To our knowledge, this is the first study to examine the effect of consumption of cherries, or a cherry product, on symptoms of exercise induced muscle damage. Consumption of a cherry juice blend for three days before a bout of eccentric exercise and for the subsequent four days was shown to decrease some of the symptoms of muscle damage. Strength loss and pain were diminished in the cherry juice trial, but motion loss and muscle tenderness were unaffected.
A randomised crossover design was used because the variability in symptoms of muscle damage between limbs within a subject is typically less than the variability in symptoms between subjects.27,28
The use of the contralateral arm rather than the same arm in the second trial (cherry juice or placebo depending on randomisation) avoided the impact of the repeated bout effect. Although it is well established that symptoms of muscle damage are diminished after a repeated bout of eccentric exercise, this protective effect does not cross over to the non‐exercised limb.28,29,30
Of the 16 subjects who began the study, nine started with the placebo trial and seven started with the cherry juice trial. However, the two subjects who left school before the end of the study started with the cherry juice trial. Therefore, only five of 14 subjects who completed the study started with the cherry juice trial. To verify that the apparent effect of cherry juice on diminished strength loss and pain was not due to a crossover protective effect, we reanalysed the data for the five subjects who started with the cherry juice trial. Despite the small sample size, the treatment by time interaction was significant for strength loss in this group of five subjects (p
0.001). Strength loss was 3 (2)% for the cherry juice trial and 24 (3)% for the placebo trial. The treatment by time interaction was not significant for pain in these five subjects (p
0.83). However, the pattern was similar to the whole group, with pain declining after 24 hours in the cherry juice trial and peaking at 48 hours in the placebo trial.
The lack of effect of cherry juice supplementation on muscle tenderness and relaxed elbow angle indicates that either these symptoms reflect different aspects of the injury response or the measurements were insensitive to real differences between cherry juice and placebo trials. Considering that muscle tenderness and pain typically follow the same time course, peaking two days after eccentric exercise of the elbow flexors,25,26
it is unlikely that they reflect different aspects of injury. Tenderness and pain also peaked two days after exercise in the present study, and therefore the effect of cherry juice would have been expected to be apparent in both measures. The fact that the tenderness measurement was only made at one site may have been a limiting factor. Tenderness was measured distally because peak tenderness has been shown to occur distally.25,31
Although measurements at additional sites may have increased the ability to detect a difference between trials, it is important to note that tenderness values were very similar between the trials, indicating no effect of cherry juice supplementation. However, the tenderness measurement is a measure of the threshold of tenderness—that is, the force at which the subject first experiences discomfort. The measurement does not indicate the magnitude of tenderness for a fixed force application. Two studies have shown an effect of anti‐inflammatory drugs on muscle tenderness.7,8
The target muscle group was the quadriceps in both studies. In one study,8
the subjects were asked to rate the soreness from 0 to 10 while a force transducer was pressed into the quadriceps at four different locations.8
In the other study, the force required to elicit soreness was recorded from multiple sites on the quadriceps, and the product of soreness intensity (N) and area (number of 2 cm sites registering a soreness measurement below a ceiling of 50 N) was recorded for analysis.7
The use of a larger muscle group and multiple sites probably improves the ability to detect treatment effects.
The relaxed elbow angle data reflect a similar lack of effect of cherry juice supplementation. Given that the average loss of motion was less than 5° in each trial and that the estimated effect size was 6°, this negative finding could be attributed to inadequate power to detect a real difference between trials. A more damaging eccentric exercise protocol or a larger sample size may be necessary to assess the effect of cherry juice supplementation on this marker of damage. Of note, only one of the six studies showing efficacy with anti‐inflammatory drugs5,6,7,8,9,10
used the elbow flexors,10
and the relaxed elbow angle was not examined in that study.
Plasma or serum measures of myoglobin or creatine kinase activity are often used as markers of muscle damage, but were not used in this study. When using blood markers, it is important to control the activity levels of the subjects immediately before and during the study to ensure that other activities are not causing increases in these markers. Such restrictions were not thought to be necessary in this study because of the crossover design. In this study, subjects were screened for previous upper extremity strengthening exercise and instructed not to use their arms in strenuous activities during the study. However, they were not instructed to avoid exercising other body parts—for example, running—and therefore serum markers were not appropriate. Serum markers might be used in future studies where activity level is strictly controlled.
Although the results of this study indicate a protective effect of cherry juice, it is not possible to conclude that cherry juice supplementation prevented muscle damage, because only two of four indirect markers of damage showed an effect. However, there was clearly a preservation of muscle function attributable to the cherry juice. For the placebo trial, strength loss was 30% at 24 hours and still 12% at 96 hours after eccentric exercise. By contrast, in the cherry juice trial, strength loss was only 12% at 24 hours, and strength was actually 6% above baseline at 96 hours. Other studies have shown a treatment effect on isometric strength, but on a smaller magnitude. Loss of isometric knee extension strength was about 3% 24 hours after eccentric exercise in subjects taking ibuprofen four hours before exercise compared with about 13% for subjects taking a placebo.7
Loss of isometric knee extension strength was about 15% 24 hours after eccentric exercise in subjects supplemented with vitamin C and E for 30 days compared with 27% in subjects taking a placebo.19
By contrast, other studies have shown no effect of ibuprofen11,13,14
or vitamin E and C15,16,17,20
on strength loss.
What is already known on this topic
- Numerous antioxidant and anti‐inflammatory agents have been identified in tart cherries, and consumption of cherries reduces circulating concentrations of inflammatory markers
- Many interventions have been studied for the prevention and treatment of exercise induced muscle damage but few have shown efficacy
What this study adds
- Consumption of cherry juice before and after eccentric exercise significantly reduced symptoms of muscle damage
- This is a practical intervention for alleviating the symptoms of muscle damage
Although it was not within the scope of this study to establish a specific mechanism of the preservation of strength, the hypothesis was that antioxidant and anti‐inflammatory effects of cherry juice supplementation may lessen the damage response. The initial damage response of eccentric contractions is a mechanical disruption of myofibrils and injury to the cell membrane. When myofibrillar disruption is extensive, this triggers a local inflammatory response that leads to an exacerbation of damage.32
Leukotrienes increase the vascular permeability, attracting neutrophils to the injury site, resulting in free radical production.33
It is possible that the anti‐inflammatory and/or the antioxidant effects of cherry juice mediated this secondary response and avoided the proliferation of myofibrillar disruption. This possibility could be examined in future work by measuring neutrophil and monocyte activation after eccentric exercise.
The apparent efficacy of this particular cherry juice in diminishing some of the symptoms of exercise induced muscle damage may be a function of the formulation of the drink. Consumption of about 45 cherries a day has been shown to reduce circulating concentrations of inflammatory markers in healthy men and women.21
In the present study, each 12 oz bottle of cherry juice contained the equivalent of 50–60 cherries, and therefore subjects were consuming the equivalent of 100–120 cherries a day. In addition, the juice contained fresh cherries—that is, not from concentrate—and it is likely that this helped to preserve the phenolic compounds and anthocyanins. The concentrations of phenolic compounds and anthocyanins reported in the methods section can provide a reference for future studies examining the efficacy of similar supplements.
In conclusion, these data show efficacy for this cherry juice in decreasing some of the symptoms of exercise induced muscle damage. Most notably, strength loss averaged over the four days after eccentric exercise was 22% with the placebo but only 4% with the cherry juice. These results have important practical applications for athletes, as performance after damaging exercise bouts is primarily affected by strength loss and pain. In addition to being an efficacious treatment for minimising symptoms of exercise induced muscle damage, consumption of cherry juice is much more convenient than many of the treatments that have been presented in the literature.33