Which exercise type is most directly responsible for increasing bone density and skeletal muscle strength?

• A. Static stretching, particularly when held for long durations several times daily, because stretching improves tendon stiffness and therefore indirectly increases bone formation.
• B. Flexibility-focused yoga practiced once per week, as it combines isometric holds and balance which directly drive bone remodeling in the absence of external loads.
• C. Resistance training (strength or weight training).
• D. Prolonged low-intensity aerobic activity done daily without additional loading, such as very long slow distance walking, because repeated movement stimulates bone through microstrain accumulation over time if loading is present.

Answer: (C)