The effects of training intensity on muscle buffer capacity in females

Saccharomyces boulardii supplementation does not affect anaerobic power gain induced by short-term sprint interval training in physically active individuals

Sprint interval training (SIT), which consists of vigorous-intensity exercise interspersed with periods of rest or low-intensity exercise, can improve human anaerobic performance. Probiotic strains, including yeasts (e.g. Saccharomyces boulardii; Sb), have beneficial effects on human health; however, evidence regarding the effects of probiotics on anaerobic performance is unavailable. The current study investigated whether Sb supplementation influences the SIT-induced changes to the following performance variables: peak (PPO) and mean (MPO) power output. Fifteen healthy individuals (twelve men and three women) were randomly divided into two groups: placebo (PLA; n=8) and Sb (n=7). The individuals performed six SIT sessions on a cycle ergometer (four to seven 30-s all-out sprints thrice weekly). During the training period, participants ingested a capsule containing PLA or at least 1×109 Sb cells daily for 14 days. Performance-related variables were compared between the first and last training sessions. Sb supplementation did not influence the changes in PPO and MPO across the two weeks of training (P>0.05); therefore, the data from both groups were analyzed collectively to assess performance changes induced by SIT. Training increased PPO, an index of anaerobic power, in the sixth session compared to the first session (by 8±11% in the first sprint; +1.0±1.2 W/kg; P=0.008) but did not change MPO. In conclusion, short-term SIT improved the participants' anaerobic performance (power), as evidenced by increased PPO. Sb supplementation did not affect the improved anaerobic power caused by SIT.

Reliability of a non-invasive method to calculate buffer capacity after exhaustive cycling exercise of 20 s to 12 min: a pilot study

Traditionally, buffer capacity (β) is measured on muscle biopsies by measuring changes in muscle pH in relation to exposure of standardized quantities of hydrochloric acid. This is an invasive approach requiring specific equipment and trained personnel which limits its usability in a normal training context. Assessing β using capillary blood lactate concentration (BLC) and pH values has been proposed as a more practical and cost-effective approach. The reliability of the input BLC and pH data on the calculations of β after maximal sprint and endurance exercise has not yet been investigated and was major aim of our study. Eleven subjects performed six maximal performance tests ranging from 20 s to 12 min duration over a 2-week period. All subjects were familiarized with the test conditions. For each performance test, pre and posttest BLC and pH was measured and used to calculate β using the Henderson-Hasselbach equation. As BLCpre and pHpre values showed poor reliability, β calculations were repeated using constants for BLCpre (1.23 mmol·L-1) and pHpre (7.426) chosen from the average values in the experimental data. Test-retest reliability for BLCpre (ICC: 0.12, 95% CI -0.49-0.65, n.s.) and pHpre (ICC: 0.40, 95% CI -0.22-0.79, n.s.) was poor, whereas BLCpost (ICC: 0.95, 95% CI 0.82-0.99, p < 0.05) and pHpost (ICC: 0.89, 95% CI 0.65-0.97, p < 0.05) displayed good to excellent reliability. Good reliability was observed for β calculated from the Henderson-Hasselbalch equation utilizing BLCpost and pHpost only (ICC: 0.86, 95% CI 0.55-0.96, p < 0.05). The validity of this method in comparison with gold-standard methods needs further scientific investigation.

Efficacy of Interval Training in Improving Body Composition and Adiposity in Apparently Healthy Adults: An Umbrella Review with Meta-Analysis

BACKGROUND

Although the efficacy of interval training for improving body composition has been summarized in an increasing number of systematic reviews in recent years, discrepancies in review findings and conclusions have been observed.

OBJECTIVE

This study aims to synthesize the available evidence on the efficacy of interval training compared with moderate-intensity continuous training (MICT) and nonexercise control (CON) in reducing body adiposity in apparently healthy adults.

METHODS

An umbrella review with meta-analysis was performed. A systematic search was conducted in seven databases (MEDLINE, EMBASE, Cochrane Database, CINAHL, Scopus, SPORTDiscus, and Web of Science) up to October 2023. Systematic reviews with meta-analyses of randomized controlled trials (RCTs) comparing interval training and MICT/CON were included. Literature selection, data extraction, and methodological quality assessment (AMSTAR-2) were conducted independently by two reviewers. Meta-analyses were performed using a random-effects model. Subgroup analyses were conducted based on the type of interval training [high-intensity interval training (HIIT) and sprint interval training (SIT)], intervention duration, body mass index, exercise modality, and volume of HIIT protocols.

RESULTS

Sixteen systematic reviews, including 79 RCTs and 2474 unique participants, met the inclusion criteria. Most systematic reviews had a critically low (n = 6) or low (n = 6) AMSTAR-2 score. Interval training demonstrated significantly greater reductions in total body fat percent (BF%) compared with MICT [weighted mean difference (WMD) of - 0.77%; 95% confidence interval (CI) - 1.12 to - 0.32%] and CON (WMD of - 1.50%; 95% CI - 2.40 to - 0.58%). Significant reductions in fat mass, visceral adipose tissue, subcutaneous abdominal fat, and android abdominal fat were also observed following interval training compared to CON. Subgroup analyses indicated that both HIIT and SIT resulted in superior BF% loss than MICT. These benefits appeared to be more prominent in individuals with overweight/obesity and longer duration interventions (≥ 12 weeks), as well as in protocols using cycling as a modality and low-volume HIIT (i.e., < 15 min of high-intensity exercise per session).

CONCLUSIONS

This novel umbrella review with large-scale meta-analysis provides an updated synthesis of evidence with implications for physical activity guideline recommendations. The findings support interval training as a viable exercise strategy for reducing adiposity in the general population.

Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance: A Systematic Review with Meta-analysis

BACKGROUND

Polarized training intensity distribution (POL) was recently suggested to be superior to other training intensity distribution (TID) regimens for endurance performance improvement.

OBJECTIVE

We aimed to systematically review and meta-analyze evidence comparing POL to other TIDs on endurance performance.

METHODS

PRISMA guidelines were followed. The protocol was registered at PROSPERO (CRD42022365117). PubMed, Scopus, and Web of Science were searched up to 20 October 2022 for studies in adults and young adults for ≥ 4 weeks comparing POL with other TID interventions regarding VO2peak, time-trial (TT), time to exhaustion (TTE) or speed or power at the second ventilatory or lactate threshold (V/P at VT2/LT2). Risk of bias was assessed with RoB-2 and ROBINS-I. Certainty of evidence was assessed with GRADE. Results were analyzed by random effects meta-analysis using standardized mean differences.

RESULTS

Seventeen studies met the inclusion criteria (n = 437 subjects). Pooled effect estimates suggest POL superiority for improving VO2peak (SMD = 0.24 [95% CI 0.01, 0.48]; z = 2.02 (p = 0.040); 11 studies, n = 284; I2 = 0%; high certainty of evidence). Superiority, however, only occurred in shorter interventions (< 12 weeks) (SMD = 0.40 [95% CI 0.08, 0.71; z = 2.49 (p = 0.01); n = 163; I2 = 0%) and for highly trained athletes (SMD = 0.46 [95% CI 0.10, 0.82]; z = 2.51 (p = 0.01); n = 125; I2 = 0%). The remaining endurance performance surrogates were similarly affected by POL and other TIDs: TT (SMD = - 0.01 [95% CI -0.28, 0.25]; z =  - 0.10 (p = 0.92); n = 221; I2 = 0%), TTE (SMD = 0.30 [95% CI - 0.20, 0.79]; z = 1.18 (p = 0.24); n = 66; I2 = 0%) and V/P VT2/LT2 (SMD = 0.04 [95% CI -0.21, 0.29]; z = 0.32 (p = 0.75); n = 253; I2 = 0%). Risk of bias for randomized controlled trials was rated as of some concern and for non-randomized controlled trials as low risk of bias (two studies) and some concerns (one study).

CONCLUSIONS

POL is superior to other TIDs for improving VO2peak, particularly in shorter duration interventions and highly trained athletes. However, the effect of POL was similar to that of other TIDs on the remaining surrogates of endurance performance. The results suggest that POL more effectively improves aerobic power but is similar to other TIDs for improving aerobic capacity.

Effect of 6-Week Sprint Training on Long-Distance Running Performance in Highly Trained Runners

PURPOSE

Long-distance running performance has been reported to be associated with sprint performance in highly trained distance runners. Therefore, we hypothesized that sprint training could enhance distance running and sprint performance in long-distance runners. This study examined the effect of 6-week sprint training on long-distance running and sprint performance in highly trained distance runners.

METHODS

Nineteen college runners were divided into control (n = 8) and training (n = 11) groups. Participants in the training group performed 12 sprint training sessions in 6 weeks, while those in the control group performed 12 distance training sessions. Before and after the interventions, maximal oxygen uptake (V˙O2max), O2 cost during submaximal running (290 m·min-1 and 310 m·min-1 of running velocity), and time to exhaustion (starting at 290 m·min-1 and increased 10 m·min-1 every minute) were assessed on a treadmill. Additionally, the 100-m and 400-m sprinting times and 3000-m running time were determined on an all-weather track.

RESULTS

In the control group, no measurements significantly changed after the intervention. In the training group, the time to exhaustion, 100-m and 400-m sprinting times, and 3000-m running time improved significantly, while V˙O2max and O2 cost did not change.

CONCLUSIONS

These results showed that 6-week sprint training improved both sprint and long-distance running performance in highly trained distance runners without a change in aerobic capacity. Improvement in the time to exhaustion without a change in V˙O2max suggests that the enhancement of long-distance running performance could be attributable to improved anaerobic capacity.

Influence of Ingestion of Bicarbonate-Rich Water Combined with an Alkalizing or Acidizing Diet on Acid-Base Balance and Anaerobic Performance

During high-intensity (HI) exercise, metabolic acidosis significantly impairs exercise performance. Increasing the body's buffering capacity through training and exogenous intake of alkalizing supplements may improve high-intensity performance. Manipulating water and diet intake may influence the acid-base balance. The aim of this study was to determine the effects of mineral water rich in bicarbonate ions (STY) or placebo water (PLA) on circulating biomarkers and anaerobic performance and to verify whether alkalizing (ALK) or acidizing (ACI) diet would modulate these effects. Twenty-four athletes, assigned either to ALK (n = 12) or ACI (n = 12) diet for four weeks, completed a 1-min rowing Wingate Test in a double-blind and randomized trial after one week of daily hydration (1.5 to 2L/d) with either STY or PLA. Blood samples were taken before and after each test, and urine samples were collected each week. Chronic consumption of bicarbonate-rich water significantly impacted resting urinary pH irrespective of alkalizing or acidizing dietary intake. STY induced a significant increase in blood pH, lactate, and HCO3 - ion concentration post-exercise compared to PLA. Similar changes were observed when STY was associated with the ALK diet. In contrast, STY combined with the ACI diet only significantly affected urine pH and peak blood lactate compared to PLA (p < 0.05). No effect of bicarbonate-rich water was reported on anaerobic performance (p > 0.05). Our results suggest that consumption of bicarbonate-rich water alters acid-base balance during a warm-up and after HI exercise, could potentiate beneficial effects of an alkalizing diet on the acid-base balance after HI exercise, and reduces the acid load induced by an acidifying diet.

Endurance Performance Adaptations between SSG and HIIT in Soccer Players: A Meta-analysis

The objective of this systematic review with meta-analysis was to compare the endurance performance chronic adaptations induced by running-based high-intensity interval training (HIIT), small-sided games (SSGs), and combined HIIT+SSGs in male and female youth and adult soccer players. The studies included in this review followed the PICOS criteria: (i) healthy soccer players; (ii) interventions based on SSGs; (iii) comparators exposed to only HIIT or combined SSGs+HIIT; (iv) endurance performance variables. Studies were searched for in the following databases: (i) PubMed; (ii) Scopus; (iii) SPORTDiscus; (iv) Web of Science. After conducting an initial database search that retrieved a total of 5,389 records, a thorough screening process resulted in the inclusion of 20 articles that met the eligibility criteria. Sixteen studies reported outcomes related to endurance performance measured through field-based tests, while five studies provided results from direct measurements of maximal oxygen uptake (VO2max). Results showed a non-significant small-magnitude favoring effect for the HIIT groups compared to the SSG groups (ES=0.37, p=0.074) for endurance, while a non-significant small-magnitude favoring SSGs was observed (ES=-0.20, p=0.303) for VO2max. Despite the very low certainty of evidence, the findings suggest similar effects induced by both SSG and HIIT on improving endurance performance and VO2max.

Aerobic capacity and V ˙ O 2 kinetics adaptive responses to short-term high-intensity interval training and detraining in untrained females

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics (τV ˙ O 2 p ) along with the O2 delivery and utilization (heart rate kinetics, τHR; deoxyhemoglobin/V ˙ O 2 ratio, ∆[HHb]/V ˙ O 2 ) adaptations of untrained female participants responding to 4 weeks of high-intensity interval training (HIIT) and 2 weeks of detraining.

METHODS

Participants were randomly assigned to HIIT (n = 11, 4 × 4 protocol) or nonexercising control (n = 9) groups. Exercising group engaged 4 weeks of treadmill HIIT followed by 2 weeks of detraining while maintaining daily activity level. Ramp-incremental (RI) tests and step-transitions to moderate-intensity exercise were performed. Aerobic capacity and performance (maximal oxygen uptake,V ˙ O 2 max ; gas-exchange threshold, GET; power output, PO), body composition (skeletal muscle mass, SMM; body fat percentage, BF%), muscle oxygenation status (∆[HHb]),V ˙ O 2 , and HR kinetics were assessed.

RESULTS

HIIT elicited improvements in aerobic capacity (V ˙ O 2 max , + 0.17 ± 0.04 L/min; GET, + 0.18 ± 0.05 L/min, P < 0.01; PO-V ˙ O 2 max , ± 23.36 ± 8.37 W; PO-GET, + 17.18 ± 3.07 W, P < 0.05), body composition (SMM, + 0.92 ± 0.17 kg; BF%, - 3.08% ± 0.58%, P < 0.001), and speed up the τV ˙ O 2 p (- 8.04 ± 1.57 s, P < 0.001) significantly, extending to better ∆[HHb]/V ˙ O 2 ratio (1.18 ± 0.08 to 1.05 ± 0.14). After a period of detraining, the adaptation in body composition and aerobic capacity, as well as the accelerated τV ˙ O 2 p were maintained in the HIIT group, but the PO-V ˙ O 2 max and PO-GET declined below the post-training level (P < 0.05), whereas no changes were reported in controls (P > 0.05). Four weeks of HIIT induced widespread physiological adaptations in females, and the majority of improvements were preserved after 2 weeks of detraining except for power output corresponding toV ˙ O 2 max and GET.

Aerobic Training With Blood Flow Restriction for Endurance Athletes: Potential Benefits and Considerations of Implementation

ABSTRACT

Smith, NDW, Scott, BR, Girard, O, and Peiffer, JJ. Aerobic training with blood flow restriction for endurance athletes: potential benefits and considerations of implementation. J Strength Cond Res 36(12): 3541-3550, 2022-Low-intensity aerobic training with blood flow restriction (BFR) can improve maximal oxygen uptake, delay the onset of blood lactate accumulation, and may provide marginal benefits to economy of motion in untrained individuals. Such a training modality could also improve these physiological attributes in well-trained athletes. Indeed, aerobic BFR training could be beneficial for those recovering from injury, those who have limited time for training a specific physiological capacity, or as an adjunct training stimulus to provide variation in a program. However, similarly to endurance training without BFR, using aerobic BFR training to elicit physiological adaptations in endurance athletes will require additional considerations compared with nonendurance athletes. The objective of this narrative review is to discuss the acute and chronic aspects of aerobic BFR exercise for well-trained endurance athletes and highlight considerations for its effective implementation. This review first highlights key physiological capacities of endurance performance. The acute and chronic responses to aerobic BFR exercise and their impact on performance are then discussed. Finally, considerations for prescribing and monitoring aerobic BFR exercise in trained endurance populations are addressed to challenge current views on how BFR exercise is implemented.

Augmented muscle deoxygenation during repeated sprint exercise with post-exercise blood flow restriction

Blood flow restriction (BFR) during low-intensity exercise has been known to be a potent procedure to alter metabolic and oxygen environments in working muscles. Moreover, the use of BFR during inter-set rest periods of repeated sprint exercise has been recently suggested to be a potent procedure for improving training adaptations. The present study was designed to determine the effect of repeated sprint exercise with post-exercise BFR (BFR during rest periods between sprints) on muscle oxygenation in working muscles. Eleven healthy males performed two different conditions on different days: either repeated sprint exercise with BFR during rest periods between sets (BFR condition) or without BFR (CON condition). A repeated sprint exercise consisted of three sets of 3 × 6-s maximal sprints (pedaling) with 24s rest periods between sprints and 5 min rest periods between sets. In BFR condition, two min of BFR (100-120 mmHg) for both legs was conducted between sets. During the exercise, power output and arterial oxygen saturation (SpO2 ) were evaluated. Muscle oxygenation for the vastus lateralis muscle, exercise-induced changes in muscle blood flow, and muscle oxygen consumption were measured. During BFR between sets, BFR condition presented significantly higher deoxygenated hemoglobin + myoglobin (p < 0.01) and lower tissue saturation index (p < 0.01) than those in CON condition. However, exercise-induced blood lactate elevation and reduction of blood pH did not differ significantly between the conditions. Furthermore, power output throughout nine sprints did not differ significantly between the two conditions. In conclusion, repeated sprint exercise with post-exercise BFR augmented muscle deoxygenation and local hypoxia, without interfering power output.

Extracellular Buffering Supplements to Improve Exercise Capacity and Performance: A Comprehensive Systematic Review and Meta-analysis

BACKGROUND

Extracellular buffering supplements [sodium bicarbonate (SB), sodium citrate (SC), sodium/calcium lactate (SL/CL)] are ergogenic supplements, although questions remain about factors which may modify their effect.

OBJECTIVE

To quantify the main effect of extracellular buffering agents on exercise outcomes, and to investigate the influence of potential moderators on this effect using a systematic review and meta-analytic approach.

METHODS

This study was designed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Three databases were searched for articles that were screened according to inclusion/exclusion criteria. Bayesian hierarchical meta-analysis and meta-regression models were used to investigate pooled effects of supplementation and moderating effects of a range of factors on exercise and biomarker responses.

RESULTS

189 articles with 2019 participants were included, 158 involving SB supplementation, 30 with SC, and seven with CL/SL; four studies provided a combination of buffering supplements together. Supplementation led to a mean estimated increase in blood bicarbonate of + 5.2 mmol L^-1 (95% credible interval (CrI) 4.7-5.7). The meta-analysis models identified a positive overall effect of supplementation on exercise capacity and performance compared to placebo [ES_0.5 = 0.17 (95% CrI 0.12-0.21)] with potential moderating effects of exercise type and duration, training status and when the exercise test was performed following prior exercise. The greatest ergogenic effects were shown for exercise durations of 0.5-10 min [ES_0.5 = 0.18 (0.13-0.24)] and > 10 min [ES_0.5 = 0.22 (0.10-0.33)]. Evidence of greater effects on exercise were obtained when blood bicarbonate increases were medium (4-6 mmol L^-1) and large (> 6 mmol L^-1) compared with small (≤ 4 mmol L^-1) [β_Small:Medium = 0.16 (95% CrI 0.02-0.32), β_Small:Large = 0.13 (95% CrI - 0.03 to 0.29)]. SB (192 outcomes) was more effective for performance compared to SC (39 outcomes) [β_SC:SB = 0.10 (95% CrI - 0.02 to 0.22)].

CONCLUSIONS

Extracellular buffering supplements generate large increases in blood bicarbonate concentration leading to positive overall effects on exercise, with sodium bicarbonate being most effective. Evidence for several group-level moderating factors were identified. These data can guide an athlete's decision as to whether supplementation with buffering agents might be beneficial for their specific aims.

Physiological profile comparison between high intensity functional training, endurance and power athletes

INTRODUCTION

High intensity functional trainings (HIFT), a recent development of high intensity trainings, includes in the same training session components of endurance exercises, elements of Olympic weightlifting and powerlifting, gymnastics, plyometrics and calisthenics exercises. Therefore, subjects practicing this type of activity are supposed to show physiological features that represent a combination of both endurance and power athletes. The aim of this study was to compare the physiological profile of three groups of age-matched endurance, HIFT and power athletes.

METHODS

A total of 30 participants, 18 to 38-year-old men were enrolled in the study. Participants were divided in three groups: HIFT (n = 10), endurance (END, n = 10), and power (POW, weightlifters, n = 10) athletes. All were evaluated for anthropometric characteristics, VO_2peak, handgrip, lower limb maximal isometric and isokinetic strength, countermovement vertical jump and anaerobic power through a shuttle run test on the field.

RESULTS

VO_2peak/kg was higher in END and HIFT than POW athletes (p = 0.001 and p = 0.007, respectively), but there were no significant differences between the first two. POW and HIFT athletes showed significant greater strength at the handgrip, countermovement jump and leg extension/flexion tests than END athletes. HIFT athletes showed highest results at the dynamic isokinetic test, while there were no significant differences at the shuttle run test among groups.

CONCLUSIONS

As HIFT reach aerobic levels similar to END athletes and power and strength output similar to POW athletes, it appears that HIFT programs are effective to improve both endurance-related and power-related physical fitness components.

High-Intensity Conditioning for Combat Athletes: Practical Recommendations

Combat sports have been practiced for millennia and today are predominant sports at the Olympic games, with international organizations that host world, continental and national championships at amateur standard. There are also an increasing number of professional combat sports with global audiences. The growing popularity of professional combat sports and their importance at the Olympic games have led to an increase in scientific studies that characterize the physical, physiological, nutritional, biomechanical and training strategies of combat sports athletes. These studies characterize combat sports as high-intensity sports which require training strategies to develop the high-intensity capabilities of athletes. Therefore, the aim of this article is to (i) summarize the physiological demands of combat sports; (ii) present the primary considerations required to program high-intensity conditioning for athletes; (iii) define and present key high-intensity conditioning methods; and (iv) provide guidance for scientists and coaches to help prepare athletes under common but differing circumstances.

Training-intensity Distribution on Middle- and Long-distance Runners: A Systematic Review

Training-intensity distribution (TID) is considered the key factor to optimize performance in endurance sports. This systematic review aimed to: I) characterize the TID typically used by middle-and long-distance runners; II) compare the effect of different types of TID on endurance performance and its physiological determinants; III) determine the extent to which different TID quantification methods can calculate same TID outcomes from a given training program. The keywords and search strategy identified 20 articles in the research databases. These articles demonstrated differences in the quantification of the different training-intensity zones among quantification methods (i. e. session-rating of perceived exertion, heart rate, blood lactate, race pace, and running speed). The studies that used greater volumes of low-intensity training such as those characterized by pyramidal and polarized TID approaches, reported greater improvements in endurance performance than those which used a threshold TID. Thus, it seems that the combination of high-volume at low-intensity (≥ 70% of overall training volume) and low-volume at threshold and high-intensity interval training (≤ 30%) is necessary to optimize endurance training adaptations in middle-and long-distance runners. Moreover, monitoring training via multiple mechanisms that systematically encompasses objective and subjective TID quantification methods can help coaches/researches to make better decisions.

Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance

Exercise causes major shifts in multiple ions (e.g., K⁺ , Na⁺ , H⁺ , lactate^- , Ca²⁺ , and Cl^- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K⁺ , Na⁺ , and Ca²⁺ during fatiguing exercise, while changes in gradients for Cl^- and Cl^- conductance may exert either protective or detrimental effects on fatigue. Myocellular H⁺ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca²⁺ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na⁺ /K⁺ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K⁺ and Cl^- , respectively via metabolic regulation of the ATP-sensitive K⁺ channel (K_ATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.

Biological and methodological factors affecting V ̇ O 2 max response variability to endurance training and the influence of exercise intensity prescription

NEW FINDINGS

What is the topic of this review? Biological and methodological factors associated with the variable changes in cardiorespiratory fitness in response to endurance training. What advances does it highlight? Several biological and methodological factors exist that each contribute, to a given extent, to response variability. Notably, prescribing exercise intensity relative to physiological thresholds reportedly increases cardiorespiratory fitness response rates compared to when prescribed relative to maximum physiological values. As threshold-based approaches elicit more homogeneous acute physiological responses among individuals, when repeated over time, these uniform responses may manifest as more homogeneous chronic adaptations thereby reducing response variability.

ABSTRACT

Changes in cardiorespiratory fitness (CRF) in response to endurance training (ET) exhibit large variations, possibly due to a multitude of biological and methodological factors. It is acknowledged that ∼20% of individuals may not achieve meaningful increases in CRF in response to ET. Genetics, the most potent biological contributor, has been shown to explain ∼50% of response variability, whilst age, sex and baseline CRF appear to explain a smaller proportion. Methodological factors represent the characteristics of the ET itself, including the type, volume and intensity of exercise, as well as the method used to prescribe and control exercise intensity. Notably, methodological factors are modifiable and, upon manipulation, alter response rates to ET, eliciting increases in CRF regardless of an individual's biological predisposition. Particularly, prescribing exercise intensity relative to a physiological threshold (e.g., ventilatory threshold) is shown to increase CRF response rates compared to when intensity is anchored relative to a maximum physiological value (e.g., maximum heart rate). It is, however, uncertain whether the increased response rates are primarily attributable to reduced response variability, greater mean changes in CRF or both. Future research is warranted to elucidate whether more homogeneous chronic adaptations manifest over time among individuals, as a result of exposure to more homogeneous exercise stimuli elicited by threshold-based practices.

Hormonal Contraceptive Use Does Not Affect Strength, Endurance, or Body Composition Adaptations to Combined Strength and Endurance Training in Women

ABSTRACT

Myllyaho, MM, Ihalainen, JK, Hackney, AC, Valtonen, M, Nummela, A, Vaara, E, Häkkinen, K, Kyröläinen, H, and Taipale, RS. Hormonal contraceptive use does not affect strength, endurance, or body composition adaptations to combined strength and endurance training in women. J Strength Cond Res 35(2): 449-457, 2021-This study examined the effects of a 10-week period of high-intensity combined strength and endurance training on strength, endurance, body composition, and serum hormone concentrations in physically active women using hormonal contraceptives (HCs, n = 9) compared with those who had never used hormonal contraceptives (NHCs, n = 9). Training consisted of 2 strength training sessions and 2 high-intensity running interval sessions per week. Maximal bilateral isometric leg press (Isom), maximal bilateral dynamic leg press (one repetition maximum [1RM]), countermovement jump (CMJ), a 3,000-m running test (3,000 m), body composition, and serum hormone levels were measured before and after training between days 1-5 of each subject's menstrual cycle. Both groups increased 1RM and CMJ: HC = 13.2% (p < 0.001) and 9.6% (p < 0.05), and NHC = 8.3% (p < 0.01) and 8.5% (p < 0.001). Hormonal contraceptive improved 3,000 m by 3.5% (p < 0.05) and NHC by 1% (n.s.). Never used hormonal contraceptive increased lean mass by 2.1% (p < 0.001), whereas body fat percentage decreased from 23.9 ± 6.7 to 22.4 ± 6.0 (-6.0%, p < 0.05). No significant changes were observed in body composition in HC. No significant between-group differences were observed in any of the performance variables. Luteinizing hormone concentrations decreased significantly (p < 0.05) over 10 weeks in NHC, whereas other hormone levels remained statistically unaltered in both groups. It seems that the present training is equally appropriate for improving strength, endurance, and body composition in women using HC as those not using HC without disrupting hypothalamic-pituitary-gonadal axis function.

Effects of high intensity interval exercise on cerebrovascular function: A systematic review

High intensity interval exercise (HIIE) improves aerobic fitness with decreased exercise time compared to moderate continuous exercise. A gap in knowledge exists regarding the effects of HIIE on cerebrovascular function such as cerebral blood velocity and autoregulation. The objective of this systematic review was to ascertain the effect of HIIE on cerebrovascular function in healthy individuals. We searched PubMed and the Cumulative Index to Nursing and Allied Health Literature databases with apriori key words. We followed the Preferred Reporting Items for Systematic Reviews. Twenty articles were screened and thirteen articles were excluded due to not meeting the apriori inclusion criteria. Seven articles were reviewed via the modified Sackett’s quality evaluation. Outcomes included middle cerebral artery blood velocity (MCAv) (n = 4), dynamic cerebral autoregulation (dCA) (n = 2), cerebral de/oxygenated hemoglobin (n = 2), cerebrovascular reactivity to carbon dioxide (CO₂) (n = 2) and cerebrovascular conductance/resistance index (n = 1). Quality review was moderate with 3/7 to 5/7 quality criteria met. HIIE acutely lowered exercise MCAv compared to moderate intensity. HIIE decreased dCA phase following acute and chronic exercise compared to rest. HIIE acutely increased de/oxygenated hemoglobin compared to rest. HIIE acutely decreased cerebrovascular reactivity to higher CO₂ compared to rest and moderate intensity. The acute and chronic effects of HIIE on cerebrovascular function vary depending on the outcomes measured. Therefore, future research is needed to confirm the effects of HIIE on cerebrovascular function in healthy individuals and better understand the effects in individuals with chronic conditions. In order to conduct rigorous systematic reviews in the future, we recommend assessing MCAv, dCA and CO₂ reactivity during and post HIIE.

Heart rate and stroke rate misrepresent supramaximal sprint kayak training as quantified by power

This study examined the utility of novel measures of power output (PO) compared to traditional measures of heart rate (HR) and stroke rate (SR) for quantifying high-intensity sprint kayak training. Twelve well-trained, male and female sprint kayakers (21.3 ± 6.8 y) completed an on-water graded exercise test (GXT) and a 200-, 500- and 1000-m time-trial for the delineation of individualised training zones (T) for HR (5-zone model, T1-T5), SR and PO (8-zone model, T1-T8). Subsequently, athletes completed two repeat trials of a high-intensity interval (HIIT) and a sprint interval (SIT) training session, where intensity was prescribed using individualised PO-zones. Time-in-zone (minutes) using PO, SR and HR was then compared for both HIIT and SIT. Compared to PO, time-in-zone using HR was higher for T1 in HIIT and SIT (P < 0.001, d ≥ 0.90) and lower for T5 in HIIT (P < 0.001, d = 1.76). Average and peak HR were not different between HIIT (160 ± 9 and 173 ± 11 bpm, respectively) and SIT (157 ± 13 and 174 ± 10 bpm, respectively) (P ≥ 0.274). In HIIT, time-in-zone using SR was higher for T4 (P < 0.001, d = 0.85) and was lower for T5 (P = 0.005, d = 0.43) and T6 (P < 0.001, d = 0.94) compared to PO. In SIT, time-in-zone using SR was lower for T7 (P = 0.001, d = 0.66) and was higher for T8 (P = 0.004, d = 0.70), compared to PO. Heart rate measures were unable to differentiate training demands across different high-intensity sessions, and could therefore misrepresent the training load in such instances. Furthermore, SR may not provide a sensitive measure for detecting changes in intensity due to fatigue, whereas PO may be more suitable.

The Effect of Low-Volume High-Intensity Interval Training on Body Composition and Cardiorespiratory Fitness: A Systematic Review and Meta-Analysis

BACKGROUND

Evidence for the efficacy of low-volume high-intensity interval training (HIIT) for the modulation of body composition is unclear.

OBJECTIVES

We examined the effect of low-volume HIIT versus a non-exercising control and moderate-intensity continuous training (MICT) on body composition and cardiorespiratory fitness in normal weight, overweight and obese adults. We evaluated the impact of low-volume HIIT (HIIT interventions where the total amount of exercise performed during training was ≤ 500 metabolic equivalent minutes per week [MET-min/week]) compared to a non-exercising control and MICT.

METHODS

A database search was conducted in PubMed (MEDLINE), EMBASE, CINAHL, Web of Science, SPORTDiscus and Scopus from the earliest record to June 2019 for studies (randomised controlled trials and non-randomised controlled trials) with exercise training interventions with a minimum 4-week duration. Meta-analyses were conducted for between-group (low-volume HIIT vs. non-exercising control and low-volume HIIT vs. MICT) comparisons for change in total body fat mass (kg), body fat percentage (%), lean body mass (kg) and cardiorespiratory fitness.

RESULTS

From 11,485 relevant records, 47 studies were included. No difference was found between low-volume HIIT and a non-exercising control on total body fat mass (kg) (effect size [ES]: - 0.129, 95% confidence interval [CI] - 0.468 to 0.210; p = 0.455), body fat (%) (ES: - 0.063, 95% CI - 0.383 to 0.257; p = 0.700) and lean body mass (kg) (ES: 0.050, 95% CI - 0.250 to 0.351; p = 0.744), or between low-volume HIIT and MICT on total body fat mass (kg) (ES: - 0.021, 95% CI - 0.272 to 0.231; p = 0.872), body fat (%) (ES: 0.005, 95% CI - 0.294 to 0.304; p = 0.974) and lean body mass (kg) (ES: 0.030, 95% CI - 0.167 to 0.266; p = 0.768). However, low-volume HIIT significantly improved cardiorespiratory fitness compared with a non-exercising control (p < 0.001) and MICT (p = 0.017).

CONCLUSION

These data suggest that low-volume HIIT is inefficient for the modulation of total body fat mass or total body fat percentage in comparison with a non-exercise control and MICT. A novel finding of our meta-analysis was that there appears to be no significant effect of low-volume HIIT on lean body mass when compared with a non-exercising control, and while most studies tended to favour improvement in lean body mass with low-volume HIIT versus MICT, this was not significant. However, despite its lower training volume, low-volume HIIT induces greater improvements in cardiorespiratory fitness than a non-exercising control and MICT in normal weight, overweight and obese adults. Low-volume HIIT, therefore, appears to be a time-efficient treatment for increasing fitness, but not for the improvement of body composition.

High intensity interval training and molecular adaptive response of skeletal muscle

Increased cardiovascular fitness, V˙O_2max, is associated with enhanced endurance capacity and a decreased rate of mortality. High intensity interval training (HIIT) is one of the best methods to increase V˙O_2max and endurance capacity for top athletes and for the general public as well. Because of the high intensity of this type of training, the adaptive response is not restricted to Type I fibers, as found for moderate intensity exercise of long duration. Even with a short exercise duration, HIIT can induce activation of AMPK, PGC-1α, SIRT1 and ROS pathway as well as by the modulation of Ca²⁺ homeostasis, leading to enhanced mitochondrial biogenesis, and angiogenesis. The present review summarizes the current knowledge of the adaptive response of HIIT.

Effect of β-alanine supplementation during high-intensity interval training on repeated sprint ability performance and neuromuscular fatigue

The study investigated the influence of β-alanine supplementation during a high-intensity interval training (HIIT) program on repeated sprint ability (RSA) performance. This study was randomized, double-blinded, and placebo controlled. Eighteen men performed an incremental running test until exhaustion (TINC) at baseline and followed by 4-wk HIIT (10 × 1-min runs 90% maximal TINCvelocity [1-min recovery]). Then, participants were randomized into two groups and performed a 6-wk HIIT associated with supplementation of 6.4 g/day of β-alanine (Gβ) or dextrose (placebo group; GP). Pre- and post-6-wk HIIT + supplementation, participants performed the following tests: 1) TINC; 2) supramaximal running test; and 3) 2 × 6 × 35-m sprints (RSA). Before and immediately after RSA, neuromuscular function was assessed by vertical jumps, maximal isometric voluntary contractions of knee extension, and neuromuscular electrical stimulations. Muscle biopsies were performed to determine muscle carnosine content, muscle buffering capacity in vitro (βmin vitro), and content of phosphofructokinase (PFK), monocarboxylate transporter 4 (MCT4), and hypoxia-inducible factor-1α (HIF-1α). Both groups showed a significant time effect for maximal oxygen uptake (Gβ: 6.2 ± 3.6% and GP: 6.5 ± 4.2%; P > 0.01); only Gβ showed a time effect for total (−3.0 ± 2.0%; P = 0.001) and best (−3.3 ± 3.0%; P = 0.03) RSA times. A group-by-time interaction was shown after HIIT + Supplementation for muscle carnosine (Gβ: 34.4 ± 2.3 mmol·kg−1·dm−1and GP: 20.7 ± 3.0 mmol·kg−1·dm−1; P = 0.003) and neuromuscular voluntary activation after RSA (Gβ: 87.2 ± 3.3% and GP: 78.9 ± 12.4%; P = 0.02). No time effect or group-by-time interaction was shown for supramaximal running test performance, βm, and content of PFK, MCT4, and HIF-1α. In summary, β-alanine supplementation during HIIT increased muscle carnosine and attenuated neuromuscular fatigue, which may contribute to an enhancement of RSA performance.

NEW & NOTEWORTHY β-Alanine supplementation during a high-intensity interval training program increased repeated sprint performance. The improvement of muscle carnosine content induced by β-alanine supplementation may have contributed to an attenuation of central fatigue during repeated sprint. Overall, β-alanine supplementation may be a useful dietary intervention to prevent fatigue.

Movement patterns of players in the Australian Women's Rugby League team during international competition

OBJECTIVES

To describe the movement patterns of the Australian Women's Rugby League team during international competition.

DESIGN

Retrospective observational study.

METHODS

Global Positioning Systems technology recorded the movements of players from the Australian Women's Rugby League team (n=31) during seven international rugby league matches. A subgroup of players (n=18) that played at least 80min in a match were categorized into three positional groups: forwards (n=7), backs (n=7) and halves (n=4), and analysed for external outputs that were classified into multiple speed zones. Mean speed (mmin^-1) and mean speed when travelling >12kmh^-1 (MS₁₂; mmin^-1) were calculated for each 10% interval of playing time of both groups to assess changes in match intensity.

RESULTS

Total distance travelled was greater in the first half (3332.9m compared to 3249.0m), along with distances travelled at speeds >15kmh^-1 (p<0.05), whereas players travelled further at speeds <6kmh^-1 in the second half (p=0.005). Backs travelled further at speeds <6kmh^-1 (p=0.002) and >15kmh^-1 (p=0.007) compared to forwards. Mean speed significantly reduced across the first and second halves (p<0.05), while MS₁₂ reduced by ∼40% in the first half of the match (i.e. first ∼5min compared to the last ∼5min).

CONCLUSION

These results provide coaches with sport-specific activity profiles of female rugby league players that can be used to individualise training prescription. Given that match-intensity deteriorated across the first and second halves, programs may be targeted at improving endurance and supramaximal exercise tolerance in order for female players to withstand high match-demands of international competition.

Post-exercise Supplementation of Sodium Bicarbonate Improves Acid Base Balance Recovery and Subsequent High-Intensity Boxing Specific Performance

The aim of this study was to assess the effects of post-exercise sodium bicarbonate (NaHCO₃) ingestion (0.3 g.kg⁻¹ body mass) on the recovery of acid-base balance (pH, HCO3-, and the SID) and subsequent exercise performance in elite boxers. Seven elite male professional boxers performed an initial bout of exhaustive exercise comprising of a boxing specific high-intensity interval running (HIIR) protocol, followed by a high-intensity run to volitional exhaustion (T_LIM1). A 75 min passive recovery then ensued, whereby after 10 min recovery, participants ingested either 0.3 g.kg⁻¹ body mass NaHCO₃, or 0.1 g.kg⁻¹ body mass sodium chloride (PLA). Solutions were taste matched and administered double-blind. Participants then completed a boxing specific punch combination protocol, followed by a second high-intensity run to volitional exhaustion (T_LIM2). Both initial bouts of T_LIM1 were well matched between PLA and NaHCO₃ (ICC; r = 0.94, p = 0.002). The change in performance from T_LIM1 to T_LIM2 was greater following NaHCO₃ compared to PLA (+164 ± 90 vs. +73 ± 78 sec; p = 0.02, CI = 45.1, 428.8, g = 1.0). Following ingestion of NaHCO₃, pH was greater prior to T_LIM2 by 0.11 ± 0.02 units (1.4%) (p < 0.001, CI = 0.09, 0.13, g = 3.4), whilst HCO3- was greater by 8.8 ± 1.5 mmol.l⁻¹ (26.3%) compared to PLA (p < 0.001, CI = 7.3, 10.2, g = 5.1). The current study suggests that these significant increases in acid base balance during post-exercise recovery facilitated the improvement in the subsequent bout of exercise. Future research should continue to explore the role of NaHCO₃ supplementation as a recovery aid in boxing and other combat sports.

Cardiorespiratory coordination reveals training-specific physiological adaptations

PURPOSE

To compare the effects of high-intensity interval training (HIIT) and moderate-intensity training (CONT), matched for total work, on cardiorespiratory coordination and aerobic fitness.

METHODS

This is a two-arm parallel group single-blind randomised study. Twenty adults were assigned to 6 weeks of HIIT or volume-matched CONT. Participants completed a progressive maximal cycling test before and after the training period. Principal component (PC) analysis was performed on the series of cardiorespiratory variables to evaluate dimensionality of cardiorespiratory coordination, before and after lactate turnpoint. PC₁ eigenvalues were compared.

RESULTS

Both HIIT and CONT improved aerobic fitness (main effects of time, p < 0.001, [Formula: see text] ≥ 0.580), with no differences between groups. CONT decreased the number of PCs from two to one at intensities both below and above the lactate turnpoint; PC₁ eigenvalues increased after CONT both below (Z = 2.08; p = 0.04; d = 0.94) and above the lactate turnpoint (Z = 2.10; p = 0.04; d = 1.37). HIIT decreased the number of PCs from two to one after the lactate turnpoint only; PC₁ eigenvalues increased after HIIT above the lactate turnpoint (Z = 2.31; p = 0.02; d = 0.42).

CONCLUSIONS

Although CONT and HIIT improved aerobic fitness to a similar extent, there were different patterns of change for cardiorespiratory coordination. These changes appear training-intensity specific and could be sensitive to investigate the individual response to endurance training.

High-Intensity Interval Training Augments Muscle Carnosine in the Absence of Dietary Beta-alanine Intake

PURPOSE

Cross-sectional studies suggest that training can increase muscle carnosine (MCarn), although longitudinal studies have failed to confirm this. A lack of control for dietary β-alanine intake or muscle fiber type shifting may have hampered their conclusions. The purpose of the present study was to investigate the effects of high-intensity interval training (HIIT) on MCarn.

METHODS

Twenty vegetarian men were randomly assigned to a control (CON) (n = 10) or HIIT (n = 10) group. High-intensity interval training was performed on a cycle ergometer for 12 wk, with progressive volume (6-12 series) and intensity (140%-170% lactate threshold [LT]). Muscle carnosine was quantified in whole-muscle and individual fibers; expression of selected genes (CARNS, CNDP2, ABAT, TauT, and PAT1) and muscle buffering capacity in vitro (βmin vitro) were also determined. Exercise tests were performed to evaluate total work done, V˙O2max, ventilatory thresholds (VT) and LT.

RESULTS

Total work done, VT, LT, V˙O2max, and βmin vitro were improved in the HIIT group (all P < 0.05), but not in CON (P > 0.05). MCarn (in mmol·kg dry muscle) increased in the HIIT (15.8 ± 5.7 to 20.6 ± 5.3; P = 0.012) but not the CON group (14.3 ± 5.3 to 15.0 ± 4.9; P = 0.99). In type I fibers, MCarn increased in the HIIT (from 14.4 ± 5.9 to 16.8 ± 7.6; P = 0.047) but not the CON group (from 14.0 ± 5.5 to 14.9 ± 5.4; P = 0.99). In type IIa fibers, MCarn increased in the HIIT group (from 18.8 ± 6.1 to 20.5 ± 6.4; P = 0.067) but not the CON group (from 19.7 ± 4.5 to 18.8 ± 4.4; P = 0.37). No changes in gene expression were shown.

CONCLUSIONS

In the absence of any dietary intake of β-alanine, HIIT increased MCarn content. The contribution of increased MCarn to the total increase in βmin vitro appears to be small.

Alkaline water improves exercise-induced metabolic acidosis and enhances anaerobic exercise performance in combat sport athletes

Hydration is one of the most significant issues for combat sports as athletes often use water restriction for quick weight loss before competition. It appears that alkaline water can be an effective alternative to sodium bicarbonate in preventing the effects of exercise-induced metabolic acidosis. Therefore, the main aim of the present study was to investigate, in a double blind, placebo controlled randomized study, the impact of mineral-based highly alkaline water on acid-base balance, hydration status, and anaerobic capacity. Sixteen well trained combat sport athletes (n = 16), were randomly divided into two groups; the experimental group (EG; n = 8), which ingested highly alkaline water for three weeks, and the control group (CG; n = 8), which received regular table water. Anaerobic performance was evaluated by two double 30 s Wingate tests for lower and upper limbs, respectively, with a passive rest interval of 3 minutes between the bouts of exercise. Fingertip capillary blood samples for the assessment of lactate concentration were drawn at rest and during the 3rd min of recovery. In addition, acid-base equilibrium and electrolyte status were evaluated. Urine samples were evaluated for specific gravity and pH. The results indicate that drinking alkalized water enhances hydration, improves acid-base balance and anaerobic exercise performance.

Aerobic Exercise Supplemented With Muscular Endurance Training Improves Onset of Blood Lactate Accumulation

Farrell III, JW, Lantis, DJ, Ade, CJ, Cantrell, GS, and Larson, RD. Aerobic exercise supplemented with muscular endurance training improves onset of blood lactate accumulation. J Strength Cond Res 32(5): 1376-1382, 2018-Studies have shown that when aerobic exercise is supplemented with muscular endurance training metabolic adaptions occur that result in the delay of the onset of blood lactate accumulation (OBLA). However, previous studies have not explored any submaximal cardiorespiratory adaptations that may result from this training protocol. The aim of the current investigation was to evaluate the effect of supplementing an aerobic exercise training program with a muscular endurance training program on various cardiorespiratory and metabolic measurements. Fourteen aerobically active men performed an incremental exercise test to determine the OBLA, gas exchange threshold (GET), and maximal oxygen uptake (V[Combining Dot Above]O2max). Maximal strength was measured using 1 repetition maximum (1RM) for leg press (LP), leg curl (LC), and leg extension (LE). Eight subjects supplemented their aerobic activity (experimental [EX] group) with 8 weeks of muscular endurance training, while 6 continued their regular aerobic activity (control [CON] group). No significant group differences were observed for all pretraining variables. After 8 weeks of training, no significant differences in body mass, GET, and V[Combining Dot Above]O2max were observed for either group. However, the EX group showed a significant improvement for both absolute and relative V[Combining Dot Above]O2 at OBLA compared with the CON group. Leg curl and LE 1RM assessments for the EX group showed a significant improvement compared with CON group. Muscular endurance training did not improve GET and V[Combining Dot Above]O2max, but significantly increased V[Combining Dot Above]O2 at OBLA, LP, and LC. These findings suggest that this training protocol maybe useful in the development of submaximal aerobic performance and leg strength for endurance athletes.

EFFECTS OF REPEATED SPRINT TRAINING ON ISOCAPNIC BUFFERING PHASE IN VOLLEYBALL PLAYERS

ABSTRACT Introduction: The region between the ventilatory threshold (VT) and respiratory compensation point (RCP) is defined as the isocapnic buffering (ICB) phase and represents a phase of compensation for exercise-induced metabolic acidosis. There is sparse literature examining the effects of physical training on ICB phase in athletes. Objectives: The purpose of this study was to examine the effects of a repeated sprint training program on the ICB phase of college volleyball players. Methods: Eighteen male volleyball players were randomly assigned to either an experimental group (n=9) or a control group (n=9) and followed a traditional volleyball training program three times per week for six weeks. The experimental group additionally performed a repeated sprint training protocol immediately before each volleyball training session. Before and after the 6-week training period, all participants performed an incremental treadmill test to determine VT, RCP, and maximal oxygen uptake (VO2max). The ICB phases were calculated as VO2 (ml/kg/min) and sprint speed (km/h). Results: The experimental group showed significant improvements in ICB phase, RCP, VO2max and maximal sprint speed after training (p<0.01). There were no significant changes in VT after training in the experimental group (p>0.05). None of these variables changed significantly in the control group (p>0.05). Conclusions: These findings indicate that repeated sprint training can enhance the ICB phase of volleyball players, which may be attributable to an improvement in buffering capacity leading to a shift in RCP towards higher intensities without any change in VT. The increase in the ICB phase may an important factor in terms of improvement in the high-intensity exercise tolerance of athletes. Level of Evidence II; Therapeutic studies - Investigating the results of treatment.

Chronic Ketogenic Low Carbohydrate High Fat Diet Has Minimal Effects on Acid-Base Status in Elite Athletes

Although short (up to 3 days) exposure to major shifts in macronutrient intake appears to alter acid-base status, the effects of sustained (>1 week) interventions in elite athletes has not been determined. Using a non-randomized, parallel design, we examined the effect of adaptations to 21 days of a ketogenic low carbohydrate high fat (LCHF) or periodized carbohydrate (PCHO) diet on pre- and post-exercise blood pH, and concentrations of bicarbonate (HCO₃-) and lactate (La-) in comparison to a high carbohydrate (HCHO) control. Twenty-four (17 male and 7 female) elite-level race walkers completed 21 days of either LCHF (n = 9), PCHO (n = 7), or HCHO (n = 8) under controlled diet and training conditions. At baseline and post-intervention, blood pH, blood [HCO₃-], and blood [La-] were measured before and after a graded exercise test. Net endogenous acid production (NEAP) over the previous 48-72 h was also calculated from monitored dietary intake. LCHF was not associated with significant differences in blood pH, [HCO₃-], or [La-], compared with the HCHO diet pre- or post-exercise, despite a significantly higher NEAP (mEq·day-1) (95% CI = [10.44; 36.04]). Our results indicate that chronic dietary interventions are unlikely to influence acid-base status in elite athletes, which may be due to pre-existing training adaptations, such as an enhanced buffering capacity, or the actions of respiratory and renal pathways, which have a greater influence on regulation of acid-base status than nutritional intake.

Oral Contraceptive Use Dampens Physiological Adaptations to Sprint Interval Training

PURPOSE

Oral contraceptive (OC) use reduces peak aerobic capacity (V˙O2peak); however, whether it also influences adaptations to training has yet to be determined. This study aimed to examine the influence of OC use on peak performance (peak power output [PPO]) and physiological adaptations (V˙O2peak and peak cardiac output [Q˙peak]) after sprint interval training (SIT) in recreationally active women.

METHODS

Women taking an OC (n = 25) or experiencing natural regular menstrual cycles (MC; n = 16) completed an incremental exercise test to assess V˙O2peak, PPO, and Q˙peak before, immediately after, and 4 wk after 12 sessions of SIT. The SIT consisted ten 1-min efforts at 100% to 120% PPO in a 1:2 work-rest ratio.

RESULTS

Though V˙O2peak increased in both groups after SIT (both P < 0.001), the MC group showed greater improvement (OC, +8.5%; MC, +13.0%; P = 0.010). Similarly, Q˙peak increased in both groups, with greater improvement in the MC group (OC, +4.0%; MC, +16.1%; P = 0.013). PPO increased in both groups (OC, +13.1%; MC, +13.8%; NS). All parameters decreased 4 wk after SIT cessation, but remained elevated from pretraining levels; the OC group showed more sustained training effects in V˙O2peak (OC, -4.0%; MC, -7.7%; P = 0.010).

CONCLUSION

SIT improved peak exercise responses in recreationally active women. However, OC use dampened V˙O2peak and Q˙peak adaptation. A follow-up period indicated that OC users had spared V˙O2peak adaptations, suggesting that OC use may influence the time course of physiological training adaptations. Therefore, OC use should be verified, controlled for, and considered when interpreting physiological adaptations to exercise training in women.

High but not moderate-intensity endurance training increases pain tolerance: a randomised trial

PURPOSE

To examine the effect of high-intensity interval training (HIIT) compared to volume-matched moderate-intensity continuous training (CONT) on muscle pain tolerance and high-intensity exercise tolerance.

METHODS

Twenty healthy adults were randomly assigned (1:1) to either 6 weeks of HIIT [6-8 × 5 min at halfway between lactate threshold and maximal oxygen uptake (50%Δ)] or volume-matched CONT (~60-80 min at 90% lactate threshold) on a cycle ergometer. A tourniquet test to examine muscle pain tolerance and two time to exhaustion (TTE) trials at 50%Δ to examine exercise tolerance were completed pre- and post-training; the post-training TTE trials were completed at the pre-training 50%Δ (same absolute-intensity) and the post-training 50%Δ (same relative-intensity).

RESULTS

HIIT and CONT resulted in similar improvements in markers of aerobic fitness (all P ≥ 0.081). HIIT increased TTE at the same absolute- and relative-intensity as pre-training (148 and 43%, respectively) to a greater extent than CONT (38 and -4%, respectively) (both P ≤ 0.019). HIIT increased pain tolerance (41%, P < 0.001), whereas CONT had no effect (-3%, P = 0.720). Changes in pain tolerance demonstrated positive relationships with changes in TTE at the same absolute- (r = 0.44, P = 0.027) and relative-intensity (r = 0.51, P = 0.011) as pre-training.

CONCLUSION

The repeated exposure to a high-intensity training stimulus increases muscle pain tolerance, which is independent of the improvements in aerobic fitness induced by endurance training, and may contribute to the increase in high-intensity exercise tolerance following HIIT.

Physiological Adaptations to Hypoxic vs. Normoxic Training during Intermittent Living High

In the setting of “living high,” it is unclear whether high-intensity interval training (HIIT) should be performed “low” or “high” to stimulate muscular and performance adaptations. Therefore, 10 physically active males participated in a 5-week “live high-train low or high” program (TR), whilst eight subjects were not engaged in any altitude or training intervention (CON). Five days per week (~15.5 h per day), TR was exposed to normobaric hypoxia simulating progressively increasing altitude of ~2,000–3,250 m. Three times per week, TR performed HIIT, administered as unilateral knee-extension training, with one leg in normobaric hypoxia (~4,300 m; TR_HYP) and with the other leg in normoxia (TR_NOR). “Living high” elicited a consistent elevation in serum erythropoietin concentrations which adequately predicted the increase in hemoglobin mass (r = 0.78, P < 0.05; TR: +2.6%, P < 0.05; CON: −0.7%, P > 0.05). Muscle oxygenation during training was lower in TR_HYP vs. TR_NOR (P < 0.05). Muscle homogenate buffering capacity and pH-regulating protein abundance were similar between pretest and posttest. Oscillations in muscle blood volume during repeated sprints, as estimated by oscillations in NIRS-derived tHb, increased from pretest to posttest in TR_HYP (~80%, P < 0.01) but not in TR_NOR (~50%, P = 0.08). Muscle capillarity (~15%) as well as repeated-sprint ability (~8%) and 3-min maximal performance (~10–15%) increased similarly in both legs (P < 0.05). Maximal isometric strength increased in TR_HYP (~8%, P < 0.05) but not in TR_NOR (~4%, P > 0.05). In conclusion, muscular and performance adaptations were largely similar following normoxic vs. hypoxic HIIT. However, hypoxic HIIT stimulated adaptations in isometric strength and muscle perfusion during intermittent sprinting.

Rest interval duration does not influence adaptations in acid/base transport proteins following 10 wk of sprint-interval training in active women

The removal of protons (H+) produced during intense exercise is important for skeletal muscle function, yet it remains unclear how best to structure exercise training to improve muscle pH regulation. We investigated whether 4 wk of work-matched sprint-interval trining (SIT), performed 3 days/wk, with either 1 ( Rest-1; n = 7) or 5 ( Rest-5; n = 7) min of rest between sprints, influenced adaptations in acid/base transport protein content, nonbicarbonate muscle buffer capacity (βmin vitro), and exercise capacity in active women. Following 1 wk of posttesting, comprising a biopsy, a repeated-sprint ability (RSA) test, and a graded-exercise test, maintenance of adaptations was then studied by reducing SIT volume to 1 day/wk for a further 5 wk. After 4 wk of SIT, there was increased protein abundance of monocarboxylate transporter (MCT)-1, sodium/hydrogen exchanger (NHE)-1, and carbonic anhydrase (CA) XIV for both groups, but rest interval duration did not influence the adaptive response. In contrast, greater improvements in total work performed during the RSA test after 4 wk of SIT were evident for Rest-5 compared with Rest-1 (effect size: 0.51; 90% confidence limits ±0.37), whereas both groups had similarly modest improvements in V̇o2peak. When training volume was reduced to 1 day/wk, enhanced acid/base transport protein abundance was maintained, although NHE1 content increased further for Rest-5 only. Finally, our data support intracellular lactate as a signaling molecule for inducing MCT1 expression, but neither lactate nor H+ accumulation appears to be important signaling factors in MCT4 regulation.

Effects of high-intensity interval training on canoeing performance

The purpose of this study was to compare the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) utilizing a canoeing ergometer on endurance determinants, as well as aerobic and anaerobic performances among flat-water canoeists. Fourteen well-trained male flat-water canoeists were divided into an HIIT group or an MICT group. All subjects performed a continuous graded exercise test (GXT) and three fixed-distance (200, 500, and 1000 m) performance tests on a canoeing ergometer to determine canoeing economy, peak oxygen uptake (VO₂peak), and power at VO₂peak, and to calculate the critical velocity (CV) and anaerobic work capacity before and after the training programmes. The training programme involved training on a canoeing ergometer three times per week for four weeks. HIIT consisted of seven 2 min canoeing bouts at an intensity of 90% VO₂peak separated by 1 min of rest. The MICT group was trained at an intensity of 65% VO₂peak continuously for 20 min. After four weeks of training, performance in the 200-m distance test and the power at VO₂peak significantly improved in the HIIT group; performance in the 500 m and 1000 m distances and CV significantly improved in the MICT group. However, all variables were not significantly different between groups. It is concluded that HIIT for four weeks is an effective training strategy for improvement of short-distance canoeing performance. In contrast, MICT improves middle-distance canoeing performances and aerobic capacity.

Influence of training intensity on adaptations in acid/base transport proteins, muscle buffer capacity, and repeated-sprint ability in active men

McGinley C, Bishop DJ. Influence of training intensity on adaptations in acid/base transport proteins, muscle buffer capacity, and repeated-sprint ability in active men. J Appl Physiol 121: 1290–1305, 2016. First published October 14, 2016; doi: 10.1152/japplphysiol.00630.2016 .—This study measured the adaptive response to exercise training for each of the acid-base transport protein families, including providing isoform-specific evidence for the monocarboxylate transporter (MCT)1/4 chaperone protein basigin and for the electrogenic sodium-bicarbonate cotransporter (NBCe)1. We investigated whether 4 wk of work-matched, high-intensity interval training (HIIT), performed either just above the lactate threshold (HIITΔ20; n = 8), or close to peak aerobic power (HIITΔ90; n = 8), influenced adaptations in acid-base transport protein abundance, nonbicarbonate muscle buffer capacity (βmin vitro), and exercise capacity in active men. Training intensity did not discriminate between adaptations for most proteins measured, with abundance of MCT1, sodium/hydrogen exchanger (NHE) 1, NBCe1, carbonic anhydrase (CA) II, and CAXIV increasing after 4 wk, whereas there was little change in CAIII and CAIV abundance. βmin vitro also did not change. However, MCT4 protein content only increased for HIITΔ20 [effect size (ES): 1.06, 90% confidence limits × / ÷ 0.77], whereas basigin protein content only increased for HIITΔ90 (ES: 1.49, × / ÷ 1.42). Repeated-sprint ability (5 × 6-s sprints; 24 s passive rest) improved similarly for both groups. Power at the lactate threshold only improved for HIITΔ20 (ES: 0.49; 90% confidence limits ± 0.38), whereas peak O2 uptake did not change for either group. Detraining was characterized by the loss of adaptations for all of the proteins measured and for repeated-sprint ability 6 wk after removing the stimulus of HIIT. In conclusion, 4 wk of HIIT induced improvements in each of the acid-base transport protein families, but, remarkably, a 40% difference in training intensity did not discriminate between most adaptations.

Endurance Training Intensity Does Not Mediate Interference to Maximal Lower-Body Strength Gain during Short-Term Concurrent Training

We determined the effect of concurrent training incorporating either high-intensity interval training (HIT) or moderate-intensity continuous training (MICT) on maximal strength, counter-movement jump (CMJ) performance, and body composition adaptations, compared with single-mode resistance training (RT). Twenty-three recreationally-active males (mean ± SD: age, 29.6 ± 5.5 y; V˙O2peak, 44 ± 11 mL kg⁻¹·min⁻¹) underwent 8 weeks (3 sessions·wk⁻¹) of either: (1) HIT combined with RT (HIT+RT group, n = 8), (2) work-matched MICT combined with RT (MICT+RT group, n = 7), or (3) RT performed alone (RT group, n = 8). Measures of aerobic capacity, maximal (1-RM) strength, CMJ performance and body composition (DXA) were obtained before (PRE), mid-way (MID), and after (POST) training. Maximal (one-repetition maximum [1-RM]) leg press strength was improved from PRE to POST for RT (mean change ± 90% confidence interval; 38.5 ± 8.5%; effect size [ES] ± 90% confidence interval; 1.26 ± 0.24; P < 0.001), HIT+RT (28.7 ± 5.3%; ES, 1.17 ± 0.19; P < 0.001), and MICT+RT (27.5 ± 4.6%, ES, 0.81 ± 0.12; P < 0.001); however, the magnitude of this change was greater for RT vs. both HIT+RT (7.4 ± 8.7%; ES, 0.40 ± 0.40) and MICT+RT (8.2 ± 9.9%; ES, 0.60 ± 0.45). There were no substantial between-group differences in 1-RM bench press strength gain. RT induced greater changes in peak CMJ force vs. HIT+RT (6.8 ± 4.5%; ES, 0.41 ± 0.28) and MICT+RT (9.9 ± 11.2%; ES, 0.54 ± 0.65), and greater improvements in maximal CMJ rate of force development (RFD) vs. HIT+RT (24.1 ± 26.1%; ES, 0.72 ± 0.88). Lower-body lean mass was similarly increased for RT (4.1 ± 2.0%; ES; 0.33 ± 0.16; P = 0.023) and MICT+RT (3.6 ± 2.4%; ES; 0.45 ± 0.30; P = 0.052); however, this change was attenuated for HIT+RT (1.8 ± 1.6%; ES; 0.13 ± 0.12; P = 0.069). We conclude that concurrent training incorporating either HIT or work-matched MICT similarly attenuates improvements in maximal lower-body strength and indices of CMJ performance compared with RT performed alone. This suggests endurance training intensity is not a critical mediator of interference to maximal strength gain during short-term concurrent training.

Effects of high-intensity interval training on cardiometabolic health: a systematic review and meta-analysis of intervention studies

The current review clarifies the cardiometabolic health effects of high-intensity interval training (HIIT) in adults. A systematic search (PubMed) examining HIIT and cardiometabolic health markers was completed on 15 October 2015. Sixty-five intervention studies were included for review and the methodological quality of included studies was assessed using the Downs and Black score. Studies were classified by intervention duration and body mass index classification. Outcomes with at least 5 effect sizes were synthesised using a random-effects meta-analysis of the standardised mean difference (SMD) in cardiometabolic health markers (baseline to postintervention) using Review Manager 5.3. Short-term (ST) HIIT (<12 weeks) significantly improved maximal oxygen uptake (VO₂ max; SMD 0.74, 95% CI 0.36 to 1.12; p<0.001), diastolic blood pressure (DBP; SMD -0.52, 95% CI -0.89 to -0.16; p<0.01) and fasting glucose (SMD -0.35, 95% CI -0.62 to -0.09; p<0.01) in overweight/obese populations. Long-term (LT) HIIT (≥12 weeks) significantly improved waist circumference (SMD -0.20, 95% CI -0.38 to -0.01; p<0.05), % body fat (SMD -0.40, 95% CI -0.74 to -0.06; p<0.05), VO₂ max (SMD 1.20, 95% CI 0.57 to 1.83; p<0.001), resting heart rate (SMD -0.33, 95% CI -0.56 to -0.09; p<0.01), systolic blood pressure (SMD -0.35, 95% CI -0.60 to -0.09; p<0.01) and DBP (SMD -0.38, 95% CI -0.65 to -0.10; p<0.01) in overweight/obese populations. HIIT demonstrated no effect on insulin, lipid profile, C reactive protein or interleukin 6 in overweight/obese populations. In normal weight populations, ST-HIIT and LT-HIIT significantly improved VO₂ max, but no other significant effects were observed. Current evidence suggests that ST-HIIT and LT-HIIT can increase VO₂ max and improve some cardiometabolic risk factors in overweight/obese populations.

Effects of 4 Weeks of High-Intensity Interval Training and β-Hydroxy-β-Methylbutyric Free Acid Supplementation on the Onset of Neuromuscular Fatigue

This study investigated the effects of high-intensity interval training (HIIT) and β-hydroxy-β-methylbutyric free acid (HMB) supplementation on physical working capacity at the onset of neuromuscular fatigue threshold (PWC(FT)). Thirty-seven participants (22 men, 15 women; 22.8 ± 3.4 years) completed an incremental cycle ergometer test (graded exercise test [GXT]); electromyographic amplitude from the right vastus lateralis was recorded. Assessments occurred preceding (PRE) and after 4 weeks of supplementation (POST). Participants were randomly assigned to control (C, n = 9), placebo (P, n = 14), or supplementation (S, n = 14) groups. Both P and S completed 12 HIIT sessions, whereas C maintained normal diet and activity patterns. The PWC(FT) (W) was determined using the maximal perpendicular distance (D(MAX)) method. Electromyographic amplitude (μVrms) over time was used to generate a cubic regression. Onset of fatigue (TF) was the x-value of the point on the regression that was at D(MAX) from a line between the first and last data points. The PWC(FT) was estimated using TF and GXT power-output increments. The 2-way analysis of variance (ANOVA) (group × time) resulted in a significant interaction for PWC(FT) (F = 6.69, p = 0.004). Post hoc analysis with 1-way ANOVA resulted in no difference in PWC(FT) among groups at PRE (F = 0.87, p = 0.43); however, a difference in PWC(FT) was shown for POST (F = 5.46, p = 0.009). Post hoc analysis among POST values revealed significant differences between S and both P (p = 0.034) and C (p = 0.003). No differences (p = 0.226) were noted between P and C. Paired samples t-tests detected significant changes after HIIT for S (p < 0.001) and P (p = 0.016), but no change in C (p = 0.473). High-intensity interval training increased PWC(FT), but HMB with HIIT was more effective than HIIT alone. Furthermore, it seems that adding HMB supplementation with HIIT in untrained men and women may further improve endurance performance measures.

The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans

To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4–6 × 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO₂peak, sprint performance (two 30-s Wingate tests with 4-min recovery), muscle efficiency and time-trial performance (TT, 5-min all-out) were assessed and biopsies from the m. vastus lateralis and m. triceps brachii taken before and after training. VO₂peak and Wmax increased 3–11% after training, with a more pronounced change in the arms (P < 0.05). Gross efficiency improved for the arms (+8.8%, P < 0.05), but not the legs (−0.6%). Wingate peak and mean power outputs improved similarly for the arms and legs, as did TT performance. After training, VO₂ during the two Wingate tests was increased by 52 and 6% for the arms and legs, respectively (P < 0.001). In the case of the arms, VO₂ was higher during the first than second Wingate test (64 vs. 44%, P < 0.05). During the TT, relative exercise intensity, HR, VO₂, VCO₂, V_E, and V_t were all lower during arm-cranking than leg-pedaling, and oxidation of fat was minimal, remaining so after training. Despite the higher relative intensity, fat oxidation was 70% greater during leg-pedaling (P = 0.017). The aerobic energy contribution in the legs was larger than for the arms during the Wingate tests, although VO₂ for the arms was enhanced more by training, reducing the O₂ deficit after SIT. The levels of muscle glycogen, as well as the myosin heavy chain composition were unchanged in both cases, while the activities of 3-hydroxyacyl-CoA-dehydrogenase and citrate synthase were elevated only in the legs and capillarization enhanced in both limbs. Multiple regression analysis demonstrated that the variables that predict TT performance differ for the arms and legs. The primary mechanism of adaptation to SIT by both the arms and legs is enhancement of aerobic energy production. However, with their higher proportion of fast muscle fibers, the arms exhibit greater plasticity.

Performance in sports--With specific emphasis on the effect of intensified training

Performance in most sports is determined by the athlete's technical, tactical, physiological and psychological/social characteristics. In the present article, the physical aspect will be evaluated with a focus on what limits performance, and how training can be conducted to improve performance. Specifically how intensified training, i.e., increasing the amount of aerobic high-intensity and speed endurance training, affects physiological adaptations and performance of trained subjects. Periods of speed endurance training do improve performance in events lasting 30 s-4 min, and when combined with aerobic high-intensity sessions, also performance during longer events. Athletes in team sports involving intense exercise actions and endurance aspects, such as soccer and basketball, can also benefit from intensified training. Speed endurance training does reduce energy expenditure and increase expression of muscle Na(+), K(+) pump α subunits, which may preserve muscle cell excitability and delay fatigue development during intense exercise. When various types of training are conducted in the same period (concurrent training), as done in a number of sports, one type of training may blunt the effect of other types of training. It is not, however, clear how various training modalities are affecting each other, and this issue should be addressed in future studies.

Nutritional Strategies to Modulate Intracellular and Extracellular Buffering Capacity During High-Intensity Exercise

Intramuscular acidosis is a contributing factor to fatigue during high-intensity exercise. Many nutritional strategies aiming to increase intra- and extracellular buffering capacity have been investigated. Among these, supplementation of beta-alanine (~3–6.4 g/day for 4 weeks or longer), the rate-limiting factor to the intramuscular synthesis of carnosine (i.e. an intracellular buffer), has been shown to result in positive effects on exercise performance in which acidosis is a contributing factor to fatigue. Furthermore, sodium bicarbonate, sodium citrate and sodium/calcium lactate supplementation have been employed in an attempt to increase the extracellular buffering capacity. Although all attempts have increased blood bicarbonate concentrations, evidence indicates that sodium bicarbonate (0.3 g/kg body mass) is the most effective in improving high-intensity exercise performance. The evidence supporting the ergogenic effects of sodium citrate and lactate remain weak. These nutritional strategies are not without side effects, as gastrointestinal distress is often associated with the effective doses of sodium bicarbonate, sodium citrate and calcium lactate. Similarly, paresthesia (i.e. tingling sensation of the skin) is currently the only known side effect associated with beta-alanine supplementation, and it is caused by the acute elevation in plasma beta-alanine concentration after a single dose of beta-alanine. Finally, the co-supplementation of beta-alanine and sodium bicarbonate may result in additive ergogenic gains during high-intensity exercise, although studies are required to investigate this combination in a wide range of sports.