Decreased muscle protein breakdown the day after eccentric exercise improves net protein balance but is unaffected by protein-polyphenol intervention

Protein and polyphenol ingestion can improve recovery from muscle-damaging eccentric exercise, but the contribution of muscle protein breakdown (MPB) is unknown. We characterised postabsorptive MPB, muscle protein synthesis (MPS) and net balance (MPNB) the day after eccentric exercise, and investigated whether this was manipulated by ingesting protein-polyphenol. Twenty-five recreationally active participants (age 23 ± 5 y, BMI 24 ± 3 kg m −2 ) were randomised to consume either 25 g protein and 650 mg pomegranate extract (PP; n = 12), or maltodextrin placebo (PLA; n = 13), prior to and immediately after 300 maximal, unilateral, eccentric, knee extensor contractions. The following day, participants received L-[ ring - 2 H 5 ]-phenylalanine and L-[ 15 N]-phenylalanine infusions to determine MPS, MPB, and MPNB. Blood samples and muscle biopsies from the control (CON) and eccentric (ECC) legs were collected throughout. Muscle isokinetic function was determined before eccentric exercise and after the final biopsy. Muscle function decreased in ECC after eccentric exercise ( P < 0.001), but was unaffected by intervention. MPB was lower in ECC versus CON (PLA: 0.071 ± 0.049 vs. 0.119 ± 0.046 %·h −1 ; PP: 0.083 ± 0.050 vs. 0.109 ± 0.057 %·h −1 ; P < 0.01), but unaffected by intervention. MPS did not differ between legs in PLA (0.092 ± 0.040 vs. 0.092 ± 0.023 %·h −1 ), but was greater in ECC vs. CON of PP (0.141 ± 0.067 vs. 0.097 ± 0.037 %·h −1 ; interaction P < 0.01). Although MPNB was greater in ECC vs. CON ( P < 0.01) this was unaffected by intervention. We show for the first time that maximal, high-volume, eccentric exercise reduces MPB the following day, generating positive MPNB. Protein-polyphenol ingestion did not influence MPB and MPNB, suggesting that strategies to accelerate recovery need not focus on ameliorating MPB and act through alternative mechanisms.