Which of the following improves core strength?

Planks are an effective exercise for improving core strength because they specifically target the muscles of the abdomen, lower back, and pelvis, collectively known as the core. When performing a plank, the body is held in a straight line from head to heels, requiring the core muscles to engage continuously to maintain stability and proper alignment. This isometric contraction helps to strengthen these muscles over time, leading to better overall core stability.

Running primarily focuses on cardiovascular fitness and leg strength, although it does engage the core to some extent for balance and stability. However, it does not isolate or primarily target the core muscles like planks do. Jumping jacks serve as a full-body workout that includes aerobic benefits and some degree of core engagement, but they are not as specialized for core strength as planks. Side lunges, while beneficial for lower body strength and flexibility, do not focus on the core in the same way as planks.

Overall, planks are considered one of the most effective exercises for isolating and strengthening core muscles, making them the best choice for this question.