Author(s): SHINKAI, H., SHIRAI, T., UEMICHI, K., IWATA, T., TANIMURA, R., IWAI, R., SUGIYAMA, S., TAKEMASA, T., Institution: UNIVERSITY OF TSUKUBA, Country: JAPAN, Abstract-ID: 1160

INTRODUCTION:
Concurrent training (CT) is a combination of different modalities of exercise. It has been reported that CT, especially which consists of resistance exercise (RE) and endurance exercise (EE), suppresses muscle strength and muscle hypertrophy compared with RE alone, this is a phenomenon known as the interference effect (Hickson, 1980). The interference effect is thought to be caused by the suppression of mTOR, which promotes RE-associated protein synthesis, by AMPK, which is activated by EE (Coffey & Hawley, 2017). Intensity of exercise is one of the key factors that influences metabolic adaptation, so its modulation may reduce interference effects. Therefore, we focused on high intensity interval exercise (HIIE) and conducted experiments based on the hypothesis that interference effects would not occur in CT consisting of RE and HIIE.
METHODS:
Male C57/BL6J mice were used as experimental animals. Mice were devided into 3 groups, The Sham group; underwent sham operation, the myotenectomy induced functional overload (OL) group; underwent compensatory plantaris muscle hypertrophy with Achilles tendon resection as a RE model, and the OL+HIIE group; underwent HIIE by forced swimming exercise in addition to OL (n=6-8 for each group). After 4 weeks of intervention, plantaris muscles were collected and analyzed.
RESULTS:
Plantaris muscle wet weight and muscle fiber cross-sectional area, and molecular signals related to muscle hypertrophy, were significantly higher in the OL and OL+HIIE groups than the Sham group (p<0.05). Metabolism-related protein and mRNA expression levels were significantly higher in the OL+HIIE group than the Sham group (p<0.05).
These results indicate that CT combined with RE and HIIE does not suppress muscle hypertrophy. HIIE is a modality of exercise in which the glycolytic system is utilized, and recently the involvement of the glycolytic system in muscle hypertrophy has been focused. Previous studies have reported that dihydroxyacetone phosphate (DHAP), an intermediate metabolite of the glycolytic system, promotes mTOR activity (Orozoco et al., 2020), and that 2-deoxy-D-glucose, an inhibitor of the glycolytic system, decreases protein synthesis after electrical stimulation: an RE model (Suginohara et al., 2021). Therefore, it is possible that the enhancement of the glycolytic system by HIIE suppressed the interference effect directly or indirectly through metabolites such as DHAP, lactate, and exerkines.
CONCLUSION:
CT combined with RE and HIIE does not cause interference effects and induces muscle hypertrophy as when RE alone is performed.