Participation in group exercise events has risen dramatically over the past twenty years. The number of Americans finishing organized running races has risen from approximately 4.2 million in 1990 to over 15.5 million in 2012 [1]. The total active membership of USA Triathlon has grown from just under 65,000 in 1994 to over half a million in 2012 [2]. This trend is indicative of an increase in exhaustive training programs. Intermediate runners training for a half-marathon run an average of 25–30 miles per week, and can often exceed 35 miles per week in the three months before the race [3].

Exhaustive exercise increases oxygen consumption and stimulates mitochondria and lymphocytes, resulting in the production of reactive oxygen and nitrogen species (RONS) [4, 5]. At low to moderate levels, RONS are critical for cellular regulation of gene expression and cell signaling [6]. In muscle cells, they act as signals for cell adaptation and are thus necessary for muscle growth [7]. At high levels they become destructive to tissues, damaging cells and inhibiting muscle growth [8]. Oxidative stress or damage occurs when RONS react with cellular constituents and deform the constituent to an unusable form [9].

Two primary groups of biological constituents damaged by oxidative stress are DNA bases and fatty acids [9]. High levels of RONS become genotoxic when in contact with DNA. Guanine has the lowest oxidation potential of the four bases and thus is most commonly oxidized, forming 8-hydroxy-2′- deoxyguanosine (8-OHdG). When the body repairs the damage 8-OHdG is removed and excreted, becoming a marker for the oxidative stress. This damage, although possible in most tissues, occurs primarily in muscle tissue and circulating lymphocytes. DNA damage occurring as a result of oxidative stress may play an important role in the etiology of cancer, diabetes, and arteriosclerosis [10]. Lipids within the cell membrane are also damaged when high levels of RONS are present in the body. Oxidation of fatty acids in the membrane result in lipids degrading into malondialdehyde (MDA) [11]. MDA is a mutagenic byproduct and reacts with deoxyadenosine and deoxyguanosine in DNA, forming DNA adducts, and is itself damaging to the body, sometimes causing cell lysis and cell death [12]. Breaking of muscle cells releases creatine kinase (CK) and lactate dehydrogenase (LDH) into the blood stream – two enzymes found at high levels in muscle cells [8, 13]. In this study, 8-OHdG, a measure of oxidative stress, was chosen as the primary outcome measure. The secondary measure of MDA also measured oxidative stress. The secondary outcomes of muscle damage were measured through cellular enzymes (CK and LDH), and muscle pain and joint pain were measured using a visual analogue scale (VAS).

Physical training adapts the body to higher levels of RONS and increases its ability to manage the excess oxidative potential. However, long bouts of exercise still produce an unmanageable amount of oxidative stress. It has been suggested that the relationship between health and exercise is U-shaped, with negative health outcomes present both at low and very high levels of exercise [14]. Many negative health outcomes associated with very high levels of exercise are caused by excessive oxidative stress on the tissues. These outcomes include increased muscle fatigue, lower force production, and delayed onset muscle soreness (DOMS) [6, 13].

Methylsulfonylmethane (MSM) is a small sulfur-based molecule comprised of a sulfur atom with two double-bonded oxygen atoms and two methyl groups. It is a naturally occurring molecule found in a variety of foods including fruits, vegetables, grains and milk. Although it is most commonly supplemented to improve joint health, recent studies indicate that MSM may also be effective in seasonal allergic rhinitis, interstitial cystitis, autoimmune disease and cancer chemoprevention [15]. Studies have demonstrated that it has both anti-inflammatory and antioxidative properties [16, 17]. Although MSM, when ingested, has an antioxidative effect in vivo, the molecule itself does not directly quench oxidant activity. Instead, MSM reduces the body’s production of RONS [18]. It takes repeated doses over at least one week for MSM to build to an efficacious level within the body. This characteristic comes from its quick absorption rate and slower excretion rate [19].

In animal models, MSM has been shown to bolster the antioxidative capacity of cells compared to placebo controls, suggesting the presence of protective physiological pathways. In one study, MSM significantly decreased malondialdehyde (MDA), myeloperoxidase (MPO), and IL-1β, while increasing glutathione (GSH) and catalase (CAT) production [20]. Another study showed that MSM pre-treatment significantly attenuated damaging effects of acetaminophen including decreased GSH and superoxide dismutase (SOD), and increased MDA and MPO [21]. Using monocrotaline-induced pulmonary hypertensive rats, one study found significantly lower levels of CAT, SOD, and GSH in the hypertensive rats, and these levels recovered to control levels in MSM-treated rats [16].

Initial human exercise studies have suggested that MSM supplementation may reduce exercise-induced oxidative stress and muscle damage. In untrained males, supplementation of 50 mg/kg/day reduced levels of MDA, PC, and oxidized glutathione after an acute bout of exercise, when compared to placebo [22], and 50 mg/kg/day MSM supplementation increased the total antioxidant capacity (TAC) and reduced CK and bilirubin levels after exhaustive exercise compared to placebo [23]. Another study evaluating moderately-trained men noted reduction in muscle soreness and fatigue with increased MSM dosage, while trolox equivalent antioxidant capacity (TEAC) increased and homocysteine decreased at 3.0 g/day [24]. These studies suggest that MSM may bolster pathways that protect against excessive oxidative stress from exercise.

These studies evaluated untrained and moderately-trained men. The effects of MSM on trained individuals and women is still unknown. Determining MSM’s effectiveness on trained individuals is important because it is the population to most likely benefit from reduced oxidative and muscle damage. In addition, the current study was designed to observe the effects of MSM in a real-world application. We hypothesized that supplementing MSM at 3 g/day for three weeks reduces the oxidative damage induced by a bout of exhaustive exercise, and that the reduction of oxidative stress results in reduced muscle damage and subsequently reduces muscle soreness and joint pain.

Muscle and joint pain levels were lower in the MSM group at all post-race time points for both muscles and joints, although overall group comparisons were non-significant. Between group time comparison for muscle pain at 15 min did result in a statistical trend (p = 0.063) for lower pain in the MSM group. It is important to note that although treatment did not result in statistical significance, the size of the differences between the MSM and Placebo groups at 15 min, 90 min and one day were clinically significant (Δ > 10 mm). A reduction of 10 mm or greater is generally accepted as clinically relevant [25, 26]. The reduction of 19.8 mm for muscle pain, although not statistically significant, is bolstered by its clinical relevance. Between-group outcomes for joint pain resulted in clinically significant lower pain levels of between 9 and 10 mm. Although the results did not reach statistical significance, the clinically significant effect combined with similar results across two pain measures suggests that MSM may be effective in reducing exercise-induced pain.

While no between-group comparisons reached statistical significance at any time point, there was a statistical trend for lower 8-OHdG levels in the Placebo group two days after the race. The differences in 8-OHdG between MSM and Placebo groups that occurred at one and two days after the race appear to have occurred in part due to Placebo group levels falling below baseline. Treatment appeared to have almost no effect on the muscle damage markers CK and LDH. Logarithmically adjusted CK levels were slightly higher in the MSM group at each time point, but differences were minimal and statistically equivalent. Group comparisons for LDH showed slightly lower levels in the MSM group for race day time points, and slightly higher levels in the one and two day time points.

This study aimed at recruiting a group of participants who are not year-round competitive runners, but rather people who have decided to enter a race as a means of increasing their exercise for personal accomplishment, or for social benefits. By having a group of participants who were not overly trained, we hoped to create a group for which running a half-marathon would induce a measurable oxidative stress response. Because the body adapts to exercise, a group of highly trained individuals may not have a strong oxidative stress response to running a distance that is regularly achieved. Overall, the recruitment criteria were effective in creating a study group reflective of this larger population. A key element in this success was recruiting from a pool of people who already opted-in to running the race. The study group was slightly overweight, had an average age of 35 years, and completed the race in just over two and a half hours, on average. Body mass index was similar to U.S. population, age was similar to all half-marathon participants, and race time was slightly higher than overall U.S. average times – reflective of first or second attempts [1, 30]. A higher number of female runners is typical in distance running, but our study did not include enough men to reasonably test for potential gender differences in outcome measurements. However, because women are an underrepresented group in studies of this type, we consider the high number of female participants in our study population to be a strength of our study.

Three previous studies evaluating the effects of MSM on untrained men showed significant reductions in the oxidative stress markers MDA and protein carbonyls, a reduction in the muscle damage markers CK and bilirubin, as well as an increase in total antioxidant capacity (TAC) and glutathione [22, 23, 31]. These studies used a similar exercise intervention (14 km run) as the present study. Another clinical trial showed MSM supplementation at 3 g/day increased trolox equivalent antioxidant capacity (TEAC) in moderately trained males after completing knee extensions [24]. One possible explanation for this discrepancy is differing study populations. The study population was comprised of moderately trained participants. It is possible that the ability of MSM to attenuate exercise-induced oxidative stress and muscle damage in untrained and moderately-trained men does not work in broader populations, including women, populations with higher BMIs, and varying training levels. In addition, knee extensions have a very different effect on physiological pathways than running a half-marathon [24].

Interestingly, the results of this study suggest that MSM supplementation may simultaneously reduce muscle and joint pain, yet increase oxidative stress markers. It also suggests a correlation between higher levels of oxidative stress and muscle pain (data not shown). Although statistical significance was not reached in the group comparisons, overall patterns seem to place these findings at odds. This discrepancy may have resulted from the lack of a true baseline measurement. Baseline levels were measured approximately one month prior to the race, representing a pre-training measurement rather than a pre-race measurement. A pre-training baseline measurement is not able to account for varying training regimens, which have a considerable impact on oxidative stress responses. A measurement either the night before or immediately before the race would have provided a better representation of a pre-race baseline level. A baseline blood-draw was not taken directly before the race due to logistical constraints and the excessive burden it would have placed on the participants.

If the discrepancy did not result from a lack of true baseline, MSM must reduce pain through a separate mechanism of action. Several studies have indicated that MSM may have anti-inflammatory properties. MSM has been shown to reduce levels of NF-κβ, IL-1, IL-6, IL-8, TNF-α, and the activation of inflammasomes [17, 32, 33]. It is possible that the reduction in pain stems from a reduction in inflammation.

The body adapts to repetitive exercise, including attenuation of oxidative stress [5]. This is especially true for habitual exercise routines [34], and it is common for the intensity of training regimens to be highest the month prior to the race [3]. Differences in training, individual response to training, and level of individual athleticism in the month prior to the race can have major impacts on normal levels of oxidative stress and muscle damage [6, 35]. Oxidative stress levels in this study were lower at one and two days after the race than at baseline, indicating a biochemical adaptation occurred during the month between baseline and the race. Furthermore, previous research gives no evidence that training regimens affect normal, or baseline pain levels. Therefore the baseline pain measurements, unlike the serum measurements, were likely similar at the start of the race to those measured one month prior, and resulted in changes more reflective of previous research.

The study suggests that MSM supplementation may attenuate exercise-induced muscle and joint pain at clinically relevant levels, but that it does not reduce post-exercise markers of oxidative stress or muscle damage from pre-training levels. We also observed that running a half-marathon reliably induces muscle and joint pain, oxidative stress and muscle damage, over a predictable time course. It still remains uncertain whether MSM supplementation attenuates exercise-induced oxidative stress and muscle damage from pre-race levels, or whether results observed in previous research only apply to narrow populations. Further research on the effects of MSM on pre-exercise levels of oxidative stress and muscle damage, and research examining the effects of MSM supplementation on post-exercise pain among a larger sample of broadly-trained participants is warranted.