Antioxidants for preventing and reducing muscle soreness after exercise: a Cochrane systematic review

OBJECTIVE

To determine whether antioxidant supplements and antioxidant-enriched foods can prevent or reduce delayed-onset muscle soreness after exercise.

METHODS

We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, SPORTDiscus, trial registers, reference lists of articles and conference proceedings up to February 2017.

RESULTS

In total, 50 studies were included in this review which included a total of 1089 participants (961 were male and 128 were female) with an age range of 16-55 years. All studies used an antioxidant dosage higher than the recommended daily amount. The majority of trials (47) had design features that carried a high risk of bias due to selective reporting and poorly described allocation concealment, potentially limiting the reliability of their findings. We rescaled to a 0-10 cm scale in order to quantify the actual difference between groups and we found that the 95% CIs for all five follow-up times were all well below the minimal important difference of 1.4 cm: up to 6 hours (MD -0.52, 95% CI -0.95 to -0.08); at 24 hours (MD -0.17, 95% CI -0.42 to 0.07); at 48 hours (mean difference (MD) -0.41, 95% CI -0.69 to -0.12); at 72 hours (MD -0.29, 95% CI -0.59 to 0.02); and at 96 hours (MD -0.03, 95% CI -0.43 to 0.37). Thus, the effect sizes suggesting less muscle soreness with antioxidant supplementation were very unlikely to equate to meaningful or important differences in practice.

CONCLUSIONS

There is moderate to low-quality evidence that high-dose antioxidant supplementation does not result in a clinically relevant reduction of muscle soreness after exercise of up to 6 hours or at 24, 48, 72 and 96 hours after exercise. There is no evidence available on subjective recovery and only limited evidence on the adverse effects of taking antioxidant supplements.

Antioxidants for preventing and reducing muscle soreness after exercise

BACKGROUND

Muscle soreness typically occurs after intense exercise, unaccustomed exercise or actions that involve eccentric contractions where the muscle lengthens while under tension. It peaks between 24 and 72 hours after the initial bout of exercise. Many people take antioxidant supplements or antioxidant-enriched foods before and after exercise in the belief that these will prevent or reduce muscle soreness after exercise.

OBJECTIVES

To assess the effects (benefits and harms) of antioxidant supplements and antioxidant-enriched foods for preventing and reducing the severity and duration of delayed onset muscle soreness following exercise.

SEARCH METHODS

We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, SPORTDiscus, trial registers, reference lists of articles and conference proceedings up to February 2017.

SELECTION CRITERIA

We included randomised and quasi-randomised controlled trials investigating the effects of all forms of antioxidant supplementation including specific antioxidant supplements (e.g. tablets, powders, concentrates) and antioxidant-enriched foods or diets on preventing or reducing delayed onset muscle soreness (DOMS). We excluded studies where antioxidant supplementation was combined with another supplement.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened search results, assessed risk of bias and extracted data from included trials using a pre-piloted form. Where appropriate, we pooled results of comparable trials, generally using the random-effects model. The outcomes selected for presentation in the 'Summary of findings' table were muscle soreness, collected at times up to 6 hours, 24, 48, 72 and 96 hours post-exercise, subjective recovery and adverse effects. We assessed the quality of the evidence using GRADE.

MAIN RESULTS

Fifty randomised, placebo-controlled trials were included, 12 of which used a cross-over design. Of the 1089 participants, 961 (88.2%) were male and 128 (11.8%) were female. The age range for participants was between 16 and 55 years and training status varied from sedentary to moderately trained. The trials were heterogeneous, including the timing (pre-exercise or post-exercise), frequency, dose, duration and type of antioxidant supplementation, and the type of preceding exercise. All studies used an antioxidant dosage higher than the recommended daily amount. The majority of trials (47) had design features that carried a high risk of bias due to selective reporting and poorly described allocation concealment, potentially limiting the reliability of their findings.We tested only one comparison: antioxidant supplements versus control (placebo). No studies compared high-dose versus low-dose, where the low-dose supplementation was within normal or recommended levels for the antioxidant involved.Pooled results for muscle soreness indicated a small difference in favour of antioxidant supplementation after DOMS-inducing exercise at all main follow-ups: up to 6 hours (standardised mean difference (SMD) -0.30, 95% confidence interval (CI) -0.56 to -0.04; 525 participants, 21 studies; low-quality evidence); at 24 hours (SMD -0.13, 95% CI -0.27 to 0.00; 936 participants, 41 studies; moderate-quality evidence); at 48 hours (SMD -0.24, 95% CI -0.42 to -0.07; 1047 participants, 45 studies; low-quality evidence); at 72 hours (SMD -0.19, 95% CI -0.38 to -0.00; 657 participants, 28 studies; moderate-quality evidence), and little difference at 96 hours (SMD -0.05, 95% CI -0.29 to 0.19; 436 participants, 17 studies; low-quality evidence). When we rescaled to a 0 to 10 cm scale in order to quantify the actual difference between groups, we found that the 95% CIs for all five follow-up times were all well below the minimal important difference of 1.4 cm: up to 6 hours (MD -0.52, 95% CI -0.95 to -0.08); at 24 hours (MD -0.17, 95% CI -0.42 to 0.07); at 48 hours (MD -0.41, 95% CI -0.69 to -0.12); at 72 hours (MD -0.29, 95% CI -0.59 to 0.02); and at 96 hours (MD -0.03, 95% CI -0.43 to 0.37). Thus, the effect sizes suggesting less muscle soreness with antioxidant supplementation were very unlikely to equate to meaningful or important differences in practice. Neither of our subgroup analyses to examine for differences in effect according to type of DOMS-inducing exercise (mechanical versus whole body aerobic) or according to funding source confirmed subgroup differences. Sensitivity analyses excluding cross-over trials showed that their inclusion had no important impact on results.None of the 50 included trials measured subjective recovery (return to previous activities without signs or symptoms).There is very little evidence regarding the potential adverse effects of taking antioxidant supplements as this outcome was reported in only nine trials (216 participants). From the studies that did report adverse effects, two of the nine trials found adverse effects. All six participants in the antioxidant group of one trial had diarrhoea and four of these also had mild indigestion; these are well-known side effects of the particular antioxidant used in this trial. One of 26 participants in a second trial had mild gastrointestinal distress.

AUTHORS' CONCLUSIONS

There is moderate to low-quality evidence that high dose antioxidant supplementation does not result in a clinically relevant reduction of muscle soreness after exercise at up to 6 hours or at 24, 48, 72 and 96 hours after exercise. There is no evidence available on subjective recovery and only limited evidence on the adverse effects of taking antioxidant supplements. The findings of, and messages from, this review provide an opportunity for researchers and other stakeholders to come together and consider what are the priorities, and underlying justifications, for future research in this area.

The effect of Polbax extract on lipofuscin accumulation in cultured neonatal rat cardiac myocytes

Polbax, a water-soluble extract of fresh pollen grains and pistils, was tested for its ability to influence the accumulation of lipofuscin (age pigment) in cultured neonatal rat cardiac myocytes. Exposure for 3 weeks to Polbax at concentrations of 0.1, 1.0 or 10 mg/L decreased lipofuscin accumulation morphometrically assayed using laser scanning microscopy images (green excitation light) of formaldehyde-fixed cells, by 24%, 41% or 43%, respectively. Based on the knowledge that oxidative stress and iron-catalysed peroxidation play an important role in lipofuscinogenesis, we suggest that Polbax may slow lipofuscin formation due to antioxidant activities, perhaps involving intralysosomal dismutation of superoxide produced by autophagocytosed mitochondria and/or iron-chelation.

Antioxidants: what role do they play in physical activity and health?

Exercise appears to increase reactive oxygen species, which can result in damage to cells. Exercise results in increased amounts of malondialdehyde in blood and pentane in breath; both serve as indirect indicators of lipid peroxidation. However, not all studies report increases; these equivocal results may be due to the large intersubject variability in response or the nonspecificity of the assays. Some studies have reported that supplementation with vitamins C and E, other antioxidants, or antioxidant mixtures can reduce symptoms or indicators of oxidative stress as a result of exercise. However, these supplements appear to have no beneficial effect on performance. Exercise training seems to reduce the oxidative stress of exercise, such that trained athletes show less evidence of lipid peroxidation for a given bout of exercise and an enhanced defense system in relation to untrained subjects. Whether the body's natural antioxidant defense system is sufficient to counteract the increase in reactive oxygen species with exercise or whether additional exogenous supplements are needed is not known, although trained athletes who received antioxidant supplements show evidence of reduced oxidative stress. Until research fully substantiates that the long-term use of antioxidants is safe and effective, the prudent recommendation for physically active individuals is to ingest a diet rich in antioxidants.

Response of serum indicators of myocardial infarction following exercise-induced muscle injury

The purpose of this investigation was to determine the response of three parameters used in the assessment of acute myocardial infarction (AMI) after a single bout of eccentric exercise designed to elicit skeletal muscle injury. Total creatine kinase (CK), CK-MB isoenzyme (CK-MB), and the leukocyte differential were determined after a 20-minute bench-stepping exercise in 21 men ranging in age from 30 to 45 years. Comparison of several criteria showed that the use of CK-MB or the relative lymphocyte percentage alone resulted in 11% and 1.8%, respectively, of data collection points exceeding cutoff values suggestive of AMI. However, the use of both parameters in combination completely eliminated false-positive results with no data collection points meeting the criterion. It is thus suggested that CK-MB activity in conjunction with the relative lymphocyte percentage may not only provide incremental value in the detection of AMI but also reduce the incidence of misdiagnosis associated with exercise.

Lipid peroxides production after strenuous exercise and in relation to muscle morphology and capillarization

The antioxidative capacity of slow twitch muscle fibers has been reported to be higher than that of fast twitch ones. The purpose of this study was to relate the production of lipid peroxides during exercise to the morphology and capillarization of human muscles. Twenty-seven healthy volunteers performed a strenuous 90-min exercise. The content of malonyldialdehyde (MDA) in the middle portion of vastus lateralis muscle was found positively correlated with percentage and the relative cross-sectional area of the type 1 of muscle fibers (r = 0.46, P < 0.05, r = 0.43, P < 0.05, respectively) but negatively with type II muscle fibers (r = -0.46, P < 0.05, r = -0.43, P < 0.05, respectively), especially type IIB. The content of MDA in the vastus lateralis muscle correlated positively with the number of capillaries around type II muscle fibers (r = 0.71, P < 0.001). It is suggested that the production of lipid peroxides parallels the exercise-induced increase of oxygen uptake in the muscle, being highest in more oxidative and better perfused, oxygen-consuming muscle fibers.