Background
Rhaponticum carthamoides (Willd.), commonly known as Maral root or Rhaponticum, is a perennial herb found in the Altai and Saian Mountains of South Siberia and has been introduced in various regions of Central and Eastern Europe in the last few decades [
1]. Currently,
Rhaponticum is used in preparations such as dietary supplements for its adaptogenic and tonic properties that promote muscle growth and increase the body’s resistance to stress, such as trauma and fatigue [
2]. In the last century, the muscle- and strength-building qualities of
Rhaponticum have been largely investigated in Russia, where various preparations were commonly used by elite Soviet and Russian athletes who were exhausted by hard training to increase psychological and physical performance [
3]. Several different classes of compounds have been previously isolated from various parts of
Rhaponticum, mainly steroids, particularly ecdysteroids, and phenolics [
1]. Ecdysteroids affect certain major metabolic pathways in mammals: protein synthesis, lipid metabolism and carbohydrate metabolism [
4]. A number of research studies, which are not currently available in English [
5], suggest that phytoecdysteroids (PEs) possess a broad spectrum of biological, pharmacological, and medicinal properties in mammals without androgenic effects. 20-Hydroxyecdysone (20HE), also called ecdysone or ecdysterone, is one of the main ecdysteroids present in
Rhaponticum, comprising 0.1 to 1% of the dry matter of roots [
6].
Rhodiola rosea (golden root, roseroot) is a plant that grows in the mountainous and arctic regions of North America, Europe, and Asia.
Rhodiola is known to reduce physical and mental fatigue, improve cognitive function, and exert antidiabetic effects. The functional claim of
Rhodiola dietary supplements mentioned in the consolidated list of Article 13 Health Claims of the European Food Safety Authority (EFSA) is that it “contributes to optimal mental and cognitive activity”.
Rhodiola contains a range of biologically active substances, including organic acids, flavonoids, tannins and high amounts of rosavins (rosin, rosavin, rosarian), which are
Rhodiola-specific glycosides, and salidroside, which are present in all species of
Rhodiola [
7].
Rhodiola is used to improve cognitive function and endurance performance, reduce mental fatigue and reactive oxygen species (ROS) production, and exert antidiabetic effects [
7]. Interestingly, it has been shown that
Rhodiola exhibits antidepressant, adaptogenic, anxiolytic-like, and stimulating effects in mice [
8]. The molecular mechanisms underlying the effects of
Rhodiola are currently unknown, although it has been hypothesized that it enhances the activity of monoamines and opioid peptides [
9]. Thus,
Rhodiola could improve the consumption of substrates, enhancing lipid oxidation and sparing glycogen [
7].
Given the current knowledge on the effects of both plant extracts, their use to promote human health in both preventive and curative applications appears justified. On one hand,
Rhaponticum-based supplementation has been shown to increase body weight and muscle mass [
2] On the other hand, some ergogenic effects of
Rhodiola supplementation have been found but most of them derive from behavioral effects and not, for the moment, from effects on muscle physiology [
8] As athletic performance involves both central (behavioral) and peripheral (muscular) qualities, it became evident that we should test their combination. Moreover, as some of their biological effects may improve muscle function, one can expect that supplementation with mixed extracts could increase muscle performance. Indeed, it is essential for athletes to ensure that they have optimal amounts of muscle mass for maximum performance.
Most animal studies that address muscle mass gain have focused their attention on PE, especially 20HE, but no study has investigated the effect of a combination of
Rhaponticum and
Rhodiola. Moreover, although positive effects of ecdysterone have been reported, significant data are not available, making evaluation of the experimental design and quality of the research difficult [
10]; currently, it is hard to draw robust conclusions regarding the efficacy of supplements containing
Rhaponticum in humans. The current study aimed to investigate the acute and chronic effects of resistance exercise and supplementation with
Rhaponticum and
Rhodiola on protein synthesis, muscle phenotype, and physical performance.
The primary endpoint of the chronic study was to identify the effects of Rhaponticum and Rhodiola and their potential synergistic effects on muscle mass and physical performance following resistance training. We designed an acute study to verify the potentially marked stimulation of muscle protein synthesis (MPS) by Rhaponticum in the decay of a single bout of resistance exercise and to examine whether adding Rhodiola plant extracts would affect Rhaponticum’s stimulatory effect.
Discussion
This study was conducted to examine whether 1) supplementation of Rhaponticum could stimulate MPS and maintain this effect when combined with Rhodiola, and 2) chronic supplementation of Rha + Rho coupled with resistance training could also enhance physical performance. The acute study revealed that Rhaponticum could stimulate protein synthesis above placebo in response to resistance exercise. Interestingly, combining Rhodiola and Rhaponticum plant extracts stimulated higher muscle protein synthesis than Rhaponticum alone. When given chronically, Rhaponticum augmented mechanical power above placebo, but the combination of plant extracts did not further augment muscle performance above Rhaponticum plant extracts alone.
From a physiological point of view, physical performance is highly correlated with muscle mass which rely mostly upon protein synthesis in healthy conditions but also with motivational aspects. The rationale of the study was that chronic administration with a combination of Rhaponticum and Rhodiola plant extracts could enhance physical performance, taking advantage of the peripheral effect (protein synthesis) of Rhaponticum and adaptogenic effect of Rhodiola. We first designed an “acute” study in which we verified the potential stimulatory effect Rha + Rho supplementation on MPS in the context of a single bout of resistance exercise. Our first hypothesis was that Rhaponticum exerts an effect through enhanced muscle protein synthesis and that adding Rhodiola plant extracts does not affect Rhaponticum’s stimulatory effect.
We used a rat model of resistance exercise known to increase MPS [
14]. The three main forearm muscles involved in the climbing activity were harvested (the FDP, deltoid, and biceps muscle) 2 hours after administration of supplements by oral gavage immediately after the exercise bout to ensure the animals were in the “anabolic window”. Interestingly,
Rhodiola alone was not able to stimulate protein synthesis regardless of the muscle studied, while,
Rhaponticum alone modestly increased protein synthesis in the biceps and FDP (
p < 0.05 for biceps;
p = 0.059 for FDP). However, when combined,
Rhaponticum and
Rhodiola plant extracts were able to increase protein synthesis at all dosages tested, except for the lowest dose (
Rha + Rho D4). Subtle nuances were observed between the different active muscles, which were most likely directly linked to their implication in climbing movement and/or their phenotype. For example, the FDP muscle, which is the muscle most involved in this exercise model, responded to every
Rha + Rho dose (from HED = 100 mg to 1000 mg) compared to the control group. Overall, the
Rha + Rho doses that engendered the largest increase in protein synthesis after exercise were the three highest doses, i.e., HED = 1000, 500 and 250 mg, regardless of the muscle studied. Taken together, these results suggest that bioactive compounds in
Rhaponticum extract were able to stimulate MPS and that some bioactive compounds in
Rhodiola extract could exert a synergistic effect, as observed by puromycin incorporation (Fig.
1a, b and c).
This increase in protein synthesis induced by
Rha + Rho could be explained at least in part by the anabolic effect of phytoecdysteroids, which are enriched in the extracts. Ecdysteroids are a class of polyhydroxylated ketosteroids with long carbon side-chains that are produced primarily in insects, and their analogues in plants are phytoecdysteroids such as
Rhaponticum. Indeed, phytoecdysteroids have been shown to stimulate growth in several animal species, including mice [
4,
15], rats, sheep, pigs, and quail [
16]. The increased physical performance without training observed in a forced swim rat model is of particular interest [
10]. In that study, in addition to increased performance, the authors found an increase in myofibrillar protein synthesis in the soleus and EDL muscles [
10]. One of the most common ecdysteroids found in plants is 20HE. 20HE does not bind to the androgen receptor, suggesting that phytoecdysteroids, including 20HE, may exert their anabolic effect through an androgen-independent mechanism [
17]. Some evidence indicates that ecdysteroids and 20HE activate Akt [
18]. We performed western blotting of phosphorylated and total forms of Akt and we did not find any increase in the p-Akt/Akt ratio between the control and Rhaponticum or Rhaponticum+Rhodiola groups. Moreover, none of the downstream effectors i.e. mTOR, 4-EBP1 and rpS6, were upregulated (phosphorylated/total isoform ratio, see Additional figure
1). To date we have no explanation for the discrepancy between the acute increased protein synthesis and the absence of any significant stimulation of the mTOR pathway. Taken together, the results of the acute study confirmed that Rhaponticum alone is able to stimulate higher muscle protein synthesis than resistance exercise alone and even higher when combined with Rhodiola plant extracts, suggesting a synergistic effect. Further experiments investigating the role of the Akt/mTOR pathway in chronic supplementation are needed.
We next extended the study to chronic supplementation using, in addition to Rho or Rha doses alone (HED = 250 mg), the dose that best stimulated protein synthesis i.e. 500 mg
Rha + Rho (dose 2) coupled with a 4-week resistance training program. In the chronic study, physical performance was evaluated using the mean mechanical power produced at the same relative workload before and after the training period. Compared to the control and
Rhodiola groups, the
Rhaponticum and
Rha + Rho groups showed increases in climbing mechanical power output, suggesting that the repeated increases in muscle protein synthesis after each bout of resistance exercise could participate in physical performance. Surprisingly, if
Rhaponticum augmented mechanical power above placebo, the combination of plant extracts did not further augment muscle performance above
Rhaponticum plant extracts alone. Interestingly, compared to the trained control condition,
Rhodiola alone did not elicit any increase in mechanical power (Fig.
4a). It was expected a synergistic effect of
Rhodiola, due to its adaptogenic properties leading to an improved cognitive function [
19] or at least in part coming from a reduced mental fatigue as described by [
20] in young militaries. However, our results are in accordance with those of De Bock et al. (2004) [
21], since they did not observe changes in muscle strength after 4 weeks of Rhodiola supplementation, as we didn’t notice any synergestic effect in chronic study. The mechanisms underlying the increased physical performance of all the groups include, but are not restricted to, the following: 1) an increase in motor command with an increase in the activated motor neuron pool and probably an increase in motor unit coordination, 2) an increase in fiber size and strength, 3) an increase in the power produced by each fiber type, and 4) an increase in myofibrillar ATPase activity for a given myosin isoform. Unfortunately, we did not measure the activation level; however, the hypothesis that
Rhaponticum and/or
Rhodiola extracts alters cortical output by modulating the motivation of the animals, leading to an increased physical performance, should not be excluded. In support, a stimulatory effect of intraduodenally administered doses of
Rhaponticum extracts on the central nervous system of rats had been demonstrated [
2]. Similarly, 20HE could produce an increase in acetylcholinesterase (AChE) in the rat brain [
22], which could enhance learning capacity. Concerning the increase in fiber size and strength, our study lacks a true control (untrained) group to clearly show the effect of resistance training on fiber size. However, in a previous study that used rats of the same age and weight, we showed that the non-exercised control group had a mean FDP CSA value of 1440 ± 84 μm
2 [
14], which is notably lower than the value of 2291 ± 182 μm
2 of the present trained control group. Clearly, the increase in strength is directly related to fiber CSA. It has been shown that resistance training can elicit a direct effect on developed power by each specific fiber type [
23]. Indeed, resistance training can increase contraction velocity and absolute strength measured at the fiber level. Thus, even though we only observed a tendency of increase in the ratio of type I to type II fibers in the treated groups, these results do not exclude the possibility that the power of both fiber types was increased in response to the resistance training protocol. Indeed, after 4 weeks of resistance training using the same model, a mean increase in myofibrillar ATPase activity of 135.6% has been observed in FDP, biceps, and deltoid muscles, for a given myosin heavy chain isoform [
24]. This effect could explain the increased performance of each treated group, except for the Rho group (Fig.
4b). In our experiments,
Rhodiola was administered owing to its adaptogenic activity under strenuous physical effort, delaying fatigue and exerting metabolic effects such as promoting fatty acid utilization [
7].
In order to a subsequent transfer to the clinic, requiring the product’s cost reduction especially for Rhodiola plant extracts, and based on the results of the acute study, we applied a combination consisted of the smallest 50%/50% dose of Rhaponticum plant extracts that had an effect on every muscle and the smallest 50%/50% dose of Rhodiola that had an effect at least in one studied muscle. Thus, we designed a mix dose of 175 mg
Rha (70%) + Rho (30%) that was administered to animals that received also resistance training for 4 weeks. Interestingly, this combination dose produced the same enhancement in mechanical power as the 500 mg
Rha + Rho 50%/50% dose (see Additional figure
4A). Further studies testing other
Rha + Rho ratios and doses close to those used in this study should be performed to optimize the
Rha/Rho ratio.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.