effective in developing the VO₂max compared to the block program. In terms of developing other parameters characterizing the cyclists' aerobic capacity, the block and polarized program induced similar results.

Intensity Control During Block-Periodized High-Intensity Training: Heart Rate and Lactate Concentration During Three Annual Seasons in World-Class Cross-Country Skiers

Purpose: To describe heart rate (HR) and blood lactate (Bla⁻) responses during high-intensity interval training (HIT) in a long-term block-periodized HIT regimen in world-class cross-country (XC) skiers.

Methods: Data were collected in 14 world-class female XC skiers (aged 25 ± 5 years; body mass, 60.4 ± 6.5 kg; and maximal HR, 194 ± 8 beats · min⁻¹) throughout three entire seasons. The HR and Bla⁻ values were determined at the end of 572 intervals performed during 63 sessions and 17 HIT blocks utilizing different exercise modes: running, running with poles, and skiing (on-snow and roller ski) with classic and skating techniques.

Results: The mean HR was 91 ± 3% of HR_max with a corresponding Bla⁻ of 7.3 ± 2.1 mmol · L⁻¹. The average HR and Bla⁻ values were relatively similar across the different exercise modes, except for a lower HR (~90 vs. 92% of HR_max) for on-snow and roller ski classical skiing and lower Bla⁻ values (5.9 vs. 7.0–7.8 mmol · L⁻¹) for on-snow classical skiing compared to the other modes, both P < 0.05. An increase in HR and Bla⁻ was observed from interval working periods 1 to 3 (90–92% of HR_max and 6.5–7.7 mmol · L⁻¹) and further from 3 to 5 (92–93% of HR_max and 7.7–9.0 mmol · L⁻¹), all P < 0.05.

Conclusions: We describe long-term use of HIT-block periodization among world-class XC skiers who achieved target HR and Bla⁻ levels in all six exercise modes employed. According to athletes and coaches, the key to successful blocks was intensity control to allow for high-quality HIT sessions throughout the entire HIT block.

High-Intensity Interval Training Shock Microcycle for Enhancing Sport Performance: A Brief Review

Dolci, F, Kilding, AE, Chivers, P, Piggott, B, and Hart, NH. High-intensity interval training shock microcycle for enhancing sport performance: A brief review. J Strength Cond Res 34(4): 1188-1196, 2020-High-intensity interval training (HIIT) is a powerful strategy to develop athletes' fitness and enhance endurance performance. Traditional HIIT interventions involve multiple microcycles (7-10 days long) of 2-3 HIIT sessions each, which have been commonly supported to improve athletic performance after a minimum period of 6 weeks training. Regardless of the efficacy of such an approach, in recent years, a higher frequency of HIIT sessions within a unique microcycle, commonly referred to as an HIIT shock microcycle, has been proposed as an alternative HIIT periodization strategy to induce greater and more efficient endurance adaptation in athletes. This review article provides an insight into this new HIIT periodization strategy by discussing (1) HIIT shock microcycle format and design; (2) the sustainability of this training strategy; (3) effects on performance and physiological parameters of endurance; and (4) potential mechanisms for improvements. Evidence advocates the sustainability and effectiveness of HIIT shock microcycle in different athletes to improve intermittent and continuous running/cycling performance and suggests mitochondria biogenesis as the main acute physiological adaptation following this intervention.

Block periodization of endurance training - a systematic review and meta-analysis

Background

Block periodization (BP) has been proposed as an alternative to traditional (TRAD) organization of the annual training plan for endurance athletes.

Objective

To our knowledge, this is the first meta-analysis to evaluate the effect BP of endurance training on endurance performance and factors determinative for endurance performance in trained- to well-trained athletes.

Methods

The PubMed, SPORTdiscus and Web of Science databases were searched from inception to August 2019. Studies were included if the following criteria were met: 1) the study examined a block-periodized endurance training intervention; 2) the study had a one-, two or multiple group-, crossover- or case-study design; 3) the study assessed at least one key endurance variable before and after the intervention period. A total of 2905 studies were screened, where 20 records met the eligibility criteria. Methodological quality for each study was assessed using the PEDro scale. Six studies were pooled to perform meta-analysis for maximal oxygen uptake (VO₂max) and maximal power output (Wmax) during an incremental exercise test to exhaustion. Due to a lower number of studies and heterogenous measurements, other performance measures were systematically reviewed.

Results

The meta-analyses revealed small favorable effects for BP compared to TRAD regarding changes in VO₂max (standardized mean difference, 0.40; 95% CI=0.02, 0.79) and Wmax (standardized mean difference, 0.28; 95% CI=0.01, 0.54). For changes in endurance performance and workload at different exercise thresholds BP generally revealed moderate- to large-effect sizes compared to TRAD.

Conclusion

BP is an adequate, alternative training strategy to TRAD as evidenced by superior training effects on VO₂max and Wmax in athletes. The reviewed studies show promising effects for BP of endurance training; however, these results must be considered with some caution due to small studies with generally low methodological quality (mean PEDro score =3.7/10).

Sustainable Sport: Cardio-Differentiated Planning of Fitness Programs for High School Boys Engaged in Speed Skiing

In speed skiing, an athlete’s functional readiness is tested by means of a bicycle ergometer (EGM). The purpose of this research is to make various mesocycle plans for high school boys, engaged in speed skiing, with due account for their cardio-functional indicators obtained by means of the EGM. The study was attended by the 16–17 years old, first-category and sub-master racing skiers, included in the junior regional teams of the Russian Federation (Republic of Tatarstan and Udmurtia). The total number of subjects included eight men. In training young racing skiers, a differentiated approach combined with leg muscle testing will allow an improvement in sports results more effectively at different stages, as well as monitoring the young athlete’s response to the cardiovascular load. Low cardiac capacity indices have a negative impact on the racing skier’s performance. EGM testing allows determining the maximum cardiac capacity by measuring the amount of oxygen delivered to the working muscles at the HR of 190 beats per minute. Therefore, case-specific aerobic load was planned for each mesocycle according to these data. Based on the cardiac capacity growth, such means of physical training as interval, high-speed, and tempo training were planned.

Block vs. Traditional Periodization of HIT: Two Different Paths to Success for the World's Best Cross-Country Skier

In short-term studies, block periodization of high-intensity training (HIT) has been shown to be an effective strategy that enhances performance and related physiological factors. However, long-term studies and detailed investigations of macro, meso, and micro-periodization of HIT blocks in world-class endurance athletes are currently lacking. In a recent study, we showed that the world’s most successful cross-country (XC) skier used two different periodization models with success throughout her career. One including extensive use of HIT blocks, namely BP, and one using a traditional method namely TRAD. In this study, we compare BP with TRAD in two comparable successful seasons and provide a detailed description of the annual use of HIT blocks in BP. The participant is the most-decorated winter Olympian, with 8 Olympic gold medals, 18 world championship titles, and 114 world cup victories. Training data was categorized by training form (endurance, strength, and speed), intensity [low (LIT), moderate (MIT), and HIT], and mode (running, cycling, and skiing/roller skiing). No significant difference was found in the total endurance training load between BP and TRAD. However, training volume in BP was lower compared to TRAD (15 ± 6 vs. 18 ± 7 h/wk, P = 0.001), mainly explained by less LIT (13 ± 5 vs. 15 ± 5 h/wk, P = 0.004). Lower volume of MIT was also performed in BP compared to TRAD (13 vs. 38 sessions/year), whereas the amount of HIT was higher in BP (157 vs. 77 sessions/year). While BP included high amounts of HIT already from the first preparation period, followed by a reduction toward the competition period, TRAD had a progressive increase in HIT toward the competition period. In BP, the athlete performed seven HIT blocks, varying from 7 to 11 days, each including 8–13 HIT sessions. This study provides novel insights into successful utilization of two different periodization models in the worlds best XC skier, and illustrates the macro, meso and micro- periodization of HIT blocks to increase the overall amount of HIT.

Sex-based differences in speed, sub-technique selection, and kinematic patterns during low- and high-intensity training for classical cross-country skiing

OBJECTIVES

We investigated sex-based differences in speed, sub-technique selection, and kinematic patterns during low- (LIT) and high-intensity training (HIT) for classical cross-country (XC) skiing across varying terrain.

METHODS

Six male and six female elite XC skiers with an approximately 15% differences in VO2max (men: 68.9±2.9 mL·min-1·kg-1, women: 60.1±3.3 mL·min-1·kg-1) were monitored using a multi-sensor system to collect time-synchronised data of heart rate, speed, and multiple tri-axial inertial measurements units while XC skiing on a 5-km competition track.

RESULTS

Men skied 21% faster than women during HIT (5.9±0.3 m·s-1 vs. 4.9±0.2 m·s-1, P < .001), with the greatest difference (26%) while skiing on flat terrain, whereas skiing speed did not significantly differ between men and women during LIT. At similar instructed intensity and rating of perceived effort, women exhibited significantly higher relative heart rate (85±2% vs. 71±3% of maximum) and blood lactate levels (4.0±1.3 vs. 1.2±0.2 mmol/L) during LIT (all P < .001) than men, whereas physiological responses did generally not differ between the sexes during HIT. During both intensities and among both sexes, double poling (DP) was the sub-technique most used relative to distance, followed by miscellaneous sub-techniques (MISC), diagonal stride (DIA), kick double poling (DK) and herringbone (HRB). In relation to distance women used DIA more than men during LIT (22% vs. 17%, P = .009) and HIT (23% vs. 12%, P = .001), whereas men used MISC, including tucking and turning, more than women during LIT (39% vs. 25%, P = .017) and HIT (41% vs. 30%, P = .064). In particular, men used DP more than women while skiing the uphill sections during both LIT (24% vs. 11%, P = .015) and HIT (39% vs. 13%, P = .002).

CONCLUSIONS

Our findings provide novel insights into sex-based differences in speed, sub-technique selection, and kinematic patterns during LIT and HIT for classical skiing.

5-Hydroxymethylfurfural and Alpha-Ketoglutaric Acid as an Ergogenic Aid During Intensified Soccer Training: A Placebo Controlled Randomized Study

Intensified training may lead to fatigue or even a state of overreaching with temporary reductions in performance. Any aid helping to prevent these consequences and to better tolerate such a training regime would be of great importance. 5-hydroxymethylfurfural (5-HMF) and α-ketoglutaric acid (α-KG) supplementation has been suggested to support favorable training outcomes but its effectiveness to facilitate adaptations during an intensified training period has never been investigated. During an in-season competition break (2 weeks), seventeen young outfield soccer players (age:14.7 ± 0.4 yr) performed a 9-day lasting shock microcyle including 5-7 repeated sprint exercise sessions in addition to the regular training (∼6 sessions/wk) and match (1-2 matches/wk) schedule. Before the training period a treadmill test to exhaustion, a YOYO intermittent recovery level 2 (YYIR2) and a repeated sprint ability (RSA) test were performed. The treadmill test was repeated 3 days after the shock microcycle whereas the YYIR2 and the RSA test on day 10 after the training. Magnitude based inference analysis showed likely positive effects of the 5-HMF/α-KG compared to the control group for changes in the maximal running velocity (+0.3 ± 0.7 vs. -0.3 ± 0.8 km/h) and running velocity at lactate turn-point 1 (+0.2 ± 0.4 vs. -0.2 ± 0.6) and lactate turn-point 2 (+0.4 ± 0.4 vs. -0.2 ± 0.6 km/h, for the 5-HMF/α-KG and placebo group, respectively). Training improved YYIR2 performance (+180 ± 67 vs. +200 ± 168m) and RSA (mean time: -0.1 ± 0.1 vs. -0.1 ± 0.1s, for the 5-HMF/α-KG and placebo group, respectively) in both groups and to the same extent. In conclusion, an in-season shock microcyle including repeated sprint training improves YYIR2 performance and RSA in youth soccer players. Supplementation with 5-HMF/α-KG did not modify training adaptations but led to likely positive exercise performance responses shortly after the intensified training regime.