"These results have important practical applications for athletes, as performance after damaging exercise bouts is primarily affected by strength loss and pain," wrote lead author Declan Connolly from the Human Performance Laboratory at the University of Vermont.
The study was sponsored by US-based company Cherrypharm, maker of a tart cherry juice which is marketed at athletes for "less muscle damage, less pain and faster recovery".
However, the new study, published ahead of print in the British Journal of Sports Medicine (doi:10.1136/bjcm.2005.025429), claims to be the "first study to examine the effect of consumption of cherries, or a cherry product, on symptoms of exercise-induced muscle damage".
The researchers performed a randomised, placebo-controlled, crossover study with 14 men (average age 22, average BMI 28.4 kg per sq metre). Subjects received either placebo (unsweetened black cherry drink, Kool-aid, Kraft) or freshly prepared tart cherry juice from Cherrypharm.
Baseline tests were performed four days before the start of the trial. The volunteers were then given their placebo or tart cherry juice drink and told to drink two 12-ounce bottles (340 grams) every day, one in the morning and one in the evening, for the next eight days.
The trial consisted of two sets of 20 maximal eccentric contractions of the elbow flexor using a curl apparatus. Measurements of elbow flexion strength, pain and muscle tenderness were measured every 24 hours for 96 hours.
Two weeks later the trial was repeated but those on placebo now taking the cherry juice, and vice versa.
The researchers found that the weakening of the elbow flexion strength in the cherry group was significantly lower than the placebo group. The strength loss after four days, tested on an arm curl bench, was only four per cent for the cherry juice group, but was 22 per cent for the placebo group.
The development of pain in the muscles, quantified by the volunteers themselves on a scale of zero to ten (zero for no pain, ten for excruciating pain), was also significantly lower for the cherry group (2.4) compared to the placebo group (3.2).
No difference was observed in either the loss of range of motion after exercise, or muscle tenderness.
One previous study (Journal of Nutrition, Vol. 136, pp. 981-986) reported that a daily consumption of 45 cherries could reduce circulating concentrations of inflammatory markers, and the Vermont researchers propose a similar mechanism.
The researchers propose that the flavonoids and anthocyanins in the cherries exert an anti-inflammatory effect and may lessen the damage response to exercise. The 12-ounce bottles of cherry juice use in this experiment is reported to contain the equivalent of 50 to 60 cherries, giving a daily dose of between 100 and 120 cherries.
"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," said the researchers.
It is possible that the anti-inflammatory and/or antioxidant properties of the flavonoids and anthocyanins could mediate this secondary response and thereby reduce the level of muscle fibre damage.
According to market analyst Mintel, the sports drink market in the UK was worth £137m ($252m, €200m) in 2003, and is dominated by isotonic drinks like Lucozade Sport, Powerade and Gatorade.
In the US, the sports drinks market is reported to have generated almost $3bn (£1.6bn, €2.4bn) with Gatorade dominating the market with 82 per cent of the market. Powerade is a distant second with a reported 13 per cent of the market.