Final answer:
Wide hand placement push-ups are generally easier than narrow hand placements due to the involvement of larger muscle groups. When bending the arm, the biceps contracts and the triceps relaxes, while the opposite occurs when straightening the arm. Muscles work in pairs because they can only pull, not push.
Step-by-step explanation:
Performing push-ups with various hand placements targets different muscle groups and affects the difficulty of the exercise. With wide hand placements, the focus is more on the pectoral muscles (chest) and shoulders, making it generally easier due to the greater muscle mass involved. Medium hand placements provide a balance, recruiting the chest, shoulders, and the triceps. The narrow hand placements, often referred to as diamond or triceps push-ups, primarily engage the triceps and are considered the hardest because they rely on a smaller muscle group with less mechanical advantage.
Regarding muscle function, when you bend your arm, the biceps muscle contracts, while the triceps muscle relaxes. Conversely, when you straighten your arm, the triceps contracts and the biceps relaxes. Muscles can only pull, not push, which is why they work in pairs to move joints in opposite directions. This is explained by the skeletal muscles' attachment to the skeleton, which allows them to produce movement by contracting and pulling on bones. Since muscles can only exerct pulling forces, opposing muscle pairs (agonist and antagonist) must work together to control limb movement.
Skeletal muscles must work in opposing pairs for efficient movement, balancing the pull in one direction with a pull in the opposite direction. For example, during a push-up, as the triceps muscle at the back of the upper arm contracts to straighten the arm, the biceps must relax and lengthen to allow this motion.