The key findings from the present study are that acute microencapsulated cocoa intake did not affect: (1) isometric muscle strength recovery (MVIC); (2) muscle damage recovery (plasma myoglobin); (3) perceived muscle soreness (DOMS); (4) inflammation (plasma CRP); and (5) redox balance (plasma GSH and MDA) markers following the eccentric exercise protocol. These findings suggest that a single dose of microencapsulated cocoa (containing 75 mg of total flavonoids) does not improve muscle recovery or biomarkers of inflammation and oxidative stress following exercise-induced muscle damage in resistance-trained individuals.
The muscle damage caused by eccentric exercise stems at least partly from inflammation and excess reactive oxygen species (ROS) generation that leads to oxidative stress (24). The accumulation of inflammatory cells (i.e., leukocytes, macrophages, and neutrophils) in the muscle tissue produces large amounts of ROS to lyse cellular debris and begin regeneration. However, it has been proposed that during this process, ROS may also induce lipid peroxidation in nearby healthy tissues (25). Furthermore, a large amount of ROS produced has been demonstrated to impair calcium handling and sensitivity resulting in reduced contractile force development (26–28). Therefore, the increased inflammation and ROS production provoked by strenuous eccentric exercise may intensify muscle damage and at least partly explain why decrements in muscle function and increased muscle soreness can persist for several days after exercise (29).
Polyphenols from cocoa have been demonstrated to modulate inflammation supposedly by influencing signaling cascades via an alteration to eicosanoid production (30) and reducing the activation of certain inflammatory transcription factors (e.g., nuclear factor kappa-beta) (31). This may attenuate some symptoms caused by the EIMD, such as muscle soreness and decreases in force development (32, 33).
In the present study, a single dose of microencapsulated cocoa did not promote significant changes in the oxidative stress (i.e., MDA and GSH) and inflammatory (i.e., CRP) markers in the days following EIMD. These observations agreed with Decroix et al. (33) study in that CF did not affect plasma MDA concentration after an exhaustive cycling time trial exercise. Wiswedel et al. (34) also found no significant difference of a single dose of CF on plasma MDA levels following cycling exercise in healthy untrained men. On the other hand, Fraga et al. (35) observed decreases in plasma MDA after 14 days of supplementing a food containing cocoa flavanols (186 mg) in football players, and Taub et al. (37) demonstrated an increased ratio of reduced versus oxidized glutathione and decreased protein carbonylation after 3 months supplementing with 175 mg cocoa flavanols in untrained men.
It is important to point out that the eccentric exercise protocol used in the present study did not increase the oxidative stress parameters analyzed in the participants. This may explain the lack of effect of microencapsulated cocoa on plasma GSH and MDA after the exercise-induced muscle damage protocol. Therefore, it seems that polyphenols may not effectively improve antioxidants' status in conditions where ROS production from exercise does not outweigh their neutralization due to an efficient endogenous antioxidant defense system. In such circumstances, it may not be possible to demonstrate an antioxidant effect after cacao supplementation. Furthermore, there is large variation across studies investigating plasma oxidative stress markers levels in response to strenuous exercise, with some studies demonstrating evidence of increase (36, 38–40) and others finding no significant changes (37, 41, 42), becoming it difficult to make a strong conclusion about the effect of cocoa on the redox balance.
Exercise-induced muscle damage has been associated with increases in inflammatory markers, including c-reactive protein (CRP) (43), which are typically increased for several hours following exercise and may persist for several days depending on the severity of the damage (44). Furthermore, the exercise-induced inflammation has been associated with muscle function loss, suggesting the acute inflammatory response plays a role in the recovery after exercise (45). In the present study, the plasma levels of CRP increased 2h following the exercise protocol, and the microencapsulated cocoa intake was not able to blunt the exercise-induced increases in plasma CRP. Currently, the only study using the EIMD protocol to investigate the effect of cocoa-based food on inflammation was conducted by Morgan et al. (42). The authors did not observe significant differences between groups in IL-6 and CRP after performing 100 maximal leg extensions. The low dose (74 mg) of cocoa flavanols used in this study may be the main reason for the lack of significant effect. The limited number of studies demonstrating a significant reduction in inflammation following EIMD suggests no anti-inflammatory effect of cocoa irrespective of delivery systems used to improve cocoa polyphenols bioavailability (i.e., food microencapsulation).
In the present study, muscle strength was negatively impacted by the EIMD protocol, with significant reductions in muscle force been evident at 24h, 48h, and 72h following exercise. Although a previous study has found that cocoa supplementation enhances muscle function as evaluated by improved recovery of countermovement jump height (42), a single dose of microencapsulated cocoa (75 mg of total flavonoids) did not improve MIVC after 24h, 48h, and 72h of the eccentric exercise. Our observation corroborates with other studies that investigated the effects of cocoa supplementation on exercise-induced changes in maximal voluntary contraction (41, 42, 46, 47), besides one study (47) has found large effect sizes in MVC after as an acute high dose of cocoa (1245 mg) compared to the control at 24 and 48 h post-exercise.
Myoglobin is released after strenuous exercise due to the degradation of protein structures within the muscle. Therefore, myoglobin has been used as a useful biochemical marker for monitoring muscle damage after EIMD (48). Microencapsulated cocoa supplementation did not affect the exercise-induced increases in the muscle damage marker myoglobin (Mb). Furthermore, muscle soreness increased following EIMD and persisted until 72h post-EIMD, probably caused by the microtrauma of myofibers and subsequent inflammation. However, microencapsulated cocoa was not able to reduce DOMS, corroborating with the existing literature demonstrating that cocoa polyphenols did not attenuate the exercise-induced DOMS (41, 42, 46, 47).
In conclusion, this study demonstrated that microencapsulated cocoa was not enough to promote anti-inflammatory and antioxidant effect and did not speed muscle strength recovery after exercise-induced muscle damage in healthy and physically-active individuals, at least when consumed in a single dose. Long-term studies are warranted to investigate whether food encapsulation may be a useful technological procedure to ensure proper nutrient delivery and biological effect.
Experimental considerations
Experimental variation across studies may, in part, explain the lack of significant effect and/or differences between studies, such as the type of exercise performed (i.e., resistance exercise versus cycling), frequency of exercise stimulus (i.e., acute versus chronic), the training status of participants (i.e., sedentary versus physically-active), and the use of a variety of biomarkers to detect oxidative stress, inflammation, and muscle damage. It is also possible that the polyphenol dose (i.e., 75 mg of total flavonoids) and the delivery system (i.e., microencapsulation of cocoa using maltodextrin to protect the active ingredient) provided in our study had been not sufficient to induce antioxidant or anti-inflammatory effects. Furthermore, the elbow flexors were relatively refractory to muscle damage (participants had an average of 20% reduction in isometric strength), which may contribute to the lack of polyphenol effects in this population.