Delayed onset muscle soreness (DOMS) is defined as pain or discomfort that occurs after an unaccustomed or high-intensity bout of physical activity [1]. Individuals of all fitness levels can experience DOMS following exercise. Following an extensive training session, DOMS typically occurs within 8-24 hours and peaks within 24-72 hours following exercise [2,3]. DOMS resolves on its own within 5-7 days [2,3]. The duration for healing is dependent on the severity of the muscle damage and fitness level of the individual [1,4]. Eccentric exercise is well documented as the culprit of DOMS [5]. Any exercise that contains an eccentric component (plyometric exercise, squatting, jumping, downhill running, and the lowering phase of resistance training) will produce muscle fiber damage, inflammation, DOMS, and muscle function deficits [6]. The sensation of pain can deter an individual from adhering to an exercise program, interfere with activities of daily living, and decrease athletic performance [3].

Recently, there has been an increased interest in nutritional supplements and their ability to alleviate pain and inflammation associated with DOMS. An herbal supplement that may offset the adverse effects of DOMS is willow bark. Willow bark (Salix alba L.) is obtained from the whole or fragmented dried bark of young (2-3 years old) branches or twigs from various species of Salix, belonging to the Salicaceae family [7]. Historical records show that willow bark has been used for thousands of years in ancient China, Egypt, Greece, and South Asia to alleviate headaches, fever, pain and treat numerous other illnesses [8]. The discovery of the pharmacological active ingredient salicin and its constitute salicylic acid in the 1800s paved the way for chemists to synthetically produce the acetylated derivative of salicylic acid into the most popular drug world wide, Aspirin [7,9]. Today, willow bark is often refereed as the herbal counterpart of Aspirin with similar analgesic and anti-inflammatory properties with a lower risk of experiencing gastrointestinal upset.

Currently, there is no uniform recommended dosage for willow bark extract. The European Medicine Agency (EMA) suggest a dose of 393-1572mg extract corresponding to no more than 240mg salicin per day [10]. In addition to salicin, willow bark is shown to contain high levels of polyphenols (salicylates, flavonoids, proanthocyanidins, and tannins) that contribute to its overall analgesic and anti-inflammatory effects. The exact mechanism willow bark acts upon to produce both anti-inflammatory and analgesic effects is not agreed upon. It is theorized that willow bark has inhibitory actions on the arachidonic acid pathway. More specifically, willow bark may target COX-1 and COX-2, to decrease pain and inflammation.

To date, the effects of willow bark on pain and inflammation has been studied in individuals with osteoarthritis [11,12] chronic low back pain [13-16] and rheumatic pain with results showing a potential for willow bark in alleviating pain and inflammation [11, 16-18]. To our knowledge, no studies have been conducted on the potential of willow bark in alleviating pain and inflammation in a non-clinical population. The aim of this pilot study was to investigate the effectiveness of white willow bark (WWB) on alleviating pain and inflammation associated with DOMS in healthy collage age individuals following an exhaustive lower body resistance training session.

The characteristics of the participants are presented in <Table 1>. Twenty-five healthy males (n = 10) and females (n = 15) took part in this investigation. Fourteen were randomly placed in the placebo group (male: 6; female: 8) and 11 in the WWB (male: 4; female: 7) group. The results of the independent t-test revealed no significant differences (p > 0.05) between the groups in age, height, weight, and body mass index (BMI). All 25 participants reported no adverse effects during the investigation.

To the best of our knowledge, this was the first investigation to examine the effects of WWB on the parameters of DOMS, as well as the potential of WWB to decrease both pain and inflammation following exercise in healthy adults. Despite not being statistically significant, WWB decreased subjective pain and soreness evaluated by the VAS and preserved pressure pain threshold more than the placebo. For the daily measurements during the five-day supplementation period, those in the WWB group rated their muscle discomfort lower than the placebo with a pronounced lower VAS rating for muscle soreness or discomfort 24-72hrs following exercise. The tendency of WWB being superior to placebo in decreasing subjective muscle soreness is in agreement with other studies that examined the effectiveness of willow bark on decreasing pain [11-13]. Biegert et al. [11] found that willow bark decreased joint pain more than the placebo after six weeks of treatment (15% vs. 4% respectively). Schmidt et al. [12] found after two weeks of consuming 240mg of salicin, osteoarthritis pain was decreased by 14% while those in the placebo group had a 2% increase in pain. Churbaskik et al. [13] concluded that WWB with a salicin content ranging from 120-240mg provided significantly more pain reduction than placebo. However, caution should be warranted with interpreting the results since participants were allowed to take tramadol as a rescue medication.

Using a VAS to rate individual soreness is shown to be reliable and is used in previous investigations regarding DOMS and pain [23,24]. The subjective nature of these scales should be discussed. The ability to deal with pain and discomfort will vary among individuals and may be influenced by their current and past training experiences. Dealing with pain or discomfort is reflected to the individuals’ pain threshold and their ability to cope with both the mental and physical manifestations of pain (pain tolerance) [25]. While there is no difference in pain threshold in athletes and no-athletes, athletes have a superior pain tolerance over non-athletes [26]. While the exact mechanism leading to an athletes’ superior pain tolerance is not known, it is suggested that both current and past athletes have developed superior cognitive coping strategies to redirect their focus from the pain (dissociation) or focus on the pain to reinterpret it (association) [25,26]. While none of the participants were actively taking part in a lower body resistance training program at the time of the study, their past training history may have influenced their perceived muscle soreness and discomfort. Those accustomed to the feeling of DOMS may have rated this perceived muscle soreness or discomfort as minimal compared to those with less experience of DOMS, or with a lesser cognitive coping strategy.

The placebo effect may have influenced the ratings of subjective muscle discomfort or pain following DOMS. The placebo effect is a powerful phenomenal aspect that can influence the physiological mechanisms and outcomes of pain [27]. In an investigation by Carvalho et al. [28], patients suffering from chronic low back pain were given an open label placebo prescription to take with their treatment as usual. At the end of the three week study, patients taking the label placebo prescription experienced significant (p < 0.05) pain relief and a decrease in back pain-related disability more than those who continued their treatment as usual. The consumption of a possible analgesic medication along with an expectation of the medication is providing possible relief can lead to an analgesic response [29]. In this investigation, 60% of participants, regardless of group, believed they had the WWB and 40% of the participants believed they had the placebo. When the data was broken down into individual treatment groups, 25% of those in the placebo believed they had the WWB and 36% in the WWB correctly guessed they had WWB. The participants belief that they were consuming WWB, regardless of grouping, may resulted in a lower pain rating due to their belief that the supplement or placebo was working. In addition, neutral stimulus such as the color, taste, or smell of the supplement could have led to the association of taking an analgesic and enhancing the pharmacological effect of the supplement [27]. Research has shown that white placebo pills are perceived as analgesics and large capsules are perceived to offer stronger pharmacological effects [30]. In this investigation, the placebo pills contained powdered sugar in large capsules. The appearance of the placebo in this investigation could have led to the belief that they had the WWB and resulted in a perceived analgesic effect.

When collapsed across groups, there was a significant (p < 0.05) time difference for right mid-thigh pressure pain threshold with day three (72hrs) following resistance training and significantly lower than day six (post-supplementation). The pressure pain threshold for day three in the placebo group was 5.20% and 10.03% lower than the baseline measurements for the right and left mid-thigh, respectively. WWB partially eliminated the detrimental effects that inflammation and muscle damage had on pressure pain threshold. The average pressure pain threshold in the WWB was 1.71% and 3.69% lower than baseline during the peak of muscle soreness for the right and left mid-thigh, respectively. The results of the investigation revealed, while not statistically significant, WWB was superior to the placebo in maintaining pressure pain threshold. The data suggest that WWB has a potential to maintain pressure pain threshold following exercise.

In this investigation, thigh circumference was used to measure the acute inflammatory response following DOMS. Assessing circumference is often used in research to measure changes in inflammation over time [2,31,32]. Measurements of thigh circumference is an indicator of acute changes in the thigh volume due to inflammation associated with exercise induced muscle injury [32]. In the current investigation, the increase in mid-thigh circumference developed quickly following the cessation of exercise and continued to stay elevated. Thigh circumference was significantly higher immediately following exercise compared to both baseline and day-six (post-supplementation). The immediate inflammatory response resulting in the increase of thigh circumference is consistent with other studies that examined acute responses of DOMS on parameters of muscle damage [2,31,33]. During this six day study, both groups showed a similar pattern of declining inflammation following training. Due to no obvious differences between the two treatment conditions, the effect of WWB deceasing inflammation assessed by thigh circumference is inconclusive.

There were limitations that need to be considered in the present study. The primary limitation of the current study was the small sample size. It is speculated that increasing the sample size may have elicited significant differences between the groups regarding the subjective rating of muscle soreness or discomfort and the pressure pain threshold. A secondary limitation in the study is the lack of a control group. The placebo effect may have impacted the VAS scores and pressure pain threshold. The inclusion of a control group that did not take part in any treatment could bring more clarity on the analgesic effects of WWB by counteracting the placebo effect that may have occurred.

In this double-blind placebo-controlled study, the effects of WWB on the parameters of DOMS on apparent healthy adults was examined. After the five-day supplementation period following the induction of DOMS, there were no significant differences between the treatment conditions on any variable. Despite not being statistically significant, WWB decreased subjective pain and soreness evaluated by the VAS and preserved pressure pain threshold more than the placebo. Based on the findings, we believe WWB may offer some analgesic effects following a bout of exhaustive exercise as observed by the lower VAS scores and increased pressure pain threshold compared to the placebo. To confirm these results, future research will need to continue to study the analgesic and anti-inflammatory properties of WWB in non-clinical populations to determine if WWB would be a successful alternative to aspirin or other NSAIDs to treat DOMS following exercise.