Summary of findings for the main comparison. Summary of findings: antioxidants versus placebo.
| Antioxidants compared with placebo or no treatment for preventing and reducing muscle soreness after exercise | ||||||
|
Patient or population: mainly physically active individuals1 partaking in exercise2 designed to produce delayed onset muscle soreness Settings: controlled laboratory studies and field‐based studies Intervention: antioxidant supplements3. These fell into 3 main categories: whole natural food source (e.g. bilberry juice, cherry, pomegranate juice); antioxidant extract or mixed antioxidants (e.g. black tea extract, curcumin); and vitamin C or E or both combined. Comparison: all were placebo controls | ||||||
| Outcomes | Illustrative comparative risks (95% CI) |
Relative effect (95% CI) |
No of participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control (placebo or no antioxidants) | Antioxidant supplementation | |||||
|
Muscle soreness Follow‐up: immediately up to 6 hours post‐exercise |
The mean level of muscle soreness in the control group ranged from 1.0 to 8.3 cm (adjusted to a 0 to 10 cm scale) | The mean level of muscle soreness after antioxidant supplementation was 0.30 standard deviations lower (0.56 to 0.04 lower) |
SMD ‐0.30 (‐0.56 to ‐0.04) |
525 (21 studies4) | ⊕⊕⊝⊝ low5 | One 'rule of thumb' is that 0.2 represents a small difference, 0.5 a moderate difference and 0.8 a large difference. Based on this 'rule of thumb', this result equates to a small to moderate difference in favour of antioxidant supplementation. However, when we rescaled the data to a 0 to 10 cm scale, the MD was lower by 0.52 cm (0.95 to 0.08 cm lower). These are all under the typical MID for pain (taken here as 1.4 cm). |
|
Muscle soreness Follow‐up: 24 hours |
The mean level of muscle soreness in the control group ranged from 0.21 to 8.8 cm (adjusted to a 0 to 10 cm scale) | The mean level of muscle soreness after antioxidant supplementation was 0.13 standard deviations lower (0.27 to 0.00 lower) |
SMD ‐0.13 (‐0.27 to ‐0.00) |
936 (41 studies4) | ⊕⊕⊕⊝ moderate6 | Based on the above 'rule of thumb', this result equates to a small difference in favour of antioxidant supplementation. However, when we rescaled the data to a 0 to 10 cm scale, the MD was lower by 0.17 cm (0.42 lower to 0.07 higher). These are all under the typical MID for pain (taken here as 1.4 cm). |
|
Muscle soreness Follow‐up: 48 hours |
The mean level of muscle soreness in the control group ranged from 0.32 to 9.56 cm (adjusted to a 0 to 10 cm scale) | The mean level of muscle soreness after antioxidant supplementation was 0.24 standard deviations lower (0.42 to 0.07 lower) |
SMD ‐0.24 (‐0.42 to ‐0.07) |
1047 (45 studies7) | ⊕⊕⊝⊝ low8 | Based on the above 'rule of thumb', this result equates to a small difference in favour of antioxidant supplementation. However, when we rescaled the data to a 0 to 10 cm scale, the MD was lower by 0.41 cm (0.69 to 0.12 lower). These are all under the typical MID for pain (taken here as 1.4 cm). |
|
Muscle soreness Follow‐up: 72 hours |
The mean level of muscle soreness in the control group ranged from 0.5 to 8.5 cm (adjusted to a 0 to 10 cm scale) | The mean level of muscle soreness after antioxidant supplementation was 0.19 standard deviations lower (0.38 to 0.00 lower) |
SMD ‐0.19 (‐0.38 to ‐0.00) |
657 (28 studies4) | ⊕⊕⊕⊝ moderate6 | Based on the above 'rule of thumb', this result equates to a small difference in favour of antioxidant supplementation. When we rescaled the data to a 0 to 10 cm scale, the MD was lower by 0.29 cm (0.59 lower to 0.02 higher). These are all under the typical MID for pain (taken here as 1.4 cm). |
|
Muscle soreness Follow‐up: 96 hours |
The mean level of muscle soreness in the control group ranged from 0.2 to 5.6 cm (adjusted to a 0 to 10 cm scale) | The mean level of muscle soreness after antioxidant supplementation was 0.05 standard deviations lower (0.29 lower to 0.19 higher) |
SMD ‐0.05 (‐0.29 to 0.19) |
436 (17 studies4) | ⊕⊕⊝⊝ low8 | Based on the above 'rule of thumb', this result equates to a small difference in favour of antioxidant supplementation but also includes a small effect in favour of placebo or no antioxidants. However, when we rescaled the data to a 0 to 10 cm scale, the MD was lower by 0.03 cm (0.43 lower to 0.37 higher). These are all under the typical MID for pain (taken here as 1.4 cm). |
| Subjective recovery | See comment | See comment | — | See comment | — | None of the 50 studies included in this review measured subjective recovery (return to previous activities without signs or symptoms). |
| Adverse events | See comment | See comment | — | See comment 9 studies (216 participants) |
⊕⊝⊝⊝ very low9 | Adverse effects were considered in only 9 studies and actual events reported in 2 studies. One study reported that all 6 participants in the antioxidant supplementation group10 had diarrhoea (5 mild, 1 severe); 4 participants also reported mild indigestion. One placebo group participant also had mild indigestion. The second study reported mild gastrointestinal distress in 1 of 26 participants taking the antioxidant supplement. |
| CI: confidence interval; RR: risk ratio; MD: mean difference; MID: minimal important difference; SMD: standardised mean difference | ||||||
| GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Thus we are confident that the true effect lies close to what was found in the research Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Thus, the true effect is likely to be close to what was found, but there is a possibility that it is substantially different Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Thus, the true effect may be substantially different from what was found Very low quality: We are very uncertain about the estimate. | ||||||
1Although some participants were sedentary, the majority of participants were recreationally active or moderately trained athletes. No data were included from highly trained elite athletes. Most trial participants were male.
2Muscle damage was induced either mechanically (e.g. resistance‐based exercise) or through whole body aerobic exercise (e.g. running, cycling, bench stepping).
3Typically, supplementation was taken before, the day of and after exercise for up to several days. The supplements were all taken orally, either as capsules, powders or drinks. All studies used an antioxidant dosage higher than the recommended daily amount.
4In this analysis, one study tested two antioxidants compared with placebo control.
5We downgraded the quality of evidence one level for serious study limitations (high/unclear risk of bias) and one level for serious inconsistency.
6We downgraded the quality of evidence one level for serious study limitations (high/unclear risk of bias).
7In this analysis, two studies tested two antioxidants compared with placebo control.
8We downgraded the quality of evidence one level for serious study limitations (high/unclear risk of bias) and one level for serious inconsistency.
9We downgraded the quality of evidence three levels for very serious study limitations, in particular reflecting bias relating failure to record or report on adverse events by the majority of trials.
10Notably the antioxidant used was NAC (N‐acetylcysteine), which is a prescription medicine with antioxidant properties. Listed side effects of NAC include nausea, vomiting and diarrhoea or constipation.