Following a period of chronic high-intensity resistance training, which adaptation would NOT be expected consequent to this type of anaerobic exercise?

• A. Transition from Type IIx to Type IIa muscle fiber
• B. Increased pennation angle in certain muscle groups
• C. Reduced SR and T-tubule density
• D. Elevated NA-K ATPase activity

Answer: (C)

When muscles adapt to chronic high-intensity resistance training, the body enhances features that support force production, speed, and repeated contractions. The system responsible for calcium release and uptake inside the muscle fiber—the sarcoplasmic reticulum and the T-tubules—tends to be maintained or optimized to support rapid EC coupling; a reduction in SR and T-tubule density would actually hinder calcium handling and contraction speed, so it’s not something you’d expect from anaerobic training.

Other adaptations you would anticipate include a shift in some fast-twitch fibers from a IIx profile toward a IIa profile, reflecting greater oxidative capacity and fatigue resistance while retaining fast contraction speed. Muscles also hypertrophy, and the architectural changes—such as an increased pennation angle in some muscles—allow more fibers to pack into a given volume, boosting force. Additionally, repeated high-intensity activity increases the demand on ion transport systems, so Na+/K+ ATPase activity rises to help restore membrane potential after contractions.