Résumé
We previously reported in C2C12 myotubes that a Rhaponticum carthamoides root extract (RCE) was able to significantly stimulate protein synthesis and induce an activation of the Akt/mTOR signalling pathway (induction of Akt and S6K1 phospohrylations), that a Rhodiola rosea root extract (RRE) had also the capacity to induce protein synthesis and to inhibit myostatin gene expression and that the combination of both exhibited inhibition of atrogin gene expression (unpublished). Therefore, we aimed to investigate the effects of RCE or RRE alone or combinations of both on acute muscle protein synthesis stimulation and on performance gain following a 4-week resistance training program in adult rats. Acutely, rats were trained on a ladder making 3 repetitions of 10 climbs with a load that successively reached 0%, 50% and 75% of their body mass and were fed (oral gavage) just after training with either placebo, whey protein (910 mg/kg bw) as a positive control, RRE (43 mg/kg bw), RCE (43 mg/kg) and different doses of a 50:50 combination of both (87, 43, 22 or 9 mg/kg bw). RCE alone but not RRE was able to significantly stimulate protein synthesis as measured by western blot quantitative analysis of puromycin incorporation in the flexor digitorum profondus (FDP) and in comparison to placebo (200% versus 100% for RCE and placebo group respectively). Any doses of the combination was significantly superior to RRE alone (300% versus 150%) or RCE alone (300% versus 200%) and also significantly superior to whey proteins (300% versus 150%). The same results were obtained in the biceps and deltoid muscles. In the second part of the study rats followed a 4-week progressive resistance training program while consuming RRE alone (22 mg/kg), RCE alone (22 mg/kg) and different ratio and doses of the combination (50:50 ratio: 43, 22 or 9 mg/kg bw; 83 RCE:17 RRE ratio: 26 mg/kg; 76 RCE:24 RRE ratio: 28 mg/kg; 70 RCE:30 RRE ratio: 15 mg/kg. Training sessions (19) consisted in one set of 10 repetitions with 2 minutes rest between trials and 5 minutes between each set, were held five times a week with initial load fixed at 50% of the rat body weight and increased progressively until 200% after 4 weeks. Maximal repetition was determined as the maximum weight carried up the exercise ladder by the rats in one climb and performance gain was calculated as delta power (post versus pre resistance training). As shown in Figure 1, RCE alone but not RRE was able to significantly increase performance gain in comparison to placebo after 4 weeks of resistance training (0.66±0.08 versus 0.39±0.08 W respectively, + 65%, p<0.05). A synergistic effect on performance gain was detected for the 50:50 combination but interestingly, the combination ratio 70:30 warranted the best improvement of performance gain with the lower daily dosage (15 mg/kg bw) in comparison to placebo (0.62±0.08 versus 0.39±0.08 W respectively, + 59%, p<0.05). These results clearly demonstrated synergy of the combination of extracts on protein synthesis stimulation in the FDP, deltoid and biceps muscles following acute resistance exercise and an improvement of performance gain following a 4-week resistance training program. Those effects are currently investigated in recreationally active men and histological analysis of muscle fibers are under investigations in rats to understand what could drive the effect on performance.