It is well-documented that running for distances in excess of typical training distances causes acute muscle injury, and that eccentric muscle actions, such as downhill running, exacerbate injury and soreness . The Hood to Coast relay requires participants to run three separate race segments over an approximately 24 hour period, including segments that ascend or descend steep terrain. It is expected, therefore, that Hood to Coast runners will experience inflammation and pain during the strenuous race. In our study, runners in both groups reported more pain upon completion of the race. However, participants who drank the tart cherry juice twice daily for one week prior to and the day of the race reported a significantly smaller increase in pain after the race (mean post-race increase of 12 mm in the cherry juice group, compared with a 37 mm increase in the placebo group). The relative post-race reduction in pain in the cherry group (25 mm lower VAS than placebo) suggests that tart cherry juice provided a protective benefit against the acute muscle pain caused by distance running.
Pain associated with acute muscle injury is most likely due to oxidative tissue damage which leads to an inflammatory response, causing further production of free radicals and augmenting secondary muscle soreness [23–25]. Because of that pathogenesis, nutritional antioxidants have been proposed as a means of mitigating muscle soreness and strength loss caused by damaging exercise . Tart cherries contain flavinoids and anthocyanins, with high antioxidant and anti-inflammatory properties [13, 14]. Consumption of about 45 cherries a day has been shown to reduce circulating inflammatory markers in healthy men and women . Moreover, Kelley et al. reported that serum inflammatory markers including C-reactive protein (CRP) decreased by 25% after 28 days of consuming Bing sweet cherries . Additionally, when studied in healthy young adults, consumption of cherry juice equivalent to 100-120 cherries daily reduced strength loss and pain associated with exercise-induced delayed-onset muscle soreness (DOMS) . In our study, participants consumed two 355 mL bottles of tart cherry juice daily, (~90 to 100 cherries) for just seven days prior to and on the day of the race. The attenuated pain in the cherry juice group suggests that even short term (~1 week) supplementation with tart cherry juice is effective at reducing the acute pain caused by repeated bouts of distance running. Our results are similar to those reported by Howatson et al. , in which runners who consumed tart cherry juice for 5 days prior to and 48 hours after a marathon showed faster recovery of muscle strength as well as reduced inflammation.
Due to methodological limitations, our results should be interpreted with caution. One limitation to the study was the subjective of assessment of pain by participants. However, the VAS is commonly used to determine acute levels of pain and has consistent and well-defined clinically meaningful thresholds [21, 28]. A second limitation is the possibility of cross contamination of the intervention and placebo drinks, as participants may have potentially switched drinks to compare flavor and effects. This limitation was addressed by assigning participants on the same relay team to the same beverage condition.