Differences in rat skeletal muscles after incline and decline running

Area of Science:

• Exercise physiology
• Muscle biology
• Biomechanics

Background:

• Eccentric contractions, involving muscle lengthening under tension, can cause muscle damage.
• Previous research suggests that muscle adaptations may influence resistance to eccentric exercise-induced damage.

Purpose of the Study:

• To investigate the effects of incline and decline treadmill training on rat vastus intermedius muscle structure and function.
• To determine if adaptations from eccentric training (decline) increase resistance to damage from lengthening contractions.

Main Methods:

• Rats underwent 5 days of incline or decline treadmill running.
• Angle-torque relationships of vastus intermedius muscles were measured.
• Muscle fiber and sarcomere lengths were analyzed after acid digestion.
• Muscles were subjected to lengthening contractions to assess torque maintenance and optimal angle stability.

Main Results:

• Decline-trained muscles generated maximum active torque at significantly greater lengths compared to incline-trained muscles.
• Muscle fibers from decline-trained rats had a greater estimated number of sarcomeres in series.
• Muscles from decline-trained rats showed less torque reduction and optimal angle shift during lengthening contractions, indicating greater damage resistance.

Conclusions:

• Decline treadmill training increases the number of sarcomeres in series in the vastus intermedius muscle.
• A greater number of sarcomeres in series may contribute to enhanced resistance to muscle damage induced by eccentric contractions.