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Commentaries on Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning?
2017; American Physiological Society; Volume: 122; Issue: 3 Linguagem: Inglês
10.1152/japplphysiol.00030.2017
ISSN8750-7587
AutoresLuca Angius, Antonio Crisafulli, Thomas J. Hureau, Ryan M. Broxterman, Markus Amann, Anthony V. Incognito, Jamie F. Burr, Philip J. Millar, Helen Jones, Dirk J Thijssen, Stephen D. Patterson, Owen Jeffries, Mark Waldron, Bruno M. Silva, Thiago Ribeiro Lopes, Lauro C. Vianna, Joshua R. Smith, Steven W. Copp, Gary P. Van Guilder, Li Zuo, Chia-Chen Chuang,
Tópico(s)Cardiac Arrest and Resuscitation
ResumoViewpointCommentaries on Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning?Published Online:16 Mar 2017https://doi.org/10.1152/japplphysiol.00030.2017MoreSectionsPDF (75 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Luca Angius.Author AffiliationsUniversity of Kent.to the editor: Cruz and colleagues (3) suggested that the ergogenic effect of ischemic preconditioning (IP) is in part caused by a reduced activity of sensory muscle afferents (SMA). This is an intriguing hypothesis that also further highlights some important implications of SMA for endurance performance. However, given the complex and integrative role of SMA, some points should be considered. First, unlike IP, spinal blockade of SMA did not provide any ergogenic effect on healthy subjects (1, 2), albeit the last most probably has a stronger suppression of SMA activity. Second, blockade of SMA demonstrated that perception of effort (RPE) is independent of SMA activity (4) and therefore changes in RPE after IP, should not be caused by a reduced activity of SMA. Finally, the ergogenic effect of IP might be also caused by a placebo effect. Indeed, the inability to effectively perform a sham-control IP treatment still remains. The placebo effect mainly relies on the assumption that participant believes that the intervention will alter results. For IP treatment, sham procedure commonly involves a very low cuff pressure that does not induce the same sensation experienced during IP treatment. Therefore participant expectancy about the treatment is unpredictable and might explain the improvement in performance and/or an altered pacing strategy (3, 5). Accordingly, future experiments should deserve more attention to reduce this confounding variable. In conclusion, future studies are required to confirm this hypothesis and more research is needed to understand the physiological mechanisms responsible for the ergogenic effect of IP on exercise performance.REFERENCES1. Amann M, Blain GM, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Implications of group III and IV muscle afferents for high-intensity endurance exercise performance in humans. J Physiol 589: 5299–5309, 2011. doi:10.1113/jphysiol.2011.213769. Crossref | PubMed | ISI | Google Scholar2. Amann M, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans. J Physiol 587: 271–283, 2009. doi:10.1113/jphysiol.2008.163303. Crossref | PubMed | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. Marcora S. Perception of effort during exercise is independent of afferent feedback from skeletal muscles, heart, and lungs. J Appl Physiol (1985) 106: 2060–2062, 2009. doi:10.1152/japplphysiol.90378.2008. Link | ISI | Google Scholar5. Marocolo M, da Mota GR, Pelegrini V, Appell Coriolano HJ. Are the beneficial effects of ischemic preconditioning on performance partly a placebo effect? Int J Sports Med 36: 822–825, 2015. doi:10.1055/s-0035-1549857. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Amann M, Blain GM, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Implications of group III and IV muscle afferents for high-intensity endurance exercise performance in humans. J Physiol 589: 5299–5309, 2011. doi:10.1113/jphysiol.2011.213769. Crossref | PubMed | ISI | Google Scholar2. Amann M, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans. J Physiol 587: 271–283, 2009. doi:10.1113/jphysiol.2008.163303. Crossref | PubMed | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. Marcora S. Perception of effort during exercise is independent of afferent feedback from skeletal muscles, heart, and lungs. J Appl Physiol (1985) 106: 2060–2062, 2009. doi:10.1152/japplphysiol.90378.2008. Link | ISI | Google Scholar5. Marocolo M, da Mota GR, Pelegrini V, Appell Coriolano HJ. Are the beneficial effects of ischemic preconditioning on performance partly a placebo effect? Int J Sports Med 36: 822–825, 2015. doi:10.1055/s-0035-1549857. Crossref | PubMed | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Antonio Crisafulli.Author AffiliationsUniversity of Cagliari (Italy).to the editor: In this interesting Viewpoint, Cruz and colleagues (2) addressed the possible role of type III and IV nerve endings in mediating the ergogenic effect of ischemic preconditioning (IP). Although some studies have demonstrated that IP can effectively enhance performance in several kinds of exercise, others failed to find any beneficial effects. This fact is puzzling because positive and negative outcomes are both reported even by the same group (1, 5). Thus further research in this field is warranted. One aspect that authors have overlooked is that the discharge of afferent group III and IV nerve endings, along with their role in the sensation of fatigue and in the inhibitions of central motor drive, also exerts an important contribution to the cardiovascular regulation during exercise. Actually, they activate the sympathetic system on the basis of the mechanical and metabolic conditions of the working muscle (4). In our laboratory we recently conducted experiments to ascertain whether IP could improve exercise (task failure test during dynamic handgrip) and whether there was any cardiovascular effect (3). However, although IP successfully affected hemodynamics (it reduced the blood pressure and cardiac preload during the metaboreflex activation), we failed to find out any improvement in time to task failure. Thus, at least for exercise with limited muscle mass, this finding does not support any role of type III and IV nerve endings in the IP-mediated ergogenic effect.REFERENCES1. Crisafulli A, Tangianu F, Tocco F, Concu A, Mameli O, Mulliri G, Caria MA. Ischemic preconditioning of the muscle improves maximal exercise performance but not maximal oxygen uptake in humans. J Appl Physiol (1985) 111: 530–536, 2011. doi:10.1152/japplphysiol.00266.2011. Link | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Mulliri G, Sainas G, Magnani S, Palazzolo G, Milia N, Orrù A, Roberto S, Marongiu E, Milia R, Crisafulli A. Ischemic preconditioning reduces hemodynamic response during metaboreflex activation. Am J Physiol Regul Integr Comp Physiol 310: R777–R787, 2016. doi:10.1152/ajpregu.00429.2015. Link | ISI | Google Scholar4. Nóbrega ACL, O’Leary D, Silva BM, Marongiu E, Piepoli MF, Crisafulli A. Neural regulation of cardiovascular response to exercise: role of central command and peripheral afferents. BioMed Res Int 2014: 478965, 2014. doi:10.1155/2014/478965. Crossref | PubMed | ISI | Google Scholar5. Tocco F, Marongiu E, Ghiani G, Sanna I, Palazzolo G, Olla S, Pusceddu M, Sanna P, Corona F, Concu A, Crisafulli A. Muscle ischemic preconditioning does not improve performance during self-paced exercise. Int J Sports Med 36: 9–15, 2015. PubMed | ISI | Google ScholarREFERENCES1. Crisafulli A, Tangianu F, Tocco F, Concu A, Mameli O, Mulliri G, Caria MA. Ischemic preconditioning of the muscle improves maximal exercise performance but not maximal oxygen uptake in humans. J Appl Physiol (1985) 111: 530–536, 2011. doi:10.1152/japplphysiol.00266.2011. Link | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Mulliri G, Sainas G, Magnani S, Palazzolo G, Milia N, Orrù A, Roberto S, Marongiu E, Milia R, Crisafulli A. Ischemic preconditioning reduces hemodynamic response during metaboreflex activation. Am J Physiol Regul Integr Comp Physiol 310: R777–R787, 2016. doi:10.1152/ajpregu.00429.2015. Link | ISI | Google Scholar4. Nóbrega ACL, O’Leary D, Silva BM, Marongiu E, Piepoli MF, Crisafulli A. Neural regulation of cardiovascular response to exercise: role of central command and peripheral afferents. BioMed Res Int 2014: 478965, 2014. doi:10.1155/2014/478965. Crossref | PubMed | ISI | Google Scholar5. Tocco F, Marongiu E, Ghiani G, Sanna I, Palazzolo G, Olla S, Pusceddu M, Sanna P, Corona F, Concu A, Crisafulli A. Muscle ischemic preconditioning does not improve performance during self-paced exercise. Int J Sports Med 36: 9–15, 2015. PubMed | ISI | Google ScholarSMALL-DIAMETER MUSCLE AFFERENTS MAY NOT BE THE PREDOMINANT FACTOR RESPONSIBLE FOR THE ERGOGENIC EFFECT ASSOCIATED WITH ISCHEMIC PRECONDITIONINGThomas J. Hureau, Ryan M. Broxterman, and Markus Amann.Author AffiliationsUniversity of Utah.to the editor: Cruz et al. (3) suggest a mechanism potentially accounting for the improved cycling performance frequently observed after ischemic preconditioning (IP) of the lower limbs. The authors propose that an IP-evoked desensitization of group III/IV muscle afferents and the resulting decrease in neural feedback could facilitate motor drive and therefore account for this improvement. However, this hypothesis is challenged by previous observations. Specifically, although a pharmacological reduction of group III/IV-mediated neural feedback from the legs indeed improves spinal motoneuronal output during cycling exercise (i.e., attenuates central fatigue), it also decreases muscle O2 delivery and exacerbates the rate of development of peripheral fatigue (5). These are two opposing consequences, with the former (reduced central fatigue) facilitating and the latter (increased rate of peripheral fatigue) compromising endurance performance. The net effect is a compromised (1), or, at best, an unchanged performance (2). Consequently, a desensitization of group III/IV muscle afferents is likely not the only/main factor responsible for the improved cycling performance after IP. Clearly, even were IP to attenuate afferent feedback (direct evidence is currently missing) and decreases central fatigue, other changes not related to afferent feedback, such as, for example, an enhanced functional sympatholysis (4), likely also contribute to the ergogenic effect. Only that constellation can explain the fact that the proposed positive effect of attenuating muscle afferent feedback via IP (decrease central fatigue) (3) prevails over the documented limiting effect on performance (increase rate of peripheral fatigue) (1). Regardless, the ergogenic effect evoked by IP is intriguing and requires further investigation.REFERENCES1. Amann M, Blain GM, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Implications of group III and IV muscle afferents for high-intensity endurance exercise performance in humans. J Physiol 589: 5299–5309, 2011. doi:10.1113/jphysiol.2011.213769. Crossref | PubMed | ISI | Google Scholar2. Blain GM, Mangum TS, Sidhu SK, Weavil JC, Hureau TJ, Jessop JE, Bledsoe AD, Richardson RS, Amann M. Group III/IV muscle afferents limit the intramuscular metabolic perturbation during whole body exercise in humans. J Physiol 594: 5303–5315, 2016. doi:10.1113/JP272283. Crossref | PubMed | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. Horiuchi M, Endo J, Thijssen DH. Impact of ischemic preconditioning on functional sympatholysis during handgrip exercise in humans. Physiol Rep 3: e12304, 2015. doi:10.14814/phy2.12304. Crossref | PubMed | ISI | Google Scholar5. Taylor JL, Amann M, Duchateau J, Meeusen R, Rice CL. Neural contributions to muscle fatigue: from the brain to the muscle and back again. Med Sci Sports Exerc 48: 2294–2306, 2016. doi:10.1249/MSS.0000000000000923. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Amann M, Blain GM, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Implications of group III and IV muscle afferents for high-intensity endurance exercise performance in humans. J Physiol 589: 5299–5309, 2011. doi:10.1113/jphysiol.2011.213769. Crossref | PubMed | ISI | Google Scholar2. Blain GM, Mangum TS, Sidhu SK, Weavil JC, Hureau TJ, Jessop JE, Bledsoe AD, Richardson RS, Amann M. Group III/IV muscle afferents limit the intramuscular metabolic perturbation during whole body exercise in humans. J Physiol 594: 5303–5315, 2016. doi:10.1113/JP272283. Crossref | PubMed | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. Horiuchi M, Endo J, Thijssen DH. Impact of ischemic preconditioning on functional sympatholysis during handgrip exercise in humans. Physiol Rep 3: e12304, 2015. doi:10.14814/phy2.12304. Crossref | PubMed | ISI | Google Scholar5. Taylor JL, Amann M, Duchateau J, Meeusen R, Rice CL. Neural contributions to muscle fatigue: from the brain to the muscle and back again. Med Sci Sports Exerc 48: 2294–2306, 2016. doi:10.1249/MSS.0000000000000923. Crossref | PubMed | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Anthony V. Incognito, Jamie F. Burr, and Philip J. Millar.Author AffiliationsUniversity of Guelph, Canada.to the editor: Metabolically sensitive group III/IV skeletal muscle afferents influence both hemodynamic responses (through sympathoexcitation) and motor drive (through spinal/supraspinal inhibition) during exercise (1). Unknown, are the functional differences between muscle metabo-receptor subtypes, classified as ergoreceptors or metabo-nociceptors (1). In a recent Viewpoint, Cruz et al. (2) argue that exercise performance improvements after limb ischemic preconditioning (IPC) (3) may be driven by a selective desensitization of metabo-nociceptors, a subtype with high activation thresholds (1). The authors posit that reduced metabo-nociceptor discharge may attenuate motor drive inhibition independent of hemodynamic responses, explaining increases in electromyographic activity (2) but no change in blood pressure (5) during exercise after IPC. Although it is possible that IPC affects afferent subtypes differentially, one study (cited by the authors) used postexercise circulatory occlusion (PECO) after rhythmic handgrip to isolate the muscle metaboreflex (5). Such an approach, known to sustain (or increase) blood pressure and muscle sympathetic outflow after exercise, may preferentially target metabo-nociceptors, providing limited insight into active ergoreceptors during exercise (1). This study (5) reported that IPC increased systemic vascular resistance during PECO, inconsistent with the hypothesis of reduced group III/IV afferent stimulation. More directly, preliminary data from our laboratory (4) demonstrate no reductions in muscle sympathetic outflow or blood pressure during static handgrip or PECO after IPC. If group III/IV afferent desensitization mediates exercise performance benefits, how IPC influences motor drive independent of hemodynamic responses requires resolution. Last, we believe that greater emphasis should be placed on determining conclusively that IPC mediates a non-placebo ergogenic effect (3).REFERENCES1. Amann M, Sidhu SK, Weavil JC, Mangum TS, Venturelli M. Autonomic responses to exercise: group III/IV muscle afferents and fatigue. Auton Neurosci 188: 19–23, 2015. doi:10.1016/j.autneu.2014.10.018. Crossref | PubMed | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Incognito AV, Burr JF, Millar PJ. The effects of ischemic preconditioning on human exercise performance. Sports Med 46: 531–544, 2016. doi:10.1007/s40279-015-0433-5. Crossref | PubMed | ISI | Google Scholar4. Incognito AV, Doherty CJ, Lee JB, Millar PJ. Effects of ischemic preconditioning on neural and hemodynamic responses to muscle metaboreflex activation. FASEB J 30, Suppl: 1289.9, 2016.ISI | Google Scholar5. Mulliri G, Sainas G, Magnani S, Palazzolo G, Milia N, Orrù A, Roberto S, Marongiu E, Milia R, Crisafulli A. Ischemic preconditioning reduces hemodynamic response during metaboreflex activation. Am J Physiol Regul Integr Comp Physiol 310: R777–R787, 2016. doi:10.1152/ajpregu.00429.2015. Link | ISI | Google ScholarREFERENCES1. Amann M, Sidhu SK, Weavil JC, Mangum TS, Venturelli M. Autonomic responses to exercise: group III/IV muscle afferents and fatigue. Auton Neurosci 188: 19–23, 2015. doi:10.1016/j.autneu.2014.10.018. Crossref | PubMed | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Incognito AV, Burr JF, Millar PJ. The effects of ischemic preconditioning on human exercise performance. Sports Med 46: 531–544, 2016. doi:10.1007/s40279-015-0433-5. Crossref | PubMed | ISI | Google Scholar4. Incognito AV, Doherty CJ, Lee JB, Millar PJ. Effects of ischemic preconditioning on neural and hemodynamic responses to muscle metaboreflex activation. FASEB J 30, Suppl: 1289.9, 2016.ISI | Google Scholar5. Mulliri G, Sainas G, Magnani S, Palazzolo G, Milia N, Orrù A, Roberto S, Marongiu E, Milia R, Crisafulli A. Ischemic preconditioning reduces hemodynamic response during metaboreflex activation. Am J Physiol Regul Integr Comp Physiol 310: R777–R787, 2016. doi:10.1152/ajpregu.00429.2015. Link | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Helen Jones.Author AffiliationsLiverpool John Moores University.Dirk J. Thijssen.Author AffiliationsLiverpool John Moores University.Radboud University Medical Centre.to the editor: Since our observation (4) in 2010 that ischemic preconditioning (IPC) may enhance performance, researchers have explored the impact of IPC on varying modes of exercise. Fewer studies have explored the potential mechanisms for the performance improvements, leaving a number of unresolved questions. Cruz and colleagues (3) presented a well-constructed argument, based upon their own research studies, that IPC improves short-term cycling (~1–5 min), possibly through a mechanistic pathway related to muscle afferents. We believe it is important to highlight that 1) this pathway is difficult to translate to different types (e.g., endurance) and longer duration exercise (>5 min), and 2) the “dose” of IPC may affect the potential effects of IPC on exercise performance.The largest benefit of IPC to enhance exercise performance relates to aerobic exercise (5); this is important because the ergogenic mechanisms proposed by Cruz et al. likely differ to those that explain the enhancements to longer duration of exercise or different modes/intensities. Specifically for aerobic exercise, alterations in the lactate pathway have been suggested (1, 2). A later onset of blood lactate accumulation during exercise and/or differences in lactate production/uptake during near-maximal exercise may contribute to potential exercise benefits of IPC.Finally, when discussing the impact of IPC on performance, one should also consider the dose of IPC. The dose relates to the number of “ischemic” cycles and whether the dose is local or remote. These questions highlight the need for further studies around specific mechanisms, but also exercise benefits, for a wider translation and implementation.REFERENCES1. Bailey TG, Jones H, Gregson W, Atkinson G, Cable NT, Thijssen DH. Effect of ischemic preconditioning on lactate accumulation and running performance. Med Sci Sports Exerc 44: 2084–2089, 2012. doi:10.1249/MSS.0b013e318262cb17. Crossref | PubMed | ISI | Google Scholar2. Cruz RS, de Aguiar RA, Turnes T, Pereira KL, Caputo F. Effects of ischemic preconditioning on maximal constant-load cycling performance. J Appl Physiol (1985) 119: 961–967, 2015. doi:10.1152/japplphysiol.00498.2015. Link | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. de Groot PC, Thijssen DH, Sanchez M, Ellenkamp R, Hopman MT. Ischemic preconditioning improves maximal performance in humans. Eur J Appl Physiol 108: 141–146, 2010. doi:10.1007/s00421-009-1195-2. Crossref | PubMed | ISI | Google Scholar5. Salvador AF, De Aguiar RA, Lisbôa FD, Pereira KL, Cruz RS, Caputo F. Ischemic preconditioning and exercise performance: A systematic review and meta-analysis. Int J Sports Physiol Perform 11: 4–14, 2016. doi:10.1123/ijspp.2015-0204. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Bailey TG, Jones H, Gregson W, Atkinson G, Cable NT, Thijssen DH. Effect of ischemic preconditioning on lactate accumulation and running performance. Med Sci Sports Exerc 44: 2084–2089, 2012. doi:10.1249/MSS.0b013e318262cb17. Crossref | PubMed | ISI | Google Scholar2. Cruz RS, de Aguiar RA, Turnes T, Pereira KL, Caputo F. Effects of ischemic preconditioning on maximal constant-load cycling performance. J Appl Physiol (1985) 119: 961–967, 2015. doi:10.1152/japplphysiol.00498.2015. Link | ISI | Google Scholar3. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar4. de Groot PC, Thijssen DH, Sanchez M, Ellenkamp R, Hopman MT. Ischemic preconditioning improves maximal performance in humans. Eur J Appl Physiol 108: 141–146, 2010. doi:10.1007/s00421-009-1195-2. Crossref | PubMed | ISI | Google Scholar5. Salvador AF, De Aguiar RA, Lisbôa FD, Pereira KL, Cruz RS, Caputo F. Ischemic preconditioning and exercise performance: A systematic review and meta-analysis. Int J Sports Physiol Perform 11: 4–14, 2016. doi:10.1123/ijspp.2015-0204. Crossref | PubMed | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Stephen David Patterson, Owen Jeffries, and Mark Waldron.Author AffiliationsSt. Marys University, United Kingdom.to the editor: Cruz and colleagues (2) contend that lower discharge from small diameter muscle afferents explain the ergogenic effect of limb ischemic preconditioning (IPC) on exercise performance, evidenced by increased performance, higher myoelectrical activity, and decreased ratings of perceived effort during an endurance task (1). This suggests increased voluntary drive to the working muscles that could explain the higher EMG amplitude (1). In our study investigating the effect of IPC on repeated sprint exercise (4), we demonstrated that power output was increased in the first three of six sprints, suggestive of an increased voluntary drive. This evidence in humans (1) is similar to previous work in animal models, where EMG amplitude was increased and force decline attenuated in the preconditioned limb after recovery from prolonged ischemia (5).Although the proposed mechanisms may serve as a plausible explanation for performance enhancement after IPC, at this time, we cannot rule out a placebo (and nocebo) effect (3) because of the difficulty in blinding participants to the sensations felt during the IPC or sham stimulus employed in many of the studies. Furthermore, it is possible that the increased power output observed (1, 4) may be the cause of increased myoelectrical activity (1), rather than the effect. Future research should focus on, first, normalizing the EMG to pre-exercise force and, second, examining central activation after a bout of IPC to fully elucidate the mechanisms for IPC on exercise performance.REFERENCES1. Cruz RS, de Aguiar RA, Turnes T, Pereira KL, Caputo F. Effects of ischemic preconditioning on maximal constant-load cycling performance. J Appl Physiol (1985) 119: 961–967, 2015. doi:10.1152/japplphysiol.00498.2015. Link | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Marocolo M, da Mota GR, Pelegrini V, Appell Coriolano HJ. Are the beneficial effects of ischemic preconditioning on performance partly a placebo effect? Int J Sports Med 36: 822–825, 2015. doi:10.1055/s-0035-1549857. Crossref | PubMed | ISI | Google Scholar4. Patterson SD, Bezodis NE, Glaister M, Pattison JR. The effect of ischemic preconditioning on repeated sprint cycling performance. Med Sci Sports Exerc 47: 1652–1658, 2015. doi:10.1249/MSS.0000000000000576. Crossref | PubMed | ISI | Google Scholar5. Phillips DJ, Petrie SG, Zhou BH, Guanche CA, Baratta RV. Myoelectric and mechanical changes elicited by ischemic preconditioning in the feline hindlimb. J Electromyogr Kinesiol 7: 187–192, 1997. doi:10.1016/S1050-6411(97)84627-5. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Cruz RS, de Aguiar RA, Turnes T, Pereira KL, Caputo F. Effects of ischemic preconditioning on maximal constant-load cycling performance. J Appl Physiol (1985) 119: 961–967, 2015. doi:10.1152/japplphysiol.00498.2015. Link | ISI | Google Scholar2. Cruz RS, Pereira KL, Lisboa FD, Caputo F. Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning? J Appl Physiol, in press. doi:10.1152/japplphysiol.00662.2016. Link | ISI | Google Scholar3. Marocolo M, da Mota GR, Pelegrini V, Appell Coriolano HJ. Are the beneficial effects of ischemic preconditioning on performance partly a placebo effect? Int J Sports Med 36: 822–825, 2015. doi:10.1055/s-0035-1549857. Crossref | PubMed | ISI | Google Scholar4. Patterson SD, Bezodis NE, Glaister M, Pattison JR. The effect of ischemic preconditioning on repeated sprint cycling performance. Med Sci Sports Exerc 47: 1652–1658, 2015. doi:10.1249/MSS.0000000000000576. Crossref | PubMed | ISI | Google Scholar5. Phillips DJ, Petrie SG, Zhou BH, Guanche CA, Baratta RV. Myoelectric and mechanical changes elicited by ischemic preconditioning in the feline hindlimb. J Electromyogr Kinesiol 7: 187–192, 1997. doi:10.1016/S1050-6411(97)84627-5. Crossref | PubMed | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?Bruno M. Silva12, Thiago R. Lopes123, and Lauro C. Vianna4.Author Affiliations1Federal University of São Paulo, Brazil.2Olympic Center for Training and Research, Brazil.3São Paulo Association for Medicine Development, Brazil.4University of Brasília, Brazil.to the editor: We selected three points to discuss the Viewpoint by Cruz and colleagues (1). First, the investigation of ischemic preconditioning (IPC) ergogenic effects has been advancing fast, but most studies have not properly controlled placebo/nocebo effects. We recently overcame this limitation and found the IPC effect on running performance was similar to a sham intervention (4). Thus it is about time to confirm whether the IPC per se improves performance, otherwise the quest for underlying mechanisms may be wasted. Second, we agree that methodological factors may importantly influence the IPC ergogenic effect (1). For example, repeated IPC application may be necessary to manifest the ergogenic effect (3). Therefore, methodological factors must be clarified to develop a solid model to test underlying mechanisms, and even so, the mechanisms will be difficult to be examined, because the reported ergogenic effect is small (3). Third, the activation of nociceptor afferents, as hypothesized (1), could be a reasonable trigger. Yet, its activation may mediate ergogenic effects via mechanisms that are not restrained to the nociceptors itself, particularly via desensitization of transient receptor potential vanilloid subtype 1 (TRPV1) receptors. It is still unclear whether TRPV1 receptors determine exercise performance, but its desensitization by capsaicin administration was detrimental to exercise capacity (2), instead of being ergogenic. Alternatively, IPC may enhance production of endogenous opioids, which could act on opioid receptors not only at peripheral afferents, but also at the spinal cord and brain, leading to attenuated perception of effort and
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