Validation of a clinically applicable device for fast and accurate quantification of blood volume.

INTRODUCTION: Determination of blood volume (BV) using the dual-isotope (e.g., 99m Tc-labeled red blood cells [99m Tc-RBC] and 125 I-labeled human serum albumin [125 I-HSA]) injection method is limited in medicine due to the long isotope half-life. However, BV has been determined in laboratory settings for 100 years using the carbon monoxide (CO)-rebreathing-based procedure, which allows frequent BV measurements. METHODS: We investigated the reliability and accuracy of a semi-automated CO-rebreathing device by comparing it against the dual-isotope methodology and its ability to detect a known blood removal. In study A, BV was determined three times in ~2 h; twice using the device with rebreathing protocols lasting 2 (CO2min ) and 10 min (CO10min ) and once with the dual-isotope technique. In study B, the accuracy of the device was assessed by its ability to detect a 2% removal of BV. RESULTS: A good correlation was observed between both the CO-rebreathing protocols (r2 = 0.89-0.98; p < 0.001) and the dual-isotope approach (r2 = 0.89-0.95; p < 0.001). In absolute terms BV was 425 ± 263 mL and 491 ± 388 mL lower (p < 0.001) when quantified with the dual-isotope compared to the CO-rebreathing protocols. When reducing BV by 132 ± 25 mL (2%), the device quantified a lower (p < 0.001) BV of 150 ± 45 mL. CONCLUSION: This study emphasizes that the semi-automated device accurately determines small changes (i.e., 2%) in BV and that a high correlation with the dual-isotope methodology exists. The findings are clinically relevant owing to the method's simple and fast nature (the absence of radioactive tracers and reduced time requirements, i.e., ~15 min vs. ~180 min) and the possibility for repeated measurements within a single day.

Heat suit training increases hemoglobin mass in elite cross-country skiers.

PURPOSE: The primary purpose was to test the effect of heat suit training on hemoglobin mass (Hbmass ) in elite cross-country (XC) skiers. METHODS: Twenty-five male XC-skiers were divided into a group that added 5 × 50 min weekly heat suit training sessions to their regular training (HEAT; n = 13, 23 ± 5 years, 73.9 ± 5.2 kg, 180 ± 6 cm, 76.8 ± 4.6 ml·min-1 ·kg-1 ) or to a control group matched for training volume and intensity distribution (CON; n = 12, 23 ± 4 years, 78.4 ± 5.8 kg, 184 ± 4 cm, 75.2 ± 3.4 ml·min-1 ·kg-1 ) during the five-week intervention period. Hbmass , endurance performance and factors determining endurance performance were assessed before and after the intervention. RESULTS: HEAT led to 30 g greater Hbmass (95% CI: [8.5, 51.7], p = 0.009) and 157 ml greater red blood cell volume ([29, 285], p = 0.018) post-intervention, compared to CON when adjusted for baseline values. In contrast, no group differences were observed for changes in work economy, running velocity, and fractional utilization of maximal oxygen uptake (V̇O2max ) at 4 mmol·L-1 blood lactate, V̇O2max or 15-min running distance performance trial during the intervention. CONCLUSION: HEAT induced a larger increase in Hbmass and red blood cell volume after five weeks with five weekly heat suit training sessions than CON, but with no detectable group differences on physiological determinants of endurance performance or actual endurance performance in elite CX skiers.

Five weeks of heat training increases haemoglobin mass in elite cyclists.

NEW FINDINGS: What is the central question of this study? Do haemoglobin mass and red blood cell volume increase in elite cyclists training in a hot environment compared to a control group training at normal temperature? What is the main finding and its importance? Five weeks of heat training increases haemoglobin mass in elite cyclists. There are small to intermediate effect sizes for exercise parameters favouring heat training. ABSTRACT: In this study we tested the hypothesis that performing 1 h of regular light exercise in a heat chamber (HEAT; 37.8 ± 0.5°C; 65.4 ± 1.8% humidity) 5 times week-1 for a total of 5 weeks increases haemoglobin mass (Hbmass ) and exercise performance in elite cyclists ( V̇O2max  = 76.2 ± 7.6 ml min-1  kg-1 ). Twenty-three male volunteers were assigned to HEAT (n = 11) or CON (n = 12; 15.5 ± 0.1°C; 25.1 ± 0.0% humidity) training groups. Hbmass was determined before and after the intervention period in conjunction with an extensive exercise test protocol (conducted at 16-19°C). HEAT increased (P < 0.05) Hbmass by 42 g from 893 ± 78 to 935 ± 108 g whereas Hbmass remained unchanged (+6 g) in CON. Furthermore, statistical analysis revealed a time-group interaction (P < 0.05). The greater increase in Hbmass in HEAT, however, did not manifest in a greater increase in V̇O2max (225 ± 274 ml min-1 in HEAT and 161 ± 202 ml min-1 in CON). While HEAT reduced (P < 0.05) lactate levels during some of the submaximal exercise tests, there was no statistical difference between other performance parameters. There were, however, small to intermediate effect sizes favouring HEAT for lactate threshold power output (2.8 ± 3.9 vs. -0.4 ± 5.1% change, effect size (ES) = 0.34), gross economy in the fatigued state (0.19 ± 0.42 vs. -0.12 ± 0.49%-point change, ES = 0.52) and 15 min mean power (6.9 ± 8.4 vs. 3.4 ± 5.1% increase, ES = 0.22). This study demonstrates an increase in Hbmass and small to intermediate effect sizes on exercise variables in elite cyclists following a 5-week heat training intervention.

Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training.

The purpose of this study was to compare the effects of 3 weeks with three weekly sessions (ie, nine sessions in total) of short intervals (SI; n = 9; 3 series with 13 × 30-second work intervals interspersed with 15-second recovery and 3-minutes recovery between series) against effort-matched (rate of perceived effort based) long intervals (LI; n = 9; 4 series of 5-minute work intervals with 2.5-minutes recovery between series) on performance parameters in elite cyclists ( V ˙ O 2max 73 ± 4 mL min-1  kg-1 ). There were no differences between groups in total volume and intensity distribution of training during the intervention period. SI achieved a larger (P < .05) relative improvement in peak aerobic power output than LI (3.7 ± 4.3% vs -0.3 ± 2.8%, respectively), fractional utilization of V ˙ O 2max at 4 mmol L-1 [La- ] (3.0 ± 5.8 percent points vs -3.5 ± 2.7 percent points, respectively), and larger relative increase in power output at 4 mmol L-1 [La- ] (2.0 ± 6.7% vs -2.8 ± 3.4, respectively), while there was no group difference in change of V ˙ O 2max . Improvements in performance measured as mean power output during 20-minute cycling test were greater (P < .01) in SI compared with LI (4.7 ± 4.4% vs -1.4 ± 2.2%, respectively). Mean effect size of the improvement in the above variables revealed a small to large effect of SI training vs LI training. The data thus demonstrate that the present SI protocol induces superior training adaptations compared with the present LI protocol in elite cyclists.

10 weeks of heavy strength training improves performance-related measurements in elite cyclists.

Elite cyclists have often a limited period of time available during their short preparation phase to focus on development of maximal strength; therefore, the purpose of the present study was to investigate the effect of 10-week heavy strength training on lean lower-body mass, leg strength, determinants of cycling performance and cycling performance in elite cyclists. Twelve cyclists performed heavy strength training and normal endurance training (E&S) while 8 other cyclists performed normal endurance training only (E). Following the intervention period E&S had a larger increase in maximal isometric half squat, mean power output during a 30-s Wingate sprint (P < 0.05) and a tendency towards larger improvement in power output at 4 mmol âˆ™ L-1 [la-] than E (P = 0.068). There were no significant difference between E&S and E in changes in 40-min all-out trial (4 ± 6% vs. -1 ± 6%, respectively, P = 0.13). These beneficial effects may encourage elite cyclists to perform heavy strength training and the short period of only 10 weeks should make it executable even in the compressed training and competition schedule of elite cyclists.

Short-term performance peaking in an elite cross-country mountain biker.

Endurance athletes usually achieve performance peaks with 2-4 weeks of overload training followed by 1-3weeks of tapering. With a tight competition schedule, this may not be appropriate. This case investigates the effect of a 7-day overload period including daily high-intensity aerobic training followed by a 5-day step taper between two competitions in an elite cross-country mountain biker. Pre-test peak oxygen consumption was 89 ml·kg-1·min-1, peak aerobic power 6.8 W·kg-1, power output at 2 mmol·L-1 blood lactate concentration 3.9 W·kg-1, maximal isometric force 180 Nm and squat jump 21 cm. During overload, perceived leg well-being went from normal to very heavy. On day 1 after overload, vastus lateralis and vastus medialis EMGmean activity was reduced by 3% and 7%, respectively. Other baseline measurements were reduced by 3-7%. On day 4 of the taper, he felt that his legs were good and all measurements were 3-7% higher than before overload. On day 6 after the taper, his legs felt very good. This case shows that an elite mountain biker (11th in UCI World Cup one week prior to the pre-test) could achieve a rather large supercompensation by using a 12-day performance peaking protocol.

Optimizing Interval Training at Power Output Associated With Peak Oxygen Uptake in Well-Trained Cyclists.

The purpose of this study was to investigate the acute physiological responses of interval protocols using the minimal power output (MAP) that elicits peak oxygen uptake (V[Combining Dot Above]O2peak) as exercise intensity and different durations of work intervals during intermittent cycling. In randomized order, 13 well-trained male cyclists (V[Combining Dot Above]O2peak = 67 ± 6 ml·kg·min) performed 3 different interval protocols to exhaustion. Time to exhaustion and time ≥ 90% of V[Combining Dot Above]O2peak were measured with MAP as exercise intensity, and work duration of the intervals equals either 80% of Tmax, 50% of Tmax, or 30 seconds with recovery period being 50% of the work duration at intensity equal to 50% of MAP. The major findings were that the interval protocol using 30-second work periods induced longer time ≥90% of V[Combining Dot Above]O2peak and longer work duration at MAP intensity than the interval protocols using work periods of 50% of Tmax or 80% of Tmax (p ≤ 0.05). There was no difference between the protocols using work periods of 50% of Tmax or 80% of Tmax. In conclusion, the present study suggests that the 30-second work interval protocol acutely induces a larger exercise stimulus in well-trained cyclists than the protocols using work periods of 50% of Tmax or 80% of Tmax. The practical application of the present findings is that fixed 30-second work intervals can be used to optimize training time at MAP and time ≥90% of V[Combining Dot Above]O2peak in well-trained cyclists using MAP exercise intensity and a 2:1 work:recovery ratio.

HIT maintains performance during the transition period and improves next season performance in well-trained cyclists.

PURPOSE: To investigate the effects of combining low-intensity endurance training (LIT) with one high-intensity endurance training (HIT) session every 7-10 days (EXP, n = 7) vs. traditional approach focusing on LIT (TRAD, n = 6) during the transition period. The effects of different training strategies during the transition period were investigated after the transition period and at the beginning of the subsequent competition season. METHODS: Well-trained cyclists were tested after the competition season, after an 8-week transition period, and after a 16-week preparatory period, before the subsequent competition season. The only difference between groups was a larger time with HIT during the transition phase in EXP. RESULTS: It was very likely that EXP had a larger impact on power output at 4 mmol L(-1) [la(-)] after both the transition period and after the preparatory period than TRAD [between-group change (90% CI): 10.6% (8.2%) and 12.9% (11.9%), respectively]. It was very likely that EXP had a larger impact on mean power output in the 40-min all-out trial after the transition period than TRAD [between-group change 12.4% (7.6%)]. EXP was also likely to have a larger improvement in the 40-min trial performance from pre-test to after the preparatory period than TRAD [between-group change 6.0% (6.6%)]. CONCLUSION: The present findings suggest that HIT sessions should be incorporated during the transition phase to avoid reduction in fitness and performance level and thereby increase the likelihood of improved performance from the end of one season to the beginning of the subsequent season.

A time-saving method to assess power output at lactate threshold in well-trained and elite cyclists.

The purpose of this study was to examine the relationship between lactate threshold (LT) as a percentage of maximal oxygen consumption (V[Combining Dot Above]O2max) and power output at LT (LTW) and also to investigate to what extent V[Combining Dot Above]O2max, oxygen cost of cycling (CC), and maximal aerobic power (MAP) determine LTW in cycling to develop a new time-saving model for testing LTW. To do this, 108 male competitive cyclists with an average V[Combining Dot Above]O2max of 65.2 ± 7.4 ml·kg·min and an average LTW of 274 ± 43 W were tested for V[Combining Dot Above]O2max, LT %V[Combining Dot Above]O2max, LTW, MAP, and CC on a test ergometer cycle. The product of MAP and individual LT in %V[Combining Dot Above]O2max was found to be a good determinant of LTW (R = 0.98, p < 0.0001). However, LT in %V[Combining Dot Above]O2max was found to be a poor determinant of LTW (R = 0.39, p < 0.0001). Based on these findings, we have suggested a new time-saving method for calculating LTW in well-trained cyclists. The benefits from this model come both from tracking LTW during training interventions and from regularly assessing training status in competitive cyclists. Briefly, this method is based on the present findings that LTW depends on LT in %V[Combining Dot Above]O2max, V[Combining Dot Above]O2max, and CC and may after an initial test session reduce the time for the subsequent testing of LTW by as much as 50% without the need for blood samples.

Heat Suit Training Preserves the Increased Hemoglobin Mass Following Altitude Camp in Elite Cyclists.

PURPOSE: Altitude training is a common strategy used with the intent to increase hemoglobin mass (Hbmass) in athletes. However, if the Hbmass is increased during altitude camps it seems to decline rapidly upon returning to sea level. This study aimed to examine the efficacy of three weekly heat training sessions over a 3.5-week period following a 3-week altitude camp, on the maintenance of Hbmass in elite cyclists. METHODS: Eighteen male cyclists (maximal oxygen consumption: 76 ± 5 mL·min-1·kg-1) underwent a 3-week altitude training camp at ~2100 m above sea level. After the camp, participants were divided into one group performing three weekly heat sessions that was subtracted from their usual training (HEAT) while the other continuing usual training (CON). Training characteristics were recorded during the intervention, while hematological measurements were recorded before the camp as well as two days and 3.5-weeks after the altitude camp. RESULTS: The 3-week altitude camp led to an overall increase in total Hbmass of 4.1%. Afterwards, HEAT maintained Hbmass (0.2%, p = 0.738), while CON group experienced a significant reduction (-3.3%, p < 0.001) (ΔHEAT vs. ΔCON, p < 0.001). Moreover, HEAT increased plasma volume (PV) by 11.6% (p = 0.007) and blood volume (BV) by 5.8% (p = 0.007), whereas CON only showed an increase in PV (5.5%, p = 0.041). Exercise intensity and training load were not different between groups during the maintenance period. CONCLUSIONS: This study suggests that incorporating three weekly heat training sessions into the usual training routine preserves a moderately increased Hbmass in elite cyclists following an altitude camp.

The higher the fraction of maximal oxygen uptake is during interval training, the greater is the cycling performance gain.

It has been suggested that time at a high fraction (%) of maximal oxygen uptake (VO2max) plays a decisive role for adaptations to interval training. Yet, no study has, to date, measured the % of VO2max during all interval sessions throughout a prolonged training intervention and subsequently related it to the magnitude of training adaptations. Thus, the present study aimed to investigate the relationship between % of VO2max achieved during an interval training intervention and changes in endurance performance and its physiological determinants in well-trained cyclists. Twenty-two cyclists (VO2max 67.1 (6.4) mL·min-1 ·kg-1; males, n = 19; females, n = 3) underwent a 9-week interval training intervention, consisting 21 sessions of 5 × 8-min intervals conducted at their 40-min highest sustainable mean power output (PO). Oxygen uptake was measured during all interval sessions, and the relationship between % of VO2max during work intervals and training adaptations were investigated using linear regression. A performance index was calculated from several performance measures. With higher % of VO2max during work intervals, greater improvements were observed for maximal PO during the VO2max test (R2 adjusted = 0.44, p = 0.009), PO at 4 mmol·L-1 [blood lactate] (R2 adjusted = 0.25, p = 0.035), the performance index (R2 adjusted = 0.36, p = 0.013), and VO2max (R2 adjusted = 0.54, p = 0.029). Other measures, such as % of maximal heart rate, were related to fewer outcome variables and exhibited poorer session-to-session repeatability compared to % of VO2max. In conclusion, improvements in endurance measures were positively related to the % of VO2max achieved during interval training. Percentage of VO2max was the measure that best reflected the magnitude of training adaptations.

Carbon monoxide supplementation: evaluating its potential to enhance altitude training effects and cycling performance in elite athletes.

Altitude training is a cornerstone for endurance athletes for improving blood variables and performance, with optimal effects observed at ∼2,300-2,500 meters above sea level (m.a.s.l.). However, elite cyclists face challenges such as limited access to such altitudes, inadequate training facilities, and high expenses. To address these issues, a novel method involving daily exposure to carbon monoxide (CO) has been proposed to amplify altitude training adaptations at suboptimal altitudes. Thirty-one male cyclists were assigned to three groups: Live-High Train-High with CO inhalation (LHTHCO), Live-High Train-High (LHTH), and Live-Low Train-Low (LLTL). The LHTHCO group underwent CO inhalation twice daily in the afternoon/evening to elevate carboxyhemoglobin concentration to ∼10%. Hematological variables, in vivo muscle oxidative capacity, and physiological indicators of cycling performance were assessed before and after a 3-week altitude training camp at 2,100 m.a.s.l. LHTHCO demonstrated a larger increase in hemoglobin mass (Hbmass) compared to both LHTH and LLTL. Although there were no statistical differences between LHTHCO and LHTH in submaximal and maximal performance measures, LHTHCO displayed greater improvements in 1-min maximal power output during incremental testing (Wmax), power output at lactate threshold, and maximal oxygen consumption (V̇o2max) compared to LLTL. LHTH demonstrated a larger improvement than LLTL in Wmax and V̇o2max, with no group differences in Hbmass or submaximal measures. Muscle oxidative capacity did not differ between groups. These findings suggest that combining moderate-altitude training with daily CO inhalation promotes hematological adaptations more effectively than moderate altitude alone and enhances cycling performance metrics in cyclists more than sea-level training.NEW & NOTEWORTHY Three weeks of training at moderate altitude with exposure to low doses of CO can significantly enhance hematological adaptations in elite cyclists compared to moderate-altitude training alone. Cycling performance determinants improved more with CO inhalation at moderate altitude compared to sea-level training, whereas there were no differences in submaximal and maximal performance measures compared to moderate-altitude training alone. This study highlights the potential of CO supplementation as an effective adjunct to altitude training regimens.

Yearly intrasubject variability of hematological biomarkers in elite athletes for the Athlete Biological Passport.

Confounding factors including exercise and environments challenge the interpretation of individual Athlete Biological Passports (ABPs). This study aimed to investigate the natural variability of hematological ABP parameters over 1 year in elite athletes compared with healthy control subjects and the validity of a multiparametric model estimating plasma volume (PV) shifts to correct individual ABP thresholds. Blood samples were collected monthly with full blood counts performed by flow cytometry (Sysmex XN analyzers) in 20 elite xc-skiers (ELITE) and 20 moderately trained controls. Individual ABP profiles were generated through Anti-Doping Administration & Management System Training, a standalone version of the ABP's adaptive model developed by the World Anti-Doping Agency. Additionally, eight serum parameters were computed as volume-sensitive biomarkers to run a multiparametric model to estimate PV. Variability in ELITE compared with controls was significantly higher for the Abnormal Blood Profile Scores (P = 0.003). Among 12 Atypical Passport Findings (ATPF) initially reported, six could be removed after correction of PV shifts with the multiparametric modeling. However, several ATPF were additionally generated (n = 19). Our study outlines a larger intraindividual variability in elite athletes, likely explained by more frequent exposure to extrinsic factors altering hematological biomarkers. PV correction for individual ABP thresholds allowed to explain most of the atypical findings while generating multiple new ATPF occurrences in the elite population. Overall, accounting for PV shifts in elite athletes was shown to be paramount in this study outlining the opportunity to consider PV variations with novel approaches when interpreting individual ABP profiles.

Development of Cycling Performance Variables and Durability in Female and Male National Team Cyclists: From Junior to Senior.

AIM: This study investigated the development of power profiles and performance-related measures from the junior level (<19 yr) via U23 (19-23 yr) to senior level (>23 yr) in 19 female and 100 male Norwegian national team cyclists. METHODS: A total of 285 tests were performed in a 3-d laboratory-standardized testing regime. The tests included power profiles with shorter duration (6-60 s) and longer durations (12-30 min) together with performance-related measures: critical power (CP), work capacity above CP (W'), power output at 4 and 2 mmol·L -1 [BLa - ] (L 4 and L 2 ), maximal aerobic power (W max ), and maximal oxygen uptake (V̇O 2max ), gross efficiency (GE), and pedaling efficiency. RESULTS: Females and males evolve similarly when maturing from junior via U23 to senior categories (all P > 0.07), except for V̇O 2max , which increased in females (but not males) from junior to senior level (534 ± 436 mL·min -1 , P = 0.013). In general, only performances of longer durations improved with age (12 and 30 min, P = 0.028 and P = 0.042, respectively). Performance-related measures like W max , V̇O 2max , CP, L 4 , L 2 , and pedaling efficiency in the fresh state improved with age (all P ≤ 0.025). Importantly, performance in the semifatigued state during a 5-min maximal test was also improved with age ( P = 0.045) despite a higher external energy expenditure before the test ( P = 0.026). CONCLUSIONS: Junior cyclists show highly developed sprint abilities, and the primary improvements of absolute power outputs and performance-related measures are seen for durations >60 s when maturing to U23 and senior categories. However, the durability, i.e., the capacity to maintain performance in a semifatigued state, is improved with age.

Hematological, skeletal muscle fiber, and exercise performance adaptations to heat training in elite female and male cyclists.

Heat exercise training may increase exercise performance in athletes. The underlying mechanisms remain partly unresolved, and it is unknown if female and male athletes may experience comparable gains. The aims were to investigate whether heat training (HEAT) increases hemoglobin mass (Hbmass), skeletal muscle fiber characteristics, and thermoneutral exercise performance in elite female and male endurance athletes. Female (n = 20; V̇o2max = 58.2 ± 6.7 mL·min-1·kg-1) and male (n = 27; V̇o2max = 76.4 ± 7.8 mL·min-1·kg-1) cyclists were studied before and after 5 wk of randomized control or HEAT consisting of five weekly sessions each of 50 min duration, which were included in their normal training regimes. Overall, the observed relative responses to HEAT were largely similar in female and male study participants. HEAT increased (P < 0.05) Hbmass in females from 650 ± 77 to 675 ± 76 g (4.0 ± 1.6%) and from 1,008 ± 155 to 1,041 ± 147 g (3.5 ± 2.3%) in males. In contrast, skeletal muscle citrate synthase activity, fiber type distribution, and capillary density remained unchanged with HEAT. Lactate threshold, V̇o2max, and mean power output during 15-min all-out testing were all enhanced (P < 0.05) following HEAT in female and male study participants. In conclusion, 5 wk of HEAT increases Hbmass in female and male elite cyclists and improves exercise performance in a thermoneutral environment. Based on this, heat training may be recommended to elite female and male athletes aiming to perform in a thermoneutral environment.NEW & NOTEWORTHY We demonstrate in elite female and male cyclists that heat exercise training (5 × 50 min sessions/wk for 5 wk) facilities Hbmass and other hematological parameters more than control exercise training, whereas skeletal muscle properties remain unaltered. Collectively, this coincided with improvements in lactate threshold, V̇o2max, and 15-min all-out cycling performance.

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 < 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.

Case Report: Heat Suit Training May Increase Hemoglobin Mass in Elite Athletes.

PURPOSE: The present case report aimed to investigate the effects of exercise training in temperate ambient conditions while wearing a heat suit on hemoglobin mass (Hbmass). METHODS: As part of their training regimens, 5 national-team members of endurance sports (3 males) performed ∼5 weekly heat suit exercise training sessions each lasting 50 minutes for a duration of ∼8 weeks. Two other male athletes acted as controls. After the initial 8-week period, 3 of the athletes continued for 2 to 4 months with ∼3 weekly heat sessions in an attempt to maintain acquired adaptations at a lower cost. Hbmass was assessed in duplicate before and after intervention and maintenance period based on automated carbon monoxide rebreathing. RESULTS: Heat suit exercise training increased rectal temperature to a median value of 38.7°C (range 38.6°C-39.0°C), and during the initial ∼8 weeks of heat suit training, there was a median increase of 5% (range 1.4%-12.9%) in Hbmass, while the changes in the 2 control athletes were a decrease of 1.7% and an increase of 3.2%, respectively. Furthermore, during the maintenance period, the 3 athletes who continued with a reduced number of heat suit sessions experienced a change of 0.7%, 2.8%, and -1.1%, indicating that it is possible to maintain initial increases in Hbmass despite reducing the weekly number of heat suit sessions. CONCLUSIONS: The present case report illustrates that heat suit exercise training acutely raises rectal temperature and that following 8 weeks of such training Hbmass may increase in elite endurance athletes.

Increasing Oxygen Uptake in Cross-Country Skiers by Speed Variation in Work Intervals.

PURPOSE: Accumulated time at a high percentage of peak oxygen consumption (VO2peak) is important for improving performance in endurance athletes. The present study compared the acute physiological and perceived effects of performing high-intensity intervals with roller ski double poling containing work intervals with (1) fast start followed by decreasing speed (DEC), (2) systematic variation in exercise intensity (VAR), and (3) constant speed (CON). METHODS: Ten well-trained cross-country skiers (double-poling VO2peak 69.6 [3.5] mL·min-1·kg-1) performed speed- and duration-matched DEC, VAR, and CON on 3 separate days in a randomized order (5 × 5-min work intervals and 3-min recovery). RESULTS: DEC and VAR led to longer time ≥90% VO2peak (P = .016 and P = .033, respectively) and higher mean %VO2peak (P = .036, and P = .009) compared with CON, with no differences between DEC and VAR (P = .930 and P = .759, respectively). VAR, DEC, and CON led to similar time ≥90% of peak heart rate (HRpeak), mean HR, mean breathing frequency, mean ventilation, and mean blood lactate concentration ([La-]). Furthermore, no differences between sessions were observed for perceptual responses, such as mean rate of perceived exertion, session rate of perceived exertion or pain score (all Ps > .147). CONCLUSIONS: In well-trained XC skiers, DEC and VAR led to longer time ≥90% of VO2peak compared with CON, without excessive perceptual effort, indicating that these intervals can be a good alternative for accumulating more time at a high percentage of VO2peak and at the same time mimicking the pronounced variation in exercise intensities experienced during XC-skiing competitions.

Heat Training Efficiently Increases and Maintains Hemoglobin Mass and Temperate Endurance Performance in Elite Cyclists.

PURPOSE AND METHODS: To test whether heat training performed as 5 × 50-min sessions per week for 5 wk in a heat chamber (CHAMBER) or while wearing a heat suit (SUIT), in temperate conditions, increases hemoglobin mass (Hb mass ) and endurance performance in elite cyclists, compared with a control group (CON-1). Furthermore, after the 5-wk intervention, we tested whether three sessions per week for 3 wk with heat suit (SUIT main ) would maintain Hb mass elevated compared with athletes who returned to normal training (HEAT stop ) or who continued to be the control group (CON-2). RESULTS: During the initial 5 wk, SUIT and CHAMBER increased Hb mass (2.6% and 2.4%) to a greater extent than CON-1 (-0.7%; both P < 0.01). The power output at 4 mmol·L -1 blood lactate and 1-min power output ( Wmax ) improved more in SUIT (3.6% and 7.3%, respectively) than CON-1 (-0.6%, P < 0.05; 0.2%, P < 0.01), whereas this was not the case for CHAMBER (1.4%, P = 0.24; 3.4%, P = 0.29). However, when SUIT and CHAMBER were pooled this revealed a greater improvement in a performance index (composed of power output at 4 mmol·L -1 blood lactate, Wmax , and 15-min power output) than CON-1 (4.9% ± 3.2% vs 1.7% ± 1.1%, respectively; P < 0.05). During the 3-wk maintenance period, SUIT main induced a larger increase in Hb mass than HEAT stop (3.3% vs 0.8%; P < 0.05), which was not different from the control (CON-2; 1.6%; P = 0.19), with no differences between HEAT stop and CON-2 ( P = 0.52). CONCLUSIONS: Both SUIT and CHAMBER can increase Hb mass , and pooling SUIT and CHAMBER demonstrates that heat training can increase performance. Furthermore, compared with cessation of heat training, a sustained increase in Hb mass was observed during a subsequent 3-wk maintenance period, although the number of weekly heat training sessions was reduced to 3.

Training wearing thermal clothing and training in hot ambient conditions are equally effective methods of heat acclimation.

The objective was to compare the efficacy of three different heat acclimation protocols to improve exercise performance in the heat. Thirty four cyclists completed one of three 10-day interventions 1) 50-min cycling per day in 35 °C, 2) 50-min cycling per day wearing thermal clothing, and 3) 50-min cycling wearing thermal clothing plus 25 min hot water immersion per day. Pre- and post-intervention hemoglobin mass, intravascular volumes and core temperature were determined at rest. Heart rate, sweat rate, blood lactate concentration and core temperature were evaluated during 15-min submaximal and 30-min all-out cycling performance conducted in 35.2 ±â€¯0.1 °C and 61 ±â€¯1% relative humidity. There were no significant between-group differences in any of the determined variables. None of the interventions statistically altered any of the parameters investigated as part of the 15-min submaximal trial. However, following the intervention period, heat chamber, thermal clothing and thermal clothing + hot water immersion all improved 30-min all-out average power in the heat (9.5 ±â€¯3.8%, 9.5 ±â€¯3.6 and 9.9 ±â€¯5.2%, respectively, p < 0.001, F = 192.3). At termination of the 30-min all-out test, the increase in blood lactate concentration, rate of perceived exertion and sweat rate were not different between the three interventions. In conclusion, daily training sessions conducted either in ambient 35 °C, while wearing thermal clothing in temperate conditions or while wearing thermal clothing combined with hot water immersion are equally effective for improving exercise performance in the heat.