Ischemic preconditioning of one forearm enhances static and dynamic apnea

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers

Introduction

Elite breath-hold divers (BHD) enduring apneas of more than 5 min are characterized by tolerance to arterial blood oxygen levels of 4.3 kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD.

Methods and results

After 4 min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6 min), lower extremity volume assessed by DXA-scan revealed a ∼268 mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102 mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations.

Conclusion

Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.

Ischemic Conditioning to Reduce Fatigue in Isometric Skeletal Muscle Contraction

Ischemic preconditioning (IPC) is a non-invasive protective maneuver that alternates short periods of occlusion and reperfusion of tissue blood flow. Given the heterogeneity in the magnitude and frequency of IPC-induced improvements in physical performance, here we aimed to investigate, in a well-controlled experimental set-up, the local effects of IPC in exposed muscles in terms of tissue oxygenation and muscle fatigue. Nineteen subjects were enrolled in one of the two groups, IPC (3 × 5/5 min right arm ischemia/reperfusion; cuff inflations 250 mmHg) and SHAM (3 × 5/5 min pseudo ischemia/reperfusion; 20 mmHg). The subjects performed a fatiguing contraction protocol before and 30 min after the IPC treatment, consisting of unilateral intermittent isometric elbow flexions (3 s ON/OFF, 80% of maximal voluntary contraction) until exhaustion. While muscle strength did not differ between groups, post- vs. pre-treatment endurance was significantly reduced in the SHAM group (4.1 ± 1.9 vs. 6.4 ± 3.1 repetitions until exhaustion, p < 0.05) but maintained in IPC (7.3 ± 2.0 vs. 7.1 ± 4.3, n.s.). The decrease in tissue oxygenation and the increase in deoxygenated hemoglobin were significantly reduced post- vs. pre-IPC (p < 0.05), but not post- vs. pre-SHAM. The results suggest that IPC delays the onset of fatigue likely through improved metabolic efficiency of muscles.

Active Relative to Passive Ischemic Preconditioning Enhances Intense Endurance Performance in Well-Trained Men

PURPOSE

This study tested the hypothesis of whether ischemic exercise preconditioning (IPC-Ex) elicits a better intense endurance exercise performance than traditional ischemic preconditioning at rest (IPC-rest) and a SHAM procedure.

METHODS

Twelve men (average V˙O2max ∼61 mL·kg-1·min-1) performed 3 trials on separate days, each consisting of either IPC-Ex (3 × 2-min cycling at ∼40 W with a bilateral-leg cuff pressure of ∼180 mm Hg), IPC-rest (4 × 5-min supine rest at 220 mm Hg), or SHAM (4 × 5-min supine rest at <10 mm Hg) followed by a standardized warm-up and a 4-minute maximal cycling performance test. Power output, blood lactate, potassium, pH, rating of perceived exertion, oxygen uptake, and gross efficiency were assessed.

RESULTS

Mean power during the performance test was higher in IPC-Ex versus IPC-rest (+4%; P = .002; 95% CI, +5 to 18 W). No difference was found between IPC-rest and SHAM (-2%; P = .10; 95% CI, -12 to 1 W) or between IPC-Ex and SHAM (+2%; P = .09; 95% CI, -1 to 13 W). The rating of perceived exertion increased following the IPC-procedure in IPC-Ex versus IPC-rest and SHAM (P < .001). During warm-up, IPC-Ex elevated blood pH versus IPC-rest and SHAM (P ≤ .027), with no trial differences for blood potassium (P > .09) or cycling efficiency (P ≥ .24). Eight subjects anticipated IPC-Ex to be best for their performance. Four subjects favored SHAM.

CONCLUSIONS

Performance in a 4-minute maximal test was better following IPC-Ex than IPC-rest and tended to be better than SHAM. The IPC procedures did not affect blood potassium, while pH was transiently elevated only by IPC-Ex. The performance-enhancing effect of IPC-Ex versus IPC-rest may be attributed to a placebo effect, improved pH regulation, and/or a change in the perception of effort.

Blood Flow Restriction Enhances Rehabilitation and Return to Sport: The Paradox of Proximal Performance

The use of blood flow restriction (BFR) within rehabilitation is rapidly increasing as further research is performed elucidating purported benefits such as improved muscular strength and size, neuromuscular control, decreased pain, and increased bone mineral density. Interestingly, these benefits are not isolated to structures distal to the occlusive stimulus. Proximal gains are of high interest to rehabilitation professionals, especially those working with patients who are limited due to pain or postsurgical precautions. The review to follow will focus on current evidence and ongoing hypotheses regarding physiologic responses to BFR, current clinical applications, proximal responses to BFR training, potential practical applications for rehabilitation and injury prevention, and directions for future research. Interestingly, benefits have been found in musculature proximal to the occlusive stimulus, which may lend promise to a greater variety of patient populations and conditions. Furthermore, an increasing demand for BFR use in the sports world warrants further research for performance research and recovery.

LEVEL OF EVIDENCE

Level V, expert opinion.

Methodological Variations Contributing to Heterogenous Ergogenic Responses to Ischemic Preconditioning

Ischemic preconditioning (IPC) has been repeatedly reported to augment maximal exercise performance over a range of exercise durations and modalities. However, an examination of the relevant literature indicates that the reproducibility and robustness of ergogenic responses to this technique are variable, confounding expectations about the magnitude of its effects. Considerable variability among study methodologies may contribute to the equivocal responses to IPC. This review focuses on the wide range of methodologies used in IPC research, and how such variability likely confounds interpretation of the interactions of IPC and exercise. Several avenues are recommended to improve IPC methodological consistency, which should facilitate a future consensus about optimizing the IPC protocol, including due consideration of factors such as: location of the stimulus, the time between treatment and exercise, individualized tourniquet pressures and standardized tourniquet physical characteristics, and the incorporation of proper placebo treatments into future study designs.

Effect of Ischemic Preconditioning on Maximal Swimming Performance

ABSTRACT

Williams, N, Russell, M, Cook, CJ, and Kilduff, LP. Effect of ischemic preconditioning on maximal swimming performance. J Strength Cond Res 35(1): 221-226, 2021-The effect of ischemic preconditioning (IPC) on swimming performance was examined. Using a randomized, crossover design, national- and international-level swimmers (n = 20; 14 men, 6 women) participated in 3 trials (Con, IPC-2h, and IPC-24h). Lower-body IPC (4 × 5-minute bilateral blood flow restriction at 160-228 mm Hg and 5-minute reperfusion) was used 2 hours (IPC-2h) or 24 hours (IPC-24h) before a self-selected (100 m, n = 15; 200 m, n = 5) swimming time trial (TT). The Con trial used a sham intervention (15 mm Hg) 2 hours before exercise. All trials required a 40-minute standardized precompetition swimming warm-up (followed by 20-minute rest; replicating precompetition call room procedures) 1 hour before TT. Capillary blood (pH, blood gases, and lactate concentrations) was taken immediately before and after IPC, before TT and after TT. No effects on TT for 100 m (P = 0.995; IPC-2h: 64.94 ± 8.33 seconds; IPC-24h: 64.67 ± 8.50 seconds; Con: 64.94 ± 8.24 seconds), 200 m (P = 0.405; IPC-2h: 127.70 ± 10.66 seconds; IPC-24h: 129.26 ± 12.99 seconds; Con: 130.19 ± 10.27 seconds), or combined total time (IPC-2h: 84.27 ± 31.52 seconds; IPC-24h: 79.87 ± 29.72 seconds; Con: 80.55 ± 31.35 seconds) were observed after IPC. Base excess (IPC-2h: -13.37 ± 8.90 mmol·L-1; Con: -13.35 ± 7.07 mmol·L-1; IPC-24h: -16.53 ± 4.65 mmol·L-1), pH (0.22 ± 0.08; all conditions), bicarbonate (IPC-2h: -11.66 ± 3.52 mmol·L-1; Con: -11.62 ± 5.59 mmol·L-1; IPC-24h: -8.47 ± 9.02 mmol·L-1), total carbon dioxide (IPC-2h: -12.90 ± 3.92 mmol·L-1; Con: -11.55 ± 7.61 mmol·L-1; IPC-24h: 9.90 ± 8.40 mmol·L-1), percentage oxygen saturation (IPC-2h: -0.16 ± 1.86%; Con: +0.20 ± 1.93%; IPC-24h: +0.47 ± 2.10%), and blood lactate (IPC-2h: +12.87 ± 3.62 mmol·L-1; Con: +12.41 ± 4.02 mmol·L-1; IPC-24h: +13.27 ± 3.81 mmol·L-1) were influenced by swimming TT (P < 0.001), but not condition (all P > 0.05). No effect of IPC was seen when applied 2 or 24 hours before swimming TT on any indices of performance or physiological measures recorded.

Cardiac hypoxic resistance and decreasing lactate during maximum apnea in elite breath hold divers

Breath-hold divers (BHD) enduring apnea for more than 4 min are characterized by resistance to release of reactive oxygen species, reduced sensitivity to hypoxia, and low mitochondrial oxygen consumption in their skeletal muscles similar to northern elephant seals. The muscles and myocardium of harbor seals also exhibit metabolic adaptations including increased cardiac lactate-dehydrogenase-activity, exceeding their hypoxic limit. We hypothesized that the myocardium of BHD possesses similar adaptive mechanisms. During maximum apnea ¹⁵O-H₂O-PET/CT (n = 6) revealed no myocardial perfusion deficits but increased myocardial blood flow (MBF). Cardiac MRI determined blood oxygen level dependence oxygenation (n = 8) after 4 min of apnea was unaltered compared to rest, whereas cine-MRI demonstrated increased left ventricular wall thickness (LVWT). Arterial blood gases were collected after warm-up and maximum apnea in a pool. At the end of the maximum pool apnea (5 min), arterial saturation decreased to 52%, and lactate decreased 20%. Our findings contrast with previous MR studies of BHD, that reported elevated cardiac troponins and decreased myocardial perfusion after 4 min of apnea. In conclusion, we demonstrated for the first time with ¹⁵O-H₂O-PET/CT and MRI in elite BHD during maximum apnea, that MBF and LVWT increases while lactate decreases, indicating anaerobic/fat-based cardiac-metabolism similar to diving mammals.

Effects of Ischemic Preconditioning as a Warm-Up on Leg Press and Bench Press Performance

Ischemic preconditioning (IPC) has been used to increase performance in sports. The aim of this study was to compare the acute effects of IPC with different warm-up methods on the number of repetitions and total volume in resistance exercise (RE). Sixteen healthy men recreationally trained in RE participated in this study. After the anthropometric evaluation and familiarization, a one-repetition maximum (1RM) test and retest were performed in the bench press (BP) and in the leg press 45° (LP) exercise. After these tests, participants were randomly assigned to one of the five protocols: a) IPC; b) SHAM; c) a specific warm-up (SW); d) aerobic exercise (AE), and e) active stretching (AS) prior to performing 3 sets at 80% 1RM until concentric failure. The number of repetitions was higher following IPC compared to the SW following three sets both for the BP and LP. Similarly, the number of repetitions for IPC was higher in comparison to SHAM following three sets for the LP. The number of repetitions was higher following IPC compared to AE following 1^st and 2^nd sets for the LP and following the 2^nd set for the BP. Finally, the number of repetitions was higher following IPC compared to AS following 1^st and 2^nd sets for the LP. The total volume was higher following IPC compared to SHAM, SW, AE, and AS for both the BP and LP. The IPC protocol increased the number of maximum repetitions and the total volume when compared to the other tested methods, thus indicating a better utilization during the pre-work warm-up. These results indicate positive associative responses to IPC with performance maintenance, which is of importance for both athletes and coaches.

Effects of resistance training combined with ischemic preconditioning on muscle size and strength in resistance-trained individuals

BACKGROUND

The present study investigated the effects of resistance training combined with ischemic preconditioning (IPC) on muscle size and strength in resistance-trained men.

METHODS

Sixteen resistance-trained men were divided into two groups (Placebo and IPC) and trained twice a week for 6 weeks. Preconditioning protocols consisted of four, 5-min cycling bouts of ischemia/Placebo (250 or 10 mmHg, respectively) interspersed with 5 min of reperfusion (without pressure) alternated in each leg. Thirty minutes after the preconditioning protocol, participants performed 4 sets to concentric failure at 75% of one repetition-maximum (1-RM) in unilateral knee extension exercise. Muscle thickness (ultrasound) and 1RM were assessed at baseline and 72 hours after the last training session. ANCOVA was used to compare muscle thickness and 1RM changes, using muscle thickness and 1-RM baseline values, respectively, as covariates. Significance level was set at P<0.05.

RESULTS

Average of number of repetitions was higher in IPC compared to Placebo (13±4 and 11±2, respectively; P=0.0002). Muscle thickness did not change in either group from pre- to post-6 weeks (P=0.32). IPC improved 1-RM more than Placebo (P=0.04).

CONCLUSIONS

IPC may augment greater strength gains in resistance-trained men due to an increase in training volume.

Ischemic Preconditioning Maintains Performance on Two 5-km Time Trials in Hypoxia

PURPOSE

The ergogenic effect of ischemic preconditioning (IPC) on endurance exercise performed in hypoxia remains debated and has never been investigated with successive exercise bouts. Therefore, we evaluated if IPC would provide immediate or delayed effects during two 5-km cycling time trials (TT) separated by ~1 h in hypoxia.

METHODS

In a counterbalanced randomized crossover design, 13 healthy males (27.5 ± 3.6 yr) performed two maximal cycling 5-km TT separated by ~1 h of recovery (TT1 25 min and TT2 2 h post-IPC/SHAM), preceded by IPC (3 × 5 min occlusion 220 mm Hg/reperfusion 0 mm Hg, bilaterally on thighs) or SHAM (20 mm Hg) at normobaric hypoxia (fraction of inspired oxygen [FiO2] of 16%). Performance and physiological (i.e., oxyhemoglobin saturation, heart rate, blood lactate, and vastus lateralis oxygenation) parameters were recorded.

RESULTS

Time to complete (P = 0.011) 5-km TT and mean power output (P = 0.005) from TT1 to TT2 were worse in SHAM, but not in IPC (P = 0.381/P = 0.360, respectively). There were no differences in time, power output, or physiological variables during the two TT between IPC and SHAM. All muscle oxygenation indices differed (P < 0.001) during the IPC/SHAM with a greater deoxygenation in IPC. During the TT, there was a greater concentration of total hemoglobin in IPC than SHAM (P = 0.047) and greater total hemoglobin in TT1 than TT2. Further, the concentration of oxyhemoglobin was lower during TT2 than TT1 (P = 0.005).

CONCLUSION

In moderate hypoxia, IPC allowed maintaining a higher blood volume during a subsequent maximal exercise, mitigating the performance decrement between two consecutive cycling TT.

Effects of remote limb ischemic conditioning on muscle strength in healthy young adults: A randomized controlled trial

Remote limb ischemic conditioning (RLIC) is a clinically feasible method in which brief, sub-lethal bouts of ischemia protects remote organs or tissues from subsequent ischemic injury. A single session of RLIC can improve exercise performance and increase muscle activation. The purpose of this study, therefore, was to assess the effects of a brief, two-week protocol of repeated RLIC combined with strength training on strength gain and neural adaptation in healthy young adults. Participants age 18–40 years were randomized to receive either RLIC plus strength training (n = 15) or sham conditioning plus strength training (n = 15). Participants received RLIC or sham conditioning over 8 visits using a blood pressure cuff on the dominant arm with 5 cycles of 5 minutes each alternating inflation and deflation. Visits 3–8 paired conditioning with wrist extensors strength training on the non-dominant (non-conditioned) arm using standard guidelines. Changes in one repetition maximum (1 RM) and electromyography (EMG) amplitude were compared between groups. Both groups were trained at a similar workload. While both groups gained strength over time (P = 0.001), the RLIC group had greater strength gains (9.38 ± 1.01 lbs) than the sham group (6.3 ± 1.08 lbs, P = 0.035). There was not a significant group x time interaction in EMG amplitude (P = 0.231). The RLIC group had larger percent changes in 1 RM (43.8% vs. 26.1%, P = 0.003) and EMG amplitudes (31.0% vs. 8.6%, P = 0.023) compared to sham conditioning. RLIC holds promise for enhancing muscle strength in healthy young and older adults, as well as clinical populations that could benefit from strength training.

Ischemic preconditioning has no effect on maximal arm cycling exercise in women

PURPOSE

We investigated the effect of ischemic preconditioning (IPC) on performance of a 3 min maximal effort arm ergometer test in young women.

METHODS

Twenty healthy women (23.1 (SD 3.3) years) performed a 3 min maximal effort arm cycling exercise, preceded by IPC on both arms or SHAM in a counterbalanced randomized crossover design. Both blood flow (via high resolution ultrasound; n = 17) and muscle oxygenation/deoxygenation (via near infrared spectroscopy; n = 5) were measured throughout the IPC/SHAM. Performance and perceptual/physiological (i.e., heart rate, blood lactate, rating of perceived exertion, and triceps brachialis oxygenation) parameters were recorded during the exercise test.

RESULTS

Occlusion during IPC completely blocked brachial artery blood flow, decreased oxygenated hemoglobin/myoglobin (Δ[oxy(Hb + Mb)]), and increased deoxygenated Hb/Mb (Δ[deoxy(Hb + Mb)]). There were no differences (P > 0.797) in performance (peak, mean, and end power output) or in any perceptual/physiological variables during the 3 min all-out test between IPC/SHAM. During exercise, Δ[oxy(Hb + Mb)] initially decreased with no differences (P ≥ 0.296) between conditions and returned towards baseline by the completion of the test while Δ[deoxy(Hb + Mb)] increased with no differences between conditions and remained elevated until completion of the test (P ≥ 0.755).

CONCLUSIONS

We verified the successful application of IPC via blood flow and NIRS measures but found no effects on performance of a 3 min maximal effort arm cranking test in young women.

Effect of ischemic preconditioning and changing inspired O2 fractions on neuromuscular function during intense exercise

The aim of the present study was to determine whether ischemic preconditioning (IPC)-mediated effects on neuromuscular function are dependent on tissue oxygenation. Eleven resistance-trained males completed four exercise trials (6 sets of 11 repetitions of maximal effort dynamic single-leg extensions) in either normoxic [fraction of inspired oxygen ([Formula: see text]): 21%) or hypoxic [Formula: see text]: 14%] conditions, preceded by treatments of either IPC (3 × 5 min bilateral leg occlusions at 220 mmHg) or sham (3 × 5 min at 20 mmHg). Femoral nerve stimulation was utilized to assess voluntary activation and potentiated twitch characteristics during maximal voluntary contractions (MVCs). Tissue oxygenation (via near-infrared spectroscopy) and surface electromyography activity were measured throughout the exercise task. MVC and twitch torque declined 62 and 54%, respectively (MVC: 96 ± 24 N·m, Cohen’s d = 2.9, P < 0.001; twitch torque: 37 ± 11 N·m, d = 1.6, P < 0.001), between pretrial measurements and the sixth set without reductions in voluntary activation ( P > 0.21); there were no differences between conditions. Tissue oxygenation was reduced in both hypoxic conditions compared with normoxia ( P < 0.001), with an even further reduction of 3% evident in the hypoxic IPC compared with the sham trial (mean decrease 1.8 ± 0.7%, d = 1.0, P < 0.05). IPC did not affect any measure of neuromuscular function regardless of tissue oxygenation. A reduction in [Formula: see text] did invoke a humoral response and improved muscle O2 extraction during exercise, however, it did not manifest into any performance benefit.

NEW & NOTEWORTHY Ischemic preconditioning did not affect any facet of neuromuscular function regardless of the degree of tissue oxygenation. Reducing the fraction of inspired oxygen induced localized tissue deoxygenation, subsequently invoking a humoral response, which improved muscle oxygen extraction during exercise. This physiological response, however, did not manifest into any performance benefits.

Ischemic Preconditioning, O2 Kinetics, and Performance in Normoxia and Hypoxia

INTRODUCTION

Ischemic preconditioning (IPC) before exercise has been shown to be a novel approach to improve performance in different exercise modes in normoxia (NORM). Few studies have been conducted examining potential mechanisms behind these improvements, and less has been done examining its influence during exercise in hypoxia (HYP). Oxygen uptake and extraction kinetics are factors that have been implicated as possible determinants of cycling performance. We hypothesized that IPC would lead to improvements in oxygen extraction and peripheral blood flow kinetics, and this would translate to improvements in cycling time trial (TT) performance in both NORM and HYP.

METHODS

Thirteen men (age, 24 ± 7 yr; V˙O2max, 63.1 ± 5.1 mL·kg·min) participated in the study. Subjects completed trials of each combination of normobaric HYP (FiO2 = 0.16, simulating ~8000 ft/2500 m) or NORM (FiO2 = 0.21) with preexercise IPC protocol (4 × 5 min at 220 mm Hg) or SHAM procedure. Trials included submaximal constant load cycle exercise bouts (power outputs of 15% below gas exchange threshold, and 85% of V˙O2max), and a 5-km cycling performance TT.

RESULTS

Ischemic preconditioning significantly improved 5-km TT time in NORM by 0.9% ± 1.8% compared with SHAM (IPC, 491.2 ± 35.2 s vs SHAM, 495.9 ± 36.0 s; P < 0.05). Ischemic preconditioning did not alter 5-km TT performance times in HYP (P = 0.231). Ischemic preconditioning did, however, improve tissue oxygen extraction in HYP (deoxygenated hemoglobin/myoglobin: IPC, 21.23 ± 10.95 μM; SHAM, 19.93 ± 9.91 μM; P < 0.05) during moderate-intensity exercise.

CONCLUSIONS

Our data confirm that IPC is an effective ergogenic aid for athletes performing 5-km cycling TT bouts in NORM. Ischemic preconditioning did mitigate the declines in tissue oxygen during moderate-intensity exercise in HYP, but this did not translate to a significant effect on mean group performance. These data suggest that IPC may be of benefit for athletes training and competing in NORM.

Ischemic preconditioning and exercise performance: shedding light through smallest worthwhile change

Ischemic preconditioning (IPC) has been suggested as a potential ergogenic aid to improve exercise performance, although controversial findings exist. The controversies may be explained by several factors, including the mode of exercise, the ratio between the magnitude of improvement, or the error of measurement and physiological meaning. However, a relevant aspect has been lacking in the literature: the interpretation of the findings considering statistical tests and adequate effect size (ES) according to the fitness level of individuals. Thus, we performed a systematic review with meta-analysis to update the effects of IPC on exercise performance and physiological responses, using traditional statistics (P values), ES, and smallest worth change (SWC) approach contextualizing the IPC application to applied Sports and Exercise performance. Forty-five studies met the inclusion criteria. Overall, the results show that IPC has a minimal or nonsignificant effect on performance considering the fitness level of the individuals, using statistical approaches (i.e., tests with P value, ES, and SWC). Therefore, IPC procedures should be revised and refined in future studies to evaluate if IPC promotes positive effects on performance in a real-world scenario with more consistent interpretation.

An overview of ischemic preconditioning in exercise performance: A systematic review

Ischemic preconditioning (IPC) is an attractive method for athletes owing to its potential to enhance exercise performance. However, the effectiveness of the IPC intervention in the field of sports science remains mitigated. The number of cycles of ischemia and reperfusion, as well as the duration of the cycle, varies from one study to another. Thus, the aim of this systematic review was to provide a comprehensive review examining the IPC literature in sports science. A systematic literature search was performed in PubMed (MEDLINE) (from 1946 to May 2018), Web of Science (sport sciences) (from 1945 to May 2018), and EMBASE (from 1974 to May 2018). We included all studies investigating the effects of IPC on exercise performance in human subjects. To assess scientific evidence for each study, this review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The electronic database search generated 441 potential articles that were screened for eligibility. A total of 52 studies were identified as eligible and valid for this systematic review. The studies included were of high quality, with 48 of the 52 studies having a randomized, controlled trial design. Most studied showed that IPC intervention can be beneficial to exercise performance. However, IPC intervention seems to be more beneficial to healthy subjects who wish to enhance their performance in aerobic exercises than athletes. Thus, this systematic review highlights that a better knowledge of the mechanisms generated by the IPC intervention would make it possible to optimize the protocols according to the characteristics of the subjects with the aim of suggesting to the subjects the best possible experience of IPC intervention.

Fatigue-independent alterations in muscle activation and effort perception during forearm exercise: role of local oxygen delivery

The oxygen-conforming response (OCR) of skeletal muscle refers to a downregulation of muscle force for a given muscle activation when oxygen delivery (O₂D) is reduced, which is rapidly reversed when O₂D is restored. We tested the hypothesis that the OCR exists in voluntary human exercise and results in compensatory changes in muscle activation to maintain force output, thereby altering perception of effort. In eight men and eight women, electromyography (EMG), oxyhemoglobin (O₂Hb) and deoxyhemoglobin (HHb), forearm blood flow (FBF), and task effort awareness (TEA) were measured. Participants completed two nonfatiguing rhythmic handgrip tests consisting of 5-min steady state (SS) followed by two bouts of 2-min brachial artery compression to reduce FBF by ~50% of SS (C1 and C2), separated by 2 min of no compression (NC1) and ending with 2 min of no compression (NC2). When FBF was compromised during C1, EMG/Force (1.58 ± 0.39) increased compared with SS (1.31 ± 0.33, P = 0.001). However, EMG/Force was not restored upon FBF restoration at NC1 (1.48 ± 0.38, P = 0.479), consistent with C1 evoking skeletal muscle fatigue. When FBF was compromised during C2, EMG/Force increased (1.73 ± 0.50) compared with NC1 (1.48 ± 0.38, P = 0.013). EMG/Force returned to NC1 levels during NC2 (1.50 ± 0.39, P = 0.016), consistent with an OCR in C2. TEA (SS 2.2 ± 2.3, C1 3.9 ± 2.5, NC1 3.4 ± 2.7, C2 4.6 ± 2.7, NC2 3.9 ± 2.8) mirrored changes in EMG. It is noteworthy that during the second compromise and then restoration of muscle oxygenation EMG and TEA were rapidly restored to precompromise levels. We interpreted these findings to support the existence of an OCR and its ability to rapidly modify perception of effort during voluntary exercise. NEW & NOTEWORTHY In healthy individuals, when force output is maintained during rhythmic handgrip exercise, muscle activation and perception of effort rapidly increase with compromised muscle oxygen delivery (O₂D) and then return to precompromised levels when muscle O₂D is restored. These findings suggest that an oxygen-conforming response (OCR) exists and is able to modify perception of effort during voluntary exercise. Therefore, similar to fatigue, an OCR may have implications for exercise tolerance.

Remote ischemic preconditioning increases accumulated oxygen deficit in middle-distance runners

The mediators underlying the putative benefits of remote ischemic preconditioning (IPC) on dynamic whole body exercise performance have not been widely investigated. Our objective was to test the hypothesis that remote IPC improves supramaximal exercise performance in National Collegiate Athletic Association (NCAA) Division I middle-distance runners by increasing accumulated oxygen deficit (AOD), an indicator of glycolytic capacity. A randomized sham-controlled crossover study was employed. Ten NCAA Division I middle-distance athletes [age: 21 ± 1 yr; maximal oxygen uptake (V̇o2max): 65 ± 7 ml·kg−1·min−1] completed three supramaximal running trials (baseline, after mock IPC, and with remote IPC) at 110% V̇o2max to exhaustion. Remote IPC was induced in the right arm with 4 × 5 min cycles of brachial artery ischemia with 5 min of reperfusion. Supramaximal AOD (ml/kg) was calculated as the difference between the theoretical oxygen demand required for the supramaximal running bout (linear regression extrapolated from ~12 × 5 min submaximal running stages) and the actual oxygen demand for these bouts. Remote IPC [122 ± 38 s, 95% confidence interval (CI): 94–150] increased ( P < 0.001) time to exhaustion 22% compared with baseline (99 ± 23 s, 95% CI: 82–116, P = 0.014) and sham (101 ± 30 s, 95% CI: 80–123, P = 0.001). In the presence of IPC, AOD was 47 ± 36 ml/kg (95% CI: 20.8–73.9), a 29% increase compared with baseline (36 ± 28 ml/kg, 95% CI: 16.3–56.9, P = 0.008) and sham (38 ± 32 ml/kg, 95% CI: 16.2–63.0, P = 0.024). Remote IPC considerably improved supramaximal exercise performance in NCAA Division I middle-distance athletes. Greater glycolytic capacity, as estimated by increased AOD, is a potential mediator for these performance improvements.

NEW & NOTEWORTHY Our novel findings indicate that ischemic preconditioning enhanced glycolytic exercise capacity, enabling National Collegiate Athletic Association (NCAA) middle-distance track athletes to run ~22 s longer before exhaustion compared with baseline and mock ischemic preconditioning. The increase in “all-out” performance appears to be due to increased accumulated oxygen deficit, an index of better supramaximal capacity. Of note, enhanced exercise performance was demonstrated in a specific group of in-competition NCAA elite athletes that has already undergone substantial training of the glycolytic energy systems.

Impact of 8 weeks of repeated ischemic preconditioning on running performance

PURPOSE

To examine if repeated exposure to IPC treatment prior to training sessions improves oxygen uptake and 1-km running performance in highly trained middle-distance runners.

METHODS

Fourteen highly trained endurance runners (11 male/3 female, 19 ± 2 years, 64 ± 5 ml kg^-1 min^-1) completed a baseline maximal oxygen consumption ([Formula: see text]) test and 1-km running performance test before random assignment to an IPC or control group. Both groups were prescribed identical endurance training over an 8-week varsity season; however, the IPC group performed an IPC protocol (5 min ischemia, repeated 3 times, each separated by 5 min reperfusion) before every training session. After 8 weeks of training, participants completed a follow-up [Formula: see text] test and 1-km time trial.

RESULTS

[Formula: see text] did not increase from baseline in either group following the 8-week training bout (P = 0.2), and neither group varied more than the other ([Formula: see text] = IPC 0.6 ± 2 ml kg^-1 min^-1; control 1.5 ± 2 ml kg^-1 min^-1, P = 0.6) or beyond typical measurement error. The IPC decreased 1-km time trial time by 0.4% (0.5 ± 2 s), while the control group decreased by 1% (1.5 ± 3 s), but neither change was significant compared to baseline (P = 0.2). There was also no difference in time trial improvement between IPC and control (P = 0.6). However, there was a trend towards IPC significantly improving running economy at low intensity (P = 0.057).

CONCLUSION

Our data suggest that over a normal 8-week season in a population of highly trained middle-distance runners there is no benefit of undergoing chronic, repeated IPC treatments before training for augmenting maximal aerobic power or 1-km performance time.

The effect of IPC on central and peripheral fatiguing mechanisms in humans following maximal single limb isokinetic exercise

Ischemic preconditioning (IPC) has been suggested to preserve neural drive during fatiguing dynamic exercise, however, it remains unclear as to whether this may be the consequence of IPC-enhanced muscle oxygenation. We hypothesized that the IPC-enhanced muscle oxygenation during a dynamic exercise task would subsequently attenuate exercise-induced reductions in voluntary activation. Ten resistance trained males completed three 3 min maximal all-out tests (AOTs) via 135 isokinetic leg extensions preceded by treatments of IPC (3 × 5 min bilateral leg occlusions at 220 mmHg), SHAM (3 × 5 min at 20 mmHg) or CON (30 min passive rest). Femoral nerve stimulation was utilized to assess voluntary activation and potentiated twitch torque during maximal voluntary contractions (MVCs) performed at baseline (BL), prior to the AOT (Pre), and then 10 sec post (Post). Tissue oxygenation (via near-infrared spectroscopy) and sEMG activity was measured throughout the AOT. MVC and twitch torque levels declined (MVC: -87 ± 23 Nm, 95% CI = -67 to -107 Nm; P < 0.001, twitch: -30 ± 13 Nm; 95% CI = -25 to -35 Nm; P < 0.001) between Pre and Post without reductions in voluntary activation (P = 0.72); there were no differences between conditions (MVC: P = 0.75, twitch: P = 0.55). There were no differences in tissue saturation index (P = 0.27), deoxyhemoglobin concentrations (P = 0.86) or sEMG activity (P = 0.92) throughout the AOT. These findings demonstrate that IPC does not preserve neural drive during an all-out 3 min isokinetic leg extension task.

Lower limb ischemic preconditioning combined with dietary nitrate supplementation does not influence time-trial performance in well-trained cyclists

OBJECTIVES

Dietary nitrate (NO₃^-) supplementation and ischaemic preconditioning (IPC) can independently improve exercise performance. The purpose of this study was to explore whether NO₃^- supplementation, ingested prior to an IPC protocol, could synergistically enhance parameters of exercise.

DESIGN

Double-blind randomized crossover trial.

METHODS

Ten competitive male cyclists (age 34±6years, body mass 78.9±4.9kg, V⋅O_2peak 55±4 mLkgmin^-1) completed an incremental exercise test followed by three cycling trials comprising a square-wave submaximal component and a 16.1km time-trial. Oxygen uptake (V⋅O₂) and muscle oxygenation kinetics were measured throughout. The baseline (BASE) trial was conducted without any dietary intervention or IPC. In the remaining two trials, participants received 3×5min bouts of lower limb bilateral IPC prior to exercise. Participants ingested NO₃^--rich gel (NIT+IPC) 90min prior to testing in one trial and a low NO₃^- placebo in the other (PLA+IPC). Plasma NO₃^- and nitrite (NO₂^-) were measured immediately before and after application of IPC.

RESULTS

Plasma [NO₃^-] and [NO₂^-] were higher before and after IPC in NIT+IPC compared to BASE (P<0.001) but did not differ between BASE and PLA+IPC. There were no differences in V⋅O₂ kinetics or muscle oxygenation parameters between trials (all P>0.4). Performance in the time-trial was similar between trials (BASE 1343±72s, PLA+IPC 1350±75s, NIT+IPC 1346±83s, P=0.98).

CONCLUSIONS

Pre-exercise IPC did not improve sub-maximal exercise or performance measures, either alone or in combination with dietary NO₃^- supplementation.

Ischemic Preconditioning Improves Time Trial Performance at Moderate Altitude

PURPOSE

Endurance athletes often compete and train at altitude where exercise capacity is reduced. Investigating acclimation strategies is therefore critical. Ischemic preconditioning (IPC) can improve endurance performance at sea level through improved O2 delivery and utilization, which could also prove beneficial at altitude. However, data are scarce, and there is no study at altitudes commonly visited by endurance athletes.

METHODS

In a randomized, crossover study, we investigated performance and physiological responses in 13 male endurance cyclists during four 5-km cycling time trials (TT), preceded by either IPC (3 × 5 min ischemia/5-min reperfusion cycles at 220 mm Hg) or SHAM (20 mm Hg) administered to both thighs, at simulated low (FIO2 0.180, ~1200 m) and moderate (FIO2 0.154, ~2400 m) altitudes. Time to completion, power output, cardiac output (Q˙), arterial O2 saturation (SpO2), quadriceps tissue saturation index (TSI) and RPE were recorded throughout the TT. Differences between IPC and SHAM were analyzed at every altitude using Cohen effect size (ES) and compared with the smallest worthwhile change.

RESULTS

At low altitude, IPC possibly improved time to complete the TT (-5.2 s, -1.1%; Cohen ES ± 90% confidence limits -0.22, -0.44; 0.01), power output (2.7%; ES 0.21, 0.08; 0.51), and Q˙ (5.0%; ES 0.27, 0.00; 0.54), but did not alter SpO2, muscle TSI, and RPE. At moderate altitude, IPC likely enhanced completion time (-7.3 s; -1.5%; ES -0.38, -0.55; -0.20), and power output in the second half of the TT (4.6%; ES 0.28, -0.15; 0.72), increased SpO2 (1.0%; ES 0.38, -0.05; 0.81), and decreased TSI (-6.5%; ES -0.27, -0.73; 0.20) and RPE (-5.4%, ES -0.27, -0.48; -0.06).

CONCLUSIONS

Ischemic preconditioning may provide an immediate and effective strategy to defend SpO2 and enhance high-intensity endurance performance at moderate altitude.

Muscle Oximetry in Sports Science: A Systematic Review

BACKGROUND

Since the introduction (in 2006) of commercially available portable wireless muscle oximeters, the use of muscle near-infrared spectroscopy (NIRS) technology is gaining in popularity as an application to observe changes in muscle metabolism and muscle oxygenation during and after exercise or training interventions in both laboratory and applied sports settings.

OBJECTIVES

The objectives of this systematic review were to highlight the application of muscle oximetry in evaluating oxidative skeletal muscle performance to sport activities and emphasize how this technology has been applied to exercise and training.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed in a systematic fashion to search, assess and synthesize existing literature on this topic. The Scopus and MEDLINE/PubMed electronic databases were searched to 1 March 2017. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programs, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the 14,609 identified records, only 57 studies met the eligibility criteria. This systematic review highlighted a number of key findings in 16 sporting activities. Overall, NIRS information can be used as a marker of skeletal muscle oxidative capacity and for analyzing muscle performance factors.

CONCLUSIONS

Although NIRS instrumentation is promising in evaluating oxidative skeletal muscle performance when used in sport settings, there is still the need for further instrumental development and randomized/longitudinal trials to support the detailed advantages of muscle oximetry utilization in sports science.

Time-Trial Performance in Elite Speed Skaters After Remote Ischemic Preconditioning

PURPOSE

Speed skating leads to blood-flow restriction and deoxygenation in the lower limbs (especially the right leg) that may affect performance. Although the acute influence of such deoxygenation is not clearly understood, the authors tested whether remote ischemic preconditioning (RIPC) could modify muscular oxygenation and improve time-trial performance in that sport.

METHODS

Using a randomized, single-blind, placebo-controlled, crossover design, 9 elite speed skaters performed 1000-m on-ice time trials preceded by either RIPC of the upper limbs (3 × 5-min compression/5-min reperfusion cycles at 30 mm Hg >arterial systolic pressure) or placebo treatment (SHAM; 10 mm Hg). Changes in tissue saturation index, oxyhemoglobin-oxymyoglobin, deoxyhemoglobin-deoxymyoglobin, and total hemoglobin-myoglobin in the right vastus lateralis muscle were monitored using near-infrared spectroscopy (NIRS). Differences between RIPC and SHAM were analyzed using Cohen effect size (ES) ± 90% confidence limits and magnitude-based inferences.

RESULTS

Compared with SHAM, RIPC had a negligible effect on performance and NIRS variables. However, in a subgroup of sprinters (n = 5), RIPC likely lowered tissue saturation index at the beginning of the time trial (-6.1%; ES = -0.65) and likely increased deoxyhemoglobin-deoxymyoglobin at the beginning (3%; ES = 0.39), middle (2.9%; ES = 0.37), and end of the trial (-2.1%; ES = 0.27). In the middle section of the trial, these metabolic changes were concomitant with a possible increase in total hemoglobin-myoglobin.

CONCLUSION

RIPC has no practical ergogenic impact on 1000-m long-track speed-skating performance in elite athletes. The relevance of using RIPC during training to increase physiological stress in sprinters particularly deserves further investigation.

Oxygen conserving mitochondrial adaptations in the skeletal muscles of breath hold divers

Background

The performance of elite breath hold divers (BHD) includes static breath hold for more than 11 minutes, swimming as far as 300 m, or going below 250 m in depth, all on a single breath of air. Diving mammals are adapted to sustain oxidative metabolism in hypoxic conditions through several metabolic adaptations, including improved capacity for oxygen transport and mitochondrial oxidative phosphorylation in skeletal muscle. It was hypothesized that similar adaptations characterized human BHD. Hence, the purpose of this study was to examine the capacity for oxidative metabolism in skeletal muscle of BHD compared to matched controls.

Methods

Biopsies were obtained from the lateral vastus of the femoral muscle from 8 Danish BHD and 8 non-diving controls (Judo athletes) matched for morphometry and whole body VO₂max. High resolution respirometry was used to determine mitochondrial respiratory capacity and leak respiration with simultaneous measurement of mitochondrial H₂O₂ emission. Maximal citrate synthase (CS) and 3-hydroxyacyl CoA dehydrogenase (HAD) activity were measured in muscle tissue homogenates. Western Blotting was used to determine protein contents of respiratory complex I-V subunits and myoglobin in muscle tissue lysates.

Results

Muscle biopsies of BHD revealed lower mitochondrial leak respiration and electron transfer system (ETS) capacity and higher H₂O₂ emission during leak respiration than controls, with no differences in enzyme activities (CS and HAD) or protein content of mitochondrial complex subunits myoglobin, myosin heavy chain isoforms, markers of glucose metabolism and antioxidant enzymes.

Conclusion

We demonstrated for the first time in humans, that the skeletal muscles of BHD are characterized by lower mitochondrial oxygen consumption both during low leak and high (ETS) respiration than matched controls. This supports previous observations of diving mammals demonstrating a lower aerobic mitochondrial capacity of the skeletal muscles as an oxygen conserving adaptation during prolonged dives.

Combining Chronic Ischemic Preconditioning and Inspiratory Muscle Warm-Up to Enhance On-Ice Time-Trial Performance in Elite Speed Skaters

Elite athletes in varied sports typically combine ergogenic strategies in the hope of enhancing physiological responses and competitive performance, but the scientific evidence for such practices is very scarce. The peculiar characteristics of speed skating contribute to impede blood flow and exacerbate deoxygenation in the lower limbs (especially the right leg). We investigated whether combining preconditioning strategies could modify muscular oxygenation and improve performance in that sport. Using a randomized, single-blind, placebo-controlled, crossover design, seven male elite long-track speed skaters performed on-ice 600-m time trials, preceded by either a combination of preconditioning strategies (COMBO) or a placebo condition (SHAM). COMBO involved performing remote ischemic preconditioning (RIPC) of the upper limbs (3 × 5-min compression at 180 mmHg and 5-min reperfusion) over 3 days (including an acute treatment before trials), with the addition of an inspiratory muscle warm-up [IMW: 2 × 30 inspirations at 40% maximal inspiratory pressure (MIP)] on the day of testing. SHAM followed the same protocol with lower intensities (10 mmHg for RIPC and 15% MIP). Changes in tissue saturation index (TSI), oxyhemoglobin–oxymyoglobin ([O₂HbMb]), deoxyhemoglobin–deoxymyoglobin ([HHbMb]), and total hemoglobin–myoglobin ([THbMb]) in the right vastus lateralis muscle were monitored by near-infrared spectroscopy (NIRS). Differences between COMBO and SHAM were analyzed using Cohen’s effect size (ES) and magnitude-based inferences. Compared with SHAM, COMBO had no worthwhile effect on performance time while mean Δ[HHbMb] (2.7%, ES 0.48; -0.07, 1.03) and peak Δ[HHbMb] (1.8%, ES 0.23; -0.10, 0.57) were respectively likely and possibly higher in the last section of the race. These results indicate that combining ischemic preconditioning and IMW has no practical ergogenic impact on 600-m speed-skating performance in elite skaters. The low-sitting position in this sport might render difficult enhancing these physiological responses.

Impact of ischaemia-reperfusion cycles during ischaemic preconditioning on 2000-m rowing ergometer performance

PURPOSE

Although ischaemic preconditioning (IPC), induced by cycles of transient limb ischaemia and reperfusion, seems to improve exercise performance, the optimal duration of ischaemia-reperfusion cycles is not established. The present study investigated the effect of ischaemia-reperfusion duration within each IPC cycle on performance in a 2000-m rowing ergometer test.

METHODS

After incremental and familiarization tests, 16 trained rowers (mean ± SD: age, 24 ± 11 years; weight, 74.1 ± 5.9 kg; [Formula: see text] peak, 67.2 ± 7.4 mL·kg^-1·min^-1) were randomly submitted to a 2000-m rowing test preceded by intermittent bilateral cuff inflation of the lower limbs with three cycles of ischaemia-reperfusion, lasting 5 min (IPC-5) or 10 min (IPC-10) at 220 or 20 mmHg (control). Power output, [Formula: see text], heart rate, blood lactate concentration, pH, ratings of perceived exertion (RPE), and near-infrared spectroscopy-derived measurements of the vastus lateralis muscle were continuously recorded.

RESULTS

No differences among treatments were found in the 2000-m test (control: 424 ± 17; IPC-5: 425 ± 16; IPC-10: 424 ± 17 s; P = 0.772). IPC-10 reduced the tissue saturation index and oxy-haemoglobin concentration during exercise compared with control. The power output during the last 100-m segment was significantly lower with IPC-10. The IPC treatments increased the heart rate over the first 500 m and decreased the pH after exercise. No alterations were observed in [Formula: see text], blood lactate, or RPE among the trials.

CONCLUSION

In conclusion, IPC does not improve the 2000-m rowing ergometer performance of trained athletes regardless of the length of ischaemia-reperfusion cycles.

Is There an Optimal Ischemic-Preconditioning Dose to Improve Cycling Performance?

INTRODUCTION

Ischemic preconditioning (IPC) may enhance endurance performance. No previous study has directly compared distinct IPC protocols for optimal benefit.

PURPOSE

To determine whether a specific IPC protocol (ie, number of cycles, amount of muscle tissue, and local vs remote occlusion) elicits greater performance outcomes.

METHODS

Twelve cyclists performed 5 different IPC protocols 30 min before a blinded 375-kJ cycling time trial (TT) in a laboratory. Responses to traditional IPC (4 × 5-min legs) were compared with those to 8 × 5-min legs and sham (dose cycles), 4 × 5-min unilateral legs (dose tissue), and 4 × 5-min arms (remote). Rating of perceived exertion and blood lactate were recorded at each 25% TT completion. Power (W), heart rate (beats/min), and oxygen uptake ([Formula: see text]) (mL · kg^-1 · min^-1) were measured continuously throughout TTs. Magnitude-based-inference statistics were employed to compare variable differences to the minimal practically important difference.

RESULTS

Traditional IPC was associated with a 17-s (0, 34) faster TT time than sham. Applying more dose cycles (8 × 5 min) had no impact on performance. Traditional IPC was associated with likely trivial higher blood lactate and possibly beneficial lower [Formula: see text] responses vs sham. Unilateral IPC was associated with 18-s (-11, 48) slower performance than bilateral (dose tissue). TT times after remote and local IPC were not different (0 [-16, 16] s).

CONCLUSION

The traditional 4 × 5-min (local or remote) IPC stimulus resulted in the fastest TT time compared with sham; there was no benefit of applying a greater number of cycles or employing unilateral IPC.

Ischemic Preconditioning Does Not Alter Performance in Multidirectional High-Intensity Intermittent Exercise

Purpose: Research dealing with ischemic preconditioning (IPC) has primarily focused on variables associated to endurance performance with little research about the acute responses of IPC on repeated multidirectional running sprint performance. Here we aimed to investigate the effects of IPC of the arms and the legs on repeated running sprint performance with changes-of-direction (COD) movements.

Methods: Thirteen moderately-to-well-trained team-sport athletes (7 males; 6 females; age: 24 ± 2 years, size: 175 ± 8 cm, body mass: 67.9 ± 8.1 kg) performed 16 × 30 m all-out sprints (15 s rest) with multidirectional COD movements on a Speedcourt with IPC (3 × 5 min) of the legs (IPC_leg; 240 mm Hg) or of the arms (remote IPC: IPC_remote; 180–190 mm Hg) 45 min before the sprints and a control trial (CON; 20 mm Hg).

Results: The mean (±SD) time for the 16 × 30 m multidirectional COD sprints was similar between IPC_leg (Mean t: 16.0 ± 1.8 s), IPC_remote (16.2 ± 1.7 s), and CON (16.0 ± 1.6 s; p = 0.50). No statistical differences in oxygen uptake (mean difference: 0%), heart rate (1.1%) nor muscle oxygen saturation of the vastus lateralis (4.7%) and biceps brachii (7.8%) between the three conditions were evident (all p > 0.05).

Conclusions: IPC (3 × 5 min) of the legs (220 mm Hg) or arms (180–190 mm Hg; remote IPC) applied 45 min before 16 × 30 m repeated multidirectional running sprint exercise does not improve sprint performance, oxygen uptake, heart rate nor muscle oxygen saturation of the vastus lateralis muscle when compared to a control trial.

Ischemic preconditioning enhances critical power during a 3 minute all-out cycling test

This study tested the hypothesis that ischemic preconditioning (IPC) would increase critical power (CP) during a 3 minute all-out cycling test. Twelve males completed two 3 minute all-out cycling tests, in a crossover design, separated by 7 days. These tests were preceded by IPC (4 x 5 minute intervals at 220 mmHg bilateral leg occlusion) or SHAM treatment (4 x 5 minute intervals at 20 mmHg bilateral leg occlusion). CP was calculated as the mean power output during the final 30 s of the 3 minute test with W' taken as the total work done above CP. Muscle oxygenation was measured throughout the exercise period. There was a 15.3 ± 0.3% decrease in muscle oxygenation (TSI; [Tissue saturation index]) during the IPC stimulus, relative to SHAM. CP was significantly increased (241 ± 65 W vs. 234 ± 67 W), whereas W' (18.4 ± 3.8 vs 17.9 ± 3.7 kJ) and total work done (TWD) were not different (61.1 ± 12.7 vs 60.8 ± 12.7 kJ), between the IPC and SHAM trials. IPC enhanced CP during a 3 minute all-out cycling test without impacting W' or TWD. The improved CP after IPC might contribute towards the effect of IPC on endurance performance.

Ischemic Preconditioning and Acute Recovery of Performance in Rugby Union Players

Ischemic preconditioning has been used as a training and/or pre-competition strategy; however its use for post-exercise recovery is still unclear. This study aimed to evaluate the impact of ischemic preconditioning on performance and recovery ratings following a simulated match in sub-elite rugby players. Following baseline measures, male players (n=8) performed a 40 min, rugby-specific exercise protocol followed by an intervention: 21 min of ischemic preconditioning (3×5 min occlusion at 220 mmHg with 2 min reperfusion at 0 mmHg) or passive rest (control) on 2 separate days. An agility T-test, a single vertical countermovement jump and 30 s of continuous vertical jumps were performed at baseline (–24 h), immediately after exercise, and immediately after the intervention. The rugby-specific exercise protocol induced similar mean heart rates (158.3±18.0 vs. 158.7±16.0 bpm) and perceived exertion levels (8.2±0.9 vs. 8.0±1.0) for both trials with all recovery performance measures and rating of recovery (13.9±1.4 vs. 13.6±1.6) similar between ischemic preconditioning and control trials (best p=0.385). We conclude that the use of ischemic preconditioning does not improve recovery acutely (~1 h) including specific variables related to rugby performance in amateur rugby union players.

Ischemic preconditioning increases muscle perfusion, oxygen uptake, and force in strength-trained athletes

Muscle ischemia and reperfusion induced by ischemic preconditioning (IPC) can improve performance in various activities. However, the underlying mechanisms are still poorly understood. The purpose of this study was to examine the effects of IPC on muscle hemodynamics and oxygen (O2) uptake during repeated maximal contractions. In a cross-over, randomized, single-blind study, 10 strength-trained men performed 5 sets of 5 maximal voluntary knee extensions of the right leg on an isokinetic dynamometer, preceded by either IPC of the right lower limb (3×5-min compression/5-min reperfusion cycles at 200 mm Hg) or sham (20 mm Hg). Changes in deoxyhemoglobin, expressed as a percentage of arterial occlusion, and total hemoglobin ([THb]) concentrations of the vastus lateralis muscle were monitored continuously by near-infrared spectroscopy. Differences between IPC and sham were analyzed using Cohen’s effect size (ES) ± 90% confidence limits, and magnitude-based inferences. Compared with sham, IPC likely increased muscle blood volume at rest (↑[THb], 46.5%; ES, 0.56; 90% confidence limits for ES, –0.21, 1.32). During exercise, peak force was almost certainly higher (11.8%; ES, 0.37; 0.27, 0.47), average force was very likely higher (12.6%; ES, 0.47; 0.29, 0.66), and average muscle O2 uptake was possibly increased (15.8%; ES, 0.36; –0.07, 0.79) after IPC. In the recovery periods between contractions, IPC also increased blood volume after sets 1 (23.6%; ES, 0.30; –0.05, 0.65) and 5 (25.1%; ES, 0.32; 0.09, 0.55). Three cycles of IPC immediately increased muscle perfusion and O2 uptake, conducive to higher repeated force capacity in strength-trained athletes. This maneuver therefore appears relevant to enhancing exercise training stimulus.

Is delayed ischemic preconditioning as effective on running performance during a 5km time trial as acute IPC?

Ischemic preconditioning (IPC) may enhance exercise performance. Cardioprotective effects of IPC are known to re-occur 24h after the stimulus. Whether the delayed effect of IPC has similar effects as IPC on exercise performance is unknown.

OBJECTIVES

Examine whether IPC applied 24h (24-IPC) before exercise is equally effective as IPC in improving exercise performance.

DESIGN

Randomized, cross-over study METHODS: 12 healthy participants were randomly exposed to SHAM-session, IPC or 24-IPC before a self-paced 5km running trial on a treadmill. Subjects were blinded for time, speed and heart rate. Furthermore, heart rate, BORG, and the local tissue saturation index were measured during exercise, while lactate levels were determined after running. Using a regression model, we explored whether these parameters predicted the change in running time after IPC and 24-IPC.

RESULTS

We found no differences in finish time after IPC (SHAM: 1400±105s, IPC: 1381±112s, 24-IPC: 1385±113s; p=0.30). However, we observed a significant positive relation between the change in finish time after IPC and 24-IPC (p=0.016; r=0.677). Using stepwise linear regression, a lower post-exercise blood lactate level after IPC or 24-IPC was significantly related to an improvement in finish time (R²=0.47, β=-0.687, p=0.007).

CONCLUSIONS

Although no significant effect of IPC or 24-IPC on exercise performance was found, individual finish time after IPC and 24-IPC were strongly correlated. Therefore, our data suggest that, at the individual level, the effects of 24-IPC are closely related to the effects of IPC.

The Effect of Ischemic Preconditioning on Repeated Sprint Cycling Performance

PURPOSE

Ischemic preconditioning enhances exercise performance. We tested the hypothesis that ischemic preconditioning would improve intermittent exercise in the form of a repeated sprint test during cycling ergometry.

METHODS

In a single-blind, crossover study, 14 recreationally active men (mean ± SD age, 22.9 ± 3.7 yr; height, 1.80 ± 0.07 m; and mass, 77.3 ± 9.2 kg) performed twelve 6-s sprints after four 5-min periods of bilateral limb occlusion at 220 mm Hg (ischemic preconditioning) or 20 mm Hg (placebo).

RESULTS

Ischemic preconditioning resulted in a 2.4% ± 2.2%, 2.6% ± 2.7%, and 3.7% ± 2.4% substantial increase in peak power for sprints 1, 2, and 3, respectively, relative to placebo, with no further changes between trials observed for any other sprint. Similar findings were observed in the first three sprints for mean power output after ischemic preconditioning (2.8% ± 2.5%, 2.6% ± 2.5%, and 3.4% ± 2.1%, for sprints 1, 2, and 3, respectively), relative to placebo. Fatigue index was not substantially different between trials. At rest, tissue saturation index was not different between the trials. During the ischemic preconditioning/placebo stimulus, there was a -19.7% ± 3.6% decrease in tissue saturation index in the ischemic preconditioning trial, relative to placebo. During exercise, there was a 5.4% ± 4.8% greater maintenance of tissue saturation index in the ischemic preconditioning trial, relative to placebo. There were no substantial differences between trials for blood lactate, electromyography (EMG) median frequency, oxygen uptake, or rating of perceived exertion (RPE) at any time points.

CONCLUSION

Ischemic preconditioning improved peak and mean power output during the early stages of repeated sprint cycling and may be beneficial for sprint sports.

Effects of ischemic preconditioning on short-duration cycling performance

It has been demonstrated that ischemic preconditioning (IPC) improves endurance performance. However, the potential benefits during anaerobic events and the mechanism(s) underlying these benefits remain unclear. Fifteen recreational cyclists were assessed to evaluate the effects of IPC of the upper thighs on anaerobic performance, skeletal muscle activation, and metabolic responses during a 60-s sprint performance. After an incremental test and a familiarization visit, subjects were randomly submitted in visits 3 and 4 to a performance protocol preceded by intermittent bilateral cuff inflation (4 × (5 min of blood flow restriction + 5 min reperfusion)) at either 220 mm Hg (IPC) or 20 mm Hg (control). To increase data reliability, each intervention was replicated, which was also in a random manner. In addition to the mean power output, the pulmonary oxygen uptake, blood lactate kinetics, and quadriceps electromyograms (EMGs) were analyzed during performance and throughout 45 min of passive recovery. After IPC, performance was improved by 2.1% compared with control (95% confidence intervals of 0.8% to 3.3%, P = 0.001), followed by increases in (i) the accumulated oxygen deficit, (ii) the amplitude of blood lactate kinetics, (iii) the total amount of oxygen consumed during recovery, and (iv) the overall EMG amplitude (P < 0.05). In addition, the ratio between EMG and power output was higher during the final third of performance after IPC (P < 0.05). These results suggest an increased skeletal muscle activation and a higher anaerobic contribution as the ultimate responses of IPC on short-term exercise performance.

Ischemic preconditioning reduces hemodynamic response during metaboreflex activation

Ischemic preconditioning (IP) has been shown to improve exercise performance and to delay fatigue. However, the precise mechanisms through which IP operates remain elusive. It has been hypothesized that IP lowers the sensation of fatigue by reducing the discharge of group III and IV nerve endings, which also regulate hemodynamics during the metaboreflex. We hypothesized that IP reduces the blood pressure response during the metaboreflex. Fourteen healthy males (age between 25 and 48 yr) participated in this study. They underwent the following randomly assigned protocol: postexercise muscle ischemia (PEMI) test, during which the metaboreflex was elicited after dynamic handgrip; control exercise recovery session (CER) test; and PEMI after IP (IP-PEMI) test. IP was obtained by occluding forearm circulation for three cycles of 5 min spaced by 5 min of reperfusion. Hemodynamics were evaluated by echocardiography and impedance cardiography. The main results were that after IP the mean arterial pressure response was reduced compared with the PEMI test (means ± SD +3.37 ± 6.41 vs. +9.16 ± 7.09 mmHg, respectively). This was the consequence of an impaired venous return that impaired the stroke volume during the IP-PEMI more than during the PEMI test (-1.43 ± 15.35 vs. +10.28 ± 10.479 ml, respectively). It was concluded that during the metaboreflex, IP affects hemodynamics mainly because it impairs the capacity to augment venous return and to recruit the cardiac preload reserve. It was hypothesized that this is the consequence of an increased nitric oxide production, which reduces the possibility to constrict venous capacity vessels.

Effects of ischemic preconditioning on maximal constant-load cycling performance

This study investigated the effects of ischemic preconditioning (IPC) on the ratings of perceived exertion (RPE), surface electromyography, and pulmonary oxygen uptake (V̇o2) onset kinetics during cycling until exhaustion at the peak power output attained during an incremental test. A group of 12 recreationally trained cyclists volunteered for this study. After determination of peak power output during an incremental test, they were randomly subjected on different days to a performance protocol preceded by intermittent bilateral cuff pressure inflation to 220 mmHg (IPC) or 20 mmHg (control). To increase data reliability, the performance visits were replicated, also in a random manner. There was an 8.0% improvement in performance after IPC (control: 303 s, IPC 327 s, factor SDs of ×/÷1.13, P = 0.01). This change was followed by a 2.9% increase in peak V̇o2 (control: 3.95 l/min, IPC: 4.06 l/min, factor SDs of ×/÷1.15, P = 0.04), owing to a higher amplitude of the slow component of the V̇o2 kinetics (control: 0.45 l/min, IPC: 0.63 l/min, factor SDs of ×/÷2.21, P = 0.05). There was also an attenuation in the rate of increase in RPE ( P = 0.01) and a progressive increase in the myoelectrical activity of the vastus lateralis muscle ( P = 0.04). Furthermore, the changes in peak V̇o2 ( r = 0.73, P = 0.007) and the amplitude of the slow component ( r = 0.79, P = 0.002) largely correlated with performance improvement. These findings provide a link between improved aerobic metabolism and enhanced severe-intensity cycling performance after IPC. Furthermore, the delayed exhaustion after IPC under lower RPE and higher skeletal muscle activation suggest they have a role on the ergogenic effects of IPC on endurance performance.

Characterization of acute ischemia-related physiological responses associated with remote ischemic preconditioning: a randomized controlled, crossover human study

Remote Ischemic Preconditioning (RIPC) is emerging as a new noninvasive intervention that has the potential to protect a number of organs against ischemia–reperfusion (IR) injury. The standard protocols normally used to deliver RIPC involve a number of cycles of inflation of a blood pressure (BP) cuff on the arm and/or leg to an inflation pressure of 200 mmHg followed by cuff deflation for a short period of time. There is little evidence to support what limb (upper or lower) or cuff inflation pressures are most effective to deliver this intervention without causing undue discomfort/pain in nonanesthetized humans. In this preliminary study, a dose–response assessment was performed using a range of cuff inflation pressures (140, 160, and 180 mmHg) to induce limb ischemia in upper and lower limbs. Physiological changes in the occluded limb and any pain/discomfort associated with RIPC with each cuff inflation pressure were determined. Results showed that ischemia can be induced in the upper limb at much lower cuff inflation pressures compared with the standard 200 mmHg pressure generally used for RIPC, provided the cuff inflation pressure is ~30 mmHg higher than the resting systolic BP. In the lower limb, a higher inflation pressure, (~55 mmHg > resting systolic BP), is required to induce ischemia. Cyclical changes in capillary blood O2, CO2, and lactate levels during the RIPC stimulus were observed. RIPC at higher cuff inflation pressures of 160 and 180 mmHg was better tolerated in the upper limb. In summary, limb ischemia for RIPC can be more easily induced at lower pressures and is much better tolerated in the upper limb in young healthy individuals. However, whether benefits of RIPC can also be derived with protocols delivered to the upper limb using lower cuff inflation pressures and with lesser discomfort compared to the lower limb, remains to be investigated.

Remote Ischemic Preconditioning (RIPC) is emerging as a new noninvasive intervention that has the potential to protect a number of organs against ischemia‐reperfusion (IR) injury. Currently, there is little evidence to support what limb (upper or lower) or cuff inflation pressures are most effective to deliver this intervention without causing undue discomfort/pain in nonanesthetized humans. In this study we have demonstrated that limb ischemia for RIPC can be more easily induced at lower pressures and is much better tolerated in the upper limb compared with the lower limb, in young healthy individuals.

Systematic review of near-infrared spectroscopy determined cerebral oxygenation during non-cardiac surgery

Near-infrared spectroscopy (NIRS) is used to monitor regional cerebral oxygenation (rScO₂) during cardiac surgery but is less established during non-cardiac surgery. This systematic review aimed (i) to determine the non-cardiac surgical procedures that provoke a reduction in rScO₂ and (ii) to evaluate whether an intraoperative reduction in rScO₂ influences postoperative outcome. The PubMed and Embase database were searched from inception until April 30, 2013 and inclusion criteria were intraoperative NIRS determined rScO₂ in adult patients undergoing non-cardiac surgery. The type of surgery and number of patients included were recorded. There was included 113 articles and evidence suggests that rScO₂ is reduced during thoracic surgery involving single lung ventilation, major abdominal surgery, hip surgery, and laparoscopic surgery with the patient placed in anti-Tredelenburg's position. Shoulder arthroscopy in the beach chair and carotid endarterectomy with clamped internal carotid artery (ICA) also cause pronounced cerebral desaturation. A >20% reduction in rScO₂ coincides with indices of regional and global cerebral ischemia during carotid endarterectomy. Following thoracic surgery, major orthopedic, and abdominal surgery the occurrence of postoperative cognitive dysfunction (POCD) might be related to intraoperative cerebral desaturation. In conclusion, certain non-cardiac surgical procedures is associated with an increased risk for the occurrence of rScO₂. Evidence for an association between cerebral desaturation and postoperative outcome parameters other than cognitive dysfunction needs to be established.