School of Kinesiology, Auburn University, Auburn, AL, USA.
Department of Physical Education, Federal University of Sao Carlos, Sao Carlos, Brazil.
Exp Physiol. 2023 Oct;108(10):1268-1281. doi: 10.1113/EP091286. Epub 2023 Aug 17.
We recently reported that vastus lateralis (VL) cross-sectional area (CSA) increases after 7 weeks of resistance training (RT, 2 days/week), with declines occurring following 7 weeks of subsequent treadmill high-intensity interval training (HIIT) (3 days/week). Herein, we examined the effects of this training paradigm on skeletal muscle proteolytic markers. VL biopsies were obtained from 11 untrained college-aged males at baseline (PRE), after 7 weeks of RT (MID), and after 7 weeks of HIIT (POST). Tissues were analysed for proteolysis markers, and in vitro experiments were performed to provide additional insights. Atrogene mRNAs (TRIM63, FBXO32, FOXO3A) were upregulated at POST versus both PRE and MID (P < 0.05). 20S proteasome core protein abundance increased at POST versus PRE (P = 0.031) and MID (P = 0.049). 20S proteasome activity, and protein levels for calpain-2 and Beclin-1 increased at MID and POST versus PRE (P < 0.05). Ubiquitinated proteins showed model significance (P = 0.019) with non-significant increases at MID and POST (P > 0.05). in vitro experiments recapitulated the training phenotype when stimulated with a hypertrophic stimulus (insulin-like growth factor 1; IGF1) followed by a subsequent AMP-activated protein kinase activator (5-aminoimidazole-4-carboxamide ribonucleotide; AICAR), as demonstrated by larger myotube diameter in IGF1-treated cells versus IGF1 followed by AICAR treatments (I+A; P = 0.017). Muscle protein synthesis (MPS) levels were also greater in IGF1-treated versus I+A myotubes (P < 0.001). In summary, the loss in RT-induced VL CSA with HIIT coincided with increases in several proteolytic markers, and sustained proteolysis may have driven this response. Moreover, while not measured in humans, we interpret our in vitro data to suggest that (unlike RT) HIIT does not stimulate MPS. NEW FINDINGS: What is the central question of this study? Determining if HIIT-induced reductions in muscle hypertrophy following a period of resistance training coincided with increases in proteolytic markers. What is the main finding and its importance? Several proteolytic markers were elevated during the HIIT training period implying that increases in muscle proteolysis may have played a role in HIIT-induced reductions in muscle hypertrophy.
我们最近报道，股外侧肌（VL）横截面积（CSA）在 7 周的抗阻训练（RT，每周 2 天）后增加，而在随后的 7 周跑步机高强度间歇训练（HIIT，每周 3 天）后下降。在此，我们研究了这种训练模式对骨骼肌蛋白水解标志物的影响。在基线（PRE）、7 周 RT 后（MID）和 7 周 HIIT 后（POST），从 11 名未经训练的大学生男性中获得 VL 活检。对组织进行蛋白水解标志物分析，并进行体外实验以提供额外的见解。与 PRE 和 MID 相比，POST 时的 atrogene mRNAs（TRIM63、FBXO32、FOXO3A）上调（P < 0.05）。20S 蛋白酶体核心蛋白含量在 POST 时高于 PRE（P = 0.031）和 MID（P = 0.049）。与 PRE 相比，MID 和 POST 时 20S 蛋白酶体活性以及钙蛋白酶-2 和 Beclin-1 的蛋白水平增加（P < 0.05）。泛素化蛋白显示出模型意义（P = 0.019），MID 和 POST 时无显著增加（P > 0.05）。体外实验当用肥大刺激物（胰岛素样生长因子 1；IGF1）刺激后再用 AMP 激活蛋白激酶激活剂（5-氨基咪唑-4-甲酰胺核苷酸；AICAR）时再现了训练表型，与 IGF1 后用 AICAR 处理（I+A）的细胞相比，IGF1 处理的肌管直径更大（P = 0.017）。IGF1 处理的肌管的肌肉蛋白质合成（MPS）水平也高于 I+A 肌管（P < 0.001）。总之，RT 诱导的 VL CSA 随 HIIT 而减少，同时几种蛋白水解标志物增加，持续的蛋白水解可能是这种反应的原因。此外，尽管在人类中未测量，但我们从体外数据推断，与 RT 不同，HIIT 不会刺激 MPS。新发现：这项研究的核心问题是什么？确定在抗阻训练后进行 HIIT 是否会导致肌肉肥大减少，同时增加蛋白水解标志物。主要发现及其重要性是什么？在 HIIT 训练期间，几种蛋白水解标志物升高，这表明肌肉蛋白水解的增加可能在 HIIT 诱导的肌肉肥大减少中起作用。
