# Repeated Cold Water Stress Leads to Improvements in Mitochondrial Metabolism of Skeletal Muscles in Rats

## TL;DR

Cold-water swimming in older rats improves muscle metabolism and mitochondrial function by enhancing NADH utilization and antioxidant capacity.

## Contribution

This study shows cold-water swimming upregulates MAS and PFK-1, improving mitochondrial metabolism in aged rats.

## Key findings

- Cold-water swimming increased expression of all MAS enzymes involved in NADH delivery to mitochondria.
- Elevated active PFK-1 expression indicates intensified glycolysis under oxidative conditions.
- ROS production and antioxidant enzyme upregulation were observed in cold-exposed rats.

## Abstract

Background: In this study, we aimed to determine whether cold-water swimming could serve as a potential strategy to enhance antioxidant capacity, improve NADH utilization in oxidative metabolism, and consequently lead to better muscle metabolism and improved mitochondrial function in the skeletal muscles of rats. We hypothesized that cold-water swimming may upregulate malate–aspartate shuttle (MAS) expression, leading to more efficient NADH utilization in oxidative pathways and thereby improving muscle metabolism and mitochondrial function. Methods: We analyzed the expression of all MAS components, as well as the expression of phosphofructokinase I (PFK-1)—a key regulatory enzyme of glycolysis (which, under oxidative conditions, serves as a source of NADH for MAS)—in the skeletal muscles of rats subjected to cold-water swimming training. The study involved 32 male and 32 female rats aged 15 months, randomly assigned to control sedentary animals, animals training in cold water at 5 ± 2 °C, or animals training in water at thermal comfort temperature (36 ± 2 °C). The rats underwent swimming training for nine weeks, gradually increasing the duration of the sessions from 2 min to 4 min per day, five days a week. Results: Our findings revealed increased expression of all MAS enzymes involved in the delivery of NADH to mitochondria, elevated expression of the active form of PFK-1 indicating intensified glycolysis, increased reactive oxygen species (ROS) production, and upregulation of antioxidant enzymes. Conclusions: Cold-water swimming can improve metabolism and enhance mitochondrial function in the muscles of older adult rats subjected to cold-water swimming training.