Ischemic preconditioning does not improve maximal power output or maximal oxygen consumption but attenuates rating of perceived exertion

Abstract

Iskæmisk prækonditionering (IPC) er et fænomen, hvor man udsætter væv, eksempelvis hjerte- eller muskelvæv, for kortvarig, ikke-skadelig iltmangel (iskæmi), hvilket beskytter vævet mod fremtidige tilfælde af iskæmi. Effekten af IPC blev bevist i et forsøg i 1986, hvor IPC reducerede skade på hjertevævet efter længerevarende iskæmi med 75%. Sidenhen har forskningsstudier undersøgt, om IPC af muskelvæv kan forbedre sportslige præstationer. Det første studie til at undersøge dette viste i 2010, at IPC øgede maksimal ydeevne i en cykeltest og maksimal iltoptagelse. Sidenhen har over 40 forskningsstudier undersøgt effekten af IPC på præstation i mange forskellige discipliner, herunder løb, cykling, svømning og styrketræning. Resultaterne er dog inkonklusive, og der kan derfor endnu ikke drages nogle endegyldige konklusioner omkring IPC’s effekt på præstationsevnen. Det tyder dog på, at iskæmisk prækonditionering har størst potentiale inden for udholdenhedspræget sport. IPC af muskelvæv udføres i praksis ved at påføre en eller flere ekstremiteter blodtryksmanchet(ter), som pumpes op for at lukke af for blodtilførslen til ekstremiteten i korte perioder. Herefter lukkes luften ud af blodtryksmanchetterne i fem minutter, hvilket medfører, at blodet kan løbe tilbage i ekstremiteterne. Den anvendte IPC-protokol varierer fra studie til studie, men i dette studie anvendtes fire perioder af skiftevis fem minutter med aflukket blodtilførsel og fem minutter med fri blodgennemstrømning med en total varighed på 40 minutter. Formålet med dette studie var at undersøge IPC’s mulige effekt på præstationsevnen. Samtidig blev mulige underliggende mekanismer, primært maksimal iltoptagelses, iltmætning i lårmuskulaturen og den opfattede anstrengelsesgrad, undersøgt. 14 unge, raske mænd deltog i dette forsøg, hvor de, på forskellige dage, fik undersøgt deres præstationsevne i en maksimal cykeltest. På to forskellige dage modtog forsøgsdeltagerne, i tilfældig rækkefølge, to forskellige behandlinger, inden de kørte den maksimale cykeltest: Enten IPC eller en placebobehandling, hvor deltagerne fik påført blodtryksmanchetterne men med så lavt et tryk, at det ikke havde nogen fysiologisk, gavnlig effekt. I dette studie havde IPC ikke en effekt på maksimal ydeevne, maksimal iltoptagelse eller iltmætning under cykeltesten. Der var dog en dæmpning af forsøgspersonernes opfattelse af anstrengelsesgraden ved bestemte belastninger.

Purpose: Brief consecutive periods of limb ischemia and reperfusion induced by a blood pressure cuff, known as ischemic preconditioning (IPC), have been reported to increase maximal power output (MPO) and maximal oxygen consumption (VO2max) during maximal incremental cycle ergometer tests. However, the underlying mechanisms are still unclear. Therefore, the purpose of the study was to investigate the effects of IPC on MPO, VO2max, RPE, and underlying performance related parameters. Methods: A double-blinded, randomized crossover study design was utilized to investigate the effects of IPC, consisting of four five-minutes cycles of ischemia interspersed with five minutes of reperfusion, on cycle ergometer performance, underlying physiological parameters, and rating of perceived exertion (RPE). Fourteen young, healthy men reported to the laboratory three times; one familiarization session and two intervention sessions, with two and seven days of rest and washout in between, respectively. After the familiarization test, in which the maximal incremental cycle ergometer test was completed, the participants were stratified and randomized into two different conditions (IPC and sham). During the two intervention sessions, in order to counterbalance, participants initially received either the IPC (250 mmHg) or sham (20 mmHg) treatment. Subsequently, the participants performed a step-transition test and a maximal incremental cycle ergometer test. During the second intervention session, the participants received the remaining treatment to complete the crossover. The researchers responsible for the cycling tests were blinded to the intervention, and the IPC and sham responsible researcher was absent while participants cycled. During both cycling tests, MPO, VO2max, submaximal VO2, rating of perceived exertion (RPE) on a Borg 6-20 scale, heart rate (HR), blood lactate concentration (BL) as well as NIRS-derived muscle oxygenation (tissue saturation index, TSI), ▲deoxygenated hemoglobin (▲HHb) and ▲oxygenated hemoglobin (▲O2Hb) were measured. Results: MPO, VO2max, HRmax, and maximal deoxygenation (minimum TSI) did not significantly change with IPC compared to sham (all P-values > 0.13). Furthermore, IPC had no significant effect on VO2, HR, TSI, ▲HHb, and ▲O2Hb during the submaximal workloads of the incremental cycling test (all P-values > 0.18). However, IPC did significantly attenuate RPE during cycling at 245 W (P = 0.007) and 280 W (P = 0.011), but not at 105 W (P = 0.145), 140 W (P = 0.034), or 175 W (P = 0.020). The P-values at 140 W and 175 W were non-significant due to the Holm-Bonferroni correction of the significance level. Furthermore, IPC had no significant effect on VO2, HR, BL, and RPE at 50 W and at 60% of ventilatory threshold in the steptransition test (all P-values > 0.11). Conclusion: The present study demonstrated that IPC did not improve MPO and VO2max, or affect any of the measured underlying physiological parameters, for young, healthy males during a maximal incremental cycle ergometer test and a step-transition test. However, IPC significantly attenuated the RPE of the participants during cycling at 245 W and 280 W.

A master thesis from Aalborg University

Ischemic preconditioning does not improve maximal power output or maximal oxygen consumption but attenuates rating of perceived exertion - a crossover study

[Iskæmisk prækonditionering forbedrer ikke maksimal ydeevne eller maksimalt iltoptag men dæmper opfattelse af anstrengelsesgrad]