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Background: Prolonged or unaccustomed eccentric exercise may cause muscle damage and depending from its extent, this event negatively affects physical performance., Objectives: The aim of the present investigation was to evaluate, in humans, the effect of the flavonoid quercetin on circulating levels of the anabolic insulin-like growth factor 1 (IGF-I) and insulin-like growth factor 2 (IGF-II), produced during the recovery period after an eccentric-induced muscle damage (EIMD)., Methods: A randomized, double-blind, crossover study has been performed; twelve young men ingested quercetin (1 g/day) or placebo for 14 days and then underwent an eccentric-induced muscle damaging protocol. Blood samples were collected, and cell damage markers [creatine kinase (CK), lactate dehydrogenase (LDH) and myoglobin (Mb)], the inflammatory responsive interleukin 6 (IL-6), IGF-I and IGF-II levels were evaluated before the exercise and at different recovery times from 24 hours to 7 days after EIMD., Results: We found that, in placebo treatment the increase in IGF-I (72 h) preceded IGF-II increase (7 d). After Q supplementation there was a more marked increase in IGF-I levels and notably, the IGF-II peak was found earlier, compared to placebo, at the same time of IGF-I (72 h). Quercetin significantly reduced plasma markers of cell damage [CK (p<0.005), LDH (p<0.001) and Mb (p<0.05)] and the interleukin 6 level [IL-6 (p<0.05)] during recovery period following EIMD compared to placebo., Conclusions: Our data are encouraging about the use of quercetin as dietary supplementation strategy to adopt in order to mitigate and promote a faster recovery after eccentric exercise as suggested by the increase in plasma levels of the anabolic factors IGF-I and IGF-II., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Sgrò, Ceci, Lista, Patrizio, Sabatini, Felici, Sacchetti, Bazzucchi, Duranti and Di Luigi.)

This study was aimed at investigating whether quercetin (Q) may improve the recovery of neuromuscular function and biochemical parameters in the 7 days following an eccentric exercise-induced muscle damage (EEIMD). Sixteen men (25.9 ± 3.3 y) ingested Q (1000 mg/day) or placebo (PLA) for 14 days following a double-blind crossover study design. A neuromuscular (NM) test was performed pre-post, 24 h, 48 h, 72 h, 96 h and 7 days after an intense eccentric exercise. The force-velocity relationship of the elbow flexor muscles and their maximal voluntary isometric contraction (MVIC) were recorded simultaneously to the electromyographic signals (EMG). Pain, joint angle, arm circumference, plasma creatine kinase (CK) and lactate-dehydrogenase (LDH) were also assessed. The results showed that Q supplementation significantly attenuated the strength loss compared to PLA. During the recovery, force-velocity relationship and mean fibers conduction velocity (MFCV) persisted significantly less when participants consumed PLA rather than Q, especially at the highest angular velocities ( p < 0.02). A greater increase in biomarkers of damage was also evident in PLA with respect to Q. Q supplementation for 14 days seems able to ameliorate the recovery of eccentric exercise-induced weakness, neuromuscular function impairment and biochemical parameters increase probably due to its strong anti-inflammatory and antioxidant action.

The aim of the present investigation was to test the hypothesis that quercetin (Q) may prevent the strength loss and neuromuscular impairment associated with eccentric exercise-induced muscle damage (EEIMD). Twelve young men (26.1 ± 3.1 years) ingested either Q (1000 mg/day) or placebo (PLA) for 14 days using a randomized, double-blind, crossover study design. Participants completed a comprehensive neuromuscular (NM) evaluation before, during and after an eccentric protocol able to induce a severe muscle damage (10 sets of 10 maximal lengthening contractions). The NM evaluation comprised maximal voluntary isometric contraction (MVIC) and force⁻velocity relationship assessments with simultaneous recording of electromyographic signals (EMG) from the elbow flexor muscles. Soreness, resting arm angle, arm circumference, plasma creatine kinase (CK) and lactate dehydrogenase (LDH) were also assessed. Q supplementation significantly increased the isometric strength recorded during MVIC compared to baseline (+4.7%, p < 0.05). Moreover, the torque and muscle fiber conduction velocity (MFCV) decay recorded during the eccentric exercise was significant lower in Q compared to PLA. Immediately after the EEIMD, isometric strength, the force⁻velocity relationship and MFCV were significantly lower when participants were given PLA rather than Q. Fourteen days of Q supplementation seems able to attenuate the severity of muscle weakness caused by eccentric-induced myofibrillar disruption and sarcolemmal action potential propagation impairment.

Purpose: To examine the effect of acute quercetin (Q) ingestion on neuromuscular function, biomarkers of muscle damage, and rate of perceived exertion (RPE) in response to an acute bout of resistance training., Methods: 10 young men (22.1 ± 1.8 years, 24.1 ± 3.1 BMI) participated in a randomized, double-blind, crossover study. Subjects consumed Q (1 g/day) or placebo (PLA) 3 h prior to a resistance training session which consisted of 3 sets of 8 repetitions at 80% of the one repetition maximum (1RM) completed bilaterally for eight different resistance exercises. Electromyographic (EMG) signals were recorded from the knee extensor muscles during maximal isometric (MVIC) and isokinetic voluntary contractions, and during an isometric fatiguing test. Mechanical and EMG signals, biomarkers of cell damage, and RPE score were measured PRE, immediately POST, and 24 h (blood indices only) following the resistance exercise., Results: After a single dose of Q, the torque-velocity curve of knee extensors was enhanced and after the resistance exercise, subjects showed a lower MVIC reduction (Q: 0.91 ± 6.10%, PLA: 8.66 ± 5.08%) with a greater rate of torque development (+ 10.6%, p < 0.005) and neuromuscular efficiency ratio (+ 28.2%, p < 0.005). Total volume of the resistance exercises was significantly greater in Q (1691.10 ± 376.71 kg rep) compared to PLA (1663.65 ± 378.85 kg rep) (p < 0.05) with a comparable RPE score. No significant differences were found in blood marker between treatments., Conclusions: The acute ingestion of Q may enhance the neuromuscular performance during and after a resistance training session.

The polyphenolic flavonoid quercetin has been shown to be a powerful antioxidant, in vitro and in murine models. However, its effect on redox status has been poorly examined in humans, particularly in combination with strenuous exercise. We hypothesized that quercetin supplementation would beneficially affect redox homeostasis in healthy individuals undergoing eccentric exercise. To test this hypothesis, the effects of chronic consumption of quercetin on glutathione system (reduced, oxidized, and reduced to oxidized glutathione ratio), oxidative damage [thiobarbituric acid reactive substances (TBARs)], antioxidant enzymatic network (catalase, glutathione peroxidase, superoxide dismutase) and resistance to lysis, were investigated in erythrocytes, a traditional model widely used to study the effects of oxidative stress as well as the protective effects of antioxidants. In a two weeks controlled, randomized, crossover, intervention trial, 14 individuals ingested 2 caps (1 g/d) of quercetin or placebo. Blood samples were collected before, after 2 weeks of supplementation and after a bout of eccentric exercise. Quercetin, reduced significantly erythrocytes lipid peroxidation levels and the susceptibility to hemolysis induced by the free radical generator AAPH, while no differences in antioxidant enzyme activities and glutathione homeostasis were found between the two groups. After a single bout of eccentric exercise, quercetin supplementation improved redox status as assessed by reduced/oxidized glutathione ratio analysis and reduced TBARs levels both in erythrocytes and plasma. In conclusion, our study provides evidences that chronic quercetin supplementation has antioxidant potential prior to and after a strenuous eccentric exercise thus making the erythrocytes capable to better cope with an oxidative insult., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Quercetin (Q) functions as antioxidant in vitro, but its effect have been minimally examined in combination with exercise in humans. The purpose of this investigation was to determine the effects of a diet supplemented with 1 g per day of Q for 2 weeks on the erythrocytes oxidative balance before and after an acute bout of eccentric exercise (EE). Fourteen volunteer males were randomly assigned, in a double-blind crossover design, to a placebo or experimental supplemented groups. Blood samples were taken before and after 2 weeks of supplementation under resting and post-exercise conditions. Erythrocytes glutathione (GSH, GSSG, GSH/GSSG), malonaldehyde (TBARs), enzymes antioxidant activities as well as time of hemolysis were evaluated in ex vivo. Quercertin per se did not affect redox homeostasis but increased the time of hemolysis and decreased TBARs levels. Following the EE the Q group displayed a higher GSH/GSSG ratio and a less pronounced increase in TBARs, compared to placebo group. Moreover, we found that GPx enzyme activity were induced after EE only in Q group, while any significant modification of this parameter was detected in placebo group. In conclusion, the Q supplementation may be used as a countermeasure against oxidative stress inducing, in erythrocytes, a cellular adaptation allowing subjects to better cope with the oxidative stress induced by an acute exercise. [ABSTRACT FROM AUTHOR]