Fiber type changes in rat skeletal muscle after intense interval training

Area of Science:

• Exercise Physiology
• Muscle Biology
• Sports Science

Background:

• Muscle fiber type composition influences performance.
• High-intensity interval training (HIIT) is a popular training modality.
• Understanding exercise-induced adaptations is crucial for optimizing training.

Purpose of the Study:

• To investigate the effects of a 10-week HIIT program on hindlimb muscle fiber types in Sprague-Dawley rats.
• To analyze changes in citrate synthase activity as a marker of aerobic adaptation.

Main Methods:

• Female Sprague-Dawley rats underwent a 10-week HIIT program.
• Histochemical ATPase analysis determined muscle fiber type distribution (soleus, plantaris, deep vastus lateralis, superficial vastus lateralis).
• Biochemical assays measured citrate synthase activity in contralateral hindlimb muscles.

Main Results:

• Citrate synthase activity significantly increased in all tested muscles post-training.
• Soleus and superficial vastus lateralis fiber type distributions remained unchanged.
• Plantaris and deep vastus lateralis showed significant increases in type I (slow-twitch) fibers and decreases in type II (fast-twitch) fibers.
• Deep vastus lateralis exhibited shifts within fast-twitch subtypes (IIB to IIA).

Conclusions:

• HIIT induces significant muscle fiber type transformations in specific rat hindlimb muscles.
• Adaptations include shifts between slow-twitch and fast-twitch populations and within fast-twitch subtypes.
• These findings highlight the plasticity of skeletal muscle in response to intense exercise.