Author(s): ACHESON, J., BARRETT, J.S., SANKEY, K., TIEDE, D.R., GOTLA, T.Z., HEARRIS, M., SALE, C., ABOU SAWAN, S., ROBERTS, M.D., JOANISSE, S., HODSON, N., Institution: UNIVERSITY OF BIRMINGHAM, Country: UNITED KINGDOM, Abstract-ID: 2088

INTRODUCTION:
Unaccustomed resistance exercise (RE) induces acute skeletal muscle (SkM) damage that must be repaired to enable adaptation. Autophagy, a cellular quality-control process, facilitates animal SkM repair by recycling damaged cellular components [1]. However, human SkM autophagy remains poorly defined, as studies utilise static markers that do not reflect autophagic flux [2]. Moreover, nutraceuticals that enhance human SkM recovery [3] may act by increasing autophagy [4], yet this remains untested. Here, we used a novel ex vivo autophagic flux assay to test whether damaging RE alters human SkM autophagic flux and if nutraceutical supplementation augments autophagy to aid recovery.
METHODS:
Twenty healthy untrained adults (23±4 years, 22.8±2.4 kg/m2) were randomised to consume a nutraceutical supplement (curcumin, quercetin, rosehip, piperine, spermidine; n=10), or placebo (n=10) 3 weeks before, and 1 week after, performing 5 sets of leg extensions and leg presses to volitional failure (80% 1RM). Markers of SkM damage were measured pre, 0h, 24h, 72h, and 1-week post-RE. Vastus Lateralis biopsies were obtained pre, 24h and 72h post-RE. Tissue was immediately snap-frozen or incubated in control or lysosomal inhibition (NH4Cl, leupeptin) medium for 1h, allowing assessment of autophagic flux ex vivo. Western blots assessed autophagy-related proteins and myosin-heavy chain (MyHC) fragments in SkM soluble (sarcoplasmic) and myofibrillar fractions, respectively. LC3-II autophagy flux was calculated as inhibited minus control conditions. Data were analysed using a mixed-design ANOVA with Holm-Bonferroni corrected post-hoc tests if main or interaction effects were shown (p<0.05).
RESULTS:
At 0h, 24h, and 72h post-RE, quadriceps pain increased whilst leg extensor MVC decreased (p<0.05). Serum creatine kinase was elevated at all post-RE timepoints (p<0.01), indicating SkM damage. LC3-II autophagy flux was elevated at 72h (p=0.018), whereas ‘static’ markers (LC3-II/I ratio) were unchanged. Cytosolic p62 increased at 24h and 72h (p<0.01), suggesting elevated autophagic cargo post-damage. Peak MyHC fragmentation, a novel index of contractile protein damage, was elevated 76% from baseline (p=0.009). Conversely, lysosomal markers were reduced at 72h vs 24h (p<0.05), suggesting limited lysosomal capacity during elevated flux. Nutraceutical supplementation had no additional effects on autophagy or recovery.
CONCLUSION:
This study provides the first confirmation that unaccustomed RE can increase human SkM autophagic flux. Our data show that static markers fail to reflect dynamic autophagy regulation and suggest that prior studies may have misinterpreted human SkM autophagy. We also identify lysosome abundance as a potential autophagy ‘bottleneck’ previously observed in mice [1]. Future trials should employ ex vivo flux assays in various populations/interventions to better understand human SkM autophagy.

1. Call and Nichenko, 2020
2. Acheson et al., 2025
3. Tanabe et al., 2015
4. Zhang et al., 2016