Determinants and reference values for blood volume and total hemoglobin mass in women and men.

Blood volume (BV) is an important clinical parameter and is usually reported per kg of body mass (BM). When fat mass is elevated, this underestimates BV/BM. One aim was to study if differences in BV/BM related to sex, age, and fitness would decrease if normalized to lean body mass (LBM). The analysis included 263 women and 319 men (age: 10-93 years, body mass index: 14-41 kg/m2 ) and 107 athletes who underwent assessment of BV and hemoglobin mass (Hbmass ), body composition, and cardiorespiratory fitness. BV/BM was 25% lower (70.3 ± 11.3 and 80.3 ± 10.8 mL/kgBM ) in women than men, respectively, whereas BV/LBM was 6% higher in women (110.9 ± 12.5 and 105.3 ± 11.2 mL/kgLBM ). Hbmass /BM was 34% lower (8.9 ± 1.4 and 11.5 ± 11.2 g/kgBM ) in women than in men, respectively, but only 6% lower (14.0 ± 1.5 and 14.9 ± 1.5 g/kgLBM )/LBM. Age did not affect BV. Athlete's BV/BM was 17.2% higher than non-athletes, but decreased to only 2.5% when normalized to LBM. Of the variables analyzed, LBM was the strongest predictor for BV (R2 = .72, p < .001) and Hbmass (R2 = .81, p < .001). These data may only be valid for BV/Hbmass when assessed by CO re-breathing. Hbmass /LBM could be considered a valuable clinical matrix in medical care aiming to normalize blood homeostasis.

Effects of including sprints during prolonged cycling on hormonal and muscular responses and recovery in elite cyclists.

This study investigated the acute effects of including 30-second sprints during prolonged low-intensity cycling on muscular and hormonal responses and recovery in elite cyclists. Twelve male cyclists (VO2max , 73.4 ± 4.0 mL/kg/min) completed a randomized crossover protocol, wherein 4 hours of cycling at 50% of VO2max were performed with and without inclusion of three sets of 3 × 30 seconds maximal sprints (E&S vs E, work-matched). Muscle biopsies (m. vastus lateralis) and blood were sampled at Pre, immediately after (Post) and 3 hours after (3 h) finalizing sessions. E&S led to greater increases in mRNA levels compared with E for markers of fat metabolism (PDK4, Δ-Log2 fold change between E&S and E ± 95%CI Post; 2.1 ± 0.9, Δ3h; 1.3 ± 0.7) and angiogenesis (VEGFA, Δ3h; 0.3 ± 0.3), and greater changes in markers of muscle protein turnover (myostatin, ΔPost; -1.4 ± 1.2, Δ3h; -1.3 ± 1.3; MuRF1, ΔPost; 1.5 ± 1.2, all P < .05). E&S showed decreased mRNA levels for markers of ion transport at 3h (Na+ -K+ α1; -0.6 ± 0.6, CLC1; -1.0 ± 0.8 and NHE1; -0.3 ± 0.2, all P < .05) and blunted responses for a marker of mitochondrial biogenesis (PGC-1α, Post; -0.3 ± 0.3, 3h; -0.4 ± 0.3, P < .05) compared with E E&S and E showed similar endocrine responses, with exceptions of GH and SHBG, where E&S displayed lower responses at Post (GH; -4.1 ± 3.2 µg/L, SHBG; -2.2 ± 1.9 nmol/L, P < .05). Both E&S and E demonstrated complete recovery in isokinetic knee extension torque 24 hours after exercise. In conclusion, we demonstrate E&S to be an effective exercise protocol for elite cyclists, which potentially leads to beneficial adaptations in skeletal muscle without impairing muscle recovery 24 hours after exercise.

Systemic and muscular responses to effort-matched short intervals and long intervals in elite cyclists.

The purpose of this study was to compare the acute effects of time- and effort-matched high-intensity intervals on physiological, endocrine, and skeletal muscle molecular variables in elite cyclists. Eight elite cyclists performed short intervals (SI: 30-seconds) and long intervals (LI: 5-minutes) with work:recovery ratio 2:1, using a randomized crossover design. SI was associated with 14% ± 3% higher mean power output (SI; 421 ± 27 vs LI; 371 ± 22 W), and longer working time above 90% of maximal oxygen uptake (VO2max , 54% ± 76%) and 90% peak heart rate (HRpeak , 153% ± 148%) than LI (all P < .05), despite similar degrees of perceived exertion, blood lactate levels and muscle activation measured using EMG root mean square (EMG rms). In blood, SI was associated with more pronounced increases in testosterone and testosterone-to-sex hormone-binding globulin (SHBG) ratios, as well as prolonged cortisol responses (P < .05). In skeletal muscle (m. Vastus lateralis), SI and LI led to similar changes in mRNA abundance for a range of transcripts, with the exception of NHE1 mRNA, which decreased after SI (P < .05). Overall, SI was associated with more pronounced physiological and endocrine responses than LI in elite cyclists, suggesting that such training might lead to superior adaptations in elite cyclists.

Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression.

BACKGROUND: Skeletal muscle mitochondria and capillaries are crucial for aerobic fitness, and suppressed levels are associated with chronic and age-related diseases. Currently, evidence-based exercise training recommendations to enhance these characteristics are limited. It is essential to explore how factors, such as fitness level, age, sex, and disease affect mitochondrial and capillary adaptations to different exercise stimuli. OBJECTIVES: The main aim of this study was to compare the effects of low- or moderate intensity continuous endurance training (ET), high-intensity interval or continuous training (HIT), and sprint interval training (SIT) on changes in skeletal muscle mitochondrial content and capillarization. Secondarily, the effects on maximal oxygen consumption (VO2max), muscle fiber cross-sectional area, and fiber type proportion were investigated. METHODS: A systematic literature search was conducted in PubMed, Web of Science, and SPORTDiscus databases, with no data restrictions, up to 2 February 2022. Exercise training intervention studies of ET, HIT, and SIT were included if they had baseline and follow-up measures of at least one marker of mitochondrial content or capillarization. In total, data from 5973 participants in 353 and 131 research articles were included for the mitochondrial and capillary quantitative synthesis of this review, respectively. Additionally, measures of VO2max, muscle fiber cross-sectional area, and fiber type proportion were extracted from these studies. RESULTS: After adjusting for relevant covariates, such as training frequency, number of intervention weeks, and initial fitness level, percentage increases in mitochondrial content in response to exercise training increased to a similar extent with ET (23 ± 5%), HIT (27 ± 5%), and SIT (27 ± 7%) (P > 0.138), and were not influenced by age, sex, menopause, disease, or the amount of muscle mass engaged. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in mitochondrial content. Per total hour of exercise, SIT was ~ 2.3 times more efficient in increasing mitochondrial content than HIT and ~ 3.9 times more efficient than ET, while HIT was ~ 1.7 times more efficient than ET. Capillaries per fiber increased similarly with ET (15 ± 3%), HIT (13 ± 4%) and SIT (10 ± 11%) (P = 0.556) after adjustments for number of intervention weeks and initial fitness level. Capillaries per mm2 only increased after ET (13 ± 3%) and HIT (7 ± 4%), with increases being larger after ET compared with HIT and SIT (P < 0.05). This difference coincided with increases in fiber cross-sectional area after ET (6.5 ± 3.5%), HIT (8.9 ± 4.9%), and SIT (11.9 ± 15.1%). Gains in capillarization occurred primarily in the early stages of training (< 4 weeks) and were only observed in untrained to moderately trained participants. The proportion of type I muscle fibers remained unaltered by exercise training (P > 0.116), but ET and SIT exhibited opposing effects (P = 0.041). VO2max increased similarly with ET, HIT, and SIT, although HIT showed a tendency for greater improvement compared with both ET and SIT (P = 0.082), while SIT displayed the largest increase per hour of exercise. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in VO2max. Women displayed greater percentage gains in VO2max compared with men (P = 0.008). Generally, lower initial fitness levels were associated with greater percentage improvements in mitochondrial content, capillarization, and VO2max. SIT was particularly effective in improving mitochondrial content and VO2max in the early stages of training, while ET and HIT showed slower but steady improvements over a greater number of training weeks. CONCLUSIONS: The magnitude of change in mitochondrial content, capillarization, and VO2max to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex and presence of disease. While training load (volume × intensity) is a suitable predictor of changes in mitochondrial content and VO2max, this relationship is less clear for capillary adaptations.

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.

Performance-Related Physiological and Haematological Changes During Pregnancy and Postpartum in a Well-Trained Cyclist Performing Endurance Training.

Purpose: To describe the performance-related physiological and haematological changes in a well-trained cyclist (peak oxygen uptake, VO2peak: 54.9 ml min-1·kg-1) performing endurance training during pregnancy and postpartum. Methods: Training data was systemized by training form (endurance and resistance), intensity (low- (LIT), moderate-, and high-intensity training), and modality (cycling, running, hiking, XC-skiing, strength training and other). Power output at 4 mmol L-1 [BLa-] (L4), maximal aerobic power (Wmax), and VO2peak as well as haemoglobin mass, blood volume, plasma volume and red blood cell volume (RBCV) were measured at different time points during pregnancy and 12 weeks postpartum. Results: L4 and Wmax increased by 3% while absolute VO2peak was unaltered from gestational wk 2 to 14, despite 12 and 14% increases in RBCV and BV. After delivery, BV was reduced by 7% but RBCV was maintained 5% above start-pregnancy levels, while VO2peak almost returned to (-1%), and Wmax increased by 5% above start-pregnancy levels 12 weeks postpartum. Conclusion: This case-study illustrates a disassociation between increases in haematological values and VO2peak during pregnancy. Furthermore, a quick resumption of LIT and a gradually increasing intensity of training in the 12 weeks following delivery ensured a return to start-pregnancy levels of VO2peak and corresponding improvements in Wmax. Although general recommendations cannot be given on the basis of these data, this study provides a framework for investigating pregnant endurance athletes and contributes to the generation of new hypotheses in this field.

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 (Wmax) and power output (PO) at 4 mmol·L-1 blood lactate (W4mmol), 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 VO2peak were unaltered in both groups. The muscle protein content of ß-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.

The Aerobic and Anaerobic Contribution During Repeated 30-s Sprints in Elite Cyclists.

Although the ability to sprint repeatedly is crucial in road cycling races, the changes in aerobic and anaerobic power when sprinting during prolonged cycling has not been investigated in competitive elite cyclists. Here, we used the gross efficiency (GE)-method to investigate: (1) the absolute and relative aerobic and anaerobic contributions during 3 × 30-s sprints included each hour during a 3-h low-intensity training (LIT)-session by 12 cyclists, and (2) how the energetic contribution during 4 × 30-s sprints is affected by a 14-d high-volume training camp with (SPR, n = 9) or without (CON, n = 9) inclusion of sprints in LIT-sessions. The aerobic power was calculated based on GE determined before, after sprints, or the average of the two, while the anaerobic power was calculated by subtracting the aerobic power from the total power output. When repeating 30-s sprints, the mean power output decreased with each sprint (p < 0.001, ES:0.6-1.1), with the majority being attributed to a decrease in mean anaerobic power (first vs. second sprint: -36 ± 15 W, p < 0.001, ES:0.7, first vs. third sprint: -58 ± 16 W, p < 0.001, ES:1.0). Aerobic power only decreased during the third sprint (first vs. third sprint: -17 ± 5 W, p < 0.001, ES:0.7, second vs. third sprint: 16 ± 5 W, p < 0.001, ES:0.8). Mean power output was largely maintained between sets (first set: 786 ± 30 W vs. second set: 783 ± 30 W, p = 0.917, ES:0.1, vs. third set: 771 ± 30 W, p = 0.070, ES:0.3). After a 14-d high-volume training camp, mean power output during the 4 × 30-s sprints increased on average 25 ± 14 W in SPR (p < 0.001, ES:0.2), which was 29 ± 20 W more than CON (p = 0.008, ES: 0.3). In SPR, mean anaerobic power and mean aerobic power increased by 15 ± 13 W (p = 0.026, ES:0.2) and by 9 ± 6 W (p = 0.004, ES:0.2), respectively, while both were unaltered in CON. In conclusion, moderate decreases in power within sets of repeated 30-s sprints are primarily due to a decrease in anaerobic power and to a lesser extent in aerobic power. However, the repeated sprint-ability (multiple sets) and corresponding energetic contribution are maintained during prolonged cycling in elite cyclists. Including a small number of sprints in LIT-sessions during a 14-d training camp improves sprint-ability mainly through improved anaerobic power.

Effects of Including Sprints in LIT Sessions during a 14-d Camp on Muscle Biology and Performance Measures in Elite Cyclists.

PURPOSE: This study investigated the effects of including sprints within low-intensity training (LIT) sessions during a 14-d training camp focusing on LIT, followed by 10-d recovery (Rec), on performance and performance-related measures in elite cyclists. METHODS: During the camp, a sprint training group (SPR; n = 9) included 12 × 30-s maximal sprints during five LIT sessions, whereas a control group (CON; n = 9) performed distance-matched LIT only. Training load was equally increased in both groups by 48% ± 27% during the training camp and subsequently decreased by -56% ± 23% during the recovery period compared with habitual training. Performance tests were conducted before the training camp (Pre) and after Rec. Muscle biopsies, hematological measures, and stress/recovery questionnaires were collected Pre and after the camp (Post). RESULTS: Thirty-second sprint (SPR vs CON: 4% ± 4%, P < 0.01) and 5-min mean power (SPR vs CON: 4% ± 8%, P = 0.04) changed differently between groups. In muscle, Na+-K+ ß1 protein content changed differently between groups, decreasing in CON compared with SPR (-8% ± 14%, P = 0.04), whereas other proteins showed similar changes. SPR and CON displayed similar increases in red blood cell volume (SPR: 2.6% ± 4.7%, P = 0.07; CON: 3.9% ± 4.5%, P = 0.02) and V˙O2 at 4 mmol·L-1 [BLa-] (SPR: 2.5% ± 3.3%, P = 0.03; CON: 2.2% ± 3.0%, P = 0.04). No changes were seen for V˙O2max, Wmax, hematological measures, muscle enzyme activity, and stress/recovery measures. CONCLUSIONS: Inclusion of 30-s sprints within LIT sessions during a high-volume training camp affected competition-relevant performance measures and Na+-K+ ß1 protein content differently from LIT only, without affecting sport-specific stress/recovery or any other physiological measure in elite cyclists.

The Inclusion of Sprints in Low-Intensity Sessions During the Transition Period of Elite Cyclists Improves Endurance Performance 6 Weeks Into the Subsequent Preparatory Period.

PURPOSE: To investigate the effects of including repeated sprints in a weekly low-intensity (LIT) session during a 3-week transition period on cycling performance 6 weeks into the subsequent preparatory period (PREP) in elite cyclists. METHODS: Eleven elite male cyclists (age = 22.0 [3.8] y, body mass = 73.0 [5.8] kg, height = 186 [7] cm, maximal oxygen uptake [VO2max] = 5469 [384] mL·min-1) reduced their training load by 64% and performed only LIT sessions (CON, n = 6) or included 3 sets of 3 × 30-second maximal sprints in a weekly LIT session (SPR, n = 5) during a 3-week transition period. There was no difference in the reduction in training load during the transition period between groups. Physiological and performance measures were compared between the end of the competitive period and 6 weeks into the PREP. RESULTS: SPR demonstrated a 7.3% (7.2%) improvement in mean power output during a 20-minute all-out test at PREP, which was greater than CON (-1.3% [4.6%]) (P = .048). SPR had a corresponding 7.0% (3.6%) improvement in average VO2 during the 20-minute all-out test, which was larger than the 0.7% (6.0%) change in CON (P = .042). No change in VO2max, gross efficiency, or power output at blood lactate concentration of 4 mmol·L-1 from competitive period to PREP occurred in either group. CONCLUSION: Including sprints in a weekly LIT session during the transition period of elite cyclists provided a performance advantage 6 weeks into the subsequent PREP, which coincided with a higher performance VO2.

The Effect of 30-Second Sprints During Prolonged Exercise on Gross Efficiency, Electromyography, and Pedaling Technique in Elite Cyclists.

BACKGROUND: Cycling competitions are often of long duration and include repeated high-intensity efforts. PURPOSE: To investigate the effect of repeated maximal sprints during 4 hours of low-intensity cycling on gross efficiency (GE), electromyography patterns, and pedaling technique compared with work-matched low-intensity cycling in elite cyclists. METHODS: Twelve elite, male cyclists performed 4 hours of cycling at 50% of maximal oxygen uptake either with 3 sets of 3 × 30-second maximal sprints (E&S) during the first 3 hours or a work-matched cycling without sprints (E) in a randomized order. Oxygen uptake, electromyography, and pedaling technique were recorded throughout the exercises. RESULTS: GE was reduced from start to the end of exercise in both conditions (E&S: 19.0 [0.2] vs 18.1 [0.2], E: 19.1% [0.2%] vs 18.1% [0.2%], both P = .001), with no difference in change between conditions (condition × time interaction, P = .8). Integrated electromyography increased from start to end of exercise in m. vastus lateralis and m. vastus medialis (m. vastus medialis: 9.9 [2.4], m. vastus lateralis: 8.5 [4.0] mV, main effect of time: P < .001 and P = .03, respectively) and E&S increased less than E in m. vastus medialis (mean difference -3.3 [1.5] mV, main effect of condition: P = .03, interaction, P = .06). The mechanical effectiveness only decreased in E&S (E&S: -2.2 [0.7], effect size = 0.24 vs E: -1.3 [0.8] percentage points: P = .04 and P = .8, respectively). The mean power output during each set of 3 × 30-second sprints in E&S did not differ (P = .6). CONCLUSIONS: GE decreases as a function of time during 4 hours of low-intensity cycling. However, the inclusion of maximal repeated sprinting does not affect the GE changes, and the ability to sprint is maintained throughout the entire session.

Effects of Including Sprints in One Weekly Low-Intensity Training Session During the Transition Period of Elite Cyclists.

The purpose of this study was to investigate the effects of including 30-s sprints in one weekly low-intensity training (LIT) session during a 3-week transition period in elite cyclists. Sixteen male elite cyclists (maximal oxygen uptake, VO2max: 72 ± 5 ml·kg-1·min-1) reduced their training load by ~60% for 3 weeks from the end of competitive season and performed only LIT or included 30-s sprints (SPR) in one weekly LIT-session. Performance and physiological capacities were evaluated during a prolonged (~2.5 h) test-session, including a strength test, a submaximal blood lactate profile test, an incremental test to exhaustion to determine VO2max, 1 h continuous cycling including four maximal 30-s sprints, and a 20-min all-out test. In addition, mental recovery was evaluated using the Athlete Burnout Questionnaire (ARQ). The only significant between-group change during the transition period was an 8 ± 11% larger improvement in 30-s sprint performance in SPR compared to control (CON; SPR: 4 ± 5%, CON: -4 ± 5%, p = 0.01). Although not different from CON, SPR maintained 20-min all-out performance (-1 ± 5%, p = 0.37) and fractional utilization of VO2max (1.9 ± 6.1%-points, p = 0.18) during the 20-min all-out test, whereas corresponding declines were observed in CON (-3 ± 5%, p = 0.04, and -2.5 ± 2.9%-points, p = 0.02, respectively). Power output at 4 mmol·L-1 blood lactate concentration decreased similarly in SPR (-4 ± 4%, p = 0.02) and CON (-5 ± 5%, p = 0.01), while VO2max, maximal aerobic power (Wmax), and total burnout score were unaffected in both groups. Including sprints in one weekly LIT-session in the transition period improves sprint performance and maintains 20-min all-out power and fractional utilization of VO2max without compromising mental recovery. Inclusion of sprints in LIT-sessions may therefore be a plausible, time-efficient strategy during short periods of reduced training.

Effect of tapering after a period of high-volume sprint interval training on running performance and muscular adaptations in moderately trained runners.

The effect of tapering following a period of high-volume sprint interval training (SIT) and a basic volume of aerobic training on performance and muscle adaptations in moderately trained runners was examined. Eleven (8 men, 3 women) runners [maximum oxygen uptake (V̇o2max): 56.8 ± 2.9 ml·min-1·kg-1; mean ± SD] conducted high-volume SIT (HV; 20 SIT sessions; 8-12 × 30 s all-out) for 40 days followed by 18 days of tapering (TAP; 4 SIT sessions; 4 × 30 s all-out). Before and after HV as well as midway through and at the end of TAP, the subjects completed a 10-km running test and a repeated running test at 90% of vV̇o2max to exhaustion (RRT). In addition, a biopsy from the vastus lateralis muscle was obtained at rest. Performance during RRT was better ( P < 0.01) at the end of TAP than before HV (6.8 ± 0.5 vs. 5.6 ± 0.5 min; means ± SE), and 10-km performance was 2.7% better ( P < 0.05) midway through (40.7 ± 0.7 min) and at the end of (40.7 ± 0.6 min) TAP than after HV (41.8 ± 0.9 min). The expression of muscle Na+-K+-ATPase (NKA)α1, NKAß1, phospholemman (FXYD1), and sarcoplasmic reticulum calcium transport ATPase (SERCA1) increased ( P < 0.05) during HV and remained higher during TAP. In addition, oxygen uptake at 60% of vV̇o2max was lower ( P < 0.05) at the end of TAP than before and after HV. Thus short-duration exercise capacity and running economy were better than before the HV period together with higher expression of muscle proteins related to Na+/K+ transport and Ca2+ reuptake, while 10-km performance was not significantly improved by the combination of HV and tapering. NEW & NOTEWORTHY Short-duration performance became better after 18 days of tapering from ~6 wk of high-volume sprint interval training (SIT), whereas 10-km performance was not significantly affected by the combination of high-volume SIT and tapering. Higher expression of muscle NKAα1, NKAß1, FXYD1, and SERCA1 may reflect faster Na+/K+ transport and Ca2+ reuptake that could explain the better short-duration performance. These results suggest that the type of competition should determine the duration of tapering to optimize performance.

Effect of speed endurance training and reduced training volume on running economy and single muscle fiber adaptations in trained runners.

The aim of the present study was to examine whether improved running economy with a period of speed endurance training and reduced training volume could be related to adaptations in specific muscle fibers. Twenty trained male (n = 14) and female (n = 6) runners (maximum oxygen consumption (VO2 -max): 56.4 ± 4.6 mL/min/kg) completed a 40-day intervention with 10 sessions of speed endurance training (5-10 × 30-sec maximal running) and a reduced (36%) volume of training. Before and after the intervention, a muscle biopsy was obtained at rest, and an incremental running test to exhaustion was performed. In addition, running at 60% vVO2 -max, and a 10-km run was performed in a normal and a muscle slow twitch (ST) glycogen-depleted condition. After compared to before the intervention, expression of mitochondrial uncoupling protein 3 (UCP3) was lower (P < 0.05) and dystrophin was higher (P < 0.05) in ST muscle fibers, and sarcoplasmic reticulum calcium ATPase 1 (SERCA1) was lower (P < 0.05) in fast twitch muscle fibers. Running economy at 60% vVO2 -max (11.6 ± 0.2 km/h) and at v10-km (13.7 ± 0.3 km/h) was ~2% better (P < 0.05) after the intervention in the normal condition, but unchanged in the ST glycogen-depleted condition. Ten kilometer performance was improved (P < 0.01) by 3.2% (43.7 ± 1.0 vs. 45.2 ± 1.2 min) and 3.9% (45.8 ± 1.2 vs. 47.7 ± 1.3 min) in the normal and the ST glycogen-depleted condition, respectively. VO2 -max was the same, but vVO2 -max was 2.0% higher (P < 0.05; 19.3 ± 0.3 vs. 18.9 ± 0.3 km/h) after than before the intervention. Thus, improved running economy with intense training may be related to changes in expression of proteins linked to energy consuming processes in primarily ST muscle fibers.

Effect of increased and maintained frequency of speed endurance training on performance and muscle adaptations in runners.

The aim of the study was, in runners accustomed to speed endurance training (SET), to examine the effect of increased and maintained frequency of SET on performance and muscular adaptations. After familiarization (FAM) to SET, 18 male (n = 14) and female (n = 4) runners (V̇o2max: 57.3 ± 3.4 ml/min; means ± SD) completed 20 sessions of maintained low-frequency (LF; every fourth day; n = 7) or high-frequency (HF; every second day; n = 11) SET. Before FAM as well as before and after an intervention period (INT), subjects completed a series of running tests and a biopsy from m. vastus lateralis was collected. Ten-kilometer performance improved (P < 0.05) ~3.5% during FAM with no further change during INT. Time to exhaustion at 90% vV̇o2max was 15 and 22% longer (P < 0.05) during FAM and a further 12 and 16% longer (P < 0.05) during INT in HF and LF, respectively. During FAM, muscle expression of NHE1 and maximal activity of citrate synthase (CS) and phosphofructokinase (PFK) increased (P < 0.05), running economy (RE) improved (P < 0.05), and V̇o2max was unchanged. During INT, both HF and LF increased (P < 0.05) muscle expression of NKAß1, whereas maximal activity of CS and PFK, RE, and V̇o2max were unchanged. Furthermore, during INT, muscle expression of FXYD1 and SERCA1, and FXYD1 activity increased (P < 0.05) in HF, while muscle expression of SERCA2 decreased (P < 0.05) in LF. Thus increased or maintained frequency of SET leads to further improvements in short-term exercise capacity, but not in 10-km running performance. The better short-term exercise capacity may be associated with elevated expression of muscle proteins related to Na+/K+ transportation and Ca2+ reuptake. NEW & NOTEWORTHY: Ten speed endurance training (SET) sessions improved short-term exercise capacity and 10-km performance, which was followed by further improved short-term exercise capacity, but unchanged 10-km performance after 20 SET sessions performed with either high frequency (4 per 8 days) or continued low frequency (2 per 8 days) in trained runners. The further gain in short-term exercise capacity was associated with changes in muscle expression of proteins of importance for the development of fatigue.