Gymnastik- och idrottshögskolan, GIH

Introduction

It is well known that ultra-endurance exercise, such as Adventure racing and military operations, often induce substantial energy deficits. This suggests a catabolic state, but the exact effects on protein turnover have not yet been sufficiently investigated. The aim of this study was to examine several markers involved in muscle protein turnover before and after a multi-day physically demanding military training operation.

Methods

Seven female (age 21 ± 5 years, weight 71.2 ± 6.6 kg) and seventeen male (age 20 ± 1 years, weight 76.6 ± 6.2 kg) performed a 185 hours military training operation. Energy intake was estimated from food supply and energy expenditure was calculated from continuous heart rate and accelerometer recordings. Muscle biopsies were taken from M Vastus Lateralis before and after the operation.

Results

A negative energy balance of 1,500-2,000 kcal/24 hours was estimated. Body weight declined 3.4 (95% CI 3.0-3.8) kg and muscle explosive strength, evaluated from squad and counter movement jumps, was reduced 5 and 6 %, respectively, after the operation with no difference between genders. Muscle glycogen content was reduced from 269 ± 58 to 181 ± 44 mmol/kg dry muscle (p<0.05) with no difference between genders. Muscle content of mTOR and p70 as well as MAFbx were unchanged while the protein content of MuRF-1 was significantly down regulated in both genders.

Discussion

The study indicated that prolonged low intensity exercise with substantial energy deficit reduces muscle function and muscle glycogen content. Proteins for muscle synthesis mTOR and p70 were unchanged while the down regulation of MuRF-1 indicates a protection against muscle break down during the energy deficit situation, preserving the muscle mass.