Skeletal muscle fatigue in vitro is temperature dependent

Area of Science:

• Physiology
• Muscle Biology
• Exercise Science

Background:

• Muscle fatigability is a critical factor in physical performance and endurance.
• Understanding the influence of environmental factors like temperature on muscle function is essential.

Purpose of the Study:

• To investigate the impact of varying temperatures on the fatigability of isolated rat soleus and extensor digitorum longus (EDL) muscles.
• To determine the optimal temperature range for maximal muscle endurance during repeated isometric contractions.

Main Methods:

• Isolated rat soleus and EDL muscles (70-90 mg) were subjected to repeated isometric contractions in vitro at temperatures ranging from 20-40°C.
• Fatigability was assessed by measuring the time and number of stimuli required to reach 50% of the initial force (P).
• Stimulation protocols included variable force (approx. 70% of maximum force, Po) and constant frequency (28 Hz).

Main Results:

• Soleus muscles exhibited longer fatigue times than EDL muscles across all tested temperatures.
• Increased temperature led to a shortened fatigue time during stimulation at approximately 70% Po.
• The number of stimuli to reach fatigue showed a bell-shaped curve relationship with temperature, peaking between 25-30°C for both muscle types.

Conclusions:

• Temperature significantly affects muscle fatigability, with an optimal range for endurance between 25-30°C.
• The observed temperature optima suggest direct effects on intrinsic muscle contractile properties and energy metabolism.
• These findings have implications for understanding muscle performance in varying thermal environments.